Crustaceans and biodiversity crisis

Abstract

Talitrid amphipod crustaceans were recorded at about 240 sites around ireland using both published records and recent seashore surveys. Five species were present, the beachfleas Orchestia gammarellus and O. mediterranea, and sandhoppers Talitrus saltator, Talorchestia deshayesii, and Talorchostia brito. This is the first record of the last mentioned species in Ireland and it was present at only two sites. In general, species occurred on all coasts indicating that local rather than regional factors influenced their occurrence. Analysis of the co-occurrence of species, field observations on microhabitats, and contrasting occurrence of species in sandy beach and wider sampling surveys, indicated that T. saltator and T. deshayesii prefer coarser and finer sand, respectively, whereas O. gammarelus prefers gravel and stony substrata. The absence of O. mediterranea from 89 beaches surveyed indicates it is not found on sandy beaches. The two sites with T. brito had a large median sand grain size supporting observations elsewhere in Europe that the species inhabits more wave exposed beaches. The findings show the species have similar habitats in Ireland as elsewhere in Europe. Talitrids can be used to define two distinct biotopes, supralittoral sand with burrowing Talorchestia and Talitrus species, and supralittoral gravel with O. gammarellus. Further field studies may demonstrate a mid to upper shore sand biotope characterised by T. brito, and supralittoral drift weed on rock or salt-marsh biotope characterised by O. mediterranea. The microhabitats of the species are further defined based on the results of this study and a review of the literature. A working model of the spatial distribution of the species in relation to sea level and substrata is proposed.