TEXEL–Extensive research in a bay on French St. Martin and the coastline of Yucatán in Mexico has shown that seagrass beds are so effective in protecting tropical beaches from erosion that they can reduce the need for regular, expensive beach nourishments that are used now.
In a recent article in the journal BioScience, titled Maintaining Tropical Beaches with Sea grass and Algae: A Promising Alternative to Engineering Solution, biologists and engineers from the Netherlands and Mexico described experiments and field observations around the Caribbean Sea.
The team of scientists argued that preserving and restoring vegetated beach foreshore ecosystems offers a viable, self-sustaining alternative to traditional engineering solutions, increasing the resilience of coastal areas to climate change.
“A foreshore with both healthy seagrass beds as well as calcifying algae is a resilient and sustainable option in coastal defence,” said lead author Rebecca James, a PhD-candidate at University of Groningen and the Royal Dutch Institute for Sea Research NIOZ in the Netherlands. “Because of erosion, the economic value of Caribbean beaches literally drains into the sea.”
The authors looked at beaches in the Caribbean, where almost a quarter of the gross domestic product (GDP) is earned in tourism which centres around the beaches.
“With the increase of coastal development, the natural flow of water and sand is disrupted, natural ecosystems are damaged, and many tropical beaches have already disappeared into the sea,” said co-author Rodolfo Silva, a professor of Coastal Engineering at Universidad Nacional Autónoma of Mexico.
“Until now, expensive coastal engineering efforts, such as repeated beach nourishments and concrete walls to protect the coast, have been made to combat erosion. Rising sea-level and increasing storms will only increase the loss of these important beaches,” said Silva.
Natural foreshore stabilisation and nourishment may provide a sustainable and resilient long-term solution. Field flume and ecosystem process measurements, along with data from the literature, show that sediment stabilisation by seagrass in combination with sediment-producing calcifying algae in the foreshore forms an effective mechanism for maintaining tropical beaches.
To find out to what extent seagrass beds are able to hold sand and sediment on the beach foreshores, Rebecca James and her promoter, professor Tjeerd Bouma of NIOZ and Utrecht University, conducted a simple but telling experiment. With a portable and adjustable field flume to regulate water motion in a French St. Martin bay, they observed when particles on the sea bed started moving.
“We showed that seagrass beds were extremely effective at holding sediment in place,” said James. “Especially in combination with calcifying algae that ‘create their own sand,’ a foreshore with healthy seagrass appeared a sustainable way of combating erosion.”
Along the coastline of the Mexican peninsula of Yucatan, the team put their theory to the test.
“By looking at beaches with and without protection of healthy seagrass beds, we showed that the amount of erosion was strongly linked to the amount of vegetation: more seagrass meant less erosion,” said co-author Dr. Brigitta van Tussenbroek of Universidad Nacional Autónoma in Mexico.
At beaches where seagrass beds were destroyed, the researchers saw a sudden strong increase in erosion, resulting in an immediate need for expensive beach nourishments.
According to co-author Johan Stapel of Caribbean Netherlands Science Institute in St. Eustatius, this will require a multilateral approach in conservation and restoration, as seagrass faces increasing pressure from various sources of pollution and invasive species. NIOZ has a strong tradition in successfully restoring all kinds of coastal vegetation from seagrass to mangroves.
The research was carried out by marine scientists from the Netherlands (NIOZ, Utrecht University, Radboud University Nijmegen, Technical University Delft and Deltares), Mexico (Universidad Nacional Autónoma de México) and St. Eustatius (Caribbean Netherlands Science Institute).
Source: The Daily Herald https://www.thedailyherald.sx/islands/84200-seagrass-saves-beaches-and-money-scientists-conclude
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