Seaweeds are ecologically important primary producers, competitors, and ecosystem engineers that play a central role in coastal habitats ranging from kelp forests to coral reefs. Although seaweeds are known to be vulnerable to physical and chemical changes in the marine environment, the impacts of ongoing and future anthropogenic climate change in seaweed-dominated ecosystems remain poorly understood. In this review, we describe the ways in which changes in the environment directly affect seaweeds in terms of their physiology, growth, reproduction, and survival. We consider the extent to which seaweed species may be able to respond to these changes via adaptation or migration. We also examine the extensive reshuffling of communities that is occurring as the ecological balance between competing species changes, and as top-down control by herbivores becomes stronger or weaker. Finally, we delve into some of the ecosystem-level responses to these changes, including changes in primary productivity, diversity, and resilience. Although there are several key areas in which ecological insight is lacking, we suggest that reasonable climate-related hypotheses can be developed and tested based on current information. By strategically prioritizing research in the areas of complex environmental variation, multiple stressor effects, evolutionary adaptation, and population, community, and ecosystem-level responses, we can rapidly build upon our current understanding of seaweed biology and climate change ecology to more effectively conserve and manage coastal ecosystems.

ABSTRACT. As oil transportation worldwide continues to increase, many communities are at risk of oil spill disasters and must anticipate and prepare for them. Factors that influence oil spill consequences are myriad and range from the biophysical to the social. We provide a summary literature review and overview framework to help communities systematically consider the factors and linkages that would influence consequences of a potential oil spill. The focus is on spills from oil tanker accidents. Drawing primarily on empirical studies of previous oil spill disasters, we focused on several main domains of interest: the oil spill itself, disaster management, the physical marine environment, marine biology, human health, economy, and policy. Key variables that influence the severity of consequences are identified, and significant interactions between variables are delineated. The framework can be used to clarify the complexity of oil spill impacts, identify lessons that may be transferable from other oil spill disasters, develop scenarios for planning, and inform risk analysis and policy debates in localities that are seeking to understand and reduce their vulnerability to potential spill disasters. As a case study, the framework is used to consider potential oil spills and consequences in Vancouver, Canada. Major increases in oil tanker traffic are anticipated in this region, creating urgent new demands for risk information, disaster management planning, and policy responses. The case study identifies particular conditions that distinguish the Vancouver context from other historic events; in particular, proximity to a densely populated urban area, the type of oil being transported, financial compensation schemes, and local economic structure. Drawing lessons from other oil spill disasters is important but should be undertaken with recognition of these key differences. Some types of impacts that have been relatively inconsequential in previous events may be very significant in a Vancouver case.

While changes in the abundance of keystone predators can have cascading effects resulting in regime shifts, the role of mesopredators in these processes remains underexplored. We conducted annual surveys of rocky reef communities that varied in the recovery of a keystone predator (sea otter, ) and the mass mortality of a mesopredator (sunflower sea star,) due to an infectious wasting disease. By fitting a population model to empirical data, we show that sea otters had the greatest impact on the mortality of large sea urchins, but that decline corresponded to a 311% increase in medium urchins and a 30% decline in kelp densities. Our results reveal that predator complementarity in size-selective prey consumption strengthens top-down control on urchins, affecting the resilience of alternative reef states by reinforcing the resilience of kelp forests and eroding the resilience of urchin barrens. We reveal previously underappreciated species interactions within a 'classic' trophic cascade and regime shift, highlighting the critical role of middle-level predators in mediating rocky reef state transitions.

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