- The European green crab (Carcinus maenas) has persisted in Oregon and Washington coastal estuaries since the late 1990s. After the arrival of a strong year class in 1998, significant recruitment to the populations occurred only in 2003, 2005, 2006, 2010, 2015, 2016, 2017, 2018 and 2019. Warm winter water temperatures, high Pacific Decadal Oscillation (PDO) and Multivariate ENSO (El Niño Southern Oscillation) Indices, and a high abundance of southern copepods are all correlated with strong year classes and vice versa (Behrens Yamada, Peterson and Kosro 2015; Behrens Yamada, Fisher and Kosro 2020 in review). Prior to 2015, green crabs were too rare (<0.2 per trap) to exert measurable effects on the native benthic community and on shellfish culture in Oregon and Washington. But after the 2015-2016 El Niño, we document the arrival of five strong year classes. Average catches steadily increased from 0.5 crabs per trap, in 2015 to around 3 crabs per trap in 2017 to 2019. The catches in the last 3 years are much higher than in any of the previous years, including 1998. Catches in some hot spots exceed 10 crabs per trap, a level at which measurable ecological impact can be expected (Grosholz et al. 2011). Since green crabs live for 6 years, these five consecutive year classes can produce larvae until 2025. A switch to cooler ocean conditions in the coming years will result in poor recruitment, but a return to high PDO and strong El Niño patterns would signal good recruitment and higher green crab densities. For example, green crabs were first documented in New England in 1817, but it took warm ocean conditions during the 1950s for their numbers to build to a level at which they decimated the soft-shelled clam industry in Maine (Welch 1968). With the recent warm trend on the East Coast, green crabs are again abundant. Not only are they preying on shellfish, they are also damaging valuable eelgrass habitat by ripping up the plants in their search for food (Neckles 2015).
Even though green crab abundance in Oregon and Washington is still low when compared to Europe, eastern North America, Tasmania, California and the west coast of Vancouver Island, it is imperative to continue monitoring efforts for two reasons:
1) to elucidate the process of range expansion and population persistence of this model non-indigenous marine species with planktonic larvae, and
2) to predict the arrival of strong year classes from ocean conditions and alert managers and shellfish growers of possible increases in predation pressure from this invader.
- Dataset: Yamada, S. B., Schooler, S., Heller, R., Donaldson, L., Takacs, G.T., Randall, A. & Buffington, C. (2020). Dataset for Status of the European Green Crab, Carcinus maenas, in Oregon and Washington coastal Estuaries in 2019 (Version 1) [Data set]. Oregon State University. https://doi.org/10.7267/028712995