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Seagrass meadows are among the most productive and diverse marine ecosystems, providing essential structure, functions, and services. They are also among the most impacted by human activities and in urgent need of better management and protection. In Canada, eelgrass ( Zostera marina) meadows are found along the Atlantic, Pacific, and Arctic coasts, and thus occur across a wide range of biogeographic conditions. Here, we synthesize knowledge of eelgrass ecosystems across Canada’s coasts, highlighting commonalities and differences in environmental conditions, plant, habitat, and community structure, as well as current trends and human impacts. Across regions, eelgrass life history, phenology, and general species assemblages are similar. However, distinct regional differences occur in environmental conditions, particularly with water temperature and nutrient availability. There is considerable variation in the types and strengths of human activities among regions. The impacts of coastal development are prevalent in all regions, while other impacts are of concern for specific regions, e.g., nutrient loading in the Atlantic and impacts from the logging industry in the Pacific. In addition, climate change represents a growing threat to eelgrass meadows. We review current management and conservation efforts and discuss the implications of observed differences from coast to coast to coast.

Plankton communities account for at least half of global primary production and play a key role in the global carbon cycle. Warming and acidification may alter the interaction chains in these communities from the bottom and top of the food web. Yet, the relative importance of these potentially complex interactions has not yet been quantified. Here, we examine the isolated and combined effects of warming, acidification, and reductions in phytoplankton and predator abundances in a series of factorial experiments. We find that warming directly impacts the top of the food web, but that the intermediate trophic groups are more strongly influenced by indirect effects mediated by altered top‐down interactions. Direct manipulations of predator and phytoplankton abundance reveal similar strong top‐down interactions following top predator decline. A meta‐analysis of published experiments further supports the conclusion that warming has stronger direct impacts on the top and bottom of the food web rather than the intermediate trophic groups, with important differences between freshwater and marine plankton communities. Our results reveal that the trophic effect of warming cascading down from the top of the plankton food web is a powerful agent of global change., Plankton communities account for at least half of global primary production and play a key role in the global carbon cycle. Warming and acidification may alter the interaction chains in these communities from the bottom and top of the food web. Here, we examine the isolated and combined effects of warming, acidification, and reductions in phytoplankton and predator abundances in a series of factorial experiments. We find that warming directly impacts the top of the food web, but that the intermediate trophic groups are more strongly influenced by indirect effects mediated by altered top‐down interactions.

The nature of the relationship between diversity and stability has become the subject of intense research effort over the last few decades as the role of diversity as a major driver of ecosystem functioning and stability has come to the forefront of ecological interest. Here, we present a meta-analysis of the impact of twelve experimental design factors on the strength and direction of relations between biotic richness and temporal variability at both the aggregate community- and population-level. Based on 35 studies that report 59 community-level and 36 population-level relations, our results show that biotic richness has a highly general stabilizing effect on community properties that are only marginally affected by the nuances of experimental design. In contrast, experimental design factors have a highly significant effect on mean effect sizes and the resulting interpretation of relations between richness and population-level variability. The strongest dichotomous effect was observed based on the method of calculating the response variable, such that when population variability was calculated as the mean variability of populations across all replicates, biotic richness showed a negative (stabilizing) mean effect size. In contrast, when population variability was calculated on a per replicate basis, biotic richness showed a positive (destabilizing) mean effect size. This latter result suggests that a renewed focus on the mechanisms by which populations can be stabilized (and destabilized) by diversity is needed.

Disturbances often lead to changes in average values of community properties; however, disturbances can also affect the predictability of a community's response. We performed a meta-analysis to determine how response predictability, defined as among-replicate variance in diversity and community abundance, is affected by species removals, species invasions, nutrient addition, temperature increase, and habitat loss/fragmentation, and we further determined whether response predictability differed according to habitat and trophic role. Species removals and nutrient addition decreased response predictability, while species invasions increased response predictability. In aquatic habitats, disturbances generally led to a decrease in response predictability, whereas terrestrial habitats showed no overall change in response predictability, suggesting that differences in food web and ecosystem structure affect how communities respond to disturbance. Producers were also more likely to show decreases in response predictability, particularly following species removals, highlighting widespread destabilizing effects of species loss at the producer level. Overall, our results show that whether disturbances cause changes in response predictability is highly contingent on disturbance type, habitat, and trophic role. The nature of changes in response predictability--for example, strong decreases following species invasions and increases following species removals--will likely play a major role in how communities recover from disturbance.