Seagrass Science

Scientists discover and analyze the important function of seagrass beds as not only habitats, but as buffer zones and water purifiers.

BEAUFORT — A group sits in the corner of a lab at the University of North Carolina Institute of Marine Sciences. Giant screens with rims of PVC pipes and netting spread from side to side sit before the group, leaning on counters. One by one, group members thread strips of green, plastic ribbon through the net and then tie them. Some strips are long, some short; some of the ribbons are thick, some are thin. 

The creation almost looks like an abstract piece of wall art. Wall art it is not, but it is a window into a vital ocean habitat that scientists don’t know much about: seagrass. 

Seagrass forms some of the most important coastal habitats in the watery world. Without it, many juvenile fish, including several commercially important species such as grouper and red drum, likely wouldn’t survive.

“You find a lot of juvenile fish and crabs and even oysters so it’s a great habitat,” says Danielle Keller, a Ph.D. candidate in ecology who leads the net making group in the lab. “Seagrass is so important because organisms can hide from predators; they have a safe haven from getting eaten up and survive to adulthood so they can sustain their population.” 

Actually seagrass provides more than just a nursery habitat in the ocean. It also provides a buffer zone for wave energy, so it helps to protect the coastline. Seagrass also helps with water quality: if there are sediments in the water, seagrass provides a filter to clear out some of the sediments. 

“It’s just a great place for fish to grow up, but in addition, it also gives a lot of benefits to humans that you can’t replace,” adds Keller. 

There’s no doubt, then, that seagrass is valuable. Fortunately for North Carolina, there is more seagrass along its coast than all of the other states on the East Coast, except for Florida. That’s because the Outer Banks shelters giant sounds, such as Pamlico, Albermarle, Currituck and others. Seagrass thrives in shallow, sheltered bays, where the water is only a couple of feet deep. 

North Carolina is also located within the coastline range limits of two types of seagrass. Shoal grass grows year round. It has thin blades and grows about six inches tall. You’ll also find eel grass in the cooler spring and fall months. It's thicker and grows to about eight inches. 

“It all means that we’re a really important coastal state in terms of this habitat which may be hugely important for supporting a large variety of fish that then make their way all along the coast,” says Joel Fodrie, Ph.D., an assistant professor of coastal biological oceanography at the University of North Carolina Institute of Marine Sciences. 

But as important as seagrass is, scientists don’t really know just how fish utilize seagrass. 

“It’s not hard to convince people habitat is important,” explains Fodrie. “Everybody gets that habitat is important for animals and when we’re talking about the ocean, for fishery production. But it’s really hard to quantify how some area of seagrass produces a certain amount of fish, or crabs or shrimp.” 

And that’s where those giant screens of green ribbon come in. 

The “weavers” are graduate students who were knitting together 16 artificial seagrass beds. They used 30 rolls of ribbon, which equals about 120 thousand yards of the material. The artificial beds were built with “grass” of differing heights and densities, just like what is found in real seagrass beds in the ocean. 

“That’s why we have all the varieties of the fake stuff,” says Keller, as she pilots a boat into Back Sound, just off the coast of Beaufort. The waters here are only about three feet deep. The water is also relatively clear, and seagrass meadows are visible all around. Great care is taken to not deploy the artificial beds over sensitive areas of sea floor. The plastic ribbons aren’t out long enough to pose any danger to sea life. 

“We’ll put our fake seagrass beds throughout this area, right next to the real beds, which will give the fish and crabs options so they can choose which ones they prefer,” Keller adds, as she slows the boat and prepares to send one of the fake beds to the bottom. 

Keller and another student toss one of the seagrass beds into the water. A stake is driven into the bottom to tie up the frame so it won’t float away. Several bricks are then attached to anchor it to the sandy floor of the sound. 

The bed will stay on the bottom for about one week. 

“It doesn’t take long for fake beds to look pretty real,” says Keller. “After a couple days the epiphytic algae will start to grow onto the blades. There will be critters, and shrimp and even barnicles, so it’s a pretty quick process.” 

“There are several types of algae that will actually grow onto the blades, which is why scientists like to use them because it is just like real grass,” adds Shelby Ziegler, a graduate student in ecology, as she carefully pushes the frame to the bottom. “There are also crustacaens that come in and live on it and the fish will eat those, so you have a nice community starting to grow.” 

And sure enough, within a week, the researchers discovered an amazing assortment of life inside the fake seagrass beds. You could call it an “aquatic party pad.” 

“I count pig fish, pin fish, blue crab and even a nice baby flounder,” exclaims Keller as she moves her hands through the mix of algae and seaweed sitting in the bucket that was used to catch everything that had fallen out of the artificial bed. 

“Lots of other fish too,” adds Ziegler, “And they are all juveniles, probably from this summer. Oysters too!” 

It’s all further confirmation for the researchers of the importance of seagrass habitat. The team hopes to discover what type of habitat is best. They also want to learn how habitat will change as water temperatures warm and eel grass, which thrives in cooler waters, dies off. 

The findings will help guide protection plans for seagrass meadows along the coast, and ultimately help protect important commercial and recreational fish stocks. 

“Throughout the season, fish grow up a lot and then they no longer rely on seagrass as they go offshore and they change their habitat use,” says Keller, as she takes one last count of what was living in her seagrass beds before returning them to the water. “So having this grass can help us to know if they will use this habitat for a long period of time or some other habitat offshore.” Which in the end helps them learn what's best for the fish.

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