Farming of Marine Species (Cambridge (CIE) IGCSE Environmental Management): Revision Note

What is marine aquaculture?

• Marine aquaculture is the farming of marine species in captivity

• Organisms are raised in controlled conditions rather than being caught in the wild

• Marine aquaculture is used to:

  • increase food supply

  • reduce pressure on wild fish stocks

  • support coastal economies

Fish

• Many marine farms raise fish in cages or tanks in the sea

• Fish are fed and monitored to help them grow quickly and safely

• Farming fish reduces the need to catch wild populations

• This helps protect natural fish stocks from overfishing

Crustaceans

• Crustaceans such as prawns, shrimp or crabs can be farmed in ponds or coastal enclosures

• Farmers manage water quality, feeding and breeding

• Farming crustaceans provides a reliable supply for the seafood market

• This helps meet demand without relying only on wild harvesting

Seaweeds

• Seaweeds can be grown on ropes or frames placed in the sea

• They absorb nutrients from the water and grow without needing feed

• Seaweed farming is low-impact and supports food, fertiliser and cosmetic industries

• Seaweeds also remove excess nutrients from coastal waters

Impacts of marine aquaculture

• Marine aquaculture increases food production but also creates environmental and ecological impacts

  • Some impacts are beneficial, while others can affect wild ecosystems if farming is not well managed

Reduced exploitation of natural fisheries

• Farmed fish provide an alternative source of seafood

• This reduces pressure on wild fish stocks

• Lower fishing pressure helps wild populations to recover

• Sustainable aquaculture can protect oceans from overfishing

Increased food supply for humans

• Marine aquaculture produces large quantities of fish, crustaceans and seaweed

• This helps meet the growing global demand for protein

• Farming provides a steady and predictable supply

  • This helps to make seafood more affordable and widely available

Risk of escape

• Farmed species may escape from cages or tanks

• Escaped fish can compete with wild fish for food and habitat

• Some escaped species may interbreed with wild populations

• This can reduce genetic diversity and weaken wild fish resilience (e.g. make them more vulnerable to diseases)

• Non-native species may become invasive

  • They can disrupt local ecosystems

Risk of disease

• Fish are often kept at high densities

• This makes it easier for diseases and parasites to spread

• Diseases from farms can reach wild fish if water flows between enclosures and the open seas

  • This can harm wild populations or reduce reproduction

• Farmers may use antibiotics or chemicals to control disease

  • Overuse can lead to pollution of surrounding waters or antibiotic resistance in the farmed fish

Local food webs

• Aquaculture can alter predator–prey relationships in coastal areas

  • For example, escaped fish may become new predators or new prey

• Wildlife may be attracted to fish cages, looking for food

  • This can increase human-animal conflict with predators such as birds or seals

Nutrient enrichment from waste

• Uneaten feed and fish waste fall into the water beneath farms

• This increases levels of nitrates and phosphates

• This can lead to eutrophication, causing rapid algae growth

  • Algal blooms reduce oxygen, harming wild fish and marine life

• Sediment build-up beneath cages can smother seabed habitats

  • This reduces the biodiversity of seabed communities

Energy usage

• Aquaculture systems require electricity for pumps, aeration, feeding systems and transport

• Energy use increases carbon emissions if electricity is from fossil fuels

• Offshore farms may require boats and machinery

  • This adds to the overall environmental impact of fish farms

Source of food for farmed species

• Many farmed species (e.g. carnivorous fish) require feed made from wild-caught fish

  • This can increase fishing pressure on smaller forage fish

  • Producing this feed is energy-intensive and resource-heavy

  • This can counteract some of the environmental benefits of aquaculture

• Researchers are developing plant-based or alternative feeds

  • These could lower the need for wild fish in aquaculture diets