The conservation status of 845 zooxanthellate reef-building coral species was assessed by using International Union for Conservation of Nature Red List Criteria. Of the 704 species that could be assigned conservation status, 32.8% are in categories with elevated risk of extinction. Declines in abundance are associated with bleaching and diseases driven by elevated sea surface temperatures, with extinction risk further exacerbated by local-scale anthropogenic disturbances. The proportion of corals threatened with extinction has increased dramatically in recent decades and exceeds that of most terrestrial groups. The Caribbean has the largest proportion of corals in high extinction risk categories, whereas the Coral Triangle (western Pacific) has the highest proportion of species in all categories of elevated extinction risk. Our results emphasize the widespread plight of coral reefs and the urgent need to enact conservation measures.
Coral cover at lower mesophotic depths (particular- ly >75 m) by zooxanthellate scleractinians is usually very scarce, largely due to the extremely low irradiance levels at these depths. An exception are the Leptoseris communities observed near the Hawaiian islands (Central Pacific) that form dense fields, supporting a broad range of associated organ- isms. Here, we describe a similar high-cover coral community at lower mesophotic depths, but in the Caribbean. The com- munity was observed on the leeward side of Curaçao (Southern Caribbean) using a manned submersible (Curasub), and was predominantly composed of plating Agaricia corals and an assemblage of reef fishes. Some of the fish species were known from similar depths at other lo- calities, whereas others obtained new depth records. Future surveys are required to establish the extent of similar high- coral communities around Curaçao, and more broadly in the western Atlantic.
The stoplight parrotfish, Sparisoma viride, is one of the dominant herbivores on the reefs of Bonaire. The effects of macroalgae herbivory have been well documented but the potential of S. viride to act as a shuttle for zooxanthellae remains unknown. Although coral is not considered a food item of S. viride they occasionally bite living tissue off of colonies of the scleractinians Montastrea annularis and Colpophyllia natans. Coral tissues contain large amounts of symbiotic dinoflagellates of the genus Symbiodinium, commonly referred to as zooxanthellae. Symbiodinium may be the key primary producer of the reef ecosystem and are found almost exclusively in symbiotic relationships with cnidarians. It is the aim of this article to examine the potential role of S. viride as a vector for transport of Symbiodinium throughout the reef environment as a result of parrotfish white spot biting. The purpose of coral biting is not known but territoriality is suspected in focused biting. Depending on the effect of parrotfish ingestion on the Symbiodinium cells, parrotfish white spot biting behavior could result in transport of Symbiodinium throughout the reef environment, increasing the genetic diversity of zooxanthellae populations.
A coral is made up of key associations between endosymbiotic zooxanthellae, protists, bacteria, archaea, viruses, and fungi. These microbe-coral interactions can be very beneficial, some associations providing key functions in reproduction, nutrition, and antimicrobial protection. However, as a coral becomes thermally stressed, the ability to regulate microbe growth in its surface mucus layer becomes diminished and opportunistic pathogens are able to colonize. Corals may be able to adapt for the changing reef ecosystem by selecting for more beneficial associations: one of the facets of the coral probiotic hypothesis. The invasive azooxanthellate coral Tubastraea coccinea is able to colonize very shallow, hot and turbid areas that are not favorable for settlement by other species. However, not much is known about T. coccinea other than its invasive nature in the Caribbean. The purpose of this investigation was to determine if the surface microbial communities of T. coccinea are one of the factors aiding its survival. Culturing on Thiosulfate Citrate Bile Salt plates was used to visualize and compare the overall culturable Vibrio spp. communities present in T. coccinea and other widespread shallow corals. At each site, the numbers of Vibrio spp. were not significantly different between the three species, but numbers of a gram-positive bacteria, Enterococcus spp., were found to be significantly higher in T. coccinea.
An integrated suite of imaging techniques has been applied to determine the three-dimensional (3D) morphology and cellular structure of polyp tissues comprising the Caribbean reef building corals Montastraeaannularis and M. faveolata. These approaches include fluorescence microscopy (FM), serial block face imaging (SBFI), and two-photon confocal laser scanning microscopy (TPLSM). SBFI provides deep tissue imaging after physical sectioning; it details the tissue surface texture and 3D visualization to tissue depths of more than 2 mm. Complementary FM and TPLSM yield ultra-high resolution images of tissue cellular structure. Results have: (1) identified previously unreported lobate tissue morphologies on the outer wall of individual coral polyps and (2) created the first surface maps of the 3D distribution and tissue density of chromatophores and algae-like dinoflagellate zooxanthellae endosymbionts. Spectral absorption peaks of 500 nm and 675 nm, respectively, suggest that M. annularis and M. faveolata contain similar types of chlorophyll and chromatophores. However, M. annularis and M. faveolata exhibit significant differences in the tissue density and 3D distribution of these key cellular components. This study focusing on imaging methods indicates that SBFI is extremely useful for analysis of large mm-scale samples of decalcified coral tissues. Complimentary FM and TPLSM reveal subtle submillimeter scale changes in cellular distribution and density in nondecalcified coral tissue samples. The TPLSM technique affords: (1) minimally invasive sample preparation, (2) superior optical sectioning ability, and (3) minimal light absorption and scattering, while still permitting deep tissue imaging.