Matthew C. Ferner

Ecological Consequences of Chemically Mediated Prey Perception

To locate food, mobile consumers in aquatic habitats perceive and move towards sources of attractive chemicals. There has been much progress in understanding how consumers use chemicals to identify and locate prey despite the elusive identity of odor signals and the complex effects of turbulence on chemical dispersion. This review highlights how integrative studies on behavior, fluid physics, and chemical isolation can be fundamental in elucidating mechanisms that regulate species composition and distribution. We suggest three areas where further research may yield important ecological insights. First, although basic aspects of stimulatory molecules are known, our understanding of how consumers identify prey from a distance remains poor, and the lack of studies examining the influence of distance perception on food preference may result in inaccurate estimation of foraging behavior in the field. Second, the ability of many animals to find prey is greatest in unidirectional, low turbulence flow environments, although recent evidence indicates a trade-off in movement speed versus tracking ability in turbulent conditions. This suggests that predator foraging mode may affect competitive interactions among consumers, and that turbulence provides a hydrodynamic refuge in space or time, leading to particular associations between predator success, prey distributions, and flow. Third, studies have been biased towards examining predator tracking. Current data suggest a variety of mechanisms prey may use to disguise their presence and avoid predation; these mechanisms also may produce associations between prey and flow environments. These examples of how chemical attraction may mediate interactions between consumers and their resources suggest that the ecology of chemically mediated prey perception may be as fundamental to the organization of aquatic communities as the ecology of chemical deterrence.

Slow-moving predatory gastropods track prey odors in fast and turbulent flow

SUMMARY Olfactory searching by aquatic predators is reliant upon the hydrodynamic processes that transport and modify chemical signals. Previous studies indicate that the search behavior of some benthic crustaceans is hindered by rapid water flow and turbulent mixing of prey chemicals, but different sensory strategies employed by other taxa might offset such detrimental effects. Using a laboratory flume, we investigated the odor-tracking behavior of a marine gastropod whelk (Busycon carica) to test the generalization that turbulence interferes with chemically mediated navigation. We exposed individual whelks to turbulent odor plumes in free-stream velocities of 1.5, 5, 10 or 15 cm s–1, or with one of two obstructions placed upstream of the odor source in an intermediate flow of 5 cm s–1. Measurements of velocity and stimulus properties confirmed that obstruction treatments increased turbulence intensity and altered the fine-scale structure of downstream odor plumes. In all conditions tested, between 36–63% of test animals successfully located the odor source from 1.5 m downstream with no significant effect of flow treatment. Search behaviors, such as cross-stream meander were reduced at higher flow velocities and in the presence of obstructions, allowing whelks to reach the odor source significantly more quickly than in slower, less turbulent conditions. Our results demonstrate that whelks can respond to chemical information in fast and turbulent flow, and we suggest that these slow-moving predators can forage in hydrodynamic environments where the olfactory abilities of other taxa are limited.

The Sensory Ecology of Nonconsumptive Predator Effects

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.

Alteration of sensory abilities regulates the spatial scale of nonlethal predator effects

Many studies have shown that nonlethal predator effects such as trait-mediated interactions (TMIs) can have significant impacts on the structure and function of communities, but the role that environmental conditions play in modulating the scale and magnitude of these effects has not been carefully investigated. TMIs occur when prey exhibit behavioral or physiological responses to predators and may be more prevalent when abiotic conditions increase prey reactions to consumers. The purpose of this study was to determine if turbulence would alter the distance over which prey in aquatic systems respond to chemical cues emitted by predators in nature, thus changing the scales over which nonlethal predator effects occur. Using hard clams and blue crabs as a model predator–prey system, we investigated the effects of turbulence on clam reactive distance to predatory blue crabs in the field. Results suggest that turbulence diminishes clam reactions to predators and that the environmental context must be considered when predicting the extent of indirect predator effects in natural systems.

Turbulent shear spurs settlement in larval sea urchins

Marine invertebrates commonly produce larvae that disperse in ocean waters before settling into adult shoreline habitat. Chemical and other seafloor-associated cues often facilitate this latter transition. However, the range of effectiveness of such cues is limited to small spatial scales, creating challenges for larvae in finding suitable sites at which to settle, especially given that they may be carried many kilometers by currents during their planktonic phase. One possible solution is for larvae to use additional, broader-scale environmental signposts to first narrow their search to the general vicinity of a candidate settlement location. Here we demonstrate strong effects of just such a habitat-scale cue, one with the potential to signal larvae that they have arrived in appropriate coastal areas. Larvae of the purple sea urchin (Strongylocentrotus purpuratus) exhibit dramatic enhancement in settlement following stimulation by turbulent shear typical of wave-swept shores where adults of this species live. This response manifests in an unprecedented fashion relative to previously identified cues. Turbulent shear does not boost settlement by itself. Instead, it drives a marked developmental acceleration that causes “precompetent” larvae refractory to chemical settlement inducers to immediately become “competent” and thereby reactive to such inducers. These findings reveal an unrecognized ability of larval invertebrates to shift the trajectory of a major life history event in response to fluid-dynamic attributes of a target environment. Such an ability may improve performance and survival in marine organisms by encouraging completion of their life cycle in advantageous locations.

Hydrodynamic sensory stressors produce nonlinear predation patterns.

Predators often have large effects on community structure, but these effects can be minimized in habitats subjected to intense physical stress. For example, predators exert large effects on rocky intertidal communities on wave-protected shores but are usually absent from wave-swept shores where hydrodynamic forces prevent them from foraging effectively. The physical environment also can affect predation levels when stressors are not severe enough to be physically risky. In these situations, environmental conditions may constrain a predators ability to locate prey and alleviate predation pressure. Yet, stress models of community structure have rarely considered the implications of such sensory or behavioral stressors, particularly when the sensory abilities of both predators and prey are affected by the same types of environmental conditions. Ecologists may classify certain environmental conditions as refuges if they impede predator foraging, but these conditions may not actually decrease predation levels if they simultaneously increase prey vulnerability to consumers. Using blue crabs (Callinectes sapidus) and hard clams (Mercenaria mercenaria) as a model system, we investigated the relationship between predation intensity and environmental stress in the form of hydrodynamics (i.e., flow velocity and turbulence). Blue crabs and hard clams are less responsive to each other in faster, more turbulent flows, but studies exploring how flow modulates the outcomes of crab-clam interactions in the field are lacking. We manipulated turbulence within field sites and compared predation levels within and between sites that differed in flow velocity and turbulence. Our results suggest that blue crabs are most effective foragers in flows with intermediate velocities and turbulence levels. Although these conditions are not ideal for blue crabs, lab studies indicate that they also compromise the ability of clams to detect and react to approaching crabs and, thereby, increase clam vulnerability to predators. Our results suggest that environmental stresses on perception (sensory stressors) may not cause a steady decay in predation rates when they simultaneously affect the behaviors of both predators and prey. Moreover, the relative contribution of lethal vs. nonlethal predator effects in communities also may be influenced by environmental forces that enhance the predator-avoidance abilities of prey or the foraging efficiency of predators.

Testing local and global stressor impacts on a coastal foundation species using an ecologically realistic framework

Despite the abundance of literature on organismal responses to multiple environmental stressors, most studies have not matched the timing of experimental manipulations with the temporal pattern of stressors in nature. We test the interactive effects of diel-cycling hypoxia with both warming and decreased salinities using ecologically realistic exposures. Surprisingly, we found no evidence of negative synergistic effects on Olympia oyster growth; rather, we found only additive and opposing effects of hypoxia (detrimental) and warming (beneficial). We suspect that diel-cycling provided a temporal refuge that allowed physiological compensation. We also tested for latent effects of warming and hypoxia to low-salinity tolerance using a seasonal delay between stressor events. However, we did not find a latent effect, rather a threshold survival response to low salinity that was independent of early life-history exposure to warming or hypoxia. The absence of synergism is likely the result of stressor treatments that mirror the natural timing of environmental stressors. We provide environmental context for laboratory experimental data by examining field time series environmental data from four North American west coast estuaries and find heterogeneous environmental signals that characterize each estuary, suggesting that the potential stressor exposure to oysters will drastically differ over moderate spatial scales. This heterogeneity implies that efforts to conserve and restore oysters will require an adaptive approach that incorporates knowledge of local conditions. We conclude that studies of multiple environmental stressors can be greatly improved by integrating ecologically realistic exposure and timing of stressors found in nature with organismal life-history traits.

System-Wide Monitoring Program of the National Estuarine Research Reserve System: Research and Monitoring to Address Coastal Management Issues

Abstract The National Estuarine Research Reserve System (NERRS) consists of 28 coastal reserves located across the United States. A system-wide monitoring program was established in 1995 to develop quantitative measurements of short-term variability and long-term changes in abiotic and biotic properties of estuarine ecosystems for the purpose of informing effective coastal management. The hallmarks of this program are its two decades of data collection, the use of common protocols and instrumentation across all observing platforms, and a centralized approach to data quality assurance/quality control (QA/QC). By using standardized procedures at all reserves, this monitoring program generates a national database on estuarine ecosystems, and it creates a network of sentinel sites for detecting and understanding the effects of climate change. Examples of how these data inform coastal managers include water quality assessment, habitat mapping and change analysis, establishment of nutrient criteria for estuaries, and understanding the predicted impacts of climate change.

Rethinking competence in marine life cycles: ontogenetic changes in the settlement response of sand dollar larvae exposed to turbulence.

Complex life cycles have evolved independently numerous times in marine animals as well as in disparate algae. Such life histories typically involve a dispersive immature stage followed by settlement and metamorphosis to an adult stage on the sea floor. One commonality among animals exhibiting transitions of this type is that their larvae pass through a ‘precompetent’ period in which they do not respond to localized settlement cues, before entering a ‘competent’ period, during which cues can induce settlement. Despite the widespread existence of these two phases, relatively little is known about how larvae transition between them. Moreover, recent studies have blurred the distinction between the phases by demonstrating that fluid turbulence can spark precocious activation of competence. Here, we further investigate this phenomenon by exploring how larval interactions with turbulence change across ontogeny, focusing on offspring of the sand dollar Dendraster excentricus (Eschscholtz). Our data indicate that larvae exhibit increased responsiveness to turbulence as they get older. We also demonstrate a likely cost to precocious competence: the resulting juveniles are smaller. Based upon these findings, we outline a new, testable conception of competence that has the potential to reshape our understanding of larval dispersal and connectivity among marine populations.

Evaluation of Error Reduction Techniques on a LIDAR-Derived Salt Marsh Digital Elevation Model

ABSTRACT McClure, A.; Liu, X.; Hines, E., and Ferner, M.C., 2016. Evaluation of error reduction techniques on a LIDAR-derived salt marsh digital elevation model. Accurate elevation information is a necessity for conservation and management of tidal salt marshes where elevation differences can be as little as 2 m and where sea-level rise is a critical threat. This study applied an existing method to evaluate and improve the vertical accuracy of a 1-m LIDAR-derived digital elevation model (DEM) using a real-time kinematic (RTK) GPS dataset with a vertical accuracy of ±0.02 m and local vegetation data within a tidal salt marsh. Correction factors were generated for vegetation species within each major vegetation class and produced a modified DEM of the site. Comparison between the original and modified DEM showed that the mean error was reduced from 0.16 m to −0.004 m and the root mean squared error was reduced from 0.212 m to 0.098 m. These results demonstrate that it is possible to significantly reduce vertical error contained within a salt marsh DEM derived from a LIDAR dataset using highly accurate RTK GPS data combined with vegetation data collected on a per site basis.