Atlantic fishes in the Mediterranean: using biological traits to assess the origin of newcomer fishes

Abstract

Two important facets of global environmental change are alteration of climatic regimes and the introduction of alien species. From a biogeographical perspective, these 2 processes lead to very similar results: a change in the distribution of species. Here, we considered Atlantic fish species that are recent newcomers in the Mediterranean Sea, using biological traits to assess their origin. For this purpose, we first re-evaluated all records of Atlantic fish species in the Mediterranean (n = 103) to exclude those not considered recent newcomers (n = 33). Based on faunistic data, we classified the true newcomers into 4 origin categories: alien, vagrant, range-expansion or cryptogenic. Then, we compared biological traits of species we characterised as aliens (n = 7), vagrants (n = 14) or range-expanders (n = 23). Finally, we re-assessed the origin of cryptogenic species (n = 26) using multivariate discriminant analysis, measuring the distance of individual species to the centroids of aliens, vagrants or range-expanders, allowing us to infer their probable ‘mode of origin’. The body size, depth range, temperature range, habitat and ability to undertake long-distance migration were the most important traits that could be related to alien, vagrant or range-expanding fishes. It was possible to assign 10 cryptogenic species a specific origin category with reasonable confidence, while the remaining cryptogenic species combined trait values of different origin categories. These results indicate that biological trait analysis can be coupled with faunistic data to help assess the most likely origin of a newcomer species, thus informing management decisions.