Mark W. Denny's research while affiliated with Stanford University and other places

Publications (133)

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Accurate forecasting of organismal responses to climate change requires a deep mechanistic understanding of how physiology responds to present-day variation in the physical environment. However, the road to physiological enlightenment is fraught with complications: predictable environmental fluctuations of any single factor are often accompanied by...
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Even though mollusks' capacity to repair shell damage is usually studied in response to a single event, their shells have to defend them against predatory and environmental threats throughout their potentially multi-decadal life. We measured whether and how mollusks respond to chronic mechanical stress. Once a week for 7 months, we compressed whole...
Article
Thermal performance curves are commonly used to investigate effects of heat acclimation on thermal tolerance and physiological performance. However, recent work indicates that metrics of these curves heavily depend on experimental design and may be poor predictors of animals’ survival during heat events in the field. In intertidal mussels, cardiac...
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Collective behaviors in biological systems such as coordinated movements have important ecological and evolutionary consequences. While many studies examine within‐species variation in collective behavior, explicit comparisons between functionally similar species from different taxonomic groups are rare. Therefore, a fundamental question remains: h...
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To better understand life in the sea, marine scientists must first quantify how individual organisms experience their environment, and then describe how organismal performance depends on that experience. In this review, we first explore marine environmental variation from the perspective of pelagic organisms, the most abundant life forms in the oce...
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The distributions of marine ectotherms are governed by physiological sensitivities to long-term trends in seawater temperature and dissolved oxygen. Short-term variability in these parameters has the potential to facilitate rapid range expansions, and the resulting ecological and socioeconomic consequences may portend those of future marine communi...
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Hard external armors have to defend against a lifetime of threats yet are traditionally understood by their ability to withstand a single attack. Survival of bivalve mollusks thus can depend on the ability to repair shell damage between encounters. We studied the capacity for repair in the intertidal mussel Mytilus californianus by compressing live...
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Climate change is not only causing steady increases in average global temperatures but also increasing the frequency with which extreme heating events occur. These extreme events may be pivotal in determining the ability of organisms to persist in their current habitats. Thus, it is important to understand how quickly an organism's heat tolerance c...
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Increases in global temperatures are expected to have dramatic effects on the abundance and distribution of species in the coming years. Intertidal organisms, which already experience temperatures at or beyond their thermal limits, provide a model system in which to investigate these effects. We took advantage of a previous study in which experimen...
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Mollusk shells protect against diverse environmental and predatory physical threats, from one-time impacts to chronic, low-magnitude stresses. The effectiveness of shells as armor is often quantified with a test of shell strength: increasing force is applied until catastrophic fracture. This test does not capture the potential role of fatigue, a pr...
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Climate change is increasing the temperature variability animals face, and thermal acclimatization allows animals to adjust adaptively to this variability. While the rate of heat-acclimatization has received some study, little is known about how long these adaptive changes remain without continuing exposure to heat stress. This study explored the r...
Article
Hemocytes are immune cells in the hemolymph of invertebrates that play multiple roles in response to stressors; hemocyte mortality can thus serve as an indicator of overall animal health. However, previous research has often analyzed hemolymph samples pooled from several individuals, which precludes tracking individual responses to stressors over t...
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Accelerating shifts in global climate have focused the attention of ecologists and physiologists on extreme environmental events. However, the dynamic process of physiological acclimatization complicates study of these events' consequences. Depending on the range of plasticity and the amplitude and speed of environmental variation, physiology can b...
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Body temperature affects plants’ and animals’ performance, but these effects are complicated by thermal variation through time within an individual and variation through space among individuals in a population. This review and synthesis describes how the effects of thermal variation—in both time and space—can be estimated by applying a simple, nonl...
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To support conservation practices, societal demand for understanding fundamental coastal ocean ecosystem mechanisms has grown in recent decades. Globally, these regions are among the world’s most productive, but they are highly vulnerable to extractive and non-extractive stresses. In 1999, we established the Partnership for Interdisciplinary Studie...
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Intertidal communities of wave-swept rocky shores have served as a powerful model system for experiments in ecology, and mussels (the dominant competitor for space in the mid-intertidal zone) play a central role in determining community structure in this physically stressful habitat. Consequently, the ability to account for mussels' physiological r...
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Animals must balance their rates of energetic intake and expenditure while foraging. Several mathematical models have been put forward as energetically optimal foraging strategies when the food environment is sparse (i.e., the distance between food patches in the environment is much larger than the distance from which the forager can perceive food)...
Article
The structure (both gross morphology and internal cellular) of rhodoliths (free-living forms of coralline algae) are important factors in the ability of rhodoliths to create complex habitats. Using Finite Element Analysis, models of the internal structure of rhodoliths have been interrogated to assess how changes to the cellular structure affect st...
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As Earth's climate warms, plants and animals are likely to encounter an increased frequency and severity of extreme thermal events, and the ensuing destruction is likely to play an important role in structuring ecological communities. However, accurate prediction of the population-scale consequences of extreme thermal events requires detailed knowl...
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This study uses field observations within a single kelp bed in southern Monterey Bay, California, to evaluate the retention of cold, hypoxic water within depressions in the rocky reef following relaxation of internal wave events. Just as tide pools in the rocky intertidal zone persist in depressions following the relaxation of surface waves and tid...
Article
![Figure][1] John Gosline in 1998. Photo credit: University of British Columbia Public Affairs. John M. Gosline, Professor Emeritus in the Department of Zoology at the University of British Columbia (UBC), Canada, died on 7 November 2016 at home in Vancouver after a protracted battle
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Biologists often cope with variation in physiological, environmental and ecological processes by measuring how living systems perform under average conditions. However, performance at average conditions is seldom equal to average performance across a range of conditions. This basic property of nonlinear averaging-known as 'Jensen's inequality' or '...
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At a proximal level, the physiological impacts of global climate change on ectothermic organisms are manifest as changes in body temperatures. Especially for plants and animals exposed to direct solar radiation, body temperatures can be substantially different from air temperatures. We deployed biomimetic sensors that approximate the thermal charac...
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The effect of grazers on the diversity, distribution, and composition of their principal food source has rarely been described for the high intertidal zone of rocky shores, a model system for studying the potential effects of climate change. Along rocky, wave-swept shores in central California, the microphytobenthos (MPB) supports diverse assemblag...
Article
By incorporating joints into their otherwise rigid fronds, erect coralline algae have evolved to be as flexible as other seaweeds, which allows them to thrive - and even dominate space - on wave-washed shores around the globe. However, to provide the required flexibility, the joint tissue of Calliarthron cheilosporioides, a representative articulat...
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Flexibility is key to survival for seaweeds exposed to the extreme hydrodynamic environment of wave-washed rocky shores. This poses a problem for coralline algae, whose calcified cell walls make them rigid. Through the course of evolution, erect coralline algae have solved this problem by incorporating joints (genicula) into their morphology, allow...
Article
Hydrodynamic forces produced by breaking waves make the rocky intertidal zone one of the most physically stressful environments on the planet, and for many ecological studies, it is important to quantify intertidal flows. However, hydrodynamic measurements with a response time rapid enough to reliably identify "impingement events" - large, transien...
Article
Breaking waves can impose enormous forces on intertidal plants and animals. While some hydrodynamic forces (drag, lift, and the acceleration reaction) are well-studied, the factors affecting the magnitude of a fourth force – the impingement force – remain unknown. Characterized by a sharp, transient spike in force at the instant of wave arrival, im...
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In this review we consider how small-scale temporal and spatial variation in body temperature, and biochemical/physiological variation among individuals, affect the prediction of organisms' performance in nature. For 'normal' body temperatures - benign temperatures near the species' mean - thermal biology traditionally uses performance curves to de...
Article
Rocky intertidal organisms are often exposed to broadly fluctuating temperatures as the tides rise and fall. Many mobile consumers living on the shore are immobile during low tide, and can be exposed to high temperatures on calm, warm days. Rising body temperatures can raise metabolic rates, induce stress responses, and potentially affect growth an...
Conference Paper
Background/Question/Methods Increases in average air and sea temperatures are already implicated in alterations of species interactions, population dynamics, and community structure, but we know comparatively little about the potential effects of changing temperature variability. In rocky intertidal communities, an increase in temperature variati...
Article
The mussel Mytilus californianus is a dominant competitor for space on wave-swept rocky shores, where it forms dense beds. Byssal threads anchor each mussel both to the substratum and to neighbors, allowing mussels to resist the onslaught of waves. When incident hydrodynamic stress exceeds a mussel's tenacity, the threads are broken, the mussel is...
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Squid are the largest jet propellers in nature as adults, but as paralarvae they are some of the smallest, faced with the inherent inefficiency of jet propulsion at low Reynolds number. In this study we describe the behavior and kinematics of locomotion in 1 mm paralarvae of Dosidicus gigas, the smallest squid yet studied. They swim with hop-and-si...
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Intertidal organisms are subjected to intense hydrodynamic forces as waves break on the shore. These repeated insults can cause a plant or animal's structural materials to fatigue and fail, even though no single force would be sufficient to break the organism. Indeed, the survivorship and maximum size of at least one species of seaweed is set by th...
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The interaction of surface waves and currents with kelp forests was examined under controlled conditions using a dynamically matched 1/25-scale physical model in a laboratory flume. In experiments with kelp mimics, waves increased the time-averaged drag by a factor of 2 and altered the shape of current profiles. Relative motion between model kelp a...
Article
Ecologists have long grappled with the problem of scaling up from tractable, small-scale observations and experiments to the prediction of large-scale patterns. Although there are multiple approaches to this formidable task, there is a common underpinning in the formulation, testing, and use of mechanistic response functions to describe how phenome...
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As the air temperature of the Earth rises, ecological relationships within a community might shift, in part due to differences in the thermal physiology of species. Prediction of these shifts - an urgent task for ecologists - will be complicated if thermal tolerance itself can rapidly evolve. Here, we employ a mechanistic approach to predict the po...
Article
Many organisms reproduce by releasing gametes into the surrounding fluid. For some such broadcast spawners, gametes are positively or negatively buoyant, and, as a result, fertilization occurs on a two-dimensional surface rather than in the bulk of the air or water. We here rationalize this behaviour by considering the encounter rates of gametes on...
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Sea ice typically forms at the ocean's surface, but given a source of supercooled water, an unusual form of ice--anchor ice--can grow on objects in the water column or at the seafloor. For several decades, ecologists have considered anchor ice to be an important agent of disturbance in the shallow-water benthic communities of McMurdo Sound, Antarct...
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Sea ice typically forms at the ocean’s surface, but given a source of supercooled water, an unusual form of ice—anchor ice—can grow on objects in the water column or at the seafloor. For several decades, ecologists have considered anchor ice to be an important agent of disturbance in the shallow-water benthic communities of McMurdo Sound, Antarctic...
Article
For organisms living in the intertidal zone, temperature is an important selective agent that can shape species distributions and drive phenotypic variation among populations. Littorinid snails, which occupy the upper limits of rocky shores and estuaries worldwide, often experience extreme high temperatures and prolonged aerial emersion during low...
Article
Seaweeds inhabiting the extreme hydrodynamic environment of wave-swept shores break frequently. However, traditional biomechanical analyses, evaluating breakage due to the largest individual waves, have perennially underestimated rates of macroalgal breakage. Recent laboratory testing has established that some seaweeds fail by fatigue, accumulating...
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Ocean waves drive a wide variety of nearshore physical processes, structuring entire ecosystems through their direct and indirect effects on the settlement, behavior, and survivorship of marine organisms. However, wave exposure remains difficult and expensive to measure. Here, we report on an inexpensive and easily constructed instrument for measur...
Article
The intertidal zone of wave-swept rocky shores is a potentially useful system in which to monitor, experimentally manipulate, and possibly forecast the ecological consequences of impending changes in environmental temperature. However, the spatial and temporal complexity of the shoreline's thermal environment challenges ecologists' ability to progr...
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Evolutionary theory predicts that, in variable environments, it is advantageous for ectothermic organisms to prefer a body temperature slightly below the physiological optimum. This theory works well for many terrestrial organisms but has not been tested for animals inhabiting the hypervariable physical environment of intertidal shores. In laborato...
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Evolutionary theory predicts that, in variable environments, it is advantageous for ectothermic organisms to prefer a body temperature slightly below the physiological optimum. This theory works well for many terrestrial organisms but has not been tested for animals inhabiting the hypervariable physical environment of intertidal shores. In laborato...
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As the velocity of flow increases, smooth, symmetrical objects such as spheres and cylinders exhibit an abrupt transition from a laminar to a turbulent boundary layer. As a consequence, these shapes experience a substantial reduction in fluid-dynamic drag at velocities above the transition. The possibility was explored that this form of drag reduct...
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The effects of a Macrocystis pyrifera forest on currents and turbulence were investigated in a controlled laboratory setting using a dynamically matched 1/25-scale model. Two kelp configurations with surface canopies and one without a surface canopy were considered. Profiles of mean velocities and turbulence statistics were measured using acoustic...
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Predicting when, where and with what magnitude climate change is likely to affect the fitness, abundance and distribution of organisms and the functioning of ecosystems has emerged as a high priority for scientists and resource managers. However, even in cases where we have detailed knowledge of current species' range boundaries, we often do not un...
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The emerging field of marine ecomechanics provides an explicit physical framework for exploring interactions among marine organisms and between these organisms and their environments. It exhibits particular utility through its construction of predictive, mechanistic models, a number of which address responses to changing climatic conditions. Exampl...
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We begin by giving away our punch line: A lack of physiological insight is the primary impediment to the successful prediction of the ecological effects of climatic change. To be sure, there are uncertainties in our predictions of future climate, especially at the local scale, and the complexities of ecological interactions stretch our ability to m...
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Ecological studies often focus on average effects of environmental factors, but ecological dynamics may depend as much upon environmental extremes. Ecology would therefore benefit from the ability to predict the frequency and severity of extreme environmental events. Some extreme events (e.g., earthquakes) are simple events: either they happen or t...
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Summary • Small-scale distributions of rocky intertidal organisms may be determined in part by temperature and desiccation stress during low tide and the ability of organisms to resist such stresses. Biophysical modelling techniques, coupled with data on the physiological tolerance of organisms can be used to predict the frequency and severity of a...
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Lignified cell walls are widely considered to be key innovations in the evolution of terrestrial plants from aquatic ancestors some 475 million years ago. Lignins, complex aromatic heteropolymers, stiffen and fortify secondary cell walls within xylem tissues, creating a dense matrix that binds cellulose microfibrils and crosslinks other wall compon...
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Hydrodynamic forces dislodge and kill large numbers of organisms in intertidal and subtidal habitats along rocky shores. Although this feature of wave-driven water motion is well recognized, the mechanics of force imposition on compliant organisms is incompletely understood. Here we undertake a field examination of two processes that are thought to...
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Are there absolute limits to the speed at which animals can run? If so, how close are present-day individuals to these limits? I approach these questions by using three statistical models and data from competitive races to estimate maximum running speeds for greyhounds, thoroughbred horses and elite human athletes. In each case, an absolute speed l...
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Previous studies have demonstrated that fleshy seaweeds resist wave-induced drag forces in part by being flexible. Flexibility allows fronds to 'go with the flow', reconfiguring into streamlined shapes and reducing frond area projected into flow. This paradigm extends even to articulated coralline algae, which produce calcified fronds that are flex...
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Previous studies have hypothesized that wave-induced drag forces may constrain the size of intertidal organisms by dislodging or breaking organisms that exceed some critical dimension. In this study, we explored constraints on the size of the articulated coralline alga Calliarthron, which thrives in wave-exposed intertidal habitats. Its ability to...
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Summary • On thermally stressful rocky shores, small, slow-moving ectotherms such as limpets exhibit morphological characteristics such as high-spired and heavily ridged shells which may reduce the likelihood of reaching stressful or lethal body temperatures. • The effects of shell height and shell surface area on predicted limpet body temperatures...
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For marine algae, the benefits of drying out are often overshadowed by the stresses involved. Here we used laboratory and field experiments to examine both the costs and benefits of desiccation in the intertidal turf alga Endocladia muricata (Endlichter) J. Agardh. Laboratory experiments showed that when Endocladia is dry, photosynthesis stops, but...
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Diverse phenomena, ranging from the way shorebirds feed to self-cleaning by leaves, can be explained through surface tension effects.
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We measured the variability in hydrodynamic forces among locations separated by only centimeters along three horizontal transects on a steep rocky shore. Our results extend previous work showing that wave forces have the characteristics of 1 /"f"-noise, in which variability in wave forces decreases exponentially with decreasing scales of measuremen...
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Wave-swept macroalgae are subjected to large hydrodynamic forces as each wave breaks on shore, loads that are repeated thousands of times per day. Previous studies have shown that macroalgae can easily withstand isolated impositions of maximal field forces. Nonetheless, macroalgae break frequently. Here we investigate the possibility that repeated...
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Biomechanical analyses of intertidal and shallow subtidal seaweeds have elucidated ways in which these organisms avoid breakage in the presence of exceptional hydrodynamic forces imposed by pounding surf. However, comparison of algal material properties to maximum hydrodynamic forces predicts lower rates of breakage and dislodgment than are actuall...
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Unlike most bivalves, scallops are able to swim, relying on a shell with reduced mass and streamlined proportions, a large fast-twitch adductor muscle and the elastic characteristics of the shell's hinge. Despite these adaptations, swimming in scallops is never far from failure, and it is surprising to find a swimming scallop in Antarctica, where l...
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Although they are subjected to one of the most stressful physical environments on earth, wave-swept rocky shores support a highly diverse community of plants and animals. The surprising presence of such diversity amidst severe environmental adversity provides a unique opportunity for exploration of the role of extreme water flows in community ecolo...
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Living at the interface between the marine and terrestrial environments, intertidal organisms may serve as a bellwether for environmental change and a test of our ability to predict its biological consequences. However, current models do not allow us to predict the body temperature of intertidal organisms whose heat budgets are strongly affected by...
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When coupled with long-term meteorological records, a heat-budget model for the limpet, Lottia gigantea, provides a wealth of information regarding environmental and topographic controls of body temperature in this ecologically important species. (1) The maximum body temperature predicted for any site (37.5 degrees C) is insufficient to kill all li...
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Intertidal algae are exposed to the potentially severe drag forces generated by crashing waves, and several species of brown algae respond, in part, by varying the strength of their stipe material. In contrast, previous measurements have suggested that the material strength of red algae is constant across wave exposures. Here, we reexamine the resp...
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Understanding the role of scale is critical to ecologists' ability to make appropriate measurements, to ''scale up'' from local, short-term experiments to larger areas and longer times, to formulate models of community structure, and to address important conservation problems. Although these issues have received increased attention in recent years,...
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Phenotypic plasticity, the capacity of a given genotype to produce differing morphologies in response to the environment, is widespread among marine organisms (1). For example, acorn barnacles feed by extending specialized appendages (the cirral legs) into flow, and the length of the cirri is plastic: the higher the velocity, the shorter the feedin...