How does eutrophication impact bundles of ecosystem services in multiple coastal habitats using state-and-transition models

Highlights

• Gradients of eutrophication modify bundles of coastal ecosystem services.

• Nutrient and pathogen regulation as well as cultural services are particularly impacted.

• State-and-transition model is a powerful framework for environmental management.

• Managers can balance the few gains of eutrophication with the losses of ecosystem services.

Abstract

One of the current major scientific challenges to sustain social-ecological systems is to improve our understanding of the spatial and temporal dynamics of the relationships between biodiversity, ecosystem functioning and ecosystem services. Here, we analyse the bundles of ecosystem services supplied by three coastal ecosystems (coastal lagoons, coral reefs and sandy beaches) along a gradient of eutrophication. Based on a state-and-transition model, we analyses the dynamic responses of ecological communities to environmental change and management actions. Although few exceptions are highlighted, increasing eutrophication in the three ecosystem types leads to a degradation of the ecosystem service bundles, particularly for nutrient and pathogen regulation/sequestration, or for the support of recreational and leisure activities. Despite few obstacles to their full use, state-and-transition models can be very powerful frameworks to integrate multiple functions and services delivered by ecosystems while accounting for their temporal dynamics.

Introduction

The demographic and economic growth of societies is increasingly facing the ecological limits of the planet (Meadows et al., 2004). This global ecological crisis, as illustrated by major changes in ecosystem states with decreasing availability of natural resources, is accelerated by climate change. The consequences of this crisis are already observable within societies and will most likely spread and generalize in future decades (Cardinale et al., 2012; Isbell et al., 2017). One of the major scientific challenges for biodiversity conservation is to improve the understanding of the relationships between biodiversity, ecosystem functioning and ecosystem services (ES) to analyse the compatibility and the interdependence between biodiversity conservation objectives and ES maintenance (Harrison et al., 2014).

The ES concept seeks to account for the dependence of human societies on ecosystems, commonly defined as the contributions of ecosystem structure and function to human well-being (MA, 2005). Originally, ES and its monetary valuation (see Costanza et al., 1997) were primarily intended to alert public opinion and governments about the importance of well-functioning ecosystem for societies and the risks associated with the ecological crisis. Scientific developments of this concept, encouraged by its institutionalization (Mongruel et al., 2016) i.e. the dissemination of the concept in the area of environmental management decision-making, have gradually clarified its scope. It also defined multi-criteria analysis as the most robust way to evaluate ES, seeking to inform decision-making processes and the establishment of public policy and management policies (Keune and Dendoncker, 2013; Saarikoski et al., 2016). However, 50% of ES studies focus on a single service, or on a limited number of services, without considering interactions and feedback with other services (Lee and Lautenbach, 2016). This monofocal vision can lead to an operational ecosystem management based on the maximization of a single ES and potentially to the detriment of the other ones (Couvet et al., 2016).

Indeed, ES depend on complex interactions among species and their abiotic environment, complex use and utilization patterns and various perceptions by beneficiaries. ES bundles are defined as sets of ES that repeatedly appear together across space or time (Raudsepp-Hearne et al., 2010). It is thus a useful concept for improving the management of ecosystems and identifying common ES tradeoffs and synergies: trade-offs arise when the provision of one service is enhanced at the cost of reducing the provision of another service, and synergies arise when multiple services are enhanced simultaneously (Raudsepp-Hearne et al., 2010). Bundle analysis seeks to inform management and decision-making for reducing the cost of both tradeoffs and synergies. For example, the maximization of food produced by agricultural ecosystems in the context of intensive agriculture has led to an erosion of supporting (e.g. soil fertility), regulating (e.g. regulation of nutrients) and cultural (e.g. homogeneous landscapes) ES (Power, 2010).

More recent scientific developments indicate that separating, a minima, the supply and demand of ES helps to refine and clarify the bundle analysis (Villamagna et al., 2013; Burkhard et al., 2014; Levrel et al., 2016; Crouzat et al., 2016). The supply represents the ecosystem capacity to provide ES (also called potential), whereas the demand is the amount of services used, consumed but also desired by the society (Villamagna et al., 2013). Different approaches can be used to analyse trade-offs and synergies depending on whether the focus is on supply or demand for ES (Mouchet et al., 2014).

Coastal habitats are among the habitats the most exposed to current direct and indirect drivers of change (Henson et al., 2017). Among them, sandy beaches, coastal lagoons and coral reefs are particularly vulnerable (Defeo et al., 2009; Kennish and Paerl, 2010; Pendleton et al., 2016). Among these drivers of change, eutrophication is particularly important, prevalent and at the origin of significant ecological and social changes (Diaz and Rosenberg, 2008; Wilkinson, 2017). Although the ecological impacts of eutrophication on these ecosystems are well studied today, its effects on ES bundles are little explored. The ES approach can provide an interesting perspective to understand the ecological impacts and associated risks of eutrophication to better inform decision-making processes and management strategies. Here, we assess the effects of eutrophication in sandy beaches, coastal lagoons and coral reefs on ES bundles. Our aim is to identify trade-offs and synergies between ES and the possible societal benefits associated to the recovery of the ecological functions for these ecosystems.