By Teresa L. Carey
Commercial oyster aquacultures can restore lost biodiversity by cleaning up polluted waterways, according to new research. A new study presented at the 2016 American Geophysical Union Fall Meeting in San Francisco found oyster farms in the Delaware Bay increased biodiversity when introduced into the waterway and could possibly restore the bay to its previous, healthier state, according to the researchers.
Pollution from human activities such as agriculture, shipping and industry has degraded the water quality of the Delaware bay and led to a in loss marine life over the past several decades. Commercial oyster farming could provide jobs and food in the area, but the practice was banned in Delaware until 2013. It is the only East Coast state without a shellfish aquaculture industry.
Local community members, complaining of the visual impact of oyster farms, have thwarted any attempt to establish an oyster farming industry in the state, said Gulnihal Ozbay, assistant professor in the Department of Agriculture and Natural Resources at Delaware State University.
Ozbay wondered if introducing commercial oyster farms could increase biodiversity in the bay and clean up the polluted waters in addition to providing jobs and food.
“Our job is to fix the damage,” said Melanie Fuoco, a student on Ozbay’s research team. “Especially when it’s as easy as putting oysters back into the bay.”
Champions of the ocean
Despite their humble appearance, oysters are hard-working champions in the ocean. As filter feeders, they take in algae, organic matter and nitrogen. Excess nitrogen from fertilizer run-off can cause harmful algal blooms. One oyster can filter 50 gallons of seawater each day, creating healthy habitats for seagrass, small fish, and other species to grow. But the oyster population in the Delaware Bay today is only a fraction of its historical size.
Delaware Bay oysters were hit hard with a series of setbacks that caused a drastic decline in their population. After being over-harvested, they were hit by devastating parasitic diseases in the 1950s and 1990s.
To find out if oyster presence would increase biodiversity, Ozbay and her team obtained a special research license to build three oyster aquacultures. They positioned the aquacultures in three inland bays, which are especially sensitive to pollution due to low flushing rates and shallow depths. They began by growing oysters in the lab until they were “spat,” oysters that are large enough to attached to hard surfaces. The researchers anchored the cages filled with oysters in open water, stepped back, and left the oysters to grow.
“We just watch them grow,” Fuoco said. “They already have everything they need right in the bay.”
The team collected sediment samples below and around the cages each month, using seabottom worm species as biodiversity indicators. Fuoco sifted out worms in seafloor mud samples, then counted the number and variety of worms. She repeated this process monthly for five months.
She found that in two of the bays both the number and type of worm increased the longer the oysters were present. This was especially true for the samples closest to the oysters, she said. In one bay, they only found four worms, an incredibly low amount. The researchers suspect it was because the clay was very thick and without oxygen, a poor environment for life in general.
Restoring what was lost
Overall, the results support the idea that biodiversity is higher with the presence of oysters, according to the authors. They attribute the increase in biodiversity to the oysters filtering the water, making the surrounding area a better environment for sea life.
“We had only about 200-400 oysters,” Ozbay said. “Imagine what would happen if you have thousands of oysters.”
The researchers’ next step is to consider other types of organisms in addition to seafloor worms. After preliminary studies catching fish in nets, Ozbay found evidence of increased biodiversity of fish species near oyster farms.
In an additional effort, Fuoco and Ozbay have been working with interested members of the community to start oyster gardens. For now, the small-scale farming of oysters is strictly to recover the wild population. Once large enough, the oysters would be placed back into the natural environment to support a healthier ecosystem. With commercial oyster farming, the team suspects biodiversity could increase in the entire bay, possibly restoring it to what it was when the bay was healthy.
“They don’t need to reinvent anything,” Ozbay said. “All they need to do is look back and see what the oyster did. Nature itself gives the message.”
—Teresa L. Carey is a graduate student in the Science Communication program at UC Santa Cruz. Follow her on Twitter at @teresa_carey.