Effects of habitat structure on the size distribution and abundance of Hemigrapsus oregonensis in False Bay, Washington

Abstract

Climate change is transforming the biodiversity of intertidal communities with increasing speed through rising temperatures and anoxic conditions. One shallow water dwelling invertebrate that has very low tolerance to these conditions is Hemigrapsus oregonensis, normally found in estuary settings along the west coast of the United States. This study was focused on their presence in False Bay, located in the San Juan Islands in Washington State. There, two locations were sampled, one adjacent to False Bay Creek and another at Forest Creek. Each zone was sampled six times looking at the number of rocks, rock area, crab abundance, crab carapace width, and percent coverages of algal species. This data found relationships between habitat structure, crab abundance, and crab size distribution. In total 194 Hemigrapsus crabs were located with crabs preferring rocks that had a larger area for habitat. Two species of Hemigrapsus crabs were seen, H. oregonenesis and H. nudus. All crabs were located at Forest Creek, which had more algal species for shelter and food, as well as less opportunity for human disturbance. Algal species coverage, weather conditions, and human disturbance are all possible explanations for absence of crabs at False Bay Creek. This research can be applied to Hemigrapsus, and other shore crab species research, to further identify the relationship between habitat structure, crab abundance, and crab size distribution.