Are there environmental benefits derived from coastal aquaculture of Sargassum fusiforme?

Seaweed farming may alleviate coastal eutrophication and acidification, and contribute to the coastal ecosystems. Sargassum fusiforme has nutritional and medicinal benefits, and its cultivation in China has expanded in recent years. However, the environmental benefits of coastal S. fusiforme farming to the surface seawater remain unclear. In this study, we compared cultured and non-cultured areas, during the culture and non-culture seasons, in the main S. fusiforme coastal growing area of China. The results showed that S. fusiforme farming slightly increased the dissolved oxygen content and pH of surface seawater but decreased the nutrient content and chemical oxygen demand. Furthermore, the eutrophication level of seawater decreased by 36% on average. In the later stage of cultivation, with large S. fusiforme biomass, the eutrophication level of the surface seawater decreased by >50%. In addition, S. fusiforme farming increased the phytoplankton biomass and diversity index, and in conjunction with environmental factors, altered the phytoplankton community structure. After the harvest of S. fusiforme, the dominant phytoplankton mostly comprised red tide microalgae, and their abundance was relatively large. Experiments and harvest evaluations showed that S. fusiforme cultivation removed 8082 t of carbon, 642 t of nitrogen, and 61 t of phosphorus from coastal China during one culture period. This study showed that large-scale cultivation of S. fusiforme can slightly improve coastal surface seawater quality by removing nutrients, alleviating eutrophication, and actively altering phytoplankton community structure. These environmental benefits may play an important role in maintaining the health of coastal ecosystems. Schematic diagram of effects of Sargassum fusiforme aquaculture on seawater quality and phytoplankton community. The direction of the red arrow indicates the increase or decrease of the corresponding index. [Display omitted] •Scale cultivation of S. fusiforme alleviated eutrophication and acidification.•S. fusiforme farming alters the diversity and structure of the phytoplankton community.•Sargassum farming removes nutrients and sequesters carbon.