Marine aquaculture is the controlled cultivation of aquatic animals and plants in saltwater environments. This practice, also called mariculture, can occur in the ocean or in man-made systems on land, such as tanks and ponds filled with seawater. It involves intervention in the rearing process like stocking, feeding, and protection from predators to enhance production. This form of farming is distinct from freshwater aquaculture, which deals with organisms in non-saline water.
Farmed Marine Species
Finfish represent a significant portion of marine aquaculture production. Species like salmon are farmed extensively in coastal net pens in countries such as Norway, Chile, and Scotland. In the Mediterranean, European sea bass and gilthead seabream are primary species. Other commercially farmed finfish include cobia and Atlantic bluefin tuna, which are ranched in cages.
Crustaceans, particularly marine shrimp, are another major component of the industry, often utilizing pond systems. Mollusks are also widely cultivated, and their farming is considered self-supporting as it does not require feed inputs. Oysters, clams, and mussels are leading examples, with methods like bag, cage, or rope cultivation being common in nearshore bays and estuaries.
Aquatic plants, specifically macroalgae like seaweed and kelp, constitute a rapidly growing sector. These plants are cultivated for various uses, including food, pharmaceuticals, and biofuels.
Cultivation Systems and Methods
Open-ocean net pens are one of the most common methods, particularly for finfish like salmon. These systems consist of submerged cages moored in offshore areas, relying on natural currents to circulate water and disperse waste. Their exposure to open-ocean conditions requires robust engineering to withstand storms and strong currents.
Near-shore cages and pens are situated in more protected coastal areas like bays and estuaries. This method is used for both finfish and some shellfish. The calmer waters provide a more controlled environment compared to offshore systems.
Land-based recirculating aquaculture systems (RAS) represent a technological shift, moving marine farming from the ocean to indoor tanks. These systems continuously filter and recycle water, allowing for precise control over water quality and temperature. RAS can be located almost anywhere and significantly reduce water usage and the risk of fish escapes.
Integrated multi-trophic aquaculture (IMTA) is an approach that mimics natural ecosystems by cultivating multiple species from different trophic levels together. The waste products from a fed species, like finfish, are used as a food source for extractive species, such as shellfish and seaweed. For instance, mussels can filter organic particles, while seaweed absorbs dissolved inorganic nutrients. This method reduces waste and creates additional marketable products, improving the farm’s sustainability and economic viability.
Role in Global Food Supply
Marine aquaculture plays an expanding part in global food security, bridging the gap between the rising demand for seafood and the stagnant output of wild-capture fisheries. For decades, the global harvest from wild fisheries has remained relatively flat. Aquaculture now supplies more than half of all seafood consumed by humans worldwide, a figure that is expected to continue rising.
In 2022, aquaculture surpassed wild-capture fisheries as the main producer of aquatic animals for the first time. Global aquaculture production reached 130.9 million tonnes, with 94.4 million tonnes being aquatic animals. This increase is largely attributed to technological advancements and improved farming efficiencies.
This production provides a consistent source of high-quality protein, essential fatty acids, and micronutrients. As the global population is projected to exceed nine billion by 2050, the demand for protein will continue to climb. Marine aquaculture is positioned to be a contributor to meeting this future demand.
Environmental Considerations
A primary concern is the management of waste from farms, such as uneaten feed and metabolic byproducts. In open-water systems, these nutrients can be released into the surrounding water. This can lead to localized pollution and eutrophication if not managed through careful site selection and stocking densities.
Another issue is the potential for disease and parasite transfer between farmed and wild populations, as fish are raised at high densities. To address this, the industry has developed vaccines and improved animal husbandry practices, which have reduced the need for antibiotics in many sectors. The escape of farmed fish, which can compete with or interbreed with wild stocks, is a risk being mitigated through stronger containment technologies.
Conversely, some forms of marine aquaculture offer direct environmental benefits. The cultivation of shellfish like oysters and mussels improves water quality as these organisms filter nutrients from the water column. Seaweed farming absorbs excess nitrogen and phosphorus, helping to counteract nutrient pollution. Innovations in feed composition are also reducing the industry’s reliance on wild-caught fish for fishmeal and fish oil, with plant-based proteins and algae emerging as alternatives.