Coral-Algal Symbioses in Mesophotic Montastraea cavernosa in the Gulf of Mexico

Mesophotic reefs represent biodiverse ecosystems that may act as a refuge for
depth-generalist coral species threatened in shallow habitats. Despite the importance of
coral-algal symbioses, few studies focus on mesophotic zooxanthellae assemblages and
their influence on connectivity. This study compared zooxanthellae in Montastraea
cavernosa at shallow and mesophotic depths at Flower Garden Banks National Marine
Sanctuary and McGrail Bank. Mesophotic corals contained more zooxanthellae and more
chlorophyll a and c2 per unit area coral. Increased zooxanthellae within mesophotic
corals may represent an adaptive strategy to optimize light capture in low-light
environments. Genetic profiles for zooxanthellae assemblages from shallow and
mesophotic corals showed similar diversity across banks and between depths. The
dominant sequence making up assemblages was identified as Symbiodinium type C1.
Similar assemblage diversity suggests that zooxanthellae assemblages will not limit
connectivity potential between shallow and mesophotic corals at these reefs.