Green Crab Larval Retention in Willapa Bay, Washington: An Intensive Lagrangian Modeling Approach

Abstract

The European green crab (Carcinus maenas) is invasive on the U.S. West Coast. This study uses a high-resolution circulation model to determine the likelihood that green crab larvae spawned in Willapa Bay, Washington could be retained by circulation and behavior long enough to reach maturity and re-settle within the bay. A particle-tracking method (the "diffusive Lagrangian return map") is presented that makes it possible to track the dispersion of hundreds of thousands of model larvae-each subject to three-dimensional advection, vertical turbulent diffusion, and imposed vertical migration behavior-over their full 30-50 d development time with modest computational resources. Larvae spawned in summer show significant retention (5-40%) in the southern and western portions of the bay, including the Stackpole shoals near the mouth, the area most likely to be colonized by late-stage megalopae arriving from the coastal ocean. Larvae spawned in spring show much less retention throughout the bay, because of 1) increased flushing caused by increased river input relative to summer conditions and 2) longer development times caused by lower water temperatures. The role of larval swimming behavior is secondary to hydrodynamics in setting these spatial and seasonal patterns of retention.

Modeling of the larval response of green sea urchins to thermal stratification using a random walk approach

“…A few attempts at incorporating behavioral components that simulate vertical migration into biophysical models of larval dispersal have been made recently (Banas et al, 2009;Dekshenieks et al, 1996;DiBacco et al, 2001;North et al, 2008). However, these attempts utilized mean swimming velocity for a particular ontogenetic stage and/or stimulus intensity (i.e.…”

“…However, the framework used by Rothlisberg et al (1983) fixed larvae to a certain water layer at any given time, and the lack of simulated swimming precluded any interaction with vertical advection. Similarly, Banas et al (2009) showed that diel and tidal vertical migration affected the larval dispersal of Carcinus maenas. However, the role of larval swimming was less important than seasonal differences in hydrodynamics in explaining the difference in dispersal between spring and summer spawnings.…”

“…Currently, most bio-physical models do not incorporate vertical migration (Metaxas and Saunders, 2009) except in a handful of studies, where it affected the larval dispersal potential across a number of species (Banas et al, 2009;Dekshenieks et al, 1996;DiBacco et al, 2001;North et al, 2008). An early attempt using the shrimp Penaus latisulcatus did not model swimming behavior, but rather evaluated the effect of actual vertical position on dispersal (Rothlisberg et al, 1983).…”

Reconstructing the range expansion and subsequent invasion of introduced European green crab along the west coast of the United States

“…The few cards that did reach Oregon from San Francisco did so when released in the fall, but they took 90 days to get there, which is approaching the upper limit of C. maenas larval development time. In another modeling study, Banas et al (2009) suggest that for smaller estuaries with similar shape (e.g., Willapa Bay), there are significant opportunities for larval retention within that estuary.…”

“…Recently, some studies have been conducted on the West Coast. Yamada et al (2005) characterizes the life history of green crabs in Oregon estuaries, while Banas et al (2009) found ovigerous female green craps in Willapa Bay, Washington between January and August.…”