Community composition of the intertidal in relation to the shellfish aquaculture industry in coastal British Columbia, Canada
Introduction
A major industrial development to coastal ecosystems as a consequence of the ever increasing demand for a secure source of protein is finfish and shellfish aquaculture (Naylor et al., 2000). On the west coast of British Columbia (BC), Canada, industry and the federal and provincial governments are aggressively expanding shellfish aquaculture with Venerupis (Ruditapes) philippinarum (A. Adams and Reeve, 1850) one of the main products farmed. V. philippinarum is an invasive species which “hitch-hiked” on oyster seed brought over from Japan in the mid 1930s (Gillespie et al., 2012, Quayle and Bourne, 1972).
Currently there are 284 tenures for V. philippinarum culture in BC with the greatest intensity occurring within Baynes Sound (Gillespie et al., 2012). Dumbauld et al. (2009) have suggested that shellfish aquaculture can be viewed as a disturbance to the coastal environment in three ways; 1) changes in materials processing (e.g., nutrient flux), 2) addition of physical structures (e.g., anti-predator netting) and 3) pulse disturbances such as harvesting. Although not noted in their review, near-bottom marine aquaculture of V. philippinarum that includes seeding with juvenile clams at densities of 200 to 700/m2 could also be considered as a “pulse disturbance”.
All of the above listed disturbances have the potential to alter the existing intertidal environment and hence community. Sorokin et al. (1999), Bartoli et al. (2001), Beadman et al. (2004) and Bendell-Young et al. 2010 have all shown that netted farm sites accumulate more organic matter and silt as compared to sites not farmed. Intensive shellfish farming has also been reported to decrease benthic diversity and change the intertidal species composition to one dominated by bivalves and deposit feeding worms (Bendell-Young, 2006, Spencer et al., 1997). By contrast, McKindsey et al. (2007) note that application of anti-predator nets to the intertidal increases its structural complexity and in some cases may increase the abundance of intertidal organisms taking advantage of the new three dimensional habitat. For example, Powers et al. (2007) report that macroalgae growing on anti-predator netting enhanced nursery habitat for mobile invertebrates and juvenile fishes as compared to an unstructured sand flat.
Possibly contributing to the conflicting reports is that studies to date have been limited in geographical scope and have not taken into consideration the intensity of shellfish farming that can occur. Hence, the objective of this study was through a comparison of farm versus reference intertidal sites from three regions of coastal BC which experience different intensities of industrial shellfish farming activity, to assess the potential effects of applying anti-predator netting in combination with seeding on the intertidal macroflora, epibenthic (surface) and endobenthic (sub-surface) communities. Such information will add to a better understanding as to how the intertidal community responds to the practices of shellfish farming structure such that we can better manage these sensitive ecosystems. This study also represents the most comprehensive intertidal survey of the low to high tide regions of coastal BC.
Section snippets
Study area
Three distinct regions of coastal BC were chosen for the study; Barkley Sound, Baynes Sound and Desolation Sound (Fig. 1). The number of BC shellfish tenures licensed for the culture of V. philippinarum reported in 2012 for Baynes, Desolation and Barkley Sounds were 101, 32 and 21 respectively (Gillespie et al., 2012). Baynes Sound has been a site of industrial scale shellfish aquaculture since the 1940s and of the three regions has been the most intensively exploited for this purpose with over
Sediment particle size
For both survey years, PCA analysis indicated that the first principal component accounted for 80% of the variation among sites with this first PC being weighted most heavily by % gravel (Fig. 2) with sites A1 and A1.5 within Baynes Sound being most different from all other sites (Fig. 2).
Intertidal macroflora
With the net community included, farm sites were dominated by Ulva sp. (Enteromorpha sp., Hayden et al., 2003) as compared to reference sites (ANOVA p < 0.01, Fig. 3). Other important taxa present included; Z.
Discussion
Of the three regions surveyed, Baynes Sound which experiences the greatest intensity of shellfish aquaculture, was the most altered with the greatest numbers of the invasive species, Batillaria sp. and H. oregonensis. Barkley Sound, the region with the lowest industrial intensity, was characterized by M. trossulus and the absence of H. oregonensis. The mid-intensity region, Desolation Sound, was characterized by L. scutulata and T. persona. Further, within Baynes Sound, seeding appears to be
Acknowledgments
The field assistance of J. Whiteley M. Kirk, I. McKeachie, K. Henderson, D. Leung, N. Martens, V. Sadler, R. Davidson, B. Bartezen, R. Dickson and T. Lewis is gratefully appreciated. Funding for this study was through a National Science and Engineering Research Council (NSERC) Strategic Operating Grant (STPGP246079-01) awarded to LB as principle investigator.
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