RECOVERY OF KNOWN-AGE HYALELLA-AZTECA (AMPHIPODA) FROM SEDIMENT TOXICITY TESTS

Recovery of 1-, 7-, 14-, or 21-d-old Hyalella azteca from sediment was evaluated. Recovery of 1- and 7-d-old amphipods was below an acceptab ility criterion of 80% survival for sediment tests. Another important aspect to consider when conducting sediment tests with H. azteca is de fining mortality. A second study was conducted to evaluate the decompo sition rate of dead amphipods in sediment. Regardless of sediment type , greater than or equal to 90% of the amphipods started to break apart within 12 h of death; specifically, the head separates from the body. Therefore, if an immobile amphipod with its head and body intact is r ecovered in sieved material, it was probably alive within 12 h of the end of the test (an amphipod may be alive before sieving but may die d uring the sieving process). However, immobile amphipods removed from t he sediment surface before sieving are known to be dead.