Review of Environment, Energy and Economics - Re3 Acidification in the Mediterranean sea: impacts and adaptation strategies


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Acidification in the Mediterranean sea: impacts and adaptation strategies
by Francesco Bosello, Elisa Delpiazzo and Fabio Eboli
Environment - Articles

This article addresses one of the main threats for the marine ecosystem: Ocean Acidification. Caused by anthropogenic CO2 emissions, it affects the whole marine ecosystem. To cope with it and lower its negative socio-economic effects, it is necessary to adopt a comprehensive adaptation strategy to enforce resilience and reduce local stressors.  

Keywords: Ocean Acidification, Adaptation, Mediterranean Sea

JEL classification: Q22, Q54, Q57

Suggested citation: Bosello, Francesco, Delpiazzo, Elisa and Eboli, Fabio, Acidification in the Mediterranean sea: impacts and adaptation strategies (March 12, 2015). Review of Environment, Energy and Economics (Re3),

Every year oceans, and seas, absorb about a quarter of the CO2 we release into the atmosphere. In the last five decades they absorbed between 24% and 30% of total anthropogenic carbon dioxide emissions (Billé et al., 2013). Although this is an important contribution to slow the global warming process, the CO2 absorbed is changing the chemistry of the seawater. This phenomenon is known as Ocean Acidification (OA). Since the industrial revolution, the pH of surface ocean waters has fallen by 0.1 pH units and might decrease by 0.1-0.35 additional units by 2100 (Gattuso et al., 2011; IAEA, 2010; NOAA, 2010).

From biogeochemical reactions to socio-economic impacts
When CO2 is absorbed by seawater, chemical reactions occur that reduce seawater pH, carbonate ion concentration, and saturation states of biologically important calcium carbonate minerals (i.e. calcite and aragonite). Calcium carbonate minerals are the building blocks for the skeletons and shells of many marine organisms. Therefore, organisms that use aragonite for their shells or skeletons are the first to be adversely affected by acidification, because aragonite dissolves more easily under the changing conditions due to its different crystal structure. Another response related to pH modification is the increase in energy requirements to maintain their healthy metabolism.

These physical and biological reactions directly affect many important marine ecosystem services and impact indirectly social economic activities in coastal communities that often largely depend upon them.

Firstly, OA influences marine ecosystem supporting services. These relate to the basic functions upon which all other ecosystem services rely. For instance, many species that could be negatively impacted by pH changes (i.e. many calcifiers) are habitat-forming organisms. Therefore they provide shelter, and indirectly food and nursery functions to many other marine species, including commercially important fish species. Secondly, OA alters provisioning services, which refer to marine ecosystem direct contribution to production activities. Although there are important local specificities, mollusks and crustaceans harvested for food are likely to be affected as they have calcareous shells and exoskeletons. Some other species may be indirectly impacted by changes in their food chain (i.e. changes in prey-predator relationships) and habitat. Accordingly, coastal communities relying upon shellfish and fish aquaculture for export and for protein intake would be particularly concerned. Thirdly, OA can negatively affect regulating services: particularly,  coastal defense and carbon storage. Many marine communities indeed dissipate the energy in waves reaching the coasts, influence sedimentation rates and levels of coastal erosion. Thus, as OA occurs, people, infrastructure, lagoon and estuarine ecosystems, including mangroves, sea grass meadows, salt marshes, become increasingly vulnerable to growing waves and storm impacts experiencing fundamental alterations in the nature of coastlines and the resources available. Finally, OA impacts cultural services. The effect on cultural ecosystem services is particularly difficult to assess. While impacts to tourism, leisure and recreation can be partially quantified, for instance through potential degradation of reefs, many cultural services (i.e. spiritual enrichment and aesthetic appreciation) are intangible in nature and hard to measure.

A glance at acidification in the Mediterranean Sea
When OA entered the scientific agenda two decades ago, scientists were mainly concerned with its impact on Southern Oceans and coral reefs. More recently, the EU decided to investigate the potential consequences of OA for its countries and seas. This originated two important research projects: EPOCA (European Project on OCean Acidification) (2008-2011) which analysed its biological, ecological, biogeochemical, and societal implications in the EU. Then, MEDSEA (MEDiterranean Sea Acidification in a changing climate) (2011-2014) that focused specifically on the Mediterranean, due to its unique biodiversity, richness of endemic species and benthic ecosystems, such as Posidonia oceanica meadows, and vermetid reefs (the Mediterranean equivalent of coral reefs). Both projects highlighted either a high vulnerability to acidification of the Mediterranean or its relevance, especially for Southern European countries.

The Mediterranean Sea has shown an average temperature increase of 0.67°C over the last 25 years. In the same period, in the Northwestern Mediterranean Sea, acidity has increased by more than 10 %. Scientists forecast an increase of the average surface warming of 1-1.5°C in the Eastern Mediterranean, Aegean and Adriatic Sea between 2000 and 2050 implying that acidification will increase by 60% compared to preindustrial level within the same period and by 150% at the end of the century (MedSeA, 2014). Although, the Mediterranean covers only 0.82% of the world ocean’s surface and includes 0.28% of its volume, about 17,000 species live there (i.e. 4%–18% of the world’s recorded species).

How to cope with Acidification: general principles and sector-specific actions
Here, we present some general principles for a successful adaptation strategy to OA learning from non-EU experiences that could potentially suit the Mediterranean Area. Key elements of an adaptation strategy to OA include:

  • Improving ecosystem diversity with high biodiversity and/or redundancy of functional groups (SCBD, 2009). This suggests that biodiversity improvement/preservation is a logical mean of sustaining ecosystems against OA. This means on the one hand to exploit the acclimation potential of many calcifying species of the Mediterranean, on the other hand to protect other species. The strategy can be substantively strengthened by the establishment of marine protected areas (MPAs). These can neither halt climate change and OA, nor prevent invasion by alien species, but have proven to be an important tool for enhancing the resilience and adaptive capacities of ecosystems (Otero et al., 2013).
  • Involving stakeholders by engaging the private sector to contribute in facing OA (IGBP, IOC, SCOR, 2013).
  • Creating marine spatial planning (OSPAR Commission, 2009). As any climate change adaptation policy, OA adaptive measures do not affect each location in the same way. There are different likely impacts among and within regions. Shorelines, estuarine, shallow coastal zones and deep waters face different threats, to be engaged with different tools.
  • Promoting research and building capacity to better understand the impacts of OA on marine ecosystems (IOC/UNESCO, IMO, FAO, UNDP, 2011). The potential consequences of OA may take many years to be realized but will persist for a very long time. Reducing uncertainty about the probability, frequency, magnitude, and timing of potential future problems created by OA is essential in designing the appropriate response.
  • Reducing local stressors (IGBP, IOC, SCOR, 2013). A successful strategy should envisage sector-specific measures to directly cope with specificities. Here, we focus on three marine related sectors (i.e. fisheries, aquaculture and tourism) and other sectors not directly related to fisheries (i.e. agriculture, infrastructure) .

Fishing activity
Generally, as said, OA can change the production of a particular commercial fishing activity, causing a change in income and employment for fishermen, and for all the commercial activities more or less directly related to this sector (sellers of inputs, processors, retailers, recreational fishing outfitters and so on). These economic impacts may be minimized if the fishing activity is more “sustainable”, therefore not already experiencing decrease in catches induced by overexploitation of the fish stock. New “catch share” management systems, reallocation to new or underutilized fisheries, diversification into multiple fisheries, designing new harvest strategies and management systems, controlling overfishing and rebuilding fish stocks are only some of the most common practices to cope with OA. These strategies have already been implemented in a number of U.S. fisheries and provide fishermen with incentives and more flexibility to reduce harvest costs and increase the quality and value of catch as well as to combat destructive fishing practices and illegal or unregulated fisheries.

The aquaculture sector could be negatively impacted as well. Selecting alternative breeding techniques allows exploring other seafood production options (e.g. resistant strains of shellfish), assessing the options for development of environmentally sustainable ‘aquaculture’ productions using species that are resistant to lowered/controlled pH. Switching to freshwater aquaculture operations, altering seawater chemistry, exploiting shellfish production to support healthy marine waters, and new engineering solutions in seawater systems are all strategies to isolate cultures from acidified water or to enhance beneficial conditions in water (i.e. increasing filtering effects of shellfish organism, or increasing alkalinity conditions). Moving mussels to the river mouths to isolate their cultures from acidified waters and to have fresher water in summer is a common practice among shellfish farmers in Southern France. In Maryland, instead, a $500 tax credit to residents who raise oysters because of the ecosystem services they provide is levied to make water cleaner. In Oregon and Washington states, oyster growers switch the pump off and their production relies on a closed seawater system when a critical pH seawater level is reached.

Tourism oriented strategies include reducing loss or degradation of marine environments, and reducing trawling. The first strategy aims to prevent a worsening marine ecosystem and avoiding negative socio-economic impacts in those regions that particularly attract tourists for recreational activities such as diving and bathing. The last strategy, instead, attempts to protect sediment-dominated habitats, which occupy a large fraction of the area of the oceans, playing a crucial role in several key ecosystem functions and processes in shelf sea environments. This strategy has been adopted in Puget Sound (Washington State) where along the waterfront of Port Townsend, an ‘Anchor Out for Eelgrass’ zone was created, preventing recreational boaters from damaging this critical shallow water habitat.

Complementary to supply side strategies, the change in consumers and tourists preferences could promote a persistent shift in consumption patterns. However, this option is particularly difficult to pursue since it depends on culture, values, and social institutions.

Agriculture and infrastructure
Although other sectors are not directly related to marine ecosystem they can reduce the stress locally improving resilience against OA. This is the case of reducing pollution runoff. The most dangerous polluting substances are fertilizers and nitrates, exacerbating acidification mainly in estuarine and shallow coastal zones. This strategy may be achieved through the concerted effort of many different actors (i.e. farmers, landowners, watershed groups, non-governmental organizations, state and local authorities). Examples of existing/emerging tools that remove/reduce nutrients and organic carbon include structural or engineered control devices and systems (i.e. retention ponds) to treat polluted runoff, besides operational, procedural practices, technologies to address nutrient loading, especially from nonpoint sources, and innovative approaches, such as the nutrient trading market established in Ohio, Indiana, and Kentucky.

Agricultural activities can worsen OA processes through nutrient discharges in coastal waters and freshwater coming into oceans. Forests can function as natural filters to remove nutrients and sequester carbon. These phytoremediation techniques include maintaining or planting vegetation in buffer zones, using seaweeds or sea grasses within shellfish hatcheries for better larval survival and growth, co-culturing eelgrass and shellfish, using seaweed farming to capture and remove carbon, and harvesting algae from shellfish-growing gear for use onshore as a fertilizer.  An illustrative example is given in Puget Sound where on Ebey’s Prairie a bioswale has been installed to percolate runoff through roots and soil.

Finally, also the infrastructure sector may support adaptation strategies and increase resilience of coastal zones. Key elements of this strategy include increasing coastal protection, and improving management of coastal infrastructure construction and urbanization to preserve, and when impossible, replace marine ecosystem anti-erosion services. A consequent adaptation measure is the building of protection infrastructures (i.e. dikes, sea-walls, or flood defense systems). Complementary to that, strategies for the sustainable use and development of coastal zones have to be outlined.

This article briefly presents the causal chain potentially relating biological effects of OA to  socioeconomic impacts and policy prescriptions. We note that, despite the large amount of scientific data on OA collected over the last decade, a significant gap still concerns their concrete use to gain insights into the “bio-socio-economic” impacts of OA. While waiting for these assessments, policies addressing other types of marine ecosystem degradation could be considered useful in contrasting acidification. In particular, a careful management of marine environment, its sustainable exploitation and the protection of key habitats can improve its resilience against the many different pressures that are and will affect it.


The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) ‘‘European Mediterranean Sea Acidification in a changing climate’’ (MedSeA) under grant agreement n° 265103.


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Francesco Bosello, Università di Milano, Fondazione Eni Enrico Mattei, Centro Euro-Mediterraneo sui Cambiamenti Climatici

Elisa Delpiazzo, Centro Euro-Mediterraneo sui Cambiamenti Climatici

Fabio Eboli, Fondazione Eni Enrico Mattei, Centro Euro-Mediterraneo sui Cambiamenti Climatici