September 1, 2016.
With a carapace width ranging up to 35 mm for adult males and 29 mm for adult females, Hemigrapsis oregonensis is a native shore crab typically found in the rocky intertidal zone along the Northern Pacific coast. Although this habitat provides protection against desiccation as well as changes in temperature, it may also expose H. oregonensis to predators who prefer the same habitat. The goal of this research was to investigate both the predation on H. oregonensis and the abundance of various crabs of Tiscornia Marsh in San Francisco Bay. We hypothesize that the largest predation will occur in the mud with no vegetation habitat, followed by the mud with Spartina foliosa habitat, then the rock with no vegetation habitat and rock with Spartina foliosa habitat will have equal rates of predation. In regards to the abundance of crabs, we hypothesize that the rock with no vegetation and rock with Spartina foliosa habitats will have an equal abundance of crabs, followed by the mud with Spartina foliosa, and finally the mud with no vegetation having the least amount of crabs. At each of these four different habitat types, 20 tethers were set out to monitor predation rates over a 24 hour period. Then, 10 traps were used at each habitat to record the abundance of crabs every 24 hours spanning three days, for a total of 30 traps. Results supported the hypothesis that the largest amount of crabs would be found in the rocks with no vegetation, however, the results did not support the hypothesis that the largest predation rate would occur in the mud habitat. Instead, the most predation on H. oregonensis was found in the rock with Spartina foliosa habitat. Based on these results, more research needs to be conducted to determine if the distribution throughout the different habitats of H. oregonensis is due to the presence of Spartina Foliosa, predators, or another factor.
Romberg Tiburon Center for Environmental Studies (RTC)
This project has been made possible with support from Chevron (www.chevron.com) and the California State University STEM Teacher Researcher Program.