The interest in sustainable aquaculture in Ireland is on the rise. The Irish seafood industry is exploring many possible ways to develop finfish, shellfish and seaweed aquaculture as a productive, environmentally sound and cost-effective way to sate Europe’s longstanding appetite for seafood.
One avenue under exploration is what’s known as integrated multi-trophic aquaculture (IMTA). In this type of set up, multiple species that live in different parts of the water column (called trophic levels) are farmed together, as a potential way to reduce pollution caused by salmon farming.
Scientists want to see if by farming many species together, they can improve efficiency, reduce waste, and provide ecosystem services like bio-remediation, which is when one species naturally cleans up the biological mess created by another species.
In an IMTA system, plants, shellfish and invertebrates that grow on sunken long lines and suspended baskets consume food waste and feces from finfish (usually salmon) pens that sit just below the water’s surface. The fish farmers can then harvest and sell the salmon, and also the plants, shellfish and invertebrates.
The research site is one of several in Europe and South America that contribute to an aquaculture data collection and implementation effort called the Astral Project. Operated by scientists at the Irish Marine Institute, Lehanagh Pool sits a quarter mile from the rocky shore in Bertraghboy Bay. This protected area of the Irish coast has an aquacultural history that dates back to the 1950s and includes commercially farmed salmon and experimental farmed cod.
The extractive species at Lehanagh Pool, which filter out particulate waste from the water as food, are large great (or king) scallops, smaller variegated scallops, and native Ostrea edulis oysters. Minerals and carbon already dissolved into the water are extracted by several types of seaweed. If this were a commercial operation, all these species could be sold to consumers.
At the same time, benthic scavengers (or bottom feeders), in this case, sea cucumbers, remove particulates from the upper surface of the seafloor, such as uneaten food and waste from finfish. Again, were this a commercial IMTA, the sea cucumbers could be exported and sold to the Chinese market.
Many environmentalists oppose salmon farms because the fish can escape from their pens and breed with wild populations. That concern is outside the scope of testing at this project, Astral Project lead scientist Elisa Ravagnan said.
For now, the Lehanagh Pool IMTA is still in the research phase. O’Donahoe and her team have so far spent three years collecting data about the growth of each species and the project’s environmental impacts. When enough data has been collected and analyzed, the scientists would next need to test whether the system can be implemented commercially, O’Donahoe said.