Characterizing the extent of the oceanic 60–150 m deep mesophotic zone in Tuamotu-Gambier Archipelago atolls using multibeam bathymetry and geomorphology data
摘要
The mesophotic zone between 60 and 150 m of water depth is of increasing interest to science and management considering its biological communities, the species physiology, and the biological and physical connections with the shallower domain at a variety of ecological and evolutionary time scales. For tropical coral reefs, it is believed that the extent of mesophotic coral ecosystems (MCEs) can be much larger than their shallow coral reef counterparts, prompting arguments on which areas conservation funds should be devoted to. In French Polynesia, using a compilation of multibeam bathymetric data collected on 17 Tuamotu-Gambier atolls, and an atoll geomorphology database for 69 atolls, we estimated that the oceanic 60–150 m deep mesophotic zone of 69 atolls spread across 1700 × 800 km of oceanic territory only covers 349 km2. This mesophotic zone is very steep. Average of slope minimums and maximums for the 17 atolls was 27 and 73 degrees, respectively. The 60–150 m surface area represents only 3% of the extent of the lagoons for the same 69 atolls. The consequences of these findings for conservation decisions are multiple and discussed, and future MCE work in Tuamotu-Gambier is envisioned.