Abstract
The study of marine coastal food webs has a central role in the application of the integrated ecosystem approach for marine management. Changes in food webs caused by natural or anthropic drivers can lead to dramatic shifts in the overall structure and function of coastal marine ecosystems and deterioration of their services. The present review investigates the methodological approaches employed for the assessment of coastal shelf food webs at a global scale and highlights existing gaps and limitations. Out of 1652 published articles that initially met our search criteria, 880 passed the initial screening and 493 were found relevant and were fully analysed. The information extracted included the spatiotemporal coverage of the studies; the main methodological approaches utilized for the assessment of population state variables (i.e. biomass, size, abundance) and trophic levels; the biotic components and driving factors considered; indices used to describe the structure and functioning of coastal food webs; and main knowledge gaps. Results showed that most studies have been conducted at a subnational level, mostly in the Temperate Northern Atlantic marine realm. Overall, 54% of the studies provided quantitative information on food web structure. The most common methodological approach utilized was modelling (40%), followed by non-experimental-based correlations (30%), and natural or manipulative experiments (14%). Information on population state variables was provided by 69% of the studies, while 42% employed some of the following trophic level determination techniques: stable isotopes, gut contents, fatty acids, and molecular analysis, which were either combined or used in isolation. Specific natural or human drivers were incorporated in 76% of the studies, with fishing being the most common driver. Modelling approaches included multiple indices to describe food web attributes and/or the structure and functioning of coastal shelf ecosystems. Despite the great progress achieved through the development of new tools and techniques, food web analysis still suffers from important knowledge gaps and limitations of the methodological approaches, which are extensively discussed. The present review establishes a useful knowledge base to provide guidance for future research and assessments on coastal shelf food webs, and to support ecosystem-based management.
Highlights
In the emerging era of the Anthropocene (Steffen et al, 2015), growing human pressures on marine ecosystems and their cumulative effects have caused widespread degradation of marine habitats (Hughes et al, 2017), substantial biomass declines of marine communities (Myers and Worm, 2003), local extinctions (Thibaut et al, 2014), and regime shifts (Rocha et al, 2015; Wernberg et al, 2016)
As an “index” we considered any mathematical expression, ratio or correlation used by the authors in order to quantify key features and properties of food webs and marine ecosystems, describing characteristics of energy flow, resilience, structure, and functioning; (37) Number of indices used; (38) Names of indices used to describe food webs: free text; (39) Economic analysis performed: yes, no; (40) Knowledge gaps and future work highlighted: free text
Most studies (71%) regard ecosystems exclusively on or above the coastal shelf, 20% integrated both coastal shelf and offshore waters, while 9% referred to coastal marine ecosystems but without clarifying the studied depth zone
Summary
In the emerging era of the Anthropocene (Steffen et al, 2015), growing human pressures on marine ecosystems and their cumulative effects have caused widespread degradation of marine habitats (Hughes et al, 2017), substantial biomass declines of marine communities (Myers and Worm, 2003), local extinctions (Thibaut et al, 2014), and regime shifts (Rocha et al, 2015; Wernberg et al, 2016). Overfishing (Jackson et al, 2001; Sala et al, 2012), pollution (Tornero and Hanke, 2016), coastal development (Meinesz et al, 1991; Bulleri and Chapman, 2010), invasive species (Katsanevakis et al, 2014), destructive fishing practices (Saila et al, 1993; Guidetti, 2011), and climate change (Rilov, 2016) are responsible for high rates of biodiversity loss in coastal shelf ecosystems (Lotze et al, 2006; Waycott et al, 2009) Such severe impacts on marine ecosystems have raised worldwide concerns and prompted a fundamental shift in the management of marine living resources, toward a holistic and integrated approach, recognizing the full area of interactions within ecosystems (Katsanevakis et al, 2011). The complex and dynamic nature of coastal ecosystems and the absence of complete knowledge or understanding of their functioning, poses a major challenge in the successful application of this approach
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