Are we farming the right species?

Despite their modest position relative to the rest of the food chain, seaweed, sea squirts or shellfish, might just hold the key to sustainable seafood farming.

The most commonly farmed species that you are likely to have seen in shops or restaurants in Europe are the following three:

• Salmon: Recent technological advancements, selective breeding and high market value have made the familiar pink-fleshed fish available to meet customers’ demands. Farmed salmon comprises over 70% of the salmon market, so chances are if you have eaten salmon, then you have eaten farmed fish._[1]
• Tuna: Farmed tuna only accounts for less than 1% of the total tuna market._[2] All the tuna that you would typically eat for sushi or even canned is wild-caught. The only tuna species that are farmed is Bluefin and Yellowfin tuna. But, farmed tuna will rarely be seen in the tins on shelves at your supermarket. Instead, they are sold at fresh markets or exported frozen to high-end restaurants.
• Pangasius (‘basa’ or ‘pangas’): Sold in over 130 countries, the humble ‘basa’ or ‘pangas’ is sold primarily as frozen budget fillets. Wild-caught pangasius lack any regulation, so almost all basa sold globally is now derived from farmed sources._[3,4]Pangasius fish doesn’t require much oxygen to breathe, is pollutant tolerant, and quick breeding by nature, all making it an ideal species for productive aquaculture._[5] Pangasius basa fish also have a low food conversion ratio, meaning that it takes less food to grow more.

However, in terms of sustainability, farming species belonging to a lower trophic level*, such as seaweed, sea squirts, or shellfish, brings additional benefits.

_{*Trophic level: an organism’s position in the food web where apex predators (like sharks and tuna) are at the top of the pyramid and primary producers (like plants and algae) at the bottom.}

Why is farming seaweed more sustainable and cheaper than salmon?

To first understand why trophic levels matter for sustainability, we need to take a look at how energy moves through the food chain: primary producers like seagrass and algae (level 1) become food for first-order consumers like shellfish (level 2), who are then consumed by intermediate predators (level 3), and so on.

_{How energy moves through a food web}

The energy needed to support the same weight of an organism gradually increases as you go up each trophic level._[6] This means that almost 1,000 kg of seaweed (level 1) is needed to support a single kilogram of salmon (level 4).

Salmon need more energy and food per kilogram of fish than fish at lower trophic levels, regardless of whether that energy comes in the form of animal-based or plant-based feed._[7]

_{Almost 1000kg of seaweed is needed to support a single kg of salmon}

While developments in aquaculture feed have seen improved feed conversion ratios (meaning less food is needed to produce more fish), fish feed still often accounts for over half of the total aquaculture production costs and is further contributing to land clearing to produce this feed._[8]

On the other hand, low-trophic species require only a fraction of the energy input to grow into a product that we can eat – cutting both costs and the resources needed to grow our food.

_{Energy needed to support the same weight of an organism}

Which are the benefits of bivalve and algae farming?

If designed correctly, both bivalve and algae farms can actually positively impact the environment around them – all while producing nutritious foods._[9]

• Bivalves (shellfish): Shellfish are non-discriminate filter feeders – meaning they’ll happily filter up to 100L of water per day, picking out excess nutrients, organic matter and naturally purifying their surroundings while removing CO2 from the environment._[10,11]
• Macroalgae (seaweed): It needs little more than sunlight and naturally available nutrients to thrive, growing faster and producing more oxygen than any land-based plants, with some species growing up to half a metre per day._[12]

On top of this, macroalgae also offers coastal protection from storms by buffering wave energy, provides biodiversity-boosting habitats for neighbouring species and even reduces the effects of ocean acidification in local areas. Seaweed farms also hold significant carbon capture potential: a recent study estimated that global macroalgae farming captures 2.48 million tons of CO2 per year, making it a possible solution for actively mitigating climate change._[13]

For small producers and lower-income regions, it provides a real low-input, low-cost and sustainable route towards improved food security and livelihoods. It’s also a good differentiation strategy. Monoculture food production systems – whether on land or at sea – are a high-risk, high-reward business. They leave producers incredibly vulnerable especially as uncertainty around climate change continues to mount.

Turning trash into treasure – a multi-trophic approach

Low-trophic species can also offer aquaculture producers new ways to turn waste back into useful materials. Integrated-Multi-Trophic Aquaculture or IMTA – a concept dating back to 2100 BCE in China – involves the joint farming of species from different trophic levels that are ‘ecologically complementary’._[14] For example, seaweed and shellfish could be grown mutually alongside salmon farms, feeding off nutrients produced by the salmon.

While doing so, the seaweed would be filtering the surrounding water to provide a cleaner environment for salmon to thrive in and add to biodiversity in the area – a true win-win.

Why are low trophic species’ and IMTA’s farms still rare?

These are some reasons:

• This alternative farming requires a significant investment of money, time, and expertise in order to create a new farming model that is both economically profitable and achievable at large scale. The majority of commercial aquaculture producers have opted to use the knowledge and infrastructure that is already tried and tested.
• Marine environments are hugely dynamic and ecologically complex, which makes regulating new uses of marine space incredibly difficult.
• Consumer demand for many low-trophic species is still scarce.
• In many regions, regulations for single-species production are already lacking, so developing and implementing more complex regulatory frameworks and industry expertise needed to support more dynamic multi-species systems (e.g. IMTA) will take time.

Author: Oliver Fredriksson

Let’s discuss:

• Have you ever tasted algae? Do you like them?
• Would you swap fish for a low-trophic species like seaweed or shellfish?
• As part of the EU’s Horizon 2020 programme a new research and innovation project called AquaVitae is now compiling one of the world’s largest and most comprehensive multi-national low-trophic task forces. Their mission – to introduce low-trophic species, products and processes in marine aquaculture value chains across the Atlantic. Do you think Europeans will consume more low-trophic farmed food in the future?