MULTI TROPHIC AQUACULTURE UK
Integrated Multi-Trophic Aquaculture is a form of polyculture which mimics the nutrient flows in natural systems to produce multiple outputs from a food production system.
In conventional fin fish farming, around 60% of the nitrogen in the fish feed is lost to the wider ecosystem and can have negative ecological impacts if presented in high concentrations.
Growing seaweed, shellfish and other marine life are grown in close proximity to the farmed fin fish in order to maximise uptake of the nutrients.
The shellfish benefit from the organic particulates and the seaweed from the soluble nutrients including nitrogen. Polyculture, the process of growing multiple crops in the same space, can also provide a more resilient production system; both in a commercial sense from having a wider product range to sell and in an ecological sense from being based on a managed ecosystem.
Here at Green Ocean Farming, we are looking at setting up multi trophic aquaculture sites so that each of the crops or harvests benefit from the others around them.
Our aim is to farm a small number of fin fish other than Salmon or Trout, which will be farmed in unison with shellfish such as Scallops, Oysters or Clams grown alongside seaweed and also bottom feeder such as sea cucumbers and possibly sea urchins.
Investing in Green Ocean IMTA will start at £45,000 more information will be available in the near future.
The economic and environmental benefits of nutrient recycling can be used as the basis for a more resilient fin fish farming industry and for the wider renewable marine aquaculture sector.
Other IMTA Benefits - The Nutrient Pollution Problem
The main pollutant in many coastal bodies is nutrient over enrichment. Nutrient pollution causes an increase in phytoplankton in a water body. The increased nutrients stimulate plant growth, reducing the sunlight reaching the lower depths of the water body. The inability for phytoplankton to photosynthesize at lower depths causes the phytoplankton to die, creating eutrophic conditions. The decrease in plant life reduces the amount of dissolved oxygen in the water body.
The remains of the plant life sink to the bottom, where they are consumed by bacteria, further decreasing the dissolved oxygen levels, creating hypoxic conditions.
Shellfish as a Solution for Nutrient Removal Nutrient pollution can be addressed through the reduction in nitrogen emissions. Nitrogen reduction in coastal areas can be addressed in two ways:
Top down approach that reduces the nitrogen in the water body through the use of shellfish aquaculture as well as enhancing tidal exchange.
Bottom up approach focuses on reducing emissions from point sources, including wastewater treatment plants as well as reducing nitrogen inputs from population and run-offs from fertiliser used in agriculture. Bivalve shellfish - oysters, clams and mussels - feed on algae and other microscopic food found in coastal bays and estuaries. The food eaten by shellfish contains nutrients that are available in the food, including nitrogen, phosphorus and carbon. When bivalves feed on these particles, they use these nutrients to grow, filtering and cleaning coastal waters, benefitting underwater plants and other marine life. The bivalve tissue and shells contain nitrogen from the filtering of nutrients for growth.
When bivalves are harvested, this nitrogen is removed from the water column. Bivalves also tend to enrich the sediments around them through bio deposits. This organic waste and material is filtered out of the water but not digested. Denitrifying bacteria in the sediments use the nitrogen that is released from the bio deposits for their energy, converting some of it into nitrogen gas that escapes from the water body.
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