Recent changes of macrophytes dominances and distributions related to different typology of human-induced stress in a meso-eutrophic lagoon (Orbetello, Italy)

This study evaluates recent distribution changes of three phanerogam (Ruppia cirrhosa, Cymodocea nodosa, Nanozostera noltii) and seven macroalgae taxa (Acetabularia acetabulum, Chaetomorpha linum, Cladophora vagabunda, Cladophora battersii, Gracilariopsis longissima, Spyridia filamentosa., Ulva laetevirens, Valonia aegagrophyla) in a meso-eutrophic Mediterranean coastal lagoon (Orbetello, Italy). The aim of this study was to relate, on a statistical basis, distribution and dominance changes to different factors: low-range trophic differences between lagoon areas (basin), temporal changes (year), levels of surfactants (pollution). In July 2003, 2009, and 2011 the percentage of coverage of each considered species was estimated in 38 sites equally distributed inside Western and Eastern basins. Collected data were analysed using SURFER v8.0 and Primer E package v6.0 software to produce respectively geostatistical distribution maps and associated probabilities. Surfer maps evidenced changes in macroalgae distribution during the studied period and statistical analyses supported observed differences related to factors years, basin, and pollution. Major effects are due to changes recorded for only changes of Nanozostera, Cladophora and Spyridia taxa concerning both distributions and abundances. Observed changes could have been due to management activities performed during 2003-2009. The removal of direct nitrate inputs produced specie-specific shifts characterized by a rarefaction of C. linum, Cladophora sp., and Spyridia sp. and an increase of G. longissima and V. aegagrophyla.