Meeting Abstract

P2.147  Saturday, Jan. 5  Fish kairomone-induced defenses during larval development of an estuarine crab CHARPENTIER, C.L.*; COHEN, J.H.; University of Delaware; University of Delaware charpecl@udel.edu

Zooplankton in marine, estuarine, and freshwater environments exhibit diel vertical migrations, descending during the higher light conditions of daytime to avoid visual predators and ascending at night to feed. Fish kairomones have been shown to increase zooplankton behavioral response to light, which would enhance the timing and magnitude of vertical movement. Freshwater zooplankton have also been shown to display pronounced morphological and developmental changes upon fish kairomone exposure; such morphological effects are less clear for marine species. We examined the photobehavior and morphology of Rhithropanopeus harrisii throughout its zoeal larval stages, comparing individuals reared in odor-free control seawater to those reared in the presence of odor from a predatory fish, Fundulus heteroclitus. Larvae exposed to either control seawater or fish kairomones throughout larval development had a similar lower light intensity threshold (3.64 × 10 ¹² photons m^-2 s^-1) for a light-mediated descent response when tested in a simulated underwater angular light distribution. However, kairomone-reared zoea exhibited a greater proportion of descending individuals, most pronounced in stage 3 zoea. Morphological effects were only evident in stage 3 larvae with increased lateral spine length in those reared in fish kairomones. These data show that chemosensory inputs such as fish odor increase both morphological and behavioral predator-avoidance strategies in R. harrisii larvae. Further study is required to better understand the specific neural processes that contribute to the phenotypic plasticity of these sensory responses.