Aquaculture and the Environment

Aquaculture is an essential component of global food production, playing a crucial role in reducing pressure on wild fisheries stocks. However, like all forms of food production, it has environmental impacts that vary depending on the species farmed, farming techniques used, and local ecological conditions.

These can range from positive impacts associated with low trophic aquaculture farming to more negative associated with fish open pen farming. whilst the later may have historically have had negative impacts, after scrutiny and with modern techniques and technologies, even fish farming has becoming more environmentally aware.

Direct Environmental Challenges of Aquaculture

When we look at aquaculture largest industries, fish farming traditionally undertaken in open-net pen farming systems, can contribute to environmental degradation through fish waste, uneaten feed, and metabolic byproducts are released directly into surrounding waters. This can lead to:

• Excess nitrogen and phosphorus entering the water column, promoting harmful algal blooms (HABs), which deplete oxygen levels and can lead to hypoxic (dead) zones.

• Biofouling accumulation on aquaculture infrastructure, which can degrade local water quality.

• Coastal eutrophication, where excessive nutrients alter marine ecosystems, potentially reducing biodiversity.

However, over time our understanding of these impacts have grown considerably, and with that mitigation and site selection has become even more vital and in UK and European countries and is undertaken alongside, habitat regulation assessments, is in place to ensure licensing authorities ensure that appropriate steps have been taken to assess these impact on protected habitats.

Some forms of aquaculture, particularly shrimp and finfish farming, have, globally, led to the destruction of vital coastal habitats, including mangroves, seagrass beds, and salt marshes, which act as natural buffers against erosion and serve as crucial breeding grounds for marine life. Whilst, increased sedimentation and water turbidity, which can affect seafloor habitats and disrupt local ecosystems.

Filter-feeding shellfish and seaweed farms can mitigate this issue by removing excess nutrients, helping to balance water quality, and as some research has shown, potentially regenerate sites acting as defects MPA’s and creating new biogenic reefs. This has led some researchers and operators to look to balance one systems waste with these extractive species, in methods referred to as Integrated Multi Trophic Aquaculture (IMTA). Although these methods still have technical challenges before they can be widely adopted.

This highlight the need for greater national understanding of UK aquaculture as part of food security which can ensure that farmed species are avoiding all possible negative consequences on the environment and maximising their potential for good.

Indirect Impacts

While aquaculture reduces pressure on wild fish stocks by providing a controlled source of seafood, farmed species also require their own nourishment. This is particularly relevant for carnivorous species such as salmon, which have historically relied on fishmeal and fish oil derived from wild-caught fish. This dependence raises concerns not only about marine ecosystem impacts but also the carbon footprint of aquaculture feeds.

A key issue is the overfishing of small pelagic fish—such as anchovies, sardines, and menhaden—which are harvested in vast quantities to produce feed. These fish are essential components of marine food webs, supporting predators like seabirds, marine mammals, and commercially important wild fish species. Their depletion risks disrupting ecosystems and reducing biodiversity.

Another concern is the conversion ratio of wild fish to farmed fish. Historically, producing one kilogram of farmed salmon required multiple kilograms of wild fish in feed, creating a net loss in marine protein availability. However, advancements in feed formulationare reducing this dependency.

The embodied carbon footprint of aquaculture feeds is another significant issue. The production, processing, and transportation of feed ingredients contribute to the total emissions of farmed seafood.

• Fishmeal and Fish Oil – Wild-caught fish used in feed not only impact marine ecosystems but also have a high carbon cost. The fishing fleets that target small pelagic species consume large amounts of fuel, and the subsequent processing—including cooking, pressing, drying, and milling—requires significant energy inputs. Once produced, these ingredients are often transported across global supply chains, further increasing emissions.

• Soy and Terrestrial Crops – Some feeds incorporate terrestrial plant proteins such as soy, which can contribute to deforestation, biodiversity loss, and land-use change in major producing regions like South America. Additionally, industrial-scale crop farming relies on fertiliser production, irrigation, and mechanised harvesting, all of which have their own carbon footprint.

Alternative Proteins – Efforts to transition towards more sustainable feed ingredients must also account for their carbon costs:

• Insect-Based Proteins – While promising, large-scale insect farming requires energy for rearing, processing, and drying, which can be carbon-intensive depending on the energy source.

• Algae and Microalgae – These provide a sustainable source of omega-3 fatty acids, but large-scale cultivation requires nutrients, water, and processing.

• Fermentation-Derived Proteins – Using bacterial and fungal fermentation to produce protein-rich feed components can be more sustainable, but energy requirements for bioreactors must be considered.

To address both marine resource use and carbon emissions, the aquaculture industry is increasingly investing in feed innovation. The development of circular economy approaches, such as using fish processing byproducts and waste-to-feed technologies as well as co locating aquaculture facilities with those that produce waste heat, to help reduce reliance on wild fish and lower the carbon footprint of aquaculture. Advances in precision nutrition, where feeds are formulated to optimise growth with minimal waste, are also improving efficiency, reducing both feed conversion ratios (FCRs) and emissions per unit of farmed seafood.

Unintentional Risk

The escape of farmed fish into the wild can have several ecological consequences. Hybridisation with wild populations may lead to reduced genetic diversity and weaker stock resilience, making native species more vulnerable to environmental changes. Escaped fish can also compete for food and habitat, particularly when they exhibit higher growth rates than their wild counterparts, potentially outcompeting native species. Additionally, the introduction of non-native species can disrupt local ecosystems, altering predator-prey relationships and habitat dynamics.

High-density farming environments further increase the risk of disease transmission. Pathogens such as sea lice and viral infections can spread from farmed fish to wild populations, threatening marine biodiversity. The use of antibiotics in aquaculture, while sometimes necessary, has in certain cases contributed to antimicrobial resistance (AMR) in marine ecosystems, posing a broader risk to aquatic and human health. Furthermore, nutrient pollution from aquaculture can fuel algal blooms, which in turn may create toxic conditions that impact both farmed and wild stocks.

To mitigate these risks, the industry is implementing strict biosecurity measures, vaccination programmes, tailored precision feed promoting health and natural disease management strategies, reducing reliance on antibiotics while improving fish health and environmental sustainability.

Low-Impact and Restorative

Aquaculture has the potential to be a low-impact, environmentally beneficial method of food production when managed responsibly. Unlike conventional fish farming, which can rely on high-energy feeds, antibiotics, and intensive management, a focus on low-trophic species

Certain aquaculture systems are dominated by species that have a net positive impact on the marine environment which allows for minimal environmental disturbance while providing ecosystem services. These include:

Mussels, oysters, and scallops – These filter-feeding bivalves play a crucial role in maintaining water clarity and quality by removing suspended particles, algae, and excess nutrients from the water column. Their farming does not require artificial feed, antibiotics, or chemical treatments, making them among the most sustainable forms of aquaculture.

Kelp and seaweed – Seaweed farms absorb carbon dioxide and excess nutrients such as nitrogen and phosphorus, which can otherwise lead to eutrophication and harmful algal blooms. This natural process helps to rebalance coastal ecosystems and contributes to the mitigation of ocean acidification. Additionally, seaweed cultivation does not require freshwater, fertilisers, or pesticides, reducing its environmental footprint. Whilst the carbon sequestration potential of farmed seaweeds is hotly debated, the potential is there and could be utilised depending on the the farms operators onward market.

These low-trophic species are integral to restorative aquaculture, a concept in which farming enhances rather than depletes marine ecosystems. Their ability to improve water quality, sequester carbon, and provide habitat makes them a key component of future-proof, sustainable seafood production. Whilst there are still concerns regarding the infrastructure requirements of these farms, including moorings, ropes and buoys, these have been demonstrated to provide de-facto MPA’ effect, where trawling and other activities cant be undertaken, creating a refugee for marine species.

So is Aquaculture Sustainable?

Well sustainable is a broad topic and depends upon your interest, broadly, the sector is reducing pressure on marine stocks, and continuously improving its operations to reduce environmental degradation. New research has been showing the potential for aquaculture systems to benefit local biodiversity, which will likely provide spill over effects to other the broader region. If there’s one thing shown, that aquaculture under the right management can be force for good and sustainability, its important for us to celebrate the potential and share the methods that can improve our impact and provide any net gain benefits wherever possible.