Recent changes in macroalgae distribution patterns in the Orbetello lagoon (Italy)

Abstract

1 - This study related recent distribution changes in seven macroalgae taxa (Acetabularia acetabulum, Chaetomorpha linum, Cladophora sp., Gracilariopsis longissima, Spyridia sp., Ulva laetevirens, Valonia aegagrophyla) to spatial (basin) and temporal (time) trophic differences in a meso-eutrophic Mediterranean coastal lagoon (Orbetello, Italy).
2 - In July 2003 and July 2009, the coverage percentage (CP) of each considered taxon was measured in 38 stations equally distributed in the Western and Eastern lagoon basins. All data were analysed using SURFER v8.0 software along with ANOVA, ANOSIM and multivariate analyses to produce geostatistical spatial distribution maps and to estimate statistical probabilities for “basin” and “time” factors.
3 - Data from this study were integrated with data on phanerogams reported by Giovani et al. (2010) to evaluate changes occurring at a functional group level from 2003-2009 using the Ecological Evaluation Index (EEI).
4 - Observed macroalgae changes may have been due to lagoon management activities performed during the study period. The removal of direct nitrate inputs seems to have forced specie-specific shifts that were highly significant only in the Western basin.
5 - Statistically significant differences at the taxon level have been indicated for Spyridia sp. (basin and time) and Cladophora sp. (time) taxa. Other non-significant changes included a rarefaction of Chaetomorpha linumin the Western basin and Spyridia sp. in the Eastern basin, and an increase of Gracilariopsis longissima, C. linum and Valonia aegagrophyla in the Eastern basin.
6 - EEI application indicated a general improvement in water quality due to management measures applied in Western basin, whereas the Eastern basin evidences stability/slight degradation from 2003-2009