Multi-Trophic Impacts of an Introduced Crab Predator: Indirect Effects on Shorebirds in CaliforniaEPA Grant Number: U915821
Title: Multi-Trophic Impacts of an Introduced Crab Predator: Indirect Effects on Shorebirds in California
Investigators: Estelle, Veronica B.
Institution: Colorado State University
EPA Project Officer: Packard, Benjamin H
Project Period: September 1, 2000 through September 1, 2003
Project Amount: $85,646
RFA: STAR Graduate Fellowships (2000) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Ecological Indicators/Assessment/Restoration , Fellowship - Ecology
The objective of this research project is to investigate the interactions among shorebirds, their invertebrate prey, and the introduced European green crab, Carcinus maenas. The overall hypothesis is that green crabs indirectly affect wintering, nonbreeding shorebirds through shared food resources. The hypothesis is that the mechanism for this effect is a decrease in the quality of shorebird foraging habitat due to prey depletion and diffuse interspecific competition with the green crab.
To evaluate the hypothesis, the approach will be to: (1) quantify experimentally the impacts of green crab predation and shorebird predation on shared food resources; and (2) compare pre- and post-invasion shorebird diets within Bodega Harbor and Bolinas Lagoon, California. First, a manipulative enclosure experiment will be conducted in the field with green crabs and with shorebirds. This experiment will be used to determine the effect of each predator on the benthic invertebrates they consume and to elucidate the potential for competition as a mechanism of interaction between green crabs and shorebirds. Crabs will be held in one-half of an enclosure throughout the experiment. Dunlin (Calidris alpina) will be allowed to forage in the entire pen (on the +crab side and on the -crab side of the pen) during the low tide. Small plexiglas plates will be placed within the enclosure, elevated just above the mudflat, to keep birds and crabs from feeding in random locations within the enclosure. Core samples taken in pairs (underneath and beside the plates) will be used to determine the abundance and identity of prey items consumed by birds and crabs. Bird foraging will thus be evaluated in the presence and absence of green crabs. Second, historic and current shorebird diet data will be compared to investigate whether shorebird prey items have changed since the invasion of the crab in 1993. Stomach pumping of shorebirds will be used to obtain the diet samples; this method is preferable to bird collection as it is non-lethal.
The data will show that the mechanism for green crabs indirectly affecting food resources of wintering, nonbreeding shorebirds is the result of a decrease in the quality of shorebird foraging habitat due to prey depletion and diffuse interspecific competition with the green crab. Ultimately, it is hoped that this research will inform managers and legislators about potential multi-trophic impacts in marine systems by non-native species.