Deep zooxanthellate coral reefs, also known as mesophotic reefs, present in insular shelf and slopes below 30 m depth, can cover large areas of the Puerto Rico—US Virgin Island insular platform. In 2002–2004, deep zooxanthellate coral reef surveys in Puerto Rico and the US Virgin Islands using the Seabed autonomous underwater vehicle (AUV) (Singh et al. 2004), showed large areas of healthy coral reefs with average living coral cover of 43% at depths of 30–47 m (Armstrong et al. 2006). The AUV digital imagery revealed well-developed coral reefs dominated by Montastraea franksi. Other coral species present included Montastraea cavernosa, Porites astreoides, Siderastreasiderea, Colpophyllia natans, Leptoseris cucullata and others of the genera Agaricia, Mycetophyllia, and Scolymia. Macroalgal coverage, mainly by Lobophora variegata, was also abundant at these depths as well as turf and coralline algae. Geodia neptuni, Xestospongia muta and several species of the genera Aplysina and Agelas were the most abundant sponges. The Seabed AUV provided the high resolution imaging capabilities necessary for large-scale quantitative assessments of these largely undescribed, ecological important habitats (Fig. 1).
Autonomous Underwater Vehicle (AUV)