A paramount challenge in coral reef ecology is to estimate the abundance and composition of the communities residing in such complex ecosystems. Traditional 2D projected surface cover estimates neglect the 3D structure of reefs and reef organisms, overlook communities residing in cryptic reef habitats (e.g., overhangs, cavities), and thus may fail to represent biomass estimates needed to assess trophic ecology and reef function. Here, we surveyed the 3D surface cover, biovolume, and biomass (i.e., ash-free dry weight) of all major benthic taxa on 12 coral reef stations on the island of Curaçao (Southern Caribbean) using structure-from-motion photogrammetry, coral point counts, in situ measurements, and elemental analysis. We then compared our 3D benthic community estimates to corresponding estimates of traditional 2D projected surface cover to explore the differences in benthic community composition using different metrics. Overall, 2D cover was dominated (52 ± 2%, mean ± SE) by non-calcifying phototrophs (macroalgae, turf algae, benthic cyanobacterial mats), but their contribution to total reef biomass was minor (3.2 ± 0.6%). In contrast, coral cover (32 ± 2%) more closely resembled coral biomass (27 ± 6%). The relative contribution of erect organisms, such as gorgonians and massive sponges, to 2D cover was twofold and 11-fold lower, respectively, than their contribution to reef biomass. Cryptic surface area (3.3 ± 0.2 m2 m−2planar reef) comprised half of the total reef substrate, rendering two thirds of coralline algae and almost all encrusting sponges (99.8%) undetected in traditional assessments. Yet, encrusting sponges dominated reef biomass (35 ± 18%). Based on our quantification of exposed and cryptic reef communities using different metrics, we suggest adjustments to current monitoring approaches and highlight ramifications for evaluating the ecological contributions of different taxa to overall reef function. To this end, our metric conversions can complement other benthic assessments to generate non-invasive estimates of the biovolume, biomass, and elemental composition (i.e., standing stocks of organic carbon and nitrogen) of Caribbean coral reef communities.

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Black corals (Antipatharia) are among the most common and diverse taxa in mesophotic and aphotic rocky habitats. Studies of their ecology and biology are limited mostly because of the technical challenges involved in deep-water work. Here, we describe taxonomic traits, habitat, and nutrition of 2 species from the upper mesophotic zone of the northern Red Sea, Gulf of Aqaba, Israel. Our study describes a broader distribution of the branched Antipathes griggi, which to date has been primarily found in the Hawaiian Archipelago. Additionally, a new record is reported regarding the coiled Stichopathes spp. discovered at the upper mesophotic zone. The branched A. griggi were more abundant than the coiled Stichopathes spp. in all explored sites, and differences in light and water flow conditions significantly affected their distribution. Both species lacked symbiotic algae (Symbiodiniaceae). Analysis of the amino acid compound-specific stable isotope signature (AA-CSIA) revealed that both antipatharian species show a high trophic position relative to known mixotrophic and heterotrophic corals. Although both species inhabit the same area and are planktivorous, their carbon signature suggests they have different carbon sources. Our findings imply that antipatharians have a vital role in the trophic dynamics of mesophotic coral ecosystems, a unique habitat whose ecology remains largely unexplored.

Information on the status of the pillar coral Dendrogyra cylindrus across its global distribution range is needed to plan and implement effective conservation interventions at both the national and regional level. Knowledge on the species distribution and abundance on the southernmost edge of its range was limited to qualitative data gathered in the 1980s. In 2014, we started using local ecological knowledge and extensive surveys to assess the status of the pillar coral in Archipelago Los Roques National Park, Venezuela; also evaluating the species representativeness within the MPA according to the level of protection established by the park’s zoning. Between 2014 and 2016, we recorded over 1,000 colonies-the highest abundance reported to date for the species- within 14 different habitat types. Disease, bleaching and partial mortality prevalence were below 4%. Size frequency distribution was uni-modal for the MPA and dominated by medium size colonies (40cm -70cm height) suggesting potential for intrinsic population growth. However, the structure of size classes varied among reefs (Pseudo-F=2.70, p=0.03), indicating asynchronous dynamics mostly driven by reef-scale processes. Overall, our results indicate that Los Roques could be a stronghold for the species. But, to maintain the conservation value for coral reefs and the pillar coral, the MPA’s zoning designation needs to be urgently revised and the extension of its high-protection zones expanded to increase habitat redundancy as well as the singular habitats composed by thickets of Acropora cervicornis and mounds of Madracis sp. This work confirms the species as extant in one of the four localities within its national range in Venezuela. However, further research on genetic diversity and connectivity among reefs within the MPA is needed to estimate effective population size and assess viability.