Underwater sea grass

Volunteer divers help scientists re-establish underwater meadows

10 min read

06 May 2021

Text

David J. Cord

Photo

Metsähallitus/Juuso Haapaniemi

10 min read

06 May 2021

Text:

David J. Cord

Photo:

Metsähallitus/Juuso Haapaniemi

The sea is filled with spectacular lifeforms, but some of the most important are humble. Off the coast of Finland, divers are trying to give the critical eelgrass a helping hand. 

Eelgrass is easy to overlook when compared with some sea life. The modest grass doesn’t quite have the panache of whales, coral reefs or octopuses. Yet, we are beginning to learn the importance of this little green plant. Unfortunately, the species is also declining. 

“Eelgrass is a key species in the Baltic, meaning that many other species depend on its existence. These underwater meadows are high-value habitats and are important for the entire marine ecosystem,” explains Aija Nieminen, specialist in marine conservation with Parks & Wildlife Finland (Metsähallitus), Finland’s state-owned company that manages the country’s public lands and waters.  

It may look unassuming, but the plant is critical to the marine environment. Eelgrass provides foraging areas and shelters for young fish. The grass is food for waterfowl and sea turtles. Some types of fish use eelgrass meadows as spawning grounds. With their roots, eelgrass can stabilise the sea bottom and reduce coastal erosion from waves. 

Eelgrass is also important for humans. It can decrease turbidity in the water, making it popular for beach-goers who like clear water. It can bind nutrients such as nitrogen. Seagrass also plays a critical role as a carbon sink.

The decline of eelgrass could have severe consequences on marine ecosystems and the oceans’ sequester of carbon. The situation could be particularly troublesome in the eastern Baltic which is struggling with eutrophication. 

“Nutrient runoff into the Baltic can induce an excessive growth of algae,” Nieminen explains. “Algae can grow on eelgrass and kill it.” 

It is, however, possible to re-establish the species. A few years ago, researchers in the waters of western Sweden were able to transplant eelgrass to places where it had disappeared. Finnish scientists were interested in trying the same thing, but they couldn’t do it alone. 

Watching grass grow is more exciting than you might think 

With the importance of eelgrass firmly established, the Metsähallitus experts were ready to begin their transplantation experiment.

“Before we could do the transplantation, we needed to select sites and get local permissions,” Nieminen says. “We mapped potential sites by drone and then either snorkelled or dived to get a closer look.” 

Some of the environmental factors they took into consideration include temperature, luminosity, sediment and potential disturbances like drifting algae mats and epiphytic algae that grows on eelgrass. 

They picked two places, with varying depths and seafloor, in a national park about 100 kilometres west of Helsinki. The idea was to see what works with transplanting eelgrass and compare their results to what the Swedish researchers experienced. The main goal of the pilot is to test the transplantation method. For this reason, they chose locations where eelgrass already grows, so they know the conditions are right for it. 

“In principal, transplantation is done when a species has disappeared from an area for one reason or another,” Nieminen says. “In those cases, it is crucial to study environmental factors more precisely.” 

Some of the tools they use to measure conditions are simple, such as floats on ropes to test how much algae grows. But they also wanted more high-tech tools. 

“According to the Swedish study, luminosity and temperature are the two most important factors for eelgrass, so we wanted to measure them precisely,” Nieminen says. “I’m a scientific diver, but I have never used sensors like the way we now wanted to use them. We had to find divers with the skills we needed.” 

Volunteer divers answer the call for help 

“The marine scientists at Metsähallitus heard about our Wärtsilä Project Baseline volunteer divers building sensor stations to detect oil leaks on old wrecks. They got in touch with us and asked if we were interested in helping with the eelgrass project,” says diver Mauro Sacchi.  

“I was delighted to hear that they needed our help,” says diver Mikko Gustafsson. “We’re volunteers, citizen scientists, and it made my day to learn that we could be of value to researchers. It’s very rewarding work.” 

It is also demanding work. The first thing Sacchi and Gustafsson needed was a design for a sensor station which fit Metsähallitus’ needs. 

“It needed to be simple and sturdy to handle the Baltic’s winter storms and swells,” Gustafsson says. “The station had to anchor securely into the sediment which could vary in different sites. It needed to be simple so we could modify it on the go. It had to be easy for scientists to get their data.” 

Working together to reach common goals 

It was a tall order, but their previous experience building sensor platforms came in handy. They built a station with a frame of PVC piping which supported sensors for luminosity and temperature. The sensors would take readings close to the seabed and one metre up. The data could be retrieved with a tablet computer or the sensor could be easily pulled and taken to the surface for downloading data. Metsähallitus approved the design. 

The project is a good example of how different groups work together for common goals. It became a partnership between government researchers, private citizens and corporations, working together to solve modern problems in a modern collaborative fashion. 

The public Metsähallitus group does important conservation work, yet has limited resources. Sacchi and Gustafsson are volunteers, but they both work for the energy and marine technology company Wärtsilä, where Sacchi is Director for Business Development and Gustafsson is Chief Project Engineer.  

The value of a blade of grass 

One goal for the project could be to establish value for the eelgrass. Policymakers often face trade-offs in allocating limited resources - and assigning value to species can provide a context to their value. However, scarce resources could also be spent on protecting marine areas, compensation payments for ecosystem damages or stimulating environmental markets.

“It would be worthwhile to evaluate eelgrass meadows and put a price tag on their value,” says Nieminen. “It is easier to estimate eelgrass’s value for commercial fishing and the binding of carbon and nutrients. It is more difficult to value eelgrass’s role in maintaining water visibility and marine biodiversity.” 

The Swedish study estimated that a hectare of eelgrass was worth 11,114 Swedish krona annually (approximately EUR 1100 ). This considerable number included the value the plant brought to commercial fishing, climate mitigation and nutrient regulation. 

The Swedish study found that fishing only represented a quarter of the total value of eelgrass. Regulating the nutrient nitrogen made up almost half of the economic value. Of course, the humble eelgrass has also intrinsic value that cannot be valued just by its economic impact.

Initial results look promising 

In mid-August 2020 eelgrass was collected and transplanted. Sacchi and Gustafsson made their dive to place the light and temperature sensors, and five weeks later the marine scientists dived to see how their new plants were doing. 

“At one of the sites we had 50% mortality in one plot and 10% in another,” Nieminen says. 

At the second site the mortality rate was better, ranging from 3  to 40%. Nieminen mentions that while the sediment at the first site was 42% sand, at the second site the sediment was 98% sand. 

“The composition of bottom sediment is very relevant when transplanting eelgrass,” she explains. “It needs to be coarse enough. For example, sand is optimal.” 

Another issue might be eelgrass’s tendency to adapt itself to precise local conditions. The eastern Baltic has such low salinity that eelgrass never flowers. Instead, it reproduces asexually through the growth of rhizomes in what is called vegetative reproduction. 

“Eelgrass here is very locally adapted. It is possible that shoots from one site are suited to one set of conditions and will not thrive in another site with different conditions,” says Nieminen. 

A labour of love 

In May 2021 they will return to the sites and see how the eelgrass nursery fared during the winter. Nieminen is eager to see the results, because the conditions off the coast of Finland can be different from what the researchers experienced in Sweden. 

“Ice conditions are also important for eelgrass,” she says. “In Finnish coastal waters ice effectively scrapes the bottom flora when it is shallow enough.” 

The marine scientists will look for more sites for eelgrass transplantation and combine the transplantation method with other restoration techniques. They will also see if this could work for other species of marine plants. If they need any more help in placing sensors, they know where to turn. 

“I’m happy that our experience designing and installing underwater environment monitoring stations is useful for this project,” Sacchi says. “We are doing this because we love the sea and want to help protect it. It is a privilege to be part of the cooperation between Metsähallitus and Wärtsilä. We are all driven by the same values.”