Spring and summer proliferation of floating macroalgae in a Mediterranean coastal lagoon (Tancada Lagoon, Ebro Delta, NE Spain)

During the last 10 years, a drastic change in the structure of the communit y of primary producers has been observed in Tancada Lagoon (Ebro Delta, NE Spain). This consisted of a decrease in the abundance of submerged rooted m acrophyte cover and a spring and summer increase in floating macroalgae. Tw o spatial patterns have been observed. In the west part of the lagoon, Chae tomorpha linum Kutzing, dominated during winter and decreased progressively in spring when Cladophora sp. reached its maximum development. In the east part of the lagoon, higher macroalgal diversity was observed, together wit h lower cover in winter and early spring. Cladophora sp., Gracilaria verruc osa Papenfuss and Chondria tenuissima Agardh, increased cover and biomass i n summer. Maximum photosynthetic production was observed in spring for G. v errucosa (10.9 mg O-2 g(-1) DW h(-1)) and C. tenuissima (19.0 mg O-2 g(-1) DW h(-1)) in contrast with Cladophora sp. (15.9 mg O-2 g(-1) DW h(-1)) and Chaetomorpha linum (7.2 mg O-2 g(-1) DW h(-1)) which reached maximum produc tion in summer. Increased conductivity from reduced freshwater inflow, and higher water temperatures during periods of lagoon isolation, mainly in sum mer, were the main physical factors associated with an increase in floating macroalgal biomass across the lagoon. Reduced nitrogen availability and te mperature-related changes in carbon availability during summer were related to a decrease in abundance of C. linum and increases in G. verrucosa and C ladophora sp. (C) 2000 Academic Press.