Seagrass meadows are ecosystems that provide various ecosystem services, such as habitat and maternity for various commercially valuable species and carbon dioxide superabsorption, with an estimated capacity to remove 15 times more carbon dioxide than the rainforest. The recent mapping carried out in Cape Verde exceeded expectations, noting that there are larger and richer areas than previously identified, including a new species. It is now important to continue working to preserve these systems, which are so rich and important for biodiversity and human subsistence.

Seagrasses are marine flowering plants found on the coasts of all continents except Antarctica. Seagrasses are angiosperms (Division Antophyta, Class Liliopsida, subclass Alismatidae), which are distributed in coastal waters, lagoons and estuaries, up to 70 meters deep. There are around 70 species worldwide, grouped into 12 genera, four families and two orders.

Seagrass meadows are among the most threatened marine ecosystems in the world, but they also provide very important and productive essential ecosystem services that benefit humans. For example, they serve as a habitat for multiple life stages of commercially valuable fish and invertebrates, support local communities as sources of livelihood, improve water quality, stabilize sediments and provide coastal protection services by attenuating the energy of currents, waves and tides.

In addition, seagrasses, like mangroves and wetlands, are collectively known as blue carbon ecosystems for their essential role in mitigating climate change due to their efficient capacity to sequester and store organic carbon in sediments over the long term. Research in recent years has shown that one hectare of seagrass can absorb as much carbon dioxide per year as 15 hectares of rainforest. Despite all the essential benefits at local and global scales, there has been a decline in seagrass cover worldwide, which is mainly attributed to anthropogenic impacts.

Three seagrass species occur in West Africa: Zostera noltii, Cymodocea nodosa and Halodule wrightii recorded in seven countries. Although Ruppia maritima is also found in West Africa, it can be classified as a salt-tolerant freshwater species, although the IUCN Red List includes all species of the genus Ruppia as seagrasses (Grid-Arendal 2022). However, this small number of species does not reflect the high importance of seagrass ecosystems that provide a protected, nutrient-rich habitat for marine flora and fauna.

The main functions of seagrass are:

• Super absorption of carbon. Seagrasses absorb carbon from the atmosphere 35 times more than tropical jungles, making them a strong ally in the fight against global warming.
• Global carbon storage. Despite covering only 0.02% of the seabed, seagrasses account for 10% of annual global carbon storage.
• Coastal protection. Underwater meadows form a natural barrier against erosion, protecting coastal communities from the impact of rising sea levels.
• Habitat for fish. It’s not just commercially important fish such as grouper, bream or whiting that benefit from the seagrass ecosystem; numerous species depend on this habitat to survive.
• Oxygen production. Seagrasses are essential in supplying oxygen, contributing to the health of the ocean and sustaining various forms of marine life.
• Clearing up the sea. By absorbing and filtering polluting nutrients, seagrasses play a vital role in keeping the ocean clean and safeguarding its delicate balance.

In Cape Verde, seagrass meadows have been incorporated into the nationally determined contribution (NDC), the non-binding commitment submitted to the United Nations Framework Convention on Climate Change to reduce greenhouse gas emissions at the national level and adapt to the impacts of climate change. Cape Verde and Sierra Leone are among the first countries to include seagrass in their NDCs, not just in Africa, but in the world (Grid-Arendal 2022).

The first record of seagrass in Cape Verde was reported in 2016 by Creed et al. (2016) at a wave-protected site between Gamboa and Santa Maria Islet, Praia, Santiago Island.

In 2023, the ECOCV Association in partnership with the National Directorate for the Environment, in collaboration with NeptuneCV, Prof. W.J.Szymaniak of UniPiagetCV and artisanal fishermen, carried out the exploration and mapping of seagrass meadows on the island of Santiago. The results exceeded the initial objectives with the recording of meadows in four new locations, in addition to Gamboa (Holodule wrightii) and Pedro Badejo Lagoon, Santa Cruz (Rupia marítima), seagrasses were confirmed in: Baia de São Francisco, Praia (Holodule wrightii), Porto Lobo, São Domingos (Holodule wrightii), Baia Nossa Sra. da Luz, São Domingos (Holodule wrightii) and Baia de Angra, Tarrafal (Holodule wrightii, Cymodocea nodosa). Cymodocea nodosa was recorded as a new marine species for Cape Verde. The mapping of the meadows showed that Angra Bay has the largest meadow in Santiago with an area of 55,214 m2. As a result of the project, knowledge of the coverage of coastal areas with seagrass on the island of Santiago increased 14-fold, from 6,000 m2 in 2021 to 91,846 m2 in 2023.

However, anthropogenic impacts were also noted in each of the seagrass meadows on Santiago Island, including: plastic/garbage pollution; damage caused by fishing anchors, with the greatest impact in Angra Bay, damage from net fishing in the meadow areas, sand harvesting in coastal areas and coastal development and construction, which cause pollution and coastal erosion.

Based on the results of the monitoring, recommendations were developed to support the development of an Action Plan for the conservation of seagrass meadows in Cape Verde and to protect the ecosystem services of these species and their habitats.

A high level of urgency and the establishment of special protection zones are recommended in at least three areas with the largest seagrass meadows to minimize negative anthropogenic impacts in Baía de Angra with priority given to it being the largest meadow with the two seagrass species and holding the greatest marine biodiversity of all the areas assessed. Intense artisanal and semi-industrial fishing has been recorded with consequent damage and fragmentation of the meadows Porto Lobo Bay with a high amount of rhizomes on the surface possibly due to anchor damage, and discoloration of the leaves requiring further monitoring to identify the causes, as well as sand extraction on both coasts of the bay and Gamboa as a unique urban ecosystem, exposed to coastal development and urban pollution. Continuous monitoring is necessary to prioritize and implement mitigation measures for the impacts identified. In-depth assessment of ecosystem services by each meadow and as a whole needs to be implemented to evaluate the potential of seagrass meadows as a nature-based solution for climate change mitigation and ecosystem resilience on Santiago Island. It is essential to strengthen the involvement of coastal communities and citizens in the participatory conservation and monitoring of seagrass meadows. Finally, it is recommended to explore options for blue carbon credits or carbon offsets as part of blue finance for the sustainable development of the blue economy in Cape Verde.

Bibliographical references

Creed, J. C., Engelen, A. H., Oliveira, E. C. D., Bandeira, S., and  Serrão, E. A. (2016). First record of seagrass in Cape Verde , eastern Atlantic. Marine Biodiversity Records, 1–4.https://doi.org/10.1186/s41200-016-0067-9

GRID-Arendal (2022) Campos do Conhecimento: Colocando a África Ocidental no Mapa Global de Ervas Marinhas. ResilienSEA (GRID-Arendal/ RAMPAO/WIACO): Arendal, Noruega, p.

Author

Edita Magileviciute
Bióloga Marinha Associação ECOCV