Mollusc-shell debris derived from aquaculture can promote macrofaunal communities with a high bioturbation capacity

Abstract

Marine aquaculture releases mollusc shell debris which can accumulate on the seabed. Due to its low degradability, mollusc shell debris becomes integrated into the sediment, modifying both its structure and associated biogeochemical processes. These changes are expected to influence the biological assemblages within the sediment, which play a key role in the biogeochemical processes due to bioturbation. We performed an in-situ experiment to test the effects of mollusc shell-hash on the bioturbation capacity of the macrofaunal assemblages within the sediments affected by marine aquaculture. The aquaculture facilities chosen were a fish farm in an oligotrophic area of the Mediterranean over a sandy sediment, and a mussel farm in the Atlantic located in an estuary over silty sediment. Mollusc shell-hash promoted macrofaunal assemblages with a high bioturbation potential, regardless of the influence of aquaculture. Nevertheless, in the sediment from the mussel-farm, the shell-hash did not have a marked effect on the macrofaunal assemblages. The effect of shell-hash on promoting macrofaunal communities with a high bioturbation potential capacity is therefore dependent on the existing environmental conditions in the area, including the natural organic matter input and grain size of the sediment. Shell-hash could be used a strategy to improve the ecosystem function of sediments as a circular economy-oriented management practice.