No full-text available
To read the full-text of this research,
you can request a copy directly from the author.
Mediterranean coralligenous assemblages: A synthesis of present knowledge
Abstract
Coralligenous concretions, the unique calcareous formations of biogenic origin in Mediterranean benthic environments, are produced by the accumulation of encrusting algae growing in dim light conditions. This review provides an overview of the results obtained by the main studies dealing with these formations, including the environmental factors which influence the development of coralligenous communities, their distribution, types, assemblages, builders and eroders, the biotic relationships and processes that create and destroy coralligenous assemblages, their dynamics and seasonality, and the functioning of several outstanding and key species. Special attention is devoted to the biodiversity of coralligenous communities and a first estimation of the number of species reported for this habitat is provided. Major disturbances affecting coralligenous communities are discussed, ranging from large-scale events that are probably related to global environmental changes to degradation by waste water or invasive species. Degradation by fishing activities and by divers is also considered. Finally, the main gaps in current scientific knowledge of coralligenous communities are listed and some recommendations are made regarding their protection. © R. N. Gibson, R. J. A. Atkinson, and J. D. M. Gordon, Editors Taylor & Francis.
... The project "CRESCIBLUREEF Grown in the blue: new technologies for knowledge and conservation of Mediterranean reefs" aimed to explore the components, growth-rate, and accretion style of the Mediterranean algal reefs (i.e., coralligenous reefs). Coralligenous reefs are among the most monumental bioconstructions of the Mediterranean Sea (Ballesteros, 2006), and are mainly built by crustose coralline algae (Laubier, 1966;Hong, 1980;Di Geronimo et al., 2002;Ballesteros, 2006;Bracchi et al., 2022;Basso et al., 2022). Minor contributions are made by other habitat-forming, skeletonized invertebrates such as bryozoans and serpulids, as well as sponges and autochthonous-micrite (Laubier, 1966;Ballesteros, 2006;Bertolino et al., 2019;Cipriani et al., 2023Cipriani et al., , 2024Rosso et al., 2023;Sanfilippo et al., 2023Sanfilippo et al., , 2025. ...
... The project "CRESCIBLUREEF Grown in the blue: new technologies for knowledge and conservation of Mediterranean reefs" aimed to explore the components, growth-rate, and accretion style of the Mediterranean algal reefs (i.e., coralligenous reefs). Coralligenous reefs are among the most monumental bioconstructions of the Mediterranean Sea (Ballesteros, 2006), and are mainly built by crustose coralline algae (Laubier, 1966;Hong, 1980;Di Geronimo et al., 2002;Ballesteros, 2006;Bracchi et al., 2022;Basso et al., 2022). Minor contributions are made by other habitat-forming, skeletonized invertebrates such as bryozoans and serpulids, as well as sponges and autochthonous-micrite (Laubier, 1966;Ballesteros, 2006;Bertolino et al., 2019;Cipriani et al., 2023Cipriani et al., , 2024Rosso et al., 2023;Sanfilippo et al., 2023Sanfilippo et al., , 2025. ...
... Coralligenous reefs are among the most monumental bioconstructions of the Mediterranean Sea (Ballesteros, 2006), and are mainly built by crustose coralline algae (Laubier, 1966;Hong, 1980;Di Geronimo et al., 2002;Ballesteros, 2006;Bracchi et al., 2022;Basso et al., 2022). Minor contributions are made by other habitat-forming, skeletonized invertebrates such as bryozoans and serpulids, as well as sponges and autochthonous-micrite (Laubier, 1966;Ballesteros, 2006;Bertolino et al., 2019;Cipriani et al., 2023Cipriani et al., , 2024Rosso et al., 2023;Sanfilippo et al., 2023Sanfilippo et al., , 2025. The building of these reefs results in a complex and very heterogeneous substrate, forming both discrete structures and tabular banks (Bracchi et al., 2017). ...
The coralligenous algal reefs are priority ecosystems of the Circalittoral zone of the Mediterranean Sea shelves. Characterized by decimeter- to meter-high build-ups, these reefs create a complex environment hosting high biodiversity. Despite their common occurrence, the roles of mollusks within coralligenous structures have been overlooked until recently. To address this gap, the CRESCIBLUREEF project investigated samples of coralligenous build-ups collected from diverse settings at similar depths (33.5- 37.2 m) along the SE Sicilian shelf (Italy). In the studied samples, we identified 158 mollusk species –mostly autochthonous– including some previously undocumented for this habitat. Our study underscores the importance of using appropriate sampling techniques in studying mollusk biodiversity and the pivotal role algal reefs play in supporting a diverse array of mollusk species, spanning not only those associated with hard substrates but also epiphytic, cryptic, and infaunal species. Despite the samples being sourced at similar depths, multivariate statistical analysis based on mollusk abundance indicated a distinction between coralligenous morphologies in the living assemblage. Overall, our findings contribute to improving the knowledge on mollusks associated with coralligenous reefs and emphasize the valuable role of mollusks as sensitive indicators of environmental conditions, confirming their vital importance in conservation science and benthic ecology.
... While in tropical waters the most widely recognized marine bioconstructions are coral reefs (Spalding and Grenfell 1997), in the temperate waters of the Mediterranean Sea the best-known biogenic structure is the coralligenous (Ballesteros 2006), mainly built by encrusting coralline algae, which act as primary builders developing primary or secondary hard substrates of biogenic origin. These algal-based bioconstructions occur under dim-light conditions and grow on vertical walls and horizontal platforms creating complex three-dimensional habitats that support a wealth of associated species (Laborel 1961;Pérès and Picard 1964). ...
... The presence of such animal-based structures highlighted the great diversity of habitat-forming species in temperate mesophotic ecosystems, which are mostly found in the Mediterranean Sea, North Atlantic and Pacific Oceans (Pyle and Copus 2019;Cerrano et al. 2019;Bell et al. 2022). As these bioconstructions are not built by calcareous algae, they do not meet the definition of coralligenous sensu stricto (Ballesteros 2006). Previous studies (Montefalcone et al. 2021;Cerrano et al. 2015) have highlighted the importance of standardized terminology in the description of marine benthic habitats, to ensure a common framework and a shared technical terminology among scientists involved in this field. ...
... These authors distinguished between algae-dominated coralligenous bioconstructions and those dominated by invertebrates, based on the predominant taxonomic groups or facies present. In this paper, we emphasize the need for an additional nomenclature that considers the mesophotic bioconstructions in which algae play no role as bioconstructors and, therefore, cannot be classified as coralligenous sensu stricto (Ballesteros 2006). ...
A comprehensive overview of the benthic assemblages associated with bioconstructions in the mesophotic zone of the southern Adriatic Sea is provided through a comparison of algal- and invertebrate-based bioconstructions. To characterize these bioconstructions, sampling was conducted at six sites along the Apulian coast (Italy). Algal-based bioconstructions were found in shallower areas and corresponded to coralligenous sensu stricto, while two distinct invertebrate-based bioconstructions, built by scleractinians and bivalves, were observed at greater depths. A multi-taxa approach, which recorded 511 benthic taxa, revealed significant differences in the taxonomic composition of their associated benthic assemblages, although similar species richness values were observed across all types of bioconstructions. Given the marked difference in terms of primary constructor species between the coralligenous sensu stricto and invertebrate bioconstructions, we propose referring to the latter as Mesophotic Coral Bioconstructions (MCB) and Mesophotic Oyster Bioconstructions (MOB). β-diversity analysis identified a turnover in benthic fauna along the North–South gradient, with higher β-diversity values between distant sites and lower values between nearby sites, likely driven by North–South circulation dynamics in the region. Additionally, the distinctions observed along the depth gradient are consistent with the decrease in irradiance, which causes a shift from photoautotrophic to heterotrophic builder species. These findings underscore the role of mesophotic bioconstructions along the Apulian coast as biodiversity hotspots and confirm their importance in understanding mesophotic ecosystem dynamics in the Mediterranean Sea.
... With these concerns in mind, we revisited a red coral Corallium rubrum (Linnaeus, 1758) restoration (23) via trait-based approaches to assess whether it has facilitated the recovery of ecological functions in a Mediterranean coralligenous habitat. These habitats are biogenic temperate reefs situated in dim light conditions and are composed of a variety of calcareous algae and invertebrates (such as cnidaria, porifera, bryozoan, and tunicate), which act as biodiversity "hot spots" (37) and support a large variety of ecosystem services (38) (e.g., food provision, natural medicine availability, or recreationally attractive submerged seascapes). The structural complexity of these habitats can be greatly improved by the formation of red coral monospecific "animal forests" (39). ...
... as "precoralligenous" assemblages (37), to a dominance of filter feeders more typically associated withs coralligenous assemblages under dimlight conditions (37) and assemblages dominated by C. rubrum (55). In Mediterranean rocky benthic communities, this transition of algae to animals is usually observed with depth and is attributed to changes in abiotic factors, such as light, water movement, temperature, nutrients, or sedimentation (56,57). ...
... as "precoralligenous" assemblages (37), to a dominance of filter feeders more typically associated withs coralligenous assemblages under dimlight conditions (37) and assemblages dominated by C. rubrum (55). In Mediterranean rocky benthic communities, this transition of algae to animals is usually observed with depth and is attributed to changes in abiotic factors, such as light, water movement, temperature, nutrients, or sedimentation (56,57). ...
Whether restoration actions achieve full ecological recovery is still debated. This is particularly controversial in the marine realm, where the success of restoration is mostly evaluated in terms of the short-term survival of transplanted organisms. In view of this, we combined population and trait-based approaches to explore the long-term effectiveness of active restoration of a key Mediterranean octocoral. For this purpose, an assemblage with restored Corallium rubrum colonies was monitored over 10 years and compared with a nearby reference site. Our results revealed growth of the transplanted colonies followed by a change in the functional structure (i.e., dominance and diversity of traits) of the restored assemblage. This change was related not only to the development of the coral but also to the arrival and/or increase of species with different traits. Overall, our findings provide an example of how active restoration of long-lived octocorals can be an effective tool for recovering high-diverse coralligenous assemblages at decadal timescales.
... Coralligenous reefs represent the most important circalittoral bioconstruction in the Mediterranean Sea for extent, biodiversity, and carbon dynamics [3,4]. They are an iconic underwater seascape providing multifarious ecosystem services, but they are also a very sensitive habitat vulnerable to both global and local disturbances; thus, coralligenous reefs are included in the European Red List of Habitats and their monitoring and quality assessment are required under European Directives and international treaties. ...
... Moreover, both the richness and the heterogeneity of the assemblages decrease under stressed conditions [2]. In fact, coralligenous assemblages are usually characterized by a high variability at small spatial scale and consequently by high values of β-diversity, which is related to the heterogeneity of the substrate and competition for space [3]; under stressed conditions, the loss of structuring perennial species and proliferation of ephemeral algae lead to a widespread biotic homogenization, with consequent loss of βdiversity [2]. ...
... Bioconstruction by coralline algae is considered highly vulnerable to most effects of climate change, such as global warming and ocean acidification, but also to other environmental alterations, such as mucilage blooms, increasing sedimentation and mechanical damages by anchoring and fishing [3]; therefore, structure and health of coralline algae represent a primary descriptor of the ecological status of coralligenous cliffs. ...
The 10th International Symposium Monitoring of Mediterranean Coastal Areas: problems and measurements techniques was organized by CNR-IBE in collaboration with Italian Society of Silviculture and Forest Ecology , and Natural History Museum of the Mediterranean and under the patronage of University of Florence, University of Catania, Accademia dei Lincei, Accademia dei Geogofili, Italian Association of Physical Geography and Geomorphology, Tuscany Region, The North Tyrrhenian Sea Ports System Authority, Livorno Municipality and Livorno Province. This edition confirmed the Symposium as the international occasion to present the research carried out in recent years on the monitoring of the Mediterranean Coastal Areas and therefore as a space to present new proposals and promote actions for the protection of the marine and coastal environment. In the Symposium, Scholars had illustrated their activities and exchanged innovative proposals, with common aims to promote actions to preserve coastal marine environment. In this 10th edition, in fact, we had more than 130 participants from 16 countries; this is a sign of great success and willingness to be presence in Livorno to discuss problems and propose solutions for the Mediterranean coastal areas.
... Korallijen, güneş ışığının az nüfus ettiği deniz alanlarında ve derinliklerde kayalık yüzeyler üzerinde örtücü kalkerli alglerin (korallin alglerin) oluşturduğu biyojenik bir habitattır (Ballesteros 2006). Korallijen habitatı sirkalittoral bölgede daha yaygın olmasına rağmen, ışığın örtücü kalkerli kırmızı alglerin yaşamını sağlayacak şekilde loş olması koşuluyla, infralittoral bölgede de bulunabilir. ...
... oluşturulur ve Akdeniz endemiği olarak kabul edilir (Ballesteros 2006). Her ne kadar 20 ila 120 m derinlik arasında yaygın olsa da bazen bu habitat üretkenliğin yüksek olduğu bölgelerde daha sığ sularda da oluşabilir (Casellato ve Stefanon 2008). ...
... Bu biyojenik oluşum hem yapısal hem de işlevsel olarak oldukça karmaşık olup, algler, süspansivörler, deliciler ve hatta habitatın yarık ve oyuklarında biriken sedimentte yaşayan yumuşak substrat faunasını da barındırır (UNEP-MAP-RAC/SPA 2017). Bu habitatı karakterize eden bazı türler uzun ömürlü olup, çevresel ve antropojenik değişikliklere karşı çok hassastır (Ballesteros 2006;Salomidi ve diğ. 2012). ...
Korallijen, güneş ışığının az nüfus ettiği deniz alanlarında ve derinliklerde kayalık yüzeyler üzerinde örtücü kalkerli alglerin (korallin alglerin) oluşturduğu biyojenik bir habitattır. Korallijen, üç boyutlu ve karmaşık bir yapı sergilediğinden, ticari değeri yüksek ve nesli tehdit altında olan türler de dahil olmak üzere çok sayıda deniz türünün beslendiği, barındığı ve ürediği bir yaşam alanıdır. Akdeniz endemiği olan bu habitat çok sayıda alg birliğini ve hayvan fasiyeslerini barındırır. Bu eşsiz habitat, deniz çayırları ve denizaltı mağaraları ile birlikte Akdeniz'de deniz biyoçeşitliliğinin sıcak noktası olarak kabul edilir. Ülkemiz sularında bu habitat üzerine yapılan biyo-ekolojik çalışma sayısı oldukça azdır. Ildır Körfezi’nde Ayrıktaş ve İkiz Adalar korallijen habitatlarında fotokuadratla yapılan örneklemelerde 9 taksonomik gruba ait toplam 49 makrobentik tür saptanmıştır. Ayrıktaş korallijen habitatında en baskın türler sırasıyla Peyssonnelia squamaria, Lithophyllum stictiforme ve Spirastrella cunctatrix; İkiz Adalar korallijen habitatında en baskın türler ise sırasıyla Mesophyllum alternans, P. squamaria ve P.dubyi’dir. Bölgede korallijen habitatları üzerine olumsuz etki eden faktörlerin balıkçılık faaliyetleri, istilacı yabancı türler, demirleme, sedimantasyon ve iklimsel değişiklikler olduğu belirlenmiştir. Çeşme Yarımadası ve çevresinde korallijen habitatlarının dağılım gösterdiği alanlar belirlenerek bu habitatların biyoçeşitlilik durumlarının tespit edilmesi ve izlenmesi gerekmektedir.
... Mediterranean coralligenous temperate reefs represent a highly diverse habitat of particular ecological concern, threatened by local and global stressors including overharvesting, marine pollution, invasive species, recreational activities, and, more recently, warming-driven mass mortality events (Ballesteros 2006;Bevilacqua et al. 2021;Garrabou et al. 2022). Within these systems, gorgonians play a key structural role by creating dense forests that support a wide range of species (Ballesteros 2006). ...
... Mediterranean coralligenous temperate reefs represent a highly diverse habitat of particular ecological concern, threatened by local and global stressors including overharvesting, marine pollution, invasive species, recreational activities, and, more recently, warming-driven mass mortality events (Ballesteros 2006;Bevilacqua et al. 2021;Garrabou et al. 2022). Within these systems, gorgonians play a key structural role by creating dense forests that support a wide range of species (Ballesteros 2006). These characteristics make them particularly valuable for marine conservation, and their loss could lead to cascading effects throughout the entire ecosystem (e.g. ...
... Bathymetry has been identified as a determining factor driving the distribution of marine benthic species (e.g., Pulido Mantas et al. 2022;Anakha et al. 2023;Bellin and Rossi 2023; but see Tittensor et al. 2009). In this study, the bathymetric range was restricted to depths ranging from 0 to 150 m, excluding areas devoid of coralligenous habitats (Ballesteros 2006) from the modelled habitat suitability estimation. Temperature, nutrients, current velocity, and light have been highlighted as main factors driving their distribution. ...
Aim
Determining the species distribution and factors shaping it is a major challenge for conservation planning. Ecological niche models (ENMs) facilitate the comprehension of how environmental factors may influence species occurrence, providing spatially explicit information relevant to conservation. Therefore, our aim was to estimate the potential distribution of key habitat‐forming Mediterranean gorgonians, whose conservation would protect many co‐occurring species.
Location
Mediterranean Sea.
Methods
We modelled the potential distribution of the Mediterranean gorgonians Eunicella singularis , Eunicella cavolini , Paramuricea clavata and Corallium rubrum , using an ensemble ENM that combines nine algorithms. An extensive dataset of presence records (> 4378) collected through scientific surveys and citizen‐science was intersected with oceanographic and topographic information within the coralligenous habitat depth range (< 150 m). This approach was used to map the habitat suitability of the study area for each species, assess related uncertainty, identify the most important factors shaping their distribution, and evaluate the overlap with the current network of Marine Protected Areas.
Results
The model identified higher habitat suitability for the occurrence of each gorgonian species in the NW Mediterranean, with roughness and temperature as the main drivers of their distribution. Conversely, the poorly sampled SE Mediterranean showed low habitat suitability, although there is a greater uncertainty associated with this estimate. The combined potential distribution of the four species is estimated to cover a quarter of Mediterranean shallow and mesophotic waters, but only 19% was included within protected areas.
Main Conclusions
The habitat suitability and uncertainty maps provide a valuable tool for the conservation and management of Mediterranean gorgonian species by offering spatially explicit information critical for marine spatial planning. The model estimates of habitat suitability showed low uncertainty for most of the study area, with few exceptions in the SE Mediterranean. Further studies, particularly in the SE Mediterranean will contribute to validate these results and will provide new information to improve future modelling efforts.
... CCA represent pivotal foundation taxa in the photic zone, encompassing a diverse group of marine species renowned globally for their ecological importance. These species offer a variety of ecosystem services, including habitat formation (Bressan et al., 2001;Ballesteros, 2006;Ingrosso et al., 2018) and carbonate production (Canals and Ballesteros, 2007;Cebrìan et al., 2020). Their role as marine calcifiers is critical, characterized by the precipitation of calcium carbonate in their cell walls, primarily in the form of high-Mg calcite and, mainly in tropical species, aragonite (Nash and Adey, 2017). ...
... In the Mediterranean Sea, CCA are the main builders of coralligenous concretions which represent one of the most important habitats of interest to the European Community due to the ecological services they provide, from fishing to their crucial role in the CO 2 balance (Ballesteros, 2006;Martin and Gattuso, 2009;Thierry de Ville d'Avray et al., 2019). Coralligenous reefs are also considered among the most threatened Mediterranean habitats having been included in the Habitat 1170 "Reefs" of the Habitat Directive (E.C., 1992) and listed as "special habitat types" under the European Marine Strategy Framework Directive (MSFD, E.C., 2008). ...
... Several studies have evaluated their vulnerability to both warming (Garrabou et al., 2009;Gómez-Gras et al., 2019;Verdura et al., 2019;Ceccherelli et al., 2020;Garrabou et al., 2022) and local human impacts such as pollution (Piazzi et al., 2011) and mechanical damage due to recreational diving (Betti et al., 2019) and fishing activities (Ferrigno et al., 2018;Betti et al., 2020). Mechanical damage poses a significant threat to coralligenous reef, primarily due to the slow growth rate of most species (Ballesteros, 2006) which results in a limited capacity for restoration. Furthermore, damaged reefs may exhibit increased sensitivity to other forms of human impact (Piazzi et al., 2012), suggesting potential synergistic effects between local mechanical stress and global climate changes. ...
... Coral reefs are among the most biodiverse ecosystems on the planet, in both tropical (Pandolfi et al., 2011) and temperate environments (Ballesteros, 2006;Teixidóet al., 2013;Martin et al., 2014). Healthy coral reefs exhibit a rich and complex soundscape, characterised by diverse sounds generated by fish, invertebrates, and other marine organisms. ...
... The coralligenous is defined as biogenic temperate reefs primarily formed by the accumulation of calcareous encrusting algae (e.g., crustose coralline algae and Peyssonneliales), along with animals such as bryozoans, anthozoans, and serpulids, typically found in the circalittoral zone (at depths between 20 and 120 meters), under sciaphilous condition (Ballesteros, 2006). Due to its high complexity and heterogeneity, the coralligenous ecosystem hosts several communities (La Rivière et al., 2021), supporting one of the highest biodiversity hotspots in the Mediterranean Sea (Ballesteros, 2006). ...
... The coralligenous is defined as biogenic temperate reefs primarily formed by the accumulation of calcareous encrusting algae (e.g., crustose coralline algae and Peyssonneliales), along with animals such as bryozoans, anthozoans, and serpulids, typically found in the circalittoral zone (at depths between 20 and 120 meters), under sciaphilous condition (Ballesteros, 2006). Due to its high complexity and heterogeneity, the coralligenous ecosystem hosts several communities (La Rivière et al., 2021), supporting one of the highest biodiversity hotspots in the Mediterranean Sea (Ballesteros, 2006). Consequently, this ecosystem is protected under European regulations, including the 92/43/CE Habitat Directive and the 2008/56/EC Marine Strategy Framework Directive. ...
In this study, we explored the fish acoustic community at two coralligenous sites in Sardinia (Tavolara and Santa Teresa, western Mediterranean Sea) during the summer 2023. Our goal was to understand spatial and temporal patterns of fish acoustic activity on different temporal scales to offer insights for optimizing acoustic monitoring of this crucial ecosystem. We identified seventeen distinct sound types, revealing a diverse acoustic community. Tavolara had higher acoustic richness and abundance compared to Santa Teresa, which may be attributed to site-specific factors such as habitat structure, species composition, or levels of protection. Temporal analysis revealed clear diel patterns, with certain sounds associated with nocturnal or diurnal periods, reflecting the daily rhythms of different species. The study also examined how recording duration influenced acoustic richness, finding that longer recordings (15 minutes per hour and 15 minutes per hour at night) provided a more comprehensive detection of acoustic activity. Additionally, the number of recording days required to detect species richness varied depending on the site. While extended recordings improve the likelihood of detecting rare or sporadic sounds, they also present challenges in data management and equipment maintenance. The study underscores the importance of carefully planning sampling strategies to optimize acoustic monitoring and ensure effective and sustainable ecological research in coralligenous ecosystems.
... Coralligenous bioconstructions are calcareous formations of biogenic origin, produced by the accumulation of crustose coralline algae (Corallinophycidae, Rhodophyta), which grow in dim light conditions, in benthic environments [1]. The irradiance reaching the sea floor defines the depth range for the formation of coralligenous frameworks. ...
... According to Ballesteros [2], coralligenous communities can develop at solar irradiances from 3% to 0.05% of the surface irradiance. On vertical slopes, the minimum depth is about 20 m, but it can be much lower (e.g., 12 m) in areas where coralligenous communities thrive in highly turbid waters near river mouths) [1]. On flat substrata, coralligenous banks frequently occur in the mesophotic zone, where rhodolith beds mostly thrive at 30-75 m depth [3][4][5][6][7], with the deepest occurrences in very clear waters at 130-170 m [8,9]. ...
... The greatest number of species identified belonged to 3 Phyla: Rhodophyta, Porifera, and Cnidaria. Some of these taxa are sciaphilic, typical of coralligenous assemblages (Ballesteros, 2006), such as the crustose coralline algae Lithophyllum spp., Mesophyllum spp., and Peyssonnelia spp., and the sponges of the genus Axinella; otherwise, some photophilic taxa were observed, such as the Cnidaria Eunicella singularis (Esper, 1791) and Cladocora caespitosa (L., 1767). ...
Coralligenous bioconstructions are biogenic calcareous formations developing at low irradiance on littoral rocky cliffs or on the deeper sub-horizontal bottom in the Mediterranean Sea. Unusually shallow coralligenous banks on the sandy coast of Sinuessa (Mondragone City, Gulf of Gaeta, SW Italy) were investigated. Their communities and the surrounding biogenic detritus were characterized. Geophysical and acoustic data revealed the presence of coralligenous banks between 7.5 and 15 m depth, showing constant thickness and sub-horizontal geometry, incised by sub-perpendicular channels. Sediment deposits ranging from silty sands to bioclastic gravel occur in the area. The biogenic detritus of the soft bottom sampled around the coralligenous banks is highly heterogeneous. Through the thanatocoenosis analysis of macrozoobenthos, different biocenoses were detected, among which the coralligenous and photophilic habitats are mainly represented, followed by the well-calibrated fine sands and the relit sands. A total of 16 different species and 10 epimegabenthic morphological groups (MGs) were detected on the coralligenous banks, of which 4 are included in European regulation for threatened species. The density of epimegabenthic organisms has an average of 10.34 ± 5.46 individuals or colonies/100 m². Cladocora caespitosa is the dominant species, with a height of 17 ± 5 cm. This and other structuring species (SS) were larger in size in the sampled sites than in the literature data. Overall, coralligenous had a “medium” health status, with 52% of the individuals or colonies in healthy conditions, compared to 47% with epibiosis phenomena and 1% with entanglement. Longlines were the most common anthropogenic litter, with a density of 2/100 m². Ad hoc monitoring programs and conservation measures would be desirable to protect and guarantee the well-being of these sensitive and rare shallow bioconstructions.
... The megabenthos found along the northern coast of the Ionian Sea are typical of coralligenous habitats [35,43,44], developing on a biogenic substrate realized by calcareous red algae. Invertebrates, even contributing significantly, do not act as structural components of the bioconstructions. ...
... The coralligenous bottoms form here a heterogeneous mosaic that varies on a small spatial scale, allowing multiple assemblages to coexist in a reduced space, a common scenario across all the Mediterranean bioconstructions [44,61,62]. According to Montefalcone et al. [45], these habitats can show a dominance of invertebrate species that, although not structuring, can form real specific facies (e.g., sponges, bryozoans, and anthozoans facies). ...
... The red coral constitutes a typical facies of coralligenous habitats, widely distributed throughout circalittoral semi-dark caves and overhangs all over the Mediterranean Sea [44,46]. A recent study by Toma et al. [46] investigated the occurrence, relative abundance, and habitat characteristics of Corallium rubrum along the Italian coasts, reporting that red coral colonies settle both on coralligenous concretions and rocky substrates, with a preference for biogenic sub-vertical habitats. ...
The taxonomic composition, structure, and distribution patterns of the macrobenthos associated with Corallium rubrum were studied along the coast of Taranto (Ionian Sea), together with the main features of their red coral population. Underwater video transects were performed by professional divers at three sites in correspondence with coralligenous formations at depths from 50 to 65 m. The results revealed a patchy distribution of red coral, with colonies predominantly located in cavities on sub-vertical cliffs and large boulders. Biometric analysis indicated that young colonies predominated at all sites, while older colonies were lacking, likely because of illegal harvesting. The lower density values were recorded at S1, while S2 and S3 presented higher values. A total of 76 taxa were recorded. S1, the shallowest site, showed a prevalence of calcareous algae, while S2 and S3 showed a greater abundance of filter-feeding invertebrates (Porifera and Cnidaria) with the highest presence of Porifera at S3. The results emphasize the heterogeneity of the macrobenthos together with the high vulnerability of the red coral population, highlighting the necessity of site-specific conservation strategies to contribute to the conservation and management of benthic ecosystems in the northern Ionian Sea.
... The CCA belong to the red algal subclass Corallinophycidae and occur worldwide, from polar to tropical regions within the photic zone (Liu and Lin 2023). Previous studies have reported that algal reefs are typically found in littoral or shallow sublittoral zones (Ballesteros 2006;Tuya et al. 2023). Algal reefs are intricate and porous structures that serve as suitable habitats and nurseries for a diverse array of marine organisms (Ballesteros 2006;Yu, Huang, and Lin 2020). ...
... Previous studies have reported that algal reefs are typically found in littoral or shallow sublittoral zones (Ballesteros 2006;Tuya et al. 2023). Algal reefs are intricate and porous structures that serve as suitable habitats and nurseries for a diverse array of marine organisms (Ballesteros 2006;Yu, Huang, and Lin 2020). Unlike corals, the accretion of CCA is relatively slow, and they thrive in environments characterized by specific factors such as depth, temperature, and water wave energy (Belanger and Gagnon 2021;Schluter et al. 2021). ...
... As a result, large-scale algal reefs are less common than coral reefs in subtropical and tropical (Liou, Yang, and Chen 2017). However, extensive algal reefs occur worldwide, such as in the Mediterranean Sea (Ballesteros 2006;Martin et al. 2014), northern Taiwan (Liou, Yang, and Chen 2017), and northern Norway (Freiwald and Henrich 1994). The climate and hydrological conditions of algal reef ecosystems in tropical and subtropical regions differ significantly from those in temperate regions. ...
Coastal algal reef ecosystems, which are formed by the skeletal carbonate of crustose coralline algae (CCA), provide vital habitats for a diverse range of marine organisms and serve as valuable archives of long‐term environmental data. Despite the importance of these reef ecosystems, there is currently a lack of available information regarding the accretion rates of CCA in subtropical intertidal zones in the Taoyuan algal reef. We measured the vertical accretion and horizontal growth of CCA cultured in two aquaculture tanks over a 9‐month period. The vertical accretion and horizontal growth rate of CCA was approximately 0.29–0.43 and 5.5 μm·day ⁻¹ (the extrapolated annual value is equivalent to 0.11–0.16 and 2.0 mm·year ⁻¹ , respectively). Newly colonized CCA had faster horizontal growth of approximately 110 μm·day ⁻¹ (equivalent to 40.2 mm·year ⁻¹ ). These results highlight the slow and gradual process of algal reef ecosystem formation in the subtropical intertidal zones. The CCA had a faster lateral growth rate as seen in the newly settled CCA. These findings contribute to our understanding of the overall growth dynamics of CCA.
... In the Mediterranean Sea, mesophotic habitats mainly include coralligenous assemblages (Martin et al. 2014), biogenic hard substrates produced through the slow layering of the thalli of calcareous red algae, occasionally embedding polychaete tubes and skeletons of anthozoans, molluscs and bryozoans (Ballesteros 2006). The synergic action of builders and eroders contributes to the creation of a highly complex bioconstruction (Cerrano et al. 2001) hosting a peculiar assemblage, in which four layers of organisation can be distinguished: (i) cryptic/boring species, (ii) encrusting species, (iii) massive species, and (iv) arborescent species (Valisano et al. 2019). ...
... and Sarcotragus foetidus) often represent the largest erect species and can form dense aggregations called marine animal forests (MAFs) (Cerrano et al. 2010;Gori et al. 2011Gori et al. , 2017Rossi et al. 2017;Ponti et al. 2018;Chimienti 2020;Pulido Mantas et al. 2022). Due to the high three-dimensional (3D) complexity of these communities, environmental factors such as current velocity, light intensity and sedimentation rates can vary by orders of magnitude in relation to the presence or absence of MAFs (Ballesteros 2006;Scinto et al. 2009). Additionally, habitat complexity has a positive effect on biodiversity by increasing the number of ecological niches and the overall available area (Torres-Pulliza et al. 2020), making the coralligenous one of the most diverse assemblages in the Mediterranean (Ballesteros 2006). ...
... Due to the high three-dimensional (3D) complexity of these communities, environmental factors such as current velocity, light intensity and sedimentation rates can vary by orders of magnitude in relation to the presence or absence of MAFs (Ballesteros 2006;Scinto et al. 2009). Additionally, habitat complexity has a positive effect on biodiversity by increasing the number of ecological niches and the overall available area (Torres-Pulliza et al. 2020), making the coralligenous one of the most diverse assemblages in the Mediterranean (Ballesteros 2006). For all these reasons, coralligenous habitats are protected as 'Reefs' of the type 'Biogenic concretions', recognised as natural habitats of community interest and special areas of conservation at European level by the Habitats Directive (92/43/EEC, code 1170). ...
Coralligenous, a typical Mediterranean mesophotic habitat, is a highly diverse assemblage, severely threatened by several stressors, including fishing litter. To characterise the coralligenous of the upper mesophotic of the Portofino Promontory (Ligurian Sea, Italy), video transects at 35 and 50 m depth were performed at four sites. Benthic assemblages and lost fishing gears were recorded, and the two depths compared. A higher coverage of taxa with complex 3D structures was found at 50 m, mainly due to the gorgonian Paramuricea clavata . However, the overall low density of this species (0.4–6.6 colonies/m ² ), together with the impact caused by 120 fishing lines found along the transects, highlights the need for tailored conservation measures. With climate change moving further down the water column and fishing impacts being a major cause of degradation, the design of marine protected areas needs to be extended to include mesophotic depths, contributing to the 30 × 30 targets agreed upon at the COP15.
... The evidence emerging from the study of coralligenous assemblages of the Central-Western Mediterranean fits with the definition of community puzzle given by Ballesteros (2006) and actively contributes to opening new perspectives introducing the metacommunity concept (Leibold et al., 2004), such as a set of regional communities linked by the dispersal of multiple potentially interacting species and characterized by local spatial dynamics. Such an approach was already considered when dealing with the heterogeneity of benthic habitats in the northern Adriatic Sea (Bandelj et al., 2012;Falace et al., 2015) and should be effectively integrated into future studies of coralligenous reefs. ...
... As reported by Ceccherelli et al. (2020) where the chlorophyll and nitrate concentrations due to river runoff negatively affect seawater features (Balata et al., 2005;Montefalcone et al., 2017). The composition of coralligenous assemblages is influenced by changes in nutrient concentrations (Ballesteros, 2006;Piazzi et al., 2012). Specifically, an increase in nitrates and phosphates has been found to have a different effect on diversity. ...
... The encrusting red algae (Corallinales, Hapalidiales and Peyssonneliales), the percentage cover of seasonal turf algae, and the erect algal taxa characterized the above-mentioned six clusters. Given their role as primary builders within the reef(Ballesteros, 2006), encrusting red algae are the most abundant taxonomic/morphological group in all sectors of the Mediterranean(Çinar et al., 2020;Piazzi et al., 2010;Sini et al., 2019). The clusters CL1 and CL2 reflected the accepted stratified structure and general F I G U R E 6 Response curves of the β-entropy (Y-axis) to environmental variables and the geographical coordinates in the GAM analysis. ...
Aim
Coralligenous reefs are the main marine bioconstructions in terms of spatial distribution within the Mediterranean basin. Two distinct reef morphologies can be distinguished based on the surface and topographical features of the seafloor: cliffs developing vertical slopes and banks found on gently steep or horizontal bottoms. Despite their importance for monitoring and conservation efforts, observations regarding the variability of biogeographical patterns are scarce. Here, we aimed to assess the differences in the composition and structure of these cliffs across ecoregions and estimate the relative role of abiotic environmental features, geographic location, and connectivity in shaping diversity patterns.
Location
The study was carried out in the Central‐Western Mediterranean Sea. Samples were collected at 65 sites across the Algero‐Provençal Basin, the Ionian Sea and the Tyrrhenian Sea.
Methods
We assessed the composition and structure of coralligenous cliffs through photographic samplings collected by scuba divers. Patterns in α‐ and β‐diversity were associated with 9 abiotic environmental variables, latitudinal and longitudinal gradients, and connectivity measures using Generalized Additive (GAM) and Conditional Autoregressive (CAR) models.
Results
Coralligenous cliffs were primarily composed of algae and displayed a high degree of variability. The Partition Around Medoids (PAM) clustering method successfully delineated seven distinct clusters with a non‐uniform distribution within the studied ecoregions. The α‐diversity increased in eastern and northern sites and with phosphate concentration, while decreased with temperature, chlorophyll and nitrates concentration. β‐diversity at the site level increased with temperature, while it was negatively affected by northward current speed and chlorophyll concentration. Moveover, β‐diversity increased within connected sites.
Main Conclusions
Coralligenous cliff diversity responds both to the physico‐chemical features of the habitat and between‐habitats connectivity. However, our findings suggest that small‐scale abiotic and biotic processes could contribute to explaining the variability observed. These findings can significantly enhance the monitoring and conservation efforts of this Mediterranean endemic ecosystem.
... Coralligenous reefs are among the most impacted habitats by ALDFG (Ferrigno et al., 2017;Enrichetti et al., 2019a;Ruitton et al., 2019;Gimenez et al., 2022). Although it covers only 0.1 % of the total area of the Mediterranean basin, coralligenous habitat hosts 20 % of the Mediterranean species (Martin et al., 2014), representing one of the most important marine habitats globally due to its extensive coverage, rich biodiversity, and high productivity (Ballesteros, 2006). Coralligenous habitat occurs typically at depths starting from 30 to 40 m and extends to the limit of the photic zone, even up to 200 m (Ferrigno et al., 2018a). ...
... Moreover, nets and longlines often get entangled in the complex three-dimensional structure that characterizes these habitats, causing breakage and necrosis in many erect species, other than capturing vagile organisms and suffocating sessile algae and animals (Bo et al., 2014). These effects often result in a decrease in habitat heterogeneity, structural integrity, biodiversity, and ecosystem function (Bavestrello et al., 1997;Ballesteros, 2006;Martin et al., 2014;Enrichetti et al., 2019a;Do and Armstrong, 2023). ...
... Coralligenous reefs are one of the hotspots of biodiversity in the Mediterranean Sea, thus deserving particular attention in conservation policies and marine resource management [1][2][3]. These biogenic structures, primarily composed of calcareous macroalgae, soft corals, sponges, and other benthic species, form complex three-dimensional ecosystems [1,[3][4][5] that provide shelter, feeding grounds, and breeding areas for numerous marine species, including fish, crustaceans, mollusks, and many other organisms [3,[6][7][8]. ...
... Coralligenous reefs are one of the hotspots of biodiversity in the Mediterranean Sea, thus deserving particular attention in conservation policies and marine resource management [1][2][3]. These biogenic structures, primarily composed of calcareous macroalgae, soft corals, sponges, and other benthic species, form complex three-dimensional ecosystems [1,[3][4][5] that provide shelter, feeding grounds, and breeding areas for numerous marine species, including fish, crustaceans, mollusks, and many other organisms [3,[6][7][8]. In parallel, coralligenous reefs actively assist in mitigating climate change by contributing to carbon sequestration [9][10][11], and they constitute an important resource for coastal communities, supporting economic and social activities such as fisheries, scuba diving, tourism, and scientific research [6,8,[11][12][13]. ...
Coralligenous bioconstructions are priority habitats crucial for the protection of Mediterranean marine biodiversity. Among these bioconstructions, the mesophotic biogenic reefs of the northern Adriatic are of particular concern due to their ecological relevance and the high levels of human pressure in the region. Thus, effective monitoring strategies are vital for the conservation and management of these fragile environments. In this study, we investigated the multivariate spatial and temporal patterns of sessile macrobenthos on biogenic reefs within two areas of a Natura 2000 site in the northern Adriatic over a four-year period. We also classified the ecological status of reefs based on the NAMBER index, specifically tailored for these peculiar bioconstructions. Our findings revealed that temporal trajectories of assemblages significantly differed between the two investigated areas, mostly due to larger fluctuations in algal turf abundance in the area closest to the coast, which is putatively more exposed to human impacts. In this area, the index identified a “Moderate” status during the period of peaking turf abundance, while the reef status consistently remained “Good” in other periods and in the area located further from the coast. This highlights the index sensitivity in reflecting actual changes in assemblages potentially associated with reef degradation.
... The remaining species have been assigned to the least concern category (eight species), seventeen are data deficient, while two species have not yet been evaluated for their conservation status (Table 2). In the Mediterranean Sea scleractinians are known to contribute to the so-called 'mesophotic coral ecosystems' (Soares et al., 2020b) and to coralligenous bioconstructions, which represents the main calcareous formation of biogenic origin in the basin (Ballesteros, 2006). Scleractinia can build "forests" in the form of facies (e.g., facies with zooxanthellate and azooxanthellate Scleractinia in the infralittoral zone, facies with Scleractinia in the circalittoral zone) according to the interpretation manual of the Barcelona Convention Reference List of Marine Habitat Types in the Mediterranean Sea (UNEP/MAP-SPA/RAC, 2021). ...
... Scleractinia can build "forests" in the form of facies (e.g., facies with zooxanthellate and azooxanthellate Scleractinia in the infralittoral zone, facies with Scleractinia in the circalittoral zone) according to the interpretation manual of the Barcelona Convention Reference List of Marine Habitat Types in the Mediterranean Sea (UNEP/MAP-SPA/RAC, 2021). Although most Mediterranean scleractinian species are solitary (Ballesteros, 2006), species such as Balanophyllia regia and Caryophyllia spp. have been reported to form dense clusters. ...
Some marine benthic invertebrates increase the structural complexity of the seabed, thereby providing suitable habitats to several associated species, resulting in biodiversity hotspots. Marine Animal Forests (MAFs) encompass a set of the most important marine benthic habitats into which diversified sessile suspension feeders like sponges, corals, sea pens, tube worms, bivalves, bryozoans and ascidians occur. Such a mix of sessile species brings characteristic assemblages and supports important ecosystem functions. In the last decades, some species which form MAFs have been the object of international conventions, EU directives, and national policies aiming to address natural and human-induced disturbances. Effective conservation, monitoring, and restoration actions require summarizing the available information to include MAFs in conservation plans. In the present work, the main international policies for the protection of coastal and marine fauna were screened in order to provide a list of protected species which form Mediterranean MAFs. These international normative documents include the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), the Convention on the Conservation of European Wildlife and Habitats (Bern Convention), the European Habitats Directive, and the Protocol concerning Specially Protected Areas and Biological Diversity in the Mediterranean (SPA/BD Protocol) of the Barcelona Convention. The analysis of the normative items revealed that 62 Mediterranean potential MAF-forming species have been included in one or more legal annexes as protected species. These species belong to different phyla, including Porifera, Cnidaria, Bryozoa and Mollusca. A wider view was proposed by the International Union for Conservation of Nature (IUCN), setting the bases of a legal acknowledgement of the MAFs as one of the largest biomes on Earth. This study represents a first step to obtain a baseline of MAF legal protection framework in order to support the further implementation of management measures aimed at increasing the effective protection of MAFs. Reporting the status of the Mediterranean MAF species that should be considered in management plans and conservation measures will be crucial for policymakers, as well as for mitigating current and future impacts on these distinctive marine environments.
... Cystoseira (sensu lato) forest did not explain such depth zonation (given its taxonomic resolution in this study), as it was found across the entire depth range. On the other hand, deep sites (25 -35 m) attested the intrusion of typical coralligenous species (Ballesteros, 2006) into the infralittoral communities, with Eunicella cavolini being the most abundant gorgonian species, Axinella verrucosa a circalittoral-like erect sponge and an increasing cover of encrusting corallines. While the vertical zonation pattern was evident here, the transition to coralligenous communities appeared gradual as evidenced by a mix of infralittoral and circalittoral species in the 25 -35 m depth range. ...
... In the western Mediterranean, the 25 -35 m depth range is considered shallow for coralligenous reefs, where they begin to develop mostly on vertical walls and overhangs and are referred to as "cliff morphology" (~20 -50 m) (Bracchi et al., 2017;Piazzi et al., 2022). Further down (usually below 50 m), the "platform morphology" of coralligenous reefs develops horizontally (Ballesteros, 2006;Piazzi et al., 2022). Further analyses were then replicated at each depth range to avoid the confounding effect of depth ranges when discussing spatial structure, given the transition in reef communities. ...
The Mediterranean Sea is a “sea under siege”, facing numerous anthropogenic pressures leading to the spread of invasive species and the degradation of reefs, particularly the reduction of habitat-forming macroalgae to turf algae or sea urchin barrens. The coastal waters of Corsica, often considered as a “reference state” due to their lower human impact, have not been thoroughly studied with regard to infralittoral reef communities. This study aimed to characterize these communities and identify their biotic and abiotic drivers through an innovative monitoring protocol (VIT-Reef). From 2019 to 2021, we monitored infralittoral reef communities at 59 sites between 15 and 35 m depth within and adjacent to three MPAs, using innovative rapid assessment dive surveys for 74 benthic taxa. Our results highlighted vertical zonation in reef communities, in particular the depth extent of photophilic algae and the emergence of pre-coralligenous communities. Important ecological implications of taxa covariation were discussed, such as the negative relationship between canopy-forming macroalgae and the invasive algae, Caulerpa cylindracea. Notably, geographical contrasts were observed along northern, southern and western MPAs, primarily influenced by algal community changes. Cystoseira (sensu lato) forests were identified as the climax state on western reefs, while northern and southern reefs showed significant cover of Dictyota spp. and crustose corallines respectively, with concerning levels of Caulerpa cylindracea in deeper southern reefs. Our results underscored the structuring role of Cystoseira spp. forests and the effects of light, nutrients and Posidonia oceanica meadows extending into the reefs. This study highlighted the role of algae in structuring reef communities and will contribute to establish a baseline for conservation planning and predicting future changes in these high priority infralittoral communities.
... Coralligenous reefs are among the most impacted habitats by ALDFG (Ferrigno et al., 2017;Enrichetti et al., 2019a;Ruitton et al., 2019;Gimenez et al., 2022). Although it covers only 0.1 % of the total area of the Mediterranean basin, coralligenous habitat hosts 20 % of the Mediterranean species (Martin et al., 2014), representing one of the most important marine habitats globally due to its extensive coverage, rich biodiversity, and high productivity (Ballesteros, 2006). Coralligenous habitat occurs typically at depths starting from 30 to 40 m and extends to the limit of the photic zone, even up to 200 m (Ferrigno et al., 2018a). ...
... Moreover, nets and longlines often get entangled in the complex three-dimensional structure that characterizes these habitats, causing breakage and necrosis in many erect species, other than capturing vagile organisms and suffocating sessile algae and animals (Bo et al., 2014). These effects often result in a decrease in habitat heterogeneity, structural integrity, biodiversity, and ecosystem function (Bavestrello et al., 1997;Ballesteros, 2006;Martin et al., 2014;Enrichetti et al., 2019a;Do and Armstrong, 2023). ...
... Corals, together with long-living organisms such as encrusting red algae, polychaetes and bryozoans, are major carbonate producers, or bioengineers, in the Mediterranean Sea (Laborel, 1987;Bianchi, 1997Bianchi, , 2002Peirano et al., 1998Bianchi & Morri, 2000Cocito & Ferdeghini, 2001;Kružić et al., 2012;Kružić, 2014). Depending on ecological factors, these organisms may grow to a large size, such as banks of corals or bioherms of red algae (like Lithophyllum stictiforme (Areschoug) Hauck 1877)) or bryozoans (Ballesteros, 2006;Biacchi et al., 2022). The colonial scleractinian coral Cladocora caespitosa (Linnaeus, 1767) occurs on rocky and sandy bottoms mostly from 5 to 30 m depth (Zibrowius, 1980). ...
... Mortality of the coral C. caespitosa and other sessile marine invertebrates caused by elevated seawater temperatures has been previously described (e.g., Rodolfo-Metalpa et al., 2000, 2006Garrabou et al., 2009;Jiménez et al., 2013Jiménez et al., , 2014Kersting et al., 2013aKersting et al., , 2014aKružić et al., 2016). Another impact of high sea temperature on C. caespitosa polyps is their bleaching, an event that is more common in tropical symbiotic corals. ...
The Mediterranean endemic stony coral Cladocora caespitosa (Linnaeus, 1767) is the only reef-building and obligate zoox-anthellate coral in the Mediterranean Sea. This endangered species is threatened by climate and anthropogenic impacts affecting the coastal zone of the Mediterranean Sea. Growth rates and colony state were monitored over 20 years on a C. caespitosa bank in the Marine Protected Area of Veliko Jezero in the Adriatic Sea (Mljet National Park, Croatia). The growth rate of corallites (from 2.02 mm to 5.32 mm annually) was similar to relevant studies in different areas of the Mediterranean Sea and showed a positive correlation with the average annual sea temperature. The coral colonies formed a highly aggregated bank and beds on rocky and sandy bottoms, from 6 to 18 m depth, within a semi-enclosed bay with high water exchange caused by tides. The marine area has experienced abnormally warm summers during the last two decades, with sea temperatures reaching up to 30°C driving population damage to the coral bank. Mortality events of C. caespitosa colonies caused by polyp bleaching and tissue necrosis, showed a positive correlation with high sea temperature anomalies during summer and autumn resulting in complete or partial mortality of the colonies. The excessive growth of macroalgal species on coral colonies seems to be a direct consequence of sewage discharges from nearby villages. The present climate-warming trend together with urbanization has severely and negatively affected the C. caespitosa coral bank in the Mljet National Park causing concerns for future viability.
... Laminaria rodriguezii is also considered a priority conservation species according to the Barcelona Convention and included in the Annex II as an endangered and threatened species. According to Ballesteros (2006), as this species develops best in rhodolith beds, from where it has almost disappeared due to trawling activities, coralligenous bottoms now constitute its only refuge. ...
... The concurrent recovery of both benthic habitats is not surprising considering their overlap (Ballesteros 2006; and the fact that rodolith beds provide Fig. 6). Consistently, during our surveys in the Menorca Channel, we found L. rodriguezii mostly growing on rhodolith-forming species. ...
Rhodolith beds and Laminaria rodriguezii forests constitute marine habitats of high conservation value. In the Menorca Channel (Balearic Islands, Western Mediterranean) rhodolith beds predominate in the sedimentary bottoms of the continental shelf and in some areas, these bottoms present an erect stratum with L. rodriguezii. Bottom trawling has negative impacts on rhodolith beds and, specially, on L. rodriguezii forests due to the direct effects of extraction and mechanical destruction and indirect effects related to sediment resuspension and posterior settlement that promotes burial. In this work we compare the distribution of rhodolith beds and L. rodriguezii forests in the Site of Community Importance (SCI) of the Menorca Channel before and after 2016, when a Fishing Protection Zone (FPZ) banning trawling was established. Since the implementation of the FPZ the extension of both rhodolith beds and L. rodriguezii forests have shown an increase of 6% and 54% respectively, and biomass of rhodolith-forming species and L. rodriguezii showed higher values than before the FPZ. The improvement of these habitats in the SCI Menorca Channel evidences that the bottom trawl ban is an effective measure for the conservation and restoration of benthic communities and habitats. This is particularly relevant in the case of rhodolith beds and L. rodriguezii forests due to their ecological importance and their role as essential fish habitats that improve the sustainability of marine living resources.
... Modern algal reefs are mostly located in subtropical or temperate regions. Examples include the Mediterranean Sea (Ballesteros, 2006;Langar et al., 2011), Bermuda in the northwest Atlantic Ocean (Ginsburg & Schroeder, 1973), Norway in the North Sea (Freiwald, 1998), and Taiwan in the northwest Pacific Ocean (Dai et al., 2009;Liou et al., 2017). Crustose coralline algae are well known as reef-building coralline algae and are located extensively in coral reefs, rocky shores, and shallow sea basins worldwide (Adey, 1978;Bosence, 1983;Chisholm, 2003;Cornwall et al., 2023;Costa et al., 2019;Littler & Littler, 2013). ...
... The genera Lithophyllum, Lithothamnion, Mesophyllum, Neogoniolithon, and Porolithon are commonly observed in CCA reefs around the tropical and subtropical regions in the Pacific and Atlantic Oceans (Adey, 1975;Adey & Macintyre, 1973;Littler & Littler, 2013;Teichert, 2024). In temperate regions, Lithophyllum and Lithothamnion are dominant components of the coralligenous concretions formed by an accumulation of calcified and encrusting algae growing in dim light conditions in Mediterranean benthic environments (Ballesteros, 2006). In addition, Neogoniolithon brassica-florida constitutes a reef formation in the lagoon of Bahiret el Bibane (Langar et al., 2011). ...
The composition and abundance of crustose coralline algae (CCA) have been documented in the Xinfeng algal reef (XAR). Eight CCA species were identified, including four in Phymatolithon ( P. margoundulatum , P. taiwanense , P. variabile , and Phymatolithon sp.) and four only identified to the genus level ( Chamberlainium sp. and three Dawsoniolithon spp.). Chamberlainium sp. was the most abundant species, while the three species of Dawsoniolithon were rarely observed. The CCA coverage varied from 18% ± 15% to 27% ± 21% in spring seasons of 2021–2024, but there were no significant differences. Based on carbon‐14 dating, the CCA sediments in the XAR were estimated to be 5850–5990 years old. These CCA sediments were primarily composed of two paleo‐CCA species, resembling modern Chamberlainium sp. and Dawsoniolithon sp. 1. However, the modern species of Phymatolithon , which are widespread and abundant in the algal reefs of northwestern Taiwan, were not observed in the CCA sediments. It is unclear whether their absence was due to fragile thalli after their death or their lack of occurrence, and this requires further investigation. The paleoenvironmental data and biogenic sediment composition analysis suggests that the XAR started to develop ~6000 years ago when the sea surface temperature began to decrease and seawater turbidity increased due to rainfall. Additional CCA sediment samples from this algal reef are needed to fully understand the historical changes in the paleo‐environments in the XAR.
... Among marine ecosystems in the Mediterranean Sea, coralligenous reefs represent one of the most important biodiversity hotspots [5] together with Posidonia oceanica meadows [6]. They are the main biogenic habitat constituted by calcareous structures edified by crustose coralline algae (mostly belonging to the Lithophyllum, Lithothamnium and Mesophyllum genera) occurring in the circalittoral zone from about 20 m to about 150 m deep, forming complex three-dimensional systems supporting high biodiversity levels [7,8]. The stocks develop on rocky or sandy bottoms, in waters with relatively constant values of temperature, currents and salinity. ...
... The results show that "algae" play a consistent role with their high biomass (ranging from 174.24 to 221.27 gC m −2 ) in building these heterogenic habitats. Indeed, the coralligenous habitat consists of bioconstructions, with thickness ranging from a few centimeters up to 2 m, formed by the multilayer deposition of calcium carbonate mainly produced by crustose coralline algae and the aggregation of other marine calcifiers [7,[50][51][52]. Additionally, the high values of fish biomass (ranging from 88.12 to 202.6 gC m −2 ) highlight the key role of these complex habitats as feeding, recruitment and nursery sites for many species, often of commercial interest, also explaining why coralligenous bioconstructions are widely threatened by fishing impacts [53][54][55]. ...
Coralligenous bioconstructions are a key Mediterranean ecosystem for their associated biodiversity and role in the blue carbon cycle. They are also sensitive to environmental alterations (e.g., climate change) and other anthropic impacts related to coastal anthropization (e.g., fishing activities). Marine-coastal zone protection, conservation programs and management strategies are essential to guarantee a good ecological status of the coralligenous habitat. In this context, environmental and ecosystem accounting are useful tools to measure natural capital stocks and ecosystem service flows associated with marine ecosystems, conveying their importance in scientific and policy contexts. Indeed, the importance of marine ecosystems is often overlooked due to the difficulty of expressing their value in common units, making it challenging for decision-makers to explore trade-offs between conservation and exploitation of marine ecosystems. In this study, a biophysical and trophodynamic environmental accounting model was used to assess the biophysical value of natural capital stocks of the coralligenous habitat in three Marine Protected Areas (MPAs) of the Campania Region (Southern Italy): Punta Campanella, Santa Maria di Castellabate, and Costa degli Infreschi e della Masseta. The natural capital value per unit area associated with the coralligenous habitat ranged from 2.44 × 10¹² to 4.72 × 10¹² sej m⁻² for Santa Maria di Castellabate and Punta Campanella, respectively. Despite the different intensive values of natural capital calculated for the MPAs, there were no significant differences both in the biomass values of the taxonomic groups and in the biomass-based Shannon diversity index. Additionally, the biophysical values were also converted into monetary units, with the aim of facilitating the understanding of the importance of natural stocks in socio-economic and political contexts. The economic equivalent of natural capital value refers to the total extent of the coralligenous habitat and ranged from about EUR 1 to 15 million for Costa degli Infreschi e della Masseta and Santa Maria di Castellabate, respectively. The results of this study could be useful for local managers and policy makers and may make them more likely to achieve biodiversity conservation and sustainable development goals in MPAs. This is the first study devoted to the assessment of natural capital value of coralligenous habitats. Future studies could complement the results of this study with biophysical and economic assessments of ecosystem service flows generated by coralligenous habitats, focusing on the role they play in human well-being.
... Gorgonians are among the most affected by MMEs in the Mediterranean Sea . These species are considered habitat forming species in Mediterranean rocky bottom communities (Ballesteros, 2006;Gori et al., 2011a), displaying, in general, slow population dynamics, which limits their recovery capacity to face recurrent perturbations such as MHWs (Linares et al., , 2008aGarrabou et al., 2021;Gómez-Gras et al., 2021a). Consequently, MMEs could cause severe impacts for the populations persistence that cascade to dramatic changes at habitat level due to their ecological structural role (Pey et al., 2013;Garrabou et al., 2021;Gómez-Gras et al., 2021a), essential for the development and maintenance of highly diverse communities (Verdura et al., 2019;Gómez-Gras et al., 2021b). ...
... The north of the Catalan coast is characterized by a thermal latitudinal gradient, with lower temperatures in the northern area in comparison with the southern one (Fig. 1d). Moreover, the north of the Cap de Creus is highly exposed to strong currents (Northern Current) coming from the Gulf of Lions, which provide food and hydrodynamics to the area, essential for the development of coralligenous assemblages and the associated gorgonian populations (Ballesteros, 2006;Linares et al., 2008a) (Fig. 1e). ...
Mediterranean gorgonians are being threatened by the impact of recurrent extreme climatic events, such as marine heatwaves (MHWs). The white gorgonian Eunicella singularis was suggested to be the most resistant gorgonian species in the NW Mediterranean, mainly due to the presence of symbiotic algae. However, a sub-stantial shift in the conservation condition of the species has been observed in the recent years. The aim of this study is to evaluate the lethal and sublethal effects of recent MHWs on the populations of E. singularis. Our results show that recurrent MHWs have impacted both the demography and reproduction of the species between 2002 and 2020, driving mortalities up to 36%, an increase in the percentages of non-reproducing adult colonies (11–58%), and a significant decrease in the recruitment rates. Although E. singularis is a highly dynamic species in comparison with other temperate gorgonians, the present study suggests that the persistence of this species may be severely compromised under recurrent MHWs, at least at shallowest depths.
... The coralligenous habitat is one of the most important biocenosis of the Mediterranean Sea for its high structural complexity that promotes a huge floral and faunal abundance and diversity (Garrabou et al., 2002;Ferrigno et al., 2018;Ballesteros, 2006). For this reason, it represents the most important hotspot of biodiversity (Ferrigno et al., 2024), after Posidonia oceanica meadows (Boudouresque, 2004). ...
... Due to its high associated biodiversity, coralligenous habitat provides a wide range of important ecosystem services to humans (Tonin, 2018). In particular, they provide provisioning services through fishing, regulating services such as climate regulation through sequestration and storage of carbon, and cultural services due to the beauty of marine landscapes and diving tourism (Ballesteros, 2006;Buonocore et al., 2020a,b;Chimienti et al., 2017). ...
Among marine habitats, the coralligenous represents one of the most important biodiversity hotspots, also playing an important role in the carbon cycle. Coralligenous is a biogenic habitat of the circalittoral zone formed by calcareous structures built by crustose coralline algae and other assemblages of calcifying organisms. Due to its structural complexity, it is also considered one of the most vulnerable marine habitats, very sensitive to environmental changes, such as climate change, and to other anthropogenic impacts such as fishing activities. Trawling is the most harmful fishing method that is causing the degradation of large areas of coralligenous reef concretions. Small-scale and sport fishing can also cause damage to the most sensitive organisms of the coralligenous habitat that can be damaged or removed by fishing gear, both during the fishing activity and in the case of the involuntary abandonment of stranded or damaged fishing nets, also known as “ghost nets”. In this study, the global scientific literature on coralligenous habitat was explored, with a particular focus on human impacts and fishing activities. The analysis was carried out using the VOSviewer software, generating network maps based on literature data retrieved from the Scopus database. The results show that the scientific literature is mainly concentrated in Italy, proving the important contribution provided by the Italian research on the topic. The results also highlight a research gap in the application of environmental accounting methods to quantify and value natural capital and ecosystem services associated to the coralligenous habitat, and their loss due to human impacts.
... The Mediterranean Sea, and especially the NW coastal region, is considered a biodiversity hotspot (Lejeusne et al., 2010;Coll et al., 2012), with Posidonia oceanica Delile 1813 meadows and coralligenous reefs being important hosts of numerous species (Boudouresque, 2004;Ballesteros, 2006;Boudouresque et al., 2017). A key species in coralligenous habitats is the octocoral Corallium rubrum (Linnaeus, 1758;red coral), an ecosystem-engineering cnidarian that increases the complexity of the habitat, serving as refuge for several species (Picciano et al., 2007;Tsounis et al., 2010;Mallo et al., 2019;Rossi & Rizzo, 2020). ...
Temporal trends of the main Mediterranean benthic coastal marine habitats point to an overall decline of their extent and health status. We assessed recreational scuba divers’ perceptions of the temporal change abundance of two key Mediterranean ecosystem engineering species in the Cap de Creus Marine Protected Area: the red coral Corallium rubrum (an octocoral, component of coralligenous assemblages) and Posidonia oceanica (a seagrass, forming meadow formations on soft bottoms). We conducted semi-structured interviews and a target survey to recreational scuba divers of the area. Scuba divers reported decreasing abundance for C. rubrum, but not for Posidonia oceanica meadows during the last four decades. Qualitatively comparable ecological data for the area are only available for the last two decades and suggest stability in the abundance of both species. We explain the mismatch between data sources regarding C. rubrum arguing that, while ecological data mainly focus on no-take areas inside Cap de Creus, divers mainly visit areas where red coral colonies are unprotected. For P. oceanica, stability over the last two decades is indicated both in ecological data and in divers’ responses, suggesting that this habitat did not suffer major decline during the study period. The results of this study are overall limited by a low replication. However, it highlights local expert knowledge (i.e., recreational divers’ knowledge) as an untapped source of observations that could contribute to increase information of the historical ecological trends of these key species.
... Hard bottom benthic marine communities of coastal areas are heavily influenced by anthropogenic activities, especially in locations close to urban settlements and industrial zones [2][3][4][5]. Encrusting algae, such as Corallina officinalis Linneaus, the subject of this research, are common in coastal area because their structure makes it easier to withstand harsh conditions created by turbulent seawater movements and the destructive action of sea waves [6]. As it is obvious that every year there is increasing pressure on the coastal area, especially due to intensified urbanization, it is very important to know what kind of habitats and species are present in such areas and what their role is in the ecosystem [7,8]. ...
A very common intertidal alga, Corallina officinalis, serves as a refuge for numerous invertebrates within its settlements. The composition and structure of invertebrates may differ in relation to different natural or human-induced stress, and this study examined the effects of anthropogenic impact on the abundance and diversity of mollusks residing within C. officinalis settlements. Sampling was conducted during two seasons (Season 1 = algae’s maximum vegetation growth and Season 2 = algae’s minimum vegetation growth). Gastropods and bivalves made up 50% of all invertebrates identified, with a total of 47 species of gastropods, 25 species of bivalves, and one polyplacophoran species recorded. Considering the overall count of individuals, 4562 gastropods, 21,738 bivalves, and 260 polyplacophorans were collected from all available Corallina samples. The results indicated that locations under human impact showed a reduced number of the most abundant gastropod and bivalve species and a reduced average number of individuals.
... The diversity and abundance of gorgonians was related to presence of hard bottoms specifically bedrock and biogenic rock. These habitats support rich gorgonian forests and associated fauna, primarily between 29 and 75 m depth (Table 3), resembling the "Coralligenous" communities of the Mediterranean (Ballesteros 2006). However, the Moroccan Atlantic gorgonian communities differ significantly from their Mediterranean and Atlantic Iberian Peninsula (Portugal) counterparts in terms of species richness, composition, and densities. ...
This study is the first comprehensive documentation of the distribution and fauna of gorgonian forests along the Atlantic Coast of Morocco. The presence of shallow water gorgonian ecosystems was mapped in 2020 using ROV as part of the FAO-NANSEN habitat mapping program. The seabed was visually mapped at depths from 27 to 112 m using an ROV at 37 localities and 400 m in long video transect was conducted at each locality. The recorded megafauna and substrate were annotated using the software “VideoNavigator”. Video-transects were subdivided into 109 sampling units based on substratum and fauna patterns were identified using the multivariate analysis TWINSPAN and DCA. The relation to 10 environmental variables was indicated by correlation with DCA ordination axes. In total, 28,919 organisms and 143 taxa were recorded, with the highest diversity linked to the presence of hard substratum. Eight fauna-groups were identified that related mainly to a gradient in depth and mud along ordination Axis 1 and degrees north and sand along Axis 2. Six of the fauna-groups were gorgonian garden ecosystems on hard substratum and two were sea pen and gorgonian ecosystems associated with soft sediments. Hard substratum at 27–76 m, Group III and IV, were dominated by Leptogorgia viminalis, Eunicella species and E. paraplexaurides. Hard substratum at 59–75 m, Group V, was dominated by E. verrucosa, E. labiata, and Leptogorgia species and E. paraplexaurides. Hard substratum at 76–112 m, Group I and II, was dominated by Ellisella paraplexaurides and sponges. Soft sediments at 38–75 m, Group IV and VIII, were dominated by Pennatula rubra. Soft sediments at 72 m, Group VII was characterized by E. verrucosa and P. rubra. An observed threat to the gorgonian ecosystems were the sand that due to strong swell covered the hard bottom in many places where gorgonians forest occurs. The moving sand threatens both to bury the colonies and damage the tissue on lower parts of the colonies. This emphasizes the importance of conservation efforts to protect these delicate ecosystems.
... The species were collected in May 2014 in the sublittoral zone at 80 -100 m depth as bycatch from a bottom set net. The sampled seabed consists mainly of coralline algae pebbles (maerl), a typical Mediterranean underwater substrate at dim light conditions [41]. The sea urchins had been air-dried when used for sample preparation. ...
... Coralline algae are the deepest known macroalgae and have been found at 268-m depth (Littler et al. 1985), with encrusting nongeniculate coralline algae often being the dominant component of photo-limited marine animal forests (M1.5), forming coralligenous reefs. Coralligenous reefs (also known as coralligenous assemblages, formations, concretions or simply coralligenous) are typical mesophotic habitats of the Mediterranean Sea (Ballesteros 2006). They are among some of the best studied coralline algal habitats (Ferrigno et al. 2023) and were first described by Marion (1883). ...
Linguistic uncertainty is a prime source of uncertainty pervading ecology and conservation. Coralline algae are a widespread and diverse group of calcifying red macroalgae that underpin coastal ecosystem function and service provision. Recent increasing interest in coralline algae in the scientific literature has revealed a diverse but confusing terminology at organism to habitat scales. Coralline algal research and conservation are international and multidisciplinary, so there are geographic and disciplinary imbalances in research and conservation efforts. To reach consensus and reduce uncertainty, we propose a unified terminology. We review trends in cultural and scientific use of coralline algal terms and propose a system based on six morphologies: (1) attached, (2) free-living geniculate, (3) encrusting and free-living nongeniculate coralline algae, the latter either being (4) This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
... Coralligenous is another habitat of primary interest for much of the Mediterranean biodiversity and the ecosystem processes due to its high biodiversity and ecological importance. Coralligenous habitats are characterized by the presence of a complex community of organisms, including algae, invertebrates, and fishes, which form a three-dimensional structure that provides shelter and food for a variety of species (Ballesteros 2006). Moreover, coralligenous habitats are important for ecosystem functioning, including nutrient cycling, carbon sequestration, and sediment stabilization (Teixido et al., 2011). ...
Officially designated MPAs (MPAs with a national statute, marine Natura 2000 sites and the Pelagos Sanctuary) represent around8.3 % of the Mediterranean at the end of 2019 (an increase of 2 points since the end of 2016). If we exclude the two major sanctuaries dedicated to the protection of marine mammals, the percentage of coverage falls to around 3.7 % (an increase of 0.4points since the end of 2016). If we focus only on MPAs with a national statute, by the end of 2019 they cover around 3.2 % of the Mediterranean (an increase of 1.9 points since the end of 2016), but if we exclude the Cetaceans Corridor, they will be reduced to just 1.3 % (an increase of 0.05 points since the end of 2016). Moreover, MPAs are very unevenly distributed between regions. In fact, 97.3 % of the areas protected by MPAs are located in the theoretical European’s EEZ. Similarly, the Western Mediterranean is by far the most covered by MPAs (20.4 %, but only 6.7 % when excluding sanctuaries), ahead of the Adriatic (4.8 %). In 2020, the no-go, no-take, or no-fishing areas still only cover 0.04 % of the Mediterranean Sea, similar to 2016.
Only 13 % of MPAs with a national statute do have a business plan. Only 5 % have a suitable budget, all of which are located in EU member states and in the western basin. Similarly, this budget is fully secured in only 7 % of national MPAs, all of which are located in European countries. A small 12 % seemed to be satisfied with their human resources. The level of equipment and facilities appears to be suitable for 20 % of MPAs with a national statute. This 2020 MPA Status shows that only 26 % of MPAs with a national statute state that they have a management plan (being fully implemented for 7 %). Clearly measurable objectives have been defined for 23 % of national MPAs, and clearly defined scientifically-based indicators for 19 % of them. Regulation is suitable for 12 % of MPAs with a national statute, and regular surveillance is implemented for 13 % of them. Only 17 % have field staff qualified to carry out police missions, and sanctions are applied to a sufficient extent for 11 % of them.
Given the strong and intensifying pressures on the Mediterranean marine environment (human activities, pollution, invasive species, climate change, etc.), it is essential to strengthen the network of MPAs in areas where there are shortfalls, but also to create the right conditions for effective management and ecological benefits.
... singularis, E. cavolini, P. clavate, and C. rubrum) within MPAs aligns with empirical evidence supporting the effectiveness of MPAs in conserving slow-growing, structurally complex species [31,32]. These keystone species of Mediterranean coralligenous assemblages are highly vulnerable to overfishing, habitat destruction, and climate change [33][34][35][36]. Diver observations of healthier populations in MPAs suggest that these areas can enhance resilience and recovery [37]. ...
The Mediterranean Sea, a global biodiversity hotspot, faces significant threats that compromise its ecological health. While Marine Protected Areas (MPAs) play a crucial role in biodiversity conservation, their effectiveness is debated, and empirical data on their impact remain limited. This study evaluates the utility of Local Ecological Knowledge (LEK) from divers along the Spanish Mediterranean coast to assess perceived abundance of sentinel species in both MPAs and non-protected areas, in relation to empirical data, alongside divers’ attitudes toward ocean threats and conservation strategies. Divers perceived higher abundance and subjective health indicators of key species, such as Posidonia oceanica, octocorals, and top predators within MPAs, which aligns with empirical evidence supporting MPA effectiveness in conserving biodiversity and mitigating human disturbances. Notably, divers showed knowledge gaps, particularly underestimating climate change impacts while overemphasizing pollution threats. Diver education emerged as a critical factor in shaping conservation attitudes, with higher education levels correlating with increased environmental awareness and stronger support for conservation measures. This study underscores the potential of leveraging LEK in marine conservation strategies while acknowledging limitations related to self-reported data and regional specificity, advocating for expanded geographic scope and integration with empirical data in future research.
... The red gorgonian, Paramuricea clavata (Risso 1826), is a long-lived, slowgrowing marine invertebrate, endemic to the Mediterranean Sea (Coma et al. 1998(Coma et al. , 2004Linares et al. 2007Linares et al. , 2008. This species plays an important role in the Mediterranean coralligenous community founding from depths of 6-7 meters in the Mediterranean, and it is generally abundant between 40-60 meters, preferring vertical walls and rocks as substrates (Ballesteros 2006). It is typically found at greater depths than E. cavolini, reaching up to 100 meters (Carpine and Grasshoff 1975;Weinberg 1976). ...
Between 1973 and 2023, a total of 63 species had been protected in Turkish marine areas according to national legislation 1380 (Official Notice for Regulating Commercial Fisheries of Water Resources, No. 5/1). Notably, sturgeon species were at the forefront of these conservation efforts, with initiatives beginning in 1976 and continuing to the present day. Among marine flora, only two species (Posidonia oceanica and Zostera noltii) were granted protected status, while the other species were not accorded such protection. The protected fauna included 13 marine mammal species and 22 species of sharks and rays, the latter representing the most extensively protected category. In addition, three species of sea turtles, seven species of corals, six species of mollusks, one species of crustaceans, and three species of fish are also under protection. Comprehensive details regarding the years when these species were protected, the rationale behind their protection, their IUCN Red List statuses, and the institutions advocating for their protection are summarized. Turkish Marine Research Foundation (TUDAV) has been the main driver for the protection of sharks and rays, corals, and mollusks, successfully placing 18 species under protection in recet years. The first coralligenous species to be protected was the black coral Savalia savaglia, while the first size limitation was established for Huso huso, and the first protected species was the Mediterranean monk seal (Monachus monachus).
... In line with previous findings, our analysis of the taxonomic diversity provides evidence that also deep-water reefs formed by N. cochlear can harbor highly biodiverse assemblages [35][36][37][38][39] . Species richness of deep-water oyster reefs (DWOR) assemblages was high and comparable to that of coralligenous (C), and cnidarian-dominated (CN) assemblages, widely recognized as hotspots of biodiversity at mesophotic depths in the Mediterranean Sea 51,52 . ...
Anthropogenic and climate factors are increasingly affecting the composition and functions of many marine biogenic reefs globally, leading to a decline in associated biodiversity and ecosystem services. Once dominant ecological component, modern oyster reefs in the Mediterranean and Black Sea and the Atlantic Ocean have already been profoundly altered by overharvesting, habitat loss and the introduction of alien species. Far less known are deep-water oyster reefs, which can however form substantial biogenic structures below 30 m depth. Here we analyze the diversity of benthic assemblages associated with deep-water oyster reefs formed by the gryphaeid Neopycnodonte cochlear, and other mesophotic habitats in the central Mediterranean Sea using a taxonomic and functional approach. Our findings suggest that deep-water oyster reefs may act as hotspots of biodiversity and ecological functions in the Mediterranean Sea under current conditions, having also an edge in survival in a changing ocean.
... The coralligenous reef assemblages are considered among the major biodiversity 'hot spot' in the Mediterranean Sea (Ballesteros, 2006). Portofino MPA's coralligenous reefscape is typically dominated by Octocorallia (Anthozoa), such as Paramuricea clavata (Risso, 1826) and Corallium rubrum (Linnaeus, 1758) (Morri et al., 1986;Cánovas-Molina et al., 2016;Azzola et al., 2022). ...
... 1 Several anthozoan species are known to be habitat builders. In the Mediterranean Sea, some invertebrate species including anthozoans, together with coralline algae, contribute to the production of protected biogenic (EU Fisheries andEnvironmental Legislation-Council Regulation EC 1967/2006 92/43/EEC) and coralligenous habitats (Ballesteros, 2006;Çinar et al., 2020). ...
... Coralligenous is an endemic benthic assemblage of the Mediterranean Sea, considered a hotspot of biodiversity (Ballesteros, 2006). Due to its key functional and ecosystem roles, and its high sensitivity to human activities, coralligenous reefs are monitored in Italy within the Marine Strategy Framework Directive (MSFD) to evaluate the maintenance or achievement of good environmental status (GES) (MSFD, 2008). ...
Mesophotic and cold-water coral ecosystem session
... à toutes les profondeurs explorés. D'autre part, les sites profonds (25 -35 m) attestent de l'incursion d'espèces typiques du coralligène (Ballesteros, 2006), à savoir Eunicella cavolini (gorgone la plus commune), Axinella verrucosa (éponge dressée du circalittoral) et une couverture croissante des algues corallines encroûtantes. Même si l'on détecte ces différences, la transition vers les assemblages coralligènes reste graduelle comme l'atteste un mélange d'espèces infralittorales et circalittorales à 25 -35 m, que l'on pourrait donc qualifier d'assemblage pré-coralligène. ...
Depuis 2006, le Muséum national d’histoire naturelle (MNHN) est à l’initiative d’un vaste programme d’explorations naturalistes intitulé « La Planète Revisitée » (LPR). La cible : la biodiversité négligée des territoires tropicaux, à savoir les algues et invertébrés marins et terrestres, mal connus et pourtant très riche en espèce. Plusieurs centaines de scientifiques du monde entier ont ainsi pris part à des explorations afin d’étudier différents points chauds (hotspots) de la biodiversité : Vanuatu, Mozambique, Madagascar, Papouasie-Nouvelle-Guinée, Guyane et Nouvelle-Calédonie. Un des enjeux forts de « La Planète Revisitée » est de raccourcir le temps taxinomique, c’est-à-dire la durée entre la découverte d’une nouvelle espèce sur le terrain et sa description dans une publication scientifique, qui conditionne sa disponibilité pour la communauté scientifique et les acteurs de la conservation.
Les kilomètres parcourus ne font pas oublier pour autant que des réservoirs de biodiversité se trouvent sous nos yeux. Fragment de continent devenu île, la Corse regorge aussi d’une diversité de paysages terrestres et marins remarquables. Elle présente un taux d’endémisme exceptionnel en milieu terrestre et il s’y décrit encore de 5 à 20 nouvelles espèces chaque année !
En mai 2019, les scientifiques de La Planète Revisitée entament en Corse un programme d’expéditions conduit par le Muséum national d’Histoire naturelle, en partenariat avec la Collectivité de Corse et l’Agence française pour la Biodiversité. Ce programme a pour objectif de réaliser un échantillonnage des espèces d’algues et d’invertébrés marins et terrestres de l’île.
Le programme est prévu pour une durée de 4 ans (2019 – 2022) avec un volet marin et un volet terrestre. Les objectifs clés du volet marin sont :
- Établir un état de référence pour la Corse dans les localités choisies pour leur grande variété d’habitats marins. Il contribue à la production d’un socle de connaissance naturaliste pour de nombreux programmes de gestion et de conservation et vient compléter les données scientifiques collectées, jour après jour, par les acteurs de la conservation de la nature et du développement durable de l'Île.
- Valoriser un effort d’échantillonnage proche de l’exhaustivité grâce aux méthodes de collecte complémentaires déployées pour capter les espèces benthiques de 0 à 150m.
- Rafraîchir et moderniser les collections d’histoire naturelle de référence du MNHN de ce secteur biogéographique grâce aux images numériques et aux échantillons de tissus destinés au séquençage ADN.
Le choix des sites et des groupes taxinomiques a été défini en concertation avec les partenaires. La première année d’exploration se déroule dans le Parc naturel marin du cap Corse et de l’Agriate en 2019, puis dans la Réserve naturelle des Bouches de Bunifaziu en 2020 pour finir sur la côte occidentale depuis Carghjese jusqu’à la Pointe de la Revellata en 2021.
... Paramuricea clavata (Risso, 1827) (Anthozoa, Octocorallia) is a cornerstone species within the highly diverse coralligenous communities of the Mediterranean Sea, playing Communicated by B. W. Hoeksema an essential role in maintaining biomass and structural complexity within these ecosystems (Ballesteros 2006). Red gorgonians typically inhabit rocky substrates at depths ranging from 5 m to at least 110 m (Linares et al. 2008), predominantly occupying areas subject to strong currents, and they are widely distributed across the western Mediterranean Sea. ...
The pervasive presence of marine litter represents a significant threat to Mediterranean biogenic reefs, leading to habitat degradation and a negative impact on associated structuring organisms, such as sponges and gorgonians. This communication highlights one of the detrimental effects caused by abandoned or lost fishing gear on colonies of Paramuricea clavata (Risso, 1827) from MPA Asinara Island (Mediterranean Sea). The study is part of the Strong Sea Life project (Survey and Treatment ON Ghost Nets SEA LIFE), aimed at mitigating the effects of abandoned fishing gear and enhance the conservation status of priority habitats of Posidonia oceanica (Linnaeus) Delile, 1813 and coralligenous reefs.
... Likewise, shallower MPAs were the ones mostly interested by MMEs, mainly affecting organisms belonging to coralligenous assemblages. The coralligenous (i.e., unique landscapes built by calcareous algae frameworks growing in dim-light conditions; Ballesteros, 2006) is considered the most representative Mediterranean mesophotic habitat (Castellan et al., 2022a;Garrabou et al., 2022b). Despite listed as natural habitats of community interest by the EU Habitats Directive (92/43/EEC, code 1170), with an ad hoc action plan developed for its safekeeping (UNEP-MAP-RAC, SPA, 2008), no standardized and effective conservation measures have been implemented so far (Gómez-Gras et al., 2021;Pulido Mantas et al., 2022). ...
Coastal areas conservation strategies often left deeper habitats, such as mesophotic ones, unprotected and exposed to anthropogenic activities. In this context, an approach for including the mesophotic zone inside protection plans is proposed, considering 27 Italian Marine Protected Areas (MPAs) as a model. MPAs were classified considering their bathymetries, exposure to marine heat waves (MHWs), mass mortality events (MMEs) and, using a local ecological knowledge (LEK) approach, the estimated resilience of certain sessile species after MMEs. Only 8 MPAs contained considerable mesophotic areas, with stronger MHWs mainly occurring in shallower MPAs, and MMEs mostly affecting coralligenous assemblages. Even with only a 10% response rate, the LEK approach provided useful information on the resilience of certain species, allowing us to suggest that the presence of nearby mesophotic areas can help shallower habitats facing climate change, thus making the "deep refugia" hypothesis, usually related to tropical habitats, applicable also for the Mediterranean Sea.
... Characteristic benthic communities of the western Mediterranean basin and the Adriatic Sea are coralligenous assemblages. They are composed of hard substrates made from biogenic material and are mainly formed by calcareous encrusting algae (Ballesteros, 2006). Coralligenous assemblages are home to about 10% of all species in the Mediterranean Sea, for example to sessile invertebrates like corals, sponges, bryozoans and ascidians (Gomez-Gras et al., 2021). ...
In the last three decades, the Mediterranean Sea experienced a rapid increase in sea surface temperatures and ocean heat content. The impact rising temperatures will have on characteristic species assemblages in the Mediterranean Sea are not predictable. However, a better understanding of responses to thermal stress in benthic organisms can shed some light on this problem. In this study, we compared the thermal tolerance limits of a common native solitary ascidian, Halocynthia papillosa, an important member of coralligenous assemblages in the Mediterranean Sea to a non-native solitary ascidian, Styela plicata. We found that S. plicata starts to respond to thermal stress with behavioral modulation and heat shock protein 70 (HSP70) upregulation at lower temperatures in relation to its thermal limit than H. papillosa. For example, the highest absolute thermal limit for S. plicata was at 38°C with an initial heat shock response at 29°C. Whereas H. papillosa’s highest absolute thermal limit was at 34°C, but the heat shock response was delayed until 30°C. The absolute thermal limits rose with increasing acclimation temperatures and slower rates of temperature increase. Furthermore, H. papillosa displayed temperature-dependent food consumption and deficiencies in fast response reactions during thermal stress. The differences in response to thermal stress between these two species can be one reason why S. plicata has a wide distribution range while H. papillosa is mainly restricted to the Mediterranean Sea. The high plasticity in S. plicata under thermal stress may facilitate its success in establishing in non-native regions. Regarding the distribution of H. papillosa in the Adriatic Sea, we conclude that thermal tolerance is likely not the limiting factor of the vertical distribution along a depth gradient yet but further increasing temperatures in shallow zones might limit the species to deeper habitats in future.
... This distribution pattern is common for gorgonian species since they are considered ecosystem engineers (Verdura et al. 2019). In open areas, relatively eutrophic and have moderate occurrence of macroalgae, gorgonians can be dominant organisms, especially in healthy environments (Ballesteros 2006). However, this aggregate form of occurrence can be a threat to populations, as any harmful event, such as fishing with nets, disorderly tourism or even natural events (e.g., surface water warming, hazards and natural disor-ders), can drastically affect the local population. ...
Octocorals are extremely important animals for forming coral reefs and maintaining life in the marine environment and are widely distributed. The focus species Plexaurella grandiflora is an endemic species from Brazil. It is subject to the most varied external stressors, from ocean surface warming, pollution, damage caused by tourism, and predation by other animals. In this sense, the present study aimed to survey the population characteristics of P. grandiflora in a shallow tropical reef where it occurs in the Northeast of Brazil. Furthermore, we evaluated the stress and damage caused by coral-eating gastropods of the Muricidae family, found associated with colony structure. Through free dives between the years 2016 and 2017, 143 colonies of P. grandiflora were marked and observed, and they were analyzed in their size, supporting substrate, distribution, presence of damage, and impact by coral-eating gastropods. The cataloged colonies were larger than those recognized in the literature and were distributed in aggregate. A total of 85 gastropods of two species (Coralliophila aberrans and Coralliophila salebrosa) were recorded preying on gorgonians. The damage ranged from light to deep, from polyp removal to exposure of the protein axis. Predation occurred predominantly at the base of the colonies. As it is an endemic species and in need of studies, this study warns of the need for studies focused on the ecology and conservation of this gorgonian and its critical habitats.
Marine caves are complex habitats characterized by intense environmental gradients from the entrance towards the innermost dark sectors. The submarine caves at the Cape of Otranto (Mediterranean, SE Italy) host skeletonized invertebrates able to build 3D structures by intermingling their hard body parts with microbial carbonates, thus acting as bio-constructors of true marine animal forests. Complex bio-constructions named “biostalactites” (BSTs) with a core of calcareous tubes of Protula sp. (Serpulidae, Annelida) have been recently found in the dark sector of the “lu Lampiùne” submarine cave, one of the most complex and largest in the area. In the present study, we examined the outer surface of a BST from “lu Lampiùne” in order to evaluate species richness, abundance and distribution of Serpulidae at proximal, intermediate, and distal positions along the BST and on the two opposite sides of the BST with different textures (coarse vs. smooth). The BST surface hosted 1252 specimens belonging to 9 Serpulidae species differently distributed along the BST and on differently textured surfaces. As expected, sciaphilic Serpulidae dominated in terms of number of species and individuals. Remarkably, the large Protula tubes of the BST core that allowed it to grow from 6000 years ago have been largely replaced by small-sized Serpulidae species. The present study contributes to increase the knowledge of the metazoans associated with biostalactite fields from “lu Lampiùne” cave and allows for a comparison with findings from other Mediterranean BSTs.
Banks are ecologically relevant seafloor structures recognized as biodiversity hotspots, covering a wide range of depths in several geological contexts and encompassing heterogeneous habitat types and benthic assemblages. They support vulnerable species and habitats of conservation interest, including coralligenous outcrops that are well known as nursery areas for several species, including commercial fish species, and as carbon-flow regulating regions. The vulnerability of this habitat, characterized by species with slow growth rates, long recovery periods and exposed to multiple anthropogenic pressures, makes the implementation of appropriate conservation and management measures an urgent priority. The present work aimed to investigate: the diversity and patterns of distribution of this benthic habitat, with a focus on habitat-forming species, together with the abundance and composition of benthic litter of a protected Mediterranean bank at several depth ranges. Overall, ROV video analyses highlighted the presence of 73 taxa, including species of high biological interest protected by international conventions, and provided evidence of the presence of invasive species in the investigated bank, such as the native polychaete Hermodice carunculata and the non-indigenous seaweed Caulerpa cylindracea. Coralligenous outcrops are impacted by anthropogenic marine litter, confirming the exploitation of the bank as a fishing area. All marine litter was represented by artificial polymer materials, consisting of Abandoned, Lost or otherwise Discarded Fishing Gears (ALDFGs). The contextual high abundance of ALDFGs and the low abundance of erect habitat-forming species observed in the deep waters document a long history of mechanical disturbance caused by both operating and lost demersal fishing gears. This study represents an integrative baseline of information for the implemented Special Area of Conservation (SAC) “Secca di Amendolara” and the recently instituted homonymous regional marine park, showing the importance of fine scale data to support management measures aimed at increasing the effectiveness of ongoing conservation plans.
Crustose coralline algae (CCAs) are key components and primary builders of coralligenous reefs, which are among the most biodiverse marine habitats in the Mediterranean Sea. Beyond their structural role, CCAs play a crucial role in promoting larval settlement in a variety of invertebrate species, including corals. In addition, CCAs form complex holobionts through association with symbiotic microorganisms that can modulate their ability to induce larval settlement and provide information on their health status. Despite their ecological significance and potential for biomonitoring, the microbial communities associated with Mediterranean CCA holobionts remain largely understudied. Using electron microscopy and barcoding techniques, we identified Lithophyllum stictiforme complex and Macroblastum dendrospermum, two widespread CCAs from the Western Mediterranean Sea, living in sympatry with gorgonians. The 16S rRNA gene amplicon sequencing revealed that these CCAs host distinct and diverse bacterial communities, even among thalli of the same species, with closer thalli showing more similar bacterial assemblages. Our findings suggest that the primary factors influencing the bacterial communities include the host genotype, local environmental conditions at the individual thallus scale, and possible horizontal transfer between adjacent thalli. The predominance of bacterial sequences affiliated to the Blastopirellula genus and Pir4_lineage in phylum Planctomycetes across all CCA individuals examined is noteworthy. These bacterial groups have been hypothesized to promote coral larvae settlement in tropical regions, raising the possibility of a similar facilitative interaction between CCAs and Mediterranean coral larvae.
Extensive knowledge exists about the ecology of gorgonian species dwelling in coastal areas of the Mediterranean, but less information is available regarding populations found in deep circalittoral and bathyal environments. In recent years, the use of marine imaging technology has led to the discovery of dense coral gardens below SCUBA depths. This is the case of Eunicella cavolini (Koch, 1887) populations dwelling on the continental shelf off Cap de Creus (northwestern Mediterranean), an area included in a Site of Community Importance (SCI) of the Natura 2000 Network. We characterized the environmental niche of this species using a combination of density data extracted from 60 underwater video transects (80 to 400 m depth) and a set of environmental factors of a geomorphologic, oceanographic and human nature. Populations of E. cavolini develop within a restricted combination of environmental conditions, predominantly in areas of the mid continental shelf (95-110 m depth) characterized by a mixture of substrates (gravels, pebbles and rocks) with intermediate yearly average bottom current velocities (0.11-0.13 m·s-1) and where no records of bottom trawling activity were registered in the years prior to the surveys. The species forms dense aggregations that average 6-8 col·m-2, with local high-density peaks above 15 col·m-2. Areas suitable for the development of E. cavolini were modelled by means of a Random Forest algorithm, which predicted that an area extending over 14 ha could potentially host populations with densities over 5 col·m-2. Bottom current velocity emerged as the most important factor determining the spatial distribution of the species, followed by depth and presence of rocks. Colony height measurements indicated that populations are dominated by small-to-medium sized colonies, with average colony height positively correlated with gorgonian density. The reduced average colony height observed might respond to the strong bottom current regime characteristic of Cap de Creus, but also to the increased likelihood of larger colonies to be captured as by-catch by trammel nets, a common type of fishing gear used in the area. This study provides relevant information about the ecology of E. cavolini populations dwelling on deep circalittoral habitats, useful for policymakers when formulating specific management measures to foster the conservation of this species inside the SCI. Additionally, the data provided could assist on the restoration actions already taking place in Cap de Creus, and be used as baseline data to monitor the evolution of E. cavolini populations through time once management plans are implemented.
Understanding of non-geniculate coralline algal (NGCA) diversity, prevalence, and distribution in the tropical western North Atlantic is currently limited by reliance on morphological and anatomical features that are inadequate for species identifications. Reef surveys from two study sites, the Florida Keys (Florida, USA) and Roatán (Honduras), provided prevalence data for the main benthic organisms as well as relative abundance for NGCA genera. NGCA collected during these surveys and from additional sites and depths were identified using DNA sequences from two plastid genes, psbA and rbc L, and two nuclear genes, SSU and LSU, and supported by morphological and anatomical descriptions. Bayesian and Maximum Likelihood phylogenetic analyses, along with species delimitation and genetic distance methods, resolved 11 genera within two orders. Within the Corallinales, the genera Dawsoniolithon , Porolithon and Spongites each had one species, Harveylithon and Lithophyllum had two, Titanoderma three, Hydrolithon four, Neogoniolithon eight, and an unknown genus within the subfamily Neogoniolithoideae had 11 putative species. Within the Hapalidiales, the genera Phymatolithon and Roseolithon each had one species. This study reinforces the inability of morphological and anatomical features to distinguish NGCA species in the tropical western North Atlantic, resulting in substantial underestimations of species richness and diversity.
This paper outlines the history of scientific research developed in the Portofino Promontory, located in the centre of the Ligurian Sea. The chronicles span over two centuries, from the late 18th century to the present day. Portofino is now recognised as one of the best-known areas in the world regarding marine biological communities and their temporal dynamics, particularly in relation to current climate changes. In addition, since 1999, with the establishment of the Marine Protected Area, significant research related to marine environment conservation has developed in Portofino. The role of the University of Genoa, the Natural History Museum, other important institutions, and the researchers involved in the Portofino area has been outlined.
Describes the fauna associated with the supralittoral, mediolittoral, infralittoral and circalittoral of the almost tideless Western Mediterranean Sea, distinguishing assemblages from soft and hard substrates, and noting the contributions made by Posidonia seagrass meadows in the infralittoral. The biotas of submarine caves and tunnels are characterised. Biomass, energy flow and systemic properties of the benthos are outlined, partlicularly in connection with succession/regression, ecological strategies and trophic ecology.-P.J.Jarvis
The aim of this study was to ascertain the influence of different algal substrata on the species of benthic Amphipoda that live on them. 120 samples were collected at depths between 0 and 30 m along the coast of Catalonia (NE Spain). Well-defined groups of species appeared, which matched the classification of samples in substratum types, thus allowing for the definition of amphipod taxocoenoses related to the substrata studied. Correspondence analysis was used to depict the spatial ordination of samples and species in a low-dimensional space. This suggested a pattern that is well correlated with hydrodynamism, which is interpreted as a key parameter in determining the composition of the amphipod taxocoenoses.
Although the confirmed fossil range of this family extends only to the Early Cretaceous, striking similarities between these aragonitic forms and some late Paleozoic phylloid algae suggest that they may be closely related. Their ability to grow on soft mud substrates and form structures composed of irregular arched sheets with extensive pore space, as well as their brittle nature, so susceptible to fragmentation, are all characteristics of mound-forming fossil phylloid algae. -from Authors
This paper reports the results of a study about the geographical distribution of A. preissii in the Tuscan Archipelago. Moreover, vertical distribution, seasonal dynamics and reproductive phenology of A. preissii, on hard bottom and Posidonia oceanica beds, were investigated around Gorgona Island. Some considerations regarding the effects of A. preissii turfs on benthic communities are reported. -from Authors
Growth parameters of Mesophyllumalternans and Lithophyllumfrondosum were studied in the northwestern Mediterranean. Growth and shrinkage rates, in terms of area gained or lost per month, were measured for both crustose corallines over a 2 year period by photographic and computer-assisted image analysis. No seasonal pattern in growth or shrinkage was found for either species. M.alternans grew and shrank at significantly higher rates than L.frondosum. Growth rates for both species were over an order of magnitude lower than those previously reported for other Mediterranean and tropical species, and were similar to reports for crustose corallines in Arctic and temperate waters. Almost 50% of monitored M.alternans thalli underwent at least one fission or fusion event over the 2 year monitoring period, while in L.frondosum these events were rarely observed. Interspecific differences in rates of growth, shrinkage, fission and fusion appear to depend on differences in thallus thickness (M.alternans is thin and L.frondosum is thick). These differences were interpreted as distinct biological strategies of persistence and the occupation of primary substratum.
Calcareous algae are important in micropaleontology as records of ancient life, and they can be used in the interpretation of pale environments and for age determinations of strata. The calcareous algae comprise an artificial group that cuts across both taxonomic and disciplinary boundaries. Investigations of calcareous algae traditionally have included only the benthic forms, and have excluded planktonic calcareous algae, the coccolithophores. Fossil calcareous algae are studied chiefly in thin sections of lithified rocks with the light microscope at magnifications of about 10 to 150 times. Most benthic calcareous algae are macroscopic plants ranging from several millimeters to tens of centimeters in overall size, yet they are usually treated as microfossils. This is because they disaggregate into small segments on the death of the plant, break up into fine particles in the depositional environment, or require the microscope to discern small-scale morphological features. Fossil calcareous algae can be distinguished into two major categories—preserved skeletal remains representing direct or indirect evidence of algal tissues; and nonskeletal biosedimentary structures, generally called stromatolites, caused by algae.
The lectotype of Lithophyllum expansum Philippi, previously recognized as a Mesophyllum and considered a heterotypic synonym of Mesophyllum lichenoides, has been reinvestigated and compared to recent samples. On the basis of recently introduced new criteria, the taxon is elevated to the rank of species and named Mesophyllum expansum (Philippi) comb. nov. Five species of Mesophyllum are thus reported in European waters: M. expansum, M. lichenoides, M. alternans, M. macroblastum, M. macedonis. Their main diagnostic features are here recalled; this clarification should help to improve in the future the knowledge of bathymetric and geographic distribution of these species.
New infralittoral bioconcretions have been found in a fault of the rocky inlet of Gameou (La Ciotat-French mediterranean coast). This pillar-shaped Coralligenous proceeds from a ecomorphic form of Mesophyllum lichenoides (Ellis) Lemoine to a strong hydrodynamism and a dim illumination. Its building up by the superposing of the thalli which are reinforced by a biophysio-chemical magnesian calcite. This compact structure allowed us to determine the mean growth rate of 5 pillars by the radiocarbon dating method. We obtained a value equal to 0,19 mm.year-1.
Quantitative decapod studies carried out on calcareous seaweeds and Posidonia oceanica beds (mainly rhizome stratum), from shallow coastal waters of Almería (S, SE Spain), revealed that these biotopes represent part of the habitat of the same decapod crustacean community. A gradual transition from the decapod community in Posidonia to those in calcareous concretions is shown. This transition appears to depend on the relative developments of, and the interrelations between, both biotopes, as well as on the influence of a number of extrinsic factors such as the presence of crevices, photophilic seaweeds and sedimentation.
However, when these two biotopes are well developed and independent they could be recognized by their differing quantitative species compositions, that is by the high dominance of a small number of and different species.
The behaviour of Mediterranean octocoral planulae was studied in light-dark situations and in a light gradient. Larvae of Eunicella singularis (Esper, 1794) reacted photopositively but it is uncertain which mechanism (klinotaxis or klinokinesis) determines this property. The blind larvae probably possess a dermal light sense, but it cannot be excluded that the yolk contains photosensitive carotenoids while the symbiotic zooxanthellae may also play a role. The photopositive behaviour of planulae of this species explains some aspects of the distributional ecology of adult colonies. It was also found that for the induction of settlement and metamorphosis the chemical properties of a given substratum seem to be far more important than its roughness. Larvae of Corallium rubrum (Linnaeus, 1758) are geonegative and indifferent to light. This latter fact is surprising, since in nature the colonies are exclusively found in dark places. It is supposed, therefore, that tolerance of the colonies rather than larval choice determines light-dependent zonation of this species in nature.