Given the scale of bivalve aquaculture globally, the benefits it provides to local economies cannot be overstated. And that’s before you consider the products that come from bivalve aquaculture, such as pearls, poultry feed grit and, of course, the food on our plate. But as Andrew van der Schatte Olivier, PhD student at Bangor University points out: “There is so much more to bivalve aquaculture than we currently think.”
Around 20 years ago, the concept of ecosystem services – “the benefits people obtain from ecosystems” – emerged as a way to aid sustainable development. In the language of ecosystem services, those products we gain directly from cultured bivalves are known as “provisioning services”. Alongside job creation and local economic benefits, provisioning services are typically what dominates policy and business discussions but considering ecosystem services requires us to look further. Which is why van der Schatte Olivier set out to uncover the other services bivalve aquaculture provides us.
There are three other types of ecosystem services aside from provisioning services. Underpinning all are what are known as supporting services. In terms of bivalve aquaculture, this includes nutrient cycling and providing habitat for other species. Then there are regulating services which include sediment movement and carbon storage. Finally, there are the more intangible cultural services, which range from recreational fishing to seafood festivals to spiritual and religious symbolism. If we were to put a global economic value on just the regulating and provisioning services, van der Schatte Olivier estimates that to be some U$30 billion per year.
Whether planted reefs on the seabed or hanging from trestles, cultured bivalves will eventually be harvested, and new ones planted in their place. Whilst these short-lived life cycles suit provisioning and some cultural services, supporting and regulating services arguably function better with time. Throughout their short-lived life, van der Schatte Olivier notes, it is not uncommon for farmed bivalves to spawn and potentially seed reefs elsewhere. If these reefs are left alone, either because they have not been discovered, have been protected, or are in an area that cannot easily be fished, then these offshoot reefs will grow naturally providing, for example, more complex habitats that support diverse and stable communities of marine life – including commercially important species.
According to van der Schatte Olivier’s estimates, the bulk of bivalve aquaculture’s economic value comes from provisioning services (U$24 billion), but this does not mean that the other services are any less important. In fact, one of the most pressing issues of our time may also, in some way, benefit from one regulating service bivalve aquaculture can provide.
The latest Intergovernmental Panel on Climate Change (IPCC) report warns we have just twelve years to make drastic cuts to carbon dioxide emissions to limit global warming to 1.5°C and minimise the worst impacts of climate change on people, livelihoods, and the environment. Alongside emission cuts, mitigation strategies such as carbon storage solutions also have a vital role to play in improving our future.
When carbon dioxide combines with dissolved calcium in the sea, it creates calcium carbonate -the main ‘ingredient’ for shellfish to build their shells. Although the shell-building process does release carbon dioxide, some becomes locked away in the shell. The more bivalves there are, the theory goes, the more carbon is locked in their shells.
Bivalve aquaculture is not the only form of aquaculture that potentially has a part to play in carbon storage. Like their terrestrial counterparts, seaweeds need carbon dioxide to grow and thrive. As a result, they store carbon within their tissues. When farmed seaweeds are taken out of the water intact, they take the carbon with them.
Farmed bivalves are also removed from the ocean whole, meaning the carbon locked inside them is also taken out. Just like with seaweed, what happens to the carbon locked in farmed bivalves next depends on what happens to the shells. If the shells are ground up, van der Schatte Olivier notes, then the carbon will be quickly released. If they remain whole, then the carbon stays locked away – at least natural breakdown occurs, which can take centuries. The question then becomes what to do with these whole shells. The answer, van der Schatte Olivier enthuses, may lay in part in reef restoration.
A good deal of the bivalves goes to the consumer whole. Once we have eaten the flesh, the shells end up in the bin, destined for a life in the landfill. Rather than sending shells to already overburdened landfills, some groups in the USA are using the waste to restore oyster reefs that have been destroyed. The idea is simple. Empty shells are collected from restaurants or donated by home-consumers, cleaned and carefully placed back in the sea. Whether pre-seeded with oyster larvae or not, these empty shells then form a base for live oysters to settle and grow.
Van der Schatte Olivier stresses that his values are estimates - and most likely underestimates of the true value of bivalve aquaculture. Whilst hard values for provisioning services tend to be well documented, supporting and regulating services are not something we currently pay for. Instead, we have to estimate what the cost would be if we were to do these things ourselves. Cultural services are even more difficult to value, particularly when it comes to things integral to a culture but are essentially non-tangible; “[Cultural services are] actually one of the most interesting aspects, but one that is mostly ignored for a long time,” van der Schatte Olivier explained.
Indeed, the concept of giving such things an economic value can seem a little disingenuous, but for van der Schatte Olivier, is an important one. “When you are talking to policymakers and people need to have debates, they need a common language. By putting a financial value, at least it is in something we can discuss and compare.” Perhaps work like van der Schatte Olivier’s will be one of many steps into bringing the full range of services into the discussion.
This story appeared on The Fish Site.