Food-web interactions in a coastal ecosystem influenced by upwelling and terrestrial runoff off North-West Spain

https://doi.org/10.1016/j.marenvres.2020.104933Get rights and content

Highlights

  • A mass-balance model of a human impacted coastal ecosystem off NW Spain was created.

  • Ecopath described a relatively immature ecosystem with wasp-waist control.

  • This ecosystem had characteristics of upwelling areas fjords and coastal embayments.

  • Key fish species highlight the vulnerability of the ecosystem to intense fishing.

Abstract

Ecopath with Ecosim has been used to create mass-balance models of different type of ecosystems around the world to explore and analyse their functioning and structure. This modelling framework has become a key tool in the ecosystem approach to fisheries management, by providing a more comprehensive and holistic understanding of the interactions between the different species. Additionally, Ecopath with Ecosim has provided a useful framework to study ecosystem maturity, changes in the ecosystem functioning over time and the impact of fisheries and aquaculture on the ecosystem, among other aspects. The present work explores the ecosystem functioning and structure in an anthropogenically impacted coastal area, influenced by seasonal coastal upwelling and high input of nutrients from rias (ancient drowned tectonic valleys) off North-West Spain. A mass-balance model with 23 functional groups was created using Ecopath to study the trophic interactions in the ecosystem during the post-upwelling period (August to October) in 2017. The model described an immature, wasp-waist ecosystem, that shared characteristics of ecosystems found in upwelling areas and ecosystems found in fjords or coastal embayments. Deeper analyses highlighted the importance of small planktivorous pelagic fish as a keystone functional group, and of zooplankton, blue whiting (Micromesistius poutassou) and phytoplankton as structuring groups in the ecosystem. Additionally, the study revealed that the existing fishing pressure on species of intermediate-high trophic levels could alter ecosystem functioning and structure, and ultimately affect top predators in the area. Findings of this study provide baseline information in ecosystem functioning and structure in the area and highlight the need to deeper study the effects of fisheries and their potential impacts on top predators.

Introduction

Marine coastal ecosystems, particularly those close to densely populated areas, are heavily impacted by human activities (Halpern et al., 2008). Interestingly, some of the most productive marine ecosystems are located in coastal areas, typically linked to upwelling systems, estuaries or terrestrial runoff (Field et al., 1998; Jarre-Teichmann et al., 1998; Carr, 2001). These areas are of interest, not only due to their high biodiversity and production, but also because they provide important goods and services for coastal communities (Pauly and Christensen, 1995; Worm et al., 2006). Conservation and management strategies that consider the ecosystem as a whole, such as the ecosystem modelling approach, are needed to improve our knowledge of coastal marine ecosystem functioning, ensure their resilience, and make predictions about the effects of human activities (Coll et al., 2009a,b).

Ecopath with Ecosim (EwE) is a modelling software developed to create mass-balance models of exploited aquatic and marine ecosystems (Christensen and Walters, 2004; Heymans et al., 2016). Based on the work of Polovina (1984) and Ulanowicz (1986), EwE evolved to be a software capable of modelling complex ecosystems, considering not only the energy flows within the ecosystem, but also fisheries impact (Pauly et al., 2000). Since its development in the late 1980s, EwE has become a useful and crucial tool to create ecosystem mass-balance models that have been applied to a variety of scenarios in different ecosystems, ranging from oceanic to coastal regions, with emphasis on bays, fjords, estuaries and upwelling areas (Colléter et al., 2015). Although it has been mainly used as a tool for an ecosystem approach to fisheries management (Pauly et al., 2000), EwE has also been successfully applied to study ecosystem maturity (Christensen, 1995), compare similar ecosystems (Torres et al., 2013), analyse the temporal change of ecosystems (Shannon et al., 2003; Heymans et al., 2004; Ruzicka et al., 2012), evaluate the impact of environmental changes (Tam et al., 2008), and to assess the impact of fisheries or aquaculture on ecosystems (Sánchez and Olaso, 2004; Coll et al., 2006; Díaz López et al., 2008; Outeiro et al., 2018). The widespread use of EwE allows for comparisons between different marine ecosystems globally and provides reference information for future mass-balance models (Heymans et al., 2014; Colléter et al., 2015). However, there is also a need to develop fine-scale mass-balance models describing specific productive coastal areas impacted by human activities at a regional scale. In this regard, studies providing baseline information on ecosystem functioning and structure are crucial to analyse changes in future scenarios and develop enhanced ecosystem management and conservation strategies.

The continental shelf off North-West Spain is a highly productive coastal area, heavily impacted by human activities, such as fisheries and aquaculture (López et al., 2003; Outeiro et al., 2018). Seasonal upwelling events coupled with terrestrial runoff bring nutrients to the photic layer in coastal waters, enhancing primary production (Alvarez et al., 2012). As a consequence, fisheries and aquaculture have become the main economic activities in the area, turning it into one of the most important regions for these activities in Europe (Rodríguez Rodríguez et al., 2011; Surís-Regueiro and Santiago, 2014). Despite the uniqueness of the area, and its influence in the local and regional economies, there is limited information regarding the ecosystem functioning and structure of the waters of the Galician continental shelf (Outeiro et al., 2018). The paucity of information on the ecosystem dynamics in this area poses great uncertainty around the likely responses (such as alteration in primary production and species distribution (Pérez et al., 2010; Casabella et al., 2014; Sousa et al., 2017)) of the studied ecosystem to changes in upwelling regimes triggered by climate change.

The present study aims to understand the functioning of the Rías Baixas shelf ecosystem, located in a coastal area influenced by coastal upwelling and high input of nutrients from rias (ancient drowned tectonic valleys) on the north-western coast of Spain, and to present a mass-balance model that could be used as baseline for future works. Special attention is given to marine top predators (i.e. cetaceans and seabirds) and to the fisheries impact on the ecosystem. The study offers a good opportunity to improve the scientific knowledge by creating the first EwE model of the Rías Baixas shelf ecosystem located in a highly productive and impacted coastal area off North-West Spain, providing a new and powerful tool for ecosystem-based management strategies.

Section snippets

Study area and period

Galicia is an autonomous region in North-West Spain, located on the northern limit of the North-West Africa upwelling system (Gonzalez-Nuevo et al., 2014). The region is influenced by wind-driven seasonal coastal upwelling events, which carry deep, cold and nutrient-rich waters to the photic layer, enhancing primary production (Torres et al., 2003; Alvarez et al., 2012). Upwelling events are a consequence of sustained northerly winds (Torres et al., 2003) and typically occur during spring and

Results and discussion

The model resulting from the balancing process had a pedigree index of 0.532, which is above the mean pedigree index value calculated from previously constructed models for which such information was available, and falls within the higher end of the variation range (Morissette, 2007; Colléter et al., 2015).

Conclusions

This study presents the first comprehensive mass-balance model of the Rías Baixas shelf ecosystem, a coastal ecosystem located in a highly productive area influenced by coastal upwelling and terrestrial runoff, and heavily impacted by human activities off North-West Spain. EwE proved to be a useful tool to create a mass-balance model describing the trophic interactions among the different functional groups and species in the area which could be used as baseline information for future work

Funding

This research has been exclusively funded by the Bottlenose Dolphin Research Institute (BDRI, www.thebdri.com) and did not receive any specific grant from funding agencies in the public, commercial or not-for-profit sectors.

Author contribution

B.D.L. and O.G.P. conceived and designed this study. B.D.L., S.M. and O.G.P. collected the data. O.G.P. developed the model with input from B.D.L. O.G.P. wrote the manuscript with significant input from B.D.L., S.M. and E.R. All authors contributed critically to the manuscript and gave final approval for publication.

Declaration of competing interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work has been carried out as part of a long-term study developed and funded by the Bottlenose Dolphin Research Institute (BDRI). The authors warmly thank all the BDRI interns and volunteers who have been involved in data collection and transcription without whom this work would not have been possible. Thanks are also extended to the editor Professor Inna Sokolova and two anonymous reviewers for their editing and constructive comments that improved this manuscript. Data collection was

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