Assessing anthropogenic pressures on coastal marine ecosystems using stable CNS isotopes: State of the art, knowledge gaps, and community-scale perspectives

Abstract

In recent decades, the analysis of carbon, nitrogen and sulfur stable isotopes (SIA) has emerged as a powerful, viable methodology for examining food web structure and dynamics, as well as addressing a number of applied issues. Here, we provide a state-of-the-art review of the use of SIA for assessing anthropogenic pressures on natural ecosystems, in order to establish current knowledge gaps and identify promising applications for evaluating the ecological status of marine coastal waters. Specifically, the potential of SIA to provide food web-scale indicators for estimating cumulative anthropogenic pressures is addressed. The review indicates that the methodology has been used for virtually the whole spectrum of human pressures known to influence marine ecosystems. However, only the effects of chemical pollution, release of dissolved and particulate nutrients, and invasive species have been extensively investigated. For the first two pressures, substantial efforts have been made to implement isotopic quantitative approaches and metrics for inter-system comparisons; however, with the exception of nutrient release, the majority of aquatic studies have been carried out in freshwater systems, and only limited information is available on marine environments. In particular, the effects of invasive species on coastal habitats have received scant attention. Trophic position of indicator species emerges as the isotopic metric most ubiquitously adopted for measuring the impact of anthropogenic pressures. Conversely, the application of other recently implemented metrics, proven to be highly effective in integrating information on the spatial-temporal dynamics of aquatic food webs, is to date still limited. The potential of stable isotope analysis to provide a unifying methodological-theoretical framework for effective, inter-ecosystem comparisons of both single and multiple anthropogenic pressures is emphasised. Additionally, a plea for the implementation and intercalibration of community-scale isotopic metrics is made, in order to provide useful tools and indicators for current and future environmental legislative initiatives.