Eelgrass and seaweed are essential for healthy fjords and coastal waters

"Eelgrass is super important for the ecological condition of Danish fjords and coastal waters. The plants improve the water quality by e.g. to absorb nutrients, and they strengthen marine biodiversity measured as more species richness. For example, we can see more fish and benthic animals coming where we have transplanted eel grass."

This is what Karen Timmermann, professor at DTU Aqua and lead author of the new report, which gathers results on the ability of eelgrass and seaweed to collect nutrients and contribute to other good environmental effects in coastal waters, says.

Eelgrass – indicator species and strong ecological agent

In the project 'Development initiatives for marine agents', DTU Aqua, together with the four universities Southern Denmark University, Århus University, Copenhagen University and DTU and DHI Group, have experimented with transplanting eelgrass to selected areas on the bare seabed in order to obtain new knowledge about eelgrass as a marine means of action when you include both environmental effects, economic aspects and legal aspects of the method.

In the places where the researchers transplanted eelgrass and created new beds, they could measure a richer presence of benthic animals after only two months, and measurable improvements in the fish community after two to three years. And after a few years, the biodiversity in the transplanted eelgrass beds is on par with the diversity in the natural beds in the same area.

"Our report shows that eelgrass is a decisive factor for a good marine environment - even if it is not a tool that can contribute significantly to storing CO2 and saving us from climate change. These are two different things," says Karen Timmermann and elaborates in relation to the climate statement:

"In relation to sequestering CO2, eelgrass can function as at least temporary carbon storage and thus potentially contribute to reducing CO2 emissions into the atmosphere. But there is great uncertainty associated with calculating how much or how little the natural or planted eelgrass beds can store and over how many years. Therefore it cannot be included as an element in the climate accounting.”

Looking legally at the possibility of using the planting of eelgrass as a marine tool, the report generally points out that there is an EU legal obligation to actively implement the necessary initiatives to achieve a 'good ecological condition'.

For this task, eelgrass is an obvious choice, as eelgrass is seen as the central indicator species for achieving the water framework directive's environmental goals and is also a characteristic species for several of the habitat directive's habitat types

Sugar kelp – great use value and contributes to the absorption of nutrients

Sugar kelp is a large perennial brown algae that is grown on lines and in nets and harvested in widely in Europe. Seaweed is used for many things such as food, ingredients, feed, materials for bioplastics or textile fibres, energy and fertiliser. The plant is found naturally in the Danish sea.

As a marine agent, its strength is that, like eelgrass, it collects nutrients from the water. Nor can it be considered a strong remedy against C02 and climate change, as cultivated seaweed does not contribute to permanent carbon storage.

The report concludes that sugar kelp can absorb and bind nutrients, but is not of great importance for achieving good ecological condition, probably because the macroalgae primarily absorb the nutrients during the winter period.

In relation to the legal aspects, the researchers in the report draw attention to the fact that when the authorities want to give permission to set up cultivation facilities for seaweed, it is very important to first carry out a thorough investigation of the specific environmental conditions associated with the project, both the existing conditions and the project's possible environmental impact, i.e. in relation to Natura 2000 areas and environmental goals.

Basis for decision on marine instrument to achieve 'good ecological condition'

The DTU Aqua report is the first of a series on the project Development initiatives for marine instruments, which is financed by the "Agreement on the green transition of Danish agriculture" from 2021 and implemented via the Danish Environmental Protection Agency.

The results from the project, which are collected in the reports, must form the basis for a political decision on, and if applicable, how the marine measures such as "reestablishment of eel grass" and "cultivation of seaweed" can be used in water planning with a particular aim of collecting nutrients and would also like to contribute to other positive environmental effects, which can contribute to faster achieving a good ecological condition in accordance with the water framework directive in the Danish coastal sea areas.