Dungeness crabs (Cancer magister) occur throughout Washington waters, including the outer coast (mostly in coastal estuaries) and inland waters. Dungeness crabs use different habitats throughout their life cycle: as larvae they are planktonic, as juveniles they are found in intertidal mixed sand or gravel areas with algae or eelgrass (Holsman et al. 2006) and as adults they are found in subtidal or intertidal areas on sand, mud, or associated with eelgrass beds. Bare habitats are infrequently used by juveniles, most likely due to a lack of refuge from predation and decreased food abundance (McMillan et al. 1995). Vegetated, intertidal estuaries appear to be important nursery habitats for young crabs (Stevens and Armstrong 1984); older crabs have been shown to move progressively into unvegetated subtidal channels (Dinnel et al. 1986, Dethier 2006).
As predators and scavengers, Dungeness crabs feed upon a broad range of prey including small mollusks, crustaceans, clams, and fishes. They also prey for a wide variety of taxa, which varies with their life history stage. Larvae are preyed upon by coho and Chinook salmon and rockfishes; juveniles by a wide variety of fishes; and adults by fishes, seals, octopuses, and each other (generally when molting) (Orcutt et al. 1976, Reilly 1983, Dethier 2006).
Threats to Dungeness crabs include: low dissolved oxygen, variation in temperature and salinity, fisheries, habitat alteration or loss, and pollutants such as insecticides, hydrocarbons from oil spills and heavy metals. Because juvenile crabs rely on estuarine habitats and are also potentially more sensitive to toxins, early life history stages are likely to be more influenced by human activities (Dethier 2006).
As observed in Hood Canal, low-oxygen conditions can upend the lives of Dungeness crabs trying to stay alive. Levels of dissolved oxygen can alter predator-prey relationships for a multitude of species, affecting populations throughout the food web. Part two of our series "Oxygen for life" examines a crab case study.
Last summer, scientists met at the University of Washington to address alarming findings concerning the rapid acidification of the world's oceans. Experts at that symposium warned that wildlife in the Salish Sea, from salmon to shellfish, may start to see significant effects from changing water chemistry within the next 10 to 20 years. This article summarizes the symposium's key findings and was commissioned and edited by the Washington Ocean Acidification Center which hosted the gathering. Funds for the article were provided by the Washington state legislature. [A version of this article was originally published by the Washington Ocean Acidification Center.]
Ocean acidification may be twice as extreme in Puget Sound’s seagrass habitats, threatening Dungeness crabs
Ocean acidification could be up to twice as severe in fragile seagrass habitats as it is in the open ocean, according to a study published last April in the Proceedings of the National Academy of Sciences. The conditions may threaten Dungeness crabs by 2050 and will be especially pronounced in the winter, the study says.
A 2017 report from the Puget Sound Ecosystem Monitoring Program presents an overview of selected recent monitoring and research activities focused on toxic contaminants in the Salish Sea.
This is the executive summary from a technical report produced for the Puget Sound Nearshore Partnership on Valued Ecosystem Components (VEC). The entire document is included as a PDF with this summary.