The humble ecosystem engineers that protect us from rising seas

The other week, I read about New York’s Billion Oysters project, which collects used oyster shells from 45 city restaurants with the goal of building a reef that will calm big waves, help prevent coastal flooding, and ease erosion. Since the project started in 2014, they’ve collected 1.8 million pounds, which are cleaned, cured in the sun and “set” with microscopic larvae. The bags of old shells are placed around city waters and will become home for baby oysters, as well as eventually creating a reef. It’s a project that has attracted a lot of media attention, in part because there are so many ways ordinary people can help.

Photo by Ben Stern on Unsplash

“In the wild, young oysters — oyster spat — must settle on a hard surface to survive,” explains the project website. “Oyster, clam, and scallop shells provide that hard surface and are rich in calcium carbonate — making the the perfect substrate for oysters to settle on. And, thanks to New Yorkers’ lasting love for oysters, these shells are a plentiful local resource. In 2015, Billion Oyster Project started a Shell Collection Program, giving restaurants an opportunity to not only divert shells from landfills, but also to reclaim this valuable resource for the restoration of oyster reefs.”

New York’s coastline used to have a lot of oyster reefs – more than 220,000 acres (89,000 hectares). They were part of a natural system of mitigating floods. But they were devastated by the commercial oyster industry. Shells were ground up in fill to build the growing city. Now people are trying to use them to once again protect that city from the flooding that comes with rising seas.

The need became clear when Superstorm Sandy devastated Staten Island’s eastern and southern shore neighbourhoods in October 2012, causing massive damage, loss of life, and harm to the local economy. Tottenville, historically known as “the town that oyster built”, experienced some of the most destructive waves in the region. 

“Tottenville was once protected by a wide shelf and series of oyster reefs, which in turn supported a robust oyster farming industry. Over time, due to siltation, overharvesting, channel dredging, and human pathogens in the water, the once abundant oyster reef collapsed. Today, the Raritan Bay lacks not only the oysters, but the complex habitat their reefs provided and the species richness and biodiversity that they supported. Without these natural systems, the shore of Staten Island remains exposed to wave action and coastal erosion and lacking this rich environmental resource,” said the Govenor’s Office of Storm Recovery.

The Living Breakwaters project is a $60-million project to create a huge reef off Staten Island, using something that landscape architect Kate Orff calls “oyster-tecture” – rubble and shell structures implanted with living larvae. It was launched after Superstorm Sandy hit the city in 2012, tearing houses off their foundations and causing 24 deaths. And it’s a different kind of coastal infrastructure that is much closer to nature than concrete breakwaters.

It includes nine separate breakwater segments across the bay; a floating oyster nursery; an environmental-education hub; and a set of man-made tide pools at high tide. And it helps educate students about such natural infrastructure.

“The way we talk about global warming is usually dark and pessimistic,” she told the New Yorker. “It can be stifling. Part of my job is showing people new ways to see things, to offer a vision of places we can live in, responsibly, and also enjoy.”

Ecosystem engineers

So I got interested in oysters, and why they are seen as  “ecosystem engineers”. Their reefs shelter and feed other species, like fish and crabs; reduce the energy of waves by between 76% and 93%; and an individual oyster can filter as much as 50 gallons of water per day. People say that once, oysters in the Chesapeake Bay could filter all the bay’s water once a week

The oyster fishery itself is valuable – one estimate of the Chesapeake Bay fishery found that while the dockside value of oyster catch was about $44 M in 2013-2014, each $1 M of dockside value equated to $36 M in total sales and almost 1,000 jobs.

So no wonder that so much work is going into recreating oyster habitat, with many of those attempts recycling used oyster shells to create substrate that young oysters can attach to. But there is a long way to go – as many as 85% of all oyster reefs globally have been lost in the last 200 years and they are considered to be of the world’s most threatened habitats.

The NOAA Restoration Center has funded more than 70 oyster restoration projects in 15 US states. Some of the restoration techniques they’ve tried include:

  • Quickly distributing large amounts of shell with high pressure hoses to provide a suitable base for oysters.
  • Constructing a linear reef of shell and rock to stabilize the shoreline and protect seagrass plantings behind the reef, enhancing shoreline stability and providing additional habitat for other reef inhabitants.
  • Collecting and bagging oyster shell for use as cultch (the mass of stones, shell, and grit that oyster beds are made of) for spat. Like a quick-start habitat, these bags of oyster shell will help establish new reefs in intertidal areas.
  • Creating hatcheries to provide seed oysters in areas where oyster reproduction is nonexistent or unreliable. This will establish new reefs and improve local water quality.

One of the key projects is in the Chesapeake Bay, which aims to restore oysters to 10 Chesapeake tributaries by 2025. The partners develop a “blueprint” that describes where restoration will happen in each tributary, with maps of where the best places are, how many oysters will be needed, and what type of restoration is needed.

“Some areas might only need to be seeded with “spat-on-shell” baby oysters,” NOAA explains. “Others might need to have reefs constructed and to be seeded with spat on shell. Still others might need to have reefs constructed so that naturally occurring spat have a hard place on which to settle and grow.” The reefs are monitored at the three and six year mark, after restoration. It acts as a laboratory for oyster restoration, so that the results of success can be identified.

The Nature Conservancy also has been experimenting with oyster restoration strategies in the southeastern United States

And a firm in Charlottesville, Va, has developed a way to speed up the process through mixes that are like oyster shells and “a range of scalable, concrete, biomimetic reef building substrate products, modeled after intact reefs.” Having studied reefs, they developed a way to support the oyster’s natural reef-building capability.


World’s largest oyster restoration completed on Piankatank River. Virginia Mercury, Nov. 30, 2021

Protecting Louisiana’s Coastline with Oyster Shells in “What Remains”. New Yorker, Feb. 23, 2022