Effect of vertical planktonic distribution of competent larvae on spat location in a soft-bottom intertidal zone: A case study for the softshell clam (Mya arenaria) and the blue mussel (Mytilus edulis)

摘要

Larval behavior and hydrodynamics may affect the vertical distribution of planktonic larvae and, in turn, spat location in the intertidal zone. This study describes the vertical profile of competent larvae in the water column and the distribution of spat on soft-bottoms, and quantifies the relationship between both distributions for the softshell clam (Mya arenaria) and the blue mussel (Mytilus edulis). Sampling was carried out in 2007 and 2008 along the coast of New Brunswick (Canada) in two tidally contrasted regions: Bay of Fundy (high tidal amplitude) and Northumberland Strait (low tidal amplitude). The planktonic larvae were collected with a pump at three depths. Spats were collected directly from the top layer of sediments as well as with two types of collectors. Sampling in the Bay of Fundy site took the dayight cycle into account The distribution of planktonic larvae and spats in the intertidal zone was highly variable for both species. Overall, no general pattern in the larvae distribution was observed. The dayight cycle did not affect the distribution and abundance of planktonic larvae and spats. Only a few statistically significant relationships were observed between the abundance of spats in the intertidal zone and the abundance of planktonic larvae. Soft-bottom habitats are highly unstable and this characteristic may explain, in part, the absence of relationship between spat location and the vertical profile of planktonic larvae.