€105 million a year loss of ecosystem services from 90% loss of Mediterranean seagrass bed

The Gulf of Gabes (Lesser Syrtis Gulf) in the Mediterranean Sea, just off the south-east coast of Tunisia, used to be the location of the most extensive seagrass bed in the Mediterranean basin and an important habitat for benthic (bottom-living) species, including commercial fish of importance to small-scale (artisanal) fisheries. However, since the 1970s, more than 500 million tonnes of wet untreated, toxic, and radiochemical phosphogypsum¹ discharges from a fertiliser plant in Tunisia have led to the gradual loss of around 90% of the seagrass bed’s original (1970s) surface area. As seawater pollution extends beyond borders, activities such as these can have wider geographical impacts.

The researchers note that this drastic reduction in seagrass habitat is accompanied by significant losses of the ecosystem services it provides, including carbon storage and small-scale fisheries. Having calculated the monetary value associated with these losses, they were able to compare these to the profits gained from the sale of fertiliser from the industrial complex.  They also suggest that, without actions to reduce the fertiliser waste being put into the sea, the seagrass bed will continue to degrade and it will not be possible to recover the Posidonia¹ ecosystems in this region, leading to further economic, ecological and cultural losses.

Ecosystem services, particularly carbon storage, are hugely valuable to the planet in global efforts to mitigate the impacts of rising carbon dioxide levels and resultant climate change. Monetising the losses associated with biodiversity and ecosystem services reduction, versus the gains from industrial profits, enables a clear valuation to aid policymakers and industries in taking appropriate action. The European Commission is committed to transboundary protection of the Mediterranean basin from land-based pollution, under the legal framework of the Mediterranean Action Plan, part of the United Nations Environment Programme (UNEP), adopted by the European Commission, Tunisia and 15 other Mediterranean States.

The researchers identified the indirect and direct ecosystem services of the seagrass beds in the Gulf of Gabes, using the Millennium Ecosystem Assessment recommendations. The valuation method was based on existing literature on seagrass services, including provisioning, regulating and maintenance services such as small-scale/coastal fisheries, natural fertiliser, waste-water treatment, carbon storage and coastline protection. Cultural services, although considerable, were not included in this analysis.

The researchers used existing data from a recent report on the seagrass area in the central Gulf of Gabes, showing a reduction from 1300 km² in 1970 to less than 150 km² in 2014, representing a loss of ⁓90% of the seagrass ecosystem surface area. This area loss was used to calculate economic losses. They used market values for the provisioning services – largely derived from World Bank and FAO databases². For the regulation and maintenance of ecosystem processes, they applied two alternative assessments: damage costs avoided (costs avoided from loss of seagrass services) and benefit transfer methods (estimating economic value by using information from another similar location). The researchers aggregated values for the different economic services and updated these to 2022 prices in euros.  

The researchers’ analysis estimated economic losses from loss of ecosystem services at 105 million in 2014, using market valuations: this is around 115 % of the added value of the local fertiliser factories for the same year. This means that from an economic point of view, the losses due to habitat destruction surpass the benefits from exploiting the industrial facility. Most of these losses come from the loss of small-scale fisheries, natural fertiliser services and carbon storage from the seagrass ecosystem. Taking the reference year as 2014 they value the loss to small-scale fishers at € 58 million and the loss of natural fertiliser at € 35 million. The researchers note that the European CO₂ market, which was used as a reference point in this study, is volatile, with estimations ranging from € 2 million in 2014 to € 30 million in early 2022. However, they suggest the economic value of these losses will increase in the near future, since the recent COP26 agreement on climate change boosted the open (global) market for carbon credits.  This market, while also volatile, has been growing over the last seven years.

The management and protection of the coastal and marine environment requires multilateral environmental agreements to be delivered via cooperation at the international level. Studies of this kind help inform Mediterranean coastal states of the impacts of environmental degradation in regional sea areas, including the impacts of industrial activities beyond their own land and sea borders.  

Footnotes

1. Phosphogypsum is a waste product of fertiliser production.  The heavy metals it contains are toxic and it causes eutrophication (de-oxynegation of water and loss of biodiversity due to the excessive development of bacteria).
2. Much of the data were sourced from the FAO (https://www.fao.org/faostat/en/) and World Bank (https://databank.worldbank.org/) 

Source:

El Zrelli, R., Hcine, A., Yacoubi, L., Roa-Ureta, R. H., Gallai, N., Castet, S., Grégoire, M., Courjault-Radé, P., and Rabaoui, L. J. (2023). Economic losses related to the reduction of Posidonia ecosystem services in the Gulf of Gabes (southern Mediterranean Sea). Marine Pollution Bulletin, 186: 114418.

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“Science for Environment Policy”: European Commission DG Environment News Alert Service, edited by the Science Communication Unit, The University of the West of England, Bristol.

Notes on content:

The contents and views included in Science for Environment Policy are based on independent, peer reviewed research and do not necessarily reflect the position of the European Commission. Please note that this article is a summary of only one study. Other studies may come to other conclusions.