Infectious diseases are common in marine environments, but the effects of a changing climate on marine pathogens are not well understood. Here we review current knowledge about how the climate drives host-pathogen interactions and infectious disease outbreaks. Climate-related impacts on marine diseases are being documented in corals, shellfish, finfish, and humans; these impacts are less clearly linked for other organisms. Oceans and people are inextricably linked, and marine diseases can both directly and indirectly affect human health, livelihoods, and well-being. We recommend an adaptive management approach to better increase the resilience of ocean systems vulnerable to marine diseases in a changing climate. Land-based management methods of quarantining, culling, and vaccinating are not successful in the ocean; therefore, forecasting conditions that lead to outbreaks and designing tools/approaches to influence these conditions may be the best way to manage marine disease.

The prevalence and severity of marine diseases have increased over the last 20 years, significantly impacting a variety of foundation and keystone species. One explanation is that changes in the environment caused by human activities have impaired host resistance and/or have increased pathogen virulence. Here, we report evidence from field experiments that nutrient enrichment can significantly increase the severity of two important Caribbean coral epizootics: aspergillosis of the common gorgonian sea fan Gorgonia ventalina and yellow band disease of the reef‐building corals Montastraea annularis and M. franksii. Experimentally increasing nutrient concentrations by 2–5× nearly doubled host tissue loss caused by yellow band disease. In a separate experiment, nutrient enrichment significantly increased two measures of sea fan aspergillosis severity. Our results may help explain the conspicuous patchiness of coral disease severity, besides suggesting that minimizing nutrient pollution could be an important management tool for controlling coral epizootics.

Worldwide, many species are responding to ongoing climate change with shifts in distribution, abundance, phenology, or behavior. Consequently, naturalresource managers face increasingly urgent conservation questions related to biodiversity loss, expansion of invasive species, and deteriorating ecosystem services. We argue that our ability to address these questions is hampered by the lack of explicit consideration of species' adaptive capacity (AC). AC is the ability of a species or population to cope with climatic changes and is characterized by three fundamental components: phenotypic plasticity, dispersal ability, and genetic diversity. However, few studies simultaneously address all elements; often, AC is confused with sensitivity or omitted altogether from climate-change vulnerability assessments. Improved understanding, consistent definition, and comprehensive evaluations of AC are needed. Using classic ecological-niche theory as an analogy, we propose a new paradigm that considers fundamental and realized AC: the former reflects aspects inherent to species, whereas the latter denotes how extrinsic factors constrain AC to what is actually expressed or observed. Through this conceptualization, we identify ecological attributes contributing to AC, outline areas of research necessary to advance understanding of AC, and provide examples demonstrating how the inclusion of AC can better inform conservation and natural-resource management.

Life-history theory suggests that trade-offs exist between fitness components, with organisms balancing investment in reproduction against survival and future reproduction. This study examined the influence of stress on physiological trade-offs in the dominant rocky intertidal mussel Mytilus californianus on the central Oregon coast, USA. The intertidal zone is a highly heterogeneous thermal environment that could lead to intrapopulation variation in stress responses. Stress increases along a vertical gradient, with higher physical stress occurring in the higher intertidal zone, both due to reduced feeding time and longer exposure to aerial conditions. Reproduction and carotenoid content were compared in mussels from the low and high vertical edges of the mussel bed. High-edge mussels invested less relative energy in reproduction and also spawned all of their gametes in the early summer, whereas low-edge mussels continuously spawned small batches of gametes throughout the year. Highedge mussels accumulated high concentrations of carotenoid pigments into their gonadal tissues, potentially to protect gametes from damaging oxidative stress experienced during aerial exposure. A reciprocal transplant experiment revealed plastic responses in growth and reproduction to increased stress. In contrast, carotenoid content did not increase in response to stress, suggesting that carotenoids may not change rapidly or may not be easily lost or gained. Our results indicate that mussels exhibit physiological trade-offs and, under increased stress predicted from climate change scenarios, may allocate energy away from reproduction toward costly physiological defenses.