Cumulative effects of multiple anthropogenic stressors on the health of an intertidal clam (Austrovenus stutchburyi)

Abstract

Worldwide pressures arising from anthropogenic activities are causing the degradation of estuarine soft-sediment ecosystems. Among the most prominent stressors are sedimentation, nutrient enrichment and trace metal contamination, which often co-occur causing non-linear ecosystem responses (i.e., antagonisms and synergisms). Bivalves play key roles in estuarine soft-sediment ecosystems and are commonly used as bioindicators of health due to their ecological importance and sensitivity to environmental change. Therefore, understanding the combined effects of stressors on bivalve populations is critical for informing coastal management and restoration efforts, but to date, any potential interactions between these stressors are yet to be investigated in situ. To address this knowledge gap, a survey of the New Zealand infaunal bivalve, Austrovenus stutchburyi , was undertaken along a spatial gradient of sedimentation, nutrient enrichment and metal contamination across 19 sites. Distance-based linear models and generalised linear models were used to determine relationships between health parameters (population density, size and condition), and environmental variables, and to examine any potential stressor interaction patterns. Key findings were: (1) A. stutchburyi responded either negatively or positively to multiple stressors, depending on the response metric and the specific stressors involved (2) the majority of pairwise stressor combinations showed patterns consistent with additive effects (3) sedimentation (using sediment mud content and water column turbidity as proxies) was associated with nonlinear responses when combined with other stressors. This study highlights the value of conducting real-world, context and site-specific multiple stressor research to inform best management of coastal stressors and restoration efforts of important bivalve species.