Abstract
The increasing number and diversity of anthropogenic stressors in marine habitats have multiple negative impacts on biological systems, biodiversity and ecosystem functions. Methods to assess cumulative effects include experimental manipulations, which may identify non-linear responses (i.e. synergies, antagonisms). However, experiments designed to test these ideas are uncommon, generally focusing on single biological responses. We conducted a manipulative experiment to investigate the isolated and combined effects of warming (+ 6 °C), salinity variation (freshwater pulses or presses), and nutrient enrichment (natural or enriched) following one and three month’s exposure, on responses measured at multiple levels of biological complexity in a simple bivalve assemblage. More specifically, we determined effects on bivalve mortality, growth, shell mineralization, and energy content, as well as microphytobenthos biomass. Salinity variation and nutrient enrichment, individually and combined, caused strong impacts on some of the measured variables and their effect varied through time. In contrast, warming had no effect. Our work highlights the prevalence of antagonistic interactions, the importance of examining effects of single and multiple stressors through time, and of considering multiple responses to understand the complexity behind stressor interactions.
Highlights
The increasing number and diversity of anthropogenic stressors in marine habitats have multiple negative impacts on biological systems, biodiversity and ecosystem functions
Chlorophyll a concentration in the upper sediment layer was less than 5 μg g −1 dry sediment across all treatments but increased when affected by freshwater presses over time, as indicated by the significant Exposure time × Salinity interaction (Fig. 1, Table 2)
This demonstrates a dominance of freshwater presses through time, as indicated by the significantly greater chlorophyll a concentration after three months exposure to presses and that chlorophyll a concentration did not vary over time under the effect of freshwater pulses
Summary
The increasing number and diversity of anthropogenic stressors in marine habitats have multiple negative impacts on biological systems, biodiversity and ecosystem functions. Human activities (e.g. agriculture, fishing, coastal development) together with anthropogenically induced global climate change (e.g. warming) are provoking profound and irreversible changes in coastal marine ecosystems through the emergence of multiple stressors, such as organic pollution, elevated temperature, and salinity changes[6]. Such stressors impact biological processes, alter ecosystem functions, and decrease global and local biodiversity[4,7,8,9]. In the context of multiple stressors, identifying synergistic and antagonistic interactions is of particular importance to inform management decisions since they may affect ecosystem responses to interventions[18]. Antagonistic interactions may lead to overall negative effects if all stressors are not addressed together
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