A model analysis on the effect of decreasing nutrient loads on the biomass of benthic suspension feeders in the Oosterschelde (SW Netherlands).

Abstract

SMOES, a dynamic box model for the Oosterschelde ecosystem (SWNetherlands), has been applied to assess the effect of anthropogenicnutrient load reductions on suspension feeder biomass. The model, originallydeveloped to study the ecological effects of the building of a storm-surgebarrier situated in the mouth of the Oosterschelde, was repeatedlycalibrated for the years 1988-1989 (after the completion of the barrier in1987). With ten acceptable, but qualitatively different calibrations of themodel, a series of nutrient load reduction scenarios (-25%,0%, 25%, 50%, 75% and 100%) have beenanalysed. It was expected that the system receiving fewer nutrients couldonly support lower suspension feeder biomass. In this study the carryingcapacity is expressed as the ratio between the benthic suspension feederbiomass sustained by the ecosystem in one of the nutrient scenarios and thebiomass in the undisturbed ecosystem. This decrease in carrying capacityvaries widely, from 5% to 50% of nutrient reduction. SMOES has not been designed to fully answer the question of carryingcapacity. It includes a rather detailed ecosystem structure, but it lacksboth a proper population dynamic model for benthic suspension feeders and adescription of food advection towards benthic suspension feeder habitats.Despite these shortcomings, the method presents a promising instrument incarrying capacity studies.