Recovery of known-age Hyalella azteca (amphipoda) from sediment toxicity tests

Abstract 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 acceptability criterion of 80% survival for sediment tests. Another important aspect to consider when conducting sediment tests with H. azteca is defining mortality. A second study was conducted to evaluate the decomposition rate of dead amphipods in sediment. Regardless of sediment type, ≥ 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 recovered 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 during the sieving process). However, immobile amphipods removed from the sediment surface before sieving are known to be dead.