Cleaning The Seas with Mussel and Oyster Farms

Some mussel and oyster farms work in a way that produces food, minimises environmental damage and cleans up the oceans all at the same time. Is this a win-win situation?

Whether its greenhouse gas emissions, land and water use, pesticides and fertiliser use, or issues of animal welfare, most farmed meat and fish comes with an environmental cost. But there’s one kind of farm that not only avoids all these pitfalls, but actually brings a net environmental benefit: sustainable, ocean-based vertical shellfish farms. 

Does ‘Zero Input’ Farming Exist?

As their name suggests, ‘vertical ocean farms’ take an innovative approach to farming shellfish. Based on the vision of Bren Smith’s GreenWave designs, ropes are strung across the surface of the water, attached to floating buoys and seabed anchors. These ropes suspend mussel rocks and scallop nets in the ocean, while oyster and clam cages lie on the seabed attached to the farm by a long tether. From the surface these farms are almost invisible, but dip beneath the waves and these hanging baskets are teeming with life.

Incredibly, these farms are ‘zero input’ – meaning that the farmer doesn’t need to add anything into the system in order for the animals to thrive. They’re based in open waters, and since bivalves like mussels, clams, oysters and scallops can survive in a wide range of water conditions, there’s no need for farmers to artificially regulate the water quality. Bivalves are also filter feeders, meaning they grab their own food (usually plankton or other microscopic sea creatures) out of seawater as it flows by, without the farmer ever needing to spend a penny on food. At the same time, they naturally absorb all the minerals (such as nitrogen and phosphorous) they need to grow, meaning there’s no need to add any fertiliser either.¹

Farming That Protects the Environment

The good news doesn’t stop there, as it’s not just shellfish growing in these ‘zero input’ farms. Seaweed and kelp, which only require sunlight to grow, can flourish happily between the cages, nets and rocks, making the most of every inch of space. Seaweed also require no helping hand to thrive in their natural ocean environment, and they grow super-fast – allowing farmers to collect up to 8 harvests in a single year.² Growing seaweed boosts the productivity of these farms by giving farmers another product to sell, while further improving their green credentials by pulling carbon dioxide from surrounding water.³

 Learn more about how seaweed is grown and harvested.

The physical presence of vertical mussel and oyster farms can also act to help stabilise the ocean, acting like an artificial ocean reef to dampen the impact of storm surges on coastlines and coastal communities.⁴ And, if all that wasn’t enough, even the waste these farms produce can be put to good use! Bivalves excrete waste which then collects on the seafloor underneath these farms, and is packed full of organic nitrogen. This makes it a fantastic alternative fertiliser, giving farmers yet another potential product to take to market (though collecting it from the seafloor can be a tricky and expensive task).⁵

Vertical Mussel and Oyster Farms Clean the Seas

In addition to having a small environmental footprint, these farms actually contribute to improving and repairing the ocean environment too.

Aquatic ecosystems exist in a delicate state of balance, relying heavily upon two key nutrients - nitrogen and phosphorus - for a healthy equilibrium of plant and animal life. Too little of either, makes it difficult for animals or plants to get hold of what they need to grow. Too much nitrogen and phosphorus leads to the overgrowth of plankton and marine plants, which then use up too much of the water’s oxygen, depriving other marine life in the area (a process known as eutrophication).Human activities – such as using nitrogen and phosphorous-rich fertilisers on land-based farms – have leeched huge amounts of these two nutrients into many coastal waters, with devastating results: the Gulf of Mexico, for example, now features a yearly summer “dead zone” of over 5,000 square miles in which there’s too little oxygen for plants and fish to survive.⁶

Vertical ocean farms could help reverse some of that damage. Shellfish, and mussels in particular, are excellent at pulling excess nitrogen and phosphorus out of the water around them and using it to grow. In doing so, they help reduce the risk of eutrophication and protect the natural marine life around them. Recent research suggests that while these farms are not going to rescue areas as badly affected as the Gulf of Mexico, they can help repair other coastal areas that are currently at risk of ecological collapse by removing hundreds of thousands of kilograms of nitrogen from the water every year!⁷

Mussels Clean Up Polluted Waters

People have started to take note of the cleaning powers of the mighty mussel and are trying out new ways of putting them to use. For example, integrated multi trophic aquaculture (IMTA) farms links mussel farming and fish farming together for maximum efficiency: the mussels feed on the organic material excreted by the fish, which in turn cleans the water and helps the fish remain healthy.⁸

It’s not just nitrogen and phosphorous though: mussels are excellent at pulling out a wide range of harmful chemicals, bacteria and even small physical particles like microplastics out of the water.⁹ This makes them a relatively low-cost solution to filter and clean water in polluted areas, so some US states are looking seriously at investing in mussels to clean up their rivers – though since they’d be grown in poor-quality water, it’s unlikely those mussels would meet the consumption standards to end up on our dinner plates.¹⁰

How do you know when mussels are safe to eat? Learn more about shellfish poisoning and how to avoid it here.

Shellfish and Seaweed: Food for Everyone?

So why aren’t we all eating shellfish and seaweed? They’re highly nutritious, with shellfish being packed with protein, vitamin B12, vitamin C and calcium while seaweed is rich in fibre, vitamin K and magnesium.^11,12 They’re also (with the exception of oysters) relatively affordable, and given their primitive nervous system and lack of a brain it’s unlikely they feel ‘pain’ as we know it - meaning they’re perhaps more ethical to farm and eat them than other animal species.¹³

However, eating shellfish isn’t for everyone. Despite their environmental credentials, some may still feel that a plant-based diet is a more sustainable way to live, while others may argue that the eating of any animal is unethical. Beyond personal choice, some people may not be able to eat shellfish in the first place, since shellfish allergies are relatively common (affecting an estimated 0.5% to 2.5% of people worldwide) and can be extremely severe.¹⁴

Limitations to Mussel and Oyster Farms

Naturally, vertical ocean farms do have their inevitable downsides too: for example adding new species to an area can disrupt the natural ecosystem, which may then be further disturbed when harvest time comes around.¹⁵ We’ve also yet to see whether this form of farming will bring unforeseen consequences once scaled up. Ultimately though, if properly managed these farms represent a chance at something extraordinarily rare – a way to grow our food that, rather than damaging the world around us, actually helps protect it.