A Scientific Review of the Potential Environmental Effects of Aquaculture in Aquatic Ecosystems - Volume 5

A Scientific Review of Bivalve Aquaculture : Interaction between Wild and Cultured Species

T. Landry
Gulf Fisheries Centre, Fisheries and Oceans Canada, 343 University Avenue, Moncton, New Brunswick, E1C 9B6, Canada

M. Skinner
University of New Brunswick, Fredericton, New Brunswick, E3B 5A3, Canada

A. LeBlanc
Gulf Fisheries Centre, Fisheries and Oceans Canada, 343 University Avenue, Moncton, New Brunswick, E1C 9B6, Canada

D. Bourque
Gulf Fisheries Centre, Fisheries and Oceans Canada, 343 University Avenue, Moncton, New Brunswick, E1C 9B6, Canada

C. McKindsey
Maurice Lamontagne Institute, Fisheries and Oceans Canada, 850 de la Mer Road, Mont-Joli, Quebec, G5H 3Z4, Canada

R. Tremblay
Université Du Québec à Rimouski, Rimouski, Quebec, G5L 3A1, Canada

P. Archambault
Maurice Lamontagne Institute, Fisheries and Oceans Canada, 850 de la Mer Road, Mont-Joli, Quebec, G5H 3Z4, Canada

L. Comeau
Gulf Fisheries Centre, Fisheries and Oceans Canada, 343 University Avenue, Moncton, New Brunswick, E1C 9B6, Canada

S. Courtenay
Gulf Fisheries Centre, Fisheries and Oceans Canada, 343 University Avenue, Moncton, New Brunswick, E1C 9B6, Canada

F. Hartog
Maurice Lamontagne Institute, Fisheries and Oceans Canada, 850 de la Mer Road, Mont-Joli, Quebec, G5H 3Z4, Canada

M. Ouellette
Gulf Fisheries Centre, Fisheries and Oceans Canada, 343 University Avenue, Moncton, New Brunswick, E1C 9B6, Canada

J.M Sevigny
Maurice Lamontagne Institute, Fisheries and Oceans Canada, 850 de la Mer Road, Mont-Joli, Quebec, G5H 3Z4, Canada

Executive Summary

This paper reviews the present state of knowledge on interactions between wild and cultured species within the context of bivalve mariculture in Canada. It also identifies critical knowledge gaps and recommends research to address these gaps. The literature reviewed includes national and international information covering bivalve aquaculture, bivalve restoration, coastal community and ecology. This review is focused on changes affecting the pelagic community, benthic communities, predator species, genetic structures, and the risk of introducing invasive species.

Pelagic community and bivalve culture interactions

Bivalve aquaculture has two main effects on the pelagic community. First, as grazers, bivalves reduce the phytoplankton biomass that may affect the productivity of other grazing species. Limited information is available on this potential effect of bivalve aquaculture, and to date this has only been demonstrated through the use of ecosystem models. The second main effect of bivalve aquaculture on the pelagic community is via the creation of additional habitat in the water column. This is supported mainly by studies on the effect of shellfish restoration, which clearly show that three-dimensional oyster reefs increase the biomass and possibly productivity of several pelagic species benefiting from food availability or predator avoidance. Although these extrapolations may be logical, direct evidence of these interactions is lacking. Research is recommended to address the:

• effect of bivalve aquaculture on phytoplankton production and the grazing community.
• effect of the epifaunal community associated with bivalve aquaculture on the nekton community.

Benthic community and bivalve aquaculture interactions

Macrobenthic communities affect rates, directions, and pathways of the exchange of energy and materials between the water column and the sediment, and are critical in regenerating nutrients via benthic-pelagic coupling mechanisms. Shifts in benthic community structure and functioning due to biodeposition, physical alterations, and the presence of fouling organisms have been noted in the proximity of bivalve aquaculture operations, however, the extent of these changes are variable. Preliminary data suggest that bivalve aquaculture may increase coastal productivity. Research recommendations are as follows:

• examinations of the influence of bivalve aquaculture on second order relationships such as growth or reproduction of ecologically and/or commercially important species are required;
• knowledge of interactions related to seagrass communities is incomplete; hypotheses addressing growth rates and distributions of seagrass at near-field and far-field scales need to be tested to provide information for resource managers to effectively protect these areas without unnecessarily hindering the development of this burgeoning industry;
• the spatial scale of resolution on which research questions are based needs to be expanded from the lease-scale to address hypotheses of estuary/bay-wide ecological changes to structure, function, and productivity of benthic communities; and
• the potential for cumulative effects (municipal wastewater processing, fish processing plants, agricultural inputs, pulp and paper effluents, etc.) in conjunction with bivalve aquaculture on benthic ecosystem change needs to be assessed.

Predator effects related to bivalve culture

Research conducted on the relation between predators and bivalve aquaculture is primarily focused on the effect of predators on cultured bivalves. These studies deal mainly with predator control and exclusion methods. These methods have only been investigated on a local scale; their effects from an ecosystem perspective have not yet been addressed. The effect of aquaculture activities on predator densities is not clearly defined; some studies suggest aggregation of predators while others do not. In studies with increased predator densities, it is unclear if this is due to the aggregation of existing populations or an increase of the population. Research gaps that need to be addressed are as follows:

• effect of predator management methods on targeted and non-targeted species.
• effect of bivalve aquaculture on the abundance and distribution of predators.

Exotic species related to bivalve aquaculture

Historically, the introduction and transfer of bivalves for aquaculture has been one of the most important vectors for the introduction of exotic species around the world. This includes the bivalves that have been intentionally introduced into an area for aquaculture purposes – the "target" species, the animals and plants (both macroalgae and phytoplankton) that grow associated with the introduced bivalves – "hitchhiking" species, and diseases. Introduced bivalves are engineering species and may thus have a large influence on many aspects of the ecology of the receiving area. These changes may further facilitate the introduction and growth of other exotic species. Both target and hitchhiking species may have a variety of cascading effects on the receiving ecosystem. However, research on the subject is extremely limited and many such effects are simply theoretical. Ideally, thorough risk assessments should be done before any introductions and transfers are authorized. Quarantine, disinfection, and other protocols may be used to limit risk. However, the efficacy of such treatments is not always great and other measures should be considered. A number of research needs were identified to better understand and minimize the potential role of bivalve aquaculture in increasing the rate of introduction, spread and effect of exotic species. These include the following:

• preliminary risk analyses, as outlined in the section on management issues, should be done to identify knowledge gaps with respect to exotic species in bivalve culture (the cultured bivalves themselves and hitchhiking species);
• directed research should be used to address these knowledge gaps prior to the introduction of bivalves into a system for aquaculture;
• obtain baseline information on the receiving environment (physical and biological) to make predictions with respect to exotics and to evaluate and understand their influence;
• predict the ability of exotics to establish and spread in the receiving environment; and
• predict the effects of exotic species on receiving ecosystems, including interactions with local species, habitat modifications, energy flow, etc.

More information is needed on the requirements and influence of hitchhiking species in the environment. This is particularly true for a number of currently problematic species (e.g., tunicates). Specifically,

• more information is needed with respect to the natural history of most exotic species;
• more information is needed with respect to the relative importance of natural (currents, dispersion rates, etc.) and anthropogenic (stock transfers, processing, hull fouling, etc.) spread of exotic species;
• remedial measures need be developed to mitigate effects and minimize spread; and
• research is needed to understand the links between the presence of exotic species and other stressors in the environment (e.g., eutrophication, climate change, fishing activities, contamination, etc.).