Life in the highly turbulent surf zone poses a severe challenge to reproduction in free-spawning animals. Not only can breaking waves quickly dilute the gametes shed by spawning organisms, but turbulence-induced shear stresses may limit fertilization and interfere with normal development. A Couette cell was used to re-create some of the effects of turbulent water motion to study effects of environmentally relevant shear stresses on fertilization in the purple sea urchin (Strongylocentrotus purpuratus). Although low shear stresses improved fertilization success (presumably by increasing mixing), exposure to high shear stresses (of the magnitude found in the surf zone) substantially decreased fertilization success, probably by interfering with contact between egg and sperm. Furthermore, eggs fertilized at high shear stresses often showed abnormal development and low survival of eggs through the blastula stage.

Many marine crustaceans use water-borne chemical cues in ecologically critical activities such as finding food, mates and suitable habitat, detecting predators and communicating with conspecifics (Caldwell, 1979(Caldwell, , 1982Ache, 1982;Atema and Voigt, 1995;Zimmer-Faust, 1989;Weissburg and ZimmerFaust, 1993, 1994;Weissburg, 2000). The act of following an odor plume to its source is called 'plume tracking'. In turbulent environments, odor plumes consist of fine filaments containing high concentrations of odor molecules interspersed with the surrounding fluid (Murlis and Jones, 1981;Moore et al., 1994;Weissburg, 2000;Crimaldi and Koseff, 2001;Crimaldi et al., 2002). Crustaceans sample the fine structure of the odor filaments by moving their antennules through the filaments . We are interested in discovering how mantis shrimp (and by extension, other crustaceans) use the information contained in odor filaments to find the source of the odorant.Initial studies of plume tracking relied on descriptions of plumes as slowly diffusing clouds of chemicals rather than as filamentous, intermittent and dynamic structures. By recording at a point, later investigators showed that odor plumes are intermittent (Zimmer-Faust et al., 1988a,b, 1995Moore and Atema, 1988, 1991;Atema et al., 1991;Moore et al., 1994;Consi et al., 1995;Dittmer et al., 1995). More recently, planar laser induced fluorescence (PLIF) techniques have shown that odor plumes in water are filamentous Webster and Weissburg, 2001;Crimaldi et al., 2002). Koehl et al. (2001) have shown how odor filaments are encountered by a real antennule swept through a realistic plume by computer-driven motor attached to a stationary lobster carapace. Our study examines odor encounter by antennules of a live, odor-plume-tracking stomatopod.In addition, earlier plume-tracking investigations focused on unidirectional flow. While some species inhabit environments exposed to unidirectional flow (e.g. crabs and crayfish), many others live in coastal habitats and thus experience wave-affected flow. Understanding plume-tracking algorithms requires accurate information about the odor signal encountered by the animal's sensors as it tracks a plume in an environmentally relevant flow field. Our goal in this paper is to answer, for the first time, the following question: what is the instantaneous, fine-scale chemical signal encountered by the mantis shrimp as it tracks an odor plume in wave-affected and in unidirectional flow? This information, correlated with behavior, is the critical first step in deducing the algorithms used by odor-plume-tracking animals. Mantis shrimp as model systemsWe use mantis shrimp (also called stomatopods) as a model

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