Algal Forest Restoration in the Mediterranean Sea (AFRIMED)

Members of the Sargassum family, Cystoseira are a genus of brown algae. They are comprised of about 40 species and have their highest diversity in the Mediterranean Sea, followed by the Northeast Atlantic (Jódar-Pérez et al. 2020; Bruno de Sousa et al. 2017). These brown algae are typically found in the infralittoral fringe on rocky reefs, forming macroalgal forest habitats.

Cystoseira macroalgal forests are important ecosystem engineers in the Mediterranean sea, providing valuable and important ecosystem functions and services to coastal Mediterranean communities. These ecosystem services relate to coastal primary production and nutrient cycling, providing food, shelter, nurseries, and habitat for many vertebrate and invertebrate species (Cebrian et al. 2021). The delivery of these services can vary by species and composition of the macroalgal forests. Structural complexity typically varies with depth, whereas population and community dynamics (e.g. growth rates and productivity) tend to slow as depth increases (Cebrain et al. 2021).

Cystoseira macroalgal forests are being lost at an alarming rate as a result of degradation drivers including eutrophication, overgrazing (by sea urchins and herbivorous fish present in high densities), increasing coastal sediment loads, and the impacts of urbanisation. Remaining populations are experiencing increasing range contraction and fragmentation, often resulting in coastal ecosystems shifting from complex, productive systems to less structured assemblages (e.g. dominated by turf algae or sea urchin barrens) (Mancuso et al. 2021; Mineur et al. 2015). As a result, all but one Cystoseria spp. are identified as conservation priorities by the  Barcelona Convention (Annex II) .

There is little evidence of the macroalgal forests recovering naturally, even when the drivers of their loss are addressed, due to local populations becoming extinct and switching to sea urchin barrens or algal turfs (Cebrian et al. 2021). Therefore, active restoration interventions are critically important to their recovery, alongside mitigating and eliminating their stressors where possible. Due to the endangered status of Cystoseira, harvesting remaining populations and transplanting them to new locations is not desirable. Therefore, innovative actions are needed, and the AFRIMED project is aiming to address this need in the Mediterranean Sea basin.

Algal Forest Restoration In the MEDiterranean Sea (AFRIMED), is an algal forest restoration project, focusing on the restoration of Cystoseira habitats in the Mediterranean Sea. The project involves research and restoration across sites in Europe and North Africa. AFRIMED’s key objectives are to develop innovative habitat restoration methodologies; provide a vital framework to up-scale current approaches; and develop knowledge on Cystoseira ecosystems. 

Successfully restoring Cystoseira habitats is a key aim of the AFRIMED project. Alongside this, the project aims to demonstrate the benefits of restoring Cystoseira habitats through assessing changes in ecosystem service provisioning from restoration interventions. This outcome will help to communicate the importance of restoring these habitats by providing evidence of the wide range of benefits they provide.

A number of restoration techniques are being trialed and deployed by the AFRIMED project sites. These techniques include obtaining recruits from fertile branches of healthy donor populations. These are then placed either directly in the area to be restored (in-situ) or cultured in facilities and then transported to the restoration sites (ex-situ). Selection of the most appropriate technique depends on a number of factors, including the availability of facilities, distance to restoration sites, dispersal capacity of target species, hydrodynamic characteristics of the restoration sites, and grazing pressure.

Other complementary actions to improve the outcomes of restoration attempts include providing free substrate, excluding herbivores such as Sarpa Salpa (e.g. through use of exclusion cages), establishing a marine protected area (MPA), and controlling sea urchin populations through harvesting and culling (Cebrian et al. 2021).

Have a look at the images below to see the journey from the lab to the field of ex-situ cultured Cystoseira recruits by AFRIMED partner INALE in Greece.

Cystoseira species are distributed along the coast of the Mediterranean. Data from Fabrizzi et al. (2020) is shown in the map below, along with the AFRIMED restoration sites.

AFRIMED involves restoration sites throughout the Mediterannean basin, each being led by different partners and collaborators.

On the map below, the location of AFRIMED sites is shown by the green numbered dots. Information includes restoration actions, outcomes, perceived benefits and species being restored. The species fall under Cystoseira sensu lato and therefore include Ericaria and Gongolaria species. Move through the map below to explore and learn about the different sites and the organisations involved.

The boundaries and names shown and the designations used on this map do not imply official endorsement or acceptance by the United Nations.

Cystoseira macroalgal forests are important ecosystem engineers and habitat formers, providing key ecosystem functions which underpin the delivery of a range of marine ecosystem services (De La Fuente et al. 2019a). However, the benefits provided by Cystoseira habitats are not well understood or documented, particularly at larger spatial scales. Based on available literature key benefits include habitat structuring and provisioning, supporting species richness and diversity, maintaining nursery populations and habitats, nutrient cycling and primary production, bioremediation, use in medicines and food, and use as indicators of ecosystem health.

Restoring Cystoseira macroalgal forests has the potential to enhance these services to the benefit of people and nature.

Fisheries and biodiversity conservation

Cystoseira macroalgal forests provide habitat structuring functions, shelter, and protection for a diverse number of fish, invertebrates, epiphytes, and bacteria species in the Mediterranean sea (De La Fuente et al. 2019b; Ape et al. 2018). They also provide important sources of primary production, as well as food for herbivorous species, and habitat for important prey species on which consumers can feed, supporting the food chains in the Mediterranean Sea (Papadakis et al. 2021; Hinz et al. 2019; Thibaut et al., 2016). As a result, complex Cystoseira macroalgal forests support high levels of species richness and biodiversity (Mancuso et al., 2022; Bianchelli et al. 2016). However, high levels of grazing by herbivorous fish (such as Sarpa salpa) and invertebrates (such as sea urchins) are also a leading cause of their decline (Piazza and Ceccherelli 2019).

Cystoseira macroalgal forests also maintain nursery populations and habitats of species of commercial and recreational interest (e.g. for snorkeling and SCUBA diving) (Chiarore et al. 2019; Thiriet et al. 2016). Providing food and shelter for commercially and recreationally important species can play a role in maintaining the livelihoods those who depend on them.

Bioindicators and bioremediation

Cystoseira provides important nutrient and biogeochemical cycling functions (Signa et al. 2020). These functions are key to maintaining healthy, productive ecosystems.

Cystoseira, and other macroalgal forests, can play an important bioremediation function by removing excess nutrients (e.g. nitrogen) and pollutants (e.g. heavy metals) from the water (Ak et al. 2020; Celis-Plá et al. 2016). Deniz & Karabulut (2017) and Deniz and Tezel (2017) showed that a seaweed mix including Cystoseira species can be used to remove zinc and copper ions in water and Rani et al. (2016) found Cystoseira indica was efficient for the removal of cobalt. Therefore, these ecosystems have the potential to play a role in improving water quality, benefitting local communities and marine life.

Cystoseira species have also been recognised for their ability to be used as bioindicators, due to their sensitivity to several pollutants, inlcuding Chromium, Lead, and Cadmium (Benfares et al. 2015). This information can be used to understand whether coastal waters are polluted, by assessing the level of pollutant bioaccumulation in their tissues (Benfares et al. 2015), or by monitoring their distribution (Signa et al. 2020). Species known to be sensitive to certain pollutants may provide an early warning system for monitoring the health of coastal areas. In Europe, Cystoseira are one of the Biological Quality Elements (BQE) used to assess the ecological quality of coastal water bodies under the European Water Framework Directive (2000/60/EC) (Bianchelli and Donavaro 2020).

Use in food production, medicines, and bioenergy

The benefits provided by Cystoseira dont just occur in the sea. Researchers have found a range of uses for the species. Cystoseira has potential uses as food sources (Trica et al. 2019), food additives (Benslima et al. 2021), as well as potential uses in medicines due to their antioxident, anti-inflammatory, and anti-cancer properties.

Hentati et al. (2019) investigated the use of Cystoseira compressa in fish burgers and found that due to their antioxident properties they could be used as nutritious additives. Oucif et al. (2018) studied the use of C. compressa in fatty fish storage, and found that promising results for their use in quality retention during commercialisation. Cystoseira mediteranea extracts were used as a biostimulant to reduce the effect of salt stress on barley seedlings by Bensidhoum and Nabti (2021). They have also been investigated as a potential source of organic fertiliser (Atzori et al. 2020).

Cystoseira have many properties which could render them useful in medicinal applications. They are a natural source of antioxidants (Kord et al. 2021), have anti-inflammatory properties (Julião et al. 2021), and extracts from some species have exhibited antiproliferative activity against cancer cell lines (Montalvão et al. 2016; Vizetto-Duarte et al. 2016).

Finally, Cystoseira extracts have potential uses within the energy sector. Cioroiu Tirpan et al. (2019) found Cystoseira extracts could potentially be used for bioethanol production.

Carbon storage and sequestration

Macroalgal forests are an important, but often overlooked store of blue carbon. There is growing evidence that over their life cycles, their biomass can be transported into deep-sea sediments, where they can remain ‘locked up’ for potentially very long periods of time (Ortega et al. 2019; Krause-Jenson et al. 2018; Krause-Jensen and Duarte, 2016). A recent global study by Krause-Jensen and Duarte (2016) estimated that around 173 TgC yr−1 (with a range of 61–268 TgC yr−1) could be sequestered by macroalgae. They estimate that the majority of this carbon is exported to the deep sea and a small fraction is buried in coastal sediments. This estimate is larger than those of seagrass coastal habitats showing the important contribution macroalgae could make to blue carbon storage. However, these estimates must be interpreted with caution, and they include a range of macroalgal species with different carbon sequestration abilities. Furthermore, the permanence of carbon stored in these ecosystems is not well understood compared to terrestrial ecosystems (Hendriks et al. 2022).

Some studies have mentioned that Cystoseira sequesters carbon into their biomass (Celis-Plá et al. 2016). However, they found that biomass carbon varied seasonally and did not look at the long-term storage of this carbon. Therefore, there are gaps in the knowledge of the extent to which Cystoseira macroalgal forests contribute to global climate regulation.

Control of invasive algae species

Caulerpa cylindracea, a green algae species, was first found in the Mediterranean in 1985. Since then it has spread throughout the Mediterranean, threatening native ecosystems (Pierucci et al. 2019). Some species of Cystoseira have been found to resist invasion by C. cylindracea, these are Cystoseira compressa (Esper) and Cystoseira brachycarpa (Piazzi et al. 2018; Bulleri et al. 2016). However, Bulleri et al. (2016) found that some species of Cystoseira either had no effect on C. cylindracea invasion (Cystoseria barbata) or had a positive effect on invasion (Cystoseira crinita). The effectiveness of C. compressa in resisting invasion was also dependant on disturbance effects. Therefore, more research is needed to understand the potential use of Cystoseira species in resisting the expansion of Caulerpa cylindracea.

Knowledge Gaps

During expert consultations with AFRIMED partners, a number of services were highlighted where evidence is currently lacking. These included wave attenuation (coastal protection), direct links to tourism (diving and snorkeling), traditional uses, pH regulation, and oxygen production.

As we have seen, Cystoseira macroalgal forests provide a number of vital functions and services, and their loss would be detrimental to the health of coastal ecosystems, biodiversity, and local and global communities.

It is therefore vital that we better understand the extent of benefits provided by these habitats, and how they are affected by degradation, restoration, and factors such as location and species. In doing so, we can understand what we hope to gain in restoring them, and why it is so important to protect remaining habitats.

2021 marked the beginnings of both the UN Decade on Ecosystem Restoration and the UN Decade of Ocean Science for Sustainable Development.

Both of these initiatives offer opportunities to celebrate restoration projects such as AFRIMED, as well as scaling up these efforts beyond the Mediterranean and the projects lifetime.

AFRIMED can help contribute to the success of both Decades, by contributing ambitious, wide-scale restoration outcomes for Cystoseira habitats as well as evidence and scientific knowledge which can help guide both restoration practitioners and policy-makers.

 Find out more about AFRIMED here  http://afrimed-project.eu/ 

We would like to thank all members of the AFRIMED team for their contributions, insights and reviews.

Find out more about UNEP-WCMC's work restoring marine and terrestrial ecosystems here  https://unep-wcmc.org 

This project has received funding from the European Union’s EMFF programme under grant agreement - EASME/EMFF/2017/1.2.1.12/S4/01/SI2.789059.

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