Seagrass Study Gets Underway In Back Sound This Spring

Jan 18, 2017

Credit UNC Institute of Marine Sciences

A large scale sea grass study, the first of its kind, is underway at the coast.  Artificial seagrass meadows will be built in Back Sound this spring to observe how fragmenting affects fish colonization. 

The coast of North Carolina is biologically diverse with a variety of habitats; salt marsh, oyster reefs, sandy shorelines and hard bottom habitats.  These aquatic environments are important because they serve as a nursery for juvenile fish and crustaceans, support valuable commercial fisheries and can even help improve water quality by filtering out pollutants.  Researchers at the University of North Carolina’s Institute of Marine Sciences in Morehead City are involved in a three year study to learn more about an underwater habitat along our coast called seagrass beds.  Often confused with seaweed, the fully submerged vegetation form dense meadows in salty and brackish estuarine waters. Associate Professor Dr. Joel Fodrie says other than Florida, North Carolina has more sea grass than all the other East Coast states combined.

Credit UNC Institute of Marine Sciences

“In North Carolina, we sort have every possible spatial orientation of grass bed that you could imagine.  There are some places where you might be a single shoot of grass.  And there are other places like along the sound side of the Outer Banks where the grass bed extends for miles and miles.”

Here locally, in Bogue Sound and Back Sound, Dr. Fodrie says the seagrass is patchier, made up of basketball to car sized clumps of seagrass spread out across the bottom.

“And what we’re doing with our current experiments is really focusing in how those different orientations of those grass beds affect how fish and crabs and shrimp do use the grass beds.”

Dr. Fodrie received funding from the National Science Foundation, a $400,000 grant over the next three years, to conduct the study.  For months now, several technicians at IMS have been hand making artificial sea grass mats to use in the experiment.  It’s a tedious process taking about two hours to make just one mat… but it’s the standardized tool in seagrass ecology that closely mimics the natural movement and habitat functions of seagrass. 

“To make these seagrass mats, we use a material called Vexar, it’s essentially a plastic netting, fairly ridged.  And on that netting, we tie lots of green ribbon.”

Credit UNC Institute of Marine Sciences

Curling ribbon, like you would use for wrapping a gift.

“Each section of ribbon that gets tied on is essentially six inches long, which is about the length of the seagrass we have here in North Carolina.”

Dr. Fodrie says each mat, about a meter squared, will be securely anchored with 16 long staples pushed down 10 inches into the sediment. 

“And once we put it out in the field, it’ll be colonized by little tiny plants and animals called epiphytes that live on the blades of natural grass and will live on these artificial grass blades.  And these little epiphytes are often times things that are fed upon by the small shrimps or very small fishes.”

Around 400 mats have been made so far, thanks to a lot of volunteer hours.  But they need 1,800 before their experiment starts in the spring.  Using these artificial seagrass mats in research projects isn’t a new idea.  Previous studies to observe crustacean and bivalve growth have been conducted on a small scale with mats one to two meters in size.

“What’s novel about this work and probably why we received funding is that we’re working at an order or two orders of magnitude bigger scales to understand how things like fishes and blue crabs and our penaeid shrimp, like white shrimp and pink shrimp and brown shrimp, much bigger animals respond to patchiness and fragmentation and patch size.”

The current research follows up on a previous study where they explored fragmenting on natural seagrass habitats.  In the wild, seagrass patches can be broken into pieces, while others are contiguous.   Dr. Fodrie conducted fish surveys on each habitat type to determine whether or not fragmentation seemed to affect fish utilization.

Credit UNC Institute of Marine Sciences

  “And what we found is that there is interaction between those two things, habitat amount and fragmentation.  If you have a bunch of habitat and you fragment it, the fishes don’t seem to respond.  But then you cross some threshold. And if you have a small amount of habitat, if you fragment that any further, so you’re not reducing the habitat amount, you’re just changing the orientation of those patches, you do start to lose a lot of species.” 

That threshold is around a quarter of a football field in size.  Dr. Fodrie and several technicians will build seagrass meadows at that scale to explore fragmentation in greater detail.  Using the artificial mats, researchers will have more control over unpredictable environmental factors.  Certain variables like seagrass shoot density, patch size and orientation can be altered to find out which habitats support the most biodiversity.

“Now, they won’t be like complete carpets of seagrass over a whole quarter of a football field.  But 60 percent of that area will be covered by these mats, and that’s at the big end.  At the small end, it might be something like only five meters by five meters, that might be the size of the grass patch that’s at the smaller end of our landscapes that we’ll be manipulating though this experiment.”

Similar to the initial project’s findings, Dr. Fodrie hypothesizes that fragmentation on large portions of seagrass won’t have a major effect on fish density.  However, smaller patches with fragmentation will support fewer fish species and less fish than small, contiguous patches.  Their research and their findings are important for habitat and fish conservation and restoration.

Credit Exum Photography

“The value of habitat, I think we all expect and appreciate and understand.  But quantitatively, we’re sort of behind.  We try to explore how fishes and crabs and shrimp do use oyster reefs or seagrass meadows or other habitats so that we can try to put numbers to – if you lose ‘x’ amount of habitat, you might lose ‘x’ amount of fishery production.  Or if you restore ‘x’ amount, or conserve ‘x’ amount of habitat, you’re gaining or conserving ‘x’ amount of fishery production.”

Over the next two years, they hope to make a total of 3,600 mats with the help of the community, school groups and volunteers. If you’re interested in helping with the construction of the artificial seagrass beds, call the Institute of Marine Sciences in Morehead City at 252-726-6841.