Mesophotic Coral Ecosystems
Bonaire and Curaçao are oceanic islands surrounded by coral reefs on their leeward sides extending steeply down to mesophotic depths (30–150 m). Easy access from shore, as well as the geopolitical context of the two islands, has made the mesophotic coral ecosystems (MCEs) of Bonaire and Curaçao among the most well studied in the world. MCE research has been conducted in the region since the 1970s, and ongoing research employs state-of-the-art exploration technologies such as manned submersibles, autonomous underwater vehicles, and mixed-gas, rebreather technology. Mesophotic coral communities in Bonaire and Curaçao are typically dominated by agariciids, with Agaricia lamarcki and A. grahamae covering a substantial proportion of the substrate at upper mesophotic depths (30–60 m), while the lower mesophotic (>60 m) consists predominantly of A. grahamae and A. undata. Although much of the habitat is dominated by sediment with only patchy coral growth, in some locations coral assemblages can cover up to 100% of the seafloor down to depths of 70–85 m. Recent biodiversity studies, mostly focusing on fishes, sponges, and corals, documented only limited overlap between shallow and mesophotic reef communities, and that MCE biodiversity is strongly structured by depth. Since MCEs in Bonaire and Curaçao harbor highly specialized communities facing specific threats deriving from their proximity to urbanized land, these ecosystems warrant new management policies and conservation measures. These measures should protect the whole extent of these reefs, which rank among the healthiest in the Caribbean region.