Melissa A. Harbert; Institute for Wildlife Studies; PO Box 1104, Arcata, CA, 95518; (707) 822-4258;; Brian Hudgens
This study tested whether amphipods (Crangonyx sp.), traditionally thought to be detrivores, prey on Northern Red-legged Frog (Rana aurora) embryos at the Humboldt Bay National Wildlife Refuge in California (HBNWR). Following observations of embryo disappearance associated with amphipods, we performed experiments in which embryos were subjected to one of four treatments: enclosed chambers with all predators excluded, enclosed chambers with only amphipods present, chambers with fine mesh screen allowing access by all small predators including amphipods, and chambers open to all predators. Trials with the last 2 treatments were repeated at a nearby site with no amphipods (BL). We found that average predation rates of viable embryos were similar among open/screened chambers at HBNWR and open chambers at BL (21-25%), while the average predation rate in amphipod-only chambers was 15%. Predation rates were <= 1% for predator exclusion chambers at HBNWR and screened chambers at BL. We conclude that embryo predation by amphipods does occur and has the potential to be as important a mortality factor as predation by all other macroinvertebrate/vertebrate predators. However, the significance of this interaction is likely to be highly context-dependent and affected by factors such as amphipod density/food availability and the size/cohesiveness of eggmasses.
Poster Session