Vertical Distribution and Migration of Decapod Larvae in Relation to Light and Tides in Willapa Bay, Washington

We investigated the occurrence of behaviors that maximize predator avoidance and seaward transport in estuarine decapod zoeae by collecting larvae from discrete depths in a partially mixed estuary, Willapa Bay, Washington, USA, and relating their abundance and vertical distribution to a suite of environmental variables. Abundances of first zoeae of Neotrypaea californiensis and Pinnotheridae were associated with tidal phase, diel phase, and water height. Both taxa were most abundant during ebb tides, and abundances increased with water height, suggesting behaviors that enhanced seaward transport. Additionally, N. californiensis were both shallower and more abundant at night, indicative of behaviors to avoid visual predators. Our results suggest that both tidal transport and predator avoidance are important and sometimes interactive selective forces shaping larval decapod behavior.