Effects of temephos (Abate (R) 4E) on fiddler crabs (Uca pugnax and Uca minax) on a delaware salt marsh

The nontarget effects of temephos (as Abate(R) 4E, 44.6% active ingredient) on fiddler crabs were examined on the salt marsh at Bombay Hook National W ildlife Refuge, near Dover, DE. Six 170 x 170-m plots were established; 3 w ere sprayed on 4 occasions at a rate of 1.5 fl oz/acre (0.054 kg active ing redient/ha) and 3 were controls. On each plot, marsh fiddler crab (Uca pugn ax) populations were monitored by repeatedly counting the number of burrow holes in 2 counting areas marked out along tidal guts. One half of each cou nting area was covered with bird netting to evaluate sublethal toxic effect s, which, if present, could result in increased susceptibility to bird pred ation. A statistically significant linear association was established betwe en the number of holes and the number of crabs. No significant differences were found in the numbers of holes (or crabs) in the sprayed vs, control pl ots and in the covered vs. uncovered sections. However, survival of juvenil e crabs in in situ bioassays was significantly reduced (16% lower) by the s praying. Median acetylcholinesterase activity in claw muscle of red-jointed fiddler crabs (Uca minax) collected 2 days after an operational spray with Abate 4E was significantly reduced (28% lower) compared to unsprayed crabs . In view of the toxicity to juvenile crabs and the cholinesterase inhibiti on, we recommend continued monitoring and research for nontarget impacts of Abate 4E on fiddler crabs to establish whether the reported level of choli nesterase inhibition results in acute or chronic toxicity.