Integrated multi-trophic aquaculture (IMTA) is a type of aquaculture where the byproducts, including waste, from one aquatic species are used as inputs (fertilizers, food) for another. Farmers combine fed aquaculture (e.g., fish, shrimp) with inorganic extractive (e.g., seaweed) and organic extractive (e.g., shellfish) aquaculture to create balanced systems for environment remediation (biomitigation), economic stability (improved output, lower cost, product diversification and risk reduction) and social acceptability (better management practices).
Selecting appropriate species and sizing the various populations to provide necessary ecosystem functions allows the biological and chemical processes involved to achieve a stable balance, mutually benefiting the organisms and improving ecosystem health.
Ideally, the co-cultured species each yield valuable commercial "crops". IMTA can synergistically increase total output, even if some of the crops yield less than they would, short-term, in a monoculture.Neori A, Chopin T, Troell M, Buschmann AH, Kraemer GP, Halling C, Shpigel M and Yarish C. 2004. Integrated aquaculture: rationale, evolution and state of the art emphasizing seaweed biofiltration in modern mariculture. Aquaculture 231: 361-391.
IMTA is also highly beneficial for reducing the environmental footprint of aquaculture. The growth of farmed Atlantic salmon (Salmo salar), provides insight to the rapid growth of aquaculture demand. Output growth rates averaged 25.6% from 1980 to 2004, with the economic value of farmed salmon output exceeding 4 billion U.S. dollars in 2004. IMTA works by creating a closed-loop system where the by-products such as excess nutrients and organic waste from fish farming, are utilized by other species such as shellfish and seaweed. This process can decrease water pollution, minimize the need for chemical fertilizers, and improve overall ecosystem health. Furthermore, by integrating different trophic levels, IMTA can enhance biodiversity and promote more sustainable practices in marine food production.
Terminology and related approaches
"Integrated" refers to intensive and synergistic cultivation, using water-borne nutrient and energy transfer. "Multi-trophic" means that the various species occupy different trophic levels, i.e., different (but adjacent) links in the food chain.Chopin T. 2006. Integrated multi-trophic aquaculture. What it is, and why you should care... and don't confuse it with polyculture. Northern Aquaculture, Vol. 12, No. 4, July/August 2006, pg. 4.
IMTA is a specialized form of the age-old practice of aquatic polyculture, which was the co-culture of various species, often without regard to trophic level. In this broader case, the organisms may share biological and chemical processes that may be minimally complementary, potentially leading to reduced production of both species due to competition for the same food resource. However, some traditional systems such as polyculture of carps in China employ species that occupy multiple niches within the same pond, or the culture of fish that is integrated with a terrestrial agricultural species, can be considered forms of IMTA.Ruddle, K. and V. Christensen. 1993. An energy flow model of the mulberry dike-carp pond farming system of the Zhujiang Delta, Guangdong Province, China. pp. 48-55. In: V. Christensen ans D. Pauley, (eds.) Trophic Models of Aquatic Ecosystems ICLARM Conference Proceedings 26, 390pp.
The more general term "Integrated Aquaculture" is used to describe the integration of monocultures through water transfer between the culture systems. The terms "IMTA" and "integrated aquaculture" differ primarily in their precision and are sometimes interchanged. Aquaponics, fractionated aquaculture, integrated agriculture-aquaculture systems, integrated peri-urban-aquaculture systems, and integrated fisheries-aquaculture systems are all variations of the IMTA concept.
Range of approaches Today, low-intensity traditional/incidental multi-trophic aquaculture is much more common than modern IMTA. Most are relatively simple, such as fish, seaweed or shellfish.
True IMTA can be land-based, using ponds or tanks, or even open-water marine or freshwater systems. Implementations have included species combinations such as shellfish/shrimp, fish/seaweed/shellfish, fish/seaweed, fish/shrimp and seaweed/shrimp.Troell M, Halling C, Neori A, Chopin T, Buschmann AH, Kautsky N and Yarish C. 2003. Integrated mariculture: asking the right questions. Aquaculture 226: 69-90.
IMTA in open water (offshore cultivation) can be done by the use of buoys with lines on which the seaweed grows. The buoys/lines are placed next to the fishnets or cages in which the fish grows. In some tropical Asian countries some traditional forms of aquaculture of finfish in floating cages, nearby fish and shrimp ponds, and oyster farming integrated with some capture fisheries in estuaries can be considered a form of IMTA.Rice, M.A. and A.Z. DeVera (1998). Aquaculture in Dagupan City. World Aquaculture 29(1):18-24. Since 2010, IMTA has been used commercially in Norway, Scotland, and Ireland.
In the future, systems with other components for additional functions, or similar functions but different size brackets of particles, are likely. Multiple regulatory issues remain open.Chopin T, Robinson S, Sawhney M, Bastarache S, Belyea E, Shea R, Armstrong W, Stewart and Fitzgerald P. 2004. The AquaNet integrated multi-trophic aquaculture project: rationale of the project and development of kelp cultivation as the inorganic extractive component of the system. Bulletin of the Aquaculture Association of Canada. 104(3): 11-18.
Modern history of land-based systems Ryther and co-workers created modern, integrated, intensive, land mariculture.Goldman JC, Tenore RK, Ryther HJ and Corwin N. 1974. Inorganic nitrogen removal in a combined tertiary treatment - marine aquaculture system: I. Removal efficiencies. Water Research 8: 45-54.Ryther JH, Goldman JC, Gifford JE, Huguenin JE, Wing AS, Clarner JP, Williams LD andLapointe BE. 1975. Physical models of integrated waste recycling - marine polyculture systems. Aquaculture 5: 163-177. They originated, both theoretically and experimentally, the integrated use of extractive organisms—shellfish, microalgae and seaweeds—in the treatment of household effluents, descriptively and with quantitative results. A domestic wastewater effluent, mixed with seawater, was the nutrient source for phytoplankton, which in turn became food for oysters and clams. They cultivated other organisms in a food chain rooted in the farm's organic sludge. Dissolved nutrients in the final effluent were filtered by seaweed (mainly Gracilaria and Ulva) biofilters. The value of the original organisms grown on human waste effluents was minimal.
In 1976, Huguenin proposed adaptations to the treatment of intensive aquaculture effluents in both inland and coastal areas.Huguenin JH. 1976. An examination of problems and potentials for future large-scale intensive seaweed culture systems. Aquaculture 9: 313-342. Tenore followed by integrating with their system of carnivorous fish and the macroalgivore abalone.Tenore KR. 1976. Food chain dynamics of abalone in a polyculture system. Aquaculture 8: 23–27.
In 1977, Hughes-GamesHughes-Games WL. 1977. Growing the Japanese oyster (Crassostrea gigas) in sub-tropical seawater fishponds: I. Growth rate, survival and quality index. Aquaculture 11: 217-229. described the first practical marine fish/shellfish/phytoplankton culture, followed by Gordin, et al., in 1981.Gordin H, Motzkin F, Hughes-Games A and Porter C. 1981. Seawater mariculture pond - an integrated system. European Aquaculture Society Special Publication 6: 1-13. By 1989, a semi-intensive (1 kg fish/m−3) seabream and grey mullet pond system by the Gulf of Aqaba (Eilat) on the Red Sea supported dense diatom populations, excellent for feeding oysters.Neori A, Krom MD, Cohen Y and Gordin H. 1989. Water quality conditions and particulate chlorophyll a of new intensive seawater fishpond in Eilat, Israel: daily and dial variations. Aquaculture 80: 63-78.Erez J, Krom MD and Neuwirth T. 1990. Daily oxygen variations in marine fish ponds, Eilat, Israel. Aquaculture 84: 289-305. Hundreds of kilos of fish and oysters cultured here were sold. Researchers also quantified the water quality parameters and nutrient budgets in (5 kg fish m−3) green water seabream ponds.Krom MD and Neori A. 1989. A total nutrient budget for an experimental intensive fishpond with circularly moving seawater. Aquaculture 88: 345-358. The phytoplankton generally maintained reasonable water quality and converted on average over half the waste nitrogen into algal biomass. Experiments with intensive bivalve cultures yielded high bivalve growth rates.Shpigel M and Fridman R. 1990. Propagation of the Manila clam Tapes semidecussatus in the effluent of marine aquaculture ponds in Eilat, Israel. Aquaculture 90: 113-122.Shpigel M and BlaylockRA. 1991. The Pacific oyster, Crassostrea gigas, as a biological filter for a marine fish aquaculture pond. Aquaculture 92: 187-197.Shpigel M, Neori A, Popper DM and Gordin H. 1993a. A proposed model for environmentally clean landbased culture of fish, bivalves and seaweeds. Aquaculture 117: 115-128.Shpigel M, Lee J, Soohoo B, Fridman R and Gordin H. 1993b. The use of effluent water from fish ponds as a food source for the pacific oyster Crassostrea gigas Tunberg. Aquaculture & Fisheries Management 24: 529-543.Neori A and Shpigel M. 1999. Algae treat effluents and feed invertebrates in sustainable integrated mariculture. World Aquaculture 30: 46-49, 51.Neori A, Shpigel M and Scharfstein B. 2001. Land-based low-pollution integrated mariculture of fish, seaweed and herbivores: principles of development, design, operation and economics. European Aquaculture Society Special Publication 29: 190-191. This technology supported a small farm in southern Israel.
Sustainability IMTA promotes economic and environmental sustainability by converting byproducts and uneaten feed from fed organisms into harvestable crops, thereby reducing eutrophication, and increasing economic diversification.Tournay B. 2006. IMTA: template for production? Fish Farming International, Vol. 33, No. 5, May 2006, pg. 27.
Properly managed multi-trophic aquaculture accelerates growth without detrimental side-effects.Johnson E. 2004. Cleaning up the sea cages. In: Family Jewels. Saltscapes, Vol. 5, No. 3, May/June 2004, 44-48.Lander T, Barrington K, Robinson S, MacDonald B and Martin J. 2004. Dynamics of the blue mussel as an extractive organism in an integrated multi-trophic aquaculture system. Bulletin of the Aquaculture Association of Canada. 104(3): 19-28.Ridler N, Robinson B, Chopin T, Robinson S and Page F. 2006. Development of integrated multi-trophic aquaculture in the Bay of Fundy, Canada: a socio-economic case study. World Aquaculture 37(3): 43-48. This increases the site's ability to assimilate the cultivated organisms, thereby reducing negative environmental impacts.
IMTA enables farmers to diversify their output by replacing purchased inputs with byproducts from lower trophic levels, often without new sites. Initial economic research suggests that IMTA can increase profits and can reduce financial risks due to weather, disease and market fluctuations.Ridler N, Wowchuk M, Robinson B, Barrington K, Chopin T, Robinson S, Page F, Reid G and Haya K. 2007. Integrated multi-trophic aquaculture (IMTA): a potential strategic choice for farmers. Aquaculture Economics & Management 11: 99-110. Over a dozen studies have investigated the economics of IMTA systems since 1985.