Mariculture

Mariculture, sometimes called marine farming or marine aquaculture, is a branch of aquaculture involving the cultivation of marine organisms for food and other animal products, in seawater. Subsets of it include (offshore mariculture), fish farms built on littoral waters (inshore mariculture), or in artificial tanks, ponds or raceways which are filled with seawater (onshore mariculture). An example of the latter is the farming of plankton and seaweed, shellfish like shrimp or oysters, and marine finfish, in saltwater ponds. Non-food products produced by mariculture include fish meal, nutrient agar, jewellery (e.g. cultured pearls), and cosmetics.

Types

Onshore

Although it sounds like a paradox, mariculture is practiced onshore variously in tanks, ponds or raceways which are supplied with seawater. The distinguishing traits of onshore mariculture are the use of seawater rather than fresh, and that food and nutrients are provided by the water column, not added artificially, a great savings in cost and preservation of the species' natural diet. Examples of onshore mariculture include the farming of algae (including plankton and seaweed), marine finfish, and shellfish (like shrimp and oysters), in manmade saltwater ponds.

Inshore

Inshore mariculture is farming marine species such as algae, fish, and shellfish in waters affected by the tide, which include both littoral waters and their estuarine environments, such as bays, brackish rivers, and naturally fed and flushing saltwater ponds. Popular cultivation techniques for inshore mariculture include creating or utilizing artificial reefs, pens, nets, and long-line arrays of floating cages moored to the bottom. As a result of simultaneous global development and evolution over time, the term "ranch" being associated typically with inshore mariculture techniques has proved problematical. It is applied without any standardized basis to everything from marine species being raised in floating pens, nested within artificial reefs, tended in cages (by the hundreds and even thousands) in long-lined groups, and even operant conditioning migratory species to return to the waters where they were born for harvesting (also known as "enhanced stocking").

Open ocean Raising marine organisms under controlled offshore in "open ocean" in exposed, high-energy marine environments beyond significant coastal influence, is a relatively new approach to mariculture. Open ocean aquaculture (OOA) uses cages, nets, or long-line arrays that are moored or towed. Open ocean mariculture has the potential to be combined with offshore energy installation systems, such as wind-farms, to enable a more effective use of ocean space. Research and commercial open ocean aquaculture facilities are in operation or under development in Panama, Australia, Chile, China, France, Ireland, Italy, Japan, Mexico, and Norway. As of 2004, two commercial open ocean facilities were operating in U.S. waters, raising threadfin near Hawaii and cobia near Puerto Rico. An operation targeting bigeye tuna recently received final approval. All U.S. commercial facilities are currently sited in waters under state or territorial jurisdiction. The largest deep water open ocean farm in the world is raising cobia 12 km off the northern coast of Panama in highly exposed sites.

Species

Algae

Algaculture involves the farming of species of algae, including microalgae (such as phytoplankton) and macroalgae (such as seaweed). Uses of commercial and industrial algae cultivation include production of nutraceuticals such as omega-3 fatty acids (as algal oil) or natural food colorants and dyes, food, fertilizers, bioplastics, chemical feedstock (raw material), protein-rich animal/aquaculture feed, pharmaceuticals, and algal fuel, and can also be used as a means of pollution control and natural carbon sequestration. Mariculture of seaweeds can be conducted in the open ocean to regenerate decimated fish populations by providing both habitat and the basis of a trophic pyramid for marine life. Natural seaweed ecosystems can possibly be replicated in the open ocean by creating growth conditions. Von Hertzen, Gamble, and others propose that this practice could be considered to be permaculture and thereby constitute marine permaculture. The concept envisions using artificial upwelling and floating, submerged platforms as substrate to replicate natural seaweed ecosystems. Following the principles of permaculture, seaweeds and fish from marine permaculture arrays can be sustainably harvested with the potential of sequestering atmospheric carbon, should seaweeds sink below a depth of one kilometer. As of 2020, successful trials had taken place in Hawaii, the Philippines, Puerto Rico and Tasmania. The idea received substantial public attention, notably featuring as a key solution covered by Damon Gameau's documentary 2040 and in the book Drawdown: The Most Comprehensive Plan Ever Proposed to Reverse Global Warming.

Shellfish Similarly to algae cultivation, shellfish can be farmed in multiple ways in both onshore and inshore mariculture: on ropes, in bags or cages, or directly on (or within) the bottom. Shellfish mariculture does not require feed or fertilizer inputs, nor insecticides or antibiotics, making shellfish mariculture a self-supporting system. Seed for shellfish cultivation is typically produced in commercial hatcheries, or by the farmers themselves. Among the shellfish types raised by mariculture are shrimp, oysters (including artificial pearl cultivation), clams, mussels, and abalone. Shellfish can also be used in integrated multi-species cultivation techniques, where shellfish can utilize waste generated by higher trophic-level organisms. The Māori people of New Zealand retain traditions of farming shellfish.

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