First record of the invasive swimming crab Charybdis hellerii (A. Milne Edwards, 1867) (Crustacea, Portunidae) off Martinique, French Lesser Antilles

Charybdis hellerii (A. Milne Edwards, 1867), a crab native to the Indo-West Pacific, was introduced in the western Atlantic in the late 1980s, likely through transport of larvae in ballast water of ships. It has since been reported from North Carolina, southeastern coast of United States, to southern Brazil. This report from Martinique is the first from the Lesser Antilles. Specimens were collected during scuba-diving surveys conducted during March/April 2016 to study the population size, distribution, and habitat-use of this invader. Two hundred and thirteen transects, each 60 m, were searched, in 2–15 m depths, in five coves of the southwestern peninsula of the island. We observed 150 individuals, of which 135 were collected. Most (89 %) specimens were mature with a male:female sex ratio of 2.4:1. Carapace widths ranged between 17.3 and 58.1 mm, with males significantly larger than females. Most crabs (93%) were found in dense seagrass beds of Halophila stipulacea, although a few (7%) were found on bare substrate with rocks and artificial mooring blocks. C. hellerii was absent from sand, coral with rocks and sponges, and mixed beds of algae and seagrass, possibly due to the presence of predators. The maximum observed density in the dense seagrass beds was 0.37 crab m. Predatory behavior of C. hellerii on other crabs was observed, suggesting this alien crab could alter existing community structure and functioning.