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The optimal conditions for growth of Porphyra dioica gametophytes were investigated in the laboratory, focusing on bioremediation potential. Porphyra dioica is one of the most common Porphyra species along the northern coast of Portugal and can be found year-round. The influence of stocking density and photon flux density (PFD) on the growth, production and nutrient removal was tested. Maximum growth rates, up to 33% per day, were recorded with 0.1 g fw l−1 at 150 and 250 μmol photons m−2 s −1 . Growth rate decreased significantly with increasing stocking density. Productivity (g fw week−1 ) had an inverse trend, with more production at the higher stocking densities. At 150 μmol m−2 s −1 and with 1.5 g fw l−1 , 1.4 g fw week−1 were produced. At this PFD, there was no significant difference in production between 0.6 to 1.5 g fw l−1 . Nitrogen (N) content of the seaweeds decreased with increasing stocking densities and PFDs. The maximum N removal was recorded at 150 μmol m−2 s −1 , with 1.5 g fw l−1 stocking density (1.67 mg N day−1 ). However, the N removed by thalli at 50 μmol photons m−2 s −1 was statistically equal to that at 150 and 250 μmol photons m−2 s −1 , at a stocking density of 1.0 g fw l−1 . The influence of temperature and photoperiod on growth and reproduction was also assessed. Growth rates of P. dioica were significantly affected by temperature and photoperiod. In this experiment (with 0.3 g fw l−1 stocking density), the highest growth rate, 27.5% fw day−1 , was recorded at 15 °C and 16: 8¯, L:D¯. Male thalli started to release spermatia 21 days after the beginning of the experiment, in temperatures from 10 to 20 °C and with 10, 12 and 16 h of day length. Unfertilized female-like thalli were observed at 10 to 20 °C, under all photoperiods tested. Growth of these thalli declined after 4 weeks. By then, formation of young bladelets in the basal portion of these thalli was observed. After 7 weeks all biomass produced was solely due to these vegetatively propagated young thalli, growing 22.4% to 26.1% day−1 . The results of this study showed that P. dioica appears to be a candidate as a nutrient scrubber in integrated aquaculture systems.

Introduction: China is responsible for more than 60\% of global aquaculture production. As the frontiers of food production have expanded, the cultivation of marine organisms in coastal zones and the open ocean has grown rapidly. The dominant mariculture industry in China is suspended mariculture, which uses net cages, ropes, or other structures suspended in the water column to cultivate aquatic organisms. This systematic, quantitative review provides a clear and comprehensive account of research that has investigated the adverse impacts of suspended mariculture in China and reviews research that has applied Integrated Multi-Trophic Aquaculture (IMTA) systems for mitigating impacts. This work builds on 218 peer reviewed papers that have been published in English-language journals. Outcomes: Eighteen impacts were identified, including chemical, ecological, physical, and socioeconomic impacts. Eighteen measures for improving suspended mariculture were recommended consisting of government department, farm management, and ecological engineering measures. IMTA was the most frequently recommended measure. The capabilities of IMTA for bioremediation and increased farm production were the most frequently studied advantages. Seven other benefits have been explored but remain understudied. The current challenges facing the expansion of commercial IMTA include limited use of new technology, limited skills development, decreasing production of low trophic-level species, biogeographic and temporal barriers, and negative system feedbacks. Conclusion: Despite challenges, implementing commercial IMTA is a promising measure for reducing the impacts of suspended mariculture because it presents a range of secondary benefits that can improve the overall sustainability of aquaculture in the coastal zone.

We have been followingthe acceleration of theformation of non-traditionalaquaculture groups andorganizations and their morefrequent messaging aboutaquaculture in the era ofCOVID-19. We are concernedthat some of what we are reading and listening to is returning tofailed parts of our past decades and is fanciful — more hype thanreality — and misinformed. In addition, we are dismayed by thepromotion of global aquaculture information being used to informthe basis and background for local aquaculture developments,especially in the areas of the world where we work and refer tothroughout this article as aquaculture’s “new geographies,” i.e.,almost everywhere outside of Asia where aquaculture is new andnot traditional.

These new geographies are where aquaculture productionremains very small and its practices relatively rare. We are well awarethat over the past 2-3 decades there are fabulous new developments innew aquaculture geographies for aquaculture in Asia — Bangladesh(now world’s fifth largest producer) and Myanmar (now the world’sninth largest producer) come to mind (FAO 2020) — but, fromour Asian experiences, aquaculture there is so very different inits historical, social-ecological, consumer, market and political/governance contexts and settings to be almost irrelevant as modelsfor the rest of the worl