Onderwater golfbreker bevordert biodiversiteit

Submerged breakwater boosts biodiversity

Avlékété, Benin

Around the world, coastal ecosystems are under pressure. The culprits? Climate change, human activities and extreme weather events. Tropical countries, such as West African ones, are especially vulnerable. In Benin, for instance, the Atlantic Ocean swallows up more and more land. This not only threatens houses, ports, but also causes floods, and soil erosion. Insert a nature-based underwater breakwater we finalised in 2021. This to reduce erosion but also to ensure a safer area for swimming and maybe a hotspot for life underwater. Today, three years later, we return and examine the results of this construction.

Rock installation vessel Pompeï installed the submerged dyke along Benin's coastline

The project

A submerged dyke to protect Benin's coastline against the impact of the Atlantic ocean

Early 2018, we started extensive coastal protection works off the coastal town of Avlékété. The government of Benin commissioned this project.

We built a submerged breakwater parallel to the coast in combination with sand replenishment. The underwater breakwater ensures that waves continue to reach the coast but with less energy. In this we have been inspired by nature: coral reefs. These are also situated in the shallows and just off the coast.

Rock installation vessel Pompeï installed the submerged dyke along Benin's coastline
3
years
We realised the project in 3 years time.
5
km
We built a 5-km long dyke to protect the coastline.
1.2
million tonnes
We installed boulders from 1 to 3 tonnes, in total 1.2 million tonnes.
2.5
million m³
We delivered 2.5 million m³ of sand to widen the beach

Nature-based solutions

The 5-kilometre-long submerged breakwater is a great example of a Nature Inspired Design. By imitating the shape of a barrier reef, we provide coastal protection but also create the basis for a rich and thriving ecosystem. By giving Nature Inspired Design a key place from the start of the project, we were able to encourage biodiversity and improve the natural environment around the project.

Nature-based solutions

So much more than construction

We always aim to build greater and better, but we also care about the bigger results of a project. Three years after finishing the project, we continue to research the long-term impact of the 5-kilometre long submerged breakwater on the marine environment, the coastal protection and the socio-environmental dynamics. We do this by continuing our collaboration with stakeholders such as artisanal fishermen and local knowledge institutes.

  • Marine environment

    Marine environment

  • Coastal protection

    Coastal protection

  • Socio-environmental dynamics

    Socio-environmental dynamics

Video

Discover how

Our colleagues Jonas Van Acker and Ruben Geldhof recently returned to Benin to conduct marine and socio-environmental research.
Three different techniques to measure the increase in marine biodiversity

To map fish biodiversity, we monitor and identify the species found in nets deployed by the fishermen along the breakwater and compare them with an area without breakwater. We do this to see if the breakwater attracts a greater diversity of species compared to areas without such structures. The taxonomic expertise of our local partners played a crucial role in this study. The first results are promising! The breakwater contains much more diverse marine life than the comparison areas.

To analyse the marine life growing on the boulders and present in the surrounding sand, we took sediment samples and sieved out the small critters within. At the same time, a professional diving team collected corals, sponges, algae, and other marine life attached to the boulders. To identify all these critters, we are collaborating with the University of Abomey-Calavi in Benin and the Institute of Agriculture and Fisheries (ILVO) in Belgium.

 

Finally, we also apply a new and interesting technique: environmental DNA (eDNA). This method involves extracting and analysing genetic material from environmental samples like seawater to detect and identify species present in a given environment.

  • Fish biodiversity

    Fish biodiversity

  • Sediment samples

    Sediment samples

  • Environmental DNA

    Environmental DNA

How we create DNA barcodes to complete database

Since Benin is a scientifically understudied region, some of the species here do not have a DNA barcode assigned to them. These species cannot be detected using the eDNA technique. To address this issue, we are collecting DNA samples from all identified fish species in artisanal fishing nets, enabling the creation of DNA barcodes for each species. This approach generates valuable data for an understudied region and enhances the capability to detect these species in our eDNA samples.

Together with our partners we will analyse and interpret the results during the coming months. So stayed tuned for more updates on our website soon. Our objective is to compile all information to gain a comprehensive understanding of the long-term ecosystem development and socio-environmental impact resulting from the underwater breakwater in Benin. However, what we can already affirm after our visit to Benin is that not only was it a warm experience, but, most importantly, the robust resilience of this innovative solution is nothing short of remarkable.

 Together with our partners we will analyse and interpret the results during the coming months.