Plankton biodiversity along the Salento Peninsula (South East Italy). An integrated water/sediment approach

The microplankton community was studied at 9 sites (29 sampling stations) along the Salento Peninsula (SE Italy). Integrated samplings from both the water column (to collect active stages), and sediments (to collect resting stages), were carried out. More than 400 taxa were recognised in total. As for phytoplankton, 64 taxa were new records from the area. In particular, 16 of them were found only as resting stages in the sediments. A harbour, a coastal lake, and a submerged cave were investigated to understand the role of confined environments in the accumulation of resting stages. The harbour and the lake were found to be biodiversity reservoirs, due to the abundance of resting stages in their sediments. Only few species were found both in the water column, as plankton, and in the sediments, as resting stages. Furthermore, the most abundant species in the water column were not equally dominant as resting stages in the sediments. This suggests that species other than those observed in the plankton during the present work (i.e., those found as dominant among resting stages in the sediments) dominated the plankton in the past. Futhermore they could dominate the future plankton, with multiannual cycles, starting from sediment reservoirs. The search for resting stages in the sediment, thus, is useful to discover temporarily rare species, because species persist in the sediments as resting stages for longer periods than those spent as active stages in the plankton.