The boundary layer equations for plane, incompressible, and steady flow are 

$$\matrix{ {u{{\partial u} \over {\partial x}} + v{{\partial u} \over {\partial y}} = - {1 \over \varrho }{{\partial p} \over {\partial x}} + v{{{\partial ^2}u} \over {\partial {y^2}}},} \cr {0 = {{\partial p} \over {\partial y}},} \cr {{{\partial u} \over {\partial x}} + {{\partial v} \over {\partial y}} = 0.} \cr }$$

Boundary Layer Theory

The interaction between predator and prey is an evolutionary arms race, for which early detection by either party is often the key to success. In aquatic ecosystems, olfaction is an essential sourc...

/pdf/chemical-ecology-of-predator-prey-interactions-in-aquatic-1j8k0l4xre.pdf

Chemical ecology of predator–prey interactions in aquatic ecosystems: a review and prospectusThe present review is one in the special series of reviews on animal–plant interactions.

https://www.int-res.com/articles/meps/207/m207p225.pdf

Marine chemical ecology

Chemical cues constitute much of the language of life in the sea. Our understanding of biotic interactions and their effects on marine ecosystems will advance more rapidly if this language is studied and understood. Here, I review how chemical cues regulate critical aspects of the behavior of marine organisms from bacteria to phytoplankton to benthic invertebrates and water column fishes. These chemically mediated interactions strongly affect population structure, community organization, and ecosystem function. Chemical cues determine foraging strategies, feeding choices, commensal associations, selection of mates and habitats, competitive interactions, and transfer of energy and nutrients within and among ecosystems. In numerous cases, the indirect effects of chemical signals on behavior have as much or more effect on community structure and function as the direct effects of consumers and pathogens. Chemical cues are critical for understanding marine systems, but their omnipresence and impact are inadequ...

/pdf/marine-chemical-ecology-chemical-signals-and-cues-structure-3llqflfcx7.pdf

Marine chemical ecology: chemical signals and cues structure marine populations, communities, and ecosystems.

/pdf/cascading-effects-of-the-loss-of-apex-predatory-sharks-from-3rhx44zxwm.pdf

Cascading Effects of the Loss of Apex Predatory Sharks from a Coastal Ocean

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 methodologie

https://www.jstor.org/stable/10.1086/676644

The sensory ecology of nonconsumptive predator effects.

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.

Clamming up: environmental forces diminish the perceptive ability of bivalve prey

Hard clams, Mercenaria mercenaria, are sessile, filter-feeding organisms that are heavily preyed upon by blue crabs, which find their clam prey using chemical cues Clams may evade blue crabs by reducing their pumping (feeding) behavior when a threat is perceived The purpose of this study was to determine the type of signals that clams use to detect consumers Clams decreased their pumping time in response to blue crabs and blue crab effluent, but not to crab shells, indicating that chemical signals and not mechanical cues mediated the response of clams to distant predators Because predator diet can influence prey evaluation of predatory threats, we compared clam responses to blue crabs fed a steady diet of fish, clams, or that were starved prior to the experiment In addition, we used injured clams as a stimulus because many organisms detect predators by sensing the odor of injured con- or heterospecifics Clams reduced feeding in response to injured conspecifics and to blue crabs that had recently fed Clams reacted similarly to fed crabs, regardless of their diet, but did not respond to starved blue crabs Because blue crabs are generalist predators and the threat posed by these consumers is unrelated to the crab's diet, we should expect clam reactions to blue crabs to be independent of the crab's diet The failure of clams to react to starved blue crabs likely increases their vulnerability to these consumers, but clam responses to injured conspecifics may constitute a strategy that allows animals to detect an imminent threat when signals emanating from blue crabs are not detectable

Hard clams (Mercenaria mercenaria) evaluate predation risk using chemical signals from predators and injured conspecifics.

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.

Ecological consequences of chemically mediated prey perception.

Numerous studies have examined how predator diets influence prey responses to predation risk, but the role predator diet plays in modulating prey responses remains equivocal. We reviewed 405 predator–prey studies in 109 published articles that investigated changes in prey responses when predators consumed different prey items. In 54 % of reviewed studies, prey responses were influenced by predator diet. The value of responding based on a predator’s recent diet increased when predators specialized more strongly on particular prey species, which may create patterns in diet cue use among prey depending upon whether they are preyed upon by generalist or specialist predators. Further, prey can alleviate costs or accrue greater benefits using diet cues as secondary sources of information to fine tune responses to predators and to learn novel risk cues from exotic predators or alarm cues from sympatric prey species. However, the ability to draw broad conclusions regarding use of predator diet cues by prey was limited by a lack of research identifying molecular structures of the chemicals that mediate these interactions. Conclusions are also limited by a narrow research focus. Seventy percent of reviewed studies were performed in freshwater systems, with a limited range of model predator–prey systems, and 98 % of reviewed studies were performed in laboratory settings. Besides identifying the molecules prey use to detect predators, future studies should strive to manipulate different aspects of prey responses to predator diet across a broader range of predator–prey species, particularly in marine and terrestrial systems, and to expand studies into the field.

Delbert L. Smee

Papers

The sensory ecology of nonconsumptive predator effects.

Clamming up: environmental forces diminish the perceptive ability of bivalve prey

Hard clams (Mercenaria mercenaria) evaluate predation risk using chemical signals from predators and injured conspecifics.

Ecological consequences of chemically mediated prey perception.

A review of predator diet effects on prey defensive responses