Evidence is accumulating that the seawater warming is changing the pool of organisms that could establish themselves in new areas, allowing the warm water species to expand beyond their present distributions, with unpredictable consequences for native communities. The complexity of these issues necessitates a thorough understanding of the invasion process which is particularly difficult to achieve in aquatic systems where cryptic species, recruitment variability, and poor direct observation add a layer of complexity.

The present investigation faces this topic by using a multidisciplinary approach applied to some tropical fish species which migrated into the Mediterranean. New documented species were Indo-Pacific fishes which entered through the Suez Channel: Siganus luridus and Fistularia commersonii and a circumtropical species, Acanthocybium solandri, recorded just once in the Mediterranean. Such new records were reported and described according to scientific standards and a detailed update of their occurrences, fully geo-referenced, was provided. These information were organized to reconstruct the history of invasion.

Demographics and dynamic aspects of S. luridus were evaluated by using phylogeographic and demographic (coalescent) methods based on DNA sequences of the mitochondrial control region. Samples were collected in one locality in the Red Sea (Eilat) and three localities in the Mediterranean (Israel, Greece and Linosa, Italy). Data showed a lowering of the genetic diversity of the invading population (Mediterranean) compared to the parental one (Red Sea). Within the Mediterranean populations, there was no pattern of regional separation and mitochondrial diversity appeared to be preserved during the Linosa colonization, with no traces of founder events.

The reproductive condition of early settled S. luridus in the Island of Linosa was examined according to gonad morphology, fecundity, atresia and oocyte dynamics. Both males and females had reached final stages of gonad maturation. The rates of follicular atresia were moderate with high fecundity estimates. Results indicated that the early settled rabbitfishes were reproductively active at Linosa with a high invasive potential.

In order to determine whether these species werer segregated by diet and to estimate resource partitioning during the early phase of colonization, an integrated study based on gut-content analysis and stable isotope signatures was used. A certain resource partitioning between invasive and native species was resolved on the basis of trophic indexes, multivariate analyses and isotopic signatures.

Finally, information on the composition and structure of local fish communities were collected by means of Underwater Visual Census which provided a robust dataset to be used for future monitoring and for designing management responses.

Taken as a whole, these results were important to describe the spread of warm water fishes across the central Mediterranean area and represent a step forward in our understanding of the causative processes that contribute to the success of these invaders.

Contacts: eazzurr@tin.it