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Ecological interactions between two non-native clams, Venerupis philippinarum and Nuttallia obscurata, in Baynes Sound, British Columbia

University of British Columbia

Manila (Venerupis philippinarum) and varnish (Nuttallia obscurata) clams represent the most abundant clam species in the Strait of Georgia (SoG), British Columbia (BC), yet they never co-occur at relatively high densities. Transplant experiments were initiated in June 2007 in Baynes Sound, BC to examine the relative importance of ecological (relative abundance of the other species, exclusion of predators) and environmental (intertidal height, substrate composition, season) parameters on clam growth, survival and the relative distribution and abundance of these species. Varnish clam shell growth rates were highest in the high (0.30±0.019 mm wk⁻¹) and low (0.27±0.025 mm wk⁻¹) intertidal zones compared to the mid (0.19±0.019 mm wk⁻¹). Manila clam shell growth rates were higher in the low intertidal zone (0.57e±0.013 mm wk⁻¹) when compared to the high (0.46±0.013 mm wk⁻¹). When the relative density of each species was manipulated, no differences were observed in the growth rates of either species, revealing little or no apparent intra- or inter-specific competition for food or space. Neither species was preferentially preyed upon over the duration of the study (~27 wk). These results suggest intertidal height had a stronger influence than ecological interactions on the relative distribution and abundance of Manila and varnish clams in the SoG. However, the specific environmental variable(s) responsible for the observed differences in clam growth rates between intertidal heights were not tested. Other field studies have shown that varnish clams grow well in the high intertidal zone. This study found that varnish clams grew well in the low intertidal zone in addition to the high intertidal zone. This study suggests that the varnish clam invasion in the SoG was successful because this species was able to occupy the high intertidal zone, an area that appears environmentally stressful for the Manila clam. It is possible that the Manila clam is outcompeting the varnish clam at the juvenile stage. This could explain why varnish clams are not naturally observed in the low intertidal zone in the SoG.

Text

2011-01-27

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/30884

Oceanography

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/