Coral-associated microbiome and zooxanthellae of the scleractinian coral Agaricia lamarcki at a mesophotic coral reef in southwest Puerto Rico

Shallow water coral reef ecosystems have been the subject of extensive scientific research over a century, but only recently have researchers focused in coral communities at depths below 20 m deep. These communities, called Mesophotic Coral Ecosystems, are mainly formed by scleractinian coral colonies, sponges, crustose and macro algae and octoroals at depths ranging from 30 to 150 m. The distribution of these deep water ecosystems is determined mainly by light attenuation and decrease in temperature with depth, but other factors, such as local geomorphology, also play a role. As in shallow water coral reefs, scleractinian coral adaptation to mesophotic depths have been suggested to be facilitated by depth-specialst algal endosymbionts in the Family Symbiodiniaceae, but morphological plasticity, increased heterotrophy and utilization of light-harvesting pigments have also been linked to mechanisms of adaptation to low-light levels environmental conditions. MCEs off the coasts of Puerto Rico might provide the most comprehensive studies of MCEs in the Caribbean, with research off La Parguera, Puerto Rico have documented the most full-scale description of MCEs communities. As environmental conditios vary across the shallow-mesophotic depth gradient, we expect significant differences in zooxanthellae clade and microbiome communities associated with the Caribbean sheet coral Agaricia lamarcki at a mesophotic reef in southwest Puerto Rico. A better undersanding of the interaction of the coral holobiont and its associated algal endosymbionts and microbiome might be crucial for predicting coral resilience and adaptability in times of increasing degradation of shallow water coral reefs.