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Abstract. Body size plays a crucial role in determining the strength of species interactions, population dynamics, and community structure. We measured how changes in body size affect the trophic relationship [...]

Although the establishment and spread of non-indigenous species depends upon survival in the face of novel environmental conditions and novel biological interactions, relatively little attention has been focused on the specific role of native predators in limiting invasion success. The European common periwinkle, Littorina littorea, was recently introduced to the Pacific coast of Canada and provides a case study of an introduction into an area with an important predator guild (sea stars) that is functionally minor in the invader's native habitat. Here, we assess the likelihood of establishment, spread, and negative ecological impact of this introduced gastropod, with an emphasis on the role of native sea stars as agents of biotic resistance. Size frequency distributions and local market availability suggest that L. littorea was most likely introduced via the live seafood trade. Non-native hitchhikers (e.g., the trematode Cryptocotyle lingua) were found on/in both market and field specimens. Laboratory studies and field observations confirmed that L. littorea can survive seasonal low salinity in Vancouver, British Columbia. Periwinkles also readily consumed native Ulva, suggesting that periwinkles could impact native communities via herbivory or resource competition. Unlike native gastropods, however, L. littorea lacked behavioural avoidance responses to Northeast Pacific predatory sea stars (Pisaster ochraceus and Pycnopodia helianthoides), and sea star predation rates on L. littorea were much higher than predation rates on native turban snails (Chlorostoma funebralis) in common garden experiments. We therefore expect periwinkle establishment in British Columbia to be limited to areas with low predator density, as is seen in its field distribution to date. We caution that this conclusion may understate the importance of the L. littorea introduction if it also serves as a vector for additional non-indigenous species such as C. lingua., Introduction To establish and spread in a novel habitat, a non-indigenous species must survive several filters: conditions during transport, abiotic conditions in the new habitat, and biological interactions with novel [...]

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 they don't, and they are generally difficult to predict. In contrast, extreme ecological events are often compound events, resulting from the chance coincidence of run-of-the-mill factors. Here we present an environmental bootstrap method for resampling short-term environmental data (rolling the environmental dice) to calculate an ensemble of hypothetical time series that embodies how the physical environment could potentially play out differently. We use this ensemble in conjunction with mechanistic models of physiological processes to analyze the biological consequences of environmental extremes. Our resampling method provides details of these consequences that would be difficult to obtain otherwise, and our methodology can be applied to a wide variety of ecological systems. Here, we apply this approach to calculate return times for extreme hydrodynamic and thermal events on intertidal rocky shores. Our results demonstrate that the co-occurrence of normal events can indeed lead to environmental extremes, and that these extremes can cause disturbance. For example, the limpet Lottia gigantea and the mussel Mytilus californianus are co-dominant competitors for space on wave-swept rocky shores, but their response to extreme environmental events differ. Limpet mortality can vary drastically through time. Average yearly maximum body temperature of L. gigantea on horizontal surfaces is low, sufficient to kill fewer than 5% of individuals, but on rare occasions environmental factors align by chance to induce temperatures sufficient to kill >99% of limpets. In contrast, mussels do not exhibit large temporal variation in the physical disturbance caused by breaking waves, and this difference in the pattern of disturbance may have ecological consequences for these competing species. The effect of environmental extremes is under added scrutiny as the frequency of extreme events increases in response to anthropogenically forced climate change. Our method can be used to discriminate between chance events and those caused by long-term shifts in climate. Key words: disturbance and extreme events; ecological surprises; enviromental and thermal stress; envrionmental bootstrap; hydrodynamic forces; intertidal rocky shores; limpets; Lottia gigantea mussels; Mytilus californianus; patch dynamics; statistics of extremes.

Ecological responses to climate change may occur gradually with changing conditions, or they may occur rapidly once some threshold or 'tipping point' has been reached. Here, we use a high-resolution, 30-year data set on the upper vertical limit of a high intertidal alga to demonstrate that distributional shifts in this species do not keep pace with gradual trends in air temperature or sea level, but rather occur in sudden, discrete steps. These steps occur when unusually warm air temperatures are associated with unusually calm seas and are contingent in the sense that neither atmospheric nor sea conditions by themselves were sufficient to generate the underlying physiological challenge. Shifts in the upper limit did not correlate with large environmental perturbations such as El Ninos; rather, they appeared to be associated with stochastic departures from otherwise gradual environmental trends. Our results exemplify the view that multiple environmental factors should be considered when attempting to understand ecological responses to climate change. Furthermore, punctuated responses such as those we have identified urge caution when attempting to infer causal mechanisms and project future distributional shifts using data of limited temporal resolution or scope. Mazzaella parksii | intertidal zonation | range shift | sea level | temperature

Anthropogenic climate change poses a serious threat to biodiversity. In marine environments, multiple climate variables, including temperature and C[O.sub.2] concentration ([C[O.sub.2]]), are changing simultaneously. Although temperature has well-documented ecological effects, and many heavily calcified marine organisms experience reduced growth with increased [C[O.sub.2]], little is known about the combined effects of temperature and [C[O.sub.2]], particularly on species that are less dependent on calcified shells or skeletons. We manipulated water temperature and [C[O.sub.2]] to determine the effects on the sea star Pisaster ochraceus, a keystone predator. We found that sea star growth and feeding rates increased with water temperature from 5[degrees]C to 21[degrees]C. A doubling of current [C[O.sub.2]] also increased growth rates both with and without a concurrent temperature increase from 12[degrees]C to 15[degrees]C. Increased [C[O.sub.2]] also had a positive but nonsignificant effect on sea star feeding rates, suggesting [C[O.sub.2]] may be acting directly at the physiological level to increase growth rates. As in past studies of other marine invertebrates, increased [C[O.sub.2]] reduced the relative calcified mass in sea stars, although this effect was observed only at the lower experimental temperature. The positive relationship between growth and [C[O.sub.2]] found here contrasts with previous studies, most of which have shown negative effects of [C[O.sub.2]] on marine species, particularly those that are more heavily calcified than P. ochraceus. Our findings demonstrate that increased [C[O.sub.2]] will not have direct negative effects on all marine invertebrates, suggesting that predictions of biotic responses to climate change should consider how different types of organisms will respond to changing climatic variables. calcification | climate change | feeding rate | ocean acidification | Pisaster ochraceus

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. Key words: biogeography; climate change; intertidal; mussel; Mytilus californianus; signal analysis; temperature; thermal stress; U.S. Pacific Coast.

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, empirical measurements of the scales of ecologically important variables are still rare. Here, we measure the spatial and temporal scales of variability of 15 ecologically relevant physical and biological processes in the wave-swept intertidal zone at Mussel Point, near Hopkins Marine Station in California. We analyze temporal variability in wave height, ocean temperature, upwelling intensity, solar irradiance, and body temperature for periods ranging from ten minutes to fifty years. In addition, we measure spatial variation in shoreline topography, wave force, wave-induced disturbance, body temperature, species diversity, recruitment, primary productivity, and the abundances of grazers, predators, and the competitive dominant occupier of space. Each of these spatial variables is measured along three horizontal transects in the upper intertidal zone: a short transect (44 m long with sampling locations spaced at ~0.5-m intervals), a medium transect (175 m long with sampling locations spaced at ~1.7-m intervals), and a long transect (334 m long with sampling locations spaced at ~3.4-m intervals). Six different methods are used to quantify the scale of each variable. Distinct scales are evident in all but one of our temporal variables, demonstrating that our methods for quantifying scale can work effectively with relatively simple, periodic phenomena. However, our spatial results reveal basic problems that arise when attempting to measure the scale of variability for more complex phenomena. For a given variable and length of transect, different methods of calculating scale seldom agree, and in some cases estimates differ by more than an order of magnitude. For a given variable and method of calculating spatial scale, measurements are sensitive to the length of a transect; the longer the transect, the larger the estimate of scale. We propose that the 'l/f noise' nature of the data can explain both the variability among methods for calculating scale and the length dependence of spatial scales of variation, and that the 1/f noise character of the data may be driven by the fractal geometry of shoreline topography. We conclude that it may not be possible to define a meaningful spatial scale of variation in this system. As an alternative to the boiled-down concept of 'scale,' we suggest that it is more appropriate to examine explicitly the pattern in which variability changes with the extent of measurement (e.g., the spectrum). Knowledge of this pattern can provide useful ecological scaling 'rules' even when a well-defined scale (or hierarchy of scales) cannot be discerned. Key words: 1/f noise; California; rocky intertidal ecology; scale; scaling; spatial pattern; spatial statistics; spectral analysis; temporal pattern; wave exposure.

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.

Range boundaries are a fundamental expression of a species' relationship with other species and with the abiotic environment. In this study, I examined the roles of biotic and abiotic factors in setting the local range limits of Mazzaella parksii (formerly Mazzaella cornucopiae). In Washington State, this turf-forming red alga occurs almost exclusively in a discrete high intertidal band on north-facing, wave-exposed shores. I investigated the mechanisms underlying these distributional patterns via a series of intra- and extra-limital transplant experiments coupled with manipulations of interacting species and abiotic stress. The upper limit of Mazzaella was set by physiological stress; turfs transplanted above the natural Mazzaella zone bleached and died over the course of a few months. Mazzaella's lower limit was set by herbivory; turfs transplanted below the natural zone were consumed in treatments accessible to grazers but thrived in herbivore-exclusion plots. South-facing transplants at the same intertidal height as the natural north-facing Mazzaella zone declined regardless of interspecific interactions, indicating that Mazzaella's upper limit is lower on south-facing shores. However, the position of the herbivore-determined lower limit was similar between aspects. South-facing transplants could survive below the natural Mazzaella zone if the grazer-determined lower limit was extended downshore by herbivore exclusions or at Mazzaella's natural intertidal height (i.e., the height at which it persists on north-facing surfaces) if the physiologically determined upper limit was extended upshore by experimental shades. In the absence of such experimental modifications, Mazzaella was effectively excluded from south-facing shores because its upper limit had converged on its lower limit. Thus, abiotic factors and biological factors interact to set the horizontal distributional limits of this alga. This conceptual model is consistent with Mazzaella's distribution at a variety of spatial scales and has broad implications for both spatial patterns and temporal trends in the distribution and abundance of species. Key words: desiccation; herbivory; intertidal height; Lottia spp.; Mazzaella parksii; range limits; species-specific responses; substrate aspect; transplant experiment; zonation.

Light availability and consumer pressure are fundamental factors that structure aquatic communities, but their integrated effects are rarely studied in marine benthic systems. Using a factorial experiment, I investigated the effects of light availability and grazing by limpets (Lottia digitalis) to determine the relative influence of each on the growth and abundance of producers and consumers in a rocky intertidal community during the winter. Light reduction via shading reduced the abundance of filamentous algae and reduced the abundance of the herbivorous periwinkle Littorina sitkana. The effects of limpet grazing reduced the abundance of filamentous algae, Porphyra spp., and diatom mats. Higher limpet densities were also associated with significantly lower densities of adult, but not juvenile, Littorina spp. Light and limpet density interacted to determine Lottia growth, which was high in unshaded, single-limpet enclosures but was negligible in plots with two limpets, shades, or both. Variation in bottom-up (resource-driven) and top-down (consumer-driven) forces are important determinants of abundance at both trophic levels, but the effects are complex, taxon-specific, and, for littorine snails, size-specific. Because the study species accomplish most of their growth and reproduction during the winter, the interplay of light and herbivory during this season will likely influence long-term community dynamics.

The interaction of climate and the timing of low tides along the West Coast of the United States creates a complex mosaic of thermal environments, in which northern sites can be more thermally stressful than southern sites. Thus, climate change may not lead to a poleward shift in the distribution of intertidal organisms, as has been proposed, but instead will likely cause localized extinctions at a series of 'hot spots.' Patterns of exposure to extreme climatic conditions are temporally variable, and tidal predictions suggest that in the next 3 to 5 years 'hot spots' are likely to appear at several northern sites., A central goal in exploring the consequences of global climate change is to accurately predict the alteration of thermal stresses on organisms and the subsequent impact of stress on the [...]

Gradients of environmental variability have been proposed to explain spatial variation in patterns of geographical range size. We explore this relationship in NE Pacific algae and NW Atlantic gastropods by using the characteristics of species’ bathymetric distributions as a proxy for tolerance of environmental variability. NE Pacific and NW Atlantic. Data on species bathymetric and geographical distributions were compiled from the literature. For both algae and gastropods, species that inhabit highly seasonal, shallow depth zones have broader latitudinal ranges, and occupy more biogeographical provinces, than species that live in more temporally stable, deeper zones. Furthermore, species that tolerate spatial variability along the bathymetric axis, i.e. those that occur in multiple depth zones, have broader geographical ranges than species restricted to fewer depth zones. Within-range environmental variability, through both space and time, is predictive of large geographical ranges for marine algae and gastropods. Analysis of species distributions across perpendicular gradients (e.g. depth and latitude) is a powerful approach to discerning the mechanisms that govern biogeographical patterns, and provides easily obtainable broad-brush predictions regarding the biogeographical outcomes of global change. [ABSTRACT FROM AUTHOR]

Ocean acidification (OA) driven by anthropogenic CO 2 emissions affects marine ecosystems, fisheries and aquaculture. Assessing the impacts of OA using projection models facilitates the development of future scenarios and potential solutions. Here, we explored various ways to incorporate OA impacts into a multi-stressor dynamic bioclimatic envelope model to project biogeographic changes of ten commercially exploited invertebrate species. We examine three dimensions of uncertainties in modelling biophysical OA effects: model structure, parameterization, and scenario uncertainty. Our results show that projected OA impacts are most sensitive to the choice of structural relationship between OA and biological responses, followed by the choice of climate change emission scenarios and parameterizations of the size of OA effects. Species generally showed negative effects to OA but sensitivity to the various sources of uncertainty were not consistent across or within species. For example, some species showed higher sensitivity to structural uncertainty and very low sensitivity to parameter uncertainty, while others showed greatest sensitivity to parameter uncertainty. This variability is largely due to geographic variability and difference in life history traits used to parameterize model simulations. Our model highlights the variability across the sources of uncertainty and contributes to the development of integrating OA impacts in species distribution models. We further stress the importance of defining the limitations and assumptions, as well as exploring the range of uncertainties associated with modelling OA impacts. [ABSTRACT FROM AUTHOR]

Abstract: Increasing levels of anthropogenic carbon dioxide in the world''s oceans are resulting in a decrease in the availability of carbonate ions and a drop in seawater pH. This process, known as ocean acidification, is a potential threat to marine populations via alterations in survival and development. To date, however, little research has examined the effects of ocean acidification on rare or endangered species. To begin to assess the impacts of acidification on endangered northern abalone (Haliotis kamtschatkana) populations, we exposed H. kamtschatkana larvae to various levels of CO2 [400ppm (ambient), 800ppm, and 1800ppm CO2] and measured survival, settlement, shell size, and shell development. Larval survival decreased by ca. 40% in elevated CO2 treatments relative to the 400ppm control. However, CO2 had no effect on the proportion of surviving larvae that metamorphosed at the end of the experiment. Larval shell abnormalities became apparent in approximately 40% of larvae reared at 800ppm CO2, and almost all larvae reared at 1800ppm CO2 either developed an abnormal shell or lacked a shell completely. Of the larvae that did not show shell abnormalities, shell size was reduced by 5% at 800ppm compared to the control. Overall, larval development of H. kamtschatkana was found to be sensitive to ocean acidification. Near future levels of CO2 will likely pose a significant additional threat to this species, which is already endangered with extinction due in part to limited reproductive output and larval recruitment. [Copyright &y& Elsevier]