By Chris Patrick, staff writer
Over the past two years, Melissa Karp has sifted through mud, shells, and stink to measure the value of restored oyster reefs as habitat. She found that healthier reefs support a larger number of animals.
“I’m providing justification for why it’s really important to restore reef habitats,” says Karp, a Virginia Sea Grant graduate research fellow at the Virginia Institute of Marine Science. Restoration, or reef rebuilding, is one way to try to increase the historically low number of Chesapeake Bay oysters.
Karp worked with the NOAA Chesapeake Bay Office (NCBO), which spearheads tributary-scale reef restoration efforts. Until recently, NCBO’s restoration efforts focused primarily on increasing the number of oysters—not on the ecosystem-wide benefits of healthy reefs. But oyster reefs offer refuge for many animals, as well as a concentrated source of food for the predators that eat those animals.
“Oysters provide habitat for fish, crabs, worms, other mollusks, and crustaceans,” Karp says, “and those organisms are common prey items for larger fish, like striped bass, that people like to catch and eat.”
While biologists know that oyster reefs house and feed many animals, no one had quantified the diversity and abundance of animals living on restored oyster reefs yet. With NCBO’s help, Karp conducted a field study to get these numbers for restored reefs in four rivers of the lower Chesapeake Bay.
She enlisted divers to imbed 55 wire trays into oyster reefs that were originally restored by the U.S. Army Corps of Engineers and Virginia Marine Resources Commission. The divers wedged the mesh-lined trays between oysters using mini pic axes and shovels. Seven weeks later, the divers pulled up the trays, capturing any creature one millimeter and larger. Karp then brought the trays back to the lab and began the long process of inventorying their inhabitants. She identified, counted, and weighed every organism in every tray, with an average of 753 individual animals per tray. Many of these were so teeny she had to identify them using a microscope.
“It’s kind of like a scavenger hunt, with everything from little tiny amphipods to blue crabs,” Karp says. “I’m focusing on oyster reefs, but I’m getting to really dig in to all the things living there, and it’s been really cool.”
While taking inventory, Karp found all of an oyster reef’s usual suspects. These 20 common species include clam worms, which accounted for more than 40% of all trays. She also found some less common reef dwellers, like the paper mussel—one of her favorite finds during the project. Overall, she recorded a total of 41,402 individual animals spanning 61 different species, from snails to shrimps to sponges.
In addition to inventorying the trays Karp noted characteristics of the oyster reef it came from, like the number of live oysters, volume of oyster shell, and rugosity (surface topography).
When she compared animal abundance with reef characteristics, she found that restored reefs with more live oysters support more animals.
She thinks that’s because of the way live oysters grow one on top of the other, forming skyscraper-like towers reaching for the water’s surface. This three-dimensional structure provides a small animal with lots of nooks and crannies to hide in. So a reef with more live oysters offers better protection and attracts more animals than a reef with more dead oysters, which mostly lay flat on the river floor.
A reef with more live oysters also houses more prey for larger fish to come eat. A mud crab, for example, may find refuge in the tiny submerged city that is an oyster reef. This will attract the larger fish that call mud crabs food. A healthy reef can support your food, your food’s food, and the fishermen that catch your food.
“Melissa’s work illustrates the habitat value of oyster reefs and provides evidence that we need to set aside reefs off limits to harvest and allow those reef communities to grow” says Bruce Vogt, manager of Ecosystem Science and Synthesis at NCBO and Karp’s outreach mentor for this project.
Vogt and NCBO will plug numbers generated from Karp’s research into models that give values for the ecosystem and monetary benefits of restoring oyster reefs. Vogt says an example of a possible model would be one that showed how many pounds of striped bass could benefit from the prey items that live on a restored reef.
“Oysters do more than produce more oysters,” he says.
You can read more about Melissa and her project at her website, Life Among the Oysters.