Comparing Sampling Approaches to Determine the Effect of Oyster Restoration on Clam Communities

Due to habitat loss, pollution, and overfishing, native oyster populations have decreased on the U.S. west coast.   An ongoing restoration project (ORP) is exploring methods for restoring oysters (Ostrea lurida) in Newport Bay, CA by constructing beds using different depths (4 cm or 12 cm) of bagged or unbagged oyster shell.  The impact of oyster beds on clams has not been explicitly examined.  Because the different treatments have variable depths of added shell, sampling the clam community is problematic.  ORP surveyed for clams by sampling all oyster shell (0, 4, or 12 cm deep) plus underlying mud (10 cm deep), collecting different volumes of sample among treatments.  Sampling clams to 10 cm may underestimate clam species richness, because clam with long siphons burrow deeper.  We compared the ORP sampling technique to ours that sampled a fixed volume, 30 cm deep, across treatments.  We hypothesized that we would find no treatment effects on density or species richness but higher richness, compared to ORP findings.  We collected clams from each bed in 10 cm increments up to 30 cm deep (n=5/treatment) and found a depth effect on species richness and clam density; 95% of all clams were located in the top 10 cm of sampled regardless of treatment.  The two studies found comparable species richness, without treatment effects.  We also found no treatment effects for clam density, but ORP did, possibly due to sampling unequal volumes of material.  Understanding how oyster restoration influences the clam communities could inform future restoration decisions.