A population study of the Asian shore crab, Hemigrapsus sanguineus, at Point Judith Pond, RI

The Asian shore crab, Hemigrapsus sanguineus (De Haan), has recently invaded the Atlantic coast of the United States. Its large populations and continued fecundity are indicative of its successful establishment. Competitive interaction with other coastal crab species has been a subject of many studies. For example, in ex situ experiments, H. sanguineus has been shown to be superior to a long-established invader: the green crab, Carcinus maenas. Because H. sanguineus has been found in such great density on some shorelines, it has been postulated that it poses an ecological threat due to its potential to disrupt native and established species. However, many investigators have noted the invasive crab’s limiting habitat requirement for complex, rocky shorelines. After observation of Point Judith Pond, RI, we assessed whether there were enough rocky areas to support significant populations of H. sanguineus that might be disruptive to C. maenas. Using a photo-quadrat system alongside software analysis, transects were laid across areas of interest. H. sanguineus were collected and counted in each quadrat, allowing habitat metrics obtained from the photographs, such as rock size and cover, to be correlated with the density of crabs, their size, and sex. These data, paired with the observation that Point Judith Pond has ample habitat for C. maenas to be displaced to, led us to conclude that the H. sanguineus population in Point Judith Pond, RI, is likely not capable of causing severe disruption of the native C. maenas population as it currently stands, and that this trend may extend to other estuarine systems.