GRACILARIA DISTRIBUTION, PRODUCTION AND COMPOSITION IN THE LAGOON OF VENICE

Until the end of the 1980s, Gracilaria, in terms of biomass production , was the second macroalgal genus populating the lagoon of Venice. The dominant species, Gracilaria verrucosa (Huds.) Papenf., before the ma ssive harvesting for agar extraction began in the mid-1980s, accounted for a mean standing crop and an annual production of 36000 and 132000 t (wet wt), respectively. Nowadays, dense populations of this species are missing and both standing crop and production are markedly reduce d. On the basis of Gracilaria samplings conducted at three stations re presenting the main biogeochemical differences of the lagoon, it appea rs that this species, in the eutrophicated areas, has the capacity of accumulating nitrogen and phosphorus more efficiently than any other m acroalga, probably because of its higher organic content In contrast, the carbohydrate content was higher in the unpolluted areas because of the younger age of the sampled specimens. Considering the C:N:P atomi c ratios in thalli, the phosphorus availability can be suggested as a possible limiting factor for Gracilaria growth in oxic and unpolluted areas. No significant chlorinated hydrocarbon accumulation was found i n the samples from the different areas. In contrast, heavy metals, par ticularly Mn, Zn, Pb, Cu, Fe and Ni, were efficiently accumulated by t his species in the polluted areas, but only the Mn concentration was a ppreciably higher than in the other algal species.