KINGSTON–Oyster farming is on the increase in Rhode Island coastal waters, with one report indicating that at least eight million of the shellfish were sold last year alone. Is that a good thing or a bad thing? One way to answer that question is to measure the chemical changes that are created by having living organisms artificially introduced to an area. And one particular chemical that can create problems is nitrogen. Dr. Robinson Fulweiler, a research scientist from Boston University who specializes in nitrogen dynamics, addressed that question at a recent RI Sea Grant discussion held at URI’s Narragansett Bay Campus.
Nitrogen and the cake factor
“We need nitrogen; without it, there would be no you, or me, or blue whales or amoebas. But like anything else, too much of a good thing can be a problem,” Fulweiler said.
“Long ago and far away, before we began to inhabit the ecosystem, things were beautiful. There was lots of oxygen. Then we came, and we gradually built our houses on the water, and we began pumping nitrogen into our septic systems. We started producing nitrates, nitrites, and ammonium. From there, the chemicals began to flow into the coastal ecosystem. Now, we all need nitrogen, and I don’t mean to demonize it. But it’s like chocolate cake: one piece okay; five pieces, bad idea.”
Many Rhode Islanders will recall seeing periodic fish kills in different coastal waters, especially in summer when the water temperatures are up and people are putting things like fertilizers on their lawns, and thereby into the ecosystem. This is part of what produces too much nitrogen in coastal areas. “All this nitrogen alters the phytoplankton population to create things like algal blooms which are sometimes fatal to fish.” As more organisms begin to die, they fall to the bottom. There, the microorganisms that live on the bottom begin to feed on those, sucking oxygen out the of the water column, causing low oxygen and anoxic events. “They’re really connected to areas of high population density: where you have a lot of people, you have a lot of nitrogen, and then you have this sequence of events happening.”
Oysters to the rescue?
Fulweiler said there has been a global loss of about 85 percent of natural oyster reef habitat over the years. That comes from things like overharvesting, pollution, and other habitat degradations. That’s problematic for a number of reasons, Fulweiler said. Oyster reefs are extremely good at mitigating storm surge and impacts from waves. Studies from places like North Carolina indicate the oyster reefs can mitigate storm surge events by about 85%. “If you examine oysters not just as a food source but as a whole series of benefits, they provide a substantial service.” She points out that oysters are “remarkably good at filtering sediments. One oyster can filter 50 gallons of water a day.” (See a short video on oyster sediment filtration at https://www.youtube.com/watch?v=k757xZC1OzU )
Locally, Fulweiler and her team looked at three habitats: a natural oyster reef, living both on and in the bottom of the water; an oyster farm; and a section where no oysters were present. They examined the amount and effects of a series of chemicals. Along with that, they looked for changes in the conditions of the site over one, three, or seven years.
Ultimately, she found that the presence of oyster farms in Ninigret Pond and other locations are either neutral or positive. “The nitrogen removal rate (through filtration) rose early on, then leveled off. The comparison to Narragansett Bay seems neutral, but that also has a very small footprint.”
The big picture
Fulweiler says that there is an entire range of services that the shellfish provides: provisioning of materials, habitats which are important for other organisms, and all the regulating processes like the removal of nitrogen, filtration, mitigating storm surge, and the cultural impact on things like tourism. “It’s important to look at the entire picture.”
In addition, they compared the impact on greenhouse gases created by oyster farming with those in other animal farming, such as goat, chicken, or cow. They compared oyster farming with gases created through manure, fodder production, and from the animal gut (the belching that cows do as they process their food is a significant source of greenhouse gases).
“If the entire population of the US were to replace 10 percent of red meat with protein from oysters, the difference would approximate keeping 14.8 million cars off the road. So eat oysters!”