water Review Trends and Evolution in the Concept of Marine Ecosystem Services: An Overview Elvira Buonocore 1,*, Umberto Grande 2, Pier Paolo Franzese 1 and Giovanni F. Russo 1 1 UNESCO Chair on “Environment, Resources and Sustainable Development”, Department of Science and Technology, Parthenope University of Naples, 80133 Naples, Italy; [email protected] (P.P.F.); [email protected] (G.F.R.) 2 Department of Geobotany and Landscape Planning, Nicolaus Copernicus University, 87-100 Toru´n,Poland; [email protected] * Correspondence: [email protected] Abstract: The biotic and abiotic assets of the marine environment form the “marine natural capital” embedded in the global ocean. Marine natural capital provides the flow of “marine ecosystem services” that are directly used or enjoyed by people providing benefits to human well-being. They include provisioning services (e.g., food), regulation and maintenance services (e.g., carbon sequestration and storage, and coastal protection), and cultural services (e.g., tourism and recreational benefits). In recent decades, human activities have increased the pressures on marine ecosystems, often leading to ecosystem degradation and biodiversity loss and, in turn, affecting their ability to provide benefits to humans. Therefore, effective management strategies are crucial to the conservation of healthy and diverse marine ecosystems and to ensuring their long-term generation of goods and services. Biophysical, economic, and sociocultural assessments of marine ecosystem services are much needed to convey the importance of natural resources to managers and policy makers supporting the development and implementation of policies oriented for the sustainable management Citation: Buonocore, E.; Grande, U.; of marine resources. In addition, the accounting of marine ecosystem service values can be usefully Franzese, P.P.; Russo, G.F. Trends and complemented by their mapping to enable the identification of priority areas and management Evolution in the Concept of Marine strategies and to facilitate science–policy dialogue. Given this premise, this study aims to review Ecosystem Services: An Overview. trends and evolution in the concept of marine ecosystem services. In particular, the global scientific Water 2021, 13, 2060. https://doi.org/ literature on marine ecosystem services is explored by focusing on the following main aspects: the 10.3390/w13152060 definition and classification of marine ecosystem services; their loss due to anthropogenic pressures, alternative assessment, and mapping approaches; and the inclusion of marine ecosystem services Academic Editor: Genuario Belmonte into policy and decision-making processes. Received: 18 June 2021 Keywords: marine ecosystems; ecosystem services; benefits to humans; biophysical assessment; Accepted: 27 July 2021 economic valuation Published: 29 July 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in 1. Introduction published maps and institutional affil- iations. The biotic and abiotic assets of the marine environment constitute natural marine capital generating a bundle of ecosystems services vital for human well-being [1,2]. Marine ecosystem services are the output flows generated by marine natural capital stocks that are directly consumed, used, or enjoyed by people [3–6]. They include food provision, coastal protection, water purification, nutrients cycling, carbon sequestration, Copyright: © 2021 by the authors. and recreational opportunities. Licensee MDPI, Basel, Switzerland. The generation of ecosystem services depends on the physical, chemical, and biolog- This article is an open access article ical processes in marine ecosystems that underpin ecosystem functioning and maintain distributed under the terms and conditions of the Creative Commons ecosystem structures. These ecosystem processes include biomass production, organic Attribution (CC BY) license (https:// matter transformation, nutrient cycling, and physical structuring [7]. creativecommons.org/licenses/by/ Ecosystem functioning is based on the interplay between abiotic and biotic factors. 4.0/). Among the biotic factors, the importance of biodiversity is widely recognized as being Water 2021, 13, 2060. https://doi.org/10.3390/w13152060 https://www.mdpi.com/journal/water Water 2021, 13, 2060 2 of 14 fundamental [8]. Furthermore, ecosystem functions represent a significant component of ecosystem health on which the generation of ecosystem services that benefit society and human economy depends [9]. The most widely acknowledged framework for linking ecosystems and human well- being is the ecosystem service cascade model developed to highlight how the notion of ecosystem services can be used to understand the strong relationships between people and nature [10]. It represents the production chain of ecosystem services, starting from the biophysical structures and processes of ecosystems and ending with the benefits provided to society. Yet, the quantitative assessment of the relationships between biodiversity, ecosystem functioning and ecosystem services requires a deep research effort, especially in the context of marine ecosystems [11]. Marine ecosystems undergo unprecedented changes at different scales due to multi- ple human direct and indirect pressures including overfishing, eutrophication, invasive alien species, habitat destruction, plastic pollution, and climate change [12–14]. Marine biodiversity loss is a consequence of these drivers acting either alone or in synergy. In this context, the biophysical and economic assessment of marine ecosystem services is much needed to convey the importance of natural resources to managers and policy makers and to support the implementation of policies and strategies oriented toward the sustainable exploitation of marine natural capital stocks [15]. Mainstreaming ecosystem services into policy and decision making is also dependent on the availability of spatially explicit information on the state and trends of marine ecosystems. Mapping is recognized as an essential tool to bring the concept of ecosystem services into practical application [16,17]. In recent decades, there has been an increasing number of studies aimed at assessing and mapping the value of coastal and marine ecosystem services, although there are significantly less published articles than for terrestrial ecosystems [18]. In this study, the scientific literature on marine ecosystem services was firstly explored using bibliometric analysis and the VOSviewer software (version 1.6.9, Leiden University, Netherlands), a software tool based on social network analysis allowing for the creation, visualization, and exploration of maps based on bibliometric network data. Articles were collected on 16 February 2021 by research on the Scopus web search engine. The search string used was “marine ecosystem service*”. The research on the Scopus database pro- duced 237 scientific articles published from 2006 to 2021. The results were exported as .csv files and imported into the VOSviewer software. The scientific research on marine ecosys- tem services has shown a rapid increase in recent decades. The distribution of keywords in scientific publications on “marine ecosystem services” along a temporal gradient (Figure1 ) shows the evolution in the scientific literature on the topic, identifying the most recent topics and research paths. The map shows a more recent focus on the concepts of “envi- ronmental assessment”, “spatial planning”, and “sustainable development”, highlighting increasing interests and efforts in opening the science on “marine ecosystem services” to multi-disciplinary research areas linking the ecological and socioeconomic dimensions of sustainability. The concept of ecosystem services has also garnered strong international policy at- tention. Although there is no specific policy devoted to marine ecosystem services, the concept is already embedded in several recent environmentally related international poli- cies, such as the Marine Strategy Framework Directive, the 2030 Agenda for Sustainable Development, and the Biodiversity Strategy for 2030 [19–21]. Given this premise, this paper aims to review the scientific literature on marine ecosys- tem services by focusing on the following main aspects: the definition and classification of marine ecosystem services; their loss due to anthropogenic pressures, alternative assess- ment, and mapping approaches; and the inclusion of marine ecosystem services into policy and decision-making processes. Water 2021, 13, x FOR PEER REVIEW 3 of 14 Water 2021, 13, 2060 3 of 14 FigureFigure 1. 1.KeywordsKeywords related related to to “marine “marine ecosystem ecosystem services” services” in the scientificscientific literature,literature, represented represented on on the the basis basis of theof the averageaverage year year of ofpublication publication of of documents documents in in which which they they occur, occur, onon aa colorcolorgradient gradient from from blue blue (older (older publications) publications) to greento green (publications(publications equally equally distributed distributed across across the the ti timespan)mespan) and yellowyellow (more(more recent recent publications). publications). 2. Definition and Classification of Marine Ecosystem Services 2. Definition and Classification of Marine Ecosystem Services In recent decades, there has been an exponential growth in interest on the ecosys- temIn service recent conceptdecades, and there on has related been international