DISTRIBUTION PATTERNS OF TWO LABRID SPECIES IN THE WESTERN MEDITERRANEAN: IS WATER WARMING AFFECTING THEIR ECOLOGICAL INTERACTIONS?

Abstract

Climate warming should favor ‘warm water’ species over ‘cold water’ species at the same site. Regional warming in the Western Mediterranean has allowed the documented northward expansion of southern marine species. Conversely, very little is known on the response of cold loving species to temperature variations. We propose to work with two common coastal fishes: the rainbow wrasse Coris julis and the ornate wrasse Thalassoma pavo, with the general objective to exploring patterns of distribution and their potential to interact under warming conditions. Large scale quantitative observations revealed: (1) opposing trends in abundance along latitudinal (35o − 45oN) and depth gradients (0-36m), with T. pavo densities significantly higher in southern and shallow waters than those of C. julis; (2) differential distributions across shallow habitats, with C. julis occupying seagrass beds when the density of T. pavo was high; and (3) a marked depth segregation of the species only on steep coasts. These patterns are discussed with regard to the role of water warming. Significant ecological changes might occur in locations where the density of T. pavo is recently increasing.