Closely cropped algal turfs support key ecosystem functions on healthy coraldominated reefs, yet how this important reef component is affected by sedimentation, a key stressor on reefs worldwide, is relatively unknown. We used a 2-factor caging experiment to evaluate the effects of varying sediment depth and presence of herbivorous fish on algal turf height on a fringing reef in Mo'orea, French Polynesia. Without herbivory, 2 mm of sediment reduced turf growth by ~50% compared to sediment removal treatments; in contrast, growth with 4 mm of sediment was low or negligible regardless of herbivory treatment. Negative effects of sediment were linked to the development of black basal layers of sediment, indicating accumulation of hydrogen sulfide. Black sediment occurred in 60 to 70% of all 4 mm plots and in 43% of caged 2 mm plots but was not found in open 2 mm plots, implying that grazing ameliorated development of black sediment under 2 mm loads. Sediment levels of 2 mm did not deter herbivory, evidenced by the significant decrease in turf height in open compared to caged plots. Under 4 mm of sediment, black sediment inhibited both growth and herbivory where it occurred. Without black sediment, however, fish grazing balanced algal growth, resulting in negligible algal height changes across 4 mm plots but with differing underlying mechanisms. Field surveys on other sedimented reefs with healthy herbivore communities confirmed an increase in the presence of black sediment at depths over 3 mm. Thus, deeper sediment depths inhibit turf growth, yet under moderate levels of sedimentation, intact herbivorous fish communities may maintain closely cropped, healthy turf communities by preventing the negative effects of black sediment.
Biodiversity is intrinsically linked to the health of our planet-and its people. Yet, increasingly, human activities are causing the extinction of species, degrading ecosystems, and reducing nature's resilience to climate change and other threats. As a signatory to the Convention on Biological Diversity, Canada has a legal responsibility to protect 17% of land and freshwater by 2020. Currently, Canada has protected ∼10% of its terrestrial lands, requiring a marked increase in the pace and focus of protection over the next three years.Given the distribution, extent, and geography of Canada's current protected areas, systematic conservation planning would provide decision-makers with a ranking of the potential for new protected area sites to stem biodiversity loss and preserve functioning ecosystems. Here, we identify five key principles for identifying lands that are likely to make the greatest contribution to reversing biodiversity declines and ensuring biodiversity persistence into the future. We identify current gaps and integrate principles of protecting (i) species at risk, (ii) representative ecosystems, (iii) intact OPEN ACCESS
Ecological communities are subjected to multiple anthropogenic stressors at both global and local scales that are increasing in number and magnitude. Stressors can interact in complex ways and are classified as additive, synergistic or antagonistic; the nature of the interaction is key to predicting changes and understanding community resilience. Coral reefs are among the most impacted communities and have shifted from coral‐ to algal‐dominated states, and overfishing, nutrient enrichment and sedimentation are local stressors that often co‐occur and may support degraded algal states. Short algal turfs are abundant benthic space holders on healthy reefs that may be pushed by local stressors to long algal turfs, a more degraded state that may prevent recovery to coral dominance. We conducted a fully crossed three‐factor field experiment on short algal turf communities manipulating herbivory pressure (+/−cages), nutrients (+/−fertilizer) and sediments (natural accumulation/removal). We applied stressors for 16 days, removed them and monitored turf height during and after manipulations. We found that significant pair‐wise interactions between all stressors pushed the community towards a degraded state with longer algal turfs. All three types of interactions (additive, synergistic and antagonistic) were common and occurred in equal frequency, suggesting more investigations into all types are needed to accurately predict community responses to multiple stressors. For example, when herbivores were present, nutrients and sediments interacted additively, while in the absence of herbivores, nutrients and sediments interacted synergistically. All interactions broke down following termination of experimental manipulations and all effects were undetectable after 49 days, indicating that this reef may be resilient, at least when stressors are applied on a short time‐scale. Synthesis. Because management of local stressors is often more tractable than global stressors, local management has been proposed as a means to offset global stressors. However, ecological communities often experience multiple local stressors simultaneously, and interactions between stressors, including synergisms and antagonisms, may be the source of nonlinear shifts in communities or “ecological surprises.” The majority of interactions in our study were both strong and nonlinear, and we suggest that, if pervasive across systems, nonlinear interactions may drive the recent global increase in “ecological surprises.”
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.
Sharks are a taxon of significant conservation concern and associated public interest. The scientific community largely supports management policies focusing on sustainable fisheries exploitation of sharks, but many concerned members of the public and some environmental advocates believe that sustainable shark fisheries cannot and do not exist and therefore support total bans on all shark fisheries and/or trade in shark products. The belief that sustainable shark fisheries cannot and do not exist persists despite scientific evidence showing that they can and do, and are important to livelihoods. Additionally, many concerned members of the public are only aware of one threat to sharks and are unaware of other threats-or of most available policy solutions. Here we assess whether the popular press plays a role in spreading misinformation and misunderstanding about these issues via the agenda-setting, priming, and cultivation roles of the media, with the goal of better understanding the causes and consequences of public confusion.
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