Author: Layla Khazeni
Editor: Nirvan Marathe
Photo credits: Peyton Sanborn
Although it can be easy to forget while riding the subway or getting lost between skyscrapers, many of the world’s most enduring and influential urban centres are shaped by their relationships to waterways. From the Thames to the Hudson River Estuary, the cultures, economies, and histories of these modern cities are anchored in the bodies of water that define them. The aquatic ecosystems preexisting and underlying metropolitan areas have a complex, bidirectional interplay with city life: they serve as natural highways, commercial channels, environmental buffers—and, on the receiving end, as subjects of severe anthropogenic change.
Where the Hudson and East River meet the New York Bay, shellfish and the habitats they depend on are integral to the foundation of the most populous American city. The Eastern Oyster, Crassostrea Virginia, is present in local fossil records dating back ten thousand years, and their abundance supported indigenous civilizations centuries before the region was settled and labelled as part of the New World. The Lenape Americans taught newcomers how to harvest the bivalves and their method of opening them: wrapping the oysters in wet kelp, tossing them onto hot coals, and waiting for them to open. Early surveys and fishing logs suggest that 18th century oyster reefs spanned over 350 square miles of shorelines in the estuary––arguably over half of the global oyster population.
Despite some early conservation efforts, including laws prohibiting the collection of oysters during months without the letter R (those warm enough for oysters to reproduce and recruit), the population has been in steady decline since consumption practices became unsustainable and the estuary became a dumping site for industrial and municipal waste. As the nearshore ecosystems declined into near irremediable conditions, the city expanded, and the oyster cellar eatery model flourished. The chemical byproducts transported through the Hudson River and up the food web hampered oyster reproduction and establishment until the population could no longer sustain itself, nor be sustained, and the final commercial oyster bed in New York City closed in 1927.
Aquatic trade routes made oyster imports from nearby regions all-too-convenient, so many consumers may not have noticed the oyster’s disappearance from New York Harbour. However, the collapse of these thriving reefs was felt in more ways than one. Without oysters to filter the water for excess nutrients, water quality worsened. The reefs built by oysters had served as critical habitats for other species, as anchors for substrate and sediments otherwise resuspended, and, crucially, as living breakwaters, mitigating the impact of storm surges on shorelines.
Bringing the native species back to their naturally complex and radically altered habitat proved challenging for many years. Oyster restoration projects initiated at the turn of the century failed due to the high-energy environment of the harbor-estuarine system surrounding Manhattan; loose spat was quickly buried or swept away, unable to provide landing ground for oyster larvae as intended. However, creative solutions changed all of this, and became a compelling story of how cooperative, ecosystem-scale, community-led efforts can turn the tide for sustainable restoration of nearshore marine ecosystems in urbanized waterways.
In 2015, The Nature Conservancy launched a restoration campaign titled Healthy Harbor NYC, partnering with the Billion Oyster Project (B.O.P), a local nonprofit that had started as a classroom experiment at the Urban Assembly New York Harbor School. By 2021, they built their first successful oyster reef off the coast of Brooklyn using gabion “reef balls”, caged contraptions filled with recycled shells, and “community cabinet reefs”, wire mesh boxes held up by welded rebar. Researchers have been monitoring the ecological benefits of these artificial reefs, raising awareness, and scaling up at sites across the estuary ever since.
I spoke with environmental consultant and B.O.P. volunteer Peyton Sanborn to get a more intimate sense of how this initiative operates. “There’s some irony to engineering oyster reefs, who are themselves ecosystem engineers,” she points out. “And there’s something ironic about how we’ve turned to oyster reefs to protect the city, when it was our rapid urbanization of these coastlines that destroyed them.” For Peyton, working with B.O.P. is one way to reconnect with nature in a place that often feels like the antithesis of it; and to her, oysters are the ecological heartbeat of New York.
One of the Billion Oyster Project’s greatest strengths is its capacity to unite community members from a range of professional and demographic backgrounds, consolidating unique and diverse perspectives. One of the organizers that dives in the harbor to monitor restoration efforts has witnessed firsthand the inhabitable conditions created by poorly regulated city infrastructure; in a process that is likely familiar to many Londoners, any heavy rains flood the sewer system, and the excess joins the river. After such an event, diving is prohibited; not only is visibility impaired, but the water is categorically unsafe. However, one adult oyster can filter 50 gallons of water in a single day: with a billion oysters, pollutants could be removed from the entire harbor by these bivalves in a matter of days.
Another commonality between The Big Apple and The Big Smoke is that their climates are heavily influenced by the Atlantic Meridional Overturning Circulation (AMOC), a circulatory flow that carries warm surface waters northward and cold deep currents towards the equator. One of Earth’s larger-scale climate-regulating systems, the strength and regularity of this oceanic pattern have cascading effects across the globe. There is great uncertainty about what changes in this global-scale system will occur; oceanographic researchers at UCL and beyond are analyzing late-quaternary climate proxies to make predictions, a critical process that can help protect coastlines.
In the words of UCL paleoclimate researcher David Thornalley, “unprecedented changes in Atlantic circulation are occurring. This raises warning signs about the future.” In a recent BBC Science Focus article on this issue, Professor Thornalley explains that the AMOC may cross a tipping point towards extreme and unpredictable weather events, at least partially due to imbalances in the salinity of the ocean as glaciers melt. In the wake of habitat loss and fragility, and facing sea-level rise and changing ocean dynamics, New York’s waters are not only less potable, less habitable, and less observable, but also more liable to coastal hazards. As it stands, the shoreline city is engulfed in a deluge of potential natural disasters incurred by weakened mitigation mechanisms.
Nature-based solutions are a hot topic in coastal resilience, and there is plenty of empirical data to support their viability as living breakwaters, but these projects are most effective when they are conceived through collaborative, place-based decision making and sustained by local, adaptive management. Modelling studies show that habitat restoration can significantly reduce damages to property and infrastructure through flood protection and wave energy dissipation. More than 24 million people call this metropolitan area home; considering that, according to a report prepared by The State University of New York at Buffalo, total state-wide property damage between 1960 and 2014 attributed to extreme weather events amounts to 11.32 billion USD in New York City and Long Island alone, these disasters can be costly.
However, the survival of restored reefs depends on variables specific to each site, such as tidal range: in many places, oyster reefs thrive in intertidal zones, but in the temperate climate of the United States’ East Coast, their suitable habitat is limited to subtidal environments. If the restored reefs are exposed to winter air for too long during extreme lows, the oysters will die. The B.O.P. practices adaptive management, continually monitoring their progress to allow for re-evaluation of restoration strategies. This form of engagement sets a strong example for proactive, coordinated climate resilience projects in other coastal cities.
Often, the restoration of coastal habitats as a nature-based approach to climate resilience incur additional benefits by sequestering carbon and mitigating a key driver of global warming. This applies for seagrasses, kelp forests, saltmarshes, and mangroves, but the shell-building bivalves are an outlier. Despite sources, such as the WWF, claiming that oysters extract carbon from seawater, the process of calcification known as shell biosynthesis actually releases carbon dioxide (CO2) as a byproduct. This happens especially rapidly in warm, tropical waters; in temperate ones, studies suggest oyster reefs act either as a weak carbon sink or mild carbon source depending on local conditions. However, these filter-feeding bivalves still sequester carbon in other ways, accumulating and burying vast amounts of organic matter from the water column, and combat ocean acidification by converting calcium (Ca2+) and carbonate ions (CO32-) into calcium carbonate (CaCO3), the stable stuff of shells. For an in-depth and interactive look at this process, visit this virtual demonstration by the Woods Hole Oceanographic Institute.
Ultimately, while the mechanisms of carbon sequestration are not as simple as we’d like to believe, localized and socially integrative initiatives can have profound positive impacts by strengthening the social, ecological, and physical buffering capacities of coastal communities. In fact, according to a report by The Nature Conservancy, nearly half of the members of the Harbor Estuary Program Oyster Restoration Working Group perceive public engagement with the project to be a greater success than the results of restoration or research findings.
While larger, oceanic forces may be beyond our reach to impact directly, coordinated grassroots efforts such as The Billion Oyster Project can supplement reductions in exacerbating, exploitative behaviours to ensure a safer future. Fostering the rebound of native coastal habitats, such as oyster reefs, is a way to promote biodiversity and climate adaptability––and participants in the New York Harbour School effectively demonstrate how to build coastal resilience and community simultaneously. This organisation is an example of how deliberate, localised action can be an antidote to an anthropogenically-induced absence which is not only inconvenient, but existential, for New York City.
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