GROWTH OF AN AMPHIPOD AND A BIVALVE IN UNCONTAMINATED SEDIMENTS - IMPLICATIONS FOR CHRONIC TOXICITY ASSESSMENTS

This study assessed the sensitivity of the amphipod Chaetocorophium cf . lucasi, an inhabitant of New Zealand estuarine muddy sediments, and of the bivalve Macomona liliana, commonly found in New Zealand sandfla ts, to sediment particle-size distribution, total organic carbon, tota l organic nitrogen and water content, Growth and survival were evaluat ed after different test exposure times using laboratory-prepared natur al sediment mixtures of sand and mud, The results suggest that amphipo d survival was affected by the type of sand more than by the concentra tion of sand in the sediment samples, In samples with high survival ra tes, amphipod growth was impaired in sediments with higher sand propor tions after a 10-day exposure, hut after longer periods (28 or 30 days ) there were no significant differences among treatments which had les s than or equal to 76% sand, Bivalve survival and growth were not sign ificantly affected by different natural sediment characteristics. Test duration for chronic toxicity tests with the bivalve M. liliana and t ate amphipod C. cf. lucasi should be at least 28 days for the detectio n of significant growth relative to the initial size.