Habitat use of a multispecific seagrass meadow by green turtles Chelonia mydas at Mayotte Island

We investigated the habitat use in green turtles exploiting a 13-ha multispecific seagrass meadow at Mayotte Island, south-western Indian Ocean. A phyto-ecological survey shows the occurrence of eight seagrass species, dominated by Halodule uninervis and Syringodium isoetifolium, distributed according to four distinct seagrass communities along the depth gradient. Direct underwater censuses show that green turtles occurred all over the meadow. Yet when community relative surface area was taken into account green turtles preferentially frequented the most seaward, biomass-richer S. isoetifolium-dominated community, suggesting that green turtles compensate for their intrinsically nutrient-poor herbivorous diet. Additionally, smaller (< 80 cm standard curved carapace length, SCCL) individuals also preferentially occurred in the most shoreward H. univervis-dominated community where no larger (> 80 cm SCCL) individuals were sighted, suggesting habitat use is indicative of diet selection and may reflect size-specific food requirements and physiology.