EFFECT OF METAL AND METALLOID CONTAMINATED SEDIMENT ON THE SPATIAL-DISTRIBUTION OF ASIATIC CLAMS (CORBICULA-FLUMINEA)

The purpose of this study was to determine the effect of metal and metalloid contaminated sediment on the movement and spatial distribution of asiatic clam (Corbicula Fluminea) populations in the laboratory. One hundred clams were randomly placed in one meter diameter pools containing sediment collected from three sites of varying levels of metal contamination. The location of each clam was determined on days 0, 7, 14, 21 and 28. Ripley's L(t) function was used to measure the randomness or clustering of clams in experimental pools. There was no significant evidence of clustering of clam locations throughout the experiment. Further, sediment type had no significant effect on the distribution of clams in the pools, which suggests that clams were moving independently of one another. This information allowed us to estimate whether individual clams move sufficient distances to escape from patches of contaminated sediment of different sizes. Simulation results showed that after 150 weeks, clams can effectively escape from smaller contaminated patches of sediment (25-, 50-, and 100-cm radius), while less than 50% of clams could escape from a contaminated patch of 200-cm radius. These simulations suggest that an avoidance of contaminated sediment will not result in effective escape from moderately sized patches of contaminated sediment (>100-cm radius).