Historical changes in algal diversity in the Gulf of Naples

An attempt to measure historical changes in macroalgal diversity has been performed along the Gulf of Naples (South Italy), subject in the last century to intense anthropic pressures, ranging from dense urban settlements to industrial areas located on the coast, and from intense maritime traffic to land runoff. A check-list of the benthic seaweeds recorded in the Gulf of Naples since 1878 has been compiled. After nomenclature and taxonomic updating, a total of 565 species (including 381 Rhodophyta, 111 Ochrophyta and 73 Chlorophyta) have been inventoried. A comparison on algal records between the two periods 1860-1955 and 1956-2007 have been carried out. In the second period the percentage of new taxa and that have disappeared or have not been found were similar (22-24%). In the last 60 years a decreasing trend of cold affinity species in contrast to an increasing of cosmopolitan and sub-cosmopolitan species has been pointed out from the analysis of biogeographic elements. The result could testify the warming trend in the Mediterranean Basin and the increase of global trades, in particular shipping transports. In order to assess the changes in the macro algal diversity and to quantify the species loss, a research project is in progress to assess the actual occurrence of Cystoseira and Sargassum spp., canopyforming species particularly sensitive to anthropogenic pressure. Historical sites along the upper sub littoral zones of the Gulf were revisited firstly. Preliminary results confirm, even for the Gulf of Naples, a decrease in the diversity of the upper sub littoral Cystoseira species due to the loss of seven fucoids. This decrease is more evident in the inner parts of the Gulf, where the industrial and urban settlement pressures were the highest.