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Research Document - 2013/123

A Review of the Pathways-of-Effects Associated with the Removal and Release of Organic Material from Shellfish Aquaculture

By J. Chamberlain and F. H. Page


This document reviews the scientific knowledge related to the stressor category “Release and removal of nutrients, non-cultured organisms and other organic material” in relation to the Site and Stock Management of shellfish farming, as identified in the Aquaculture Pathways of Effects developed by DFO’s Aquaculture Management Directorate.  The issues discussed here relate to the nature, scale and scope of these influences and an understanding of the potential for predicting and modeling these processes, placed within a Pathways-of-Effects context.  A simplified conceptual diagram of the potential connectivity between shellfish aquaculture pressures and the state of coastal ecosystems (structure and function) is provided.  Shellfish aquaculture represents a net addition of habitat to an ecosystem and requires minimal additions to the environment.  Their food is extracted from the environment and their wastes return some nutrients and minerals back to the ecosystem.  Concerns have been raised about the possible effects of extensive shellfish culture operations on coastal marine ecosystem and the related risks to the ecological functioning and sustainability of these regions.  Such as, alterations to nutrient pathways by three basic mechanisms:  biodeposition, accumulation and remineralization of organic matter to benthic habitat; the removal of seston in a bay to support the growth of cultured shellfish can alter the water column habitat bio-diversity, particle size, and trophic structure; and the translocation of organic matter remineralization from pelagic to benthic food webs.  Key areas of stressor-effects uncertainty include impacts to higher trophic levels, farfield consequences of net reduction in production due to shellfish harvest (i.e., nutrient removal).

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