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Chapter 1. Climate change impacts on marine ecosystems and resources

Yunne-Jai Shin

p. 47-50

Résumés

The Mediterranean Sea is one of the biggest reservoirs of biodiversity in the world. Millions of people directly or indirectly depend on the ecosystem services it provides, in particular the provisioning of fisheries resources. Rather than a hot-spot of biodiversity, the Mediterranean Sea has now become a hot-spot of global change where climate change and other anthropogenic pressures (e.g., overfishing, pollution, habitat destruction) operate independently or synergistically to shape an altered Mediterranean Sea that may shift from the today picture. The set of physical-chemical changes triggered by climate change may disrupt the functioning of the biological components of ecosystems, from the individual up to the ecosystem scale, from the basis of the food webs (macrophytes, phytoplankton) up to the higher trophic levels (e.g., predator fish). Current research shows that the physiology and fish life history traits have changed, that fish distribution areas are moving northward and eastward, thus modifying the structure and the species composition of the communities. The dynamics of populations and food webs are modified as well, and species invasions increase at an unprecedented rate. Combined with fishing, climate change renders marine ecosystems more vulnerable to anthropogenic pressures, to natural hazards and to invasions by non-indigenous species. Although uncertainties remain with regard to the magnitude of expected ecological changes, the projections based on IPCC scenarios all confirm that climate change is a serious threat for the biodiversity and the sustainable exploitation of fishing resources in the Mediterranean Sea. This calls for the reinforcement of innovative and integrated research and assessment capacities to support an ecosystem-based management at the scale of the Mediterranean basin.

La Méditerranée constitue l’un des plus grands réservoirs de biodiversité à l’échelle mondiale. Des millions de personnes dépendent directement ou indirectement des services écosystémiques rendus par celle-ci, notamment l’approvisionnement en ressources marines. Plus qu’un point chaud de biodiversité marine, la Méditerranée est désormais un point chaud du changement global où changement climatique et autres pressions d’origine anthropique (e.g. surexploitation, pollution, destruction d’habitat) peuvent agir indépendamment ou en synergie pour former une Méditerranée différente de celle que nous connaissons aujourd’hui. L’ensemble des modifications physico-chimiques induites par le changement climatique conduit à un bouleversement des composantes biologiques des écosystèmes, de l’échelle individuelle à l’échelle écosystémique, des producteurs primaires (algues, phytoplancton) aux plus hauts niveaux trophiques (e.g. poissons prédateurs). Les recherches actuelles démontrent que la physiologie et les traits de vie des poissons changent et que leurs distributions spatiales se sont décalées vers le nord et l’est, modifiant la structure et la composition des communautés. La dynamique des populations et des réseaux trophiques s’en trouve également modifiée et les invasions biologiques se multiplient à un rythme encore jamais observé. Avec la pêche, le changement climatique induit une fragilisation des écosystèmes marins, rendant ces derniers moins résilients et plus instables face aux activités anthropiques, aux aléas naturels et aux invasions d’espèces exotiques. Bien que des incertitudes demeurent quant à l’ampleur des changements biologiques en Méditerranée, les projections faites à partir des scénarios émis par le GIEC s’accordent pour affirmer que le changement climatique est une sérieuse menace pour la biodiversité marine et la production de ressources vivantes. Il s’agit alors d’appuyer des systèmes de recherche et d’évaluation innovants et intégrés afin d’adopter une gestion écosystémique à l’échelle du bassin méditerranéen.

Texte intégral

Introduction

1The Mediterranean Sea is a hotspot of biodiversity. It hosts 4% to 18% of all identified marine species, which is considerable given that the Mediterranean Sea only accounts for 0.82% of the global ocean surface (Coll et al. 2010). Considered as a “factory” designed to produce endemics, the unique geological history of the Mediterranean Sea and the variety of climatic and hydrological situations have led to the co-occurrence of cold, temperate and subtropical biota (Lejeusne et al. 2010). This biodiversity hot-spot is at risk today as a result of multiple pressures. Based on global climate change projection scenarios, the Mediterranean Sea has been classified as one of the most responsive regions to climate (Giorgi, 2006). The Mediterranean Sea is also known to be the biggest recipient of exotic species with the rate of species introduction peaking at two species per ten-day period in the 2000s (Ben Rais Lasram and Mouillot 2009, Zenetos et al. 2010). Combined with critical overfishing (more than 90% of assessed-stocks were overfished in 2015 (STECF 2016)), pollution and habitat destruction, climate change may result in the Mediterranean Sea becoming a hot-spot of global change (Micheli et al. 2013).

2In this chapter, we describe how marine ecosystems and resources have shaped and, through interlinked mechanisms, may continue to shape future responses to climate change: (i) changes in primary production and in the structure of foodwebs, (ii) changes in population dynamics and life history traits, (iii) changes in species distribution range and habitats, and (iv) changes in the invasion rate of non-indigenous species. Examples are provided from different regions of the Mediterranean Sea and different biota (with a focus on fish communities), whereas marine top predators such as birds and marine mammals are not included in this review. Interactions between climate change, overfishing and habitat destruction are discussed throughout the chapter, but interactions with other direct anthropogenic pressures such as pollution, shipping, and oil spills are not addressed here.

Bibliographie

References

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