The effects of submerged aquatic vegetation as habitat on the survivorship of clams: Field surveys in St. Mary's River, Maryland and laboratory predation experiments (Callinectes sapidus, Mya arenaria)

Submerged aquatic vegetation is a complex habitat that may strongly affect the survivorship of associated animal species. Location with reference to SAV and seasonal changes have been suggested as important factors influencing species' survivorship. A field study examining natural abundances during spring and summer was conducted to examine the SAV effect on clam survivorship in St. Mary's River, a Chesapeake Bay tributary. Data revealed that SAV biomass affected clam abundances in summer, but not spring. Crab pots caught significantly greater numbers of Callinectes sapidus (blue crab) outside grass beds than inside SAV, contrary to published studies. Greater predation pressure on clams in lower SAV biomass may be causing differences in clam abundance. Experiments investigating C. sapidus predation on Mya arenaria (Soft-shell clam) in different SAV densities indicated that SAV presence significantly reduced predation. Habitat studies tracking behavior revealed crabs spent more time in vegetation but consumed more clams outside SAV.