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.

Nonconsumptive effects (NCEs) have been shown to occur in numerous systems and are regarded as important mechanisms by which predation structures natural communities. Sensory ecology-that is, the processes governing the production, propagation, and masking of cues by ambient noise-provides insights into the strength of NCEs as functions of the environment and modes of information transfer. We discuss how properties of predators are used by prey to encode threat, how the environment affects cue propagation, and the role of single sensory processes versus multimodal sensory processes. We discuss why the present body of literature documents the potential for strong NCEs but does not allow us to easily determine how this potential is expressed in nature or what factors or environments produce strong versus weak NCEs. Many of these difficulties stem from a body of literature in which certain sensory environments and modalities may be disproportionately represented and in which experimental methodologies are designed to show the existence of NCEs. We present a general framework for examining NCEs to identify the factors controlling the number of prey that respond to predator cues and discuss how the properties of predators, prey, and the environment may determine prey perceptive range and the duration and frequency of cue production. We suggest how understanding these relationships provides a schema for determining where, when, why, and how NCEs are important in producing direct and cascading effects in natural communities.

The fluid mechanical environment provides the context in which denizens of aquatic realms, as well as terrestrial creatures, use chemoperception to search for objects. Our ability to understand the nature of olfactory-guided navigation rests on our proficiency at characterizing the fluid dynamic setting and at relating properties of flow to behavioral and sensory mechanisms. This work reviews some fluid dynamical concepts that are particularly useful in describing aspects of flow relevant to chemosensory navigation, and it considers studies of orientation in animals in light of these principles. Comparisons across broadly different fluid environments suggest that particular sensory and behavioral mechanisms may be tailored to specific flow regimes and stimulus environments. This is clearly evident when examining animals that operate in high vs. low Reynolds number flows. In other cases, animals may converge on common solutions in given flow regimes in spite of differences in taxonomic class or size. Potential parallels may include behavior of aquatic vs. terrestrial arthropods, and animals without fixed reference points in flows dominated by molecular vs. turbulent diffusion. In an effort to add further fluid dynamical underpinnings to navigational strategies, I suggest how simple nondimensional categorization of behavior in relation to flow may aid in identifying the forces underlying common elements, even across animals of seemingly disparate size and scale.

The characteristics of chemical odor plumes released into a turbulent open channel flow are evaluated in the context of chemical plume tracking. The objective is to assess the availability and usefulness of chemosensory cues to animals, such as benthic crustaceans, attempting to orient in the plume. Releasing fluorescent dye into the fully developed turbulent boundary layer of a large laboratory-scale flume created turbulent odor plumes. Flow visualization of odor fields created with varying release velocity, release distance from the bed, and nozzle diameter indicated that chemosensory cues in plumes depend on the release characteristics as well as the ambient flow conditions. Thus, to understand animal behavior, it is important to quantify the plume release properties and characteristics. We chose to quantify concentration fields for the case of isokinetic release using the planar laser-induced fluorescence technique. These measurements indicate that the time-averaged concentration converges far too slowly to be useful to a foraging animal. Similarly, resolving the rise slope of a concentration burst requires sampling rates unattainable by animals, and the spatial variation of rise slope is too mild to follow without lengthy sampling periods. In addition, only mild variation with distance from the source is observed in the concentration burst magnitude and duration. Thus, the time-averaged concentration, rise slope, and burst shape all appear to have limited usefulness for plume orientation for animals known to orient effectively to these types of odor sources.Sensory systems in organisms translate spatial and temporal patterns of physical properties into electrical signals that mediate animal responses. Light, sound, pressure, and chemical concentration, among others, are stimuli that are used by animals to collect information on their external world, and which evoke various behaviors necessary for survival. Understanding the operation of perceptual systems provides information on ecological interactions mediated by various sensory modalities, as well as on basic neurological mechanisms of encoding and processing information.A fundamental tenet in the analysis of sensory systems is that they are not fully interpretable until the appropriate sensory environment is characterized or defined. In other words, unless the nature of the input to a sensory system is known, the details and functions of its operation will be obscured. For instance, the elegant construction of the eyes of some insects allows them to use polarized light as a navigational aid. This design is contingent on the orientation of regions of the eye corresponding to the orientation of the e-vector of polarized light emanating from the sector of the sky scanned by each region. Thus, the map of the eye cannot be appreciated unless one has similarly obtained a map of the sky (Wehner 1989).The physical cues used by many sensory modalities offer convenient dimensions for characterization of stimulus patterns, even in the spatial or temporal do...

The lethal and nonlethal impacts of predators in marine systems are often mediated via reciprocal detection of waterborne chemical signals between consumers and prey. Local flow environments can enhance or impair the chemoreception ability of consumers, but the effect of hydrodynamics on detection of predation risk by prey has not been investigated. Using clams as our model organism, we investigated two specific questions: (1) Can clams decrease their mortality by responding to predators? (2) Do fluid forces affect the ability of clams to detect approaching predators? Previous research has documented a decrease in clam feeding (pumping) in response to a neighboring predator. We determined the benefits of this behavior to survivorship by placing clams in the field with knobbed whelk or blue crab predators caged nearby and compared mortality between these clams and clams near a cage-only control. Significantly more clams survived in areas containing a caged predator, suggesting that predator-induced alterations in feeding reduce clam mortality in the field. We ascertained the effect of fluid forces on clam perception of predators in a laboratory flume by comparing the feeding (pumping) behavior of clams in response to crabs and whelks in flows of 3 and 11 cm/s. Clams pumped significantly less in the presence of predators, but their reaction to blue crabs diminished in the higher velocity flow, while their response to whelks remained constant in both flows. Thus, clam reactive distance to blue crabs was affected by fluid forces, but hydrodynamic effects on clam perceptive distance was predator specific. After predators were removed, clams exposed to whelks took significantly longer to resume feeding than those exposed to blue crabs. Our results suggest that prey perception of predators can be altered by physical forces. Prey detection of predators is the underlying mechanism for trait-mediated indirect interactions (TMIIs), and recent research has documented the importance of TMIIs to community structure. Since physical forces can influence prey perception, the prevalence of TMIIs in communities may, in part, be related to the sensory ability of prey, physical forces in the environment that impact sensory performance, and the type of predator detected.