Caulerpa racemosa, commonly known as "sea grapes", was one of the four macroalgae species studied by the University of Miami researchers.
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Researchers at the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science have reported that growing seaweed alongside marine finfish can reduce key waste products from aquaculture operations, including total ammonia nitrogen, which the study found could be brought below detectable levels in some conditions.
The work examined the use of macroalgae in integrated multi-trophic aquaculture (IMTA) systems, where species from different levels of the food chain are farmed together, with the waste from one species used by another. The researchers said the approach could reduce environmental impacts from marine finfish farming while producing a secondary crop.
The study was carried out at the Rosenstiel School’s Experimental Hatchery facility on Virginia Key, Florida, and published in the journal Aquaculture International. The researchers used nutrient-rich effluent from a yellowtail snapper (Ocyurus chrysurus) grow-out tank maintained at commercial-scale density and feeding rates, while four macroalgae species from the Southeast US and Caribbean were grown in replicate tanks under the same conditions, allowing comparisons of growth, nutrient removal, nutritional profile and market potential.
“With the significant interest in the development of marine aquaculture throughout the Southeast U.S. and Caribbean, these findings can be used to guide the selection of extractive macroalgae species in operations culturing marine finfish,” said lead author Haley Lasco, a marine biology graduate student at the Rosenstiel School who is now a scientist at the South Carolina Department of Natural Resources, via a press release.
At the end of each two-week trial, the team assessed the seaweeds - two red seaweed species Agardhiella subulata and Gracilaria caudata, Caulerpa racemosa, commonly known as "sea grapes", and Ulva lactuca, or "sea lettuce," - for growth, and analysed their protein, fat, fibre, ash, minerals, metals, carbon and nitrogen content, including stable isotope ratios.
The team found that Agardhiella subulata lowered total ammonia nitrogen levels below detectable limits, while Caulerpa racemosa had the highest protein content of the microalgae species tested, and Ulva lactuca registered the highest carbohydrate content, in addition to showing the most efficient carbon take-up and incorporation.
“This work shows how integrating macroalgae into marine finfish aquaculture systems can reduce waste while producing a valuable secondary crop. It provides a practical framework for selecting species based on specific production goals, improving environmental performance while creating opportunities for better production economics and more diversified products using an IMTA approach,” said John D. Stieglitz, research associate professor in the Department of Marine Biology and Ecology and principal investigator on the project.
The researchers said the findings are particularly relevant to regions where marine aquaculture of fed species such as finfish is being developed, and where waste management remains a concern for regulators, producers and coastal communities.
“Our findings support more sustainable aquaculture operations and help producers make smarter choices about macroalgae for IMTA,” Lasco said.