Crustaceans (Decapoda, Stomatopoda) in the coral mesophotic zone of Mayotte (SW Indian Ocean)
Naturae: version accepted in March 2021, in press for March 2022 Draft accepted March 2021, in press for March 2022
Technical dives (TEK) in rebreather and special gas mixtures were carried out around the island of Mayotte on the outer reef slopes at depths between 50-120 m, and more particularly around 70-80 m, from 2017 to 2020. The objective of these dives was to carry out a first faunistic inventory of the mesophotic zone, difficult to access and still poorly known. This work presents the results obtained for the group of decapod and stomatopod crustaceans with a total of 44 species photographed in high definition, of which 30 determined with confidence, 7 with doubt and 7 identified provisionally, may be new for taxonomic nomenclature. Carid shrimps (16 species), anomurans (15 species) and crabs (7 species) are the three best represented taxa. Stomatopods, pinhole shrimps, langoustines and lobsters each have 2 species. These observations make it possible to add 32 new species to the Mahorese fauna, including 4 new reports for the Indian Ocean. The species are presented in an illustrated list with a selection of photographs. The list is documented with an indication of the works or guides consulted, comments on the determinations and the update of the geographical and bathymetric distributions. For 15 species traditionally observed on shallow water (<50 m), the maximum depth is increased between 3 and 45 m. More than half of the species are free forms (26 species). The others live in association with corals or hydras (12 species), echinoderms (3 species), fish (2 species) and sponges (1 species). Some species have a cavernicolous tendency, observed in caves or under overhangs. From the inventory data of decapod crustaceans from the French tropical overseas territories, 211 species are identified as potentially present in the mesophotic zone of Mayotte. The present inventory of 44 species is therefore quite modest, but the photographs taken in situ make it possible to highlight certain associations or ways of life which were not suspected with conventional means of study. In the future, observations could be improved by giving more importance to the shells, sometimes occupied by hermit crabs not determined because they were photographed from too far away, and / or by carrying out night dives, when the crustaceans are more active. The continuation of this research program foresees the collection of some specimens, in particular for the species recognized as probably new for the taxonomic nomenclature.