CAVERNICULTURAL SWIMMING CRAB
Atoportunus dolichopus Takeda, 2003 (Crustacea, Decapoda, Portunidae) first reported in the western Indian Ocean during technical dives in the mesophotic zone.
The rare cave crab Atoportunus dolichopus Takeda, 2003, described on Kume-Jima Island, Ryukyu Archipelago, is recorded for the first time since its description. Two specimens were observed in a sea cave off Mayotte, in the western Indian Ocean, during technical dives in the mesophotic zone. The crabs were seen in total darkness at a depth of 75m, 120m from the cave entrance. No specimens were collected, but the morphological features identified in the close-up photographs agree with those of A. Dolichopus. This rare species is illustrated by comments on its remarkable geographic distribution and ecology.
The mesophotic marine zone, located at a depth of about 50 to 150 m in the tropics, is still poorly understood because it lies beyond the usual depths for recreational dives. Exploring these depths requires technical dives with re-breathing and trimix gas; techniques which are still only mastered by a few divers. The first two authors of this note are experienced technical divers. In 2018, they launched a collaborative research program to study the mesophotic zone around Mayotte (Barathieu, 2019). This program brings together several experts in marine flora and fauna around Mayotte and adds to another mesophotic research program underway around Mayotte (MesoMay, funded by DEAL Mayotte).