Long-term changes in sublittoral macroalgal assemblages related to water quality improvement

Abstract

Abstract Sampling of sublittoral macroalgal assemblages was carried out in 1982 and 1999 along the coast of Catalonia (Northwestern Mediterranean, Spain) in order to study long-term changes in species composition. Ordination analysis revealed significant differences in species composition and abundance between the two study periods. The number of stations with indicators of eutrophication, such as species of Chaetomorpha , Cladophora , and Ulva , decreased from 1982 to 1999. This decrease was not balanced by an increase in species typical of pristine environments, such as large perennial brown algae (in particular, Cystoseira mediterranea ), but rather by an increase of stress-resistant species such as Corallina elongata . The observed shifts seem to be driven by the decrease in nutrient loadings in the water column, resulting from the progressive implementation of sewage treatment management in the study region since the mid-1970s.