Marine confined areas as hot-spots of biodiversity for plankton: the case of Mar Piccolo of Taranto (Southern Italy, Ionian Sea, Mediterranean)

Resting stage production by planktonic organisms represents an adaptation to seasonal fluctuations of the environment on an annual scale and to its variations on a pluriannual scale. In the muddy bottoms of confined marine areas, high densities of plankton resting stages represent an insurance against unforeseen events. In fact, their accumulation in sediments leads to a storage of biodiversity which is expressed at the onset of favourable conditions. The Mar Piccolo of Taranto is a coastal semienclosed environment made by two sub-basins with different features. It represents the inner part of a marine system made by four areas aligned along a progressive confinement gradient. In Mar Piccolo many anthropogenic impacts persist, going from the presence of large mussel farms to chemical pollution and sewage discharges. This basin is being studied since more than 15 years about the presence and distribution of resting stages and their ecological role in plankton dynamics. Its sediments host a well structured resting stage community, reaching densities of millions of cysts m-2 of bottom and with a richness of morphotypes (more than 120, in representance of dinoflagellates, ciliates, rotifers and copepods) comparable to that of the water column.