Volunteer Divers Help Scientists Re-establish Underwater Meadows

The sea is filled with spectacular lifeforms, but some of the most important are humble and unassuming. One such species, eelgrass, doesn’t quite have the panache of whales, coral reefs, or octopuses and is easy to overlook when compared with some sea life. We are beginning to learn the importance of this little green plant; however, eelgrass, like so many other aquatic species, is declining. Off the coast of Finland, divers are trying to give the critical eelgrass a helping hand.

“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,” explained Aija Nieminen, a specialist in marine conservation with Mets?hallitus, Finland’s state-owned company that manages the country’s public lands and waters. 

Despite its obvious importance, an estimated twenty-nine percent of global seagrass area has disappeared since data recordings first began in 1879.[1]

The disappearance of seagrass is troubling, but it is possible to re-establish species. Wolves in Wyoming, beavers in the UK, and albatrosses in Japan are all successful examples of effective species re-introduction efforts. A few years ago, researchers in western Swedish waters were able to transplant eelgrass to new locations. Finnish scientists were interested in trying the same thing, but they could not do it alone.

Unassuming Doesn’t Mean Unimportant

Eelgrass (Zostera marina), is one of many types of seagrasses and can be found in the cooler waters of the northern Atlantic and Pacific oceans. Its narrow green leaves look like blades of grass. In clear, shallow waters, the leaves might be only a few centimeters long, while leaves of deeper plants could measure up to 1 m (3 ft) long. 

It may not look like much, but this plant is critical to the marine environment. Eelgrass provides foraging areas and shelters for young fish, and it is food for waterfowl and sea turtles. Some types of fish use eelgrass meadows as spawning grounds. With their roots, eelgrass can stabilize the sea bottom and reduce coastal erosion from waves.

Eelgrass is also important for humans. It can decrease the turbidity of water, making it appealing for beachgoers who like clear water. It can bind nutrients, such as nitrogen, and in addition to supporting commercial fisheries and protecting against beach erosion, seagrass plays a critical role as a carbon sink. Although seagrass only covers about 0.1 to 0.2 percent of the ocean floor, its carbon sink capacity may account for up to eighteen percent of the total oceanic carbon burial.[2]

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

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

This can turn into a vicious cycle. Eutrophication can kill eelgrass, and less eelgrass means less nitrogen is bound; less bound nitrogen makes eutrophication even worse.

Watching Grass Grow is More Exciting than You Might Think

With the importance of eelgrass firmly established, the Mets?hallitus experts were ready to begin their transplantation experiment. They approached the job methodically. 

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

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

They picked two places in a national park about 100 km (62 miles) west of Helsinki. The two sites had varying depths and different types of seafloors. The idea was to see what works and what doesn’t when it comes to transplanting eelgrass, and then compare their results with those of the Swedish researchers. Because the main goal of the pilot project was to test the transplantation method, they chose locations where eelgrass already grows, so they knew the conditions were suitable for species survival.

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

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

“According to the Swedish study, visibility and temperature are the two most important factors for eelgrass, so we wanted to measure them precisely,” Nieminen said. “I’m a scientific diver, but I have never used sensors in 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 Mets?hallitus heard about our 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,” said diver Mauro Sacchi. 

(The mission to find leaking wrecks was detailed in “Project Baseline in Finland Raises Awareness of Threats to the Baltic” in Quest Vol. 21, No. 3.) 

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

It was also demanding work. The first thing Sacchi and Gustafsson needed to do was design a sensor station that met Mets?hallitus’ needs.

“It needed to be simple and sturdy,” Gustafsson said. “It needed to be sturdy to handle the Baltic’s winter storms and swells. 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 that contained sensors for luminosity and temperature. The sensors would take two readings: 1 m (3 ft) above the seabed and then close to the seabed. The data could be retrieved with a tablet computer—similar to what the Project Baseline team had done previously—or the sensor could be easily pulled and taken to the surface for downloading. Mets?hallitus liked the design and approved it.

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

The public Mets?hallitus 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 W?rtsil?, where Sacchi is the Director, Business Development and Gustafsson is Chief Project Engineer. 

W?rtsil? encourages their employees’ volunteer work and is also directly involved in marine conservation efforts, such as sponsoring marine cleanup activities or partnering with Finnish authorities to upgrade their research vessel.

The Value of a Blade of Grass

One goal of the project was to assign an economic value to the eelgrass. It might seem odd to put a monetary value on an aquatic plant, but there are good reasons to do so. Policy makers constantly face trade-offs in how to spend limited resources on environmental protection. By determining the economic value of a species and the services they may provide, decision makers can frame the species’ importance within an economic context. Scarce resources can be more properly allocated for actions such as the establishment of protected marine areas, the development of compensation payments for ecosystem damages, or stimulating environmental markets.

“We want to evaluate eelgrass meadows and put a price tag on their value,” said 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 ($540 USD per acre) annually.[3]This not-inconsiderable 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. The researchers also noted the loss of eelgrass off the Swedish coast and the substantial reductions in fish production and mineral regulation.

And, of course, there is the intrinsic value as well. No, eelgrass might not be as engrossing to watch as seahorses, but there is an undeniable beauty to it. It should be protected for more than its impact on our profit margins.

Initial Results Look Promising

In mid-August 2020, eelgrass shoots were collected and transplanted the next day. Following the example of the Swedish study, the researchers in Finland planted the shoots 25 cm (10 in.) apart in a 1 m2 (11 ft2) plot. Each site had three plots, which each held sixteen shoots. 

Sacchi and Gustafsson dived to place the light and temperature sensors; five weeks later, the marine scientists dived to see how their new plants were doing.

“At one of the sites we had fifty percent mortality in one plot and ten percent in another,” Nieminen said. “The plot closest to the shore in the shallowest water had the highest mortality. It was less than 3 m (10 ft) deep there, and we had a very warm summer, so it is possible that heat was a factor. In the Swedish study, they determined the optimal depth was 1.5–2.5 m (5–8 ft). Maybe here in Finnish waters we will find they need to be deeper, such as 3–4 m (10–13 ft).”

At the second site, the mortality rate was better, ranging from three percent to forty percent. Nieminen mentions that while the sediment at the first site was forty-two percent sand, at the second site the sediment was ninety-eight percent sand.

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

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

“There have been cases where a hectare of eelgrass has been traced back to only two individuals,” said Nieminen. “This means that 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.”

A Labor of Love

In May 2021, divers will return to the sites to survey how the eelgrass nursery fared during the winter. Nieminen is eager to see the results because the conditions off the coast of Finland are quite a bit different than those in the earlier Swedish study.

“Ice conditions are also important for eelgrass,” she explained. “The previous study in western Sweden was in waters that don’t freeze in the winter. In Finnish coastal waters, ice conditions need to be considered, because ice effectively scrapes the bottom flora when it is shallow enough.”

The marine scientists plan to take what they learned in this pilot and continue the project. They will look for more sites for eelgrass transplantation and combine the transplantation method with other restoration techniques. They will also assess 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 with sensors is useful for this project,” Sacchi said. “We are doing this because we love the sea and want to help protect it.”

[1] https://bg.copernicus.org/articles/13/6139/2016/bg-13-6139-2016.pdf

[2] https://bg.copernicus.org/articles/13/6139/2016/bg-13-6139-2016.pdf

[3] Cole & Moksnes, 2016. Valuing Multiple Eelgrass Ecosystem Services in Sweden: Fish

Production and Uptake of Carbon and Nitrogen https://www.frontiersin.org/articles/10.3389/fmars.2015.00121/full