Life and Death in Moving Fluids: Hydrodynamic Effects on Chemosensory‐Mediated Predation

Abstract

Previous studies in taxonomically diverse marine animals have established the general existence, and importance, of the olfactory sense in a wide variety ofbehavioral processes. Evidence suggests that the sense of smell mediates predatory search in many marine animals. Past investigations have not, however, been designed to link either the degree of successful olfactory-mediated search or guidance mechanisms with the hydraulic environment in which predatory activities naturally take place. In an effort to examine the interaction between hydrodynamics and chemoreception, we investigated predatory success and search strategies of blue crabs foraging in controlled hydrodynamic environments generated in a flume. Hydrodynamics were characterized by quantifying boundary layer shear velocity (u.) and roughness Reynolds number (Re.), two measures that describe the structure of boundary layer flows. Flow properties affected the ability of crabs to orient to odor plumes emanating from actively pumping infaunal bivalves (Mercenaria mercenaria). High flow speed or large sediment particle size increased boundary layer turbulence, thereby decreasing the success of crab chemo-orientation ability. In addition, high flow speed also lessened the probability that crabs contacted odor plumes. Thus, habitats with high flows can provide hydrodynamic refuges from olfactory-mediated predation. Because search ability is contingent on the magnitude of boundary layer turbulence, olfactory-mediated predation may also be ineffective in slow flows, if bottom roughness elements can generate sufficient turbulence. Further, search ability in blue crabs is extremely sensitive to small changes in benthic boundary layer structure. The presence of a thick viscous sublayer, dominated by quasilaminar flow, seems especially critical for successful location of an odor source by crabs. Benthic estuarine crustaceans inhabit an environment where flows are transitional between smooth-and rough-turbulent conditions. Accordingly, chemosensory systems appear geared primarily to extracting information from hydraulically smooth flows. These results indicate that mechanisms governing the physical transport of odor signals can have profound influences, not only on the development of sensory and behavioral mechanisms, but also on biotic interactions such as predation, which, in tum, can mediate community structure.

Hard Clams (Mercenaria mercenaria) Evaluate Predation Risk Using Chemical Signals from Predators and Injured Conspecifics

“…Other bivalves (e.g., mussels) also use chemical cues to detect predators and respond by changing their morphology (e.g., Leonard et al, 1999) or behavior (e.g., Cote ' and Jelnikar, 1999). Previous studies have shown that blue crabs depend on chemical cues to locate clam prey (Weissburg and Zimmer-Faust, 1993;Finelli et al, 2000;Weissburg et al, 2002). The modulation of the blue crab-clam predatory interaction by chemicals is perhaps unsurprising given that the water in our study area is extremely turbid, and chemical cues are likely the only signals that can be detected from a distance in this habitat.…”

“…Blue crabs are also a threat to adult clams, as they can nip their siphons and decrease their feeding efficiency, growth, and fecundity (Peterson, 1986;Coen and Heck, 1991;Irlandi, 1994). Clams release attractive chemicals into the water as they feed, and blue crabs follow these waterborne chemical odor plumes to locate their clam prey (Weissburg and Zimmer-Faust, 1993;Weissburg et al, 2002). Irlandi and Peterson (1991) found that clams responded to the presence of predators by reducing their feeding time and hypothesized that feeding reductions would make clams less apparent to consumers.…”

Visual orientation by the crown-of-thorns starfish (Acanthaster planci)

“…Successful longdistance navigation by means of olfaction has been found in birds (Gagliardo et al 2013), fish (Keefer and Caudill 2013) and crabs (Weissburg and Zimmer-Faust 1994). Although olfaction is a well-developed sense in many marine benthic invertebrates, it is much less accurate as a directional homing cue in the presence of boundary layer turbulence (Weissburg and Zimmer-Faust 1993), which can be found close to large structures like coral reefs. At close quarters, visual detection can provide the animals with a reliable cue and is believed to be used by crown-ofthorns starfish to settle on reefs ).…”

Size-related changes in vulnerability to predators and spatial refuge use by juvenile Iceland scallops Chlamys islandica

“…Asteroids, in contrast to the above predators, are slow-moving, nonvisual predators which usually use chemodetection to search for prey (Sloan & Campbell 1982, Rochette et al 1994. Crevice use may also render Iceland scallops more difficult to detect by asteroids because odour plumes originating from scallops in crevices are likely weaker and distorted by turbulence near the bottom (Weissburg & Zimmer-Faust 1993).…”