Seasonal and geographical differences in cleaner fish activity in the Mediterranean Sea

Abstract.

Investigations into symbioses may be important in order to analyse the grade of stability in ecosystems. Host–cleaner relationships were investigated in two localities of the Mediterranean Sea: Giglio (Tuscany, Italy) and Banyuls-sur-Mer (France). The cleaner wrasse, Symphodus melanocercus, was the main cleaner. Supplementary cleaners, such as the young of several wrasses, Symphodus mediterraneus, Symphodus ocellatus, Symphodus tinca, Coris julis and Ctenolabrus rupestris, are able to help out in times when there is a shortage of cleaners. Differences between the localities were obvious by a greater fish (host) density in Banyuls, which is probably due to eutrophication and might improve and increase cleaner activities. Regarding two seasons, spring and late summer, the fishes presented a lower degree of activity in Giglio, but a higher one in Banyuls – in late summer compared with spring. The main hosts were Chromis chromis, Symphodus tinca and Coris julis; additionally Diplodus sargus in Banyuls and Apogon imberbis in Giglio. Chromis chromis may be a key host species because of its distribution in large groups in the whole Mediterranean; Coris julis is of similar abundance. Symphodus melanocercus additionally came into contact with Symphodus tinca in order to partake of the food of the peacock wrasse. During cleaning activities, Diplodus sargus and other sparids present hesitant behaviour, where the cleaner probably picks more than parasites (skin, scales?) from the body surface. Apogon imberbis (which prefers dark habitats such as caves) totally rejects the main cleaner but was cleaned exclusively by Coris julis which, unlike Symphodus melanocercus, is regularly present near cave entrances. The investigations may present models of the evolutionary processes on specialised partnerships in ecosystems.