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Explaining island-wide geographical patterns of Caribbean fish diversity: A multi-scale seascape ecology approach
Abstract and Figures
Geographical patterning of fish diversity across coral reef seascapes is driven by many interacting environmental variables operating at multiple spatial scales. Identifying suites of variables that explain spatial patterns of fish diversity is central to ecology and informs prioritization in marine conservation, particularly where protection of the highest biodiversity coral reefs is a primary goal. However, the relative importance of
conventional within-patch variables versus the spatial patterning of the surrounding seascape is still unclear in the ecology of fishes on coral reefs. A multi-scale seascape approach derived from landscape ecology was applied to quantify and examine the explanatory roles of a wide range of variables at different spatial scales including: (i) within-patch structural attributes from field data (5 × 1 m2 sample unit area); (ii) geometry
of the seascape from sea-floor maps (10–50 m radius seascape units); and wave exposure from a hydrodynamic model (240 m resolution) for 251 coral reef survey sites in the US Virgin Islands. Non-parametric statistical learning techniques using single classification and regression trees (CART) and ensembles of boosted regression trees (TreeNet) were used to: (i) model interactions; and (ii) identify the most influential environmental predictors from multiple data types (diver surveys, terrain models, habitat maps) across multiple spatial scales (1–196,350 m2). Classifying the continuous response variables into a binary category and instead predicting the presence and absence of fish species richness hotspots (top 10% richness) increased the predictive performance of the models. The best CART model predicted fish richness hotspots with 80% accuracy. The statistical interaction between abundance of living scleractinian corals measured by SCUBA divers within 1 m2 quadrats and the topographical complexity of the surrounding sea-floor terrain (150 m radius seascape unit) measured from a high-resolution terrain model best explained geographical patterns in fish richness hotspots. The comparatively poor performance of models predicting continuous variability in fish diversity across the seascape could be a result of a decoupling of the diversity-environment relationship owing to structural degradation leading to a widespread homogenization of coral reef structure.
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... mean, max, min, range, standard deviation) at a variety of spatial scales (e.g. metres to kilometres) (Knudby et al., 2011;Rees et al., 2018;Sekund & Pittman, 2017). Terrain metrics quantify properties of benthic ecosystems that underpin their role in providing habitat for fish, and variation in fish diversity and abundance has been linked to spatial variation in terrain metrics (e.g. ...
... However, many describe similar types of terrain variation and are therefore, characterized by high co-linearity with other similar terrain metrics (e.g. rugosity, slope, slope of slope) (Leitner et al., 2017;Monk et al., 2010;Sekund & Pittman, 2017). To better understand patterns of metric applications, we grouped terrain metrics into four categories based on similarities in the terrain features being indexed: ...
... seascape context), which shape the distribution, abundance and diversity of fish assemblages in most seascapes (Olson et al., 2019;Ortodossi et al., 2019;Perry et al., 2018). Seafloor terrain can also modify the movement of fish species between different habitats, and these properties likely interact with seascape context to determine the spatial distribution of fish populations (Moore et al., 2011;Sekund & Pittman, 2017;Wedding et al., 2019). We do not know, however, whether variation in the three-dimensional properties of the seafloor influence the effects of two-dimensional seascape context, and connectivity, on fish assemblages (research priority 3, Table 8). ...
The structure of seafloor terrain affects the distribution and diversity of animals in all seascapes. Effects of terrain on fish assemblages have been reported from most ecosystems, but it is unclear whether bathymetric effects vary among seascapes or change in response to seafloor modification by humans. We reviewed the global literature linking seafloor terrain to fish species and assemblages (96 studies) and determined that relief (e.g. depth), complexity (e.g. roughness), feature classes (e.g. substrate types) and morphology (e.g. curvature), have widespread effects on fish assemblages. Research on the ecological consequences of terrain have focused on coral reefs, rocky reefs, continental shelves and the deep sea (n ≥ 20 studies), but are rarely tested in estuaries (n = 7). Fish associate with a variety of terrain attributes, and assemblages change with variation in the depth and aspect of bathymetric features in reef and shelf seascapes, and in the deep sea. Fish from different seascapes also respond to distinct metrics, with fluctuations in slope of slope (coral reefs), rugosity (rocky reefs) and slope (continental shelves, deep sea) each linked to changes in assemblage composition. Terrain simplification from coastal urbanization (e.g. dredging) and resource extraction (e.g. trawling) can reduce fish diversity and abundance, but assemblages can also recover inside effective marine reserves. The consequences of these terrain changes for fish and fisheries are, however, rarely measured in most seascapes. The key challenge now is to examine how terrain modification and conservation combine to alter fish distributions and fisheries productivity across diverse coastal seascapes.
... Nevertheless, some broad groupings were evident. Several fish studies investigated the use of measures of complexity derived from relatively new remote data capture methods (LIDAR imagery from aircraft and satellites) to predict the distribution of coral reef species (Kuffner et al. 2007;Pittman et al., 2009;Walker et al. 2009;Knudby et al. 2010Knudby et al. , 2011Pittman and Brown, 2011;Catano et al. 2015;Sekund and Pittman, 2017;Stamoulis et al. 2018). Temperate studies often used hydroacoustic remote sensing, primarily investigating the efficacy of measures derived from multibeam echosounding (MBES) to model the distribution of fish in America (Iampietro et al., 2008;Young et al. 2010), Europe (Martin--Garcia et al. 2013) and Australia (Moore et al. 2009(Moore et al. , 2010Rees et al. 2013Rees et al. , 2018Cameron et al. 2014;Coleman et al. 2016;Galaiduk et al. 2017;Ferrari et al. 2018). ...
... When considered, spatial extent and resolution were important determinants of predictive performance in each study that had an a priori aim of investigating the role of spatial scale (Table 3). Algae (Holmes et al. 2008), sessile invertebrate (Dolan et al. 2008;Guinan et al., 2009;Rees et al. 2013) mobile invertebrate (Jalali et al. 2015;Galparsoro et al., 2009;Wilson et al. 2007); temperate fish (Purkis et al. 2008;Moore et al. 2009;Galaiduk et al. 2017;Rees et al. 2018) and tropical fish (Pittman et al. 2007(Pittman et al. , 2009Knudby et al. 2010;Pittman and Brown, 2011;Sekund and Pittman, 2017) studies all identified one or more discrete and important scales. Pittman et al. (2009) found the top three predictors of total and trophic group fish biomass to include metrics of complexity averaged within both small (e.g. 15 m and 25 m radii) and large (100 m and 200 m radii) spatial extents. ...
... Purkis et al. (2008) also reported that bathymetric range derived over the smallest extents (4 m and 8 m radii) of those examined (4 m-200 m radii) were most important for territorial species. Slope of slope was also most important for Caribbean reef fish species richness when quantified over 25 m radii, comparable to the home range size of these fish (Sekund and Pittman, 2017). Failure to identify the spatial extent(s) relevant to each species could hinder or prevent identification of relationships, particularly if the biotic metric included the differencing responses of functionally or trophically dissimilar groups. ...
... Both patch-based and gradient model approaches have successfully been applied to understand biophysical drivers of habitats and species in the marine environment (Ferrari et al. 2018). Because both patch-mosaic and gradient models represent ecologically relevant patterns, an integrated patch-gradient model framework that includes individual metrics derived from both models can offer further insight into ecological consequences of environmental heterogeneity (Sekund and Pittman 2017). Models predicting coral reef fish distributions in Hawaii that combined 2D and 3D explanatory variables outperformed models with only 3D or 2D variables (Wedding et al. 2019). ...
... Establishing guidelines for selecting patch and gradient metrics for ecological models and at what scale(s) to apply metrics remain important challenges for seascape ecology. Recognizing that both patch-based and gradient spatial pattern metrics have ecologically relevant characteristics, seascape ecologists studying coral reefs have combined metrics from both spatial constructs to model, map, and explain ecological associations finding that a combination of metric types best explains biological assemblages (Sekund and Pittman 2017;Wedding et al. 2019). For the deep seabed too, the value of combining different representations has been demonstrated to study the driving factors of species distributions (Moore et al. 2011;Robert et al. 2014). ...
Seascape ecology is an emerging pattern‐oriented and integrative science conceptually linked to landscape ecology. It aims to quantify multidimensional spatial structure in the sea and reveal its ecological consequences. The seascape ecology approach has made important advances in shallow coastal environments, and increasing exploration and mapping of the deep seabed provides opportunities for application in the deep ocean. We argue that seascape ecology, with its integrative and multiscale perspective, can generate new scientific insights at spatial and temporal scales relevant to ecosystem‐based management. Seascape ecology provides a conceptual and operational framework that integrates and builds on existing benthic ecology and habitat mapping research by providing additional pattern‐oriented concepts, tools and techniques to (1) quantify complex ecological patterns across multiple scales; (2) link spatial patterns to biodiversity and ecological processes; and (3) provide ecologically meaningful information that is operationally relevant to spatial management. This review introduces seascape ecology and provides a framework for its application to deep‐seabed environments. Research areas are highlighted where seascape ecology can advance the ecological understanding of deep benthic environments.
... influencing the faunal assemblages and a variety of marine ecological processes (Sekund and Pittman, 2017;Abadie et al., 2018;Santos et al., 2018Santos et al., , 2022James et al., 2021). The Venice lagoon does not make an exception in this sense: it is poorly studied from a seascape ecology perspective, but first evidences suggest a link between habitats' spatial patterns, fish assemblages and local fisheries (Scapin et al., 2018(Scapin et al., , 2022. ...
The relationships between habitat patterns and ecosystem functioning have been widely explored in terrestrial ecosystems, but less in marine and coastal ecosystems, calling for further research in this direction. This work focuses on the mosaic of submerged habitats in the Venice lagoon, Italy. It aims to describe the habitats’ spatial patterns at multiple spatial scales, and to explore their linkages with the ecological status defined according to the EU Water Framework Directive (WFD, 2000/60/EC). The submerged habitats’ mosaic has been analysed by calculating a set of seascape metrics at different spatial scales. These metrics have been linked with the biological quality elements (BQEs) that are monitored in the lagoon in compliance to the WFD. The results show that the habitats’ spatial patterns differ between the areas of the lagoon with marine-like features and the areas which still retain more lagoon characteristics. The similarity between the pattern found in the whole lagoon and those found in marine-like areas suggests a general loss of lagoon characteristics at the lagoon scale. Regarding the ecological status, every BQE seems to be associated with a different habitat configuration at the water body scale. This does not facilitate the joint improvement of the BQEs, as required by the Directive. If we cannot achieve that, at some point we will probably have to choose what to prioritize. On a broader perspective, this calls for a reflection on what lagoon we want for the future, a vision that should be shared and account for the lagoon’s complexity, current trends and challenges.
... Indeed, new remote sensing methods are delivering unprecedented performance in high spatial resolution data for shallow coastal seascapes (Hedley et al. 2016;Purkis 2018). These technological advances in remote sensing combined with high-performing predictive modeling techniques provide analytical tools to predict habitat suitability using a combination of spatial proxies for unmeasured ecological patterns and processes (Sekund & Pittman 2017;Schill et al. 2021aSchill et al. , 2021b. However, few studies have applied these spatially explicit ecological approaches to coral restoration. ...
Coral reefs are experiencing unprecedented levels of stress from global warming, ocean acidification, fishing, and water pollution. In the Caribbean and Western Atlantic, multiple stressors have resulted in widespread losses of the dominant reef‐building Acroporid corals, two of which are listed as threatened species under the 1973 U.S. Endangered Species Act. In response, active coral reef restoration through the outplanting of live corals has become a widespread intervention technique. To increase restoration success, active coral reef restoration requires significant investment and careful planning, and selection of suitable sites for coral outplanting is an essential early step with considerable influence on restoration outcomes. We applied a maximum entropy model to predict and map habitat suitability for the reef‐building coral species, Acropora palmata , around the island of St. Croix in the U.S. Virgin Islands. Based mostly on bathymetry and benthic habitat type, the highest performing model predicted approximately 21.75 km ² of the highest probability of suitable habitat, of which over half occurred within existing marine protected areas (MPAs). Outplanted coral at 60% of sites coincided with predicted maximum habitat suitability index values greater than 0.75 and 35% with values greater than 0.90. The model reveals that all three statutory MPAs with shallow water coral reefs have a considerable area (13.24 km ² ) of predicted high suitability seabed with potential for active A. palmata restoration efforts. The predictive spatial modeling approach provides a cost‐effective tool to inform future coral restoration design and to evaluate the habitat suitability of coral outplanting sites.
... rugosity, bathymetric variance and slope of the slope), its morphology (curvature and aspect), the substrate type (nature, features and engineer species) and other information (bathymetry and slope) have an influence on the presence, abundance, cover and diversity of algae and sessile invertebrates both in tropical (Duckworth, 2016), subtropical (Holmes et al., 2008;Zavalas et al., 2014;Bravo et al., 2020) and temperate environments (Castric-Fey et al., 1973;Castric-Fey and Chasse, 1991;Guinan et al., 2009;Elvenes et al., 2014). Studies have demonstrated that the terrain complexity is one of the key-factor strongly structurating the fish communities on tropical (Kuffner et al., 2007;Pittman et al., 2007Pittman et al., , 2009Knudby et al., 2010;Pittman and Brown, 2011;Sekund and Pittman, 2017), subtropical (Moore et al., 2009(Moore et al., , 2010Monk et al., 2010Monk et al., , 2011Coleman et al., 2016;Rees et al., 2018;Williams et al., 2019), and temperate reefs (Cameron et al., 2014). Therefore, the accurate characterisation of the substrate has the potential to provide a precise understanding of the relationship between sessile organisms and their substrate. ...
The fine characterization of the substrate is a baseline to thoroughly investigate the relations between organisms and their biotopes. Cutting edge spatial technologies now provide access to accurate information on biotopes and biocenoses both in terrestrial and in marine environments. Photogrammetry is one of them and has recently been applied in submarine environments especially in shallow clear water. In this study, we investigated the potential of photogrammetry to characterise benthic habitats in turbid environments. Although more challenging, turbid environments are more frequent in temperate marine coastal areas. We selected two rocky sites in the bay of Saint-Malo (Brittany, France), differentiated by their level of turbidity, one being a marine site exposed to natural tides (Buharats), while the other (Bizeux) is subjected to both natural tides and artificial currents created by the functioning of a hydroelectric dam. The different substrates observed were classified into eight classes at a centimetre resolution using photogrammetry-based spatial and multispectral predictors. The spatial benthic terrain predictors were derived from a digital surface model (DSM) at various spatial scales, and the multispectral predictors were retrieved from the red-green-blue (RGB, natural colours) orthomosaic imagery. An overall classification was computed for Buharats and Bizeux, with accuracies of 84.76% and 79.54% respectively, revealing a good quality of the substrate classification. The combination of RGB, DSM, and several spatial benthic terrain variables, with a pixel resolution of 5 and 10 mm, and a kernel size of 30, 60 and 90 pixels leads to the best benthic substrate classification (highest overall accuracy). At the class scale, producer's (PA) and user's (UA) accuracy showed that big boulders and field material were correctly distinguished. Small boulders and cobbles, having similar sizes, showed the lowest classification performances. This classification methodology provides new perspectives for mesoscale (100 m² to 1 km²) semi-automatic mapping of the fine resolution (1 cm) relationship between benthic organisms and their substrate.
... Recognition of the ecological importance of topographic complexity (e.g., rugosity), to coral reef fishes, is not new (Luckhurst and Luckhurst 1978, Gladfelter et al. 1980, Gratwicke and Speight 2005, Graham and Nash 2013, but is now increasingly demonstrated at a range of spatial scales relevant to the movement neighborhoods of fishes using threedimensional models of the seafloor (Pittman et al. 2007, Wedding and Friedlander 2008, Agudo-Adriani et al. 2016. For example, highresolution maps of the seafloor have linked high topographic complexity coral reefs in the USVI and Puerto Rico to fish diversity hotspots (Pittman et al. 2007, Pittman and Brown 2011, Sekund and Pittman 2017. Thus, coral reefs with high structural heterogeneity support a rich variety of physical habitats and niches occupied by diverse fish species and functional groups (Pittman et al. 2007, Pittman and Brown 2011, and include prey refuges (Hixon and Beets 1993) which increase functional trait richness and variation in fish assemblages. ...
Functional diversity (FD) metrics quantify the trait diversity in biological assemblages and act as a proxy for the diverse ecological functions performed in the community. Analyses of FD offer a potentially useful tool to identify functional changes in diverse, complex, and disturbed marine ecosystems such as coral reefs, yet this metric is rarely applied to evaluate community change. Here, we documented spatio-temporal variability in the trophic function of fish assemblages to identify changes in coral reef communities inside the Buck Island Reef National Monument (BIRNM) in the U.S. Virgin Islands between 2002 and 2010, which included an intense coral bleaching event in 2005. We combined six trait categories related to the trophic function of 95 fish species together with species biomass estimated from underwater surveys to calculate assemblage level descriptors of functional richness (FRic), dispersion (FDis), and evenness. We tested the effects of habitat type, time, and their interaction on fish FD using a nonÀparametric permutational multivariate analysis of variance. We found statistically significant differences for FRic and FDis between habitat types and survey years. Coral reef and other hard bottom areas supported highest levels of trophic functional richness and variation, but low functional redundancy. Fish species exhibited high functional uniqueness within the functional trait space suggesting that a significant decline in fish diversity in the BIRNM would likely result in loss of trophic functions from the fish community. Detection of temporal variations in functional trait composition subsequent to the mass coral bleaching event in 2005 indicates that FD descriptors are sensitive enough to track shifts in the emergent trophic organization of fish communities. In the BIRNM, the trophic organization in fish assemblages did not return to the pre-bleaching state even after five years of monitoring. We demonstrate a novel way to monitor resilience to disturbance by plotting and tracking the centroid of the functional trait space through time. Our findings demonstrate the utility of FD descriptors to evaluate changes to the functional integrity of diverse and spatially heterogeneous habitat structure across the seascape.
Coastal and marine classifications, both spatially explicit in the form of maps and non-spatial representations of the environment, are critical to the effective implementation of ecosystem-based management strategies such as marine spatial planning. This chapter provides an overview of a wide range of coastal classifications and classified maps developed to simplify and communicate biological, physical, social, and economic patterns in support of enhanced management decision making. Examples are provided from around the world and span a range of spatial scales from global coastal classifications to those for individual bays and estuaries. Technological advances in remote sensing, social media analyses and artificial intelligence classifiers have diversified and improved the performance and application of biophysical coastal classifications and thematic maps. In the past decade, important progress has been made in the spatial representation of cultural values through participatory mapping and the integration of social- ecological patterns for coastal risk assessment. Mapping ecosystem services has become more widespread and the desire for environmental sustainability across sectors has seen a proliferation in predictive mapping applied to conservation prioritization and marine spatial planning. The chapter offers a showcase rather than a critique of applications and concludes with a section highlighting progress and future challenges in developing more culturally meaningful coastal classifications to inform coastal management.
The relationships between habitat patterns and ecosystem functioning have been widely explored in terrestrial ecosystems, but less in marine and coastal ecosystems, calling for further research in this direction. This work focuses on the mosaic of submerged habitats in the Venice lagoon, Italy. It aims to describe the habitats’ spatial patterns at multiple spatial scales, and to explore their linkages with the ecological status defined according to the EU Water Framework Directive (2000/60/EC). The submerged habitats’ mosaic has been analysed by calculating a set of seascape metrics at different spatial scales. These metrics have been linked with the biological quality elements (BQEs) that define the ecological status in the lagoon. The results show that the habitats’ spatial patterns differ between the areas of the lagoon with marine-like features and the areas which still retain more lagoon characteristics. The similarity between the pattern found in the whole lagoon and those found in marine-like areas suggests a general loss of lagoon characteristics at the lagoon scale. Regarding the ecological status, every BQE seems to be associated with a different habitat configuration at the water body scale. This does not facilitate the joint improvement of the BQEs, as required by the Directive. If we cannot achieve that, at some point we will probably have to choose what to prioritize. On a broader perspective, this calls for a reflection on what lagoon we want for the future, a vision that should be shared and account for the lagoon’s complexity, current trends and challenges.
In the seascape, species migrate between ecosystems to complete their life cycles, such ontogenetic migrations create functional connections between ecosystems. Nevertheless, the scarcity of information on patch distribution, species life history and ecology limit its application in MPA management. We use a potential connectivity model approach to predict how Haemulon flavolineatum might move through a complex and diverse seascape, by simulating part of its life cycle among three ecosystems (reef, mangrove, and seagrass) in the MPA of Bahía Portete-Kaurrele (BPK). We used available ecosystem cover maps to conduct habitat fragmentation analyses and evaluate structural connectivity in BPK (PLAND, LPI, AREA, ENN, NP, SHAPE, CONTAG and IJI indices). With published information on H. flavolineatum home range and its ontogenetic migration distances, we estimated the potential functional connectivity (CONNECT and migration distances) between ecosystems by building bipartite graphs. Patches of different ecosystems were highly intermixed (76%) rather than grouped (58%) reflecting appropriate structural connectivity; particularly for reefs followed by mangrove and seagrass; this seascape promote the potential migration of stage 5, juveniles from mangroves to the reefs (328 links, mainly in the BPK’s southern zone). Meanwhile, the structural configuration could reduce functional connectivity of stage 4 juveniles from seagrass to mangrove (mainly in the northern and central zone; 94 and 49 links respectively). Our model is a novel methodological approach for marine species with ontogenetic migration, which integrates ecological information and the seascape to predict their life cycle. We discuss the need for ecological information of French grunts to validate future models.
Scale and hierarchy have received less attention in aquatic systems compared to terrestrial. Walleye Sander vitreus spawning habitat offers an opportunity to investigate scale’s importance. We estimated lake-, transect-, and quadrat-scale influences on nearshore walleye egg deposition in 28 Minnesota lakes from 2016-2018. Random forest models (RFM) estimated importance of predictive variables to walleye egg deposition. Predictive accuracies of a multi-scale classification tree (CT) and a quadrat-scale CT were compared. RFM results suggested that five of our variables were unimportant when predicting egg deposition. The multi-scale CT was more accurate than the quadrat-scale CT when predicting egg deposition. Both model results suggest that in-lake egg deposition by walleye is regulated by hierarchical abiotic processes and that silt/clay abundance at the transect-scale (reef-scale) is more important than abundance at the quadrat-scale (within-reef). Our results show machine learning can be used for scale-optimization and potentially to determine cross-scale interactions. Further incorporation of scale and hierarchy into studies of aquatic systems will increase our understanding of species-habitat relationships, especially in lentic systems where multi-scale approaches are rarely used.
Prioritising biodiversity conservation requires knowledge of where biodiversity occurs. Such knowledge, however, is often lacking. New technologies for collecting biological and physical data coupled with advances in modelling techniques could help address these gaps and facilitate improved management outcomes. Here we examined the utility of environmental data, obtained using different methods, for developing models of both uni- and multivariate biodiversity metrics. We tested which biodiversity metrics could be predicted best and evaluated the performance of predictor variables generated from three types of habitat data: acoustic multibeam sonar imagery, predicted habitat classification, and direct observer habitat classification. We used boosted regression trees (BRT) to model metrics of fish species richness, abundance and biomass, and multivariate regression trees (MRT) to model biomass and abundance of fish functional groups. We compared model performance using different sets of predictors and estimated the relative influence of individual predictors. Models of total species richness and total abundance performed best; those developed for endemic species performed worst. Abundance models performed substantially better than corresponding biomass models. In general, BRT and MRTs developed using predicted habitat classifications performed less well than those using multibeam data. The most influential individual predictor was the abiotic categorical variable from direct observer habitat classification and models that incorporated predictors from direct observer habitat classification consistently outperformed those that did not. Our results show that while remotely sensed data can offer considerable utility for predictive modelling, the addition of direct observer habitat classification data can substantially improve model performance. Thus it appears that there are aspects of marine habitats that are important for modelling metrics of fish biodiversity that are not fully captured by remotely sensed data. As such, the use of remotely sensed data to model biodiversity represents a compromise between model performance and data availability.
Mangrove forests are one of the world's most threatened tropical ecosystems with global loss exceeding 35% (ref. 1). Juvenile coral reef fish often inhabit mangroves, but the importance of these nurseries to reef fish population dynamics has not been quantified. Indeed, mangroves might be expected to have negligible influence on reef fish communities: juvenile fish can inhabit alternative habitats and fish populations may be regulated by other limiting factors such as larval supply or fishing. Here we show that mangroves are unexpectedly important, serving as an intermediate nursery habitat that may increase the survivorship of young fish. Mangroves in the Caribbean strongly influence the community structure of fish on neighbouring coral reefs. In addition, the biomass of several commercially important species is more than doubled when adult habitat is connected to mangroves. The largest herbivorous fish in the Atlantic, Scarus guacamaia, has a functional dependency on mangroves and has suffered local extinction after mangrove removal. Current rates of mangrove deforestation are likely to have severe deleterious consequences for the ecosystem function, fisheries productivity and resilience of reefs. Conservation efforts should protect connected corridors of mangroves, seagrass beds and coral reefs.
Fishes are the most diverse group of vertebrates, play key functional roles in aquatic ecosystems, and provide protein for a billion people, especially in the developing world. Those functions are compromised by mounting pressures on marine biodiversity and ecosystems. Because of its economic and food value, fish biomass production provides an unusually direct link from biodiversity to critical ecosystem services. We used the Reef Life Survey’s global database of 4,556 standardized fish surveys to test the importance of biodiversity to fish production relative to 25 environmental drivers. Temperature, biodiversity, and human influence together explained 47% of the global variation in reef fish biomass among sites. Fish species richness and functional diversity were among the strongest predictors of fish biomass, particularly for the large-bodied species and carnivores preferred by fishers, and these biodiversity effects were robust to potentially confounding influences of sample abundance, scale, and environmental correlations. Warmer temperatures increased biomass directly, presumably by raising metabolism, and indirectly by increasing diversity, whereas temperature variability reduced biomass. Importantly, diversity and climate interact, with biomass of diverse communities less affected by rising and variable temperatures than species-poor communities. Biodiversity thus buffers global fish biomass from climate change, and conservation of marine biodiversity can stabilize fish production in
a changing ocean.
The connectivity of marine organisms among habitat patches has been dominated by two independent paradigms with distinct conservation strategies. One paradigm is the dispersal of larvae on ocean currents, which suggests networks of marine reserves. The other is the demersal migration of animals from nursery to adult habitats, requiring the conservation of connected ecosystem corridors. Here, we suggest that a common driver, wave exposure, links larval and demersal connectivity across the seascape. To study the effect of linked connectivities on fish abundance at reefs, we parameterize a demographic model for The Bahamas seascape using maps of habitats, empirically forced models of wave exposure and spatially realistic three-dimensional hydrological models of larval dispersal. The integrated empirical-modeling approach enabled us to study linked connectivity on a scale not currently possible by purely empirical studies. We find sheltered environments not only provide greater nursery habitat for juvenile fish but larvae spawned on adjacent reefs have higher retention, thereby creating a synergistic increase in fish abundance. Uniting connectivity paradigms to consider all life stages simultaneously can help explain the evolution of nursery habitat use and simplifies conservation advice: Reserves in sheltered environments have desirable characteristics for biodiversity conservation and can support local fisheries through adult spillover.
Coral reefs are in decline worldwide and monitoring activities are important for assessing the impact of disturbance on reefs and tracking subsequent recovery or decline. Monitoring by field surveys provides accurate data but at highly localised scales and so is not cost-effective for reef scale monitoring at frequent time points. Remote sensing from satellites is an alternative and complementary approach. While remote sensing cannot provide the level of detail and accuracy at a single point than a field survey, the statistical power for inferring large scale patterns benefits in having complete areal coverage. This review considers the state of the art of coral reef remote sensing for the diverse range of objectives relevant for management, ranging from the composition of the reef: physical extent, benthic cover, bathymetry, rugosity; to environmental parameters: sea surface temperature, exposure, light, carbonate chemistry. In addition to updating previous reviews, here we also consider the capability to go beyond basic maps of habitats or environmental variables, to discuss concepts highly relevant to stakeholders, policy makers and public communication: such as biodiversity, environmental threat and ecosystem services. A clear conclusion of the review is that advances in both sensor technology and processing algorithms continue to drive forward remote sensing capability for coral reef mapping, particularly with respect to spatial resolution of maps, and synthesis across multiple data products. Both trends can be expected to continue.
Logistic Multiple Regression, Principal Component Regression and Classification and Regression Tree Analysis (CART), commonly used in ecological modelling using GIS, are compared with a relatively new statistical technique, Multivariate Adaptive Regression Splines (MARS), to test their accuracy, reliability, implementation within GIS and ease of use. All were applied to the same two data sets, covering a wide range of conditions common in predictive modelling, namely geographical range, scale, nature of the predictors and sampling method. We ran two series of analyses to verify if model validation by an independent data set was required or cross-validation on a learning data set sufficed. Results show that validation by independent data sets is needed. Model accuracy was evaluated using the area under Receiver Operating Characteristics curve (AUC). This measure was used because it summarizes performance across all possible thresholds, and is independent of balance between classes. MARS and Regression Tree Analysis achieved the best prediction success, although the CART model was difficult to use for cartographic purposes due to the high model complexity.
Aim
The purpose of this study was to create predictive species distribution models ( SDM s) for temperate reef‐associated fish species densities and fish assemblage diversity and richness to aid in marine conservation and spatial planning.
Location
California, USA.
Methods
Using generalized additive models, we associated fish species densities and assemblage characteristics with seafloor structure, giant kelp biomass and wave climate and used these associations to predict the distribution and assemblage structure across the study area. We tested the accuracy of these predicted extrapolations using an independent data set. The SDM s were also used to estimate larger scale abundances to compare with other estimates of species abundance (uniform density extrapolation over rocky reef and density extrapolations taking into account variations in geomorphic structure).
Results
The SDM s successfully modelled the species–habitat relationships of seven rocky reef‐associated fish species and showed that species’ densities differed in their relationships with environmental variables. The predictive accuracy of the SDM s ranged from 0.26 to 0.60 (Pearson's r correlation between observed and predicted density values). The SDM s created for the fish assemblage‐level variables had higher prediction accuracies with Pearson's r values of 0.61 for diversity and 0.71 for richness. The comparisons of the different methods for extrapolating species densities over a single marine protected area varied greatly in their abundance estimates with the uniform extrapolation (density values extrapolated evenly over the rocky reef) always estimating much greater abundances. The other two methods, which took into account variation in the geomorphic structure of the reef, provided much lower abundance estimates.
Main conclusions
Species distribution models that combine geomorphic, oceanographic and biogenic habitat variables can reliably predict spatial patterns of species density and assemblage attributes of temperate reef fishes at spatial scales of 50 m. Thus, SDM s show great promise for informing spatial and ecosystem‐based approaches to conservation and fisheries management.
Ecological study of coral reef fishes is shifting from a reef patch-centric approach to a broader scale seascape
perspective using concepts and techniques from landscape ecology. This change has occurred in response to increasing evidence that many “reef” fishes move among multiple reef patches and also connect different patch types, such as seagrasses and mangroves, through multi-habitat movements. As such, the spatial distribution of
patches across the seascape is ecologically relevant. Seascape ecology, the marine counterpart of terrestrial
landscape ecology, is concerned with the causes and ecological consequences of spatial patterning in the marine environment. It draws on concepts and analytical techniques from terrestrial landscape ecology supported by advances in remote sensing and spatial statistics. In the past decade, seascape ecologists have quantified effects on reef fish populations and critical ecological processes from variation in reef geometry, such as the spatial arrangement of patches and the three-dimensional morphology of seafloor terrains. This chapter provides a rationale for adopting a seascape ecology perspective for the ecological study of fishes on coral reefs. It describes key concepts central to the implementation of seascape studies, such as how seafloor spatial structure is represented, the ecological significance of mosaics and terrains and the importance of connectivity and corridors in ecology and marine ecosystem-based management. Lastly, we offer a selection of priority research themes to help guide future research.
Caribbean coral reefs are becoming structurally simpler, largely due to human impacts. The consequences of this trend for reef-associated communities are currently unclear, but expected to be profound. Here, we assess whether changes in fish assemblages have been non-random over several decades of declining reef structure. More specifically, we predicted that species that depend exclusively on coral reef habitat (i.e., habitat special- ists) should be at a disadvantage compared to those that use a broader array of habitats (i.e., habitat generalists). Analysing 3727 abundance trends of 161 Caribbean reef-fishes, surveyed between 1980 and 2006, we found that the trends of habitat-generalists and habitat-specialists differed markedly. The abundance of specialists started to decline in the mid-1980s, reaching a low of ~60% of the 1980 baseline by the mid-1990s. Both the average and the variation in abundance of specialists have increased since the early 2000s, although the average is still well below the baseline level of 1980. This modest re- covery occurred despite no clear evidence of a regional recovery in coral reef habitat qual- ity in the Caribbean during the 2000s. In contrast, the abundance of generalist fishes remained relatively stable over the same three decades. Few specialist species are fished, thus their population declines are most likely linked to habitat degradation. These results mirror the observed trends of replacement of specialists by generalists, observed in terrestrial taxa across the globe. A significant challenge that arises from our findings is now to investigate if, and how, such community-level changes in fish populations affect ecosystem function.
Multibeam sonar (MBS) hydro-acoustic technology allows for inexpensive, broad-scale, fine-resolution assessment of marine fish habitats. Parallel advancements in geographic information systems and new analytical techniques are providing researchers with the ability to generate informative surrogate predictors of biodiversity and species responses. The aim of this study was to determine whether fine-scale bathymetric derivatives of MBS survey data could be effectively applied as surrogates to explain spatial patterns in reef fish diversity and species-habitat relationships. In the absence of direct metrics of habitat, these derivatives might prove to be effective tools for marine spatial planning. Species-habitat relationships were examined across a marine reserve on the south-eastern coast of Tasmania at fine spatial scales using boosted regression tree analyses. The most important explanatory variables of community diversity were those describing the degree of reef aspect deviation from east and south (seemingly as a proxy for swell exposure), reef bathymetry (depth), plane and slope. Models could account for up to 30% of the spatial variability in measures of species diversity. Responses in species abundance and occurrence to habitat structure appeared to be largely species-specific at the scales investigated. Models accounted for up to 67% and 58% of the abundance and occurrence, respectively, for the southern hulafish Trachinops caudimaculatus. Our results demonstrate that multibeam-derived metrics of reef habitat structure, employed in combination with modern modelling approaches, have the potential to explain and predict fine-resolution patterns in temperate reef fish community structure. This knowledge is urgently required to effectively manage marine ecosystems and conserve biodiversity and fisheries resources.
For many species securing territories is important for feeding and reproduction. Factors such as competition, habitat availability, and male characteristics can influence an individual's ability to establish and maintain a territory. The risk of predation can have an important influence on feeding and reproduction; however, few have studied its effect on territoriality. We investigated territoriality in a haremic, polygynous species of coral reef herbivore, Sparisoma aurofrenatum (redband parrotfish), across eight reefs in the Florida Keys National Marine Sanctuary that were either protected or unprotected from fishing of piscivorous fishes. We examined how territory size and quality varied with reef protection status, competition, predation risk, and male size. We then determined how territory size and quality influenced harem size and female size to understand the effect of territoriality on reproductive potential. We found that protected reefs trended towards having more large predatory fishes and that territories there were smaller but had greater algal nutritional quality relative to unprotected reefs. Our data suggest that even though males in protected sites have smaller territories, which support fewer females, they may improve their reproductive potential by choosing nutritionally rich areas, which support larger females. Thus, reef protection appears to shape the trade-off that herbivorous fishes make between territory size and quality. Furthermore, we provide evidence that males in unprotected sites, which are generally less complex than protected sites, choose territories with higher structural complexity, suggesting the importance of this type of habitat for feeding and reproduction in S. aurofrenatum. Our work argues that the loss of corals and the resulting decline in structural complexity, as well as management efforts to protect reefs, could alter the territory dynamics and reproductive potential of important herbivorous fish species.
Environmental homogenization in coastal ecosystems impacted by human activities may be an important factor explaining the observed decline in fish species richness. We used fish community data (>200 species) from extensive surveys conducted in two biogeographic provinces (extent >1,000 km) in North America to quantify the relationship between fish species richness and local (grain <10 km(2)) environmental heterogeneity. Our analyses are based on samples collected at nearly 800 stations over a period of five years. We demonstrate that fish species richness in coastal ecosystems is associated locally with the spatial heterogeneity of environmental variables but not with their magnitude. The observed effect of heterogeneity on species richness was substantially greater than that generated by simulations from a random placement model of community assembly, indicating that the observed relationship is unlikely to arise from veil or sampling effects. Our results suggest that restoring or actively protecting areas of high habitat heterogeneity may be of great importance for slowing current trends of decreasing biodiversity in coastal ecosystems.
Connectivity has fundamental consequences for the productivity, persistence and management of coral reefs. The area and position of adjacent mangroves and seagrass can affect the demography of reef fish populations and the composition of reefal assemblages. To date, no studies have attempted to partition the influences of these habitats on reef fish assemblages. We used an exploratory seascape approach to separate the effects of connectivity with mangroves and seagrass on reef fish in Moreton Bay, Australia. We then compared the performance of seascape connectivity and reef complexity (i.e. coral cover, rugosity and area) in structuring these assem- blages. Our results suggest a hierarchy of seascape connectivity effects, with reef fish assem- blages being primarily distinguished by isolation (i.e. separation distance) from mangroves and secondarily by proximity (an index incorporating habitat isolation and area) to seagrass. Impor- tantly, measures of reef complexity were only useful in separating reef fish assemblages within levels of connectivity with mangroves and seagrass. We demonstrate that neighbouring man- groves and seagrasses can exert different effects on reef fish assemblages, with 25% of all species being primarily influenced by mangroves and a different 25% being affected by seagrass. These findings have important implications for the design of marine reserve networks. They show that position in the seascape can be of greater significance than reef area or complexity to the compo- sition of reef fish assemblages and highlight the value of incorporating seascape connectivity into conservation planning.
This study used a reef-up approach to map coral reef benthos, substrates and bathymetry, with high spatial resolution hyperspectral image data. It investigated a physics-based inversion method for mapping coral reef benthos and substrates using readily available software: Hydrolight and ENVI. Compact Airborne Spectrographic Imager (CASI) data were acquired over Heron Reef in July 2002. The spectral reflectance of coral reef benthos and substrate types were measured in-situ, and using the HydroLight 4.2 radiative transfer model a spectral reflectance library of subsurface reflectance was simulated using water column depths from 0.5-10.0 m at 0.5 m intervals. Using the Spectral Angle Mapper algorithm, sediment, benthic micro-algae, algal turf, crustose coralline algae, macro-algae, and live coral were mapped with an overall accuracy of 65% to a depth of around 8.0 m; in waters deeper than 8.0 m the match between the classified image and field validation data was poor. Qualitative validation of the maps showed accurate mapping of areas dominated by sediment, benthic micro-algae, algal turf, live coral, and macro-algae. A bathymetric map was produced for water column depths 0.5-10.0 m, at 0.5 m intervals, and showed high correspondence with in-situ sonar data (R-2 value of 0.93).
Decades of study have attempted to define a generalized environmentalheterogeneity- biodiversity (EH-BD) relationship, with the traditional MacArthurian nichebased hypothesis remaining as the dominant reference point; i.e., increasing heterogeneity promotes biodiversity by increasing resource opportunities. However, studies have frequently reported negative or nonsignificant relationships. In a vast majority of them, environmental heterogeneity was defined along a gradient of increasing randomness, toward complete disorder. A new conceptual framework could help to reconcile the array of observed relationships. Using an extensive literature review, we test a conceptual framework proposing that the direction of environmental-heterogeneity-biodiversity relationships is contingent on the level of human footprint to which an ecosystem is subjected (the anthropocline). The results reveal that highly modified and seminatural ecosystems are characterized by a dominance of positive and negative EH-BD relationships, respectively, whereas natural ecosystems show mixed responses. Out of this novel framework arises the revised perspective that natural ecosystems are typified, not by maximal or minimal, but by intermediate levels of environmental heterogeneity.
Coral reefs and associated fish populations have experienced rapid decline in the Caribbean region and marine protected areas (MPAs) have been widely implemented to address this decline. The performance of no-take MPAs (i.e., marine reserves) for protecting and rebuilding fish populations is influenced by the movement of animals within and across their boundaries. Very little is known about Caribbean reef fish movements creating a critical knowledge gap that can impede effective MPA design, performance and evaluation. Using miniature implanted acoustic transmitters and a fixed acoustic receiver array, we address three key questions: How far can reef fish move? Does connectivity exist between adjacent MPAs? Does existing MPA size match the spatial scale of reef fish movements? We show that many reef fishes are capable of traveling far greater distances and in shorter duration than was previously known. Across the Puerto Rican Shelf, more than half of our 163 tagged fish (18 species of 10 families) moved distances greater than 1 km with three fish moving more than 10 km in a single day and a quarter spending time outside of MPAs. We provide direct evidence of ecological connectivity across a network of MPAs, including estimated movements of more than 40 km connecting a nearshore MPA with a shelf-edge spawning aggregation. Most tagged fish showed high fidelity to MPAs, but also spent time outside MPAs, potentially contributing to spillover. Three-quarters of our fish were capable of traveling distances that would take them beyond the protection offered by at least 40-64% of the existing eastern Caribbean MPAs. We recommend that key species movement patterns be used to inform and evaluate MPA functionality and design, particularly size and shape. A re-scaling of our perception of Caribbean reef fish mobility and habitat use is imperative, with important implications for ecology and management effectiveness.
Coral reefs face a diverse array of threats, from eutrophication and overfishing to climate change. As live corals are lost and their skeletons eroded, the structural complexity of reefs declines. This may have important consequences for the survival and growth of reef fish because complex habitats mediate predator-prey interactions [1, 2] and influence competition [3-5] through the provision of prey refugia. A positive correlation exists between structural complexity and reef fish abundance and diversity in both temperate and tropical ecosystems [6-10]. However, it is not clear how the diversity of available refugia interacts with individual predator-prey relationships to explain emergent properties at the community scale. Furthermore, we do not yet have the ability to predict how habitat loss might affect the productivity of whole reef communities and the fisheries they support. Using data from an unfished reserve in The Bahamas, we find that structural complexity is associated not only with increased fish biomass and abundance, but also with nonlinearities in the size spectra of fish, implying disproportionately high abundances of certain size classes. By developing a size spectrum food web model that links the vulnerability of prey to predation with the structural complexity of a reef, we show that these nonlinearities can be explained by size-structured prey refugia that reduce mortality rates and alter growth rates in different parts of the size spectrum. Fitting the model with data from a structurally complex habitat, we predict that a loss of complexity could cause more than a 3-fold reduction in fishery productivity.
Coral reefs are complex, heterogeneous environments where it is common for the features of interest to be smaller than the spatial dimensions of imaging sensors. While the coverage of live coral at any point in time is a critical environmental management issue, image pixels may represent mixed proportions of coverage. In order to address this, we describe the development, application, and testing of a spectral index for mapping live coral cover using CASI-2 airborne hyperspectral high spatial resolution imagery of Heron Reef, Australia. Field surveys were conducted in areas of varying depth to quantify live coral cover. Image statistics were extracted from co-registered imagery in the form of reflectance, derivatives, and band ratios. Each of the spectral transforms was assessed for their correlation with live coral cover, determining that the second derivative around 564 nm was the most sensitive to live coral cover variations(r(2) = 0.63). Extensive field survey was used to transform relative to absolute coral cover, which was then applied to produce a live coral cover map of Heron Reef. We present the live coral cover index as a simple and viable means to estimate the amount of live coral over potentially thousands of km(2) and in clear-water reefs.
Theoretical models predict strong influences of habitat loss and fragmentation on species distributions and demography, but empirical studies have shown relatively inconsistent support across species and systems. We argue that species’ responses to landscape-scale habitat loss and fragmentation are likely to appear less idiosyncratic if it is recognized that species perceive the same landscapes in different ways. We present a new quantitative approach that uses species distribution models (SDMs) to measure landscapes (e.g. patch size, isolation, matrix amount) from the perspective of individual species. First, we briefly summarize the few efforts to date demonstrating that once differences in habitat distributions are controlled, consistencies in species’ responses to landscape structure emerge. Second, we present a detailed example providing step-by-step methods for application of a species-centered approach using freely available land-cover data and recent statistical modeling approaches. Third, we discuss pitfalls in current applications of the approach and recommend avenues for future developments. We conclude that the species-centered approach offers considerable promise as a means to test whether sensitivity to habitat loss and fragmentation is mediated by phylogenetic, ecological, and life-history traits. Cross-species generalities in responses to habitat loss and fragmentation will be challenging to uncover unless landscape mosaics are defined using models that reflect differing species-specific distributions, functional connectivity, and domains of scale. The emergence of such generalities would not only enhance scientific understanding of biotic processes driving fragmentation effects, but would allow managers to estimate species sensitivities in new regions.
This Technical Memorandum is part of a series of three reports that provide a quantitative spatial and temporal characterization of marine biological communities associated with marine protected areas in the U.S. Caribbean. This work was conducted as part of NOAA’s Coral Reef Conservation Program (CRCP) Caribbean Coral Reef Ecosystem Monitoring (CREM) project; a partnership effort between NOAA’s National Ocean Service (NOS), National Centers for Coastal Ocean Science (NCCOS), Center for Coastal Monitoring
and Assessment Biogeography Branch (CCMA-BB), U.S. Virgin Islands Department of Planning and Natural Resources – Division of Fish and Wildlife, U.S. Geological Survey (USGS), National Park Service (NPS), the University of the Virgin Islands (UVI), and the University of Hawaii (UH). The integration of NOAA/NPS led efforts with data generated by VI-DPNR provide spatial and temporal patterns in fish and benthic communities to characterize St. John coral reef ecosystems. The data and analyses in this report are intended to provide essential baseline biological information to support management decision making. This project was funded by CRCP, NOAA’s NCCOS, and the NPS Natural Resource Preservation Program (NRPP) at Virgin Islands National Park (VIIS) and NPS’s South Florida/Caribbean Inventory and Monitoring Program (SFCN).
Coral reef ecosystems exhibit biotic complexity and spatial heterogeneity in physical structure at multiple spatial scales. The recent application of technology to coral reef ecosystems has vastly improved the mapping and quantification of these physically complex ecological systems. Understanding the geomorphology of coral reefs, from a three-dimensional perspective, using LiDAR, offers great potential to advance our knowledge of the functional linkages between geomorphic structure and ecological processes in the marine environment.
The recent application of LiDAR in coral reef ecosystems also demonstrates the depth and breadth of the potential for this technology to support research and mapping efforts in the coastal zone. This chapter builds upon the previous one, which covered the background and principles of LiDAR altimetry, by reviewing
coral reef LiDAR applications and providing several case studies that highlight theutility of this technology. The application of LiDAR for navigational charting, engineering, benthic habitat mapping, ecological modeling, marine geology and environmental change detection are presented. The future directions of LiDAR
applications are considered in the conclusion of this chapter, as well as the next steps for expanding the use of this remote sensing technology in coral reef environments.
Seascape ecology studies indicate that the spatial arrangement of habitat types and the topographic complexity of the seascape are major environmental drivers of fish distributions and diversity across coral reef ecosystems. Impairment of one component of an ecologically functional habitat mosaic and reduction in the architectural complexity of coral reefs is likely to lower the quality of habitat for many fish including important fished species. Documented declines in coral cover and topographic complexity are reported from a decade of long-term coral reef ecosystem monitoring in SW Puerto Rico. To examine broader scale impacts we use “reef flattening scenarios” and spatial predictive modeling to demonstrate how declining seascape complexity will lead to contractions and fragmentation in the local spatial distribution of fish. This change may result in impaired connectivity, cascading impacts to ecological functioning and reduced resilience to environmental stressors. We propose that a shift in perspective is needed towards a more holistic and spatially-explicit seascape approach to ecosystem-based management that can help monitor structural change, predict ecological consequences, guide targeted restoration efforts and inform spatial prioritization in marine spatial planning.
Live corals are the key habitat forming organisms on coral reefs, contributing to both biological and physical structure. Understanding the importance of corals for reef fishes is, however, restricted to a few key families of fishes, whereas it is likely that a vast number of fish species will be adversely affected by the loss of live corals. This study used data from published literature together with independent field based surveys to quantify the range of reef fish species that use live coral habitats. A total of 320 species from 39 families use live coral habitats, accounting for approximately 8 % of all reef fishes. Many of the fishes reported to use live corals are from the families Pomacentridae (68 spp.) and Gobiidae (44 spp.) and most (66 %) are either planktivores or omnivores. 126 species of fish associate with corals as juveniles, although many of these fishes have no apparent affiliation with coral as adults, suggesting an ontogenetic shift in coral reliance. Collectively, reef fishes have been reported to use at least 93 species of coral, mainly from the genus Acropora and Porities and associate predominantly with branching growth forms. Some fish associate with a single coral species, whilst others can be found on more than 20 different species of coral indicating there is considerable variation in habitat specialisation among coral associated fish species. The large number of fishes that rely on coral highlights that habitat degradation and coral loss will have significant consequences for biodiversity and productivity of reef fish assemblages.
We present two years of experimental and descriptive data which support the hypothesis that fireweed aphids (Aphis varians) compete with intra-and interspecific aphid neighbors for the services of ant mutualists (Formica fusca and F. cinerea). Specifically, we have shown that ants are a Limited and Limiting resource for a tended aphid species. First, the presence of heavily aphid-infested fireweed shoots significantly reduced the number of ants tending neighboring conspecific populations on fireweed. Second, the presence of ant-tended aphids (Cinara sp.) on Engelmann spruce significantly reduced the number of ants tending neighboring aphid populations on fireweed. Third, the number of ants, and not just the presence of ants, had a significant effect on the fitness of fireweed aphids. Aphid populations tended by three or more F. cinerea exhibited significantly higher probabilities of persisting and growing through time than colonies tended by one or two ants. Aphid populations tended by F. fusca had a significantly higher probability of growing when tended by three or more ants only if they had declined in size during the previous week.
The majority of fish studies on coral reefs consider only non-cryptic species and, despite their functional impor-tance, data on cryptic species are scarce. This study investi-gates inter-habitat variation in Caribbean cryptobenthic fishes by re-analysing a comprehensive data set from 58 rotenone stations around Buck Island, U.S. Virgin Islands. Boosted regression trees were used to associate the density and diver-sity of non-piscivorous cryptobenthic fishes, both in the entire data set and on reef habitats alone, with 14 abiotic and biotic variables. The study also models the habitat requirements of the three commonest species. Dead coral cover was the first or second most important variable in six of the eight models constructed. For example, within the entire data set, the number of species and total fish density increased approxi-mately linearly with increasing dead coral cover. Dead coral was also important in multivariate analyses that discriminated 10 assemblages within the entire data set. On reef habitats, the number of species and total fish density increased dramatically when dead coral exceeded *55 %. Live coral cover was typically less important for explaining variance in fish assemblages than dead coral, but live corals were important for maintaining high fish diversity. Coral species favoured by cryptobenthic species may be particularly susceptible to mortality, but dead coral may also provide abundant food and shelter for many fishes. Piscivore density was a key variable in the final models, but typically increased with increasing cryptobenthic fish diversity and abundance, suggesting both groups of fishes are responding to the same habitat variables. The density of territorial damselfishes reduced the number of cryptobenthic fish species on reef habitats. Finally, habitats delineated by standard remote sensing techniques supported distinct cryptobenthic fish assemblages, suggesting that such maps can be used as surrogates of general patterns of cryptic fish biodiversity in conservation planning.
Many of the most abundant fish species using mangroves in the Caribbean also use other habitat types through daily home range movements and ontogenetic habitat shifts. Few studies, however, have considered the structure of the surrounding seascape when explaining the spatial distribution of fish within mangroves. This study develops an exploratory seascape approach using the geographical location of mangroves and the structure of the surrounding seascape at multiple spatial scales to explain the spatial patterns in fish density and number of species observed within mangroves of SW Puerto Rico. Seascape structure immediately surrounding mangroves was most influential in determining assemblage attributes and the density of juvenile Haemulon flavolineatum, which were significantly higher in mangroves with high seagrass cover (>40%) in close proximity (< 100 m) than mangroves with low (<40%) or no adjacent seagrasses. Highest mean density of juvenile Ocyurus chrysurus was found in offshore mangroves, with high seagrass and coral reef cover >40 and >15%, respectively) in close proximity (<100 m). In contrast, juvenile Lutjanus griseus responded at much broader spatial scales, and with highest density found in extensive onshore mangroves with a large proportion (> 40%) of seagrass within 600 m of the mangrove edge. We argue that there is an urgent need to incorporate information on the influence of seascape structure into a wide range of marine resource management activities, such as the identification and evaluation of critical or essential fish habitat, the placement of marine protected areas and the design of habitat restoration projects.
Many parrotfishes (Scaridae) co-occur in mixed-species aggregations as juveniles, but diverge in resource use and social structure as adults. Focal observations of 3 juvenile parrotfishes (Scarus coeruleus, Sparisoma aurofrenatum, Sparisoma viride) were conducted on inshore patch reefs in the Florida Keys to examine feeding rates, food type, habitat use, and aggressive interactions. All species overlapped extensively in their use of space and food. Home ranges physically overlapped, and the proportion of microhabitats present within home ranges was similar for all species. Home range size increased with body size for S. coeruleus and S. aurofrenatum. Diets of all species were extremely similar. All fed selectively from the available foods and fed primarily (>50% total bites) on the calcareous macroalga Halimeda opuntia despite its potentially high energetic costs of procurement, low food value, and predicted avoidance. Focal individuals interacted aggressively with conspecifics, other juvenile parrotfishes, damselfishes, and occasionally grunts and wrasses. S. aurofrenatum and S. viride were most aggressive toward conspecifics. Aggressive interactions with adult parrotfishes were rare. Both Sparisoma spp. were chased more often by damselfishes than any other species. These findings support the growing body of evidence that herbivorous fish do not feed randomly from all potential foods. The aggressive interactions observed among juvenile parrotfishes are likely affecting their use of resources and may act as a precursor to subsequent territoriality as adults.
Coral reef ecosystems are topographically complex environments and this structural heterogeneity influences the distribution, abundance and behavior of marine organisms. Airborne hydrographic lidar (Light Detection and Ranging) provides high resolution digital bathymetry from which topographic complexity can be quantified at multiple spatial scales. To assess the utility of lidar data as a predictor of fish and coral diversity and abundance, seven different morphometrics were applied to a 4 m resolution bathymetry grid and then quantified at multiple spatial scales (i.e., 15, 25, 50, 100, 200 and 300 m radii) using a circular moving window analysis. Predictive models for nineteen fish metrics and two coral metrics were developed using the new statistical learning technique of stochastic gradient boosting applied to regression trees. Predictive models explained 72% of the variance in herbivore biomass, 68% of parrotfish biomass, 65% of coral species richness and 64% of fish species richness. Slope of the slope (a measure of the magnitude of slope change) at relatively local spatial scales (15-100 m radii) emerged as the single best predictor. Herbivorous fish responded to topographic complexity at spatial scales of 15 and 25 m radii, whereas broader spatial scales of between 25 and 300 m radii were relevant for piscivorous fish. This study demonstrates great utility for lidar-derived bathymetry in the future development of benthic habitat maps and faunal distribution maps to support ecosystem based management and marine spatial planning.
Aquatic resource managers are continually faced with construction or site development proposals which, if allowed to proceed, would ultimately alter the physical structure and cover of fish habitat. In the absence of clear quantitative guidelines linking the change in habitat to fish, resource managers often use the change in habitat area as a basis for decisions. To assess the weight of scientific evidence in support of management decisions, we summarized both the observational and experimental freshwater fish-habitat literature. We then extracted data from experimental studies (where possible) for inclusion in a meta-analysis, to provide a more rigorous assessment of the published results of experimental habitat manipulations. We found relatively strong and consistent correlational evidence linking fish and physical habitat features, yet inconsistent evidence when narratively reviewing the experimental literature. On the whole, decreases in structural habitat complexity are detrimental to fish diversity and can change species composition. Increases in structural complexity showed increases, decreases, or no measurable changes in species and (or) communities. The majority of our meta-analyses resulted in supporting a direct link between habitat and fish abundance or biomass, with fish biomass responding most strongly to habitat change. Habitat alterations are most likely to affect individual species or community structure, and thus evaluating the extent of the effect on a biological basis depends on management objectives.
The importance of structural complexity in coral reefs has come to the fore with the global degradation of reef condition; however, the limited scale and replication of many studies have restricted our understanding of the role of complexity in the ecosystem. We qualitatively and quantitatively (where sufficient standardised data were available) assess the literature regarding the role of structural complexity in coral reef ecosystems. A rapidly increasing number of publications have studied the role of complexity in reef ecosystems over the past four decades, with a concomitant increase in the diversity of methods used to quantify structure. Quantitative analyses of existing data indicate a strong negative relationship between structural complexity and algal cover, which may reflect the important role complexity plays in enhancing herbivory by reef fishes. The cover of total live coral and branching coral was positively correlated with structural complexity. These habitat attributes may be creating much of the structure, resulting in a collinear relationship; however, there is also evidence of enhanced coral recovery from disturbances where structural complexity is high. Urchin densities were negatively correlated with structural complexity; a relationship that may be driven by urchins eroding reef structure or by their gregarious behaviour when in open space. There was a strong positive relationship between structural complexity and fish density and biomass, likely mediated through density-dependent competition and refuge from predation. More variable responses were found when assessing individual fish families, with all families examined displaying a positive relationship to structural complexity, but only half of these relationships were significant. Although only corroborated with qualitative data, structural complexity also seems to have a positive effect on two ecosystem services: tourism and shoreline protection. Clearly, structural complexity is an integral component of coral reef ecosystems, and it should be incorporated into monitoring programs and management objectives.
The previous chapters have been concerned with predicting the values of one or more outputs or response variables Y = (Y
1,..., Y
m
) for a given set of input or predictor variables X = (X
1,..., X
P
). Denote by x
i
= (x
i1,..., x
ip
) the inputs for the ith training case, and let y
i
be a response measurement. The predictions are based on the training sample (x
1, y
1),..., (x
N
, y
N
) of previously solved cases, where the joint values of all of the variables are known. This is called supervised learning or “learning with a teacher.” Under this metaphor the “student” presents an answer ŷ
i
for each x
i
in the training sample, and the supervisor or “teacher” provides either the correct answer and/or an error associated with the student’s answer. This is usually characterized by some loss function L(y, ŷ), for example, L(y, ŷ) = (y − ŷ)2.
Coastal marine and estuarine ecosystems are highly productive and serve a nursery function for important fisheries species. They also suffer some of the highest rates of degradation from human impacts of any ecosystems. Identifying and valuing nursery habitats is a critical part of their conservation, but current assessment practices typically take a static approach by considering habitats as individual and homogeneous entities. Here, we review current definitions of nursery habitat and propose a novel approach for assigning nursery areas for mobile fauna that incorporates critical ecological habitat linkages. We introduce the term ‘seascape nurseries’, which conceptualizes a nursery as a spatially explicit seascape consisting of multiple mosaics of habitat patches that are functionally connected. Hotspots of animal abundances/productivity identify the core area of a habitat mosaic, which is spatially constrained by the home ranges of its occupants. Migration pathways connecting such hotspots at larger spatial and temporal scales, through ontogenetic habitat shifts or inshore–offshore migrations, should be identified and incorporated. The proposed approach provides a realistic step forward in the identification and management of critical coastal areas, especially in situations where large habitat units or entire water bodies cannot be protected as a whole due to socio-economic, practical or other considerations.
The foraging-time patterns of the sexes were examined in protogynous hogfishes in the genus Bodianus (Labridae). The daily social and mating activities of males in each of these marine reef fishes are distinctly different: single males defend permanent, all-purpose territories that contain a harem of females (B. rufus; San Blas Islands, Panama), males defend temporary reproductive territories (B. diplotaenia; Gulf of California, Mexico), or males are not territorial and spawn together in groups (B. eclancheri; Galapagos Archipelago, Ecuador). Female hogfishes in all 3 species mate daily and spend relatively little time on social and mating activities. B. rufus males allocated a much smaller proportion of their time (39.7%) to foraging than did conspecific females (76.8%) . Sex change by the dominant female was initiated by removing the dominant, territorial male from his harem group. All individuals tested decreased the amount of time spent foraging and increased time allocated to social and mating activities, after they became reproductively functioning males. B. diplotaenia males also spent less time foraging (45.9%) than did conspecific females (76.5%). B. eclancheri males spent most (70.2%) of their time foraging, as did conspecific females (77.3%). Males minimize foraging time when their reproductive success depends more upon time spent in social and mating activities than upon net energy gains. The reproductive success of female hogfishes, and males that compete for mates by maximizing sperm production (B. eclancheri), appears to be limited primarily by energy available for gamete production and growth.- from Author
We develop a hierarchical model of heterogeneity that provides a framework for classifying patch structure across a range of scales. Patches at lower levels in the hierarchy are more simplistic and correspond to the traditional view of patches. At levels approaching the upper bounds of the hierarchy the internal structure becomes more heterogeneous and boundaries more ambiguous. At each level in the hierarchy, patch structure will be influenced by both contrast among patches as well as the degree of aggregation of patches at lower levels in the hierarchy. We apply this model to foraging theory, but it has wider applications as in the study of habitat selection, population dynamics, and habitat fragmentation. It may also be useful in expanding the realm of landscape ecology beyond the current focus on anthropocentric scales.
AimThe spatial extent (scale) at which landscape attributes are measured has a strong impact on inferred species–landscape relationships. Consequently, researchers commonly measure landscape variables at multiple scales to select one scale (the ‘scale of effect’) that yields the strongest species–landscape relationship. Scales of effect observed in multiscale studies may not be true scales of effect if scales are arbitrarily selected and/or are too narrow in range. Miscalculation of the scale of effect may explain why the theoretical relationship between scale of effect and species traits, e.g. dispersal distance, is not empirically well supported.LocationWorld-wide.Methods
Using data from 583 species in 71 studies we conducted a quantitative review of multiscale studies to evaluate whether research has been conducted at the true scale of effect.ResultsMultiple lines of evidence indicated that multiscale studies are often conducted at suboptimal scales. We did not find convincing evidence of a relationship between observed scale of effect and any of 29 species traits. Instead, observed scales of effect were strongly positively predicted by the smallest and largest scales evaluated by researchers. Only 29% of studies reported biological reasons for the scales evaluated. Scales tended to be narrow in range (the mean range is 0.9 orders of magnitude) and few (the mean number of scales evaluated is four). Many species (44%) had observed scales of effect equal to the smallest or largest scale evaluated, suggesting a better scale was outside that range. Increasing the range of scales evaluated decreased the proportion of species with scales of effect equal to the smallest or largest scale evaluated.Main conclusionsTo ensure that species–landscape relationships are well estimated, we recommend that the scales at which landscape variables are measured range widely, from the size of a single territory to well above the average dispersal distance.
From the reviews of the First Edition."An interesting, useful, and well-written book on logistic regression models . . . Hosmer and Lemeshow have used very little mathematics, have presented difficult concepts heuristically and through illustrative examples, and have included references."—Choice"Well written, clearly organized, and comprehensive . . . the authors carefully walk the reader through the estimation of interpretation of coefficients from a wide variety of logistic regression models . . . their careful explication of the quantitative re-expression of coefficients from these various models is excellent."—Contemporary Sociology"An extremely well-written book that will certainly prove an invaluable acquisition to the practicing statistician who finds other literature on analysis of discrete data hard to follow or heavily theoretical."—The StatisticianIn this revised and updated edition of their popular book, David Hosmer and Stanley Lemeshow continue to provide an amazingly accessible introduction to the logistic regression model while incorporating advances of the last decade, including a variety of software packages for the analysis of data sets. Hosmer and Lemeshow extend the discussion from biostatistics and epidemiology to cutting-edge applications in data mining and machine learning, guiding readers step-by-step through the use of modeling techniques for dichotomous data in diverse fields. Ample new topics and expanded discussions of existing material are accompanied by a wealth of real-world examples-with extensive data sets available over the Internet.
Spatial analyses are indispensable analytical tools in biogeography and macroecology. In a recent Guest Editorial, Hawkins (Journal of Biogeography, 2012,39, 1-9) raised several issues related to spatial analyses. While we concur with some points, we here clarify those confounding (1) spatial trends and spatial autocorrelation, and (2) spatial autocorrelation in the response variable and in the residuals. We argue that recognizing spatial autocorrelation in statistical modelling is not only a crucial step in model diagnostics, but that disregarding it is essentially wrong.
Coastal marine and estuarine ecosystems are highly productive and serve a nursery
function for important fisheries species. They also suffer some of the highest rates
of degradation from human impacts of any ecosystems. Identifying and valuing
nursery habitats is a critical part of their conservation, but current assessment
practices typically take a static approach by considering habitats as individual and
homogeneous entities. Here, we review current definitions of nursery habitat and
propose a novel approach for assigning nursery areas for mobile fauna that incorporates
critical ecological habitat linkages. We introduce the term ‘seascape nurseries’,
which conceptualizes a nursery as a spatially explicit seascape consisting of
multiple mosaics of habitat patches that are functionally connected. Hotspots of
animal abundances/productivity identify the core area of a habitat mosaic, which
is spatially constrained by the home ranges of its occupants. Migration pathways
connecting such hotspots at larger spatial and temporal scales, through ontogenetic
habitat shifts or inshore–offshore migrations, should be identified and incorporated.
The proposed approach provides a realistic step forward in the identification
and management of critical coastal areas, especially in situations where large habitat units or entire water bodies cannot be protected as a whole due to socio-economic,
practical or other considerations.
A third-generation numerical wave model to compute random, short-crested waves in coastal regions with shallow water and ambient currents (Simulating Waves Nearshore (SWAN)) has been developed, implemented, and validated. The model is based on a Eulerian formulation of the discrete spectral balance of action density that accounts for refractive propagation over arbitrary bathymetry and current fields. It is driven by boundary conditions and local winds. As in other third-generation wave models, the processes of wind generation, whitecapping, quadruplet wave-wave interactions, and bottom dissipation are represented explicitly. In SWAN, triad wave-wave interactions and depth-induced wave breaking are added. In contrast to other third-generation wave models, the numerical propagation scheme is implicit, which implies that the computations are more economic in shallow water. The model results agree well with analytical solutions, laboratory observations, and (generalized) field observations.