2. Breaking Waves: How Artificial Reefs are Protecting Coasts

Coastal Protection for Samsø Island
The BARREEF Project seen the implementation of an artificial reef east of Samsø Island. The purpose of this reef is to mitigate hydrodynamic energy, thus reducing erosion and sand wash-back along the coastline, of which there are many homes (see image below for location and erosion sites). The reef itself likely creates new habitats, different to the majority of sandy or muddy seabeds, promoting growth of seaweed and providing shelter for diverse marine life, including commercially important species like Atlantic cod (Gadus morhua). 


The reduced wave movement can also encourage the colonisation of eelgrass (Zostera marina). This aquatic plant can stabilise seafloor sediment through its horizontally growing root known as a rhizome. This rhizome creates new roots and shoots which further expands the eelgrass. Eelgrass beds can also store limited amounts of carbon from the atmosphere, and absorb some of nitrogen which can reduce eutrophication and improve the surrounding water quality. This plant can provide and support a suitable habitat for many marine animals, especially for juvenile fish and invertebrates.


Eelgrass Survey
Alongside another student, I conducted pioneer eelgrass surveys at three locations near the Samsø reef (see image below). Our first survey, right at the reef site, helped us choose two control sites – areas free from the reef's influence. It was important that these control sites were as similar as possible to the reef site (for example, similar water depth), so any future effects of the artificial reef would be clear. Since the reef had only been installed a few months prior, we predictably found 0% eelgrass at the reef site as there was not ample time for eelgrass colonisation to take place. The two control sites also showed 0% eelgrass coverage. If future surveys reveal an increase in eelgrass at the reef site, with minimal or no change at the control sites, it would be a strong indicator that the reef is successfully aiding eelgrass colonisation.


Location: Samsø, 8305 Samsø Municipality, Denmark

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