Orientation of Mediterranean fish larvae varies with location

Abstract

Fish larvae at settlement represent a determining stage for maintaining coastal fish populations. This early life stage is decisive for the dispersal, recruitment, and habitat colonisation of coastal fish species. This study aims at observing the orientation behaviour of eight Mediterranean fish taxa, in four families, at settlement stage in two experimental sites along the north-east Corsican coastline (north-west Mediterranean Sea), a Sandy and a Rocky coastal site with different environmental characteristics. The objective was to detect if there were differences in directionality (i.e. the ability of individuals to maintain a fixed bearing in their environment) and orientation (i.e. the consistency among the bearing of individuals at species level) between the two coastal sites for the tested species. We also tried to identify the environmental factors that may influence directionality and orientation. The results show strong directionality for most fish larvae, with proportions of directional individuals generally exceeding 80%, either at community or species level (4 ≤ n ≤ 46 per species). Only the white seabream, Diplodus sargus, showed significant orientation behaviour, towards a cardinal direction, towards the sun in both experimental sites, as well as towards the coast in the Sandy site and towards the open sea in the Rocky site. The other species did not show significant orientation. This study supports the theory that orientation behaviour is dependent both on species and the environment perceived by the fish larvae. This kind of work is important for developing predictive models of marine population settlement and presents key elements for protection and management of coastal areas.