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Medium scale approach (MSA) for improved assessment of coral reef fish habitat
Abstract
Habitat characteristics play a critical role in structuring reef fish communities subjected to fishing pressure. The line intercept transect (LIT) method provides an accurate quantitative description of the habitat, but in a very narrow corridor less than 1 m wide. Such a scale is poorly adapted to the wide-ranging species that account for a significant part of these assemblages. We developed an easy-to-use medium scale approach (MSA), based on a semi-quantitative description of 20 quadrats of 25 m2 (500 m2 in total). We then simulated virtual reef landscapes of different complexities in a computer, on which we computed MSA using different methods of calculation. These simulations allowed us to select the best method of calculation, obtaining quantitative estimates with acceptable accuracy (comparison with the original simulated landscapes: R2 ranging from 0.986 to 0.997); they also showed that MSA is a more efficient estimator than LIT, generating percentage coverage estimates that are less variable. A mensurative experiment based on thirty 50-m transects, conducted by three teams of two divers, was used to empirically compare the two estimators and assess their ability to predict fish–habitat relationships. Three-factor multivariate ANOVAs (Teams, Reef, Methods) revealed again that LIT produced habitat composition estimates that were more variable than MSA. Canonical analyses conducted on fish biomass data successively aggregated by mobility patterns, trophic groups, and size classes, showed the higher predictive power of MSA habitat data over LIT. The MSA enriches the toolbox of methods available for reef habitat description at intermediate scale (< 1000 m2), between the scale where LIT is appropriate (< 100 m2) and the landscape approach (> 1000 m2).
... Point Intercept Transect, Line Intercept Transect ; voir comparaison de ces méthodes par Facon et al., 2016) ou utilisant des quadrats (e.g. Medium Scale Approach ; Clua et al., 2006) ont été développées pour évaluer la composition relative des communautés benthiques (e.g. recouvrement corallien). ...
... A la Réunion, j'ai choisi d'utiliser une méthode permettant d'évaluer de façon semi-quantitative la communauté benthique d'un site à l'échelle du paysage : la Medium Scale Approach (MSA ; Clua et al., 2006). Les détails de cette méthode sont présentés dans le chapitre 3 (Materials & Methodssupporting information). ...
... All detected fishes were recorded. Benthic composition was assessed along the same transects using the Medium Scale Approach (MSA) of Clua et al. (2006). Six 5 x 5 m quadrats were evaluated on each transect. ...
Les récifs coralliens sont l’écosystème marin le plus complexe, mais aussi le plus menacé par les perturbations croissantes liées aux activités anthropiques. Leur conservation représente un véritable défi. Alors que le maintien des récifs au plus proche de leurs configurations et dynamiques actuelles doit être privilégié, nous devons également nous préparer à une évolution rapide de leur fonctionnement et adapter réseaux et outils de suivis à cette nouvelle situation. Des avancées technologiques récentes ont permis l’émergence d’outils innovants qui pourraient permettre à court terme d’augmenter considérablement la résolution spatio-temporelle des suivis. Parmi eux, l’acoustique passive est en plein essor. L’objet de cette thèse a été d’affiner son cadre d’utilisation pour évaluer et suivre l’état écologique et le fonctionnement des écosystèmes coralliens. Des enregistrements des paysages sonores et des relevés écologiques (assemblages de poissons et habitat) ont été réalisés sur 31 récifs de pente externe autour de trois îles de l’Indo-pacifique avec des caractéristiques environnementales variables, incluant des pressions anthropiques contrastées. L’analyse des résultats obtenus avec différentes combinaisons de paramètres d’échantillonnage (bande de fréquences, moment du cycle journalier choisi pour réaliser l’enregistrement, durée des échantillons de son) a permis de sélectionner un protocole d’échantillonnage basé sur les deux types d’indices écoacoustiques les plus utilisés pour l’étude des récifs coralliens. Ce protocole permet la caractérisation rapide et fiable de l’état écologique des récifs. En se basant sur ces lignes directrices, la capacité de six indices écoacoustiques à évaluer des fonctions clé de l’écosystème corallien a ensuite été démontrée. En comparant les apports de l’acoustique passive et de données environnementales pouvant être collectées par télédétection, la plus-value de l’utilisation d’indices écoacoustiques pour prédire la structure des assemblages de poissons récifaux a été identifiée et quantifiée. Une application de l’approche écoacoustique au suivi continu d’un site isolé a mis en évidence le potentiel particulièrement important de l’acoustique passive comme outil d’appui à la gestion dans ce type de contexte. Face à l’ampleur et à la vitesse des changements climatiques annoncés, les méthodes de suivi employées aujourd’hui, basées sur la présence d’observateur in situ, seront vraisemblablement insuffisantes. Combinée à d’autres outils de suivi, l’acoustique passive pourrait contribuer à détecter rapidement les perturbations des écosystèmes, condition indispensable pour en comprendre les causes et mettre en œuvre des réponses rapides et adaptées.
... Point Intercept Transect, Line Intercept Transect ; voir comparaison de ces méthodes par Facon et al., 2016) ou utilisant des quadrats (e.g. Medium Scale Approach ; Clua et al., 2006) ont été développées pour évaluer la composition relative des communautés benthiques (e.g. recouvrement corallien). ...
... A la Réunion, j'ai choisi d'utiliser une méthode permettant d'évaluer de façon semi-quantitative la communauté benthique d'un site à l'échelle du paysage : la Medium Scale Approach (MSA ; Clua et al., 2006). Les détails de cette méthode sont présentés dans le chapitre 3 (Materials & Methodssupporting information). ...
... All detected fishes were recorded. Benthic composition was assessed along the same transects using the Medium Scale Approach (MSA) of Clua et al. (2006). Six 5 x 5 m quadrats were evaluated on each transect. ...
Coral reefs are the most complex of marine ecosystems, but also the most threatened by ecological disruption resulting directly or indirectly from human activities. Their conservation represents a huge challenge. While maintaining coral reefs as close as possible to their current configurations and dynamics is among the highest priorities, we must also prepare for rapid changes in their functioning and adapt monitoring tools and networks to this new situation. Recent technological advances enabled the emergence of innovative tools with the potential to drastically increase the spatio-temporal resolution of coral reef monitoring. Among these, Passive Acoustic Monitoring (PAM) is on the rise. The aim of this thesis was to improve and facilitate the use of PAM as a tool for the assessment and monitoring of coral reefs’ ecological states and functioning. Soundscape recordings and ecological surveys (reef fish assemblages and habitat) were performed at 31 outer reef slope sites around three Indo-Pacific islands with variable environmental characteristics, including contrasted anthropogenic pressures. Analysing the results obtained with multiple combinations of sampling settings (frequency bandwidth, time of sampling (day/night), and sample duration) allowed the selection of a sampling scheme based on the two types of indices mostly used in coral reef studies. This scheme enables a rapid and reliable categorisation of reef’s ecological states. Based on these sampling guidelines, the capacity of six ecoacoustic indices to evaluate coral reef key functions was demonstrated. By comparing the contributions of PAM and coarse environmental data that could be sampled remotely, the added value of using ecoacoustic indices to predict reef fish assemblage structure was identified and quantified. An application of ecoacoustics to the continuous monitoring of a remote site highlighted the strong potential of PAM as a supporting tool for managers in such context. In view of the amplitude and velocity of expected climatic changes, current observer-based monitoring methods are likely to be exceeded. Combined to other monitoring tools, PAM could contribute to promptly detect ecosystem disturbances, which is essential to understand their causes and put in place rapid and adapted responses.
... This research was conducted in August 2018 for habitat geomorphology classification and February 2019 for coral propagation status, in Samuh beach, Nusa Dua, Bali (115°13'-115°14' E and 8°47'30-8°47'47 S), which is one of the tourism areas in Bali Province. (Figure 2), was undertaken with a mediumscale approach technique (Medium Scale Approach-MSA) [13]. A 5x5m square was estimated and benthic cover within that area was recorde [14], followed by divers calculating the Semi Quantitative Scale benthic habitat (SQS): 0 (0%), 1 (1-10%), 2 (11-30%), 3 (31-50%), 4 (51-75%) and 5 (76-100%) along with the relatively easy identification of habitats >25m [13,15]. ...
... (Figure 2), was undertaken with a mediumscale approach technique (Medium Scale Approach-MSA) [13]. A 5x5m square was estimated and benthic cover within that area was recorde [14], followed by divers calculating the Semi Quantitative Scale benthic habitat (SQS): 0 (0%), 1 (1-10%), 2 (11-30%), 3 (31-50%), 4 (51-75%) and 5 (76-100%) along with the relatively easy identification of habitats >25m [13,15]. In general, this method was carried out in-situ, although it is also possible to use photo transects [16]. ...
... Field data in the form of photographs of collected coral habitat transects was compiled and analysed visually by using computers to assess the area of cover (semi-quantitative) [13], rugosity, growth forms and dominant species [8,9]. To measure rugosity, a categorical scale of 0 -5 was employed to represent the level of variation in amplitude of the surface height -in this case, the habitat of the coral reef ecosystem. ...
MARRS (Mars Assisted Reef Restoration System) is an artificial reef method that resembles spider webs and has been implemented in several regions of Indonesia, including Samuh beach, Nusa Dua, Bali. Since July-October 2018, 761 MARRS units, supporting a total of ± 10,600 coral fragments, have been installed. The aim of this research is to provide an initial investigation into establishing a mini-coral reef park in Indonesia. Monitoring was done by identifying habitat geomorphology methods with photo transects and coral propagation status in MARRS using the random visual census method. From the process of habitat geomorphology classification in the artificial reef network, there were 9 types of habitat classified on the fringing reef, reef flats and fore reefs. Ten hard coral species from the Scleractinia group were identified from 10 randomly-selected and monitored MARRS units: Acropora formosa, A. hyacinthus, Pocillopora verucosa, P. damicornis, Psammocora sp., Symphyllia sp., Stylophora pistillata, Turbinaria sp., Echinopora sp. and Favites sp. Three significant coral factors were found to be present within the coral propagation system: resistance, competition and predators.
... Pengumpulan data lapangan dilakukan sebanyak 3 kali survei lapangan yaitu bulan Februari 2017 mengumpulkan 82 titik pengamatan sebagai ground check, April 2017 dan Agustus 2017 sebagai kontrol habitat dengan masing-masing titik pengamatan sebanyak 14 dan 8 titik. Pengambilan data lapangan (Gambar 2), dilakukan dengan teknik pendekatan skala menengah (Clua et al., 2006). Dengan pendekatan skala menengah (Medium Scale Approach-MSA) (Clua et al., 2006) dan estimasi kuadrat 5x5m dan melihat tutupan bentik (English, Wilkinson, & Baker 1997a) diikuti dengan pergerakan penyelam dalam melakukan penghitungan habitat bentik Skala Semi Kuantitatif (SSK): 0 (0%), 1 (1-10%), 2 (11-30%), 3 (31-50%), 4 (51-75%) and 5 (76-100%) dan dengan relatif mudah dapat mengidentifikasi habitat > 25m 2 . ...
... Pengambilan data lapangan (Gambar 2), dilakukan dengan teknik pendekatan skala menengah (Clua et al., 2006). Dengan pendekatan skala menengah (Medium Scale Approach-MSA) (Clua et al., 2006) dan estimasi kuadrat 5x5m dan melihat tutupan bentik (English, Wilkinson, & Baker 1997a) diikuti dengan pergerakan penyelam dalam melakukan penghitungan habitat bentik Skala Semi Kuantitatif (SSK): 0 (0%), 1 (1-10%), 2 (11-30%), 3 (31-50%), 4 (51-75%) and 5 (76-100%) dan dengan relatif mudah dapat mengidentifikasi habitat > 25m 2 . (Dahl, 1981;Clua et al., 2006) (Gambar 2). ...
... Dengan pendekatan skala menengah (Medium Scale Approach-MSA) (Clua et al., 2006) dan estimasi kuadrat 5x5m dan melihat tutupan bentik (English, Wilkinson, & Baker 1997a) diikuti dengan pergerakan penyelam dalam melakukan penghitungan habitat bentik Skala Semi Kuantitatif (SSK): 0 (0%), 1 (1-10%), 2 (11-30%), 3 (31-50%), 4 (51-75%) and 5 (76-100%) dan dengan relatif mudah dapat mengidentifikasi habitat > 25m 2 . (Dahl, 1981;Clua et al., 2006) (Gambar 2). Dimana umumnya metode ini dilakukan secara insitu, namun bisa juga dilakukan dengan foto transek (Andréfouët, 2008). ...
Coastal ecosystems covering three important parts of mangroves, seagrass beds and coral reefs are an integral part of the habitat mapping process. This study aims to mapping habitats of the island of Menjangan in West Bali National Park (TNBB), Bali. Field data was collected in February, April and August 2017. Total 110 sampling points spread across the coastal area of Menjangan island by looking at the texture differences using the ENVI v4.7 program from satellite image data Worldview 2 October 14th 2016. The results showed that the study area is divided into 6 types of main habitat (geomorphological levels) i.e., reef front, reef slope, reef flat, Sand and Terrace on which we add the mangroves, Ground-truhing data and cross-reef photograph-transects of habitats described with with medium scale approach suggest that, on reef flat and crest areas, 12 habitats has been described. This includes coral habitat (coral>30% cover) dominated by several types of hard coral (Scleractinia) ie Acropora sp, Montipora sp, Porites lutea and Porites cylindrica; mixed with rubble and algae (mostly Chlorophyta and Phaeophyta) each covering about 15%. Sand (10-15%) and seagrasses (including Syringodium sp, Cymodocea sp and Thalassia sp) (10%) are more marginally present. The blue coral Heliopora coerulea (non Scleractinia), mixed coral associations, and dead corals complete the assemblages . On the reef flat rugosity is low (1 – 2) but increases toward the crest and front reef with rugosity level at 3 - 4. On this research it can be one of data support for re-zonation in West Bali National Park especially in Menjangan Island and surrounding area.
... See text for details and type of curves in Table 12 (English et al., 1994). MSA: Medium Scale Approach (Clua et al., 2006 Table 10: Mortality rates (mean ± standard deviation, n=6) of all corals for the 6 reef flat sites. ...
... (English et al., 1994). MSA: Medium Scale Approach (Clua et al., 2006). High thematic richness could be achieved by Scopélitis et al. (2009) even with limited ground-truthing, at least to the point that they could demonstrate, using photo-interpretation techniques that an assemblage of coral communities at Saint-Leu fringing reef in La Reunion has recovered after a hurricane and moderate bleaching event across a 35-year period. ...
... Back from the field ( Figure 5, step C), the wide-angle photographs are visually analyzed on a laptop or desktop to give a semi-quantitative value of cover, rugosity, growth form, and dominant species. This is equivalent to the so-called Medium Scale Approach description (Clua et al., 2006) generally performed in situ, but which can be performed using photographs as well. Several photographs can be used for one habitat, and the average of the observations is kept. ...
The INDESO (Infrastructure Development of Space Oceanography) project, in collaboration with the Indonesian Government (Ministry of Marine Affairs and Fisheries – MMAF) and the French company CLS (Collecte Localisation Satellites), promotes the use of space technologies for monitoring coastlines and Indonesian seas. This thesis is part of coral reef monitoring component, led by the IRD (Institute de Recherche pour le Développement). The main objective was to determine wether coral reef habitats on Bunaken Island in Northern Sulawesi are resilient, using (i) newly desgined habitat maps, (ii) in situ data, and a unique 15-year time series of satellite images of different very high resolution (VHR) sensors, and (iii) ancillary data that could explain the changes detected. The results include highly detailed maps of the Bunaken reefs habitat (194 polygons mapped and a census of 175 habitats). The influence of sea level fall on coral mortality during the El-Nino event of 2015 – 2016 is presented in detail, and the importance of this process is also discussed from the interpretation of a unique time series of 15 years of VHR images. The temporal series reveals very different trajectories of the coral habitats. We conclude that Bunaken reefs demonstrate an ability to resileince and without phase shift, but that a definitive diagnosis of their resilience remains difficult to determine by imagery. Habitat trajectories can not be fully interpreted without changing some monitoring paradigms and without using a combination of remote sensing and in situ data.
... Les détails des AMPs échantillonnées sont dans le Tableau 2. (Clua et al., 2006)). ...
... Fiche « Habitat » MSA(Clua et al., 2006) Le biotope échantillonné est décrit (récif frangeant, barrière externe, platier ou pente, etc.) ainsi que les caractéristiques du milieu comme le relief ou le courant.Quatre biotopes ont été échantillonnés : 1) le récif frangeant, 2) récif intermédiaire, 3) l'arrière-récif et 4) la pente externe. Dans la mesure du possible, la pente et le platier était échantillonnés. ...
Au-delà de la perte de richesse spécifique, les activités humaines entraînent probablement la diminution de la diversité phylogénétique et fonctionnelle portée par les espèces dans les communautés. Comprendre les effets des activités humaines sur l’ensemble des facettes de la biodiversité liées au fonctionnement des écosystèmes et évaluer les outils de conservation de ces facettes restent des enjeux majeurs de l’écologie notamment en milieu marin.Les objectifs de la thèse sont donc i) d’évaluer les impacts humaines sur la diversité des lignées phylogénétiques et des fonctions au sein des communautés de poissons coralliens indépendamment des facteurs environnementaux naturels, ii) d’évaluer la capacité des aires marines protégées à conserver efficacement ces facettes et à produire des valeurs de références pour la gestion des écosystèmes et iii) de mesurer la vulnérabilité fonctionnelle intrinsèque, sans pression humaine, des communautés de poissons.. Pour cela nous avons dû échantillonner des sites très isolés des populations humaines à travers l’Indopacifique et nous avons utilisé des modèles permettant de prendre en compte les effets de seuil et les interactions pour extraire les effets ‘purs’ liés à l’homme.Dans un premier temps, nous montrons, à l’échelle du Pacifique sud-ouest, que le nombre d’espèces des poissons perroquets diminue linéairement mais uniquement de 12% le long d’un gradient d’impact humain alors que les diversités phylogénétique et fonctionnelle diminuent de 36% et de 47%, respectivement, avec de forts effets de seuil.Dans un deuxième temps, en considérant un gradient d’impact humain et une large gamme d’aires marines protégées (AMPs) en Nouvelle-Calédonie, nous démontrons que les sites très isolés des activités humaines (>20 heures de temps de trajet depuis Nouméa la capitale régionale) possèdent des communautés de poissons avec une plus forte diversité fonctionnelle et biomasses de prédateurs apicaux que la plus grande et plus ancienne AMP intégrale.Finalement, en considérant quatre sites isolés des activités humaines à travers l’Indo-Pacifique, nous avons révélé que la diversité des fonctions portées par les poissons est très vulnérable, 60% n’étant portées que par une espèce, même sans impact humain.Nos travaux montrent la très forte vulnérabilité aux activités humaines des facettes fonctionnelles et phylogénétiques de la biodiversité, avec un manque de capacité des AMPs à restaurer l’ensemble des rôles fonctionnels des poissons et une redondance très limitée pour ces fonctions même dans les sites les plus isolés.
... Percentage cover of seagrass and other substrate (algal turf, live coral boulders, sand, dead coral rubble, habitability coefficient) were estimated at all sites using the Medium Scale Approach based on a semi-quantitative description (MSA - Clua et al., 2006). Habitability coefficient corresponds to estimating habitat complexity or heterogeneity that fish perceive, by using a semi quantitative scale (1 to 4) where 1 is not complex and 4 complex. ...
... Habitability coefficient corresponds to estimating habitat complexity or heterogeneity that fish perceive, by using a semi quantitative scale (1 to 4) where 1 is not complex and 4 complex. The habitat complexity is linked to the number of components and their relative surfaces (Clua et al., 2006). To describe the habitat of each site, a diver swam along three 50 m transects placed randomly within the same area as the fish assessment, and divided in 20 non overlapping quadrates of 25 m 2 , positioned on both sides of the transect lines. ...
The present study highlights the importance of intertidal seagrass beds as nursery areas for coral reef fish juveniles along four sites (Mtsoubatsou, Sohoa, Boueni, Ngouja) on the western coast of Mayotte Island. The results collected by underwater visual census from November 2012 to January 2013 showed that mean total fish density between adults and juveniles varied significantly at each site, with juveniles always being more abundant in seagrass beds than adults. Of the total fish assemblages sampled in seagrass beds, 73% were juveniles and few adults of large species were observed. Overall, our study highlights the important functional role of intertidal seagrass beds for fish assemblages, as they are the primary habitat for the juveniles of many fish species on Mayotte reefs. Seagrass beds, however, are very vulnerable ecosystems and are decreasing worldwide. Therefore it is of primary importance to protect seagrass beds within the Indo-Pacific.
... Benthic composition was assessed along the same transects using the medium scale approach (MSA) of Clua et al. (2006). Six 5 × 5 m quadrats were evaluated on each side of the three transects (12 × 25 m 2 described for each transect). ...
... holes providing shelter for fishes or any other reef organisms) and 6 being the most complex reef matrix, with numerous refuges of diverse sizes. Several substrate covers (see Methods S1, Supporting information) were evaluated on each quadrat on a 1-5 scale (1: cover comprised between 1 and 10%; 2: between 11 and 30%; 3: between 31 and 50%; 4: between 51 and 75%; 5: between 76 and 100%) as defined by Clua et al. (2006). ...
1. Despite increasing policies of protection, few localities in the Caribbean remain spared from human impacts. These lightly affected areas can better reflect the past composition of reef fish assemblages and provide baseline information about the natural factors driving fish distributions in the region.
2. Reef fish assemblage structures were analysed in 21 Caribbean fished areas and marine protected areas (MPAs) along a gradient of distance to the nearest major market place. Assemblage structures by size and by trophic group were significantly related to the distance to market.
3. Relationships of reef fish life-history traits, families, and vulnerability indicators were examined with the seascape and the benthic composition at Los Roques Archipelago, the most isolated MPA in the analysis. Factors linked to seascape features were more important than benthic composition or human activities in explaining fish assemblage structure.
4. Wave exposure was the most influential seascape metric. Exposed habitats were dominated by octocorals and sponges. More sheltered habitats were characterized by high coral cover, while leeward sites were characterized by steep slopes with close proximity to deeper water.
5. Exposed habitats were mostly occupied by unspecialized fish species. Piscivore densities were high at south and south-west sites, and were likely related to the large concentrations of planktivorous fishes found there. South and south-west sites experience full oceanic conditions, and supported the highest species richness and densities within the archipelago.
6. Los Roques National Park is one of the oldest and most remote Caribbean MPAs. Its fish assemblage structure is healthier than other fished or protected areas, with higher species richness, higher density of piscivores, and an abundance of large species. Predator–prey relationships provided additional evidence that Los Roques reef fish assemblage presented specific characteristics.
7. The main patterns observed in this study represent a baseline for assessing reef fish assemblages elsewhere in the southern Caribbean.
... We visually characterized benthic habitat in each de ployment following a semi-quantitative scale method derived from the medium scale approach (Clua et al. 2006). Specifically, we classified habitat based on types of biogenic cover (macroalgae, seagrass, rhodoliths) as well as fine-and coarse-grain substrates (sensu Wentworth 1922) and estimated the percent composition that each habitat separately occupied in the field of view (example images in Fig. S3). ...
Arctic and sub-Arctic ecosystems are experiencing changes in environmental conditions, altering marine biodiversity through shifts in species distributions and composition. Coastal ecosystems in northern environments are vulnerable to continued environmental change, but the remoteness of these areas and challenges associated with sampling shallow, structurally complex habitats have limited studies on nearshore communities. We compared the composition and relative abundances of nearshore assemblages in 7 coastal locations spanning 10° latitude of boreal and sub-Arctic habitats in Newfoundland and Labrador, Canada, using baited remote underwater video (BRUV). We identified 14 taxa, including 11 fish species and 3 decapod crustaceans. Species richness and diversity was generally higher in southern relative to northern locations, and spatial distributions differed across taxa. Greenland cod Gadus macrocephalus ogac and large cottids Myoxocephalus spp. were the most common taxa in northern areas and the only species observed across the entire environmental gradient. In contrast, we observed Atlantic cod G. morhua , winter flounder Pseudopleuronectes americanus , and cunner Tautogolabrus adspersus exclusively in southern locations. In addition to community variability across locations, habitat differences contributed more to variation in community-level abundances than to the abundances of most individual taxa. BRUVs provided an effective method for comparing nearshore assemblages across northern coastal habitats that are challenging to other common sampling methods. Further studies incorporating BRUVs could track variability in nearshore assemblages over longer time scales and offer an accessible method for coastal communities to monitor change across habitats.
... In situ observations include systematic photographs, at least one per minute, using an underwater camera Olympus TG-7 with housing (if possible, fitted with a wide angle) and when the surveyor changes habitats. Photo interpretation of habitats based on these photographs is done using the [5] with Medium Scale Approached (MSA) [17,18]. To link with satellite image data, it is necessary to mark the positions of the observations and record its continuous tracks with a GPS (Global Positioning System), to identify the exact areas that have been observed. ...
Many studies related to marine ecotourism and coral reefs have been carried out in several locations in Indonesia. In TWP Gitanada, West Lombok, NTB coral reef habitat inventory and mapping was conducted in June 2021 by using Sentinel 2A satellite imagery and field observation. Geomorphologically, the TWP Gitanada area consisted of fringing reefs made of reef flat, fore reef/reef crest, reef slope, reef wall,and patch reef. The coral reef area is 450 ha and consists of > 200 types of coral reef benthic habitat, dominated by scleractinian corals (Acropora, Montipora, Porites and their associations with less dominant genera). All coral reef habitat data is presented here in a format which is suitable to attract the attention of visitors or tourists in understanding and supporting ecotourism development, which uses TWP Gitanada as a general case study which is relevant for all marine conservation and potential marine conservation throughout Indonesia. The information is helpful to identify which areas could be prioritized for conservation under the criteria of habitat richness or for further development by relevant stakeholders.
... The circular plot and photoquadrat methods are preferred due to their high reproducibility. However, the size of the photoquadrat stations is too small to detect mesoscale benthic variations (Clua et al. 2006) and post-processing time is high (Urbina-Barreto et al. 2021b). ...
The spatialisation of essential biodiversity variables is a crucial step in assessing the health of coral reefs. However, few studies propose a comprehensive method for a large-scale assessment, such as coral reefs around Reunion Island. This requires a trade-off between the area, the study time, and the number of sampled stations needed to achieve spatial interpolations at an acceptable human and financial cost. We estimated nine sighting benthic biodiversity variables through visual assessments conducted in 2,599 circular plots per 100 m², distributed in two zones (reef flat, outer slope) and 14 habitats present across four sites (fringing reefs) on Reunion Island. A stratified sampling plan that is homogeneous within zones and differentiate between zones is appropriate, particularly for the study of a reef at several spatial scales (site, zone, habitat). We first demonstrated that the sampling effort enabled statistical discrimination and spatialisation of the nine benthic biodiversity variables within all the landscape units. Subsequently, we investigated the reliability limits of the spatial models by reducing the sampling effort of an increasing proportion of stations using bootstrap resampling. Results showed that station densities of 0.5 to 1.2 stations.ha − 1 (outer slopes) and 1.5 to 4.3 stations.ha − 1 (reef flats) provide very satisfactory to excellent spatialisation of the essential biodiversity variables. Depending on the objectives, the resolution and the available resources, our method allows an estimation of the trade-off between required information for mapping benthic biodiversity variables of coral reefs using spatial interpolation and sampling effort.
... Step 5 (validation of trajectories) is important to be able to discuss resilience based on the changes in seabed configuration described by Steps 3 and 4. Steps 1 and 2 are not detailed here, but the applied methodology comes from Andréfouët (2008) and similar field and image processing exercises are described in Scopélitis et al. (2009Scopélitis et al. ( , 2010 or Ampou et al. (2018a, b a,b). In short, habitats were defined using a medium-scale approach (Clua et al. 2006) according to standard semi-quantitative information on benthic cover, rugosity, and coral growth forms and sizes, with taxonomic descriptions for the most dominant genera. Each new combination of these variables defined a new habitat. ...
The resilience of Moorea Island's coral reefs has been extensively discussed. In this debate, and despite their greater exposure to anthropogenic disturbances, shallow reef flats have often been overlooked compared to oceanic forereefs. This study assesses changes in the reef flat habitats over 67 years (1955–2022) in Tiahura in the northwest of Moorea, using a combination of modern satellite imagery, vintage aerial photographs and a habitat mapping survey conducted in 2023. Remotely sensed data provided time series of coral habitat surface area changes could be in some cases corroborated by historical literature reports and in situ observations from 1972 to the present, although historical data were scarce, heterogeneous, and informed at a different level of descriptions (e.g., coral cover) than the habitat scale. Contrary to expectations, the period from 1955 to 1977, perceived as pristine, exhibited a significantly lower extent of coral habitat compared to the subsequent period marked by coastal development and anthropogenic disturbances. To discuss resilience of coral habitats across the 67-year period, we relied on habitat surface changes. To understand the changes and evaluate the coral habitat resilience of the Tiahura reef flats, it was crucial to differentiate the barrier from the fringing reefs due to their distinct exposure to physical disturbances during the 1970s. The fringing reef, unlike the barrier reef, experienced substantial human-induced structural and hydrodynamical modifications. Concluding or not on coral habitat resilience depends on the period considered: 1955–2022 or 1977–2022. Beyond the Tiahura case study, we highlight the importance of defining the temporal reference for any resilience analysis, by taking into account the stability of hydrodynamic conditions that affect sedimentation and lagoon water levels.
... Experimental results show that the multi-object resource allocation algorithm is robust and efficient. [7,8] ，图像模型 [9,10] ，时间序列模型 [11,12] ，图模型 [13,14] 等等。其中， 图模型因其擅长表征对象之间的关系且适用于大数据计算 [15,16] ，近些年来在生态 建模领域被广泛应用 [17][18][19][20] 。随着海洋数据量的增多，具有数据量大、数据种类多、 更新频繁等特征的海洋大数据逐渐成为一个重要的海洋生态建模研究领域 [21,22] 。 在大数据背景下，图模型可以执行高效的计算机算法 [23,24] 。同时，作为一种根基深 厚的数学模型，图论领域拥有众多成熟的数学概念以及高效的算法可以适用于各 种应用领域 [25][26][27] 。近些年来，通过图模型模拟海洋生态状况，并通过图模型算法， 对海洋生态状况进行评估，以及通过图模型模拟算法实现海洋资源规划和保护的 例子屡见不鲜 [28][29][30] ...
随着全球变暖的加剧和人类在海洋领域活动的增多,珊瑚礁生态系统的生态状况越来越严峻。珊瑚礁白化,鱼类数量减少,濒危海洋物种数量增多等问题愈发突出。这些生态问题对全球生态稳定和人类社会的可持续发展造成了难以忽视的影响。因此,珊瑚礁生态系统的生态保护策略研究逐渐成为一个重要的研究领域。为了实现更为合理和高效的珊瑚礁生态系统修复,基于计算机图模型构建技术的资源分配方法成为珊瑚礁生态系统保护策略的重要研究方面。资源分配是指通过模拟计算实现在合理的位置新增合理规模的人工礁等人工自然资源的过程。计算机图模型构建的主要目的是,实现传统方法难以做到的全球范围生态系统建模和模拟工作。然而,目前的生态系统资源分配策略方法面临几个主要的挑战:1.在大数据背景下,种群间的依赖关系确定困难且相关数据采集难度大,因此相关领域建模效率较低;2.种群竞争压力和负载压力难以量化,导致难以对生态修复策略提供量化计算支持;3.资源分配过程难以量化,对新增资源的资源量和地理位置难以准确计算。本研究针对以上几个问题,在计算机图模型构建技术的基础之上提出了竞争图构建方法,实现了种群竞争压力和负载压力量化以及资源分配,达到了优化生态系统修复工作流程,提高生态系统修复效率,并减少生态系统修复人员的工作量的效果。资源分配算法的主要目标是,在尽可能少的增加人工礁等人工生态资源的情况下,尽可能降低生态系统中所有种群的平均竞争压力和平均负载压力。本研究以珊瑚礁生态系统内部种群为研究对象,基于计算机图模型构建技术,研究了珊瑚礁生态系统的多对象资源分配问题,主要完成了以下工作:(1)针对全球珊瑚礁生态系统的大规模种群间依赖关系确定困难,大规模种群量化建模低效的问题,本研究提出了基于地理学第一定律的竞争图模型构建方法,并提出了模型构建算法。本研究实现了大规模种群的快速建模并确定了种群间的依赖关系,为进一步实现大规模种群竞争和负载压力量化以及精准的资源分配优化过程奠定了坚实基础;(2)针对大规模种群的竞争和负载压力量化困难问题,本研究提出了竞争图上的竞争值和负载值定义并分别提出了不同的查询方法。本研究基于图局部敏感哈希方法实现了大规模种群的竞争压力量化,并实现了负载压力量化。实验结果表明了查询方法在大数据背景下的可行性和高效性,为实现量化的多对象资源分配策略提供了支持;(3)针对可量化的资源分配策略制定困难问题,本研究基于竞争压力和负载压力量化提出了多对象资源分配方法,实现了在尽可能少的增加人工生态资源的情况下,实现尽可能好的生态系统修复效果的目标。同时,本研究方法可以计算出较为精确的新增资源位置,以及新增资源的规模。实验结果说明了多对象资源分配算法的鲁棒性和高效性;
... The micro-habitat was also included in the BRUVS data. We evaluated, through a semi-quantitative scale [71], the distinct visually observable features (e.g., percent cover of coral, sand, vegetation, and more, see [72] for details on the method). Micro-habitat variables were used to calculate the Shannon habitat diversity index and assess whether micro-habitat diversity would influence fish diversity or biomass [73,74]. ...
Simple Summary
Underwater mountains, or seamounts, are deep-sea habitats collectively forming an area as large as Europe. Yet, they are one of the least studied ecosystems on earth. Known for supporting rich marine life compared to surrounding deep-sea environments, we have no information on how seamounts truly compare to other iconic biodiversity hotspots like shallow coral reefs. To assess the effective ecological value of seamounts, we compared fish communities in coral reefs and seamounts up to 500 m deep using two techniques: environmental DNA to detect the presence of species by filtering fragments of DNA lost by organisms in seawater, and underwater cameras to directly measure fish abundance and size. We found that the deepest seamounts had almost 10 times fewer fish species than coral reefs. However, the shallowest seamounts had larger fish species, including sharks, than coral reefs. We conclude that while seamounts are important and unique ecosystems, they may not be as diverse for fish species as previously thought (diversity hotspots) but rather biomass oases and refuges for endangered species. This study therefore calls for protecting the shallowest seamounts, as they are critical areas for marine life.
Abstract
Seamounts are the least known ocean biome. Considered biodiversity hotspots, biomass oases, and refuges for megafauna, large gaps exist in their real diversity relative to other ecosystems like coral reefs. Using environmental DNA metabarcoding (eDNA) and baited video (BRUVS), we compared fish assemblages across five environments of different depths: coral reefs (15 m), shallow seamounts (50 m), continental slopes (150 m), intermediate seamounts (250 m), and deep seamounts (500 m). We modeled assemblages using 12 environmental variables and found depth to be the main driver of fish diversity and biomass, although other variables like human accessibility were important. Boosted Regression Trees (BRT) revealed a strong negative effect of depth on species richness, segregating coral reefs from deep-sea environments. Surprisingly, BRT showed a hump-shaped effect of depth on fish biomass, with significantly lower biomass on coral reefs than in shallowest deep-sea environments. Biomass of large predators like sharks was three times higher on shallow seamounts (50 m) than on coral reefs. The five studied environments showed quite distinct assemblages. However, species shared between coral reefs and deeper-sea environments were dominated by highly mobile large predators. Our results suggest that seamounts are no diversity hotspots for fish. However, we show that shallower seamounts form biomass oases and refuges for threatened megafauna, suggesting that priority should be given to their protection.
... Photo-quadrat sampling is a method commonly used to determine estimates on benthic community structure on coral reefs (Leujak and Ormond 2007). Following the methods of Clua et al. (2006) and Chaves et al. (2013), 40 cm 2 quadrats were placed randomly along fixed 20 m line transects running across each site (the same sites used for the RUV samples). Using SCUBA and an Olympus TG-6 camera, 10 photo-quadrats were taken at each of the three sites (90 in total across all three habitat types). ...
Artificial reefs are now commonly used as a tool to restore degraded coral reefs and have a proven potential to enhance biodiversity. Despite this, there is currently a limited understanding of ecosystem functioning on artificial reefs, and how this compares to natural reefs. We used water sampling (bottom water sampling and pore water sampling), as well as surface sediment sampling and sediment traps, to examine the storage of total organic matter (as a measure of total organic carbon) and dynamics of dissolved inorganic nitrate, nitrite, phosphate and ammonium. These biogeochemical parameters were used as measures of ecosystem functioning, which were compared between an artificial reef and natural coral reef, as well as a degraded sand flat (as a control habitat), in Bali, Indonesia. We also linked the differences in these parameters to observable changes in the community structure of mobile, cryptobenthic and benthic organisms between habitat types. Our key findings showed: (1) there were no significant differences in inorganic nutrients between habitat types for bottom water samples, (2) pore water phosphate concentrations were significantly higher on the artificial reef than on both other habitats, (3) total organic matter content in sediments was significantly higher on the coral reef than both other habitat types, and (4) total organic matter in sediment traps in sampling periods May and September were higher on coral reefs than other habitats, but no differences were found in November. Overall, in terms of ecosystem functioning (specifically nutrient storage and dynamics), the artificial reef showed differences from the nearby degraded sand flat, and appeared to have some similarities with the coral reef. However, it was shown to not yet be fully functioning as the coral reef, which we hypothesise is due its relatively less complex benthic community and different fish community. We highlight the need for longer term studies on artificial reef functioning, to assess if these habitats can replace the ecological function of coral reefs at a local level.
... The control-impact approach has been proposed by several authors as a way to address this issue (Smith, 2002. In control (non-MPA) and impact sites (MPA), the following studies were conducted: (i) a comparative assessment of the ecological factors using the Medium Scale Approach (Clua et al., 2006), specifically designed for commercial reef fisheries, (ii) a comparative assessment of fishing effort and (iii) a comparative assessment of tourism attractiveness resulting from objective indicators of site accessibility (e.g. distance to airport, infrastructure, price) for visitors. ...
La protection côtière est un service écosystémique (SE) des récifs coralliens extrêmement important, en particulier avec les impacts négatifs imminents et croissants du changement climatique mondial (GCC). Le SE de protection côtière n'a cependant pas retenu la même attention que celle portée à des SE plus « évidents » peut-être parce que les avantages du SE ne sont visibles que sur terre (pas en mer) et sont couplés à des défis dans son évaluation tels que la détermination précise du rôle du corail vivant dans la fourniture du service. Malgré ces défis, la contribution des récifs à la prestation des SE a été scientifiquement prouvée. Les récifs coralliens sont en déclin à l'échelle mondiale à cause des impacts locaux et mondiaux, exacerbés par un financement inadéquat et non durable de leur protection et gestion. Il est impératif que nous déterminions les méthodes les plus adaptées pour améliorer la santé des récifs, dans un monde où la situation est à la fois désastreuse et sensible au temps ; avec un délai estimé à moins de 50 ans pour agir. Un élément essentiel de toute solution est de savoir comment payer pour ces améliorations, à un moment où les méthodes de financement traditionnelles semblent insuffisantes et où un financement inadéquat est identifié comme un obstacle majeur au succès de la conservation. L'objectif de cette thèse est d'étudier des solutions à la fois écologiques et financières pour améliorer la santé des récifs coralliens et son SE de protection des côtes. Nous concentrons l'analyse sur la viabilité et le financement de récifs artificiels “gris-verts” avec des solutions de restauration des récifs coralliens visant à protéger les plages de l'érosion. Le chapitre 2. Du paper pose le « décor » des chapitres suivants. Les interventions écologiques et financières interviennent dans le cadre d'une Aire Marine Protégée (AMP). Le document a analysé les données de 2 nations insulaires et via des analyses coûts-avantages a fourni des preuves de l'attractivité de l'investissement dans les AMP pour protéger les SE. Le chapitre prochaine passe en revue ce que l'on sait de la protection côtière des récifs coralliens et détermine sa faisabilité pour un système de paiement pour les services écosystémiques (PSE). Au cours du processus, le rôle du corail vivant a été analysé et les actions de gestion identifiées qui pourraient améliorer la santé des récifs pour la prestation de services ont été identifiées. Ce document identifie la restauration des coraux comme une intervention clé pour la protection côtière et fournit la justification du chapitre 5. Le chapitre 5 explore plus en détail les moyens non publics de financement de la conservation marine via des investissements à impact et des financements mixtes. Ayant identifié qu'il est logique d'investir dans les AMP au chapitre 1, nous identifions le type de financement et proposons un mécanisme de financement pour l'investissement. Les sorties sont utilisées dans le chapitre 5Le chapitre 6 utilise les résultats des chapitres 4 et 5 et développe des solutions écologiques et financières pour la protection côtière. Dans cet article, nous démontrons l'impact positif de la restauration des récifs, proposons des options pour le faire et montrons l'additionnalité obtenue en utilisant de telles solutions basées sur la nature par rapport aux infrastructures grises traditionnelles pour atténuer l'érosion côtière. Le chapitre 7 synthétise les résultats des chapitres précédents et conclut que si la restauration n'est pas une solution « parfaite », c'est peut-être notre meilleure chance d'améliorer la santé des récifs pour la protection côtière. Le fardeau du financement de telles solutions - dont le coût varie considérablement - ne devrait pas incomber uniquement aux gouvernements et devrait être partagé avec le secteur privé, en particulier ceux qui bénéficient directement de la protection côtière.
... Sur chaque vidéo, l'habitat a été caractérisé en estimant le pourcentage de couverture abiotique (non vivante) et biotique (vivante) sur l'ensemble de l'image à 360° à l'aide de la méthode « MSA » [3]. ...
... La caractérisation de l'habitat corallien a été réalisée et adaptée selon le protocole mis en place par IFREMER sur le programme AMBIO (Pelletier et al., 2015), basé sur la méthode paysagère du MSA (Clua et al., 2006) ; sur la classification de recouvrement des coraux de Wickel et Thomassin (2005); sur l'identification des morphologies des coraux de Faure et al., (2008 ...
... méthode MSA (Clua et al., 2006) pour la caractérisation des peuplements et substrat et des recouvrements (avec une cotation de dahl) l'identification des morphologies des coraux d'après Faure et al., 2008;Kelley, 2011 et adapté selon le protocole mis en place par IFREMER sur le programme AMBIO (Pelletier et al., 2015). ...
... Also, according to English et al. (1997), LIT is not suitable for mortality and recruitment studies. Besides LIT, several other methods that are often used to measure hard coral cover are Point Intercept Transect (PIT) (Dodge et al., 1982;Segal and Castro, 2001;Hill and Wilkinson, 2004) and Quadrat Method (Clua et al., 2006;Price and Harris, 2009). ...
Highlight ResearchPoint Intercept Transect Method (PIT) and Underwater Photo Transect (UPT) to monitor coral cover was comparedPercentage of hard coral cover was analyzedThe average difference of the percentage of hard coral cover obtained from the PIT and UPT was analyzed AbstractCoral reef ecosystems are vulnerable to damage and extinction. Therefore, it is imperative that, as part of conservation, their conditions are monitored using straight forward or easy-to-use methods. The research was intended to compare the effectiveness of using Point Intercept Transect (PIT) and Underwater Photo Transect (UPT) methods in calculating percent hard coral covers. It was conducted at six sites in Karimunjawa Islands, Indonesia: Cemara Besar, Cemara Kecil, Taka Malang, Tanjung Gelam, Menjangan Besar, and Menjangan Kecil. At each site, photographs of coral reefs were taken in two ranges of depths, shallow (3–6 m) and deep (9–12 m), along the length of the predefined transects (100 m for PIT and 50 m for UPT). In UPT, the photos were taken using a 58 x 44 cm frame. Fifty photo frames were collected then processed using Coral Point Count with Excel extensions (CPCe) 4.1. The results showed that PIT and UPT produced different percentages of hard coral cover at each site, with the most significant difference found in deep waters of Menjangan Besar (45.27%) and the least one in deep waters of Menjangan Kecil (0.08%). Overall, the difference in percent covers was averagely 9.79 percentage points, which is still categorized into small. Both methods have their own advantages and disadvantages. However, UPT is preferable because its results can be reanalyzed, especially the identified coral reef species.
... The habitat composition of each BRUVS was visually characterized using a Semi-quantitative Scale (SQS) method inspired from the Medium Scale Approach (MSA) (Clua et al. 2006). Specifically, a still image from each video was used to assess the percent composition of the substrate in its field of view. ...
Tropical inter-reefs represent a vast overlooked marine ecosystem that occurs between coral reefs and across the shelf. We deployed 60 baited remote underwater video stations (BRUVS) in New Caledonia to study inter-reef fish assemblages and habitats in three zones (bays, sandy lagoons, and sandy areas near the barrier reef) along an inshore-offshore gradient. Inter-reef habitats were dominated by soft bottoms with 83–98% of sand, and difference between the three zones was mainly driven by more sparse coral and macroalgae near the barrier reef. Overall, 148 fish species were recorded, and rarefaction curves extrapolated between 200 and 300 species on inter-reefs. Permutational linear models showed an increasing gradient in fish richness and abundance from the bays to the sand flats near the barrier reef with weak effect of individual habitat features. Two main fish assemblages were distinguished pertaining to an inshore and offshore cluster. While this structure partially followed the three inshore-offshore zones with distinct benthic habitat composition, it highlights that the largest ecosystem of the lagoon is dominated by commercial species. Our results using a low sampling size seem consistent with historical studies. BRUVS remain non-destructive and easy to deploy, making them a potentially good tool to study fish in marine tropical lagoons and should have applications for fishery management and conservation planning.
... The field survey was conducted as a process for testing the accuracy of the results of the supervised classification of Sentinel-2A satellite imagery and analysis of benthic habitats based on transect photographs. Field data were collected using a medium-scale approach (MSA) and quadrant estimation of 5x5m and saw the benthic cover (Clua et al. 2006). This technique was applied by Ampou et al. (2018) to study the Coral Reef in Menjangan Island. ...
Kartikasari A, Pristianto T, Hanintyo R, Ampou EE, Wibawa TA, Borneo BB. 2021. Representative benthic habitat mapping on Lovina coral reefs in Northern Bali, Indonesia. Biodiversitas 22: 4766-4774. Satellite optical imagery datasets integrated with in situ measurements are widely used to derive the spatial distribution of various benthic habitats in coral reef ecosystems. In this study, an approach to estimate spatial coverage of those habitats based on observation derived from Sentinel-2 optical imagery and a field survey, is presented. This study focused on the Lovina coral reef ecosystem of Northern Bali, Indonesia to support deployment of artificial reefs within the Indonesian Coral Reef Garden (ICRG) programme. Three specific locations were explored: Temukus, Tukad Mungga, and Baktiseraga waters. Spatial benthic habitat coverages of these three waters was estimated based on supervised classification techniques using 10m bands of Sentinel-2 imagery and the medium scale approach (MSA) transect method of in situ measurement.The study indicates that total coverage of benthic habitat is 61.34 ha, 25.17 ha, and 27.88 ha for Temukus, Tukad Mungga, and Baktiseraga waters, respectively. The dominant benthic habitat of those three waters consists of sand, seagrass, coral, rubble, reef slope and intertidal zone. The coral reef coverage is 29.48 ha (48%) for Temukus covered by genus Acropora, Isopora, Porites, Montipora, Pocillopora. The coverage for Tukad Mungga is 8.69 ha (35%) covered by genus Acropora, Montipora, Favia, Psammocora, Porites, and the coverage for Baktiseraga is 11.37 ha (41%) covered by genus Montipora sp,
... All videos were analyzed by the same experienced observer using the camera software (Kodak Pixpro SP360 PC software, v1.7.0). The habitat was characterized by estimating the percentage of abiotic and biotic coverage over the 360 • images using the "MSA" protocol [36]. The abiotic cover was classified as bare sediment (mud, sand, gravel and small boulders < 30 cm) or nonliving hard substrate (dead corals, coral slab, blocks > 30 cm). ...
Lagoon soft-bottoms are key habitats within coral reef seascapes. Coral reef fish use these habitats as nurseries, feeding grounds and transit areas. At present, most soft-bottom sampling methods are destructive (trawling, longlining, hook and line). We developed a remote, unbaited 360° video sampling method (RUV360) to monitor fish species assemblages in soft bottoms. A low-cost, high-definition camera enclosed in a waterproof housing and fixed on a tripod was set on the sea floor in New Caledonia from a boat. Then, 534 videos were recorded to assess the efficiency of the RUV360. The technique was successful in sampling bare soft-bottoms, seagrass beds, macroalgae meadows and mixed soft-bottoms. It is easy to use and particularly efficient, i.e., 88% of the stations were sampled successfully. We observed 10,007 fish belonging to 172 species, including 45 species targeted by fishermen in New Caledonia, as well as many key species. The results are consistent with the known characteristics of the lagoon soft bottom fish assemblages of New Caledonia. We provide future users with general recommendations and reference plots to estimate the proportion of the theoretical total species richness sampled, according to the number of stations or the duration of the footage.
... In a habitat and seagrass bed mapping context, several tens of stations per site are required for ground-truthing and accuracy assessment (Andréfouët et al., 2003. The field protocol for ground-truthing followed a fast-protocol for the collection of visual qualitative and semiquantitative data, and photographic records, and was similar in scope to the Medium-Scale Approach defined to visually describe benthic habitats in fish or invertebrate surveys (Clua et al., 2006). Benthic cover was measured using a semi-quantitative scale from 1 to 10 that linearly covers the 0-100% gradient (1 = 0-10%, to 10 = 90-100%). ...
Despite their ecological role and multiple contributions to human societies, the distribution of Indo-Pacific seagrasses remains poorly known in many places. Herein, we outline a hierarchical spatially-explicit assessment framework to derive nation-wide synoptic knowledge of the distribution of seagrass species and communities. We applied the framework to New Caledonia (southwest Pacific Ocean) and its 36,200 km2 of reefs and lagoons. The framework is primarily field-based but can leverage various habitat maps derived from remote sensing. Field data collection can be stratified by map products and retrospectively contribute to developing new seagrass distribution maps. Airborne and satellite remote sensing alone do not allow for the spatial generalisation of the finest attributes (species distribution and types of seagrass beds), but staged stratified field sampling provides synoptic views of these attributes. Using three examples, we discuss how the hierarchical and spatial information generated from this framework's application can inform conservation and management objectives.
... Cloud-free Sentinel-2 images (10 m resolution) available for the study area were retrieved from the Data Hub website (© Data Hub System 2.4.1, [37]; Figure 4). Data downloads provided a time-series of images from 2017 to 2019. ...
Despite the necessary trade-offs between spatial and temporal resolution, remote sensing is an effective approach to monitor macroalgae blooms, understand their origins and anticipate their developments. Monitoring of small tropical lagoons is challenging because they require high resolutions. Since 2017, the Sentinel-2 satellites has provided new perspectives, and the feasibility of monitoring green algae blooms was investigated in this study. In the Poé-Gouaro-Déva lagoon, New Caledonia, recent Ulva blooms are the cause of significant nuisances when beaching. Spectral indices using the blue and green spectral bands were confronted with field observations of algal abundances using images concurrent with fieldwork. Depending on seabed compositions and types of correction applied to reflectance data, the spectral indices explained between 1 and 64.9% of variance. The models providing the best statistical fit were used to revisit the algal dynamics using Sentinel-2 data from January 2017 to December 2019, through two image segmentation approaches: unsupervised and supervised. The latter accurately reproduced the two algal blooms that occurred in the area in 2018. This paper demonstrates that Sentinel-2 data can be an effective source to hindcast and monitor the dynamics of green algae in shallow lagoons.
... Belt Transect is a method that is often integrated with visual census methods to identify reef fish. The monitoring process uses line transects with monitoring distance left and right of 1-2 meters each [4,5]. ...
Reef fish is a constituent component for coral reef ecosystems, so it is very important to identify the distribution of reef fish species. This study aims to assess the number of reef fish species, diversity, abundance, recruitment, and frequency of size. The results showed that the number of reef fish species on Ternate Island was 42 families, 109 genera, and 265 species. The high level of diversity is 3.57 - 4.79 with an abundance of 8 - 28 ind.m ⁻² . The addition of new individuals to the population both due to reproduction and migration of 16.26 - 51.72%, the size-frequency of reef fish based on the size of the first time the gonads mature (L m ) is 45.00 - 70.00% of the total population of reef fish.
... Counts were converted to biomass (g m −2 ) from established lengthweight relationships (Kulbicki et al., 2005). Benthic cover data was obtained using the medium-scale approach described by Clua et al. (2006). This method is based on a semi-quantitative description of ten 25 m 2 (5 × 5 m) quadrats laid down on each side of the 50 m transect (i.e., 20 replicate quadrats/500 m 2 per transect). ...
Human activities are changing ecosystems at an unprecedented rate, yet large-scale studies into how local human impacts alter natural systems and interact with other aspects of global change are still lacking. Here we provide empirical evidence that local human impacts fundamentally alter relationships between ecological communities and environmental drivers. Using tropical coral reefs as a study system, we investigated the influence of contrasting levels of local human impact using a spatially extensive dataset spanning 62 outer reefs around inhabited Pacific islands. We tested how local human impacts (low versus high determined using a threshold of 25 people km −2 reef) affected benthic community (i) structure, and (ii) relationships with environmental predictors using pre-defined models and model selection tools. Data on reef depth, benthic assemblages, and herbivorous fish communities were collected from field surveys. Additional data on thermal stress, storm exposure, and market gravity (a function of human population size and reef accessibility) were extracted from public repositories. Findings revealed that reefs subject to high local human impact were characterised by relatively more turf algae (>10% higher mean absolute coverage) and lower live coral cover (9% less mean absolute coverage) than reefs subject to low local human impact, but had similar macroalgal cover and coral morphological composition. Models based on spatio-physical predictors were significantly more accurate in explaining the variation of benthic assemblages at sites with low (mean adjusted-R 2 = 0.35) rather than high local human impact, where relationships became much weaker (mean adjusted-R 2 = 0.10). Model selection procedures also identified a distinct shift in the relative importance of different herbivorous fish functional groups in explaining benthic communities depending on the local human impact level. These Frontiers in Marine Science | www.frontiersin.org 1 October 2020 | Volume 7 | Article 571115 Ford et al. Local Impacts on Pacific Reefs results demonstrate that local human impacts alter natural systems and indicate that projecting climate change impacts may be particularly challenging at reefs close to higher human populations, where dependency and pressure on ecosystem services are highest.
... A species was considered as "small" when the maximum species size was less than 30 cm. In addition to species counts, habitat was characterized for each video using the medium-scale approach (Clua et al., 2006) (see for details). ...
L’estimation de la diversité et de l’abondance des espèces de poisson est fondamentale pour comprendre la structure des communautés et la dynamique des récifs coralliens. Les observations sont généralement obtenues par des recensements visuels en scaphandre autonome (UVC). Ces informations peuvent également être obtenues de manière originale grâce aux observations issues des techniques vidéo sous-marines modernes sans plongeur qui permettent des couvertures spatiales et temporelles accrues.La première phase de ce travail de thèse synthétise l’ensemble des travaux ayant été effectués avec des techniques vidéo entre 1952 et 2012. La seconde phase, présente deux systèmes vidéo rotatifs complémentaires, utilisés pour étudier la diversité de l’ichtyofaune et des habitats marins dans le lagon de Nouvelle-Calédonie : le STAVIRO (pour « STAtion VIdéo ROtative ») et le MICADO (pour « Module d’Imagerie Côtier, Autonome pour le Développement de l’Observation sous-marine »). La troisième phase de ce travail consiste à comparer ces systèmes vidéo aux UVC puis à examiner l’effet « observateur » inhérent aux techniques vidéo rotatives. Il résulte de cette étude que : (i) les observations des communautés de poissons par UVC et STAVIRO différaient significativement, (ii) la richesse spécifique etla densité des espèces de grande taille n'étaient pas significativement différentes entre les techniques, (iii) la diversité et la densité des espèces de petite taille étaient plus élevés avec les UVC; (iv) la densité des espèces pêchées était plus élevée avec les STAVIRO et (v) seuls les UVC ont détecté des différences de structure des assemblages en fonction du type de récif. L’étude de l’effet « observateur » a montré que sur une liste d’espèces définie, les dénombrements et les identifications des individus peuvent être considérées comme similaires entre observateurs ayant une expérience suffisante (> 6 mois). La dernière phase de ce travail a permis d’appliquer la technique MICADO à l’étude des variations temporelles del’ichtyofaune d’un site corallien à l’échelle de la journée. Elle a permis de mettre en évidence des variations cycliques journalières en fonction de l’heure et de la marée et des « profils type » de variations ont pu être identifiés pour certains groupes d’espèces. Ce travail de thèse permet ainsi de participer au développement de nouvelles techniques d’observations complémentaires des techniques traditionnelles afin d’enrichir les connaissances du fonctionnement et de la dynamique des écosystèmes coralliens.
... Gili Matra merupakan salah satu kawasan pariwisata bahari di pulau Lombok yang banyak dikunjungi oleh wisatawan lokal maupun mancanegara, terutama bagi peminat wisata selam (Dirjen KP3K, KKP. 2014 (Dahl 1981;Clua et al., 2006). Metode yang digunakan untuk mengambil data tersebut adalah video transek sabuk (video-belt transect), modifikasi dari metode transek sabuk (belt transect). ...
This study aims to identify the status of reef fishes and coral reefs in Gili Meno, Air, and Trawangan or Gili Matra waters. This area is part of the North Lombok Regency, West Nusa Tenggara Province. Field observation was conducted on September 2011 at 11 (eleven) diving points. The video-transect method was used for observing the coral reef condition, while reef fishes abundance was observed by using visual-census method. The parameter that used to determine the condition of coral reef in study location are the percentage of live hard coral cover and index of coral mortality. In general, the result shows that percentage of live hard coral cover in each diving point ranged from 4.4% - 37.2% and the Coral Mortality Index (IMK) ranged form 0.40-0.92. The values describe that the condition of coral reef at eleven diving points vary from fair until poor condition. Current status of coral reef condition showed an insignificant increase from bad to moderate during the period 2011 -2018. There were 23 families of reef fishes from 46 genera were found during the study consisting of 16 genera of target fish groups, 5 genera of indicator fish group, and 25 genera of major fish group. The water quality is still within the limits of environmental quality standards.
Keywords: Reef fish, coral reef, Mortality Index, water quality, Gili Matra
... Sur chaque vidéo, l'habitat a été caractérisé en estimant le pourcentage de couverture abiotique et biotique sur l'ensemble de l'image à 360° à l'aide de la méthode de « MSA » (Clua et al., 2006 ...
Standardized method for sampling lagoon soft bottom fish using 360° video
... The medium scale approach (MSA) was used for field survey [11] on February, April and August 2017 at Menjangan island's reef flat ( Figure 2). In general, this approach were perform by in situ survey, however it also can undertake by transect photographs [12]. ...
Climate change has been identified as a stressor to coral reef ecosystem. Last El-Ninõ episode occurred in 2015-2016, leads to worldwide coral bleaching and mortality, including Indonesia. This study attempted to determine the stressor-response of reef-building corals to climate change in the Menjangan Island, Bali. Temperature data logger measurements and remote sensing dataset observing sea surface temperature (SST) and sea surface height (SSH) were used. The logger was deployed at five-meter depth recording hourly temperature during 2017. Monthly anomalies of SST and SSH covering ten years of observation (2007-2017) were calculated for the region. Monitoring of coral in the region was conducted on February, April and August 2017. Our findings indicate that there was evidence of mortality in the site, particularly on the northern reef flat, coinciding with both high positive SST and high negatives SSH anomalies occurred during the El-Ninõ period.
... The control-impact approach has been proposed by several authors as a way to address this issue (Smith, 2002, Halpern, 2003. In control (non-MPA) and impact sites (MPA), the following studies were conducted: (i) a comparative assessment of the ecological factors using the Medium Scale Approach (Clua et al., 2006), specifically designed for commercial reef fisheries, (ii) a comparative assessment of fishing effort and (iii) a comparative assessment of tourism attractiveness resulting from objective indicators of site accessibility (e.g. distance to airport, infrastructure, price) for visitors. ...
MPAs enhance some of the Ecosystem Services (ES) provided by coral reefs and clear, robust valuations of these impacts may help to improve stakeholder support and better inform decision-makers. Pursuant to this goal, Cost-Benefit Analyses (CBA) of MPAs in 2 different contexts were analysed: a community based MPA with low tourism pressure in Vanuatu, and a government managed MPA with relatively high tourism pressure, in Saint Martin. Assessments were made on six ES: fish biomass, scenic beauty, protection against coastal erosion, bequest and existence values, social capital and CO 2 sequestration, which were quantified via different approaches that included experimental fishery, surveys and benefit transfer. Total operating costs for each MPA were collected and the benefit-cost ratio and return on investment based on 25-year discounted projections computed. Sensitivity analyses were conducted on MPA impacts, and discount rates (5%, 7% and 10%). The investment indicators all showed positive results with the impact on the tourism ES being the largest estimated for all MPAs, highlighting the importance of this relationship. The study also demonstrated a relatively high sensitivity of the results to different levels of impacts on ES, which highlights the need for reducing scientific knowledge gaps.
... The habitat attributes can be dependent on the context and for BI we considered the attributes listed in Table 2. This type of description of habitats is equivalent to the so-called Medium Scale Approach (MSA) description (Clua et al., 2006) generally performed for fish census in situ, but which can be performed on a desktop using wide-angle photographs as well. Several photographs can be used for one habitat, and the average of the observations was kept. ...
The Coral Triangle is the epicenter of marine biodiversity, yet the numbers of habitats that can be found on coral reefs remain poorly described. First surveys for habitat mapping in Indonesia revealed a high number of habitats (>150) even for structurally simple reefs. To be able to represent all these habitats, typical habitat mapping procedures and performances are poorly effective even using very high resolution satellite images. Using Bunaken Island (North Sulawesi, Indonesia) as a case study, we devised a way to maintain all the in situ habitat information in remote sensing habitat map products without loss and with mapping procedures based on photo-interpretation. The result is a product which is consistent with a per-polygon fuzzy classification. As such, it is a complex product that meets our habitat representation goal, but its complexity can also limit its immediate use by managers and conservation planners when analyses per habitat are needed.
... >1,000 m 2 ) (Clua et al., 2006). These 28 characteristics were then averaged across the 20 quadrats for each transect and summarized into five categories (coral, turf algae, macroalgae, coralline crustose algae and other benthos; Table S2). ...
Anthropogenic activities such as land-use change, pollution and fishing impact the trophic structure of coral reef fishes, which can influence ecosystem health and function. Although these impacts may be ubiquitous, they are not consistent across the tropical Pacific Ocean. Using an extensive database of fish biomass sampled using underwater visual transects on coral reefs, we modelled the impact of human activities on food webs at Pacific-wide and regional (1,000s–10,000s km) scales. We found significantly lower biomass of sharks and carnivores, where there were higher densities of human populations (hereafter referred to as human activity); however, these patterns were not spatially consistent as there were significant differences in the trophic structures of fishes among biogeographic regions. Additionally, we found significant changes in the benthic structure of reef environments, notably a decline in coral cover where there was more human activity. Direct human impacts were the strongest in the upper part of the food web, where we found that in a majority of the Pacific, the biomass of reef sharks and carnivores were significantly and negatively associated with human activity. Finally, although human-induced stressors varied in strength and significance throughout the coral reef food web across the Pacific, socioeconomic variables explained more variation in reef fish trophic structure than habitat variables in a majority of the biogeographic regions. Notably, economic development (measured as GDP per capita) did not guarantee healthy reef ecosystems (high coral cover and greater fish biomass). Our results indicate that human activities are significantly shaping patterns of trophic structure of reef fishes in a spatially nonuniform manner across the Pacific Ocean, by altering processes that organize communities in both “top-down” (fishing of predators) and “bottom-up” (degradation of benthic communities) contexts.
... The map was created following the "user approach" described in Andréfouët (2008). Steps included a priori manual delineation of habitats, ground truth following the Medium Scale Approach (Clua et al. 2004), contextual editing, classification, and merging of habitat polygons. The resulting hierarchical habitat typology for the Madang Lagoon describes 28 geomorphic types (Appendix S3). ...
Marine reserve placement must account for the importance of places for resource use to minimize negative socioeconomic impacts and improve compliance. It is often assumed that placing marine reserves in locations that minimize lost fishing opportunities will reduce impacts on coastal communities, but the influence of the fishing data used on this outcome remains poorly understood. In the Madang Lagoon (Papua New Guinea) we compared three types of proxies for conservation costs to local fishing communities. We developed two types of proxies of opportunity costs commonly used in marine conservation planning: current fishing activity with fisher surveys (n = 68) and proximity from shore. We also developed proxies based on areas of importance for fishing as perceived by surveyed households (n = 52). Although all proxies led to different configurations of potential marine reserves, the three types of cost data reflect different aspects of importance for fishing and should be used as complementary measures. This article is protected by copyright. All rights reserved
... Individuals identified were also assigned to a size class ''small'', ''medium'' and ''large'' based on the maximum known length for each species. The habitat at each video drop site was characterized from the video footage using the medium-scale approach (Clua et al., 2006). In total, 442 video drops were deployed between 2008 and 2010. ...
Marine protected areas (MPA) and in particular no-take marine reserves have been identified as important tools for the conservation of reef fish and habitats. A significant challenge of reef fish monitoring is to determine the influence of temporal factors on fish counts. Fish assemblages are dynamic and changes in activity patterns throughout the day can influence the results of surveys. While many monitoring programs account for the impacts of spatial heterogeneity on fish assemblages the effects of short-term temporal variation are less well known. In the present study, we analysed data from 197 video drops inside and outside New Caledonian MPAs and examined temporal variations in various metrics commonly used to monitor marine reserves. In addition to describing short-term temporal patterns related to time of day, tide height and state, and lunar cycle; we also examined the influence of these temporal factors on the size and direction of any MPA effects detected. Fewer Serranidae were observed at full moon than the rest of the lunar cycle and there were negative correlations between Chaetodontidae and Acanthuridae abundance and tide height. We did not find any consistent effects of time of day. Generally, variation in short term temporal factors did not affect the direction MPA effects detected but did affect the size of the effects for some metrics. For both small fish abundance and species richness, bigger differences between protected and unprotected sites were detected at high tide than low tide. These results highlight how survey results can vary with timing of sampling and have implications for developing optimal monitoring programs.
... At small spatial scale, visual estimation of substrate composition (percentage of hard, detritic and soft substrate), algae and live coral was performed according to a semi-quantitative scale (Clua et al., 2006) within ten 5 9 5 m quadrats set on either side of the 50 m transect (see Mellin et al., 2006 andMacNeil et al., 2009 for a previous work using these variables). Depth, exposure to dominant swell and exposure to dominant wind were additionally considered as proxies of wave exposure. ...
Aim
We applied a multicomponent approach based on the decomposition of taxonomic (both presence–absence and abundance) and functional beta diversity to determine the influence of ecological factors in shaping spatial distribution diversity of coral reef fishes, and the implications for conservation decisions.
Location
Lagoons of ten atolls characterized by low human pressure but with contrasted geomorphology in the Tuamotu Archipelago, French Polynesia.
Methods
We computed beta diversities and their partitioning components, both at local (inter‐transect, from 200 m to 10 km) and large (among atolls, from 22 to 350 km) spatial scales. Null models were applied to test whether the observed beta diversity differed from random expectation. Multiple generalized dissimilarity models were run to test which environmental factors were the best predictors of observed beta diversities.
Results
Beta diversity was indistinguishable from randomness at both spatial scales. Species remained generally interchangeable among transects within an atoll and to some extent among atolls. However, strong deviance explained by models showed that the number of species, the number of individuals and functional traits present in transects and atolls were determined by deterministic factors (i.e. environmental factors). Modelling each beta diversity component separately also revealed partial mismatch among atolls and among species and functional dissimilarities. The influence of environmental variables strongly varied among atolls, species and functional dissimilarities.
Main conclusions
By revealing the spatial scaling of ecological factors and partial congruence among species and functional diversity, assessment of beta diversity provides insight into conservation planning. Our results support the idea that conservation planning applied to protect taxonomic diversity cannot be fully extended to functional diversity. We have addressed the dilemma of which diversity component should be favoured in conservation strategies.
... D'autres approches permettent d'entrer directement dans la problématique du design d'AMP, et consistent à évaluer la part de diversité de la variable cible capturée dans un réseau défini à partir de la variable substitut (Sarkar et al., 2005). Les environnements paysagers de chaque site (plusieurs paysages peuvent être présents par site) ont été décrits selon la méthode dite Medium-Scale Approach (MSA) (Clua et al., 2006). Cette méthode in situ consiste à d'abord décrire la géomorphologie et la topographie du récif, puis à estimer visuellement de manière semi-quantitative le pourcentage de couverture des composants benthiques contribuant au paysage observé (annexe, Tableau 7 ; Chabanet, 1994;Chabanet et al., 2010). ...
La prise en compte de critères biologiques lors de la mise en place de réseaux d'aires marines protégées (AMP) permet d'augmenter leur efficacité mais nécessite des inventaires coûteux et localisés. Dans cette étude centrée sur le site de Port-Bouquet en Nouvelle-Calédonie, nous proposons dans un premier temps d'évaluer si les habitats peuvent servir de substituts efficaces à la diversité taxonomique et fonctionnelle des communautés de poissons en milieu corallien. 11 niveaux de caractérisation d'habitats et 9 échelles spatiales différentes ont été testés par analyse de corrélation et de substitution, de manière à déterminer les conditions optimales pour lesquelles la richesse, la diversité, et la rareté des habitats permettent une bonne représentation de la richesse, la diversité, et la rareté des groupes taxonomiques et fonctionnels de poissons. Notre étude suggère que l'approche par substitution est la plus appropriée lorsqu'il s'agit d'établir un réseau d'AMP, puisque s'appui directement sur les algorithmes de sélection des sites candidats. Les algorithmes dits de « Richesse-complémentarité » et de « Rareté » utilisés dans cette étude se sont avérés sensibles aux effets du hasard et de l'échantillonnage. Des résultats encourageant ont en revanche été obtenus pour un scénario de «Diversité-complémentarité» et a pu être utilisé pour proposer un réseau d'AMP, établis sur la base de la topographie des habitats, efficace d'un point de vue de la représentativité taxonomique et fonctionnelle des poissons. (Résumé d'auteur)
... Les observations in situ sont issues de plusieurs campagnes de vérité terrain effectuées pour la cartographie des habitats, et de mon travail de terrain effectué entre mars et avril 2013 (Tableau 1). Clua et al. 2006) en se concentrant sur les paramètres des colonies de coraux scléractiniaires vivants qui sont : la couverture corallienne, la composition en genres coralliens (ou espèce, si identifiable de façon certaine) et le pourcentage de couverture de chaque genre, et enfin la forme de croissance associée. Enfin, nous avons attribué chaque communauté à une unité géomorphologique récifale (platier, pente, terrasse, fond de lagon, escarpement, crête ou éperon-sillon), qui correspond à l'unité où elle avait été majoritairement observée sur les îlots (Figure 6) ...
Le blanchissement corallien est une conséquence dramatique du réchauffement climatique qui menace les récifs et la biodiversité mondiale. A travers un cas d’étude sur les îlots du lagon Sud-ouest de la Nouvelle-Calédonie, nous avons planifié un réseau d’Aires Marines Protégées conservant des zones refuges, ayant une sensibilité au stress thermique la plus faible possible. Pour cela nous avons identifié et cartographié les communautés coralliennes présentes en tenant compte de la plus grande richesse de communautés possible. Nous avons ensuite paramétré leur sensibilité au stress thermique avec une échelle de scores semi-quantitative de 1 à 4, basée sur la littérature disponible étudiant la sensibilité propre à chaque genre corallien. Nous avons transposé ces scores pour obtenir une carte de sensibilité au stress thermique par unités de gestion, sur laquelle nous avons bâti notre réseau d’AMP. Ainsi, nous obtenons un réseau protégeant 20% de la diversité de nos communautés coralliennes tout en minimisant la sensibilité globale au stress thermique. Le protocole établi est ré-applicable, éventuellement en intégrant d’autres facteurs de la vulnérabilité des écosystèmes coralliens au stress thermique, afin de concevoir un réseau de conservation prenant en compte le changement climatique.
... The Medium Scale Approach (MSA) was used to record substrate characteristics along transects where finfish were counted by UVC. MSA has been developed by Clua et al. (2006) to specifically complement UVC surveys. The method consists in recording depth, habitat complexity, and 23 substrate parameters (% coral cover, % macro algae, etc.) within ten 5x5 m quadrats on each side of 50-m transects, for a total of 20 quadrats per transect. ...
Les objectifs spécifiques de l’étude sont les suivants :
• Organiser et réaliser en 2020 les relevés de terrain (peuplements benthiques et
ichtyologiques) selon le plan d’échantillonnage et le protocole défini,
• Assurer la bancarisation des données dans l’outil BD-Récifs,
• Rédiger un bilan de l’état de santé des récifs internes et barrière en 2020,
• Procéder à une analyse de l’évolution temporelle des récifs internes et barrière depuis la création du suivi.
L’objectif principal de la présente expertise est de fournir au PNMM un bilan actualisé en 2013 de l’état de santé des écosystèmes coralliens de la barrière et des récifs internes (suivi MSA de l’ORC), intégrant une description de l’évolution temporelle de données. Il contribuera notamment à la mise en oeuvre opérationnelle d’actions de suivi et de conservation par l’équipe du PNMM à moyen terme.
Les objectifs spécifiques sont, conformément à la proposition technique validée :
- réaliser l’ensemble des relevés de terrain,
- saisir et traiter les données récoltées,
- intégrer l’ensemble des résultats à un système d’information géographique,
- rendre compte de la vitalité corallienne en 2013 et interpréter les évolutions constatées depuis les années antérieures,
- délimiter les secteurs selon leur état de santé à partir de la couverture corallienne,
- caractériser les différents sites selon l’ensemble des paramètres,
- estimer la résistance/résilience des différents secteurs précédemment délimités,
- prendre des clichés photographiques géoréférencés des paysages sous-marins remarquables (de caractéristiques géomorphologique,
L’objectif principal de la présente expertise est de fournir au PNMM un bilan actualisé en 2013 de l’état de santé des écosystèmes coralliens de la barrière et des récifs internes (suivi MSA de l’ORC), intégrant une description de l’évolution temporelle de données. Il contribuera notamment à la mise en oeuvre opérationnelle d’actions de suivi et de conservation par l’équipe du PNMM à moyen terme.
Status of soft bottom habitats and megafauna of Entrecasteaux atolls, New Caledonia
Scalable assessments of biodiversity are required to successfully and adaptively manage coastal ecosystems. Assessments must account for habitat variations at multiple spatial scales, including the small scales (<100 m) at which biotic and abiotic habitat components structure the distribution of fauna, including fishes. Associated challenges include achieving consistent habitat descriptions and upscaling from in situ‐monitored stations to larger scales.
We developed a methodology for (a) determining habitat types consistent across scales within large management units, (b) characterizing heterogeneities within each habitat, and (c) predicting habitat from new survey data. It relies on clustering techniques and supervised classification rules and was applied to a set of 3,145 underwater video observations of fish and benthic habitats collected in all reef and lagoon habitats around New Caledonia.
A baseline habitat typology was established with five habitat types clearly characterized by abiotic and biotic attributes. In a complex mosaic of habitats, habitat type is an indispensable covariate for explaining spatial variations in fish communities. Habitat types were further described by 26 rules capturing the range of habitat features encountered. Rules provided intuitive habitat descriptions and predicted habitat type for new monitoring observations, both straightforwardly and with known confidence. Images are convenient for interacting with managers and stakeholders.
Our scheme is (a) consistent at the scale of New Caledonia reefs and lagoons (1.4 million km²) and (b) ubiquitous by providing data in all habitats, for example, showcasing a substantial fish abundance in rarely monitored soft‐bottom habitats. Both features must be part of an ecosystem‐based monitoring strategy relevant for management.
This is the first study applying data mining techniques to in situ measurements to characterize coastal habitats over regional‐scale management areas. This approach can be applied to other types of observations and other ecosystems to characterize and predict local ecological assets for assessments at larger scales.
Coral reefs interference by multiple threats from local and global source. The aggregate effects of local stressors such as tourism activity, pollution, overfishing, and coral harvesting can decrease resilience of the reefs. Furthermore, increased ocean temperatures, changing ocean chemistry, and sea level rise are the greatest global threats to coral reef ecosystems. The objective of this work is to assess coral reefs ecosystem degradation at Nusa Penida (NP), Bali. In this works, monitoring of coral reef ecosystem was conduct by transect photographs on May and October 2018. We observed the evidence of coral reefs degradation in the site, particularly on the northern and southern reefs area. We also found that algal cover much higher than our previous monitoring activities, linked to higher coral mortality at these locations.
Aim: To determine the ecoregions (spatial marine areas with similar environmental and
physical conditions associated with relatively homogeneous fish assemblages) for shallow
reef fish assemblages based on predictive models of beta diversity (b-diversity) that
account for both large-scale environmental factors and local habitat characteristics. We
assessed the influence of a spatial scale to rank the importance of these factors.
Location: New Caledonian (south-west Pacific Ocean, 17–24° S, 158–172° W)
Exclusive Economic Zone, Coral Sea Marine Park.
Taxon: Fish.
Methods: Fish and habitat data that were collected at 13 sites around New Caledonia
using unbaited rotating underwater video (285 sampling stations) were analysed.
Gradient forest modelling was used to predict the fish b-diversity along the gradients
of environmental factors. Ecoregions were obtained by applying clustering
methods to gradient forest predictions.
Results: The gradient forest models of b-diversity retained 59 species (total: 206 fish
species) with R² > 0, including 19 fish species with R² from 0.03% to 69%. For these
19 species, the models explained up to 26% of the variance. At a large scale, b-diversity
was significantly explained by nutrient concentrations, sea surface salinity and
temperature. Among the eight ecoregions that were delineated based on the b-diversity
predictions, three regions corresponded to remote sites under oceanic influence
where human pressures are low and the surface nutrient concentrations are high. On
the local scale, the benthic habitat explained b-diversity better than the physical and
chemical parameters, particularly in the areas subject to anthropogenic pressures.
Main conclusions: On the local scale, the respective importance of environmental factors
(physical and chemical parameters versus benthic habitat) differed according to
ecosystem health. Our findings suggest that nutrient enrichment due to avifauna may
have a positive effect on fish b-diversity when an ecosystem is healthy. The ecoregions
reflect fish species composition in relation to a large set of environmental parameters.
Landscape scale is used to analyze the distribution of trophic fish groups in Alacranes Reef, Yucatan, Mexico. In order to relate reef landscapes, or reefscapes, and the trophic groups of fishes, 47 sample transects were done to characterize the reefscapes and to obtain abundance fish data. Canonical Correspondence Analysis was used to detect the relationship between the mean biomass of trophic fish groups and 20 reefscape characteristics. The analysis showed three main groups : 1) fish and zooplankton feeders associated with the reefscapes Spurs and grooves (I), Calcareous bottom with algal mats (K), and Sandy bottom with algal mats (G) ; 2) 'shelled' invertebrate feeders and generalized carnivores related to Rubble (A), Seagrass flats (B), Meadow (C), Sand with branching coral patches (F), and Algae assemblages (L) reefscapes; and 3) plant and detritus feeders and sessile invertebrate feeders associated with Dead structures and soft coral (D), Dead structures and massive coral (E), Algal mats on dead structures (H), and Calcareous bottom with Palithoa (J). Environmental characteristics that were a determiner of distribution and abundance of trophic fish groups including : bottom complexity; depth; encrusting biota; algal coverage; and massive, soft and encrusting coral coverage for fish and zooplankton feeders. For generalized carnivores and 'shelled' invertebrate feeders, they included dead structure, rubble, sand, branching coral and sea grass coverage; for plant and detritus feeders and sessile invertebrate feeders they included soft coral coverage and calcareous substrata. Estimates of mean biomass, production and consumption were maximum in the Meadow reefscape (C) and minimal in the Algal mats on dead structures reefscape (H). The reefscape scale offers a different point of view for the analysis and interpretation of coral reef fish community structure and function.
The MPAs located within the New Caledonia South Lagoon Marine Park have been studied since their creation in 1989. Reef fish communities modifications within the MPAs are now well known but their interactions with unprotected areas still needs to be quantified. Prior to the study of reef fish movement patterns between MPAs and unprotected reefs, the present study was planed to compare the coral reef fish communities of two fished reefs (Crouy and Laré gnère reefs) and one protected reef (Larégnère islet) within the Park. Twelve stations were sampled on each reef using underwater visual census techniques. Three point counts were completed at each station; one on the reef flat, one on the upper part of the reef slope and one on the lower part of the reef slope. Species richness, density and biomass of all edible species in the Pacific and of commercial species in New Caledonia were calculated. No significant difference occurred between reefs for edible fish and all three indices. Significant differences occurred for the commercial species, with higher values on the protected reef for all three indices. Species richness was 15% and 28% higher, density 65% and 107% higher and biomass 94% and 158% higher in the reserve than in the unprotected reefs. Significant differences occurred for the most valuable commercial families; Serranids, Siganids, commercial Acanthurids and commercial Labrids, which were also more important in the protected reef. These effects were less significant for the Scarids. Only few species, e.g. Chlorurus microrhinos, which is one of the most targeted parrotfish, have significant higher density and biomass in the protected area. Three species assemblages were identified using a Correspondence Analysis: one assemblage affected by cyclone Erica, one protected assemblage and one unprotected assemblage. A comparison with the results of a Canonical Correspondence Analysis showed that these assemblages were primarily related to reef status and secondarily to substrate characteristics. Protection measures were responsible for a modification of reef fish organisation despite a significant effect of habitat structure. The density of commercial species in fished areas near the protected area was higher than in the reserve before the protection was effective. These results and the relative stability of the protected community during 9 years support the hypothesis of significant interactions between protected reefs and nearby unprotected reefs. These results were used to plan a three years program to test fish movement patterns between these three reefs.
Two fishing grounds were selected in each of the three archipelagos of Tonga, according to fishing pressure (high and low). In each ground, socioeconomic surveys provided an evaluation of fishing pressure. Reef fish stocks were assessed through underwater visual censuses along 241 transects and their habitat was described with a novative method (Medium Scale A p p r o a c h ) , better adapted to their life territories. The analysis of ecological and fishing data showed a variation between global fishing pressure at the archipelago level, which was responsible, in combination with ecological factors, for more differences than between the pair of sites within each archipelago. The fishing factor explains globally less variance of fish populations (1.6 to 5.7%) than factors acting at micro-scale (depth, hard substrate and live coral coverages, heterogeneity and topographic complexity) and at meso-scale (oceanic influence), that explain 23.3 to 34.3% of variance. The study confirmed fishing effects already known (such as reduction of fish populations average size, compensatory increase of density in the small size classes) and showed, at least for scarids, a “shifting dominance” phenomenon, based on the decrease of large-size target species, which benefits to small size species, less vulnerable to fishing. Clustering of species according to diet or life history traits revealed gradual changes of density and biomass in specific groups according to fishing pressure gradient. This result provides potential for setting up indicators of stock status for better management of reef fish resources.
Most studies of coral reef fish communities have been restricted to site-attached species on small. isolated patches of habitat. Few have investigated spatial variation in fish species richness in relation to predictions based on stochastic or deterministic processes of community organisation. Our aims were to. (1) compare species richness on contiguous and fragmented reef habitats, and (2) investigate the mechanisms underlying spatial variation in species richness. Quantitative comparison of species area curves for contiguous and patchy coral reef indicated that patch reefs support more species than equivalent areas of contiguous reef. However, Monte-Carlo simulated rarefaction curves indicated little difference in the species-individuals relationship for both habitats. Rarefaction was employed to eliminate variation in species richness among sites due to differences in sample size (number of fish present). After removal of sample-size effects, multiple regression models explained 30% and 25% of total variability in species richness on contiguous and patchy coral reef based on variation in habitat structure (e.g., depth, shelter availability, substratum characteristics). To investigate the likely importance of stochastic processes in determining spatial variation in species richness, we compared the species-individuals relationship from contiguous reef sites with the relationships derived from null models involving the random reallocation of fish among sites. Comparisons of the observed data with the outcomes of the null models indicated that spatial variation in species richness was not wholly attributable to stochastic processes. We suggest that the observed patterns of species richness may reflect species interactions (e.g., competition and predation) within fish communities.
Many sampling strategies have been proposed as appropriate for describing spatial patterns in marine organisms. There remain, however, many problems with the description, analysis and interpretation of temporal variation in abundances of organisms. In particular, there is a need to understand temporal error in the estimation of abundance of mobile organisms. In this paper we report estimates of temporal variation in abundances of tropical reef fishes attributable to sampling error at diurnal, daily and 'monthly' scales and compare these to inter-annual variation that might arise from processes such as mortality and recruitment. Uncertainty in estimates taken from the same sites over consecutive days was large for several species and accounted for the majority of error in estimates of abundance within years, Sources of error in estimates of abundance are discussed with consideration of the implications for long-term sampling and monitoring of fish assemblages. Shortterm temporal variation must be considered along with spatial variation in the design and interpretation of temporal studies of mobile species.
Coral reef fishes occupy habitats that are patchy and subject to frequent natural disturbances. Although different types of disturbance are likely to generate different community responses, the relationship between different disturbance agents and their effects on reef fish communities has not been examined experimentally. We studied a set of natural patch reefs, dominated by a diverse array of soft and hard coral cover, at Lizard Island on the Great Barrier Reef (northeastern Australia). The fish assemblages on the reefs were sampled over 4 mo to establish baseline values and then experimentally disturbed. Two types of disturbance were carried out in a factorial combination: pulsed mortality by removing all fish from reefs and pulsed habitat disturbance. Habitat disturbance was applied at two levels: Level 1 consisted only of damaging all live hard corals with a hammer; Level 2 consisted of damaging all live hard corals, and in addition, using a hammer to reduce the height and complexity of the reef matrix. We then monitored the experiment for a further 19 mo, including two recruitment seasons. Unmanipulated control assemblages persisted through time, and despite large changes in total abundance, species composition remained consistent relative to disturbed treatments. Assemblages disturbed by fish removal were resilient, with recolonization from both immigration and larval settlement effectively removing differences between removal treatments and controls 3 mo after manipulation. Habitat disturbance alone generated differences between experimental and control assemblages, which persisted for the duration of the experiment. The more extreme level of habitat disturbance generated more extreme changes in fish assemblages when no pulsed mortality occurred. Habitat disturbance in combination with pulsed mortality generated similar community responses as the habitat disturbance treatment alone. However, fish removal had the effect of eliminating the difference between fish assemblages on reefs subjected to different levels of habitat disturbance. Community response to habitat disturbance was driven by species-specific patterns of reduced abundance of species associated with live coral in combination with increased numbers of those associated with rubble. Declines in the abundance of coral associates on damaged reefs were abrupt, with no recovery observed for the duration of the experiment. In contrast, increases in the abundance of rubble associates were more ephemeral, in that initial high levels of recruitment and immigration were followed by a high rate of loss. Habitat disturbance also generated reefs that typically supported lower fish abundance, fewer species, and increased evenness relative to controls. Our results support a model of patch-reef fish assemblages organized by a combination of deterministic factors (such as habitat structure) and stochastic processes (such as recruitment). These disparate mechanisms operate in concert to generate reasonably consistent patterns of community structure. Habitat structure appears to mediate much of the apparent determinism and is likely to operate both as a reflection of species-specific habitat preferences and by modifying interactions among fish species. Consequently, disturbance plays a substantial role in structuring communities of coral-reef fishes by modifying both spatial and temporal heterogeneity.
Coral reef fish are bound to the pelagic environment throughout their larval stage, although they spend most of their adult life on reefs. Thus, the morphology of a lagoon and the location of a reef within the lagoon may influence the nature of its fish assemblage. Because of its asymetrical shape, the SW lagoon of New Caledonia allows us to test such a hypothesis. Several fringing reefs located 4–34 km from the open ocean were compared with one another. No influence of the reef-ocean distance could be found on the global values of diversity, density or biomass. However, presence-absence data of the 343 taxa encountered are related to this distance. Similarly, ecological structures based on diet, size and mobility of fish present strong correlations with reef—ocean distance. Thus, the major effects of an increase in reef—ocean distance concern both taxinomical and ecological structures. Suggested explicative hypotheses are linked to the fish feeding habits closely related to the environment but also to their utilisation of space. Territorial behaviour seems indeed to be important in structuring reef fish assemblage.
This chapter suggests two major patterns related to the density dependence in coral reef fish population. Demographic density dependence is generally defined as an effect of the present and/or past population sizes on the per-capita population growth rate. Coral reef fishes support major fisheries and are the object of conservation efforts in their own right. They are ideal subjects for both observational and experimental population studies. The total local recruitment rate varies in a broad variety of patterns as a function of local population size. Although recruitment is not a consistent source of demographic density dependence in every study, conversion from total to per-capita recruitment results in apparent or pseudo-density dependence, which can provide a nonmechanistic kind of local population equilibrium unrelated to the regulation of the entire metapopulation. The data on 20 species from six families shows that postsettlement mortality is often density-dependent, especially shortly after settlement, which is caused largely by predation. Overall, 17 of 20 species experienced density-dependent per-capita mortality at some time and place. In most studies that reported density-independent mortality, the study of older juvenile fishes suggested that regulation via mortality is an early postsettlement phenomenon. The prevalence of density-dependent mortality has two effects. First, local populations may be an important source of regulation for the entire metapopulation, suggesting the importance of conserving the mechanisms causing local density dependence. Second, the more restrictive version of the recruitment limitation hypothesis that predicts that postsettlement mortality may be density-independent has been falsified in most cases.
This study used underwater visual census techniques to quantify the distribution, abundance,
fork lengths and biomass of scarid fishes on multiple reefs across the continental shelf of the
northern Great Barrier Reef. Spatial patterns in fish distribution were examined over a cross shelf
environmental gradient using a hierarchical sampling design that covered a spectrum of scales ranging
from metres to tens of kilometres. The design included replicate reefs within mid and outer continental
shelf positions and replicate sheltered and exposed sites within each reef. Most of the 21 species
surveyed were found to be widely distributed across mid and outer shelf reefs and the number of
species did not change significantly between reefs, exposures or across the shelf. Despite a similar
complement of species, scarid assemblages differed markedly in the relative and absolute abundance
of taxa between exposed and sheltered habitats on mid and outer shelf reefs. Principal components
and cluster analyses indicated that changes in the numerical abundance of taxa resulted in consistently
different assemblages from 9 sheltered mid shelf sites and 9 exposed outer shelf sites at opposite
ends of the surveyed environmental gradient. Variance components calculated for scarid abundance
and biomass across 4 spatial scales revealed differences in the scales at which significant
variability occurred between sheltered and exposed reef habitats. On exposed reef crests significant
variation occurred at both scales of tens of kilometres (shelf position) and hundreds of metres (sites),
while on sheltered back reefs significant variation was attributable only to the site scale. Mean scarid
abundance (±SE) for exposed outer shelf sites (3060 ± 460 ha–1) was on average 4 times higher than in
all other habitat zones surveyed, while mean biomass (±SE) was only 3 times higher (920 ± 190 kg ha–1).
The discrepancy between abundance and biomass estimates is explained by a 30% average decline
in parrotfish fork lengths on exposed outer shelf reef crests relative to other habitats. Log-linear
analysis indicated that at least 8 species of scarids displayed significant changes in body size according
to their location across the continental shelf and/or the prevailing exposure regime. The observed
patterns of variation in density and length frequency suggest density-dependent processes and that
changes in mortality or growth rates may exist between habitats across the continental shelf.
Offers a comprehensive introduction to distance sampling, a statistical method used by many biologists and conservationists to estimate animal abundance. The text discusses point transect sampling and line transect sampling and also describes several other related techniques. There are updates on study design and field methods, laser range finders, theodolites and the GPS and advice is given on a wide range of survey methods. Analysis methods have also been generalized, through the use of various types of multiplier and exercises for students in wildlife and conservation management are included.
Abstract Although there is no one correct technique for sampling vegetation, the sampling design chosen may greatly influence the conclusions researchers can draw from restoration treatments. Considerations when designing vegetation sampling protocol include determining what sampling attributes to measure, the size and shape of the sampling plot, the number of replicates and their location within the study area, and the frequency of sampling. We installed 20 point-intercept transects (50-m long), 8 belt transects (10 × 50 m), 10 adapted Daubenmire transects (four 0.5 × 2-m plots), and 4 modified-Whittaker plots (20 × 50 m with smaller nested plots) in treatment and control units to measure understory herbaceous response in a forest restoration experiment that tested different treatments. Point-intercept transects on average recorded at least twice as much plant cover as did adapted Daubenmire transects and modified-Whittaker plots taken at the same location for all control and treatment units. Point-intercept transects and adapted Daubenmire plots on average captured fewer rare and exotic species in the control and treatment units in comparison with the belt transects and modified-Whittaker plots. Modified-Whittaker plots captured the highest species richness in all units. Early successional understory response to restoration treatments was likely masked by the response of the herbaceous community to yearly climatic variation (dry vs. wet years). Species richness and abundance were higher in wet years than dry years for all control and treatment units. Our results illustrate that sampling techniques can greatly influence perceptions of understory plant trajectories and therefore the interpretation of whether restoration goals have been achieved. In addition, our results suggest that restoration monitoring needs to be conducted for a sufficient length of time so that restoration treatment responses can be detected.
The size of a sampling unit has a critical effect on our perception of ecological phenomena; it influences the variance and correlation structure estimates of the data. Classical statistical theory works well to predict the changes in variance when there is no autocorrelation structure, but it is not applicable when the data are spatially autocorrelated. Geostatistical theory, on the other hand, uses analytical relationships to predict the variance and autocorrelation structure that would be observed if a survey was conducted using sampling units of a different size. To test the geostatistical predictions, we used information about individual tree locations in the tropical rain forest of the Pasoh Reserve, Malaysia. This allowed us to simulate and compare various sampling designs. The original data were reorganised into three artificial data sets, computing tree densities (number of trees per square meter in each quadrat) corresponding to three quadrat sizes (55, 1010 and 2020 m(2)). Based upon the 55 m(2) data set, the spatial structure was modelled using a random component (nugget effect) plus an exponential model for the spatially structured component. Using the within-quadrat variances inferred from the variogram model, the change of support relationships predicted the spatial autocorrelation structure and new variances corresponding to 1010 m(2) and 2020 m(2) quadrats. The theoretical and empirical results agreed closely, while the classical approach would have largely underestimated the variance. As quadrat size increases, the range of the autocorrelation model increases, while the variance and proportion of noise in the data decrease. Large quadrats filter out the spatial variation occurring at scales smaller than the size of their sampling units, thus increasing the proportion of spatially structured component with range larger than the size of the sampling units.
Here I investigate whether patterns of scarid biomass across the continental shelf of the northern Great Barrier Reef can be explained by species associating with particular characteristics of the reef environment. Despite the widely documented tendency of scarids to graze and browse over exposed calcareous reef surfaces, scarid biomass was not significantly correlated with the availability of feeding substrata for any species investigated. Indeed positive correlations between biomass and substrata variables were rare for the 18 species investigated, indicating that biomass in these taxa was not strongly reliant on the availability of preferred substrata quantified at the spatial scale of sites (1620m2). Rather, species specific biomass was commonly highly variable between sites, suggesting that local aggregation of scarids commonly occurs at this scale. Such spatial patchiness potentially reflects the effects of spatially variable recruitment, fishes associating with unmeasured habitat characteristics or aggregating prior to spawning. Despite variability in the biomass of individual species between replicate sites within exposure regimes, exposure was generally a far more reliable predictor of biomass than the other variables quantified. This study provides little evidence to indicate that adult scarids have strict habitat requirements, rather they appear to be habitat generalists whose biomass is strongly influenced by exposure but weakly related to the cover of particular reef substratum.
A new technique called the reef resource inventory (RRI) was developed to map the distribution and abundance of benthos and substratum on reefs. The rapid field sampling technique uses divers to visually estimate the percentage cover of categories of benthos and substratum along 220m plotless strip-transects positioned randomly over the tops, and systematically along the edge of reefs. The purpose of this study was to compare the relative sampling accuracy of the RRI against the line intercept transect technique (LIT), an international standard for sampling reef benthos and substratum. Analysis of paired sampling with LIT and RRI at 51 sites indicated sampling accuracy was not different (P>0.05) for 8 of the 12 benthos and substratum categories used in the study. Significant differences were attributed to small-scale patchiness and cryptic coloration of some benthos; effects associated with sampling a sparsely distributed animal along a line versus an area; difficulties in discriminating some of the benthos and substratum categories; and differences due to visual acuity since LIT measurements were taken by divers close to the seabed whereas RRI measurements were taken by divers higher in the water column. The relative cost efficiency of the RRI technique was at least three times that of LIT for all benthos and substratum categories and as much as 10 times higher for two categories. These results suggest that the RRI can be used to obtain reliable and accurate estimates of relative abundance of broad categories of reef benthos and substratum.
Patterns in juvenile mortality rates can have a profound affect on the distribution and abundance of adult individuals, and
may be the result of a number of interacting factors. Field observations at Lizard Island (Great Barrier Reef, Australia)
showed that for a coral reef damselfish, Pomacentrus moluccensis, juvenile mortality (over 1 year) varied between 20 and almost 100% among sites. Correlative data showed that juvenile mortality
increased as a function of initial densities (recruitment), predator densities and the availability of preferred coral substrata.
A multiple regression showed that these three variables together did not explain significantly more variation in mortality
than the single factor showing the strongest relationship. This appeared to be because recruitment, predator densities and
preferred coral substrata were all highly correlated, suggesting that one, two or all of these factors may be influencing
juvenile mortality rates. One hypothesis was that density-dependent mortality in juveniles was the result of an interaction
between predators (which appear to aggregate at high-recruitment sites) and the availability of preferred substrata (predator
refuges). We tested this hypothesis by using both laboratory and field experiments to see whether fish predation could significantly
alter survivorship of this damselfish, and whether this impact was dependent upon the coral substratum. The laboratory experiment
was designed to test the effects of three common predators (Pseudochromis fuscus, Cephalopholis boenak and Thalassoma lunare) and three different coral substrata that varied in their complexity (Pocillopora damicornis, Acropora nasuta and A. nobilis) on the survival of juvenile Pomacentrus moluccensis. There was a significant interaction between predator species and microhabitat in determining survival. Pseudochromis fuscus and C. boenak were both significantly better at capturing juvenile damselfish than T. lunare. Juvenile survivorship was significantly better when they were given the more complex corals, Pocillopora damicornis and A. nasuta, compared with those given the open-structured species A. nobilis. This pattern reflects habitat selection in the field. Predators differed in their strike rates and the proportion of strikes
that were successful, but all exhibited greater success at prey capture where A. nobilis was provided as shelter. The interaction between the effect of predator species and microhabitat structure on damselfish
survival was tested in the field for a cohort of juvenile Pomacentrus moluccensis. We examined juvenile survival in the presence and absence of two predators that co-occur on natural patch reefs (C. boenak and Pseudochromis fuscus). The experimental patch reefs we used for this purpose were constructed from both high complexity (Pocillopora damicornis) and low complexity (A. nobilis) coral substrata. Both juveniles and predators were translocated to reefs at natural densities. The effects of predation
were clearly dependent upon the microhabitat. Reefs of the high-complexity coral with predators supported the same high numbers
of Pomacentrus moluccensis as the reefs with no resident predators. However, damselfish abundance was significantly lower on low-complexity reefs with
resident predators, relative to the other treatments. Background rates of loss were high, even on preferred coral in the absence
of the manipulated predator, suggesting that transient predators may be even more important than the residents. We suggest
that adult abundances in this species were strongly influenced by the densities of different predators and the availability
of preferred refuges.
Environmental conditions on higher latitude coral reefs can be extremely variable, and may structure fish communities in ways not previously observed in the more stable, low latitude locations where communities have usually been studied. Temporal changes in fish community structure were examined in an intensive two-year study of the reef fishes of Hanalei Bay, Kauai, Hawaii. Hanalei Bay is directly exposed to winter swells with high surf, as well as frequent heavy winter rainfall and high river discharge. Twenty-two transects (25 5 m) were established in a wide variety of habitats and censused monthly (N = 1052 censuses). Over 121 000 sightings of individuals from 150 species were made during the study. Seasonal patterns in number of species, number of individuals, species diversity, and evenness were observed, with winter values usually lowest. Values of these ensemble variables tended to be higher at deeper sites and at sites with greater habitat complexity. Surf height and degree of wave exposure were negatively correlated with several measures of community organization. Groups of fishes with different levels of spatial mobility tended to occupy depths consistent with their various abilities to respond to events of heavy weather. The rank abundance of fish taxa tended to be more stable seasonally at sites with less exposure to high wave energy. These seasonal effects may suggest some type of short-range movement from more exposed and monotypic habitats to locations that are deeper or otherwise provide refuge from seasonally heavy seas.
This advanced text focuses on the uses of distance sampling to estimate the density and abundance of biological populations. It addresses new methodologies, new technologies and recent developments in statistical theory and is the follow up companion to Introduction to Distance Sampling (OUP, 2001). In this text, a general theoretical basis is established for methods of estimating animal abundance from sightings surveys, and a wide range of approaches to analysis of sightings data is explored. These approaches include: modelling animal detectability as a function of covariates, where the effects of habitat, observer, weather, etc. on detectability can be assessed; estimating animal density as a function of location, allowing for example animal density to be related to habitat and other locational covariates; estimating change over time in populations, a necessary aspect of any monitoring programme; estimation when detection of animals on the line or at the point is uncertain, as often occurs for marine populations, or when the survey region has dense cover; survey design and automated design algorithms, allowing rapid generation of sound survey designs using geographic information systems; adaptive distance sampling methods, which concentrate survey effort in areas of high animal density; passive distance sampling methods, which extend the application of distance sampling to species that cannot be readily detected in sightings surveys, but can be trapped; and testing of methods by simulation, so that performance of the approach in varying circumstances can be assessed. Authored by a leading team this text is aimed at professionals in government and environment agencies, statisticians, biologists, wildlife managers, conservation biologists and ecologists, as well as graduate students, studying the density and abundance of biological populations.
How does one explain the presence of a particular species of fish in association with another species at a specific location on a coral reef at a given time? Like all other animals, three major concerns of coral reef fish answer this question: shelter, food and reproduction. The definition as well as the principal characteristics of reef fish communities, as well as those dealing with reproduction, are first given. The vertical and horizontal spatial structure of the communities is presented and illustrated. Subsequently it is explained that this general scheme can vary as a function of periodic or aperiodic temporal events. Finally, even if fish communities show some degree of stability in space and time, this stability can be disturbed by annual recruitment phenomena which are controlled at another scale than that of the reef. The study of feeding regimes shows that 16% of coral reef fish are herbivores, 14% are omnivores and the remainder (70%) are carnivores. The activity rhythms as a function of the different regimes are then studied. Finally, the variability of feeding as a function of prey behaviour, fish size, diel rhythm and habitat is analysed. The final section reviews the different roles of fish in the functioning of coral reefs. Fish are involved in four of the five trophic levels of reefs and play an important role in bioerosion, sedimentation and environmental stability. Finally, this section recalls that fish are essential to the fishing economy of many tropical countries, a theme which is the subject of a separate article in this issue of Océanis.
Despite its ubiquitous relevance to most ecological and evolutionary processes, a comprehensive description of the structural and dynamic aspects of heterogeneity has never been constructed. Intuitively, the concept of heterogeneity is clear, but as we scrutinize it our initial impression fractures into complexity. The term appears rather simple when contrasted with homogeneity, the absence of variation. However, one can view heterogeneity from a variety of perspectives, some of which are well known and explored, but many of which are not. Some perspectives have important consequences for ecology and evolution, whereas others appear, at least initially, to be logical curiosities. Furthermore, different perspectives may be inclusive, exclusive, complementary, or overlapping, a problem that hints at the nature of the phenomenon itself.
Soil water withdrawal and vegetation characteristics of moun-tain big sagebrush (Artemisia tridentata ssp. vaseyana Rydb. Bee-tle) areas sprayed with 2,4-D (2,4_Dichlorophenoxyacetie acid) were measured for 20 years after treatment. Herbaceous productiv-ity more than doubled in the first 3 years after spraying and was still twice as great as untreated vegetation 10 to 17 years after treat-ment. Sagebrush removal reduced seasonal water depletion 9% to a 1.8-m soil depth, equal to 2.4 cm of water. The entire difference was realized from soil 0.9-1.8 m deep. Depletion from the surface 0.9 m of soil under grass-dominated vegetation slightly exceeded depletion under sagebrush-dominated vegetation. Mathematical relationships were developed that predict the percent reduction in seasonal water depletion in relation to time since sagebrush control for soil depths of 0.0-1.8 m, 0.0-0.9 m, and 0.9-1.8 m. Mountain big sagebrush was a minor vegetation constituent on treated areas 20 years after spraying. Sagebrush density increased from 2,100 to 4,400 plant/ha between 10 and 20 years after spray ing while herbaceous production ranged between 28 and 52 kg/ha. Both density and canopy cover of sagebrush on untreated areas declined significantly over the study because of the actions of a snowmold fungus.
We examined habitat use patterns at two spatial scales among six radio-tagged California Spotted Owls (Strix occidentalis occidentalis) in the Sierra Nevada. Foraging owls selected macrohabitats composed of larger trees (> 52 cm dbh) with canopy closures of 40% and greater. Owls used forests composed of medium trees (28-52 cm dbh) and habitats with less than 40% canopy closure, which is less frequently than expected. Fewer than 2% of telemetry locations occurred in clearcut/shrub/plantation habitat which represented 30% of available habitat. Foraging owls used microhabitats that were characterized by multiple vegetative strata, large tree size classes, high tree basal areas and woody debris. The median 100% minimum convex polygon home-range was 1.439 ha (n = 5, June to December. 1987). Telemetry locations were statistically independent when separated by five days. E&mat& of minimum convex polygon and modified minimum convex polygon size based on statis-tically independent telemetry data were significantly smaller than estimates based on con-tinuous and single-observation monitoring.
This paper addresses the following question: how does one relate the biological and behavioral characteristics of animals to habitat characteristics of the locations at which they are found? Ecologists often assemble data on species composition at different localities, habitat descriptions of these localities, and biological or behavioral traits of the species. These data tables are usually analyzed two by two: species composition against habitat characteristics, or against behavioral data, using such methods as canonical analysis. We propose a solution to the problem of estimating the parameters describing the relationship between habitat characteristics and biology or behavior, and of testing the statistical significance of these parameters; this problem is referred to as the fourth-corner problem, from its matrix formulation. In other words, the fourth-corner method offers a way of analyzing the relationships between the supplementary variables associated with the rows and columns of a binary (presence or absence) data table. The test case that motivated this study concerns a coral reef fish assemblage (280 species). Biological and behavioral characteristics of the species were used as supplementary variables for the rows, and characteristics of the environment for the columns. Parameters of the association between habitat characteristics (distance from beach, water depth, and substrate variables) and biological and behavioral traits of the species (feeding habits, ecological niche categories, size classes, egg types, activity rhythms) were estimated and tested for significance using permutations. Permutations can be performed in different ways, corresponding to different ecological hypotheses. Results were compared to predictions made independently by reef fish ecologists, in order to assess the method as well as the pertinence of the variables subjected to the analysis. The new method is shown to be applicable to a wide class of ecological problems.
The major factor controlling the abundance of reef fishes in Hawaii (USA) appears to be habitat complexity (bottom topographic relief and interstitial space). Fishes aggregate in areas of high habitat complexity at biomass levels which, in areas protected from fishing, may significantly (by 2 to 5 times) exceed levels supported by primary production within the ecosystem. High relief natural areas 'act' like artificial reefs in terms of aggregating fishes. Reef fish abundance is also affected by fishing pressure in the main Hawaiian Islands. Areas protected from fishing (Marine Life Conservation Districts, MLCDs) support standing crops of reef fishes that average about 45 g m(-2) higher than areas open to fishing. In areas unprotected from fishing, reef fish abundance has significantly declined in recent years. Conservation and management of reef fishes would be improved if more high relief areas were protected from fishing. Thus far, 11 MLCDs have been established in such areas in Hawaii, The discharge of primary or secondary treated sewage effluent into the ocean in Hawaii through deep ocean outfalls causes no apparent negative environmental impact to coral reef ecosystems. Deep ocean outfalls in fact attract reef fishes. Increases in abundance around the outfalls appears to result from increased habitat complexity brought about by the construction of the pipelines and surrounding caprock and concrete. A small amount of the variability (increase) in reef fish abundance around the outfalls may also be due to food subsidies (particulate organic matter) in the effluent. No species of fish, coral, invertebrate or algae at the outfalls exhibited any pathological symptoms. Hence, statewide declines in reef fish abundance in areas unprotected from fishing are not related to the discharge of sewage effluents via deep ocean outfalls. Rather, these declines appear to have been caused by overfishing.
Fish stocks found on lagoon bottoms and near reefs are characterized by a high diversity and heterogeneous habitat which make stock estimation difficult. In particular, it is necessary to combine several methods in order to evaluate the major components of these stocks. The present study aimed at estimating reef fish stocks in the Northern Province of New Caledonia, a region where they represent a major target for the local fishermen. These estimates were based on experimental fishing with handlines and bottom longlines. Handlines were used to assess the stocks near reefs, and longlines for those in areas away from reefs and on lagoon soft bottoms. Handline stations (363) were sampled in three different regions (west, north and east lagoons) and three biotopes (nearshore, middle lagoon and barrier reef). A total of 104 species were caught, the major families being Lethrinidae, Lutjanidae and Serranidae. Species composition and catch per unit of effort (CPUE) varied among regions and biotopes. In particular, the north zone showed characteristics of an unexploited area with very high yields. An increase in CPUE and fish size from the coast towards the barrier reef and with increasing depth was observed in all regions. Correlations between CPUE from handlines and the numerical density and biomass estimates from underwater visual censuses (UVC) performed on nearby reefs were significant. A total of 206 longline stations were sampled in the west and east regions. A total of 80 species were caught, the major families being the same as those caught in stations with handlines with the addition of Carangidae. The CPUE of longlines was significantly correlated with numerical density and biomass estimates made by UVC along the longlines. Stock estimates based on the correlations between CPUE from handlines or longlines and UVC estimates indicate that 90 % of the lagoon stock were found on soft bottoms and near reefs. Reefs, despite biomasses that were five times larger than soft-bottom and near-reef areas, made only a small contribution to total stock. The ratio between density and CPUE was highest for the lowest densities, thus indicating that fishing efficiency increased with density. Comparison of handline catch performed around reefs and UVC data from nearby reefs suggests that there were strong relationships between the fish assemblages of these two biotopes.
1. We examined assemblage structure of tropical fishes on small, artificial reefs to determine if differences in refuge availability could modify patterns of species richness and abundance of fishes established at recruitment. 2. Our artificial reefs were designed to provide prey refuge of two types (permanent and transient). Permanent refugia are those that physically exclude predators, i.e. small holes provide permanent refuge from large-bodied predators. Transient refugia result when habitat complexity increases the probability that prey will elude predators. These refugia do not physically exclude predators and thus provide no permanently safe sites. 3. We conducted this experiment at two widely separated locations on Australia's Great Barrier Reef. The species pools of reef fishes, recruitment rates and predator densities all differ between these locations. 4. At neither location were patterns of recruitment influenced by the presence of either type of refuge. By the end of the experiment, however, there were more resident fishes on reefs with additional refugia. 5. Species richness of residents was positively related to total abundance of residents. Therefore, refuge availability indirectly affected species richness through its effect on abundance. There was no indication, however, that permanent refugia provided any greater protection to prey species than did transient refugia. 6. Our results therefore indicate that for these communities, patterns of species richness and abundance established at settlement can be modified considerably over small spatial and temporal scales by differences in refuge availability. Furthermore, habitat complexity need not provide permanently safe sites to affect patterns of coexistence.
We present a new multivariate technique for testing the significance of individual terms in a multifactorial analysis-of-variance model for multispecies response variables. The technique will allow researchers to base analyses on measures of association (distance measures) that are ecologically relevant. In addition, unlike other distance-based hypothesis-testing techniques, this method allows tests of significance of interaction terms in a linear model. The technique uses the existing method of redundancy analysis (RDA) but allows the analysis to be based on Bray-Curtis or other ecologically meaningful measures through the use of principal coordinate analysis (PCoA). Steps in the procedure include: (1) calculating a matrix of distances among replicates using a distance measure of choice (e.g., Bray-Curtis); (2) determining the principal coordinates (including a correction for negative eigenvalues, if necessary), which preserve these distances; (3) creating a matrix of dummy variables corresponding to the design of the experiment (i.e., individual terms in a linear model); (4) analyzing the relationship between the principal coordinates (species data) and the dummy variables (model) using RDA; and (5) implementing a test by permutation for particular statistics corresponding to the particular terms in the model. This method has certain advantages not shared by other multivariate testing procedures. We demonstrate the use of this technique with experimental ecological data from intertidal assemblages and show how the presence of significant multivariate interactions can be interpreted. It is our view that distance-based RDA will be extremely useful to ecologists measuring multispecies responses to structured multifactorial experimental designs.
Asymptotic Relative Efficiencies (ARE) of the robust coordinatewise M-estimators with respect to the robust Maronna-type M-estimators proposed by Singer and Sen (1985) are computed under different elliptically symmetric error distributions. ARE of robust coordinatewise M-estimators with respect to Normal Maximum Likelihood (NML) estimators are also computed under a more general bivariate underlying distribution. The results indicate that the Maronna-type M-estimator is only slightly more efficient than the coordinatewise one, except for extreme cases like the Cauchy or for large dimensionalities where the gain in efficiency may be considerable. Both types of M-estimators perform better than the NML estimators for the proposed departures from normality. For distributions not of the elliptically symmetric type, Maronna-type estimators are not suitable, and hence, the comparison is not of real interest.
The size, density and biomass of coral reef fish in 4 fully closed marine protected areas
(MPAs) with different ages were studied over a 17 yr period. Space-for-time substitution samples
were available for a period of 4 yr before, and 36 yr after the closure. Both the height of the size structure
graph (which is a value of overall abundance-biomass) and the assemblage biomass graph are
convex polynomials with a maximum biomass of 1200 kg ha-1 at 22 yr. This suggests that full recovery
of coral reef fish assemblages in terms of abundance-biomass is considerably longer than generally
believed. Beyond 25 yr, there can be a small loss in biomass, which we suggest is due to reduced
net primary production associated with the increased abundance of calcifying algae attributable to
intense grazing. Size spectra slopes were variable at all times, changed quickly, and were probably
influenced by local environmental conditions, which made concise predictions for equilibrium coral
reef size structure rather difficult.
Abstract This paper reviews empirical studies relating communities of coral-reef fishes to the characteristics of the underlying habitat, and the effects of habitat disturbance. Many contrasting patterns in the relationships between fish communities and coral cover, habitat heterogeneity or topographic complexity have been described, including strong effects of particular habitat characteristics (both positive and negative), as well as those finding weak or no relationships. In addition, a whole range of potential responses to different kinds of disturbance, including hurricane damage, crown-of-thorns (Acanthaster planci) outbreaks, and El Niño-associated coral and sea urchin die-offs, have been described. Few workers have attempted to test among alternative models about the importance of resource limitation or responses to disturbance, so critical hypotheses have not been tested. Potential generalizations may be obscured due to a number of problems faced when making comparisons among existing studies. These include the enormous variation in the magnitude of changes to habitats observed, restrictive assumptions about the form of relationships between fish and habitat variables, inadequate descriptions of habitat and fish community structure, a heavy reliance on ‘natural’, pseudoreplicated experiments and a plethora of different numerical and analytical techniques. We conclude that the search for generalizations would be facilitated by a greater attention to theory and clearer statements of the hypotheses being tested. Evaluation of the general importance of fish-habitat interactions must await the application of common observational and experimental methodologies to a wider range of fish taxa and locations.
Performance of two Centaurea species in response to dif-ferent root-associated microbial communities and to alterations in nutrient availability. — Ann. Bot. Fennici 41: 263–271. The perennial forbs Centaurea jacea and C. scabiosa have relatively similar morpho-logical traits, but different distributions and local abundance. Both occur in ruderal sites and in calcareous grasslands, but C. jacea may dominate in calcareous grass-lands, while C. scabiosa is a subordinate species. We hypothesised that: (1) C. jacea is dependent on the presence of the root-associated microbial community of a calcareous grassland (CG inoculum), as opposed to the microbial community from a ruderal site (old field inoculum, OF), while C. scabiosa is not; and (2) if there is a positive response of C. jacea to CG inoculum, it will be more evident in oligotrophic soil conditions. In our experiment the two Centaurea species were grown with two different inocula (CG, OF) at three different nutrient levels. CG inoculation considerably increased the leaf number of C. jacea as compared with the OF inoculation. This response was inter-preted as an investment into competitive ability in the future. CG inoculum resulted in a significantly higher root biomass in C. scabiosa, while the biomass of C. jacea did not vary among differentially inoculated plants. This was interpreted as an increased allocation to storage in C. scabiosa, to improve performance in stress conditions. Thus, compared with ruderal inoculum (OF), grassland (CG) inoculum enhanced 'competitive behaviour' in C. jacea and 'stress-tolerating behaviour' in C. scabiosa. Both responses were more evident at high nutrient levels. Fertilisation decreased the shoot to root ratio in both species, which may represent an 'element of stress-tolerating behaviour', much more common among rhizomatous perennial plants than is usually recognized.
Using a hierarchical multi-scale survey design, we examined the spatial patterns of reef fish communities and tested ecological models concerning the relative importance of reef geomorphology and anthropogenic pressure possibly driving community structure. Canonical redundancy analysis was used as a form of multivariate analysis of variance (MANOVA) to asses differences in reef fish community composition at two spatial scales: broad (10 5 m) and intermediate (10 4 m). Surveys were conducted on the east coast of the Yucatan Peninsula (Mexican Caribbean fringing reef), including regions and reefs which differed in geomophologic structure and human use. Seven hundred and fourteen line transects were distributed among 13 reef localities belonging to different regions established a priori. Transects covered four types of reef habitat: lagoon, front, slope, and terrace. Tests of significance were based on permutation procedures. Significant differences among regions were found for the lagoon, slope, and terrace fish communities, consistent with the geomorphologic model, but it is only in the reef lagoon that they were consistent with the anthropogenic model, which may indicate an effect of coastal human activities. Significant differences among reefs within regions were observed, which could be associated with local environmental gradients. Canonical nested MANOVA was an appropriate method for testing ecological hypotheses about the functioning of complex biological systems. The use of a surveying strategy that explicitly incorporated the spatial structure represents an important contribution of this paper to coral reef fish ecology. D 2005 Elsevier B.V. All rights reserved.
Relationships between quantitative measures of habitat type and the biomass of Chaetodon, Scarus and Parupeneus species were investigated across 35 reef sites in the Inner Seychelles Group. Multiple regression was used to determine the proportion of variance in biomass between sites which could be explained by depth, exposure, vertical relief, topographic complexity, live coral cover, coral rubble cover, rock cover, sand cover, underlying carbonate substrate, underlying sand substrate, underlying rock substrate and an index of fishing intensity. A significant proportion of the variance in biomass was explained by habitat variables and the index of fishing intensity for 7 of 12 Chaetodon species (23–52% of variance explained), 3 of 6 Parupeneus species (33–40%), and 10 of 13 Scarus species (14–46%). Within genera, different groups of habitat variables explained the variance in biomass for different species and, of the variables studied, only the proportion of underlying sand substrate failed to explain a significant proportion of the variance in biomass for any species. Quantitative relationships between the biomass of Chaetodon and habitat were often in accordance with those suggested by previous studies of their ecology, life-history and distribution at other Indo-Pacific locations. However, the habitat associations of the Parupeneus and some Scarus species have not been studied at other locations and clearly warrant further investigation. It was concluded that habitat was an important determinant of the distribution of many Seychelles reef fishes, but that the habitat variables examined were rarely the most important determinant of biomass. However, the inclusion of a procedure to collect habitat data provided a useful means by which to reduce the unexplained variance associated with visual census biomass estimates and therefore improves the possibility of elucidating the effects of other factors on the biomass of Seychelles reef fishes.
I investigated the ability of predators to influence the patterns of species richness and abundance of non-piscivorous fishes on small, artificial reefs replenished by natural recruitment. Periodic removal of predators effectively reduced the species richness and abundance of predators on removal reefs. The difference between the number of predators on control and removal reefs was greatest immediately following the removal of predators and attenuated between removals. During periods of recruitment, species richness and total abundance of recently-recruited, non-piscivorous fishes were generally greater on predator-removal reefs than on control reefs. Species richness and total abundance of resident non-piscivorous fishes were not affected by the removal of predators in the first year of the experiment. Both abundance and species richness of residents, however, were greater on the removal reefs during the second year of the experiment. The difference in the responses of the two age classes to the removal of predators suggests that predators may affect community patterns of older age classes through time-lagged effects on the survivorship of younger age classes. At the end of the experiment, species richness was positively related to abundance for recruits and residents. The effects of removing piscivorous fishes on the abundance of non-piscivorous fishes were similar for species considered separately. A greater number of species of recruit and resident fishes were more abundant on reefs from which predators had been removed. These data suggest that predators can play an important role in structuring communities of fishes on coral reefs.
Population density, number of species, diversity, and species-area relationships of fish species in eight common coral reef-associated families were studied in three marine parks receiving total protection from fishing, four sites with unregulated fishing, and one reef which recently received protection from fishing (referred to as a transition reef). Data on coral cover, reef topographic complexity, and sea urchin abundance were collected and correlated with fish abundance and species richness. The most striking result of this survey is a consistent and large reduction in the population density and species richness of 5 families (surgeonfish, triggerfish, butterflyfish, angelfish, and parrotfish). Poor recovery of parrotfish in the transition reef, relative to other fish families, is interpreted as evidence for competitive exclusion of parrotfish by sea urchins. Reef substrate complexity is significantly associated with fish abundance and diversity, but data suggest different responses for protected versus fished reefs, protected reefs having higher species richness and numbers of individuals than unprotected reefs for the same reef complexity. Sea urchin abundance is negatively associated with numbers of fish and fish species but the interrelationship between sea urchins, substrate complexity, coral cover, and management make it difficult to attribute a set percent of variance to each factor-although fishing versus no fishing appears to be the strongest variable in predicting numbers of individuals and species of fish, and their community similarity. Localized species extirpation is evident for many species on fished reefs (for the sampled area of 1.0 ha). Fifty-two of 110 species found on protected reefs were not found on unprotected reefs.
The distribution and abundance of soft coral genera on reefs of the central Great Barrier Reef was investigated in relation
to reef position, recent history of disturbance, wave exposure, substratum slope and depth. Eighty-five 25 m long transects
were surveyed at 10 m depth on windward sides of 14 mid- and outer-shelf reefs. A further 75 transects in different zones
on one mid-shelf reef (Davies Reef) between 5 and 30 m depth were investigated. The crown-of-thorns starfish Acanthaster planci had caused large-scale mortality of scleractinians on eight of these reefs five to ten years prior to the study, and as a
result, scleractinian cover was only 35–55% of that on the six unimpacted reefs. On the impacted reefs, stony corals with
massive and encrusting growths form had smaller average colony diameters but similar or slightly lower numerical abundance.
In contrast, mean colony size, cover and abundance of branching stony corals showed no difference between impacted and unimpacted
reefs. Twenty-four genera of soft corals (in eight families) were recorded, and none showed different abundance or cover in
areas of former A. planci impact, compared to unaffected sites. Similarly, no difference was detected among locations in the numbers or area cover
of sponges, tunicates, zoanthids, Halimeda or other macro-algae. Mean soft coral cover was 2 to 5% at 10 m on sheltered mid-shelf reefs, and 12 to 17% on more current-exposed
reefs. Highest cover and abundances generally occurred on platforms of outer-shelf reefs exposed to relatively strong currents
but low wave energy. On Davies Reef, cover and colony numbers of the families Nephtheidae and Xeniidae were low within the
zone of wave impact, in flow-protected bays and lagoons, on shaded steep slopes, and at depths above 10 and below 25 m. In
contrast, distributions of genera of the family Alcyoniidae were not related to these physical parameters. The physical conditions
of a large proportion of habitats appear “sub-optimal” for the fastest growing taxa, possibly preventing an invasion of the
cleared space. Thus, in the absence of additional stress these shallow-water fore-reef zones appear sufficiently resilient
to return to their pre-outbreak state of scleractinian dominance.
A simple field technique to obtain a gross estimate of the surface area of a quadrat on a coral reef is described. This measure, termed the substrate rugosity index, was determined, in conjunction with two other substrate variables (vertical relief and coral species richness), in a series of 4 quadrats (10 to 40 m depth) along 4 transects. The mean substrate rugosity and vertical relief of a quadrat were highly correlated. A correlation analysis was made of the substrate variables and several reef fish community parameters (species richness, number of fishes and diversity). Species richness was highly correlated with substrate rugosity. This relationship was tested in two experimental quadrats and the results were generally in accord with those predicted. Stratification of the fish communities by body size revealed that the correlation with substrate rugosity was scale-dependent. The fish community parameters were poorly correlated with percentage substrate cover by corals (ramose and glomerate) and by sand. A significant area effect was determined for two species of sand-dwelling goby.