aquaculture – The Pearl Protectors

Introduction to Mariculture

The Pearl Protectors — Fri, 28 Apr 2023 11:33:47 +0000

By Janya Edirisinghe

Mariculture, commonly known as marine farming, is a specialised subset of aquaculture, that is practiced in seawater habitats and lagoons as opposed to in freshwater aquaculture. Fish like sea bream, cod, halibut, and sea bass are examples of products cultivated through mariculture. It accounts for about 40% of the world’s aquaculture production. Countries such as China, Japan and Indonesia are some of the top mariculture-producing countries.

What are the types of Mariculture?

Mollusk Culture

Clams, oysters, scallops, and mussels are popular sea animals that can be farmed in regions with temperate climates. The process of mariculture involves initially collecting larvae from natural habitats or artificially fertilized larvae grown in hatcheries. Usually, parents are captured and taken to spawn their children in captivity.

Then, the larvae are taken to a different location to grow where hanging culture is practised, where they can grow suspended on strings, trays, stacks or mesh bags that hang from long lines floating in the water.

A few other methods of growing molluscs include vertical/rack culture, where they grow directly on sticks staked into the ground or on racks upheld by posts and bottom culture in which clams, for example, grow on shells, rocks or cement slabs on the sea floor. Also, molluscs such as abalone are grown in tanks.

Crustacean culture

Shrimp are mostly grown in tropical regions. Initially, the babies are grown in hatcheries, and they are then taken to grow in ponds, concrete raceways, and tanks. The shrimp ponds used to be located in rice fields and mangrove forests all around the world, but the subsequent destruction of mangrove areas has encouraged farmers to grow shrimp in inland ponds filled with transported seawater instead.

Marine Plant Culture

Most marine aquatic plants such as seaweed are grown in temperate regions. The plants used for breeding are originally sourced from their natural environment. Most farmed plants tend to be grown in hatcheries and once they reach a certain life stage, the plants are transferred to grow sites where the young plants are grown attached to suspended lines or floating rafts, in bottom cultures anchored to the sea floor and in inland tanks, similar to the way that molluscs are grown.

Finfish culture

Finfish are farmed in both temperate and tropical regions. Their defining feature is that they have fins and an example of a finfish includes salmon, which is also an example of a diadromous fish and these are the types of fish that migrate between the ocean and freshwater. Marine farming involves raising these diadromous fish.

Farmed finfish are first born in hatcheries and are then put into tanks and transferred to growth sites after the fertilised eggs hatch.

Finfish can be grown in pens, cages and large tanks. Pens are anchored to the sea floor in shallow waters. Cages can be located inshore or offshore. Inshore cages are usually in shallow waters with more protected areas that have less water circulation compared to offshore cages that are in deep water which has better water circulation and more exposure to storms.

The fish can also be grown in ponds that feature canals and dikes to help supply and drain water from pond compartments. Recirculating systems are used to control the water supplied to these ponds and factors such as temperature, as well as physical and chemical properties are taken into consideration.

Finfish are also subject to methods of growing called enhancement and ranching. At the inception, the fish are released at a young age to help restock free-living populations. Afterwards, the fish are captured in open waters that are artificially enclosed. Sea ranching is a method of mariculture that is also used to grow molluscs, crustaceans, marine plants and other marine organisms.

Over time, the raising of fish in cages close to the shore or in bays has caused severe ecological issues including contamination, disease, increased fish mortality, and severe damage to marine ecology, quality of the environment, and tourism.

To conclude, although world fish production from capture fisheries levelled off during the 1990s, demand for seafood continues to increase rapidly. This is because of the growth of the human population and the widespread view that seafood is healthy food. Scientists believe that the natural products from the ocean will not increase so to meet the rise in demand for seafood, both mariculture and fresh-water aquaculture will have to increase significantly. However, while several species are being reared successfully by marine culturists, various desirable species such as crabs and lobsters are very difficult to rear due to their life cycles being difficult to control under culture conditions or simply because they are way too complex.

Header Image: A fish farm off the coast of Greece. Photo by Artur Rydzewski

Impact of Climate Change on Fisheries and Aquaculture

The Pearl Protectors — Tue, 11 Oct 2022 10:58:59 +0000

By Nathasha Wickramasinghe

As we move towards the future, our world is changing both positively and negatively. In terms of positive changes, there are major technological advancements. On the other hand, our earth is facing rapid climatic changes resulting in global warming.

Climate change is a global phenomenon which is the long-term/prolonged changes in weather patterns around the world. Climate change is altering biological processes in marine and freshwater fish and their food webs thus having a big impact on fisheries and aquaculture. Aquaculture which is the farming of fish, shellfish, and aquatic plants, has been affected by climate change for over decades. Aquaculture is the fastest-growing food supply sector with an average growth rate of 6.7%. This sector is an integral part of providing basic nutrients for humans.

Image by Govindraj Javali

Rising Sea Temperature

Fish are poikilothermic, which means that their body temperature varies/fluctuates depending on the temperature of the environment. Therefore, temperature plays a vital role in the growth of aquatic animals.

Despite the Paris agreement that came into effect on 4th November 2016 which stated that the collective goal of all the 193 parties that signed the agreement should be to maintain a global temperature of 2c or more (preferably 1.5c), it has not happened yet. So, as the temperature of the water rises due to the accumulation of carbon dioxide, fish will no longer be able to breathe.

Rising sea temperatures also result in thermal stress. Thermal stress is stress that is caused by changes in temperature. Stress has a severe impact on the physiology of the fish which subsequently has a direct impact on their immune system. Corals lose their integral partner which is the marine algae that give the corals their colour and produce food for the coral due to thermal stress. This results in coral bleaching. The Great Barrier Reef, one of the 7 natural wonders of the World, is suffering from coral bleaching. This not only has a drastic impact on aquatic life but also on people who depend on tourism to live.

Changes in temperature also result in nutrient distribution alterations, thus convectional breeding/growing grounds have been altered. This makes it difficult for farmers to catch fish and many fish struggle to obtain the necessary nutrients to evolve and grow to their full capacity.

Rising Sea Levels

With the ongoing climatic crisis, the Intergovernmental Panel on climate change states that the sea level is expected to rise between 10 and 30 inches (i.e. 26 to 77 centimetres) with the temperature warming 1.5c by 2100. But this is expected to change as the magnitude and the rate of the rise depend on greenhouse gas emissions.

A sea level rise will change the composition of species and ecosystem productivity. This rise can also damage aquaculture facilities such as cages, tanks, and ponds, particularly those located in lowland regions.

Sea levels rising can also destroy coastal ecosystems such as mangroves, which are required to protect the coast from coastal erosion, and even salt marshes which are crucial for maintaining fish stock. Damage to these ecosystems could put local people under pressure to move their aquaculture farms elsewhere.

Italian Fish Farmers Association

Ocean Acidification

The ocean is very important to us, not just because it provides various habitats to an eclectic mix of exotic creatures but also because it is the biggest carbon sink to exist on earth. Oceans absorb 50 times more CO2 from the atmosphere than trees on the land. Seaweed (all types) is able to store CO2 for up to a whopping 800 years! Therefore, it is important to ensure the pH levels do not fall, which would result in ocean acidification.

Ocean acidification refers to a decline in pH levels in ocean water resulting from excessive CO2 uptake. A fall in pH level to a critical level will cause water to become too acidic for marine animals and plants to survive thus leading to death. The capacity of the ocean to store CO2 decreases as aquatic plants and other species such as phytoplankton (i.e. the biggest carbon sink) die, thereby exacerbating the state of global warming.

Moreover, a rise in ocean acidity results in a decrease in the availability of carbonate for corals (Carbonate is the building block of corals). Thus, growth declines resulting in the depletion of the natural habitat. This will place much of the aquatic way of life in danger.

Rising acidity can also have a negative impact on the physiology and metabolism of aquatic species but this depends on the adaptive capacity of the species.

Fisheries is a place where fish are grown for food/where they are caught for commercial purposes. The impact of climate change on fisheries can be segmented into two categories.

1. Direct effect

2. Indirect effect

Direct effects are seen in the physiology, reproduction, behavior, and development rates of the fish. Indirect effect act through changes in the ecosystem such as nutrient distribution and availability of species.

Fishery scientists use computer-based models to monitor water temperature/acidification levels. Based on recent data from the models, the carbon dioxide content has rapidly increased, resulting in many fish struggling to survive due to oxygen deprivation. Consequently, the fishery industry will also struggle to meet the demand for fish around the world (demand>supply), thereby resulting in food insecurity.

Image by Paul Einerhand

Poverty and Climate Change

Small-scale fisheries are extremely vulnerable to climate change. There are two factors affecting this:

1. Poverty

2. Location

Many small-scale fisheries are located on waterfronts and so they are exposed to natural hazards fueled by climate change such as coastal flooding, hurricanes, ocean acidification, and coastal erosion. And due to their low income, they are unable to build effective defense barriers to protect fish farms from disasters.

Therefore, many lose their source of income and cannot support their livelihoods. Livelihood strategies may have to be modified with changes in fish migration patterns. This could potentially impose social pressure and major occupational changes.