Influence of land-derived stressors and environmental variability on compositional turnover and diversity of estuarine benthic communities

DE Clark,A Berthelsen,A Zaiko,CA Pilditch,JE Hewitt,JI Ellis,F Stephenson,RH Bulmer

doi:10.3354/meps13714

Abstract

It can be challenging to differentiate community changes caused by human activities from the influence of natural background variability. Using gradient forest analysis, we explored the relative importance of environmental factors, operating across multiple spatio-temporal scales, in influencing patterns of compositional turnover in estuarine benthic macroinvertebrate communities across New Zealand. Both land-derived stressors (represented by sediment mud content and total sediment nitrogen and phosphorus content) and natural environmental variables (represented by sea surface temperature, Southern Oscillation Index, and wind-wave exposure) were important predictors of compositional turnover, reflecting a matrix of processes interacting across space and time. Generalized linear models were used to determine whether measures of benthic macroinvertebrate diversity, which are commonly used as indicators of ecological health on a local scale, changed in a way that was consistent with the compositional turnover along the environmental gradient. As expected, compositional turnover along land-derived stressor gradients was negatively associated with diversity indices, suggesting a decline in ecological health as land-derived stressors increase. This study moves towards an ecosystem-based management approach that focusses on cumulative effects rather than single stressors by considering how multiple land-derived stressors influence indicators of estuarine health, against a background of natural variability across several spatio-temporal scales.

Highlights

Understanding the influence of human activities on coastal ecosystems requires the separation of natural and anthropogenic sources of environmental variability
We used generalized linear models (GLMs) to determine whether measures of benthic macroinvertebrate diversity, which are commonly used as indicators of ecological health on a local scale, changed in a way that was consistent with the compositional turnover along the environmental gradient
We have demonstrated that both land-derived stressors and natural environmental variables were important predictors of compositional turnover in estuarine benthic macroinvertebrate communities across New Zealand, reflecting a matrix of processes operating across multiple spatio-temporal scales

Summary

Introduction

Understanding the influence of human activities on coastal ecosystems requires the separation of natural and anthropogenic sources of environmental variability. The impact of human activities is often assessed using benthic macroinvertebrate communities because they cover numerous trophic levels, exhibit different stress-tolerances, and can integrate the effects of multiple stressors over time (Pearson & Rosenberg 1978, Dauer 1993, Borja et al 2000) These animals are an important component of estuarine systems, playing essential roles in ecosystem structure and function (e.g. nutrient cycling, energy transfer to higher trophic levels, sediment stabilization; Snelgrove 1997, Levin et al 2001, Lohrer et al 2004). Many of these stressors are diffuse, operating in incremental stages and often over broad scales, land-derived stressors like sedimentation and nutrient loading

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Discussion

Conclusion