The ecological role of bivalve shellfish aquaculture in the estuarine environment: A review with application to oyster and clam culture in West Coast (USA) estuaries

Authors: Dumbauld, Brett; RUESINK, JENNIFER - UNIVERSITY OF WASHINGTON; RUMRILL, STEVEN - OREGON DEP. STATE LANDS

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/23/2009
Publication Date: 5/31/2009
Citation: Dumbauld, B.R., Ruesink, J.L., Rumrill, S.S. 2009. The ecological role of bivalve shellfish aquaculture in the estuarine environment: A review with application to oyster and clam culture in West Coast (USA) estuaries. Aquaculture. 290: 196-223.

Interpretive Summary: Aquaculture is viewed as a way to meet the growing demand for seafood around the world. The future of bivalve shellfish aquaculture in the U. S. hinges on sustainable practices on the part of industry and a more consistent regulatory framework. Bivalve shellfish aquaculture is a recent practice relative to its history in other countries, beginning in the late 1800s along the U.S. West Coast where it is now well established with farm raised product utilizing land-based hatcheries and grow-out directly in numerous estuaries. We characterize bivalve shellfish aquaculture as an ecological disturbance or modification which can change estuarine systems in three ways: 1) changes in material processes - bivalves process food and produce wastes; 2) addition of physical structure – aquaculture introduces the cultured organisms and in some cases a physical anchoring structure; and 3) pulse disturbances like harvest and bed maintenance disturb sediments, remove other organisms in addition to the cultured organisms themselves and change the habitat. We review the literature on these modifications and the ecological role that bivalve shellfish play in estuaries worldwide with a focus on oyster and clam aquaculture in U.S. West Coast estuaries. Water column and sediment nutrient concentrations are generally relatively high and greatly influenced by the proximity to deeper nearshore ocean waters where upwelling controls production during summer months along the West coast so that bivalves are less likely to influence material processes except at local bed scales in coastal estuarine systems. Bivalve culture clearly modifies estuarine habitat at local community and at landscape scales and effects are most often evaluated against existing structured habitat in the form of submerged aquatic vegetation. Individual activities act as pulse disturbances and the most common form of vegetation affected is the native eelgrass (Zostera marina), which can recover to pre-disturbance levels relatively rapidly (< 2 years). The extent of the disturbance depends on the aquaculture being practiced. Therefore the distribution of eelgrass reflects a balance of competition for space and the state of recovery from both natural and aquaculture disturbances and is at dynamic equilibrium on most aquaculture beds. Structure provided by aquaculture appears functionally similar to eelgrass for small benthic fauna that inhabit the sediment as well as more mobile fauna on the surface. Use of aquaculture as habitat larger more mobile invertebrates and fish depends on their mobility and varies with life history stage and the species being evaluated. Further research on habitat use by important invertebrates and fish at larger estuarine landscape scales may prove useful in designing and implementing best management practices for aquaculture. Though local and short term effects from aquaculture are clearly evident in US west coast estuaries, bivalve aquaculture does not remove area from the estuary or degrade water quality like other human influences, and thus has not been implicated in large shifts to different states (like eutrophic systems with hypoxic low oxygen waters) or reduced capacity of the ecological system to adapt to future changes.

Technical Abstract: Aquaculture is viewed as a potential mechanism to meet the growing demand for seafood around the world. The future of bivalve shellfish aquaculture in the U.S. hinges on sustainable practices on the part of industry and a more consistent regulatory regime. Bivalve shellfish aquaculture is a recent practice relative to its history in other countries, beginning in the late 1800s along the U.S. West Coast where it is now well established with farm raised product utilizing land-based hatcheries and grow-out directly in numerous estuaries. Bivalve shellfish aquaculture can be viewed as a disturbance which modifies the estuarine system in three ways: 1) changes in material processes - bivalves process food and produce wastes; 2) addition of physical structure – aquaculture introduces the cultured organisms and in some cases a physical anchoring structure; and 3) pulse disturbances like harvest and bed maintenance disturb sediments, remove species in addition to the cultured organisms themselves, and change resource or habitat availability. This review suggests that water column and sediment nutrient concentrations are generally relatively high and greatly influenced by the proximity to deeper nearshore ocean waters where upwelling controls production during summer months in U.S. west coast estuaries. Although the situation may be different for small systems such as coastal lagoons or portions of large fjords like Puget Sound, bivalves are less likely to influence material processes except at local bed scales in these systems than has been shown for other culture areas. Bivalve culture clearly modifies estuarine habitat at local community and at landscape scales and effects are most often evaluated against existing structured habitat in the form of submerged aquatic vegetation. Individual activities act as pulse disturbances and eelgrass (Zostera marina) can recover to pre-disturbance levels relatively rapidly (< 2 years). Extent of disturbance depends on the practice and the distribution of eelgrass reflects a balance of space competition, pulse disturbance and recovery, and is therefore at dynamic equilibrium on aquaculture beds. Structure provided by aquaculture appears functionally similar to eelgrass for small benthic infauna and mobile epibenthic fauna while use of aquaculture as habitat depends on mobility and varies with life history stage and taxon being evaluated for larger more mobile invertebrates and fish. Scale seems a very important management consideration and further research at estuarine landscape scales especially for habitat use by important invertebrates and fish may prove useful in designing and implementing best management practices. Though local and short term effects from aquaculture are clearly evident in US west coast estuaries, bivalve aquaculture does not remove area from the estuary or degrade water quality like other anthropogenic influences, and thus has not been implicated in shifts to alternate states or reduced adaptive capacity of the larger ecological system.