Looking from the human point of view, Mediterranean ecosystems provide numerous services to human, including renewable natural resources (food, medicines, timber and mushrooms), environmental services (maintenance of biodiversity, soils and water, regulation of air quality and climate and carbon storage) and social services (recreational, educational and leisure uses, traditional cultural values, tourism and hiking) (Liquete et al. 2016). These ecosystems face unprecedented challenge due to climate and environmental changes, which impact services they provide. Higher temperatures, heat waves and decreasing rainfall are expected (Hoerling et al. 2012, Jaeger and Seneviratne 2011), as well as earlier, longer and more severe drought periods (Ruffault et al. 2014). Higher frequency of other extreme events, like forest fires, floods and storms events (e.g. Ruffault et al. 2016) is also expected. They interact with other environmental changes resulting from human activities (overexploitation, pollution and changes in land use).

Droughts and higher temperature lead to increasing aridity and desertification of Mediterranean terrestrial ecosystems (Guiot and Cramer 2016). In addition to direct consequences of climate change, terrestrial ecosystems are impacted by changes in land use including abandonment of extensive crop activities in some remote areas and mountains, as well as urbanization, inducing increasing demand for resources and landscape fragmentation (Peñuelas et al. 2017). Oases on the southern and eastern rim of the Mediterranean, despite their potential to tolerate several abiotic stresses typical of arid environment, are also impacted by the climate change amplified by strong human pressures (Sen et al. 2011).

Mediterranean islands are characterized by the presence of endemic or range-limited plant species (Médail and Diadema 2009). These ecosystems are much influenced by climate change, land-use, fragmentation of habitats and tourism. Moreover, the limited space on islands imposes a barrier to species range expansion (Vogiatzakis et al. 2016).

Human activities, like urbanization and tourism, have also a strong impact on coastal ecosystems. These activities, combined with climate and environmental change, provoke coastal erosion due to sea level rise, extreme events, sedimentation decrease and degradation of some habitats (coastal dunes, coastal cliffs and coastal terraces). Coastal wetlands, such as the Camargue (France), the Nile Delta (Egypt) and other similar regions, are particularly vulnerable (Zacharias and Zamparas 2010, AllEnvi 2016). The quality of groundwater decreases, because of overexploitation, pollution, increasing urbanization, and saltwater intrusion caused by sea level rise (Leduc et al. 2017, Mas-Pla et al. 2014). Mediterranean freshwater ecosystems are affected by falling water levels and reduced water quality (Hermoso et al. 2011).

The 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). It is also becoming a hot-spot of global change (Micheli et al. 2013). In the context of climate change marine ecosystems are mainly influenced by higher water temperature and acidification, which provoke several main types of impacts. Increased water temperature leads to changes in species composition and abundance. Cold-water species decline or extinct and warm-water species thrive (Azzurro et al. 20A1). Especially, the number of Lessepsian species in the Mediterranean (i.e. coming from the Red Sea through the Suez Canal) increases (Bilecenoglu et al. 2002, Dulčić et al. 2008).

In fisheries, the results of climate change are combined with critical overfishing (more than 90% of assessed-stocks were overfished in 2015; STECF 2016), pollution and habitat destruction. The water acidification in Mediterranean has been well documented and will continue in the future (Kapsenberg et al. 2017). It has negative impacts on many pelagic and benthic organisms with calcareous body parts, such as corals, mussels, pteropods, sponges and coccolithophores (Bramanti et al. 2013, CIESM 2008, Goodwin et al. 2014, Meier et al. 2014).

It is important to underline that in all ecosystems every species is connected with many others through a food web. Therefore, changes in the abundance of one species may have important and sometimes irreversible impact on many other species. The shifts in plankton composition will affect the abundance of organisms feeding directly on plankton and then on the whole food web. It is now recognized that primary production (90% of ocean productivity is ensured by phytoplankton) is critical to maintain biodiversity and support fishery catches in the world’s oceans (Brown et al. 2010). Increased water temperature leads also to mass mortality events (Coma et al. 2009, Garrabou et al. 2009).

13/02/2018; This article was produced by Katarzyna Marini with the support of Plan Bleu – UNEP/MAP.

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