In discussions around seafood and its environmental impacts, it’s more common to hear about what we shouldn’t eat than what we should. Amidst the frequent talk of collapsing fish stocks, polluted ecosystems and seas choked with fishing gear, we tend to hear less about how the production of certain types of seafood could instead be utilised to not only halt these trends, but actively reverse many of them too. Commercial sturgeon farming, for instance, is being explored by Seneca and WWF as a means of restoring wild populations, incentivised by caviar premiums for participating farms.
However, there is a much humbler seafood with even greater potential than this. One whose farming could likewise bolster depleted wild stock and in doing so restore habitats, boost biodiversity, protect us from the effects of climate change, and clear even some of the most polluted waters, all while generating considerable economic benefits too.
The oyster.
The Importance of being an Oyster
Despite their unassuming appearance, oysters are something of a superorganism in coastal ecosystems, not least because of their habitat-building abilities. After beginning life as microscopic larvae floating through the water column, they will soon settle on a hard substrate to complete their development. The shells of adult oysters (even dead ones) are a favoured target for settlement, as these give off chemical signals that attract the larvae to settle on them, meaning that over time, the oysters build up large, dense colonies on top of each other known as oyster reefs.
Oyster reefs provide a multitude of environmental benefits. Not only do they absorb wave energy, protecting coastlines from storm surges and erosion, but they can also grow faster than projected rates of sea level rise, making them particularly valuable for climate change adaptation. They also sequester carbon to build their shells and promote sediment deposition that creates a stable substrate for aquatic plants to establish themselves, creating additional carbon sinks and tackling ocean acidification.
As highly proficient filter feeders, oysters can sequester large amounts of nutrients and pollutants, with one study finding that just seven square metres of oyster reef can filter an Olympic swimming pool of water per day. This in turn means that farmed oysters don’t need feeding by humans, avoiding the nutrient pollution caused by excess animal feed common in other forms of aquaculture. The structural complexity of reefs also provides shelter and breeding grounds for abundant small animals, which in turn attract larger fish to feed from and even breed on the reefs themselves.
Oyster reefs have long been a source of food for humans too, feeding everyone from the Ancient Greeks to the first colonists of America, and forming the basis of a 700-year old traditional industry in Hong Kong. However, overharvesting, pollution, coastal reclamation and climate change have caused an 85% decline in oyster reefs globally, and today the industry relies heavily on aquaculture.
Farming Habitats
With wild oyster reefs in such poor condition, aquaculture –which produces millions of oysters per year– can act as a valuable means of restoring them, providing the resources, expertise and insights needed to successfully do so. Having a source of income also gives it the financial ability to support restoration efforts in the long-term.
As oyster aquaculture involves cultivating oysters on artificial substrates in the sea, it has to overcome many of the same environmental stressors as oyster reefs, including poor water quality, fluctuating temperatures, sedimentation and predators. Traditionally, aquaculture was also done by collecting juvenile oysters (known as spats) from the wild and maximizing their growth. Longstanding aquaculture farms therefore possess in-depth knowledge of locations with the best conditions for oyster larvae and optimal oyster production, and the best practices for rearing them, which can likewise be adopted for oyster reef restoration.
Oyster farms can also act as a direct source of stock, earmarking a portion of their cultivated oysters for restoration efforts, as well as empty shells for building reef substrate. Additionally, as most modern oyster aquaculture involves selective breeding in hatcheries, this allows farmers to specifically produce oysters with traits beneficial for reef establishment, including rapid growth, disease resistance and resilience to warming seas. Selective breeding could be particularly beneficial in areas where disease (a growing problem for oysters due to climate change) has depleted populations, introducing disease-resistant, genetically diverse stock with a greater capacity to adapt to environmental change. When established in close proximity to each other, oyster reefs can also be bolstered by larvae produced by farmed oysters.
The Pearl in the Oyster
Oyster reef restoration can have considerable economic as well as environmental benefits, both for participating aquaculture businesses and other parties.
The most obvious benefit for farmers is the income from selling oysters for restoration. More holistically however, having more oyster reefs in an area improves water quality and therefore the quality of any oysters they sell for market. Furthermore, just as they can offer insights on the best locations and practices for oyster reef restoration, so too can research around oyster reefs offer insights to improve their business. Habitat suitability models can inform farmers on the best locations for new oyster farms, while the findings of studies investigating the growth and survival of oysters on reefs could then be applied to improving farming practices. Providing empty shells to build oyster reefs could also reduce costs associated with waste disposal and diversify farmers’ income, although this is unlikely to be a long-term benefit as most restoration projects are one-offs.
The ecosystem services oyster reefs provide also have significant economic value to coastal communities at large. A study in the Gulf of Mexico found that the habitat and feeding grounds provided by just 10 square metres of restored oyster reef increased commercial fish and crustacean production by an extra 2.6 kilograms per year, which a later analysis valued at US$4123 per year in 2011 money. That same analysis conservatively estimated the full range of ecosystem services from oyster reefs (excluding oyster harvesting) to be worth US$5500 to 99,000 per hectare per year, and that these could recover the median costs of restoration in as little as 2 years. Conversely, the value of oysters obtained by destroying reefs could not cover the associated costs.
One potential economic hurdle to oyster restoration is that oyster shells, while the most preferred material for larval settlement, can also be fairly costly. Fortunately, a 2022 study found that cheaper substrates like limestone were almost as effective in terms of oyster establishment.
The World is Your Oyster?
Despite its benefits, oyster reef restoration, particularly when done in partnership with aquaculture, should be done with care to avoid unintended environmental harm. Like agroforestry, it has a high potential to introduce non-native species to an ecosystem, with the commonly cultivated Pacific oyster now naturalised in 17 countries. Infrastructure for oyster farming can potentially also block sunlight from the sea floor or encroach on intertidal areas, harming seagrasses and reducing habitat for wildlife. However, many of these risks can be mitigated with proper biosecurity measures and informed spatial planning.
Effective oyster reef restoration will require long term planning and conservation measures. According to a global analysis of oyster reefs, while newly restored ones do see an initial rapid surge in biodiversity in their first 2 years, the recovery rate is substantially slower after that, meaning that long term protection is needed for them to develop into mature ecosystems with biodiversity levels equivalent to those of existing reefs.
Restoration efforts must also take into account the threats posed by pollution and climate change, and here the partnership between conservation science and aquaculture can be particularly helpful. Genetic analysis of wild oyster populations exposed to pollution or temperature extremes can identify the genes that allow them to survive those stressors. This information can then be used in aquaculture to selectively breed strains of oysters with these genes. Such research is already being done by the University of Hong Kong as part of efforts to restore its struggling oyster industry.
The benefits of oyster farming prove that, in some cases at least, seafood can be a useful, even highly effective means of restoring our oceans instead of destroying them. Now, we need to properly invest in and expand these industries to achieve their full potential.
After all, an ocean that’s not fit for oysters is not fit for us.
Author: Seneca Impact Advisors
For more information, please contact info@senecaimpact.earth
