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Gracilaria aquaculture is one of the fastest‐growing sectors, contributing to 10.5% of the global seaweed feed‐stock supply chain in 2019. It predominantly caters to food‐grade agar, animal feed and non‐food sector applications viz. biotechnology, biomedical and pharmaceuticals. It has witnessed a rapid expansion triggered by increased demand due to commodity trade. Biosecurity‐related issues are the key factors constraining its expansion, but are seldom addressed. The global gracilarioids aquaculture is dominated by China and other Asian countries, namely the Republic of Korea, Indonesia, the Philippines and Vietnam. This paper provides an assessment of their national biosecurity capacity, including current risk management strategies, policies and the implementation of existing regulations. It also highlights specific gaps in national policies and regulations, which can be addressed to improve their health management systems. Biosecurity management strategies, such as the provision of clear regulatory guidance, mechanisms for notifying disease and pest outbreaks, movement of live seaweed, risk assessment, stakeholder incentivisation and certification are recommended. Further, insights into the impending biosecurity measures to the emerging countries in this domain namely India and Malaysia are discussed. We suggest, implementing a uniform format of global integrated biosecurity measures across the Gracilaria aquaculture industry, but this requires organisational, operational and procedural changes, coupled with a cross‐sectoral application of risk analysis protocols. Despite one of the important seaweed aquaculture taxa, an overview of Gracilaria production, the role of biosecurity policy and regulation in the sustainable development of this industry was still lacking, this is the first global effort in this direction. [ABSTRACT FROM AUTHOR]

We investigated the growth and bioremediation potential of five local seaweed species (Codium fragile, Ulva pertusa, Ecklonia stolonifera, Saccharina japonica and Gracilariopsis chorda), using an integrated fish‐seaweed culture system as a biofilter for effluents from black rockfish (Sebastes schlegelii) tanks. The specific growth rate, biomass and net yield values of green algae were higher than those of brown algae. The tissue N and P levels of all species increased at the end of the experiment, but N:P ratios varied among seaweed species. The uptake rate and efficiency of total ammonia nitrogen uptake were the highest in U. pertusa and lowest in S. japonica. The phosphate uptake efficiency among all species ranged from 43% for S. japonica to 30% for G. chorda. These results suggest that all species can efficiently remove enriched nitrogen and phosphorus from fish tank effluents and are suitable for integrated aquaculture and bioremediation. However, inter‐specific differences were observed among seaweeds with regard to the biofiltration performance for different forms of nitrogen. The highest total oxidized nitrogen (ToxN) uptake efficiency was observed in E. stolonifera and S. japonica, while the lowest was observed in U. pertusa. ToxN uptake rates of E. stolonifera and S. japonica was 1.8 times higher than that of U. pertusa. Thus, a seaweed polyculture that included species with varying nitrogen source‐specific biofiltration activities might allow us to remove nutrients from effluents more effectively. These results provide valuable information regarding the selection of optimal seaweed species in fish‐seaweed integrated systems. [ABSTRACT FROM AUTHOR]

There has been increasing interest in promoting the seaweed Kappaphycus alvarezii as a co‐culture species in an integrated multitrophic aquaculture system. In recent work, we observed the capability of K. alvarezii to grow and remove carbon (C), nitrogen (N), and phosphorus (P) when planted in an intensive fish floating‐net cage system in Sekotong Bay, Lombok, Indonesia. Environmental factors that may influence seaweed bioremediation were investigated. After 42 days, there was a significant difference in the seaweed growth and bioremediation capability while cultivated within the fish cage system compared to the control site. Six kilogram of K. alvarezii incorporated inside the fish cages reduced the inorganic NH4+ and PO43− on average of 22.5–34% and 5–30%, respectively, from morning to afternoon and removed 131 g C g DW−1, 4.6 g N g DW−1, and 1.18 g P g DW−1. The seaweed growth rate inside the fish cages was 3.33% d−1 and higher than at the control site. Water motion was a limiting factor for growth and nutrient bioremediation inside the fish cage system. Our results provide evidence of the potential for K. alvarezii to grow in a fish aquaculture system and reduce the nutrient discharge from fish farms. [ABSTRACT FROM AUTHOR]

Environmental challenges such as ocean acidification and eutrophication influence the physiology of kelp species. We investigated their interactive effects on Saccharina japonica (Laminariales, Phaeophyta) under two pH conditions [Low, 7.50; High (control), 8.10] and three NH4+ concentrations (Low, 4; Medium, 60; High, 120 μM). The degree of variation of pH values in the culture medium and inhibition rate of photosynthetic oxygen evolution by acetazolamide were affected by pH treatments. Relative growth rates, carbon, nitrogen, and the C:N ratio in tissue samples were influenced by higher concentrations of NH4+. Rates of photosynthetic oxygen evolution were enhanced under elevated CO2 or NH4+ conditions, independently, but these two factors did not show an interactive effect. However, rates of NH4+ uptake were influenced by the interactive effect of increased CO2 under elevated NH4+ treatment. Although ocean acidification and eutrophication states had an impact on physiological performance, chlorophyll fluorescence was not affected by those conditions. Our results indicated that the physiological reactions by this alga were influenced to some extent by a rise in the levels of CO2 and NH4+. Therefore, we expect that the biomass accumulation of S. japonica may well increase under future scenarios of ocean acidification and eutrophication. [ABSTRACT FROM AUTHOR]