Despite covering only 0.82% of the ocean’s surface, the Mediterranean Sea supports up to 18% of all known marine species, with 21% being listed as vulnerable and 11% as endangered. The accelerated spread of tropical non-indigenous species is leading to the “tropicalization” of Mediterranean fauna and flora as a result of warming and extreme heat waves since the 1990s. The acidification rate in the Mediterranean waters has ranged between 0.055 and 0.156 pH units since the pre-industrial period, affecting the marine trophic chain, from its primary producers (i.e., coccolithophores and foraminifera) to corals and coralline red algae. Projections for high emission scenarios show that endemic assemblages will be modified with numerous species becoming extinct in the mid 21st century and changes to the natural habitats of commercially valuable species, which would have many repercussions on marine ecosystem services such as tourism, fisheries, climate regulation, and ultimately on human health. Adaptation strategies to reduce environmental change impacts need effective mitigation policies and actions. They require anticipatory planning to enable them to tackle problems while they are still manageable. Given the diversity of each Mediterranean sub-basin, wider monitoring coverage is needed to strengthen our knowledge about the different adaptation processes that characterize and best suit each geographical zone. Adaptation implies the implementation of more sustainable fishing practices as well as reducing pollution from agricultural activity, sustainable tourism or developing more effective waste management. Marine protected areas can potentially have an insurance role if they are established in locations not particularly vulnerable to ocean acidification and climate change.
The coastal zone, i.e. the area in which the interaction between marine systems and the land dominate ecological and resource systems, is a hotspot of risks, especially in the south-eastern Mediterranean region. Alterations to coastal ecosystems (lagoons, deltas, salt marshes, etc.) due to climate change and human activities affect the flow of nutrients to the sea, the magnitude, timing and composition of potentially harmful/toxic plankton blooms. They also significantly increase the number and frequency of jellyfish outbreaks, and could have negative impacts on fisheries. 1.2 to 5% of seagrass meadows in the Mediterranean Sea, which represent 5 to 17% of the worldwide seagrass habitat, are lost each year. Among them, almost half of the surveyed Posidonia oceanica sites have suffered net density losses of over 20% in 10 years. As for fish, non-indigenous species and climate change cause local extinction. Projected temperature increases combined with a decrease in nutrient replenishment and ocean acidification, are expected to cause changes in plankton communities, negative impacts on fish, corals, seagrass meadows and propagation of non-indigenous species. Projected sea level rise will impact coastal wetlands deltas and lagoons. Extensive urbanization added to climate change is also expected to threaten coastal ecosystems, human health and well-being. A nexus approach is required when trying to establish adaptation methods for the entire Mediterranean, while taking into account ecosystem-based management, synergies and conflicts, integrating local knowledge and institutions. Suitable adaptation policies include reducing pollution runoff, both from agriculture and industry and waste management, and policies to limit or prevent acidification. Conservation planning and management should focus on cross-cutting approaches and building resilience between structural and functional connectivities of various fields.
Biodiversity changes in the Mediterranean over the past 40 years have occurred more quickly and been more significant than in other regions of the world. Urbanization and the loss of grasslands are key factors of ecosystem degradation across the region. Since 1990, agricultural abandonment has led to a general increase in forest areas in the northern Mediterranean, while in the southern Mediterranean, ecosystems are still at risk of fragmentation or disappearance due to human pressure from clearing and cultivation, overexploitation of firewood and overgrazing. Drylands have significant biodiversity value, with many of the plants and animals highly adapted to water-limited conditions. They are undergoing an overall increase in response to climate change and extensive land abandonment. 48% of Mediterranean wetlands were lost between 1970 and 2013, with 36% of wetland-dependent animals in the Mediterranean threatened with extinction. Because of the reduction in river flows, 40% of fish species in Mediterranean rivers are endangered. Projections for the 21st century indicate drier climate and increased human pressure, with negative impacts on terrestrial biodiversity, forest productivity, burned areas, freshwater ecosystems and agrosystems. Future projections indicate that burnt areas can increase across the region by up to 40% in a 1.5°C warming scenario and up to 100% from current levels for 3°C warming at the end of the century. Mediterranean drylands will become drier and their extent is expected to increase across the region. Projections suggest decreased hydrological connectivity, increased concentration of pollutants during droughts, changes in biological communities as a result of harsher environmental conditions, and a decrease in biological processes such as nutrient uptake, primary production, and decomposition. Promotion of ‘climate-wise connectivity’ through permeability of the landscape matrix, dispersal corridors and habitat networks are key to facilitating upward the migration of lowland species to mountains in order to adapt to new climate change conditions. Promotion of mixedspecies forest stands and sylvicultural practices such as thinning, and management of understory can promote the adaption of Mediterranean forests to climate change. Promotion of the spatial heterogeneity of the landscape matrix can help reduce fire impacts. The preservation of the natural flow variability of Mediterranean rivers and streams and wide riparian areas, along with reductions in water demand are key to the adaptation of freshwater ecosystems to future climate change.