MOLLUSCS FROM THE UPPER MESOPHOTIC ZONE IN A SCARCELY KNOWN REEF OF THE WESTERN EQUATORIAL ATLANTIC

Despite the increasing focus on biodiversity of mesophotic coral ecosystems (MCEs) on a global scale, some biological groups, such as molluscs, are still poorly investigated. The taxonomic diversity of the molluscan fauna of a scarcely known MCE of the Western Equatorial Atlantic, Northeastern Brazil, was surveyed. Samples were collected along the shallower strata of the upper mesophotic zone (between 33-36 m depth). Twenty-one taxa (nine species of gastropods, ten species of bivalves, and two taxa of chitons) were listed, two of which (Novastoa sp. and Thylaeodus sp.) are potential endemic species. A new northern limit of distribution of Persicula moscatellii was established and seven species had new bathymetric records for living specimens (Barbatia domingensis, Barbatia cancellaria, Lamychaena hians, Leiosolenus bisulcatus, Pinctada imbricata, Hipponix incurvus, and Persicula moscatellii). Hipponix costellatus are the most representative species with 49 individuals, followed by Lima caribaea with six individuals. The present work is the first contribution to the knowledge of the molluscan fauna associated with consolidated substrates from this little-known MCE. Keywords: mesophotic coral ecosystems, tropical reef, molluscan diversity, Brazilian Province, conventional SCUBA.

Millepora aff. exaesa (Cnidaria, Hydrozoa) Recorded in the Mesophotic Environment of Mount La Pérouse, Southwestern Indian Ocean—Expedition La Pérouse 2019

In recent years, mesophotic coral ecosystems have been a growing topic of interest. [...]

Zooplankton distribution in Mesophotic Corals at Bajo Frijol seamount, Colombian Caribbean

Mesophotic coral ecosystems shelter unique communities, but have not been studied enough due to the high cost for the available technologies. The zooplankton have become the primary food resource of the polyps at these environments, due to the low photosynthesis rate of its zooxanthellae, . Therefore, the purpose of this work was to study the zooplankton community associated to the MCEs in Bajo Frijol, in the Corales de Profundidad National Natural Park, and compare its composition with the zooplankton community from shallower parts of the water column. Three samples were taken, filtering 24 L of seawater (45 µm mesh size) at each station with a device designed to collect zooplankton right on top of the reef substrate. The taxonomic composition, density and relative abundance were obtained. A resemblance analysis was performed, complemented with a cluster, an MDS and a modified Kandoorp test. The analysis showed clear differences between the water column samples from those taken close to the reef. It also showed the separation of the community at the seamount into two large groups: north and center-south, both with exclusive species.

Plasticity of Porites astreoides Early Life History Stages Suggests Mesophotic Coral Ecosystems Act as Refugia in Bermuda

As the devastating impacts of global climate change and local anthropogenic stressors on shallow-water coral reefs are expected to rise, mesophotic coral ecosystems have increasingly been regarded as potential lifeboats for coral survival, providing a source of propagules to replenish shallower reefs. Yet, there is still limited knowledge of the capacity for coral larvae to adjust to light intensities that change with depth. This study elucidates the mechanisms underlying plasticity during early life stages of the coral Porites astreoides that enable survival across broad depth gradients. We examined physiological and morphological variations in larvae from shallow (8–10 m) and mesophotic (45 m) reefs in Bermuda, and evaluated differences in survival, settlement patterns and size among recruits depending on light conditions using a reciprocal ex situ transplantation experiment. Larvae released from mesophotic adults were found to have significantly lower respiration rates and were significantly larger than those derived from shallow adults, indicating higher content of energetic resources and suggesting a greater dispersal potential for mesophotic larvae compared to their shallow counterparts. Additionally, larvae released from mesophotic adults experienced higher settlement success and larger initial spat size compared to larvae from shallow adults, demonstrating a potential connection between parental origin, offspring quality, and recruitment success. Although both shallow and mesophotic larvae exhibited the capacity to survive and settle under reciprocal light conditions, all larvae had higher survival under mesophotic light conditions regardless of parental origin, suggesting that conditions experienced under low light may enable longer larval life, further extending the dispersal period. These results indicate that larvae from mesophotic Porites astreoides colonies are likely capable of reseeding shallow reefs in Bermuda, thereby supporting the Deep Reef Refugia Hypothesis.

Genetic Divergence and Polyphyly in the Octocoral Genus Swiftia [Cnidaria: Octocorallia], Including a Species Impacted by the DWH Oil Spill

Mesophotic coral ecosystems (MCEs) are recognized around the world as diverse and ecologically important habitats. In the northern Gulf of Mexico (GoMx), MCEs are rocky reefs with abundant black corals and octocorals, including the species Swiftia exserta. Surveys following the Deepwater Horizon (DWH) oil spill in 2010 revealed significant injury to these and other species, the restoration of which requires an in-depth understanding of the biology, ecology, and genetic diversity of each species. To support a larger population connectivity study of impacted octocorals in the GoMx, this study combined sequences of mtMutS and nuclear 28S rDNA to confirm the identity of Swiftia sea fans in the GoMx, compare these markers for different polyp colors in the GoMx and Atlantic, and examine the phylogeny of the genus. Two mtMutS haplotypes were identified, one seemingly endemic to the northern GoMx. Compared to other North Atlantic Swiftia, S. exserta, the type of the genus was found to be extremely divergent and distinct from the two other Swiftia at both loci, with strong evidence of polyphyly in the genus. This information refines our understanding of the geographical distribution of injured coral and highlights how little is known about MCEs. Substantial taxonomic revisions may be needed for several taxa injured by the DWH oil spill.

Unexplored Refugia with High Cover of Scleractinian Leptoseris spp. and Hydrocorals Stylaster flabelliformis at Lower Mesophotic Depths (75–100 m) on Lava Flows at Reunion Island (Southwestern Indian Ocean)

Despite increased attention over the last decade on Mesophotic Coral Ecosystems (MCEs) [...]

Mesophotic Coral Ecosystems of the Great Barrier Reef Are Understudied and Underexplored

Mesophotic coral ecosystems (MCEs) are characterized by the presence of photosynthetically active organisms such as corals and algae, and associated communities at depths ranging from 30 to 150 m in tropical and subtropical regions. Due to the increased awareness of the potential importance of these reefs as an integral part of coral reef ecosystems (i.e., deep reef refuge, specialized biodiversity, transition zone between shallow and deep-sea environments, and recreational and intrinsic values), interest from the scientific community has grown around the world over the last two decades. Several nations have already made management declarations and started to extend marine protected areas and fishery management to MCEs. The estimated area of Australian MCEs is likely equivalent to that of shallow reef ecosystems down to 30 m; however, Australian MCEs attract limited research effort compared to other major coral reef regions around the world. In this perspective, we briefly explore the reasons for this scarcity of research on mesophotic ecosystems of the Great Barrier Reef (GBR) of Australia (e.g., strict diving regulations, new researchers’ involvement, and logistics and cost). At present, research efforts on the mesophotic ecosystems of the GBR are in decline and if this trajectory is maintained, the global disparity in knowledge between MCEs near Australia and those from the other main coral reef regions worldwide will sharpen deeply. We call for action from the research community, grant agencies, and decision-makers toward a wider understanding of these important ecosystems in Australia.