Distribution and abundance of juvenile intertidal bivalves in the San Juan Islands, WA

Abstract

Adult distribution of intertidal bivalve communities is dependent on larval success and juvenile survival. Finding and predicting juvenile presence is crucial to understanding the mechanisms determining adult abundance. I sampled seven intertidal areas on San Juan Island, representing various wave exposures, sediment compositions, and beach slope to determine where juveniles are present and what factors might predict their presence. Juvenile clams were found at six of the seven sites sampled, in highest abundance at British Camp and Bell Point on the northeastern tip of the island, dominated by Nutricola spp. Juveniles of Mysella tumida, Saxidomus giganteus, Protothaca staminea, Macoma inquinata, and Macoma nasuta were also found. Clam assemblages seem to be site-specific, rather than being driven by tidal height or other individual environmental factors. Within sites, shell hash, mud and granules the best predictors of presence or absence of juveniles.