Given that its now easier to find oysters from Duxbury and mussels from Prince Edward Island than it is to get locally-sourced seafood, this locovore’s dilemma begs the question: which came first? The shellfish or the septic system? The problem or the solution?

Sometimes, when overhearing discussions among wastewater experts, the idea is floated that Cape Cod should try to get back to 1619– that is, before Pilgrims landed on these shores.

Though it took until roughly 1990 for humans to load the estuaries with enough nitrogen to kill small fish, the basis for the idea is that we should limit our inputs to the environment to basically zero, just as the native Wampanoag did.

Here's what eel grass should look like

In the past three decades, we have developed our communities to the point where the nitrogen leaching from household septic systems and fertilized lawns has caused our beloved estuaries to seriously decline.

Across the entire Cape, algal blooms clog and stink up the water, leading to unpleasant swimming and boating experiences– and signaling a major ecological disaster.

A lack of eel grass is often the first sign that nitrogen loading has tipped the scales towards an unhealthy estuary. As nitrogen seeps in with the groundwater, it causes algae to grow– and infamously, bloom, when summer temperatures heat up.

Not only is it yucky to look at, algae blocks the sunlight needed by eel grass, causing a rapid decline for this aquatic plant species– as well as the shellfish that grow on its blade and stems.

Dying eel grass: a familiar sight in Falmouth harbors

As the algae dies off, it sucks up the oxygen in the water. If the die-off is extensive, it can cause dissolved oxygen levels to get so low that fish die– or swim to less suffocating areas.

The less lucky marine creatures– snails, worms, and shellfish– are not mobile, and tend to die at much greater rates than fish.

So how do we get back to the way it was in 1619? The state, through the Massachusetts Estuary Project, has set daily maximum nitrogen loading (TMDL) targets that we’ll need to achieve to restore the estuaries, but does not offer any guidance on how to get there.

We need only take a lesson from nature to understand how the nitrogen cycle has balanced itself out over millennia.

A bi-valve solution

While towns on Cape Cod brace themselves for a lengthy, costly, and energy-intensive installation of a sewer system, some residents have taken a back-to-the-Earth approach.

Drawing on his 30 years as an aquaculture consultant with the World Bank, Woods Hole resident Ron Zweig thinks that the solution to the Cape’s water woes could be staring at us from our dinner plates.

Mr. Zweig’s experience with aquaculture in Southeast Asia and at the New Alchemy Institute in Hatchville corroborate the findings of numerous studies establishing the ability of shellfish to filter and remove nutrients (mainly nitrogen and phosphorus) from water and suspended sediments.

A Falmouth Shellfish Cooperative cage, used for growing oysters in deep water.

A 2006 study of aquaculture in Waquoit Bay by WHOI’s Marine Policy Center found that 500 oysters and quahogs removed 0.1 kilograms of nitrogen per liter from the water, and an additional 0.1 kg from the sediment underneath the growing tray per year.

According to Mr. Zweig, one oyster, on average, is capable of removing 0.65 milligrams of nitrogen per year during two years of growth.

If grown on an exponential scale, aquaculture could potentially meet TMDL targets, especially if the inlets to some coastal ponds are also widened.

In a spreadsheet analysis of four coastal ponds in Falmouth facing Vineyard Sound, Mr. Zweig recommends setting aside 8-9% of Bournes Pond, Great Pond, and Green Pond for aquaculture, and about 22% of the heavily polluted Little Pond, in order to meet the state-mandated TMDL’s.

Getting Aqua into the Culture

While these studies may be little more than numbers on paper, Mr. Zweig is working with members of the Falmouth Shellfish Cooperative, four companies that hold aquaculture permits in Buzzards Bay, to turn his hypotheses into action.

The Cooperative is currently working on a proposal to start up aquaculture plots in one or several of Falmouth’s coastal ponds. Not only would a more inland location make it easier for the farmers to get to their oyster cages, the development would also serve as an experiment on the potential for shellfish to remove nitrogen.

If successful, the Cooperative estimates that expanded aquaculture operations could create or maintain 165 permanent jobs in Falmouth, while restoring 3,700 acres of shellfish habitat.

An aquaculture site in Buzzards Bay operated by the Falmouth Shellfish Cooperative.

This summer, the Cooperative plans to market their first batch of the Sippewissett Oyster, sold straight from their retail location on Coonamessett Farm. With a fledgling mechanism already in place to put Falmouth’s seafood on the map, the oyster farmers say there is much more room to expand.

In Mashpee, Shellfish Warden Richard York hopes to build on the success of an aquaculture program he started in Mashpee River. The Mashpee Enterprise reports that Mr. York is writing a $75,000 grant to purchase, propagate, and plant 10 million quahog seeds in Waquoit Bay. Quahogs, he says, are ideal for aquaculture because of their resistance to predators.

Even if only half of the quahogs survive to maturity, the initiative will generate up to $750,000 in revenue, enough money for 15 shellfishermen to make a decent living, estimates Mr. York.

It may just turn out that doing the right thing for the environment is also good for the economy– and for our appetites.

The downside of aquaculture

However, the simple solution is not always the easiest. As Cape Codders know well, changes intended to solve environmental problems (think wind turbines) often come with a serious backlash from stakeholders.

The Marine Policy Center quantified the costs and benefits to aquaculture not only from the nitrogen removal angle, but also from the point of view of recreational users of Waquoit Bay.

Due to the potential “aesthetic costs” caused by exposed aquaculture gear at low tide, as well as decreased area for boating, the Marine Policy Center estimated that 1.5% of the head of Waquoit Bay could be used for aquaculture without negative consequences.

One additional issue that aquaculture does not address is the need for a wastewater solution that removes not only nitrogen, but a range of “contaminants of concern” from products consumed and eliminated by humans, now concentrated in your drinking water.

A typical composting toilet: the only difference is the pipe.

Even if shellfish were capable of filtering and sequestering aspirin, Viagra, and shampoo chemical residues from the water, would that solve the problem? (And would you want to eat them?) Or does it just point to a larger question: why are we contaminating fresh drinking water with our waste?

In my humble opinion, we need a variety of options to deal with our wastewater worries. If it is not conceivable to place aquaculture operations in coastal ponds on the scale necessary to remove the entire nitrogen load, it would be wise to eliminate the main cause of the contamination: septic tanks.

Even on a small scale, aquaculture can likely eliminate nitrogen released from non-point sources, namely fertilizer and road run-off. And by installing household composting toilets, we would eliminate at least half of the nitrogen load, while also pre-empting contamination by other, potentially very harmful, chemicals.

According to scientists at the Woods Hole Oceanographic Institution, 30% of the world’s carbon dioxide (CO2) emissions, known to be a leading cause of global warming, are being absorbed by the ocean. Small coincidence that over the past 50 years of global  industrialization, rising CO2 emissions have also led to a 30% increase in the average acidity of ocean surface water.

This phenomenon is just starting to attract the attention– and alarm– of policymakers and the shellfish industry.  I talked to Scott Doney and Sarah Cooley at WHOI to find out why.

How does ocean acidification happen?

When CO2 in the atmosphere combines with seawater (H2O), the molecules combine to form carbonic acid (H2CO3). This acid is weak and dissociates rapidly in basic seawater, releasing hydrogen ions. When these ions combine with the carbonate ions already present in the water to form bicarbonate, they rob coral and shellfish of the materials they need to grow their shells and skeletons.

Scientists estimate that the pH of seawater has decreased by about 0.1 units– a 30 % decline on the logarithmic pH scale– and could decline by 0.3-0.5 units more in the next 100 years, as CO2 levels rise. Over time, they warn, the ocean’s ability to absorb CO2 could diminish the development of coral reefs and marine organisms with calcium carbonate shells, with side effects reverberating throughout the ecosystem.

Scott Doney, of WHOI, explains the connection between CO2 and your favorite seafood dinner

The question is when, and where, said Dr. Doney. Using carbon emissions projections from the Intergovernmental Panel on Climate Change, he predicted that acidity levels in the ocean will double by mid-century, and carbonate ions could decline by half.

Carbon dioxide, if you look at it as a pollutant, is very long-lived, lasting from hundreds to thousands of years. It will also continue to grow through the mid-century, with no good indication that we’ll be able to stabilize it.  We’ve now increased atmospheric carbon dioxide to a range that hasn’t been seen since 800,000 years ago,  judging from ice cores.

-Scott Doney

In a 2008 paper, Drs. Cooley and Doney indicate that bivalves, such as scallops and oysters, would feel the effects of acidification more heavily than sea urchins or crustaceans, such as lobsters, shrimp, and crabs, due to their use of a more soluble form of calcium carbonate in their shells. The effects of acidification on fish is not known, but should be studied, Dr. Doney said.

“There’s no indication that this will destroy sea life, but it certainly will diminish and dislocate some species,” he said.

Calling for additional research into the socio-economic, as well as biological and political ramifications of ocean acidification, Drs. Doney and Cooley, with WHOI marine policy specialist Hauke Kite-Powell, are investigating the impacts on the shellfish industry in the Northeast.

The economic effects of ocean acidification will be felt locally, the scientists say. In New Bedford, the top American port for shellfish, they found:

• By 2060, a 25 % loss in shellfish populations would decrease landing revenues by $67 million a year, or $2.2 billion
• Losses in primary revenue from commercial harvests—or the money that fishermen receive for their catch—could add up to as much as $1.4 billion within 50 years
• In comparison, a 25 % decrease in the seafood employment sector contributed to a dramatic economic decline from in New Bedford from 1992 to 1999, when 20 % of residents were living below the federal poverty level

The Bigger Picture

Dr. Doney’s research also takes a look at the global picture, especially at areas of the developing world that are dependent on viable fisheries.

“As with so many aspects of environmental degradation, the Third World is often hit hardest, and is the least resilient,” he said. “We want to make the connections with fishing communities and how they can adapt.”

Acidification could be the death blow for coral reefs, which are already impacted by pollution and overfishing, Dr. Doney said, which will have an impact on coastal erosion, fish habitat, and tourism.

Regions that are impacted by acid rain and nutrient runoff might already be experiencing the effects of acidification, he added. While a connection between nitrogen loading and acidity has not been thoroughly studied, Dr. Doney warned that algal blooms from excess nitrogen release CO2, “an unfortunate synergy” that could occur on Cape Cod.

Results from the Global Ocean Ecosystem Dynamics (GLOBEC) program indicate that Arctic ice melt has made its way to the Gulf of Maine and Georges Bank, said Cabell S. Davis, a WHOI senior biologist.

The influx of fresh water has lowered the natural salinity of these productive fishing grounds—and coupled with rising water temperature, the impacts will be felt across the entire ecosystem, he said.

Towing an underwater video camera from the Azores to Woods Hole, Dr. Davis captured thousands of images of copepods, a food source for cod and haddock larvae, and even right whales. Putting a computer model to work, the GLOBEC team found that decreased salinity led to an earlier spring bloom of phytoplankton, the main food source for copepods.

The result was a three-fold increase in copepod populations on Georges Bank from 1995 to 1999. Longer term data sets revealed that the water in the 1990s was more fresh and had more copepods than the 1980s.

Pointing to the 2003 haddock harvest, the best year for that fishery since 1963, Dr. Davis said the changes can initially be a good thing for fish. An earlier spring bloom of phytoplankton means that copecods have more food. Higher concentrations of copepods will allow the infant cod and haddock to grow faster, and thus have better survival rates.

However, not all copecods are created equal, Dr. Davis said. There are two types living in the western North Atlantic: one cold-water species, and one tropical species. The warm-water copepod, Centropages typicus, swims too fast for the larval fish to catch.

Already, Dr. Davis said, these copepod populations have doubled in the Mid-Atlantic Bight, off New York and New Jersey, since 1977.

“Potentially, cod and haddock larvae won’t have anything to eat,” said Dr. Davis, speaking at a Marine Biological Laboratory Ecosystems Center seminar last week.

“Even with best management practices, if the projected warming trend happens in the Gulf of Maine and Georges Bank, cod and haddock could be gone by 2080.”

Worst-case scenarios

Dr. Davis based his models on a medium prediction of climate change, established by an International Panel on Climate Change scenario that includes a mix of fossil fuel and renewable energy to drive the economy. If Artic melting occurs more rapidly than the predictions—which has already been the case—Dr. Davis said that the effects on fisheries could be worse.

“As more melting occurs, the nutrients on the surface sink, leading to a decrease in productivity. In addition, a climate pattern, called the North Atlantic Oscillation, affects how deep Labrador Sea water flows southward to New York, bringing in colder, low salinity water with lower nutrients,” Dr. Davis said.

Further research will be needed to study the consequences of this ecosystem shift, and other effects of climate change, on other commercially important species, including adult cod, haddock, scallops, and lobsters.