Harvesting Asparagopsis: understanding regrowth and associated community dynamics

Abstract The red seaweed Asparagopsis taxiformis can reduce methane emissions in livestock by over 90%, but its mariculture remains in its infancy and biomass for research and commercial use relies partly on wild populations. Knowledge on the impacts of harvesting A. taxiformis is lacking, emphasising the need for ecological research to guide the development of its sustainable harvesting. This study examined the regrowth potential of A. taxiformis meadows following small-scale harvesting. A harvest experiment testing the methods, handpicking and cutting, was conducted in Gladstone, Queensland, Australia, during the austral winter, with plots monitored over six months. Harvesting immediately affected percent cover and shoot length. Handpicked and cut plots exhibited regrowth within four to five months in terms of cover, which notably exceeded or were slightly above that of control plots. The shoot length of harvested plots paralleled that of control plots and was mainly influenced by seasonality. Control plots exhibited reduced growth at three months, suggesting that harvesting mimicked the seasonal reduction in biomass after the winter peak. This study also demonstrated the importance of vegetative propagation in the regrowth of A. taxiformis . The sessile benthic community in harvested plots underwent temporal shifts similar to those in the control plots, indicating that harvesting did not substantially alter community dynamics. Approximately 19 taxa of mobile fauna were recorded within Asparagopsis meadows, potentially indicating its habitat role. Overall, these findings provide ecological insights into the harvesting impacts on this seaweed, with further studies needed to assess broad-scale and long-term impacts.