Farming of Marine Species (Cambridge International IGCSE Environmental Management)

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

Fish farming is one example of aquaculture (Photo by Lucut Razvan on Unsplash)

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

A shrimp hatchery attempts to provide a sustainable source of seafood (Image from the NOAA: [1], Public domain, via Wikimedia Commons)

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

Exam Hint Students often forget that marine aquaculture includes plants as well as animals. You are expected to know about fish, crustaceans and seaweed.

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

  • Decomposers break down the dead algae which uses up 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

Environmental impacts of open-water aquaculture

Exam Hint When describing negative impacts, avoid vague phrases like 'it harms the environment'. Instead, give a clear mechanism, such as 'nutrient enrichment leads to eutrophication'. Examiners look for this cause-and-effect link.

Don’t forget that aquaculture can have positive impacts too. Many students only list negatives, but mentioning benefits like reduced pressure on natural fisheries helps secure higher marks.