GROWTH AND GRAZING CONTROL OF ABUNDANCE OF THE MARINE MACROALGA, ULVA-LACTUCA L IN A EUTROPHIC DANISH ESTUARY

The marine macroalga, Ulva lactuca L. in its free-floating form was abundant throughout the year in the eutrophic inner parts of a Danish estuary and scarce in the outer parts. The growth rate of Ulva was not significantly different between the inner and outer parts. Grazing by invertebrates was negligible in the inner part and allowed biomass accumulation, whereas grazing pressure in the outer part matched the growth rate during summer and exceeded it by more than two-fold during autumn. Reduced grazing control is apparently an important and often overlooked factor for biomass accumulation of free-floating macroalgae under eutrophic conditions.