Abstract
Stressors associated with global change will be experienced simultaneously and may act synergistically, so attempts to estimate the capacity of marine systems to cope with global change requires a multi-stressor approach. Because recent evidence suggests that stressor effects can be context-dependent, estimates of how stressors are experienced in ecologically realistic settings will be particularly valuable. To enhance our understanding of the interplay between environmental effects and the impact of multiple stressors from both natural and anthropogenic sources, we conducted a field experiment. We explored the impact of multiple, functionally varied stressors from both natural and anthropogenic sources experienced during early life history in a common sessile marine invertebrate, Bugula neritina. Natural spatial environmental variation induced differences in conspecific densities, allowing us to test for density-driven context-dependence of stressor effects. We indeed found density-dependent effects. Under high conspecific density, individual survival increased, which offset part of the negative effects of experiencing stressors. Experiencing multiple stressors early in life history translated to a decreased survival in the field, albeit the effects were not as drastic as we expected: our results are congruent with antagonistic stressor effects. We speculate that when individual stressors are more subtle, stressor synergies become less common.
Highlights
Global changes, such as anthropogenic climate change, environmental pollution, or trophic shifts in communities, challenge our marine environments by novel stressors or unprecedented stressor levels[1, 2]
This is likely driven by an urgency to predict and potentially mitigate climate change, which often triggers multiple stressors[3, 6]
Individuals in the control group survived best, those exposed to multiple stressors survived least
Summary
Global changes, such as anthropogenic climate change, environmental pollution, or trophic shifts in communities, challenge our marine environments by novel stressors or unprecedented stressor levels[1, 2]. Most benthic marine invertebrates are adapted to commonly experienced ranges of these variables, for instance temperature can increase fitness when experienced within optimum ranges[9, 10] These common environmental variables only become stressors when experienced within pessimum ranges where energy is required to maintain metabolic functions[11]. Salinity and temperature has been the most commonly studied stressor pair in studies on marine invertebrates, with Crain et al.[5] detecting mostly antagonistic interactions on stressor responses, and Przeslawski et al.[7] detecting synergistic interactions. Perhaps their different findings where shaped by including studies focusing on different life history stages and phyla. While stressor responses appear to be highly plastic and context-dependent[5, 7, 8, 35], synergism appears to become the prevalent response when more than two stressors are tested[5]
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