Mesophotic Coral Research Articles

Beautoide A, an Anti-Osteoclastogenic Sterol from Beauveria sp. NBUF147 Associated with an Irciniidae Sponge from the Marine Mesophotic Zone.

Mesophotic coral ecosystems (MCEs), located at depths ranging from 30-150 m, host some of the most diverse yet least explored marine bioresources, particularly significant for the discovery of new bioactive molecules. The fungus Beauveria sp. NBUF147, associated with an Irciniidae sponge from the mesophotic zone at a depth of 82 m, underwent chemical investigation that led to the identification of one new sterol, beautoide A (1), and one reported sterol, 3β,5α,9α-trihydroxy-(22E,24R)-ergosta-7,22-dien-6-one (2). Their structures were determined from analysis of spectroscopic data and X-ray crystallography. Evaluation of biological activity in prednisolone-induced osteoporotic zebrafish showed that 1 was anti-osteoclastogenic in vivo at 3.0 μM.

Differential strategies developed by two light-dependent scleractinian corals to extend their vertical range to mesophotic depths

Mesophotic coral ecosystems are characterised by the presence of photosynthetic scleractinian corals despite the decreasing amounts of light available with depth. To better understand physiological strategies across a broad depth gradient, we studied the biological trait responses of Pocillopora cf. verrucosa from 6 to 60 m depth and Pachyseris “speciosa” spp. from 20 to 90 m depth at four islands of French Polynesia. Specifically, we characterised associated Symbiodiniaceae communities, photophysiological traits (Symbiodiniaceae density and chlorophyll concentrations), micro-morphology and trophic plasticity (autotrophy vs heterotrophy inferred from stable isotopes). Our results showed that both taxa can live at mesophotic depths without significant genetic structuring in their generic Symbiodiniaceae communities, mainly composed of Cladocopium and Durusdinium. Yet, the prevalence of Symbiodiniaceae ITS2 profiles revealed location-based variations that sometimes interact with depth and highlight putative shallow- or depth-tolerant taxa. For both taxa, symbiont density and chlorophyll pigment concentrations increased with increasing depth. We also found a change in their skeletal micro-morphology with an increase in the inter-corallite distance for Pocillopora cf. verrucosa and a decrease in the height of septa for Pachyseris “speciosa” spp. with depth. Finally, we found no isotopic evidence of switching to a more heterotrophic diet as their primary energy source, although host–tissue δ13C ratios became more negative with depth in both corals. Overall, our findings show similarity (across the two species) and species-specific strategies (biological trait patterns with increasing depth) underlying the capacity of symbiotic scleractinian corals to live in low-light environments.

Severe cold-water bleaching of a deep-water reef underscores future challenges for Mesophotic Coral Ecosystems

Elevated sea surface temperatures are causing an increase in coral bleaching events worldwide, and represent an existential threat to coral reefs. Early studies of Mesophotic Coral Ecosystems (MCEs) highlighted their potential as thermal refuges for shallow-water coral species in the face of predicted 21st century warming. However, recent genetic evidence implies that limited ecological connectivity between shallow- and deep-water coral communities inhibits their effectiveness as refugia; instead MCEs host distinct endemic communities that are ecologically significant in and of themselves. In either scenario, understanding the response of MCEs to climate change is critical given their ecological significance and widespread global distribution. Such an understanding has so far eluded the community, however, because of the challenges associated with long-term field monitoring, the stochastic nature of climatic events that drive bleaching, and the paucity of deep-water observations. Here we document the first observed cold-water bleaching of a mesophotic coral reef at Clipperton Atoll, a remote Eastern Tropical Pacific (ETP) atoll with high coral cover and a well-developed MCE. The severe bleaching (>70 % partially or fully bleached coral cover at 32 m depth) was driven by an anomalously shallow thermocline, and highlights a significant and previously unreported challenge for MCEs. Prompted by these observations, we compiled published cold-water bleaching events for the ETP, and demonstrate that the timing of past cold-water bleaching events in the ETP coincides with decadal oscillations in mean zonal wind strength and thermocline depth. The latter observation suggests any future intensification of easterly winds in the Pacific could be a significant concern for its MCEs. Our observations, in combination with recent reports of warm-water bleaching of Red Sea and Indian Ocean MCEs, highlight that 21st century MCEs in the Eastern Pacific face a two-pronged challenge: warm-water bleaching from above, and cold-water bleaching from below.

Diverse and ecologically unique mesophotic coral ecosystems in the central Indian Ocean

Research on Mesophotic Coral Ecosystems (MCEs; 30–150 m) has grown exponentially in the last few decades, highlighting their rich diversity and extensive distribution. However, they are still largely underexplored compared to shallow-water coral reefs and frequently remain under-protected and under-represented in marine spatial planning. One reason for the imbalance between the high ecological value of MCEs and the limited levels of protection may be that baseline data on MCEs are largely missing to date, yet are crucial to provide evidence-based information for management actions. Here, we present data on the alpha and beta diversity of the benthic communities within MCEs in the Chagos Archipelago, Indian Ocean. Using imagery collected from Remotely Operated Vehicle surveys, benthic invertebrate megafauna were surveyed along the entire depth gradient from shallow to lower mesophotic depths (15–160 m). The diversity of the benthic communities decreased with increasing depth, from shallow water to the lower mesophotic zone. Nevertheless, the deepest parts of MCEs in the Archipelago displayed higher species richness values than several other shallow subtropical regions. In addition, the benthic communities showed high dissimilarity along the depth gradient, indicating that the key driver of community composition change with depth is species turnover (species replacement), revealing the uniqueness of MCEs. This study presents novel findings on MCEs in the central Indian Ocean, demonstrating that they host a high and unique benthic diversity, and highlighting the need to protect these ecosystems to preserve the overall biodiversity of coral reefs.

Whip black corals (Antipatharia: Antipathidae: Stichopathes) of the Mesophotic Coral Ecosystem of Mo’orea (French Polynesia), with the description of a new species

Black corals are key species of marine ecosystems. They can be found in dense aggregations worldwide, but some parts of the world remain totally unexplored. This is the case of the Mesophotic Coral Ecosystem of Mo’orea where the Under the Pole scientific expedition explored mesophotic ecosystems between 60 and 120 m depth and focused on whip black corals. A total of 64 specimens were analyzed morphologically and genetically, and all belonged to the genus Stichopathes. Among them, we describe the new species Stichopathes desaturata sp. nov. It is characterized by an unbranched corallum, irregularly sinuous, with a basal diameter not exceeding 1 mm, reaching a dozen of cm in height. The polyps measure 0.50–1.0 mm in transverse diameter, the interpolypar space is well defined and up to 0.50 mm, with 6–8 polyps per cm. The polypar spines are taller than abpolypar spines, reaching 0.13 mm, perpendicular to the corallum, and conical with a pointed tip, with round and/or elongated papillae on two thirds of the spine. The abpolypar spines are conical to triangular, inclined upwards, with the same ornamentation as the polypar spines. We also identified specimens assigned as Stichopathes cf. contorta and four other putative species. Genetic analyses showed that Mo’orea specimens grouped in three different clades. Analyses of endosymbionts showed that the association with Symbiodiniaceae was likely not involved in the process of host species delineation.

Diel rhythms of fish frequentation in a temperate mesophotic antipatharian forest and sleeping behaviour of the red swallowtail perch Anthias anthias (Linnaeus, 1758)

A 21-day continuous monitoring of a highly tridimensional forest of the black coral Antipathella subpinnata (Ellis and Solander 1786) was carried out in the NW Mediterranean Sea at 63 m depth using an autonomous lander to investigate the diel short-term dynamics of the vagile fauna associated to the forest. The survey allowed to assess several aspects of the forest attractiveness and its use, especially by the ichthyofauna, including (i) the diversity and shifts of the fish community inhabiting three layers of the environment (seafloor, canopy, water column) between four light phases (dawn, day, dusk, night), (ii) the diel rhythm in forest use of the red swallowtail perch Anthias anthias (Linnaeus 1758) and its sleeping behaviour in terms of fidelity towards resting sites, duration of rests, and awakenings triggers, and, finally, (iii) the influence of biotic and abiotic variables on the fish behaviour. Considering that, so far, only spot censuses have been carried out in these habitats, this study provides a dynamic approach to the study of biodiversity in temperate mesophotic coral forests and offers an insight into the functioning of these complex and vulnerable ecosystems.

Invertebrate sounds from photic to mesophotic coral reefs reveal vertical stratification and diel diversity.

Although mesophotic coral ecosystems account for approximately 80% of coral reefs, they remain largely unexplored due to their challenging accessibility. The acoustic richness within reefs has led scientists to consider passive acoustic monitoring as a reliable method for studying both altiphotic and mesophotic coral reefs. We investigated the relationship between benthic invertebrate sounds (1.5-22.5kHz), depth, and benthic cover composition, key ecological factors that determine differences between altiphotic and mesophotic reefs. Diel patterns of snaps and peak frequencies were also explored at different depths to assess variations in biorhythms. Acoustic recorders were deployed at 20m, 60m, and 120m depths across six islands in French Polynesia. The results indicated that depth is the primary driver of differences in broadband transient sound (BTS) soundscapes, with sound intensity decreasing as depth increases. At 20-60m, sounds were louder at night. At 120m depth, benthic activity rhythms exhibited low or highly variable levels of diel variation, likely a consequence of reduced solar irradiation. On three islands, a peculiar peak in the number of BTS was observed every day between 7 and 9 PM at 120m, suggesting the presence of cyclic activities of a specific species. Our results support the existence of different invertebrate communities or distinct behaviors, particularly in deep mesophotic reefs. Overall, this study adds to the growing evidence supporting the use of passive acoustic monitoring to describe and understand ecological patterns in mesophotic reefs.

Mesoscale Eddies Influence Coral Reef Environments in the Northwest Gulf of Mexico

AbstractCoral reefs globally are experiencing more frequent and severe warming events due to anthropogenic driven climate change. Subtropical reefs experience more seasonal variability than lower latitude reefs making them typically more resilient to climate change. With relatively stable coral cover in comparison to other global coral reefs, Flower Garden Banks National Marine Sanctuary (FGBNMS) in the Gulf of Mexico is a series of 17 reefs and banks located on the continental shelf‐edge containing a variety of shallow (0–30 m) and mesophotic (30–150 m) coral reef habitats. Here, we use satellite data products to associate open ocean Argo float profiles with eddy features over FGBNMS to study the shelf‐edge reef environment spanning nearly two decades (2003–2022). Satellite data show that FGBNMS is frequently influenced (∼15 days/month) by mesoscale eddies. The upper water column variability (0–25 m) is most influenced by the seasonal mixed layer despite eddy interaction. Subsurface seasonal ranges of temperature and salinity are enhanced or suppressed depending on the influence of eddies in relation to the mixed layer depth. Within the mesophotic zone (0–150 m), the largest range of thermal variability between anticyclonic and cyclonic eddies is between 50 and 150 m upwards of 5°C. However, these observed dynamics will likely change as a result of eddy variability associated with projected warming and Loop Current weakening, leading to increased thermal stress in the future.

Sponge abundance and diversity patterns in the shallow and mesophotic reefs of the northern Red Sea

Accumulating data on the increasing degradation of coral reefs worldwide has led to a focus on the unique mesophotic coral ecosystem (MCE) as a potential refuge for threatened shallow-water species (i.e., the deep reef refugia hypothesis: DRRH). Sponges play a crucial role in coral-reef functioning but are often overlooked in benthic surveys. This knowledge gap is especially true for the Red Sea, where data on sponge abundance, coverage and species composition are scarce. Furthermore, to date, no study has examined mesophotic sponges in the Red Sea. Here we compared sponge abundance and diversity metrics between shallow and mesophotic reefs at two sites in the Gulf of Aqaba, northern Red Sea. We also examined the role of biotic and abiotic parameters in determining sponge variability between sites and depths. Sponge diversity metrics significantly varied with increasing depth and between sites. Sponge species composition also differed significantly between depth and sites. However, parameters measured in the water column, that is, Total Organic Carbon (TOC), Particulate Organic Carbon (POC), NOx, etc., did not differ between depths and sites, except for Synechococcus and Prochlorococcus concentration, which did. The findings indicated that site characteristics and biotic interactions may play an essential role in determining sponge diversity and community composition. Between-site differences in sponge fauna revealed in the study highlight the importance of considering the variability in the benthic communities and the factors controlling it when designing management tools for coral reefs, particularly for the northern Red Sea.

Climate change impacts on mesophotic regions of the Great Barrier Reef

Climate change projections for coral reefs are founded exclusively on sea surface temperatures (SST). While SST projections are relevant for the shallowest reefs, neglecting ocean stratification overlooks the striking differences in temperature experienced by deeper reefs for all or part of the year. Density stratification creates a buoyancy barrier partitioning the upper and lower parts of the water column. Here, we mechanistically downscale climate models and quantify patterns of thermal stratification above mesophotic corals (depth 30 to 50 m) of the Great Barrier Reef (GBR). Stratification insulates many offshore regions of the GBR from heatwaves at the surface. However, this protection is lost once global average temperatures exceed ~3 °C above preindustrial, after which mesophotic temperatures surpass a recognized threshold of 30 °C for coral mortality. Bottom temperatures on the GBR (30 to 50 m) from 2050 to 2060 are estimated to increase by ~0.5 to 1 °C under lower climate emissions (SSP1-1.9) and ~1.2 to 1.7 °C under higher climate emissions (SSP5-8.5). In short, mesophotic coral reefs are also threatened by climate change and research might prioritize the sensitivity of such corals to stress.

Depth and structure as environmental drivers of fish communities across a shallow to mesophotic gradient in the northern US Virgin Islands

The factors that drive fish communities on coral reefs are varied, complex, and often location specific. In the northern United States Virgin Islands, the large areas of mesophotic coral ecosystems across an insular shelf provide a multitude of gradients along which fish communities form. Using a stratified-random visual fish census, we collected comprehensive data on fish communities across a seascape scale. Fish density and diversity showed responses to depth and hard relief, with these factors occasionally interacting in ways that are species specific. Analysis of trophic groups showed that densities of all groups were positively associated with relief, but while herbivores and invertivores decreased with depth, planktivores and piscivores increased, and piscivores additionally showed an interaction. Some commercially important species occurred more frequently and in larger sizes on deeper reefs, suggesting that mesophotic reefs shelter more fisheries resources, although they are less commonly sampled in visual census programs. Understanding how fish communities change across the seascape informs patterns of ecosystem function, such as identifying areas of resilience and vulnerability. This dataset is a valuable contribution to more completely understanding the ecology and conservation of fishes in the western Atlantic.

Genomic, morphological, and physiological insights into coral acclimation along the depth gradient following an in situ reciprocal transplantation of planulae

Mesophotic coral reefs have been proposed as refugia for corals, providing shelter and larval propagules for shallow water reefs that are disproportionately challenged by global climate change and local anthropogenic stressors. For mesophotic reefs to be a viable refuge, firstly, deep origin larvae must survive on shallow reefs and, secondly, the two environments must be physically connected. This study tested the first condition. Planulae of the reef-building coral Stylophora pistillata from 5–8 and 40–44 m depth in the Gulf of Aqaba were tested in a long-term reciprocal transplantation experiment for their ability to settle and acclimate to depth in situ. We assessed survival rates, photochemical, physiological, and morphological characteristics in juveniles grown at either their parental origin or transplantation depth. Differences in gene expression patterns were compared between mesophotic and shallow corals at the adult, juvenile, and planula life stages. We found high mortality rates among all mesophotic-origin planulae, irrespective of translocation depth. Gene expression patterns suggested that deep planulae lacked settlement competency and experienced increased developmental stress upon release. For surviving shallow origin juveniles, symbiont photochemical acclimation to depth occurred within 8 days, with symbiont communities showing changes in photochemical traits without algal symbiont shuffling. However, coral host physiological and morphological acclimation towards the typical deep phenotype was incomplete within 60 days. Gene expression was influenced by both life stage and depth. A set of differentially expressed genes (DEGs) associated with initial stress responses following transplantation, latent stress response, and environmental effects of depth was identified. This study therefore refutes the Deep Reef Refugia Hypothesis, as the potential for mesophotic-origin S. pistillata planulae to recruit to the shallow reef is low. The potential remains for shallow planulae to survive at mesophotic depths.

Mesophotic corals in Hawai'i maintain autotrophy to survive low-light conditions.

In mesophotic coral ecosystems, reef-building corals and their photosynthetic symbionts can survive with less than 1% of surface irradiance. How depth-specialist corals rely upon autotrophically and heterotrophically derived energy sources across the mesophotic zone remains unclear. We analysed the stable carbon (δ13C) and nitrogen (δ15N) isotope values of a Leptoseris community from the 'Au'au Channel, Maui, Hawai'i (65-125 m) including four coral host species living symbiotically with three algal haplotypes. We characterized the isotope values of hosts and symbionts across species and depth to compare trophic strategies. Symbiont δ13C was consistently 0.5‰ higher than host δ13C at all depths. Mean colony host and symbiont δ15N differed by up to 3.7‰ at shallow depths and converged at deeper depths. These results suggest that both heterotrophy and autotrophy remained integral to colony survival across depth. The increasing similarity between host and symbiont δ15N at deeper depths suggests that nitrogen is more efficiently shared between mesophotic coral hosts and their algal symbionts to sustain autotrophy. Isotopic trends across depth did not generally vary by host species or algal haplotype, suggesting that photosynthesis remains essential to Leptoseris survival and growth despite low light availability in the mesophotic zone.

Intact shallow and mesophotic assemblages of large carnivorous reef fishes underscore the importance of large and remote protected areas in the Coral Triangle

Abstract Overfishing remains a threat to coral reef fishes worldwide, with large carnivores often disproportionately vulnerable. Marine protected areas (MPAs) can restore fish populations and biodiversity, but their effect has been understudied in mesophotic coral ecosystems (MCEs), particularly in the Coral Triangle. Videos were analysed from baited remote underwater video systems deployed in 2016 to investigate the assemblage structure of large carnivorous fishes at shallow (4–12 m) and mesophotic (45–96 m) depths in two of the largest and most isolated MPAs in the Philippines: an uninhabited, fully no‐take MPA enacted in 1988 (Tubbataha Reefs Natural Park) and an archipelagic municipality surrounded by an extensive but not fully no‐take MPA declared in 2016 (Cagayancillo). Taxa focused on were groupers (Serranidae), snappers (Lutjanidae), emperors (Lethrinidae), jacks (Carangidae) and the endangered Cheilinus undulatus (Labridae). Mean abundance and species richness were not greater in TRNP than in Cagayancillo regardless of depth despite long‐term protection in the former. Limited impacts of fishing in Cagayancillo may explain this result. Differentiation of fish assemblages was evident between TRNP and Cagayancillo but more obvious between depths at each location, probably due more to habitat than MPA effects. In Cagayancillo, overall carnivorous reef fish, grouper and jack mean abundance were 2, 2 and 10 times higher, respectively, at mesophotic depths, suggesting that MCEs can serve as deep refugia from fishing. These findings of differentiation between depths and higher abundance of certain taxa in mesophotic depths emphasize that MCEs are distinct from shallow reefs, serve as important habitat for species susceptible to overfishing and, thus, must be explicitly included in the design of MPAs. This study also highlights the value of maintaining strict protection of MPAs like TRNP for the Coral Triangle and an opportunity to safeguard intact fish assemblages in Cagayancillo by expanding its no‐take zones.

Metabolites with Anti-acetylcholinesterase Activities from Marine Mesophotic Zone Halichondria Sponge-associated Fungus Chaetomium sp. NBUF152

Background: Mesophotic coral ecosystems (MCEs) are light-dependent ecosystems found from 30 to 150 m in depth that are highly diverse and relatively understudied worldwide. Methods: One new indole alkaloid, chaetoid A (1), one known analog, indigodole B (2), and one known β-carboline type alkaloid 1-acetyl-β-carboline (3), along with three known cyclic depsipeptides, turnagainolide A (4), turnagainolide B (5), arthroamide (6)—were isolated from cultures of fungus Chaetomium sp. NBUF152 is associated with a 66 m deep mesophotic zone Halichondria sponge. Their structures were determined by analysis of spectroscopic data (NMR, HRESIMS, UV, IR, optical rotation, and ECD). The in vitro bioassay results showed that compounds 1-6 exhibited moderate inhibition against acetylcholinesterase (AchE). Results: The results showed that these compounds displayed moderate anti-AchE activities with IC50 values of 25.97 μmol/L, 25.80 μmol/L, 21.07 μmol/L, 23.49 μmol/L and 21.28 μmol/L, 25.3 μmol/L. Conclusion: This work could lead to additional investigation into the potential of marine organisms in MCEs as a source for discovering natural products with interesting structures and bioactivities.

Calcification and trophic responses of mesophotic reefs to carbonate chemistry variability

Mesophotic coral ecosystems (MCEs) are extensions of adjacent shallow water coral reefs. Accessibility to these ecosystems is challenging due to their depth limits (~ 30 – 150 m) and as a result, scientific knowledge of these reef systems is limited. It has been posited that the depth limits of MCEs diminish anthropogenic effects experienced by shallow reef systems. A lack of empirical measurements to date has made this hypothesis impossible to determine for mesophotic reef metabolism. The alkalinity anomaly technique was utilized to determine rates of net ecosystem calcification (NEC) and net ecosystem production (NEP) from 30, 40 and 60 m mesophotic reefs during a 15-month period. Seawater chemistry was determined to be chemically conducive for calcification (average aragonite saturation Ωaragonite of 3.58, average calcite saturation Ωcalcite of 5.44) with estimates of NEC indicating these reef systems were net accretive and within global average values for shallow coral reefs (< 30 m). The strongest periods of calcification occurred in late summer and were coupled with strong autotrophic signals. These episodes were followed by suppressed calcification and autotrophy and in the case of the 60 m reefs, a switch to heterotrophy. Whilst there was variability between the three reefs depths, the overall status of the mesophotic system was net autotrophic. This determination was the opposite of trophic status estimates previously described for adjacent shallow reefs. Whilst there were periods of net dissolution, the mesophotic reef system was net accretive (i.e., gross calcification > gross CaCO3 dissolution). The measured inorganic carbon chemistry and estimates of NEC and NEP represent the first such biogeochemical measurements for MCEs. The values established by this study demonstrate just how close these understudied ecosystems are in terms of the known boundary thresholds for low saturation state reefs. Making predictions on how these ecosystems will respond to future climatic conditions, will require greater sampling effort over long times scales to decouple the environmental controls exerted on such ecosystems.

Presence of coral-killing sponges in Okinawan mesophotic coral ecosystems

Shallow reefs worldwide are degrading due to multiple threats. Mesophotic coral ecosystems (MCEs; 30–150 m depth) have been investigated for their diversity and potential to serve as a coral refuge and re-seed shallow reefs. However, recent studies showed that MCEs are also disturbed by various factors, including diseases, pollution, storms, and thermal-induced bleaching. Among the disturbances, coral-killing sponges are also known to decimate many Indo-Pacific shallow reefs but are rarely reported at mesophotic depths. Here, we report the first comprehensive assessment of the coral-killing sponges Chalinula nematifera (de Laubenfels, 1954) and Terpios hoshinota Rützler and Muzik, 1993 in MCEs. Specifically, we investigated (1) their prevalence, (2) sponge-affected corals, and (3) coral-sponge interaction types at 40 m depth in Okinawa, southern Japan. We found that C. nematifera and T. hoshinota were present but at low prevalences, with the highest mean cover of 3.8% and 1.8%, respectively. Although both species appeared to be substrate-generalists, they mainly affected the dominant coral taxa, such as branching corals Acropora tenella and Seriatopora sp. Both sponges mainly interacted with corals by overgrowth, followed by tissue and peripheral contact. Due to lack of prior knowledge, it is unclear whether the current observation of the coral-killing sponges captured their expansion, decline, or steady state in Okinawan MCEs. Thus, this study provides unprecedented insights about coral-killing sponges at mesophotic depths which highlights the need to monitor more MCEs globally, prioritizing regions with shallow reefs that are already threatened by these sponges.

Benthic and fish community composition on mesophotic reefs in Grand Cayman.

Mesophotic Coral Ecosystems (MCEs) represent unique ecological habitats that range from 30 to 150 m deep, harbouring phylogenetically distinct species and offering refuge for many taxa during times of environmental stress. Yet owing to inaccessibility of ecosystems at these depths, most MCEs remain unexplored, with quantifications of ecological communities in these habitats lacking across many regions. Here, using open- and closed-circuit technical diving, we quantified benthic and fish community composition at four mesophotic reef sites (45 m depth) in Grand Cayman. We show significant differences in benthic community composition over a small spatial scale driven by disparate coverage of sponges, crustose coralline algae, and sand/rubble, yet consistent patterns of macroalgal dominance representing >50% coverage at each site and low hard coral cover at an average of 2.4%. Reef fish species richness, biomass, and density was consistent across sites, however the relative contribution of individual species to community composition differed significantly. Macrocarnivores were found to be the dominant contributors to biomass, with invertivores the most speciose, and omnivores and planktivores at the highest densities, consistent with previous descriptions of mesophotic fish assemblages in other regions. Similarly, the low hard coral cover and high macroalgae and sponge cover of the benthic communities also appear ecologically similar to several described mesophotic reefs yet is not uniform across the Caribbean. The ecological organisation of Grand Cayman's MCEs may result from a variety of factors such as isolation from other major land masses, geology, local geography, and anthropogenic activity at both the local and global scale and highlight the importance of continued exploration and documentation of MCE communities.

Ictiofauna asociada a ambientes coralinos mesofóticos, usando video remoto de bajo costo en el Parque Nacional Natural Corales de Profundidad, Caribe colombiano

The fish community inhabiting mesophotic coral ecosystems (MCE) at Corales de Profundidad National Natural Park (CPNNP), Colombian Caribbean Sea was described. Most of the species (89%) are common in shallow reef environments of an adjacent Marine Protected Area. Halichoeres maculipinna, Prognathodes aculeatus, Serranus luciopercanus and Lactophrys trigonus were recorded for the first time at CPNNP. The healthy and highly resilient characteristics of MCE is confirmed with the taxonomic composition of the found fishes. The information presented in this study provides data and techniques that help to complement the baseline of fish’s assemblages associated with mesophotic coral ecosystems in the Colombian Caribbean Sea.

Diel cycle of two recurrent fish sounds from mesophotic coral reefs

Mesophotic coral ecosystems (MCEs) are the deepest part of tropical coral reefs, ranging from depths of 30 to over 170 m. Despite their significance, MCEs remain largely unexplored due to the challenges associated with accessing these depths. However, the application of passive acoustic monitoring methods (PAM) is a suitable approach for studying fish communities within these unique habitats. In French Polynesia, recent PAM studies have unveiled a higher occurrence of frequency-modulated fish sounds in MCEs than in shallower reef environments. This study aims to further enhance our understanding of fish sounds in MCEs by examining their diel patterns, focusing specifically on the two most abundant frequency-modulated fish sounds that were recorded at depths of 60 and 120 m at six Polynesian islands. Both sound types occurred predominantly during the beginning and the end of nocturnal periods. The presence and abundance of these sounds exhibited variation between the islands, highlighting potential regional disparities in vocal activity or the bathymetric distribution of the sound-producing species. By characterizing the diel cycles and bathymetric differences in relation to their geographical distribution, this study offers preliminary insights into identifying the potential sound-producing species.