No abstract

Coral reef decline is an issue of concern around the globe. Remote and uninhabited coral areas are not exempt from facing changes in species composition and functionality due to global drivers. Quitasueño is a remote atoll within the Seaflower Biosphere Reserve, in the Southwestern Caribbean Sea. To evaluate the current status of the coral reefs in Quitasueño we sampled 120 stations through Rapid Ecological Assessment and evaluated four stations through Planar Point Intercept to compare the current percent cover of benthic groups with previous studies in the area. We found pronounced changes in coral and macroalgae covers in time, and great conspicuousness of multiple conditions of deterioration along Quitasueño, including diseases, coral predation, and aggression and invasion of coral colonies by macroalgae and sponges. The reef ecosystem seems to be facing a phase shift, in which the benthic cover previously dominated by hard corals is currently dominated by fleshy macroalgae. It is essential to evaluate the possible drivers of the extent of degradation of Quitasueño to understand the process of deterioration and mitigate the impacts.

BACKGROUNDOctocorals and antipatharians (black corals) are usually among the main biotic groups in tropical rocky reefs. With a high diversity (111 species), abundance, and endemism, octocoral communities are a dominant seascape feature in the rocky reefs of the Eastern Tropical Pacific (ETP), hosting a particular invertebrate fauna and rich fish communities (Cortés et al., 2017;Sánchez, 2017). In the Colombian Pacific, studies of octocorals in rocky substrates are scarce and are restricted to shallow waters (<30 m). Only 14 species have been found so far (Cortés et al., 2017), but there could be more than 22 species according to unpublished reports.Mesophotic environments are usually defined as those located between 30 and 150 m below the surface and have been considered as ecosystems with diverse biological communities and high levels of endemism (Sinniger et al., 2016). The habitats formed by octocorals are common in mesophotic environments around the globe, however, knowledge about biodiversity and ecology of these communities is nascent. To date, 87 genera of mesophotic octocorals are known globally, of which only eight have been reported for the ETP (Sánchez et al., 2019). The octocoral fauna colonizing mesophotic environments often differs from shallow water octocoral fauna, which seems to be especially true in the ETP. The only published comparison of shallow water (<30 m) and mesophotic (>30 m) octocoral communities in the ETP, has found 17 shallow and 18 mesophotic species in the coast of Oaxaca-Mexico, with just one species present over the entire depth range (0-70 m; Abeytia et al., 2013).In the ETP region, antipatharians have been reported off the coast of Panama, Mexico, Colombia, and Ecuador, in specific areas and especially in shallow waters (Opresko, 1976;Bo et al., 2011), although in some cases they reach the upper limit of the mesophotic zone (ca. >30 m). Only two black coral species have been reported in this region, Myriopathes panamensis (Verrill, 1869) and Antipathes galapagensis Deichmann, 1941. Myriopathes panamensis, which is the only known black coral species to date from the Colombian Pacific, has been reported up to 50 m deep in Galápagos, although in the continental waters of Ecuador it is more abundant between 15 and 30 m deep (Bo et al., 2011).There is a need for data on the poorly known communities of mesophotic octocoral and antipatharians in the ETP, especially to the south of this remote biogeographic region (Colombian Pacific). The dataset presented here is the result of the first exploration in the mesophotic environments (30-60 m deep) of the rocky reefs from the Colombian Pacific. The dataset includes taxonomic information for each collected specimen, collection data (site, depth, date), and the collection code.

To map ecological units in mesophotic coral ecosystems on the western side of San Andrés Island (Colombia) considering biotic components and geomorphic zonation among 30–140 m deep, 27 video transects were done using an ROV. In total, 14 h of video were recorded and 5742 still images were extracted from them, from which 753 met quality criteria for bottom coverage and organisms’ abundance estimations. These estimates were calculated from images through the Planar-Point Intercept method (PPI) using a 1 m × 0.5 m quadrant gridded 0.1 m × 0.1 m. CLUSTER, SIMPROF, and SIMPER analysis of benthic composition considering depth ranges in the group’s formation were done. The clusters formed were simplified and generalized using a color matrix to support the mapping process. Two geomorphological units were found, the deep reef terrace (30–60 m) and the reef slope (60–357 m), overlapping with five ecological units spanning 268 ha. The units Bioturbed sediments–Calcareous algae, Octocorals–Mixed corals, and Octocorals–Sponges sited on the deep reef terrace have been previously described in the shallow waters of the island, and the units Octocorals–Sponges–Antipatharians and Encrusting Sponges sited on the reef slope are described as new here. These findings contribute to the knowledge of Caribbean mesophotic coral ecosystems and are useful to update the Colombian coral reef atlas.

The habitat formed by the Callogorgia species, with their abundance and colony sizes, provides an important refuge for a variety of brittle stars which are recognized as the epibionts of octocorals in both shallow and deep environments. In such a relationship, ophiurans benefit directly from being elevated because they facilitate their feeding by suspension, while octocorals do not seem to benefit or be harmed. During three different expeditions developed in the Colombian Pacific from 2012 to 2013 and in the Caribbean Sea during 1998 and 2012 by the INVEMAR - Marine and Coastal Research institute, different samplings were carried out on soft bottoms through trawls with an epibenthic net. For the Pacific Ocean, 33 fragments of the octocoral Callogorgia cf. galapagensis Cairns, 2018 with 178 specimens of the ophiuroid Astrodia cf. excavata (Lütken and Mortensen, 1899) were found in two stations at depths 530 and 668 m. Considering the abundance of A. cf excavata, other biological characters such as size, presence of mature gonads, and evidence of arm regeneration were also detailed. In contrast, in the Caribbean Sea, Callogorgia gracilis (Milne Edwards and Haime, 1857) was found with ophiuroids belonging to the genera Asteroschema and Ophiomitra. The octocoral Callogorgia americana (Cairns and Bayer, 2002) was also found, but without associated brittle stars. These findings constituted the first specific association reported in the Eastern Tropical Pacific, and new relationships for the Caribbean Sea. This further reflected a possible specific association between the Callogorgia and Astrodia species that needed to be further explored. Thus, the Callogorgia species and the brittle star A. cf. excavata represented new records for the Colombian Pacific Ocean and the southern Caribbean Sea.