Larval Transport Modeling Support for Identifying Population Sources of European Green Crab in the Salish Sea

In 2016, the invasive European green crab (Carcinus maenas) was observed for the first time east of Vancouver Island in the Salish Sea. Because there are many established green crab populations in the Pacific Northwest region, the invaders' origin was unclear. Understanding likely source populations for the Salish Sea is critical to developing management strategies for the current green crab invasion and future invasion threats. To that end, this study used ocean models to investigate the likelihoods that larvae released from four potential source locations on the West Coast could be successfully transported into the eastern Salish Sea in particle tracking experiments, and then examined the roles of particle release timing and oceanographic processes (i.e., flow reversals in the Strait of Juan de Fuca) in the probability of successful transport. The potential source locations tested were Sooke Basin (British Columbia, Canada), Barkley Sound (British Columbia, Canada), Willapa Bay (Washington, USA), and Coos Bay (Oregon, USA). Model results indicate that during 2014 and 2015 particles released from as far south as Oregon and as far north as the coast of Vancouver Island could have reached the eastern Salish Sea, suggesting that multiple populations on the Pacific coast might be viable sources for the observed eastern Salish Sea invasion in 2016. Flow reversals in the Strait of Juan de Fuca co-occurred with successful invasions from Barkley Sound and Willapa Bay but not from Sooke Basin or Coos Bay. Incursions of particles into the eastern Salish Sea were episodic. Nevertheless, these results suggest that oceanographic patterns and meteorological events could be useful for identifying periods of likely green crab recruitment, particularly during years with high El Nino Southern Oscillation (ENSO) indices.