Diversity and time-series analyses of Caribbean deep-sea coral and sponge assemblages on the tropical island slope of Isla de Roatán, Honduras

Shore-based submersible operations, from 2006 to 2020, have allowed us to examine megabenthic assemblages along the island margin of Isla de Roatán from depths of about 150 to 750 m, including repeated observations of the same organisms. These dives were used to photo-document a diverse benthic assemblage and observe the health and condition of the sessile fauna in a well-explored but relatively undocumented area of the Mesoamerican Reef. Samples were collected by dip net, and some dives profiled the water column chemistry in the year 2011. The deep-sea coral assemblage observed off Roatan exhibits high abundance and diversity. The sessile habitat-forming taxa consist primarily of at least 20 different octocorals (e.g., Plexauridae, Primnoidae, Coralliidae, Isididae, and Ellisellidae) and 20 different sponges each (Demospongiae and Hexactinellida), with several known and unknown taxa of Zoantharia, Antipatharia (Bathypathes spp), and Scleractinia (e.g., Desmophyllum pertusum, Dendrophyllia alternata, Madracis myriaster, and solitary taxa). Crinoidea were also abundant and diverse, represented by at least nine species. Epifaunal assemblages associated with corals include at least 24 macroinvertebrate species dominated by Asteroschema laeve (Ophiuroidea) and Chirostylus spp. (Decapoda: Anomura). Repeated observations of a few large octocoral colonies over many years illustrate patterns of predation, recolonization, and epibiont host fidelity, including a 14-year record of decline in a plexaurid octocoral (putatively Paramuricea sp.) and loss of its resident ophiuroids. The shore-based submersible provides a practical and relatively inexpensive platform from which to study coral and sponge assemblages on a deep tropical island slope. The deep-sea coral gardens are likely to harbor new species and new discoveries if more samples can be acquired and made available for taxonomic research.

Underwater Photogrammetry Captures the Initial Recovery of a Coral Reef at Lalo Atoll

Recovery of coral reefs after physical damage sustained from storm events can be affected by various factors. Here, we examined the initial recovery of a coral reef at the southern end of uninhabited Lalo Atoll of Papahānaumokuākea Marine National Monument after its complete destruction by Hurricane Walaka in 2018. While the site was still mostly (98%) covered by a mixture of rubble and sand, surveys utilizing underwater photogrammetry allowed for detailed quantitative assessments of benthic cover and confirmed colonization of coral (Pocillopora meandrina and Porites lobata), macroalgae and sponges. The proportion of sand in the rubble–sand mixture also decreased from the level observed in 2019. Visual fish surveys confirmed the presence of 35 reef fish species, a large increase from no reef fish in 2019, despite the low biotic benthic cover. Overall, the colonization of benthic organisms and the return of reef fish, which is potentially supported by the benthos and cryptofauna in the rubble bed, offer positive signs of reef recovery. The photogrammetric surveys in the present study captured the subtle changes in the benthic cover and provided us with a procedure to continue monitoring the succession of the site. Continuous monitoring of the site should reveal whether the reef returns to the original state of Acropora coral dominance or progresses towards a coral assemblage with a different composition.

Mesophotic Gorgonian Corals Evolved Multiple Times and Faster Than Deep and Shallow Lineages

Mesophotic Coral Ecosystems (MCEs) develop on a unique environment, where abrupt environmental changes take place. Using a time-calibrated molecular phylogeny (mtDNA: mtMutS), we examined the lineage membership of mesophotic gorgonian corals (Octocorallia: Cnidaria) in comparison to shallow and deep-sea lineages of the wider Caribbean-Gulf of Mexico and the Tropical Eastern Pacific. Our results show mesophotic gorgonians originating multiple times from old deep-sea octocoral lineages, whereas shallow-water species comprise younger lineages. The mesophotic gorgonian fauna in the studied areas is related to their zooxanthellate shallow-water counterparts in only two clades (Gorgoniidae and Plexauridae), where the bathymetrical gradient could serve as a driver of diversification. Interestingly, mesophotic clades have diversified faster than either shallow or deep clades. One of this groups with fast diversification is the family Ellisellidae, a major component of the mesophotic gorgonian coral assemblage worldwide.

Spatial Patterns of Coral Community Structure in the Toliara Region of Southwest Madagascar and Implications for Conservation and Management

The Great Reef of Toliara, on the southwestern coast of Madagascar, has been documented as harbouring flourishing reef communities in the 1960s, but has since been affected by various threats, causing a coral decline last reported in 2008. In 2017, we examined the spatial heterogeneity in coral community structure in the region of Toliara. Coral assemblages were characterized by a marked spatial variability, with significant variation for most of the descriptors among the three major habitats and also among stations within habitats. We recorded high coral cover, with values >40% at six of the 10 stations, which was associated with high abundance of coral colonies. We also documented the return to an Acropora-dominated coral assemblage. While these positive results suggest a recent return to healthier coral assemblages, they must be tempered, as the diversity that we recorded was lower than in the 1960s. Moreover, we found a high cover of algae at several stations, suggesting that the ecosystem is likely close to the tipping point toward a phase shift. Finally, the population size-structure of major coral taxa was positively skewed, with few large colonies to ensure the replenishment of local populations. The marked spatial variation suggests that marine protected areas should integrate a sufficiently large area to capture the scale of this spatial heterogeneity.

Severe Heat Stress Resulted in High Coral Mortality on Maldivian Reefs following the 2015–2016 El Niño Event

Coral cover worldwide has been declining due to heat stress caused by climate change. Here we report the impacts of the 2015–2016 El Niño mass coral bleaching event on the coral cover of reefs located on central and northern atolls of the Maldives. We surveyed six reef sites in the Alifu Alifu (Ari) and Baa (South Maalhosmadulu) Atolls using replicate 20 m benthic photo transects at two depths per reef site. Live and recently dead coral cover identified from images differed between reef sites and depth. Recently dead corals on average made up 33% of the coral assemblage at shallow sites and 24% at deep sites. This mortality was significantly lower in massive corals than in branching corals, reaching an average of only 6% compared to 41%, respectively. The best predictors of live coral cover were depth and morphology, with a greater percentage of live coral at deep sites and in massive corals. The same predictors best described the prevalence of recently dead coral, but showed inverse trends to live coral. However, there was high variability among reef sites, which could be attributed to additional local stressors. Coral bleaching and resulting coral mortalities, such as the ones reported here, are of particular concern for small island nations like the Maldives, which are reliant on coral reefs.

Mesophotic gorgonian corals evolve multiple times and faster than deep and shallow lineages

1.SummaryMesophotic Coral Ecosystems (MCEs) promise hope for the shallow-water biota enduring rising temperatures and multiple environmental stressors. Using a time-calibrated molecular phylogeny (mtDNA: mtMutS), we examined the lineage membership of mesophotic gorgonian corals (Octocorallia: Cnidaria) in comparison to shallow and deep-sea lineages of the wider Caribbean-Gulf of Mexico and the Tropical Eastern Pacific. Our results show mesophotic gorgonians originating multiple times from old deep-sea octocoral lineages, whereas shallow-water species comprise younger lineages. The mesophotic gorgonian fauna in the studied areas are related to their zooxanthellate shallow-water counterparts in only two clades (Gorgoniidae and Plexauridae), where the shallow-deep gradient could serve as a driver of diversification. Interestingly, mesophotic clades have diversified faster than either shallow or deep clades. One of this groups with fast diversification is the family Ellisellidae, a major component of the mesophotic gorgonian coral assemblage worldwide.

Modelling the linkage between coral assemblage structure and pattern of environmental forcing

Geographical comparisons suggest that coral reef communities can vary as a function of their environmental context, differing not just in terms of total coral cover but also in terms of relative abundance (or coverage) of coral taxa. While much work has considered how shifts in benthic reef dynamics can shift dominance of stony corals relative to algal and other benthic competitors, the relative performance of coral types under differing patterns of environmental disturbance has received less attention. We construct an empirically-grounded numerical model to simulate coral assemblage dynamics under a spectrum of disturbance regimes, contrasting hydrodynamic disturbances (which cause morphology-specific, whole-colony mortality) with disturbances that cause mortality independently of colony morphology. We demonstrate that the relative representation of morphological types within a coral assemblage shows limited connection to the intensity, and essentially no connection to the frequency, of hydrodynamic disturbances. Morphological types of corals that are more vulnerable to mortality owing to hydrodynamic disturbance tend to grow faster, with rates sufficiently high to recover benthic coverage during inter-disturbance intervals. By contrast, we show that factors causing mortality without linkage to morphology, including those that cause only partial colony loss, more dramatically shift coral assemblage structure, disproportionately favouring fast-growing tabular morphologies. Furthermore, when intensity and likelihood of such disturbances increases, assemblages do not adapt smoothly and instead reveal a heightened level of temporal variance, beyond which reefs demonstrate drastically reduced coral coverage. Our findings highlight that adaptation of coral reef benthic assemblages depends on the nature of disturbances, with hydrodynamic disturbances having little to no effect on the capacity of reef coral communities to resist and recover with sustained coral dominance.

Shallow-water black corals (Cnidaria: Anthozoa: Hexacorallia: Antipatharia) from SW Madagascar

Antipatharians, also known as black corals, represent a small group of anthozoan hexacorallians found in all oceans of the world. They are generally considered a deep-water taxon; however, some of the most diverse communities are known from tropical shallow waters. With a few poorly detailed exceptions, shallow-water black corals from the Indian Ocean and especially those from Madagascar are mostly unknown. In this study, we report for the first time a highly diverse black coral assemblage of the Western Indian Ocean thriving in shallow waters and upper mesophotic depths (10–52 m depth) along the SW coast of Madagascar. A total of 22 species belonging to six genera (Antipathes, Arachnopathes, Cirrhipathes, Cupressopathes, Myriopathes and Stichopathes) and two families (Antipathidae and Myriopathidae) are described, of which 20 are found in the northern pass of the Great Reef of Toliara, thus representing the most diverse site of the areas investigated. Most of the shallow-water species from the Indian Ocean were originally described more than a century ago, sometimes without being reported again until now. All the descriptions herein rely solely on morphology and include detailed in situ pictures and scanning electron microscope images, in addition to range expansions for many species.

On the importance of spatial scales on beta diversity of coral assemblages: a study from Venezuelan coral reefs

Estimating variability across spatial scales has been a major issue in ecology because the description of patterns in space is extremely valuable to propose specific hypotheses to unveil key processes behind these patterns. This paper aims to estimate the variability of the coral assemblage structure at different spatial scales in order to determine which scales explain the largest variability on β-diversity. For this, a fully-nested design including a series of hierarchical-random factors encompassing three spatial scales: (1) regions, (2) localities and (3) reefs sites across the Venezuelan territory. The variability among spatial scales was tested with a permutation-based analysis of variance (Permanova) based on Bray-Curtis index. Dispersion in species presence/absence across scales (i.e., β-diversity) was tested with a PermDisp analysis based on Jaccard’s index. We found the highest variability in the coral assemblage structure between sites within localities (Pseudo-F = 5.34; p-value = 0.001, CV = 35.10%). We also found that longitude (Canonical corr = 0.867, p = 0.001) is a better predictor of the coral assemblage structure in Venezuela, than latitude (Canonical corr = 0.552, p = 0.021). Largest changes in β-diversity of corals occurred within sites (F = 2.764, df1= 35, df2 = 107, p = 0.045) and within localities (F = 4.438, df1= 6, df2 = 29, p = 0.026). Our results suggest that processes operating at spatial scales of hundreds of meters and hundreds of kilometers might both be critical to shape coral assemblage structure in Venezuela, whereas smaller scales (i.e., hundreds of meters) showed to be highly- important for the species turnover component of β-diversity. This result highlights the importance of creating scale-adapted management actions in Venezuela and likely across the Caribbean region.