Coral Forests Research Articles

Feeding biology of a habitat-forming antipatharian in the Azores Archipelago

Benthic suspension feeders have developed a variety of feeding strategies and food availability has often proven to be a key factor explaining their occurrence and distribution. The feeding biology of coral species has been the target of an increasing number of studies, however most of them focus on Scleractinia and Octocorallia, while information for Antipatharia is very scarce. The present study focused on Antipathella wollastoni, a common habitat-forming antipatharian in the Azores Archipelago, forming dense black coral forests between 20 and 150 m. The objective of the study was to investigate the food preferences of the target species upon availability of different isotopically enriched food substrates and determine its ability to capture zooplankton prey under different flow speeds. The species was able to utilize different food sources including live phytoplankton, live zooplankton and dissolved organic matter (DOM), indicating the ability to exploit seasonally available food sources. However, ingestion of zooplankton enhanced carbon (C) and nitrogen (N) incorporation in coral tissue and metabolic activity, highlighting the importance of zooplankton prey for vital physiological processes such as growth and reproduction. Maximum zooplankton capture rates occurred under 4 cm−1, however the species displayed high capacity to capture zooplankton prey over different flow rates highlighting the ability of A. wollastoni to exploit high quantities of shortly available prey.

A mesophotic black coral forest in the Adriatic Sea

A forest of the black coral Antipathella subpinnata was found from 52 to 80 m depth in three different sites at Tremiti Islands Marine Protected Area (MPA; Mediterranean Sea), with two of them hosting a monospecific forest on horizontal and vertical substrates. Colonies of A. subpinnata showed a mean density between 0.22 ± 0.03 and 2.40 ± 0.26 colonies m−2 (maximum local values of 2.4–7.2 colonies m−2). The link between the local distribution of A. subpinnata and the main oceanographic features confirmed the fundamental role of the currents in shaping the distribution of the species in presence of hard substrata. This black coral forest represents the only one known thus far in the Adriatic Sea, but it could be linked with other unseen forests all over the Mediterranean Sea. The associated megafauna highlights the importance of these forests as habitat for species of both conservation and commercial importance but, at the same time, makes such habitat a target for fishing practices, as many lost fishing gears were found within the coral forest. The enlargement of the MPA borders and the enforcement of controls in the area of the A. subpinnata forest is urgently needed for the proper conservation of this protected species.

Vulnerable Forests of the Pink Sea Fan Eunicella verrucosa in the Mediterranean Sea

The pink sea fan Eunicella verrucosa (Cnidaria, Anthozoa, Alcyonacea) can form coral forests at mesophotic depths in the Mediterranean Sea. Despite the recognized importance of these habitats, they have been scantly studied and their distribution is mostly unknown. This study reports the new finding of E. verrucosa forests in the Mediterranean Sea, and the updated distribution of this species that has been considered rare in the basin. In particular, one site off Sanremo (Ligurian Sea) was characterized by a monospecific population of E. verrucosa with 2.3 ± 0.2 colonies m−2. By combining new records, literature, and citizen science data, the species is believed to be widespread in the basin with few or isolated colonies, and 19 E. verrucosa forests were identified. The overall associated community showed how these coral forests are essential for species of conservation interest, as well as for species of high commercial value. For this reason, proper protection and management strategies are necessary.

Seasonal variation of the stable C and N isotopic composition of the mesophotic black coral Antipathella subpinnata (Ellis & Solander, 1786)

Trophic relationships significantly influence ecosystem functioning, ultimately affecting populations’ abundance, size structure and distribution. There is still a substantial knowledge gap on the trophic ecology of deep-sea organisms, particularly those living in the mesophotic depths (30–150 m), despite their crucial importance as ecosystem engineers. The trophic ecology of the most common mesophotic black coral species of the Mediterranean Sea, Antipathella subpinnata (Ellis & Solander, 1786), was studied by means of stable isotopes analysis in two seasons. The δ13C and δ15N analysis of the tissue of A. subpinnata, of the sediment, as well as the main planktonic fractions (pico-nanoplankton, microplankton, and mesozooplankton) indicate a diet based on pico-nanoplankton in autumn and mesozooplankton in spring. We calculated a trophic enrichment of 1‰ in δ13C and of 2.5‰ δ15N between prey and predator. Such information contributes towards drawing a complete picture of the pelagic-benthic coupling in the Mediterranean mesophotic coral forests.

Discovery of Deep-Water Bamboo Coral Forest in the South China Sea

A deep-water coral forest, characterized by slender and whip-shaped bamboo corals has been discovered from water depths of 1200–1380 m at the western edge of the Xisha (Paracel Islands) area in the South China Sea. The bamboo corals are often accompanied by cold-water gorgonian “sea fan” corals: Anthogorgia sp. and Calyptrophora sp., as well as assemblages of sponges, cirrate octopuses, crinoids and other animals. The coral density increased toward the shallower areas from 24.8 to 220 colonies per 100 m2 from 1380 m to 1200 m water depth. This is the first set of observations of deep-water bamboo coral forests in Southeast Asia, opening a new frontier for systematic, ecological and conservation studies to understand the deep-coral ecosystem in the region.

Exploring the deep South China Sea: Retrospects and prospects

Rapid developments of deep-sea researches in China over the past 20 years have promoted the South China Sea (SCS) into the international deep-sea frontiers. The “three deep technologies”, namely scientific drilling, long-term seafloor observation and deep submersible vehicles implemented successively in SCS studies helped to achieve a number of scientific breakthroughs. Over the 20 years, five international ocean drilling expeditions to the SCS recovered nearly 10 km of sediment cores from sites at 3–4 km water depths, and drilling into the magmatic basement at 6 sites shed light on the genesis of the SCS basin. Coupled with other deep-sea short core sediments from the SCS, these records demonstrate evidence that water and carbon cycling in the low latitude regions can directly respond to the orbital forcing, and subsequently nurture a new concept of low-latitude forcing of climate changes, which challenges the classical wisdom of the overwhelming role played by the Arctic ice-sheet in climate changes. The exploration in the continent-ocean transition zone also reveals a number of specific features that characterize the SCS as a marginal basin formed at the subduction zone in the Western Pacific. The features include active magmatism and rapid rupture of lithosphere through the basin formation process, and imply that “the SCS is not a mini-Atlantic” as they can be distinguished as “plate-edge rifting” and “inner-plate rifting” respectively, thus challenging the universality of the Atlantic model for passive margins. Many more discoveries can be assembled from long-term mooring observations and deep diving cruises in the deep SCS, such as the cyclonic nature of the deep-water circulation, deep-water sediment transport by contour currents and turbidites, manganese nodules, extinct hydrothermal vents, and cold-water coral forests. In addition, prominent progress achieved in microbiology and biogeochemistry includes the microbial carbon pump and the coupling of carbon and nitrogen cycles. Clearly, most achievements of the deep-sea explorations in the SCS over the last 20 years have always been of international scale and impact. However, the contributions from Chinese scientists are most prominent, particularly with the research activities undertaken from the major program “Deep Sea Processes and Evolution of the South China Sea (2011–2018)” supported by the National Natural Science Foundation of China.

Coral forests and Derelict Fishing Gears in submarine canyon systems of the Ligurian Sea

Biodiversity of coral forests and occurrence of Derelict Fishing Gears (DFGs) have been assessed in canyon systems of the western Ligurian Sea (Dramont, Monaco, Bordighera, Arma di Taggia and Bergeggi) exposed to different anthropic pressures. Arborescent cnidarians were elected as representative species due to their role as structuring organisms and their vulnerability to DFGs damage; hence, their occurrence, density and distribution were correlated to the presence of DFGs. The canyon systems were mapped using a Multibeam Echo Sounder and visually surveyed by means of a Remotely Operated Vehicle between 20 and 445 m depth. With the exception of the Bergeggi canyon system, all sites host rich assemblages of structuring anthozoans, accounting for more than 2000 colonies belonging to 11 species, predominantly Eunicella cavolinii, Paramuricea clavata, Corallium rubrum, Dendrophyllia cornigera, and E. verrucosa. We noticed that the large structuring gorgonians were affected most, with a high number of entangled colonies.DFGs represent 85% of the marine litter found, and are the most serious threat to resident sessile communities, most noticeably in the eastern canyons. Ports, size and fishing effort of local fleets, and socio-economical differences in the fishing activities, strongly influence the fishing footprints.Our study further confirms the role of submarine canyons as site of high coral biodiversity and vulnerability to the mechanical damages by fishing-related littering, calling for adequate management measures to reduce fishery pressure and concomitant DFGs discharge.

On the coral-feeding habit of the sea star Peltaster placenta

The predatory activity of the asteroid Peltaster placenta (Muller and Troschel, 1842) on the black coral Parantipathes larix (Esper, 1790) is here described for the first time based on video footage obtained during a Remotely Operated Underwater Vehicle (ROV) survey conducted in the Pontine Archipelago (Southern Tyrrhenian Sea, Mediterranean Sea). Feeding is carried out on the living coenenchyme of the basal axis and pinnules of the antipatharian and is confirmed by the occurrence of its cnidocysts in the sea star gut content. The chitinous skeletal parts of the black coral are left intact as bare tissue, which helps to relate colonies to the predation event. Among all black coral species present in the research area, P. placenta was observed grazing exclusively on P. larix, similarly to other goniasterids known to be deep-sea corallivores with a marked selectivity for their prey. The predatory behaviour of P. placenta was previously unknown. The extent of its feeding traces suggests a significant influence on benthic trophic relationships and, ultimately, on the functioning, structure and health status of deep Mediterranean black coral forests.

Mesophotic ecosystems: Distribution, impacts and conservation in the South Atlantic

AbstractAimThis study reviews recent research on the South Atlantic Mesophotic ecosystems (MEs) and the pressures threatening them, and offers suggestions for their management and conservation.LocationThe South Atlantic Ocean.MethodsA comprehensive compilation of the scientific literature was performed to examine the distribution, human impacts and conservation status of the South Atlantic MEs.ResultsOur review indicated that the South Atlantic Ocean (SAO) is one of the major MEs areas in the world's oceans. The South Atlantic MEs are composed of a mosaic of distinct seascapes, mainly rhodolith beds, mesophotic reefs (i.e., rocky and biogenic) and marine animal forests (e.g., sponge aggregations, octocoral and black coral forests) that occur along the East South American and West African coasts, seamounts and oceanic islands. Throughout the SAO, the distinct seascapes of MEs are usually formed on the middle and outer continental shelves, shelf‐edge, seamounts, submarine canyons, incised valleys and paleochannels, reef structures and insular shelves. We highlighted sea temperature anomalies, ocean acidification, extreme floods and droughts, fisheries, invasive species, marine debris, mining, and oil and gas exploitation as major threats to these ecosystems.Main conclusionsGiven the threats to the South Atlantic MEs, growing human pressures may degrade these ecosystems in the next years and undermine their unique biodiversity as well as their potential to provide connectivity between regions and depths. Our review revealed the existence of some extensive and unprotected formations, which urgently demand in‐depth investigations and conservation action.

Spatial distribution of the black coral Leiopathes glaberrima (Esper, 1788) (Antipatharia: Leiopathidae) in the Mediterranean: a prerequisite for protection of Vulnerable Marine Ecosystems (VMEs)

Leiopathes glaberrima is an important component of the deep coral forests of the Mediterranean Sea enhancing benthic biodiversity and forming an essential habitat for many marine organisms. It is a sessile species with high longevity; it is therefore highly affected by fishing impacts and has been listed as a representative taxon of Vulnerable Marine Ecoystems (VMEs). Since information on spatial distribution of L. glaberrima is still scanty and fragmented, an updated synopsis of its distribution in the Mediterranean is given, including two new records in the Strait of Sicily. On the basis of this updated information, hotspots of black coral off the Carloforte Island in the Sardinian Sea, on the Marco Bank and off the Pontine Islands in the Southern Tyrrhenian Sea, and on the Malta Graben in the Strait of Sicily are proposed for implementation of Fishery Restricted Areas.

Coral forests diversity in the outer shelf of the south Sardinian continental margin

Ecological theory predicts that heterogeneous habitats allow more species to co-exist in a given area, but to date, knowledge on relationships between habitat heterogeneity and biodiversity of coral forests in the outer shelf and upper slope along continental margins is rather limited. We investigated biodiversity of coral forests from 8 sites spread over two different geomorphological settings (namely, pinnacles vs. canyons) in the outer shelf along Sardinian continental margin. Using a combination of multivariate statistical analyses, we show here that differences in the composition of coral assemblages among contrasting geomorphological settings were not statistically significant, whereas significant differences emerged among sites within similar geomorphologies (i.e. among pinnacles and among canyons). Our results reveal that environmental and bathymetric factors such as sediment coverage, slope of the substrate, terrain ruggedness, bathymetric positioning index and aspect were important drivers of the observed patterns of coral biodiversity, in both settings. Spatial variability of coral forests' biodiversity is affected by environmental factors that act at the scale of each geomorphological setting (i.e. within each pinnacle and canyon) rather than by the contrasting geomorphological settings themselves. This result allows us to suggest that simple categorization of benthic communities according topographically defined habitat is unlikely to be sufficient for addressing conservation purposes.

Leiopathes glaberrima millennial forest from SW Sardinia as nursery ground for the small spotted catshark Scyliorhinus canicula

Abstract Association between habitat structuring organisms and other species has great relevance for ecosystem‐based conservation measures. Those occurring in temperate areas, particularly in the upper portion of the continental margin, are mostly unknown or not properly understood because of the difficulty to discriminate co‐occurrence and real functional linkages among species. Deep water coral assemblages over the Carloforte Shoal (south‐west Sardinia; 180–210 m depth) were investigated using ROV surveys. During the surveys, more than 740 egg‐capsules of the spotted catshark Scyliorhinus canicula, identified after hatching experiments in captivity, were found attached exclusively to colonies of the long‐living black coral Leiopathes glaberrima. Although based on a spot finding, the results show that coral forests are not only hotspots of biodiversity, but can also serve as nursery grounds for S. canicula. The protection of these millennial coral forests is therefore to be considered a priority.

Do colonies of Lytocarpia myriophyllum, L. 1758 (Cnidaria, Hydrozoa) affect the biochemical composition and the meiofaunal diversity of surrounding sediments?

Lytocarpia myriophyllum, the biggest hydroid of the Mediterranean, lives at soft bottoms. It is severely threatened by bottom trawling activities. To assess its possible influence on trophodynamics and biodiversity of surrounding sediments, we compared the organic matter content and biochemical composition, and meiofaunal biodiversity in sediments below L. myriophyllum colonies and in surrounding bare sediments. Below L. myriophyllum sediments, the protein to carbohydrate ratio, the lipid contents and meiofaunal abundance showed values higher than in bare sediments, suggesting that L. myriophyllum may influence the availability of resources for benthic consumers. The richness of meiofaunal taxa and nematode species generally decreased from below the colonies to bare sediments suggesting that the presence of L. myriophyllum colonies can have a certain influence also on benthic biodiversity. The possible influence of L. myriophyllum on trophodynamics and biodiversity of neighbouring soft bottoms claims for efforts to increase our knowledge about the trophodynamics of mesophotic coral forests and to develop adequate measures of conservation of these important and threatened habitats.

First characterisation of a Leiopathes glaberrima (Cnidaria: Anthozoa: Antipatharia) forest in Maltese exploited fishing grounds

A remotely operated vehicle (ROV) survey conducted in the deep (250–400 m) Maltese waters in 2013 revealed, for the first time, the characteristics of an extended coral forest, constituted almost exclusively by the arborescent, longevous black coral Leiopathes glaberrima. This species is a major component of the deep coral forests of the Mediterranean Sea and its occurrence in dense populations greatly enhances the benthic biodiversity of the sites in question. The existence of such a complex benthic ecosystem is particularly interesting for Malta, since this area represented, in the 1980s, the only sanctioned site within the Mediterranean basin for the commercial exploitation of black corals. The occurrence of the large black coral population hints that, at least within the investigated area, the coral resource has not greatly suffered from past coral harvesting activities. The major current concern, however, is represented by the massive anthropogenic impact due to benthic fishing activities carried out on the rocky bank, as evidenced by the high amount of discarded fishing gear directly impacting the specimens. The data here presented, despite being preliminary in nature, suggests that the investigated benthic area should be considered a vulnerable marine ecosystem valuable for future scientific monitoring exercises. Appropriate benthic fishing restrictions for the area in question, which might be considered for inclusion within an marine protected area (MPA), should be contemplated.

Deep-water bamboo coral forests in a muddy Arctic environment

Keratoisis is a genus of bamboo coral commonly reported in the northwest (NW) Atlantic as a result of fishing bycatch or by in situ observations. In 1999, a scientific trawl survey recovered fragments of Keratoisis sp. in southeast Baffin Bay (NW Atlantic), but colonies had never been seen in situ at this location until 2013, when a remotely operated vehicle (ROV) was used to survey this location. Here we report the presence of dense forests of Keratoisis sp. in a muddy environment at depths >900 m. Colonies were found as dense patches up to ~55 m long along the ROV track and were estimated to reach ~1 m in height. At this location, Keratoisis sp. appears to have branched root-like structures probably used for anchorage on mud. The majority of colonies were alive, but fragments of dead colonies were also observed, especially in the path of the 1999 bottom trawl tow. Based on visual observation, the dense stands of Keratoisis sp. in this environment seem to form structure and habitat for other invertebrates and fishes in an otherwise mainly muddy environment.

Geomorphological, trophic and human influences on the bamboo coral Isidella elongata assemblages in the deep Mediterranean: To what extent does Isidella form habitat for fish and invertebrates?

We analyzed what are the best ecological conditions for megafauna associated with the bamboo coral Isidella elongata based on the geomorphological, physical and trophic information taken in 3 stations (St1, St2, St3) off the southern Catalonian coasts at 620m depth in June 2011. Results were compared with assemblage compositions recorded in past cruises (May 1992, 1994) at the same 3 stations. St1 was in a fishing ground exploited since the 1940s over a relatively wide slope at ca. 22km from the nearest canyon head; St2 and St3 were on a narrower slope closer to canyon heads and to the Ebro river mouth than St1. I. elongata had formed (to May 1994, at least) a dense coral forest at St2–St3 (to ca. 255 colonies/ha at St3), and some isolated colonies (to ca. 0.9 colonies/ha) were still collected in 2011. Fish and invertebrate communities significantly differed between St1 and St2/St3, with two macrourid fishes (Trachrhynchus trachyrhynchus and Nezumia aequalis) and two decapods (Plesionika martia and Plesionika acanthonotus) more abundant at St2/St3. The following ecological indicators imply better food conditions for megafauna at St2–St3 and for I. elongata itself: (i) greater density of zooplankton (copepods, euphausiids, and others) as potential prey for planktivores (including I. elongata); (ii) greater biomass and mean weight of epifaunal and infaunal deposit feeders; (iii) higher feeding intensity, F, at St3 for benthos feeders (Phycis blennoides, N. aequalis and Aristeus antennatus). Also, at St2–St3 we found higher near-bottom turbidity (indicating particle resuspension: food for suspension feeders) and finer and more reduced (Eh) sediments. The results let us suggest that corals and accompanying fauna preferently found optimal ecological conditions in the same habitat, while habitat-forming capacity by I. elongata seemed weak to generate these conditions. Coral forests may enhance detritus accumulations around them, improving habitat conditions for benthos feeders (e.g. macrourid fish). At St3 our side-scan sonar recorded three types of tracks produced by trawler doors, which match with three identified vessels occasionally operating in the area. After this low fishing activity off the Ebro Delta since the mid-1990s, almost all colonies of I. elongata has been removed. However, this impact has hardly altered fish and invertebrate composition without any significant loss of diversity, pointing also toward a rather low capacity of I. elongata facies in forming habitat for megafauna on muddy bottoms of the Mediterranean slope.

Applied taphonomy of gorgonian and antipatharian corals in Atlantic Canada: experimental decay rates, field observations, and implications for assessing fisheries damage to deep-sea coral habitats

Taphonomic degradation of cold-water gorgonian and antipatharian corals may affect the record of dead or broken corals remaining on the sea floor after damage by deep-sea fisheries. A taphonomic experiment on skeletal degradation of four species of gorgonians and one antipatharian was run in aquaria for 14 months. Paragorgia arborea skeletal fragments, composed of spongy proteins and calcite spicules, were completely degraded within 14 months. Protein-skeletons of Paramuricea and antipatharian fragments gained 10-20% wet weight through hydration of their proteinaceous skeletons. Calcitic gorgonian skeletons of Primnoa resedaeformis and Keratoisis grayi experienced no significant weight change during the experiment. Field observations of dead dislodged and dead skeletons corroborated experimental results. Dislodged and dying P. arborea skeletons were rigid in their live parts, but friable and fragile in their dead parts. Subfossil calcareous gorgonian skeletons up to 2000 years in age have been recovered from the sea floor by trawl bycatch or ROV. Documenting fisheries damage to gorgonian coral forests on the sea floor requires observation within a few months after the fisheries impacts.

The Relations of the Coastal Tsetse of Kenya to the Plant Communities

Under the conditions prevailing at Kilifi G. pallidipes is evenly distributed throughout all vegetation types with the exception of cultivation from which it is at all times almost entirely absent. There is a preference for the denser vegetation in the dry season from which the tsetse spread out into the lighter vegetation in the wet and humid seasons. There is never at any time any concentration of G. pallidipes along the edges of extensive thicket or forest.The distribution of G. austeni is similar to that of G. pallidipes except that there is no tendency to spread into lighter vegetation in the wet season.There is some reason to think that G. brevipalpis prefers thicket of medium density and does not share with G. austeni a preference for tall heavy thicket.G. pallidipes was the only species staged for hunger, except for austeni in the Sokoke forest. Males are replete at all seasons. G. austeni showed a remarkably large proportion of recently fed males.Pupae and pupal cases of G. pallidipes were found on the floor of the coral rag thicket and forest. G. austeni and G. brevipalpis showed a preference for the undersides of large logs.