Simultaneous Sampling of Flow and Odorants by Crustaceans can Aid Searches within a Turbulent Plume

Abstract

Crustaceans such as crabs, lobsters and crayfish use dispersing odorant molecules to determine the location of predators, prey, potential mates and habitat. Odorant molecules diffuse in turbulent flows and are sensed by the olfactory organs of these animals, often using a flicking motion of their antennules. These antennules contain both chemosensory and mechanosensory sensilla, which enable them to detect both flow and odorants during a flick. To determine how simultaneous flow and odorant sampling can aid in search behavior, a 3-dimensional numerical model for the near-bed flow environment was created. A stream of odorant concentration was released into the flow creating a turbulent plume, and both temporally and spatially fluctuating velocity and odorant concentration were quantified. The plume characteristics show close resemblance to experimental measurements within a large laboratory flume. Results show that mean odorant concentration and it's intermittency, computed as dc/dt, increase towards the plume source, but the temporal and spatial rate of this increase is slow and suggests that long measurement times would be necessary to be useful for chemosensory guidance. Odorant fluxes measured transverse to the mean flow direction, quantified as the product of the instantaneous fluctuation in concentration and velocity, v′c′, do show statistically distinct magnitude and directional information on either side of a plume centerline over integration times of <0.5 s. Aquatic animals typically have neural responses to odorant and velocity fields at rates between 50 and 500 ms, suggesting this simultaneous sampling of both flow and concentration in a turbulent plume can aid in source tracking on timescales relevant to aquatic animals.

Orientation and food search behaviour of a deep sea lobster in turbulent versus laminar odour plumes

“…This has been suggested to be the primary orientation strategy for blue crabs (Callinectes sapidus), and is used in combination with spatial comparisons of the chemical signals (chemo-tropotaxis) to maintain contact with the plume and progress toward the source [25]. In contrast, lobsters have been suggested to use a form of eddy-chemotaxis, simultaneously employing the chemosensors and mechanoreceptors on the antennules to make spatial and temporal comparisons of eddies of odorant chemicals [19,26,27]. As turbulence affects the spatial complexity of odour plumes and the intermittency that crustaceans encounter the filaments of odorant chemicals in the plume, it has a significant effect on the foraging behaviour of a number of crustacean species, which are tuned to the turbulence they encounter in their natural habitat [28][29][30].…”

Learning to Rapidly Re-Contact the Lost Plume in Chemical Plume Tracing

“…Many animals exhibit the capability of tracing the plume of chemical stimuli to its source using the olfactory sense: Pacific salmons retain odor memories of their home stream to guide homeward migration [1]; crustacean species sense the relatively rare patches of coral reef to search for their settlement habitat [2]; crabs [3] and crayfishes [4] use chemical cues to find the source of food odor; male moths [5] navigate along pheromone plume, which consists of intermittent, wind-blown patches [6] of chemical substances separated by large voids, to locate females, etc. Mobile robots capable of such feats ( i.e.…”

Fluid Mechanics of Chemical and Flow Sensing in Aquatic Animals

“…Both flow and odor signals have been suggested to aid in search behavior [34]. Numerous behavioral studies have now shown that hydrodynamic features are important, if not essential, for odor source detection by aquatic vertebrates and invertebrates alike [100,3,34,101,6,42,102,76,103,95]. Hydrodynamic stimulation of the antennules, including flicking [75,7] and from ambient current evokes electrical activity in the central brain neurons [68,48,49].…”

“…In aquatic benthic environments, flow fields are often turbulent and the distribution of diffusing odorants is intermittent and complex. The interwoven spatial and temporal structure of the flow and chemical distribution indicates that instantaneous sensing of the flow field can be of crucial importance in chemical sensing [95]. Antennule flicking enhances the detection of odorants by allowing the animal to take discrete samples of odorant molecules in addition to shedding away the boundary layer of odorants previously present around the sensilla.…”

“…The benthic zone is often highly turbulent, and therefore these organisms are likely to be surrounded by intense gradients in both water velocities and chemical concentrations [14,95], which can provide information, but also uncertainty, when detecting and tracking movements and distant odor sources [8]. These organisms contain unimodal chemosensitive and hydrodynamically sensitive setae, along with biomadal chemo-mechanosensitive setae that respond to both flows and odors [46,7].…”