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Increase of planktonic Tunicata (Appendicularia, Thaliacea) biodiversity in the Adriatic Sea: A possible relationship with hydroclimatic changes in the Mediterranean Sea

We investigated potential connections over the past two decades between mesoscale circulation regimes in the Ionian Sea and newly-observed planktonic tunicate species and concurrent rise in sea temperature in the Adriatic Sea. Analyses of plankton samples from 1993 to 2015 in the southern Adriatic revealed marked changes in the planktonic tunicate community. Eleven appendicularian and three thaliacean species were recorded for the first time in the Adriatic. We found that incoming of these species are in connection with circulation regimes in the Northern Ionian Gyre (NIG). The occurrence of Atlantic/Western Mediterranean species coincided with anti-cyclonic circulation in the NIG, owing to the advection of Modified Atlantic Water into the Adriatic, while the presence of Lessepsian species coincided with the cyclonic pattern, which governs the entry of Eastern Mediterranean waters. The impact has been that some newcomers now make a larger contribution to the zooplankton community in the southern Adriatic and, in certain cases, have replaced native species. The synergistic effects of these processes, together with warmer Mediterranean waters, raise concerns over dramatic changes in the marine biodiversity of the Adriatic.

Ionian Sea ; planctonic tunicate species ; sea temperature ; Adriatic Sea ; zooplankton community

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