Evaluating deep-sea communities' susceptibility to mining plumes using shallow-water data.

Increased suspended sediment concentrations (SSC) are a major stressor across aquatic habitats. Here, the literature was synthesized to show that animal responses to increases in relative SSC (test concentration/natural background concentration) were similar in type and negative across different shallow-water (marine, estuarine, freshwater) habitats. Further, animal sensitivities are similar across habitats based on relative SSC and occur starting at low relative SSC increases in all habitats despite differences in natural background SSC. Based upon these similarities in relative SSC sensitivities, deep-sea sensitivity values for acute exposure to increased SSC, where empirical data are almost non-existent, were estimated. Because of the low natural SSC in deep sea environments, very small increases in absolute SSC could result in acute effects. How the methods and results can be used to inform regulatory thresholds are discussed. Because of the large variability in shallow water datasets and differences between deep-sea and shallow-water habitats, deep-sea specific data are needed to verify the estimates and improve their precision. Following the precautionary principle and the results presented here, it is recommended that the threshold for acute plume impacts is set very close to natural background levels.

Synergistic interactions among growing stressors increase risk to an Arctic ecosystem.

Oceans provide critical ecosystem services, but are subject to a growing number of external pressures, including overfishing, pollution, habitat destruction, and climate change. Current models typically treat stressors on species and ecosystems independently, though in reality, stressors often interact in ways that are not well understood. Here, we use a network interaction model (OSIRIS) to explicitly study stressor interactions in the Chukchi Sea (Arctic Ocean) due to its extensive climate-driven loss of sea ice and accelerated growth of other stressors, including shipping and oil exploration. The model includes numerous trophic levels ranging from phytoplankton to polar bears. We find that climate-related stressors have a larger impact on animal populations than do acute stressors like increased shipping and subsistence harvesting. In particular, organisms with a strong temperature-growth rate relationship show the greatest changes in biomass as interaction strength increased, but also exhibit the greatest variability. Neglecting interactions between stressors vastly underestimates the risk of population crashes. Our results indicate that models must account for stressor interactions to enable responsible management and decision-making.