Marine Science (0697) | Aquaculture

Welcome to Section 6.4: Aquaculture!

Hello Marine Scientists! This chapter is all about Aquaculture, which is essentially *farming* marine organisms like fish, molluscs, and seaweed.
Why is this important? As the human population grows, we need more food. Since wild fisheries are struggling with overfishing, aquaculture provides a vital solution.
In this section, we will explore how this industry works, the species involved, and the key environmental challenges it faces. Let's dive in!

The Role and Importance of Aquaculture (Syllabus 6.4.1 & 6.4.2)

1. Social and Economic Importance

Aquaculture provides significant benefits to local communities and global economies:

• Food Security: It provides a reliable source of protein and essential nutrients, helping to feed a growing global population.
• Employment and Income: It creates jobs in farming, processing, and distribution, improving the financial situation of coastal communities.
• Trade: Farmed species are often sold internationally, bringing income to the local area and improving infrastructure.

2. Reducing Pressure on Wild Fisheries

One of the most critical reasons for aquaculture is its potential to reduce the pressure on over-harvested wild fish stocks.

• When farmed species (like salmon or shrimp) are readily available in the market, the demand for catching their wild counterparts decreases.
• This allows wild populations time to recover and prevents them from becoming endangered species.

3. The Environmental Trade-Off

Don't worry, aquaculture isn't a perfect solution! While it helps wild populations, farming large numbers of organisms in one place inevitably impacts the marine ecosystem:

• Pollution: Waste products (faeces and uneaten feed) can pollute the surrounding water and seabed.
• Disease Spread: High density of farmed organisms can easily spread parasites and disease to wild populations.
• Habitat Destruction: Setting up farms, especially shrimp farms, can involve clearing important habitats like mangrove forests.

Species Produced and Aquaculture Systems (Syllabus 6.4.3 & 6.4.4)

1. Range of Species Produced

Aquaculture involves cultivating many different types of marine organisms:

• Macroalgae (Seaweed): e.g., Kelp. Used for human food, animal feed, and industrial products.
• Fish: e.g., Salmon, Grouper. High-demand sources of protein.
• Crustaceans: e.g., Shrimp. Highly profitable, often farmed in tropical areas.
• Molluscs: e.g., Mussel, Oyster. Often grown on ropes or racks, as they filter feed, they can sometimes improve water quality.
• Echinoderms: e.g., Sea Cucumber. Often high-value luxury food items.

Did you know? Molluscs like oysters and mussels require no added feed; they filter plankton directly from the seawater. This makes their farming generally more environmentally friendly than fish farming.

2. Aquaculture Production Systems

Marine organisms are farmed in two main types of systems, differentiated by where they are located and how controlled the environment is:

A. Open Systems (Cages and Nets)

These systems are usually found in coastal waters, fjords, or bays.

• Description: Large floating pens (cages or nets) are anchored in the sea.
• Pros: Utilizes natural water flow for oxygen and waste dispersal; lower running costs.
• Cons: High risk of disease spread to wild fish; waste directly enters the ecosystem; vulnerable to storms and predators.
• Analogy: Imagine a large, underwater pen attached to the seabed.

B. Closed Systems (Tanks)

These systems are generally land-based or contained in large indoor facilities.

• Description: Fish are held in controlled tanks, often using Recirculating Aquaculture Systems (RAS) that recycle the water.
• Pros: Highly controlled environment (temperature, salinity, pH, oxygen); zero interaction with wild species; waste can be collected and treated.
• Cons: Very high initial and running costs (pumping and filtering water requires lots of energy); technical skills needed.
• Analogy: This is like a very sophisticated, giant fish aquarium.

Detailed Methods of Producing Fish (Syllabus 6.4.5)

Aquaculture requires careful management to ensure the organisms grow quickly and healthily. Don't worry if this list seems long; focus on understanding the *reason* for each step!

1. Sourcing Initial Stock (Broodstock)

The process starts by obtaining broodstock—the mature male and female organisms used for breeding.

• The goal is to select the fastest growing organisms with the best health to be the new broodstock. This is a form of selective breeding to improve the stock over generations.

2. Maintaining Optimal Conditions

The environment must be stable and perfect for the species being farmed. Conditions monitored include:

• Temperature and Salinity: Must match the natural habitat of the species.
• Light: Important for algae/kelp growth and regulating fish behavior.
• pH and Dissolved Oxygen (O₂): Levels must be high enough to support aerobic respiration.

3. Feeding and Nutrition

Food requirements vary greatly:

• Different species require different levels of protein and lipids for optimal growth.
• Types of Feed: Feed can be pelleted (like dry dog food for fish), fresh fish, or plant-based protein.
• Environmental Impact of Feed: Using wild-caught fish (often anchovies or sardines) to feed farmed carnivorous fish (like salmon) is unsustainable, as it uses up wild resources. Plant-based feeds are often preferred to reduce this impact.

4. Maintaining Water Quality and Waste Management

Managing waste is vital to prevent pollution and disease:

• Open Systems (Cages): Farmers may move cages periodically to allow the seabed beneath them to recover from accumulated waste. They rely on adequate water flow rate to wash waste away.
• Closed Systems (Tanks): Require extensive filtration of waste water before it is reused or released.

5. Preventing Cannibalism and Competition

When many organisms are packed together, fighting and eating each other (cannibalism) can occur.

• Size Sorting: Regular sorting ensures fish of similar size are kept together.
• Regular Feeding: Reduces hunger, decreasing aggressive behavior.

6. Disease and Predator Control

In high-density farms, disease spreads rapidly:

• Low Stocking Densities: Keeping fewer animals per volume of water reduces stress and disease transmission.
• Antibiotics: Used to treat bacterial diseases (though this practice is controversial due to potential environmental impacts).
• Cleaner Species: Using small fish like wrasse (known as cleaner fish) to eat parasites off the farmed fish.
• Predator Prevention: Strong nets and physical barriers are used to prevent seals, birds, or other predators from entering the cages.

Aquaculture and Conservation (Syllabus 6.4.6)

Using Aquaculture to Restock Ecosystems

Aquaculture techniques aren't just for food production; they can be used for conservation projects, specifically to help repopulate areas damaged by human activity or environmental factors.

The core principle here is restocking: farming young organisms in a controlled environment and then releasing them into a struggling natural habitat.

A. Restocking Mangrove Forests

Mangrove trees are vital coastal protection habitats, but they are often logged for building materials or cleared for shrimp farms.

• Conservation Aquaculture Use: Seedlings (young mangrove trees) can be grown in specialized nurseries and then replanted in damaged coastal zones to aid forest recovery.

B. Restocking Coral Reefs (Coral Farming)

Coral reefs face massive threats from bleaching and physical damage (e.g., from anchors, blast fishing).

• Conservation Aquaculture Use: Pieces of healthy coral (called fragments or "frags") are grown in underwater nurseries (coral farming). Once they have grown large enough, they are attached to artificial or damaged reefs to help speed up ecosystem restoration.

This approach is particularly valuable for endangered species, ensuring that rare or commercially important organisms can be protected and eventually released back into the wild population.