Spatial Distribution and Ecophysiological Characteristics of Macrophytes in a Mediterranean Coastal Lagoon

The distribution biomass and photosynthesis of three species of rooted macrophytes, Ruppia cirrhosa (Petagna) Grande, Potamogeton pectinatus L. and Zostera noltii Hornem and a floating macroalga Chaetomorpha linum Ku¨ tz, were studied in Buda lagoon (River Ebro delta, NE Spain) during spring (May), summer (July) and autumn (October) 1995. Buda lagoon was characterized by a marked gradient of conductivity due to freshwater discharges from rice fields from June to October and by seawater input due to the regression of the delta of the River Ebro during the last 10 years. A typical spatial distribution was observed: monospecific stands of P. pectinatus developed near freshwater inputs in the inner part of the lagoon and mixed stands of R. cirrhosa and P. pectinatus developed in transitional zones between freshwater and seawater influence. The part of the lagoon where the influence of seawater was highest was covered by dense mixed stands of Z. noltii, R. cirrhosa and C. linum. Maximum biomass and production of P. pectinatus were reached in July (biomass of 501 gDW m 2, and maximum photosynthetic rates, Pm, of 14 mgO2 g 1 DW h 1 ). Maximum biomass of R. cirrhosa and Z. noltii (456·5 and 250 gDW m 2 respectively) and photosynthetic rate of R. cirrhosa (23·9 mgO2 g 1DW h 1) occurred in May, whereas no significant differences in production were detected between May and July in Z. noltii. Maximum C. linum production was reached in October (5·4 mgO2 g 1DW h 1). In October P. pectinatus coverage and production decreased, which was related to high turbidity and density of benthivorous fish due to freshwater inflows. Implications of lower freshwater inflow and higher seawater intrusion in the spatial distribution of aquatic macrophytes in this coastal lagoon are discussed.