Ocean acidification (OA), a consequence of anthropogenic carbon dioxide emissions, poses a serious threat to marine organisms in tropical, open-ocean, coastal, deep-sea, and high-latitude sea ecosystems. The diversity of taxonomic groups that precipitate calcium carbonate from seawater are at particularly high risk. Here we review the rapidly expanding literature concerning the biological and ecological impacts of OA on calcification, using a cross-scale, process-oriented approach. In comparison to calcification, we find that areas such as fertilization, early life-history stages, and interaction with synergistic stressors are understudied. Although understanding the long-term consequences of OA are critical, available studies are largely short-term experiments that do not allow for tests of long-term acclimatization or adaptation. Future research on the phenotypic plasticity of contemporary organisms and interpretations of performance in the context of current environmental heterogeneity of pCO2 will greatly aid in our understanding of how organisms will respond to OA in the future.

Abstract. Ocean acidification, chemical changes to the carbonate system of seawater, is emerging as a key environmental challenge accompanying global warming and other humaninduced perturbations. Considerable research seeks to define the scope and character of potential outcomes from this phenomenon, but a crucial impediment persists. Ecological theory, despite its power and utility, has been only peripherally applied to the problem. Here we sketch in broad strokes several areas where fundamental principles of ecology have the capacity to generate insight into ocean acidification's consequences. We focus on conceptual models that, when considered in the context of acidification, yield explicit predictions regarding a spectrum of population-and community-level effects, from narrowing of species ranges and shifts in patterns of demographic connectivity, to modified consumer-resource relationships, to ascendance of weedy taxa and loss of species diversity. Although our coverage represents only a small fraction of the breadth of possible insights achievable from the application of theory, our hope is that this initial foray will spur expanded efforts to blend experiments with theoretical approaches. The result promises to be a deeper and more nuanced understanding of ocean acidification and the ecological changes it portends.

The e ects of ocean acidification (OA) on the structure and complexity of coastal marine biogenic habitat have been broadly overlooked. Here we explore how declining pH and carbonate saturation may a ect the structural complexity of four major biogenic habitats. Our analyses predict that indirect e ects driven by OA on habitat-forming organisms could lead to lower species diversity in coral reefs, mussel beds and some macroalgal habitats, but increases in seagrass and other macroalgal habitats. Available in situ data support the prediction of decreased biodiversity in coral reefs, but not the prediction of seagrass bed gains. Thus, OA-driven habitat loss may exacerbate the direct negative e ects of OA on coastal biodiversity; however, we lack evidence of the predicted biodiversity increase in systems where habitat-forming species could benefit from acidification. Overall, a combination of direct e ects and community-mediated indirect e ects will drive changes in the extent and structural complexity of biogenic habitat, which will have important ecosystem e ects. Supplementary Fig. 1). and species richness in tropical coral reefs (Fig. 1b) leads to the 38 prediction that species richness will decline with expected changes 39 in carbonate chemistry associated with OA (Fig. 1c). 40In mussel beds of the US Pacific Northwest, the percentage of 41 cover of large Mytilus mussels is projected to decline with declining 42 pH, to be replaced by species that lack the structural complexity

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The pteropod Limacina helicina frequently experiences seasonal exposure to corrosive conditions (Ωar  < 1) along the US West Coast and is recognized as one of the species most susceptible to ocean acidification (OA). Yet, little is known about their capacity to acclimatize to such conditions. We collected pteropods in the California Current Ecosystem (CCE) that differed in the severity of exposure to Ωar conditions in the natural environment. Combining field observations, high-CO2 perturbation experiment results, and retrospective ocean transport simulations, we investigated biological responses based on histories of magnitude and duration of exposure to Ωar < 1. Our results suggest that both exposure magnitude and duration affect pteropod responses in the natural environment. However, observed declines in calcification performance and survival probability under high CO2 experimental conditions do not show acclimatization capacity or physiological tolerance related to history of exposure to corrosive conditions. Pteropods from the coastal CCE appear to be at or near the limit of their physiological capacity, and consequently, are already at extinction risk under projected acceleration of OA over the next 30 years. Our results demonstrate that Ωar exposure history largely determines pteropod response to experimental conditions and is essential to the interpretation of biological observations and experimental results.

ABSTRACT:The relationship between hydrodynamic energy and biological processes is examined for a kelp-dominated marine community in the San Juan Archipelago. Populations of a common and widely distributed kelp, Nereocystis luetkeana, were established and rates and causes of mortality followed at 7 sites differing greatly in tidally driven current velocities and wave exposure (measured by permanently deployed instrument packages). Mortality of N. luetkeana was not related to storm energy, but exhibited a significant non-linear relationship with tidal current energy such that mortality rates were highest at sites exhibiting protracted periods of calm punctuated by episodes of strong currents. The role of mesograzers (primarily the gastropod Lacuna vincta) on survivorship in these kelp populations was evaluated in the field and in laboratory flume experiments. The relationship between grazer damage and stipe breaking force was investigated by measuring the tensile forces required to break experimentally damaged stipes. Although undamaged stipes can easily withstand the tensile forces imposed by even the strongest current and wave exposures, a very small amount of damage will have highly significant negative effects on breaking strength. While apparently responsible for a significant portion of N. luetkeana mortality in low and variable energy environments, L. vincta is unable to persist on kelp stipes in high-energy environments and its role there is trivial. The relationship between L. vincta grazing and hydrodynamic energy is however nonlinear, because water movement has opposite effects on grazer foraging behavior and the drag forces imposed on kelps, and this results in a complex relationship between hydrodynamic energy and kelp survival. We suggest a conceptual model for relating kelp survival to grazing intensity in hydrodynamically variable environments. The model leads to the prediction, exhibited in our field results, that the probability of plant mortality may be maximized in regions of intermediate flow energy. KEY WORDS: Kelp · Nereocystis · Hydrodynamics · Population dynamics · LacunaResale or republication not permitted without written consent of the publisher

Ecological restoration is widely practiced as a means of rehabilitating ecosystems and habitats that have been degraded or impaired through human use or other causes. Restoration practices now are confronted by climate change, which has the potential to influence long-term restoration outcomes. Concepts and attributes from the resilience literature can help improve restoration and monitoring efforts under changing climate conditions. We systematically examined the published literature on ecological resilience to identify biological, chemical, and physical attributes that confer resilience to climate change. We identified 45 attributes explicitly related to climate change and classified them as individual- (9), population- (6), community- (7), ecosystem- (7), or process-level attributes (16). Individual studies defined resilience as resistance to change or recovery from disturbance, and only a few studies explicitly included both concepts in their definition of resilience. We found that individual and population attributes generally are suited to species- or habitat-specific restoration actions and applicable at the population scale. Community attributes are better suited to habitat-specific restoration at the site scale, or system-wide restoration at the ecosystem scale. Ecosystem and process attributes vary considerably in their type and applicability. We summarize these relationships in a decision support table and provide three example applications to illustrate how these classifications can be used to prioritize climate change resilience attributes for specific restoration actions. We suggest that (1) including resilience as an explicit planning objective could increase the success of restoration projects, (2) considering the ecological context and focal scale of a restoration action is essential in choosing appropriate resilience attributes, and (3) certain ecological attributes, such as diversity and connectivity, are more commonly considered to confer resilience because they apply to a wide variety of species and ecosystems. We propose that identifying sources of ecological resilience is a critical step in restoring ecosystems in a changing climate.

The global environment is changing. Substantial shifts in temperature, rainfall, cloud cover, and UV radiation (UVR) are all predicted as a result of anthropogenic activity. Although the actual and potential effects of changes in single environmental variables are being studied intensively, the interactive effects of multiple stressors have received little attention. Here we offer the first experimental evidence of interactive effects between UVR and temperature on germination and growth in multicellular organisms. To address the question of how temperature affects survival and growth of organisms in the presence of UVR, we exposed early life stages of two species of intertidal algae, Alaria marginata Postels et Ruprecht and Fucus gardneri Silva, to four levels of UVR at three temperatures for 56 h. PAR and day length (12:12‐h light:dark) were held constant across all treatments. UVR levels bracketed natural levels, and temperatures were within the range of ambient temperatures. Designated endpoints were germination rate and cell number, and we recorded mortality where survival was nil. Our results support the hypothesis that temperature mediates the net biological effect of UVR and vice versa. For instance, spores of A. marginata were able to survive and grow at 15° C at all UV levels and at 10° C in the absence of UVR but were unable to survive at 10° C in the presence of high levels of UVR. Our results suggest that the ability to predict the effects of global change hinges on understanding interactions among environmental variables, imposing strict limits on inferences made from single‐factor experiments.