Can oyster reef restoration across the US impact what we eat?

One oyster can filter out sediment and chemicals like nitrogen from 50 gallons of water a day

By Lela Nargi

Published January 24, 2021 4:59PM (EST)

 (Getty Images)
(Getty Images)

This article originally appeared on FoodPrint.


The plight of New York City's oysters has by now been scrupulously recounted, starting all the way back in the 1930s, with Joseph Mitchell's reporting for The New Yorker. It's really a cautionary tale, the likes of which is becoming ever more familiar in this time of climate upheaval and wildlife stressors, about (in this case) a once-vibrant fishery that collapsed in the late 19th Century due to overharvesting and manmade pollution and ambivalence about responsible stewardship of natural resources.

Some believe the tragedy lies in the disappearance of a tasty local mollusk from our tables. But it's actually a lot more significant than mere human gustatory lacking. When this keystone species all but disappeared from the Hudson River — and also dwindled in Long Island's Great South Bay, and the Delaware and Chesapeake Bays, and in estuaries throughout the South, in the San Francisco Bay and elsewhere on the West Coast — it took with it habitat and food resources for numerous species of fish, insects, birds, other animals, and plants. It eradicated critical ecosystem benefits; as has been widely touted, one oyster can filter out sediment and chemicals like nitrogen from 50 gallons of water a day. It destroyed thousands of miles of reef that protected coasts from storm surge, flooding, and erosion.

A parallel tale has begun to be told over the past decade-plus, though, ever since oyster reef restoration was begun in New York Harbor by non-profit Billion Oyster Project (BOP) and loudly called attention to what these mollusks can do when reintroduced to their natural environment. In a lot of people's minds, this work must surely herald the return of the region's native eastern oysters — Crassotrea virginica — to neighborhood fish markets. And in fact, in the state of Louisiana, oyster reef restoration efforts do have the primary purpose of bolstering that state's oyster fishery.

But the purpose of BOP and most other oyster reef-building projects isn't to feed us — at least not directly. Rather, they seek to regain those ecosystem benefits we've been losing for over 100 years and to make our coastlines more resilient.

Nevertheless, these environmental efforts still provide significant benefits to fishing and fisheries — in short, the stuff we eat. "When shellfish are planted and are able to reproduce and broadcast their larvae, that has the direct impact of increasing different fish populations, as well as improving waters so that more shellfish can survive," says David Bushek. He's director of the Haskin Shellfish Research Laboratory at Rutgers University in New Jersey. "Also, [oyster reef] habitat is used by other organisms as a nursery or place to forage, which increases those populations, including fish that [humans] go after."

In short, when oysters win, so do a lot of other species, including ours, in more ways than one.

The Oysters of San Francisco Bay

The story about what happened to the oysters in San Francisco Bay is not so familiar, even to Californians, but it mirrors New York's. This largest estuary on the West Coast supported a hardy commercial oyster fishery for over 100 years, until it crashed, too, in the early 1900s due to development, loss of habitat, and pollution.

Some of this pollution was the result of the Gold Rush, explains Marilyn Latta, project manager of California's State Coastal Conservancy(SCC), who, with a host of partners, has been working on a 50-year plan to restore 8,000 acres of native oyster habitat in the Bay, with the co-equal goals of protecting shoreline from erosion and creating habitat for diverse species. "Hydraulic mining in the Sierra foothills used pressure washing to wash away hillsides, and those sediments flowed into the Bay and changed the bottom," she says. "It used to be more hard, which is a habitat oysters like to settle on. It became more muddy and silty."

Because of the Bay's now-soft bottom, building reef from native oysters requires tailor-made techniques. In some places, loose shell can be placed on the bottom of a waterway to get a reef structure started. Here, though, shell would sink into the muck or drift out of the Bay on strong currents. So instead, Latta's team uses mesh bags filled with oyster shells, which are piled on top of each other to form a beginning reef. (Although, they're also experimenting with non-plastic-based solutions, like "Baycrete," formed from cement, sand, and shell.)

West Coast oysters have a range stretching from Chile to Alaska and are comprised of two subspecies of Ostrea lurida, the comparatively tiny Olympia oyster; where a bushel of Crassotrea virginica is comprised of about 150 of the lumpy mollusks, it takes a lot more Olympias, which are only about 60mm at their largest, to arrive at the same volume.

Unlike on the East Coast, where manmade reefs are often seeded with oyster larvae, called spat, Latta says natural oyster populations are plentiful enough in her region. "We're able to rely solely on natural recruitment," she says. That is, spat drift into the Bay from connected waterways, settle on the shellbags SCC has placed, and slowly but surely begin to grow and expand reef.

Another difference: The record of where native oyster populations once thrived here has largely been lost to time. "From shell mounds in San Francisco Bay, there's substantial evidence of consumption by the Ohlone tribes," Latta says. But other than that, "The knowledge that people used to eat oysters from the Bay is a surprise to modern folks, and there are a lot of data gaps about where they did exist." Part of the challenge of the SCC project is figuring out "Where we can appropriately restore oyster beds, maybe even in places where they didn't exist historically."

A five-year pilot project, concluded in 2017, is informing oyster reef restoration efforts. Results showed that the reef structure, placed in tandem with plantings of native eelgrass, attracts more species and provides better shoreline protection than just shell bags or grass alone. In certain kinds of tides, combined oyster/eelgrass reefs reduced wave energy by 30%.

Meanwhile, although heavy metal pollution of selenium and zinc persists in the Bay, rendering oysters inedible, other fish are finding the reef. According to Latta, "We've had over 100 species settle onto [or visit] the reefs, including some that have a food connection: many types of shrimp, commercial Red Rock and Dungeness crabs, some tagged salmon like steelhead. A year after we built the reefs we detected a green sturgeon that migrated all the way down from Washington State."

These fish are food resources for other fish, as well as birds and marine mammals. Some of them are also of interest to recreational fishermen. Because of contamination, the state's health department recommends eating no more than one Bay fish per day, although Latta points out that some species, like California halibut, only spend part of their lives in the Bay and may be less problematic.

"Ideally, I'd love to see an eatable Bay again," she says.

Louisiana's Edible Reef

Two thousand miles south and east of San Francisco, Louisiana's coastal marshes encompass the largest commercial oyster fishery in the country, providing $317 million worth of total economic impact to the state a year, according to Louisiana SeafoodCrassotrea virginica is the native species here, just as on the East Coast.

"It's not just that oysters are out there performing ecosystem services, which is wonderful," says Louisiana Department of Wildlife & Fisheries assistant secretary Patrick Banks, referencing the way reef adds "habitat value" to associated species and filters water to minimize algal blooms. "But they're a very important part of our society and our culture."

Banks says that reef habitat improvement and rehabilitation projects, using cultch, or shell, have been ongoing on public grounds since 1917. "For many decades, this method was very successful, but in the last decade and a half they haven't been as successful as they once were," he says. As a result, oystermen and women have been forced to transfer about 95% of their production to private grounds, away from what Banks calls "impacted areas."

The cause of said impacts: a suite of ecological disasters, one on the heels of the other, that has made recovery of the fishery next to impossible.

"It started in 2005 with Hurricane Katrina — that was a tremendous impact to the extensive reefs on public grounds East of the Mississippi River," says Banks. "Those started to come back, then hurricanes Gustave and Ike came in 2008. Then we had the BP oil spill 2010. We had a flood event in 2011 which put a lot freshwater over these reefs." (As Food Safety News explains, oysters die when their saltwater balances are thrown off by too much river water; says Banks, "To be very simplistic, their cells burst.")

On the heels of all that have come four years of major flooding events, including 2019's historic flooding of the Mississippi River. "Once reefs are heavily impacted, it takes three to four years to come back," says Banks. "But these episodic events are happening every three to four years, so they can't get a foothold. It's been a very difficult place to be an oyster, to be honest."

Louisiana's oyster reef restoration efforts have been focused on those public grounds, which historically comprised 1.7 million water bottom acres. There's been some new reef built and old reef restored in these areas, but also some expansion into other locales. "We're trying our best to move away from known freshwater sources like the Bonnet Carré Spillway and into areas that are more stable these days in terms of salinity," Banks says. The goal: to rebuild to a production level that supports an average of 20 oysters per square meter.

Unlike in New York and San Francisco, where oyster shell is the primary building medium for reef, Louisiana, which exports almost 60% of its oyster harvest, has a shell deficit. So, the state has turned to limestone rock and crushed concrete; since these materials are heavy, siting for new reef is extra-challenging due to muddy water bottoms. Banks says that decreased oyster numbers means they've also had to begin seeding reefs with spat —  an expensive prospect that's will be at least partially offset by federal disaster aid monies.

According to The Nature Conservancy, 170 marine species have been counted in oyster reefs in the northern Gulf of Mexico, including several that are almost as tied up as oysters in Louisiana's economy and identity. Says Banks, "We've found shrimp feeding and living around an oyster reef; blue crab is a big industry here and they love to live around oyster reefs. Speckled trout and red drum live around oyster reefs — talk to any recreational fisherman and he'll tell you he prefers to fish over oyster reef any day of the week."

While none of these species are in conservation trouble, "In Louisiana, oyster reefs are just as important habitats as marshes are," Banks says. "A lot folks feel like if you do what's good for oysters, you do what's good for estuaries. As an oyster biologist, I believe that."

Lela Nargi

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