Mixed-habitat assimilation of organic waste in coastal environments - It's all about synergy!

Fish farms are increasingly situated in strong current sites above or near to mixed-bottom habitats that include organisms not normally considered in the context of organic enrichment. This study takes a holistic view of the benthic enrichment process by combining different survey techniques on complimentary spatial scales: conventional macrofaunal cores, larger-scale visual quantification of epibiota and environmental-DNA metabarcoding of microbial communities. A large tube forming polychaete (Arenicola marina), normally found intertidally and living too deep for conventional sampling, was observed occupying an opportunistic niche in areas of high deposition and in very close association with Capitellid worm complexes. The surface-dwelling brittlestar, Ophiocomina nigra, was abundant at distances of 250-1000 m from Farm-B, suggesting a positive response to enrichment, but was displaced where sedimentation exceed 5 g m(2) d(-1). A corresponding gradient was evident within the sediment microbial communities, supporting established theories about ecosystem engineering and multispecies synergies for organic waste assimilation. Many of the bacteria present in the near-farm sediments were linked to the farmed fish and fish health issues suggesting one or two-way inoculation pressures. These functionally different benthic organisms are intrinsically linked and the resulting synergy has the potential to assimilate significant quantities of anthropogenically produced organic waste contributing to environmental sustainability. (C) 2019 The Authors. Published by Elsevier B.V.