The Effect Of Constructed Oyster Beds On Clam Density And Richness

Clams are important to marine ecosystems as filter feeders that increase water clarity, rework sediments, and contribute to shell production - activities that can each significantly change benthic environments. We examined the effects of constructed oyster beds on density and richness of clams. On a mudflat in Newport Bay, CA we constructed replicate (n=5 per treatment)  2m X 2m oyster beds from dead oyster shell of 4 treatment types, including 2 bed thicknesses (4cm versus 12cm) and 2 consolidation types (bagged versus loose shell), plus 5 control plots. We hypothesized that constructed oyster beds, regardless of treatment type, would cause a decline in density and richness of clams relative to control plots because the shell beds would, for clams, prevent access to the mudflat surface. We sampled 25cm X 25cm X 10cm depth clam cores at 0 and 6 months and excavated 25cm X 25cm oyster bed samples at 0, 6 and 12 months. We assessed density and richness of clams per unit area by identifying live clams to species, and examined the effects of treatment, time, and their interactions. After 6 months, density of non-native Venerupis philippinarum increased significantly on all plots regardless of treatment, while densities of other species remained unchanged. However, after 12 months, clam species richness within excavated beds was highest on 12cm thick beds, regardless of consolidation type. Surprisingly, oyster beds may function to not only increase epifaunal diversity, but also clam density and richness, perhaps by offering protection from predators to the clam population.