Ecosystem functioning in a disturbance-recovery context: Contribution of macrofauna to primary production and nutrient release on intertidal sandflats

Although many ecologists have described relationships between biodiversity and ecosystem functioning, changes in functioning after disturbance and during recovery are not well documented. Diversity–functioning theory predicts a decline in functioning with decreased diversity (e.g., following disturbance) and a gradual increase in functioning coincident with biotic recovery. We tested this theory empirically by measuring primary production and nutrient release (indices of sandflat functioning) at three sites at the beginning, middle and end of a year-long recovery period. Although microphytobenthos stock (sediment chlorophyll a content) recovered quickly, rates of gross photosynthetic oxygen production were reduced in disturbed plots, relative to controls, in 7 of 9 comparisons. Plots with high macrofaunal richness had enhanced ammonium efflux, and greater efflux of ammonium likely increased rates of primary production. The site with the highest bioturbation potential, which was dominated by large bivalves, exhibited the largest decline in functioning immediately after disturbance. This site also had the most persistent treatment–control differences during recovery, probably because the large bivalves remained at low abundance in treated plots throughout the year-long experiment.