Integrated multi-trophic aquaculture
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).
[2] 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.
[9][10] 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.
[14] 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.
[15][17] The phytoplankton generally maintained reasonable water quality and converted on average over half the waste nitrogen into algal biomass.
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.
[30] Nutrient recovery efficiency is a function of technology, harvest schedule, management, spatial configuration, production, species selection, trophic level biomass ratios, natural food availability, particle size, digestibility, season, light, temperature, and water flow.
These results required precise water quality control and attention to suitability for bivalve nutrition, due to the difficulty in maintaining consistent phytoplankton populations.
Mussels and kelp growing adjacent to Atlantic salmon cages in the Bay of Fundy have been monitored since 2001 for contamination by medicines, heavy metals, arsenic, PCBs and pesticides.
This finding is of particular interest because the Bay of Fundy, where this research was conducted, produces low condition index mussels during winter months in monoculture situations, and seasonal presence of paralytic shellfish poisoning (PSP) typically restricts mussel harvest to the winter months.
[35] Historic and ongoing research projects include: Japan, China, South Korea, Thailand, Vietnam, Indonesia, Bangladesh, etc.
The project leaders are Thierry Chopin (University of New Brunswick in Saint John) and Shawn Robinson (Department of Fisheries and Oceans, St. Andrews Biological Station).
[8][34][36] Pacific SEA-lab is researching and is licensed for the co-culture of sablefish, scallops, oysters, blue mussels, urchins and kelp.
The project is headed by Stephen Cross under a British Columbia Innovation Award at the University of Victoria Coastal Aquaculture Research & Training (CART) network.
[37] The i-mar Research Center[38] at the Universidad de Los Lagos, in Puerto Montt is working to reduce the environmental impact of intensive salmon culture.
Its approach leveraged local climate and recycled fish waste products into seaweed biomass, which was fed to the abalone.
[41] The Scottish Association for Marine Science, in Oban is developing co-cultures of salmon, oysters, sea urchins, and brown and red seaweeds via several projects.
[42][43][44][45] Research focuses on biological and physical processes, as well as production economics and implications for coastal zone management.
The organic and inorganic wastes produced as a byproduct of culturing could also be minimized by integrating freshwater snail and aquatic plants, such as water spinach, respectively.
