Response of a marine shallow-water sediment system to an increased load of inorganic nutrients

Abstract

Investigated the effect of an increased load of inorganic nitrogen and phosphorus on the lower trophic levels of the food web of a shallow-water sandy sediment. The sediment system responded within 2-3 wk to the nutrient enrichment. Meiofauna biomass increased, resulting in higher relative importance of oligochaetes and harpacticoid copepods. Primary productivity increased faster than meiofaunal grazing, resulting in an increase of microalgal biomass by a factor of four. Diatoms and filamentous cyanobacteria were favoured by increased nutrient levels. The stimulated photosynthetic activity had a negative feedback on the producing sediment layer, which was lifted off by oxygen bubbles entrapped in the mucus-rich top most layer. Stimulated growth of the filamentous green alga Enteromorpha clathrata resulted in a biomass of c2 g C m-2 after 4 wk, which was more than twice the biomass of microautotrophs living in the sediment. Bacterial productivity responded only weakly to the nutrient additions and the grazing pressure on bacteria was high during the experiment. Meiofauna removed on average c4% of the microalgal biomass and 12% of the bacterial biomass per day in treatments with increased nutrient levels, and about 10% of autotrophs and 7% of bacteria in treatments with ambient nutrient levels. -Authors