Will seagrass adapt to climate change?

The survival of seagrass could be tied more to their past than their future...
27 September 2022

Interview with 

Emmett Duffy, Smithsonian Institution




Seagrass is a vital source of carbon storage. In fact some species of seagrass are able to capture carbon 35 times faster than areas of tropical rainforest. Even so, seagrass only covers 0.2% of the seafloor and so maintaining its existence is paramount to fighting climate change and preserving species. Emmett Duffy, from the Smithsonian Institution, has been speaking to Will Tingle on the importance of seagrass to both marine ecosystems and humans alike, as well as the new research highlighting how climatic pressures could affect their populations going forward…

Emmett - I think of sea grasses as the Serengeti of the sea. These are big expanses of underwater grasslands that are also highly productive and support lots of wildlife, as grasslands do on land and the foundation of these ecosystems are sea grasses. These are not algae or seaweeds, but flowering plants with roots that invaded the sea millions of years ago. They are critical to ocean wildlife, lots of large animals - dugongs, manatees, sea turtles depend on sea grasses. They're also essential nurseries for fishes, and particularly in parts of the developing world. Many people in coastal regions get a large part of their protein from fishes and shellfish that live in seagrass beds. And finally, they, uh, soak up carbon that our industrial society is exhaling into the atmosphere. So there's a lot of interest in so-called blue carbon capture by sea grasses.

Will - In the research paper, it's stated that there are two populations of eelgrass, one found in the Pacific and one found in the Atlantic. What is sort of so notably distinct between these two populations and how was that difference found?

Emmett - Yeah, a big surprise from our research was finding how different the seagrass looked in the two oceans. Eelgrass is distributed globally around the Northern hemisphere. And so understanding what makes it tick is a global problem. And we needed a global team. So we got 50 of our colleagues around the world together to sample the eelgrass using the same methods. So it would be comparable and we measured both the size and density and shape of the eelgrass, but also the genetic structure. We've known that there is a lot of genetic separation among various populations of eelgrass, which occurs all over the Northern hemisphere. But we found that the seagrass in the Atlantic was consistently shorter and denser. It lives in what we would call Meadows, whereas in much of the Pacific it's closer to forests.

Will - And was there any noticeable difference between the genetic strength between the two populations?

Emmett - Yes. So eelgrass originated, it evolved originally in the Pacific ocean and there's lots of genetic variation there because that's its ancestral Homeland, so to speak. And then sometime during the Pleistocene between ice ages, the eelgrass moved through the Arctic and colonized the Atlantic. And that probably involved only a small number of plants because the genetic diversity of eelgrass in the Atlantic is much smaller than it is in the Pacific. And what we've found is that much smaller genetic variation in the Atlantic is associated with this meadow like growth form. And so probably what happened is that the pioneers who made it across the difficult journey through the Arctic were small stature plants. Meadow forming plants from the edge of the Pacific.

Will - So with these two separate populations. If one is less genetically diverse or complex than one other region, do you think that the population in the Atlantic may be at more risk from climate change or other dangers to their existence?

Emmett - What we know is that the growth form of the eelgrass in the Atlantic seems to be constrained to being relatively short. However, the good news is that eelgrass is highly adaptable. It lives in all kinds of environments from open ocean coasts to the inner Baltic Sea and from the Arctic to Baja, California, for example. So it seems to be able to adapt reasonably well to different climates. It should be able to make it very well if we can control water quality and overfishing,

Will - These seagrasses sound like essential parts of the ecosystem to protect if they're so vital to Marine ecosystems and to our own food supplies. So what is the best course of action that you or I could do to help preserve these seagrass colonies?

Emmett - The biggest threat to eelgrass and other sea grasses throughout most of the world is coastal development and particularly poor water quality. These plants need a lot of light, so they need clear water and they only grow, uh, for, in most places in relatively shallow water. And we've seen success stories in Chesapeake Bay, in the United States, in Tampa bay, in the United States and a few other places where controlling runoff and pollution of the water has allowed the sea grasses to rebound and grow back again. So the best thing we can do is keep the water clear. And of course that has lots of other benefits as well.


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