Explore the vast range of titles available.

Thermal stress has been considered to be among the most important determinants of organismal distribution in the rocky intertidal zone. Yet our understanding of how body temperatures experienced under field conditions vary in space and time, and of how these temperatures translate into physiological performance, is still rudimentary. We continuously monitored temperatures at a site in central California for a period of two years, using loggers designed to mimic the thermal characteristics of mussels, Mytilus californianus. Model mussel temperatures were recorded on both a horizontal and a vertical, north-facing microsite, and in an adjacent tidepool. We periodically measured levels of heat shock proteins (Hsp70), a measure of thermal stress, from mussels at each microsite. Mussel temperatures were consistently higher on the horizontal surface than on the vertical surface, and differences in body temperature between these sites were reflected in the amount of Hsp70. Seasonal peaks in extreme high temperatures (\"acute\" high temperatures) did not always coincide with peaks in average daily maxima (\"chronic\" high temperatures), suggesting that the time history of body temperature may be an important factor in determining levels of thermal stress. Temporal patterns in body temperature during low tide were decoupled from patterns in water temperature, suggesting that water temperature is an ineffective metric of thermal stress for intertidal organisms. This study demonstrates that spatial and temporal variability in thermal stress can be highly complex, and \"snapshot\" sampling of temperature and biochemical indices may not always be a reliable method for defining thermal stress at a site.

Understanding the effects of climate-mediated environmental variation on the distribution of organisms is critically important in an era of global change. We used wavelet analysis to quantify the spatiotemporal (co)variation in daily water temperature for predicting the distribution of cryptic refugia across 16 intertidal sites that were characterized as ‘no’, ‘weak’ or ‘strong’ upwelling and spanned 2000 km of the European Atlantic Coast. Sites experiencing weak upwelling exhibited high synchrony in temperature but low levels of co-variability at monthly to weekly timescales, whereas the opposite was true for sites experiencing strong upwelling. This suggests upwelling generates temporal thermal refugia that can promote organismal performance by both supplying colder water that mitigates thermal stress during hot Summer months and ensuring high levels of fine-scale variation in temperature that reduce the duration of thermal extremes. Additionally, pairwise correlograms based on the Pearson-product moment correlation coefficient and wavelet coherence revealed scale dependent trends in temperature fluctuations across space, with a rapid decay in strong upwelling sites at monthly and weekly timescales. This suggests upwelling also generates spatial thermal refugia that can ‘rescue’ populations from unfavorable conditions at local and regional scales. Overall, this study highlights the importance of identifying cryptic spatiotemporal refugia that emerge from fine-scale environmental variation to map potential patterns of organismal performance in a rapidly changing world.

Long-term monitoring shows that the poleward range edges of intertidal biota have shifted by as much as 50 km per decade, faster than most recorded shifts of terrestrial species. Although most studies have concentrated on species-range edges, recent work emphasizes how modifying factors such as regional differences in the timing of low tide can overwhelm large-scale climatic gradients, leading to a mosaic of environmental stress. We discuss how changes in the mean and variability in climatic regimes, as modified by local and regional factors, can lead to complex patterns of species distribution rather than simple range shifts. We describe how ecological forecasting may be used to generate explicit hypotheses regarding the likely impacts of different climatic change scenarios on the distribution of intertidal species and how related hindcasting methods can be used to evaluate changes that have already been detected. These hypotheses can then be tested over a hierarchy of temporal and spatial scales using coupled field and laboratory-based approaches.

Rocky intertidal ecosystems are characterized by marked zonation patterns in which species replace one another along the vertical gradient of emersion time. Yet, we still do not fully understand the reasons that zonation patterns are variable in space and time. Here, we use effective shore level (ESL), a metric that incorporates the modifying influence of wave splash, to describe the relationship between uninterrupted emersion time and the zonation patterns of two ecologically important species: the mussel Mytilus californianus and the barnacle Balanus glandula. At the local scale (10s to 100s of meters) on Tatoosh Island, the upper limits of both species are closely related to ESL, regardless of substrate aspect or maximum temperature. At larger spatial scales (10s to 100s of kilometers), the upper limit of Balanus is related to ESL at cool sites but not at hotter sites. Thus, although ESL explains most of the local-scale variation in zonation at a cool site, other factors (temperature, desiccation) likely become important as spatial scale increases to incorporate warmer sites. Our results emphasize that an understanding of where and when specific ecological factors are limiting is crucial for our ability to explain and predict large-scale biological patterns in space and time.

▪ Abstract  Recent meta-analyses have shown that the effects of climate change are detectable and significant in their magnitude, but these studies have emphasized the utility of looking for large-scale patterns without necessarily understanding the mechanisms underlying these changes. Using a series of case studies, we explore the potential pitfalls when one fails to incorporate aspects of physiological performance when predicting the consequences of climate change on biotic communities. We argue that by considering the mechanistic details of physiological performance within the context of biophysical ecology (engineering methods of heat, mass and momentum exchange applied to biological systems), such approaches will be better poised to predict where and when the impacts of climate change will most likely occur.

Recent studies indicate that the incidence and persistence of damage from coral reef bleaching are often highest in areas of restricted water motion, and that resistance to and recovery from bleaching is increased by enhanced water motion. We examined the hypothesis that water motion increases the efflux of oxygen from coral tissue thereby reducing oxidative stress on the photosynthetic apparatus of endosymbiotic zooxanthellae. We experimentally exposed colonies of Montastrea annularis and Agaricia agaricites to manipulations of water flow, light intensity, and oxygen concentration in the field using a novel mini-flume. We measured photosynthetic efficiency using a pulse amplitude modulated fluorometer to test the short-term response of corals to our manipulations. Under normal oxygen concentrations, A. agaricites showed a significant 8% increase in photosynthetic efficiency from 0.238 (± 0.032) in still water to 0.256 (± 0.037) in 15 cm s^sup -1^ flow, while M. annularis exhibited no detectable change. Under high-ambient oxygen concentrations, the observed effect of flow on A. agaricites was reversed: photosynthetic efficiencies showed a significant 11% decrease from 0.236 (± 0.056) in still water to 0.211 (± 0.048) in 15 cm s^sup -1^ flow. These results support the hypothesis that water motion helps to remove oxygen from coral tissues during periods of maximal photosynthesis. Flow mitigation of oxidative stress may at least partially explain the increased incidence and severity of coral bleaching in low flow areas and observations of enhanced recovery in high-flow areas.[PUBLICATION ABSTRACT]

Ecologically dominant species often define ecosystem states, but as human disturbances intensify, their subordinate counterparts increasingly displace them. We consider the duality of disturbance by examining how environmental drivers can simultaneously act as a stressor to dominant species and as a resource to subordinates. Using a model ecosystem, we demonstrate that CO2-driven interactions between species can account for such reversals in dominance; i.e., the displacement of dominants (kelp forests) by subordinates (turf algae). We established that CO2 enrichment had a direct positive effect on productivity of turfs, but a negligible effect on kelp. CO2 enrichment further suppressed the abundance and feeding rate of the primary grazer of turfs (sea urchins), but had an opposite effect on the minor grazer (gastropods). Thus, boosted production of subordinate producers, exacerbated by a net reduction in its consumption by primary grazers, accounts for community change (i.e., turf displacing kelp). Ecosystem collapse, therefore, is more likely when resource enrichment alters competitive dominance of producers, and consumers fail to compensate. By recognizing such duality in the responses of interacting species to disturbance, which may stabilize or exacerbate change, we can begin to understand how intensifying human disturbances determine whether or not ecosystems undergo phase shifts.

To elucidate the determinants of intertidal invertebrate body temperatures during aerial exposure, I developed deterministic models using the environmental inputs of solar radiation, air temperature, ground temperature, and wind speed to predict the body temperatures of intertidal mussels (Mytilus spp.). Combined with field studies, these models were used to determine the effects of body size on body temperature, and to compare the heat budgets of mussels living as solitary individuals vs. those living in aggregations (beds). On average, the model accurately predicted the body temperatures of solitary mussels in the field to within ∼1⚬C. Steady-state simulations (using constant environmental conditions) predicted that, under conditions where evaporative water loss is limited, smaller (5 cm) mussels experience lower body temperatures than larger (10 cm) mussels exposed to identical environmental parameters. When evaporative cooling is limited only by intolerance to desiccation, the trend in body size reversed due to a disproportionately greater amount of tissue (per unit length) in larger mussels, which provides them with a greater reservoir of water available for evaporative cooling. In both scenarios, larger mussels display a greater \"thermal inertia\" (time constant of change), which buffers them against rapid changes in environmental conditions. No one environmental factor controls body temperature, and thus measurements of single environmental parameters such as air temperature are very unlikely to serve as accurate indicators of mussel body temperature. Results of unsteady simulations (using fluctuating environmental conditions) further indicated a significant effect of the spectral characteristics of the physical environment on body temperature. In many cases predictions of body temperature based only on daily means or extremes of environmental parameters are off by 6⚬C or more due to the time dependence of the system. Models of body temperature must therefore be based upon repeated measurements of multiple environmental parameters, rather than simple statistical measures such as daily mean, maximum, or range. Significantly, several parameters in the model presented here are modified by the proximity of neighboring organisms, including predators and competitors. During extreme environmental conditions (using steady-state conditions), mussels living in beds are predicted to experience substantially lower (4⚬-5⚬C) body temperatures than those living in gaps. Furthermore, living within an aggregation also augments a mussel's thermal inertia, which dampens the effects of rapid temporal changes in the physical environment. In contrast to most previous studies in rocky intertidal habitats, results thus suggest that \"physical factors\" are not immutable boundaries imposed by the environment, but may be significantly altered by the organism itself through its size, morphology, and interactions with neighbors, which may create feedback loops between abiotic and biotic controls.

We present a Dynamic Energy Budget (DEB) model for the quintessential keystone predator, the rocky-intertidal sea star Pisaster ochraceus. Based on first principles, DEB theory is used to illuminate underlying physiological processes (maintenance, growth, development, and reproduction), thus providing a framework to predict individual-level responses to environmental change. We parameterized the model for P. ochraceus using both data from the literature and experiments conducted specifically for the DEB framework. We devoted special attention to the model's capacity to (1) describe growth trajectories at different life-stages, including pelagic larval and post-metamorphic phases, (2) simulate shrinkage when prey availability is insufficient to meet maintenance requirements, and (3) deal with the combined effects of changing body temperature and food supply. We further validated the model using an independent growth data set. Using standard statistics to compare model outputs with real data (e.g. Mean Absolute Percent Error, MAPE) we demonstrated that the model is capable of tracking P. ochraceus' growth in length at different life-stages (larvae: MAPE = 12.27%; post-metamorphic, MAPE = 9.22%), as well as quantifying reproductive output index. However, the model's skill dropped when trying to predict changes in body mass (MAPE = 24.59%), potentially because of the challenge of precisely anticipating spawning events. Interestingly, the model revealed that P. ochraceus reserves contribute little to total biomass, suggesting that animals draw energy from structure when food is limited. The latter appears to drive indeterminate growth dynamics in P. ochraceus. Individual-based mechanistic models, which can illuminate underlying physiological responses, offer a viable framework for forecasting population dynamics in the keystone predator Pisaster ochraceus. The DEB model herein represents a critical step in that direction, especially in a period of increased anthropogenic pressure on natural systems and an observed recent decline in populations of this keystone species.

We explicitly quantified spatial and temporal patterns in the body temperature of an ecologically important species of intertidal invertebrate, the mussel Mytilus californianus, along the majority of its latitudinal range from Washington to southern California, USA. Using long-term (five years), high-frequency temperature records recorded at multiple sites, we tested the hypothesis that local \"modifying factors\" such as the timing of low tide in summer can lead to large-scale geographic mosaics of body temperature. Our results show that patterns of body temperature during aerial exposure at low tide vary in physiologically meaningful and often counterintuitive ways over large sections of this species' geographic range. We evaluated the spatial correlations among sites to explore how body temperatures change along the latitudinal gradient, and these analyses show that \"hot spots\" and \"cold spots\" exist where temperatures are hotter or colder than expected based on latitude. We identified four major hot spots and four cold spots along the entire geographic gradient with at least one hot spot and one cold spot in each of the three regions examined Washington—Oregon, Central California, and Southern California). Temporal autocorrelation analysis of year-to-year consistency and temporal predictability in the mussel body temperatures revealed that southern animals experience higher levels of predictability in thermal signals than northern animals. We also explored the role of wave splash at a subset of sites and found that, while average daily temperature extremes varied between sites with different levels of wave splash, yearly extreme temperatures were often similar, as were patterns of predictability. Our results suggest that regional patterns of tidal regime and local pattern of wave splash can overwhelm those of large-scale climate in driving patterns of body temperature, leading to complex thermal mosaics of temperature rather than simple latitudinal gradients. A narrow focus on population changes only at range margins may overlook climatically forced local extinctions and other population changes at sites well within a species range. Our results emphasize the importance of quantitatively examining biogeographic patterns in environmental variables at scales relevant to organisms, and in forecasting the impacts of changes in climate across species ranges.