Abstract

In this study, growth tests are conducted in microcosms of 5 opportunistic macroalgal species (Gracilaria gracilis, Sphaerococcus coronopifolius, Chaetomorpha linum, Valonia aegagropila, Gongolaria barbata) that produce blooms in the Orbetello Lagoon, a eutrophic non-tidal lagoon in the Mediterranean Sea. The objective was to improve knowledge about algal blooms in the lagoon environment that occur in specific areas and times for each species, and have time-varying dominances. For the purpose, 4 of these species were grown together, competing for substrate by varying salinity and nutrient concentration. The results showed remarkable growth ability of C. linum in all microcosms for any environmental condition tested. S. coronopifolius grew best in brackish waters and at high nitrate-nitrogen concentrations; G. gracilis grew well in brackish waters with high concentrations of both nitrate and ammonia nitrogen; G. barbata preferred waters with marine salinity and low nitrogen concentrations and N/P atonic ratio. These results are consistent with the distribution of macroalgal masses in the Orbetello lagoon, from which the test thalli were sourced. Less clear were the results for V. aegagropila, which had biomass declines in most of the tests, despite constituting important near-monoxenic blooms in the Orbetello lagoon. For this species, however, there was evidence of a preference for waters with marine salinity and high nitrogen and N/P atomic ratio values.