Marine diversity shift linked to interactions among grazers, nutrients andpropagule banks

Diverse coastal seaweed communities dominated by perennial fucoids become r eplaced by species-poor turfs of annual algae throughout the Baltic Sea. A large-scale field survey and factorial field experiments indicated that gra zers maintain the fucoid community through selective consumption of annual algae. Interactive effects between grazers and dormant propagules of annual algae, stored in a 'marine seed bank', determine the response of this syst em to anthropogenic nutrient loading. Nutrients override grazer control and accelerate the loss of algal diversity in the presence but not in the abse nce of a propagule bank. This implies a novel role of propagule banks for c ommunity regulation and ecosystem response to marine eutrophication.