A few years ago, a NAPIRE student of mine, Jerry, investigated predation risk of crabs in and away from leaf litter. He found substantial predation in the assay, and, this year, Zane is picking up the idea again (more to come).
The crabs are fairly abundant in the streams, but their densities can vary greatly, and, overall, the density is lower in the larger reaches of Rio Java (greater discharge) and those crabs that we do find in the river have a larger carapace width—big crabs in the big river. Perhaps predation is driving this pattern! And look, here’s a pile of dead crabs, partially eaten, probably by a mammal adjacent to a small backwater pool within the river.
June, one of the NAPIRE students, measures and marks crabs (Allacanthos pitteiri) she’s caught with baited minnow traps. Her project has a lab focus too: she is investigating size and sex differences in coarse particulate organic matter (leaf) shredding behavior by presenting male and female crabs that vary in size with stream conditioned leaves and measuring how much they consume, or shred. This parallels a project another student performed in 2013, Joseph Jack, although Joseph varied leaf species and conditioning time.
Last year, Jerry studied predation risk in crabs and measured crab densities in stream pools. While he marked the crabs with nail polish as a mark-recapture method, the small labels June used have individual numbers (her mentor, Anne Brasher, brought them and has used them extensively with snails), which is a powerful tool.
An interesting observation: some of the crabs seemed to have rust-colored lesions on their carapace that look similar to lesions we often found on crayfish (Orconectes obscurus) caused by a chitin-eating bacteria, isolated (or at least studied) by Adam Leff’s lab at Kent State.
After some heavy rains this week, thousands of stranded amphipods were dried up in the Science Center, possibly emerging from a over flowing drain.