Coastal systems are threatened by multiple anthropogenic activities, such as urban development, organic and inorganic pollution and over-exploitation of resources. Nonetheless, current management activities are still almost exclusively developed in an impact-by-impact framework. Over the past decades, efforts have been made to incorporate natural capital into political and management decisions (Millennium Ecosystem Assessment 2005). However, there is still insufficient scientific understanding of how multiple human actions and potential interacting effects between those actions affect the provision of ecosystem services (Daily et al 2009). The concept of Ecosystem Based Management (EBM) is especially relevant when managing ecosystem resilience, i.e., the capacity of an ecosystem to absorb perturbations while retaining its essential structure, function and services, including the identities of the component species (Folke et al 2004). If ecological system’s resilience is ‘‘eroded’’, the system becomes vulnerable to sudden regime shifts, i.e. critical transitions where after the ecosystem will be characterised by a different set of species, structures, processes, functions and services (Scheffer et al. 2009).

 

A key challenge of EBM is to assess thresholds and trade-offs associated with alternative management choices. A threshold can be set as the level of human induced pressure (e.g., pollution) at which a small change produces a substantial alteration of the ecosystem’s structural (e.g., diversity) and functional (e.g., resilience) attributes (Samhouri et al. 2010). Thresholds are thus characteristic for non-linear responses. As thresholds exist for multiple human pressures, trade-offs (i.e. tradings between different properties of the system) can occur if management measures affect multiple thresholds in different ways. Unfortunately, thresholds relationships are only quantified for a few cases, and often they focus on one direction only (i.e., the risk of increasing human pressures), without exploring the reverse pathways following management actions geared towards recovery. Further, in natural systems the cumulative impact from several stressors tend to result in synergistic and antagonistic effects rather than additive ones (Crain et al. 2008, Halpern et al. 2008a). For example, fisheries exploitation and increased nutrient loadings jointly affect food webs and production in estuaries, and each affects the sensitivity of species and ecosystems to the other (Breitburg et al. 2009). As a result, there could be levels of fisheries and nutrient loadings that lead to threshold responses  and are resistant to remediation through fisheries removals and nutrient management (Scheffer et al. 2001; Breitburg & Riedel, 2005). EBM aimed at long-term sustainability requires the identification of the causes and non-linear interplay between multiple stressors. However, so far, experiments have not progressed sufficiently to identify trade-offs in management options of interacting multiple stressors.

 

Coastal wetlands and associated saltmarshes have suffered some of the most serious declines (Dugan 1993, Rippon 2000) with some estimates suggesting global losses ≥ 60-70 % (Lotze et al. 2006,  Airoldi & Beck 2007). Pollution, eutrophication, drainage, conversion to agriculture land and aquaculture uses, changes in sedimentation and hydraulic regimes, global warming, invasive species, fisheries, urban development, shipping, tourism and water sports are generally considered the most serious threats to present day coastal wetlands (e.g. Dugan 1993, Cencini 1998, Kennish 2002). Global changes in sea levels are also beginning to pose severe threats to saltmarshes and coastal wetlands because of the strong dependence of these habitats on water-level fluctuations and tidal regimes (Adam 2002, Morris et al. 2002). Wetlands are now the target of numerous international and national initiatives and regulations for conservation, wise use and restoration of critical ecosystem services. However, the degree of actual recovery of ecosystem functioning and structure from these efforts remains uncertain (Moreno-Mateos et al. 2012).

 

The objective of the proposed MARES PhD project, for which The University of Bologna and the Royal Netherlands Institute for Sea Research will join their complementary expertise and infrastructure, is to assess the interactive impacts of, and recovery pathways from multiple human pressures in degraded saltmarshes. The candidate will identify potential options for restoration, based on mitigation of interactive stresses (e.g. nutrient inputs, soil permeability, prolonged flooding, trampling or marine litter), and will test their effectiveness experimentally. Responses to experimental manipulations of multiple interactive stressors will be measured both in terms of biogeochemical functions (e.g. storage of carbon, nitrogen, and phosphorus, etc) and biological structure (patch habitat size, primary production, biodiversity, etc), from which recovery of ecosystem services will be derived. Particular attention will be spent on understanding how local environmental and biological settings can affect the rate and degree of recovery of damaged systems. For example there are suggestions that rates of recovery might differ between warm and cold climates,  the size and degree of fragmentation of the habitat, riverine inputs or tidal amplitude, etc. The latter will be achieved by combining field work in The Scheldt (NIOZ-Yerseke), Waddensea (NIOZ-Texel) and the Adriatic sea (Univ. Bologna) in combination with mesocosm experiments enabling the manipulation of multiple stressors (cf. La Nafie et al. 2012).  Along the Adriatic coastline large-scale diebacks of Spartina have occurred and this habitat has been replaced by Salicornia spp. with major losses of structural complexity. The underlying drivers of this shift are not jet fully known, but preliminary data show that recovery of Spartina grasslands is particularly slow in areas with anthropogenic stressors (i.e. nutrient enrichment, deposition of algae, and trampling).

 

References