Reproduction, growth and size of a burrowing intertidal clam exposed to varying environmental conditions in estuaries

Abstract

Bivalves in estuaries are exposed to many environmental variables but little is known about how such variables, including reduced salinity, affect reproduction and growth in burrowing clams. These were measured in the New Zealand little-neck clams, Austrovenus stutchburyi, from one urban and three rural estuaries with different contaminant inputs. Two shellfish sites were selected within each estuary reflecting high- and low-salinity exposure. Reproductive activity was seasonal and similar amongst the estuarine systems. The gravimetric condition index (CI) of the clams decreased significantly on exposure to low-salinity regimes. The gonad index increased significantly with CI and per cent glycogen in the foot tissue. At most sites, shell length increased significantly with the age of the clam, and maximum shell length and growth was reduced in clams exposed to the low-salinity regime. Reproductive indices of the clams did not correlate with sediment characteristics or sediment trace metal pollution index. It was concluded that salinity was the main factor affecting shellfish condition and that seasonal CI measurements could be a good indicator of growth and reproductive success. This knowledge is useful for the future management of this and other similar shellfish species.