Effects of benthic fauna on organic matter mineralization in fish-farm sediments: importance of size and abundance

Abstract

The effects of the polychaetes Nereis diversicolor and Capitella sp. I on organic matter mineralization in marine sediments collected under a fish farm were studied in vitro . The two species differ significantly in size, feeding, and burrowing activity. The presence of benthic fauna stimulated the total benthic metabolism (measured as O ₂ uptake, CO ₂ release, and ${\text{SO}}_4^{2-}$ reduction) substantially compared to the microbial metabolism in an azoic sediment. Nereis and Capitella stimulated mineralization over a two-month period by 135% and 87%, respectively. The stimulation was primarily microbial (54%) in Capitella sediments. Sulphate reduction remained similar to azoic sediments, indicating that in particular the aerobic activity was enhanced. Microbial stimulation was less (23%) for Nereis sediments, while sulphate reduction was reduced (42%), indicating enhanced oxidation compared to azoic sediments. The fauna-mediated oxidation of the sediment probably causes increased removal of nitrogen through increased nitrification and denitrification and enhanced binding of phosphorus, thereby reducing nutrient fluxes to the water column.