What are mesophotic coral ecosystems? We define mesophotic coral ecosystems (MCEs) as light-dependent coral communities (and associated communities of algal, sponge and fish species) that occur in the deepest half of the photic zone (starting at 30-40 m and extending to over 150 m) in tropical and subtropical regions. Previously, this depth range has also been referred to as the twilight zone. The upper boundary (30-40 m) corresponds to the lower limit of standard scientific and recreational diving, while the deeper limit (> 150m) corresponds to the maximum depth at which there is enough light to sustain photosynthesis in zooxanthellate corals. MCEs are distinct from “true” deep water azooxanthellate coral ecosystems that occur at greater depths and are not light-dependent.


Why are mesophotic coral ecosystems important? Although these ecosystems harbor many of the species found in their shallower water counterparts, they can also be colonized by a disproportionately high number of depth-endemic species of fishes and invertebrates, and corals. Mesophotic coral ecosystems that serve as refugia for shallow and mid-depth species may warrant special resource management attention and protection to help maintain local and regional biodiversity. Protection may also offer a hedge against extinction to endemic species, which are more vulnerable to disturbance due to their limited geographic ranges. Thus, a better understanding of these environments offers potential findings of major interest for resource management.


Why are we focusing on them now? Advances in technical diving methods and instrumentation, such as mixed gas diving, rebreathers, Autonomous Underwater Vehicles (AUV) and Remotely Operated Vehicles (ROV), are increasingly providing easier access to study coral ecosystems in the 30-100 m depth realm. In addition, MCEs are coming under increasing threats from deeper fishing practices, pollution, habitat destruction, and climate change so it is important that we shift our focus to this depth realm and bring together researchers, managers, and policy makers to determine research priorities and the significance of these ecosystems. The MCE Website allows for collaboration of scientists, resource managers, and other interested parties that are, or have been, involved in the research, management, and conservation of MCEs. This cooperation is in the form of a web portal that permits individuals to submit (subject to verification) their own information as it pertains to their involvement in MCE research, management, and conservation.