Growing together
Integrated aquaculture is catching on in world-wide markets, reports Julia Hollister.
Integrated multi-trophic aquaculture, or IMTA, is similar to polyculture, where two or more crops are farmed in an integrated fashion to improve efficiency, reduce waste and provide ecosystem services, such as bioremediation.
“All the research has one main goal: to feed the world,” says Michael D Chambers, PhD Research Associate Professor at the University of New Hampshire, Aquaculture Specialist, School of Marine Science and Ocean Engineering and Center for Sustainable Seafood Systems.
The Center is rethinking how seafood is produced not only in the US but the world.
The US has seafood trade deficit of approximately $16 billion (£12.6bn), with products shipped over the oceans contributing to industry’s carbon footprint. Sustainable seafood produced locally reduces this climate impact and provides jobs that enhance communities.
“For instance, innovative seafood systems can balance combinations of finfish with extractive species (shellfish, sea vegetables) and echinoderms (sea urchins and sea cucumbers) on land or at sea with positive environmental impact. Products are not only for human consumption, but also animal feed, organic fertiliser, and fuel,” Chambers says.
Multi-trophic sea farming can better utilise the three-dimensional space at a farm. It utilises the bottom, mid-column and surface areas of a site. The lower trophic species such as shellfish and seaweed provide ecosystem services through nutrient extraction from the fish in culture and from the environment.
Hog Island Oyster Co, San Francisco
As Chambers explains: “This reduces nitrogen input and provides additional income to the farmer by growing and selling multiple species from a farm. I have been advancing open ocean farming technologies for over 30 years in the US and abroad. In the US, we have managed submerged cage culture projects in the Gulf of Mexico, Hawaii and the North Atlantic.”
More recently, he has been developing and training fishermen on small scale, integrated multi-trophic aquaculture of steelhead trout, blue mussels, and sugar kelp on floating platforms.
Additional efforts at the University of New Hampshire includes development of novel submerged mussel, seaweed and sea scallop techniques that can minimise potential entanglement of marine creatures.
Species at the lower trophic level (usually plants or invertebrates) use waste products such as faeces and uneaten feed from the higher trophic species (typically finfish), as nutrients. The lower trophic species can then be harvested to give the farmer more revenue, or even to be fed back to the fish.
Combined mussel and seaweed farm, graphic
The whole Hog
The owners of Hog Island Oyster Co, north of San Francisco, which grows oysters in the bay and runs several Bay Area restaurants, have long wanted to harvest the seaweed to put into the nori butter and hand-harvested sea salt used to flavour the restaurants’ dishes.
Now, after years of planning, the edible sea lettuce and rusty-brown nori seaweed that grow there are finally being collected for culinary use.
Earlier this year the company completed its first major harvest of 500 pounds of wet seaweed, mostly nori. The nori will be dried, which shrinks it to one-tenth of its original weight.
“There are many different types of integrated aquaculture systems being utilised or researched in the United States,” says Fritz Jaenike, Executive Director of the Texas Aquaculture Association.
In many types of integrated aquaculture systems, there are bivalves such as oysters being utilised and macroalgae species such as kelp. No companies are actively utilising integrated aquaculture systems in Texas, however.
Jaenike says: “Although there are several oyster farms operating in Texas, to my knowledge, none of them are utilising integrated aquaculture systems with algae which is harvested as part of the aquaculture system. Currently several integrated aquaculture systems utilise kelp as a harvested macroalgae which is harvested as a by-product of the system. Kelp is a cold water species that we cannot grow in Texas waters.”
There is also a new integrated system being operated in Maine which is using fish and polychaete worms as a multi-trophic integrated aquaculture system.
IMTA has been the focus of worldwide research because it is seen as a way to make aquaculture more sustainable – and profitable – on land or at sea. An often-heard criticism of finfish net pen aquaculture is that wastes, and uneaten feed pollute the bottom under the pens and release nutrients such as nitrogen into the water, which in turn can fertilise algae blooms.
In IMTA, other organisms that can use these wastes as nutrients are grown by the fish farmer in proximity to the net pens. In a recent trial carried out in Canada by Cooke Aquaculture, kelp was grown nearby salmon net pens to utilise the nitrogenous wastes excreted by the fish.
The CCAR (Center for Cooperative Aquaculture Research) has worked on IMTA research since 2009, with cages in Mexico and a location near Guam.
In the first study, scientists captured wastes from a halibut tank system and fed them to marine worm beds in a series of raceways. The worms thrived on the waste feed and faeces, and required only a minimal input of additional feed. Encouraged by these findings, and with the help of funding from the Maine Aquaculture Innovation Center, workers were able to colonise the sediments under the pens with worms.
Combined mussel and seaweed farm at sea
Small scale farming systems for coastal communities offer the following:
√ Aquaculture technology that is scaled appropriately for fishermen and family farmers.
√ An affordable, user friendly platform.
√ Can locate farm near or between fishing grounds.
√ Helps fishermen diversify their trade and income on the working waterfronts.
√ Provides a new source of fresh, sustainable seafood to local markets.
√ Utilises species with high market demand.
√ Reduces nitrification from fish through integrated multi-trophic aquaculture.
