Temporal Variability in the Vertical and Mesoscale Spatial Distribution of Crab Megalopae (Crustacea: Decapoda) in the Northwestern Mediterranean

The vertical and mesoscale horizontal patterns of the distribution of crab megalopae were studied from samples taken during two consecutive cruises in the spring of 1992 off the Catalan coast (NW Mediterranean) and are analysed in relation to environmental data. The spring hydrography in the study area, which included the waters along the shelf and slope over a submarine canyon, is characterized by high hydrographic variability. The most abundant species was an undescribed portunid (coded as SP02), followed by Liocarcinus depurator and Carcinus aestuarii. Some species were mainly present in neuston samples during night-time hours, such as Atelecyclus sp., Goneplax rhomboides, Ebalia sp. or the anomuransPisidia longicornis and Porcellana platycheles; other species were present in the neuston throughout the day and night, with a slight tendency to increase their abundance during the night, such as L. depurator and C. aestuarii. The distribution of megalopae showed a high temporal variability and reflected the hydrographic structure at the surface. The variability in the geographical position of the shelf-slope hydrographic front clearly affected the distribution of the larvae. Most megalopae were associated with the inshore waters of lower salinity than open seawaters.