What happens to the climate if the ocean’s forests disappear?

Eutrophication, trawling, big storms and a warmer ocean.
There are various factors that threaten the seagrass beds outside East Africa’s coast.
“If the seagrass beds disappear, it could have major consequences for the Earth’s climate”, says climatologist Hans Linderholm.

That deforestation of forests releases large quantities of carbon dioxide that accentuates the greenhouse effect is something we’ve known for a long time. But what happens to the climate if the ocean’s forests – seagrass beds — disappear? That’s what climatologist Hans Linderholm and his colleagues want to find out in a major research project in East Africa.

Previous research has focused on what is happening to seagrass when the climate changes. What’s unique about this project is that the researchers have turned the question around and instead are studying the effect seagrass beds have on the environment.
“We have quantified how much carbon is sequestered in seagrass beds outside Tanzania, Mozambique and Madagascar”, says Hans Linderholm. “If the carbon is released in the form of carbon dioxide and other greenhouse gases, which takes place if the seagrass disappears, it could potentially contribute to accentuating the greenhouse effect quite substantially.”

The seagrass beds outside East Africa’s coasts are partly threatened by climate change. A warmer ocean can have a negative impact on seagrass, large storms create enormous waves that tear the beds apart and heavy rainfall causes torrents of sediment to gush into the sea from the land. This has an impact on seagrass beds through greater amounts of nutrients that lead to eutrophication, increased sedimentation and thereby a reduction in available light. Seagrass also is affected adversely by bottom trawling, dredging and indirectly by overfishing as well as increased tourism, which can lead to removal of seagrass to create good swimming beaches at new hotels.
“The beds are indeed an important ecosystem. They’re commonly referred to as the ocean’s nurseries. But they’re also important as carbon sinks”, says Hans. “Up to now East Africa has been an unexplored region regarding this type of studies. Our research will be an important piece of the puzzle when it comes to running models for the various factors that affect the climate globally.”

What also makes the project unusual is the way ecologists, physiologists and climatologists are working closely together. Besides Hans Linderholm, who is a climatologist and a professor of physical geography at the Department of Earth Sciences in Gothenburg, the project is being run by two researchers at Stockholm University: Associate Professor Martin Gullström and Professor Mats Björk at the Department of Ecology, Environment and Plant Sciences. The two Stockholm-based researchers had conducted research in this area in East Africa for two decades when Hans Linderholm entered the picture almost eight years ago.
“They had studied the seagrass beds in East Africa based on a number of ecological and physiological issues. I thought it would be exciting to study the beds in a larger perspective. In addition to the ecological and economic importance in the region, I wanted to take a broader approach and see how seagrass beds affect climate globally.”

Working together, members of the research team have collected large amounts of field data along the eastern coasts of Africa for a number of years. The collection of data is now concluded, and what remains is performing calculations to get real numbers on the seagrass beds’ climate impact and how average temperatures could be affected if the carbon in the beds is released.

Hans Linderholm usually works in a mountainous environment, where he takes samples of trees to study regional climate fluctuations in Europe and Asia from about 2,000 years back in time to the next 100 years. Working underwater was a completely new experience.
“It’s been really exciting to study marine ecosystems. And challenging. It’s not always the easiest environment to work in. You dive with air tanks and have oxygen for only a certain amount of time, you have to take account of tides and currents and aggressive animals can crop up at times. Sharks, for example.”

Hans has not encountered any sharks, however, although he was told that tiger sharks sometimes swim up the river channels, jump up and seize prey going along the water’s edge right where he has stood, taking samples of mangrove trees.
“On the first day you might be a little nervous, but then you relax. You get so caught up in what you’re doing that you forget to keep a lookout”, he notes.

Hans Linderholm takes samples from the mangrove tree

Although environmental pollution and the ravages of humans have caused some damage to seagrass beds in East Africa, as in other parts of the world, Hans doesn’t want to take a dark view of the future. He feels that once problems are identified, it’s important to focus on solutions.
“If we lose faith in the future, nobody will have the energy to make decisions about changing our lifestyle. We have to concentrate on the opportunities and what can be done.”

Consequently, Hans and his colleagues are keen on involving the local populace in the places where their study has been carried out.
“We have a lot of discussions with the villagers. We must find solutions tailored for the population that involve the residents and make them feel that new methods of fishing, for example, actually benefit them in the long run.”

The project has also caused ripples because it has been partially conducted in collaboration with students and researchers in a Sida-funded bilateral programme in Tanzania.
“Many of the students are already working in government agencies or within academia in Tanzania and are learning things during their education that can be of direct benefit in their daily work. That’s incredibly valuable.”

The East Africa project in brief

Name: Assessment of carbon sequestering capacity in East African seagrass ecosystems affected by multiple stressors in a changing climate and Improving the understanding of carbon storage and sequestration and ecosystem services of blue forests: analysis of carbon flux in degraded seagrass beds.

Number of researchers involved: Three senior researchers plus several postdocs, doctoral students, master’s and undergraduate students.

Ongoing since: 2011.

Funders: Sida and Global Environmental Facilities, International Union for Conservation of Nature (IUCN), United Nations Environment Programme.