Seaweed Farms Provide Refugia From Ocean Acidification

Seaweed farming has been proposed as a strategy for adaptation to ocean acidification, but evidence is largely lacking. Changes of pH and carbon system parameters in surface waters of three seaweed farms along a latitudinal range in China were compared, on the weeks preceding harvesting, with those of the surrounding seawaters. Results confirmed that seaweed farming is efficient in buffering acidification, with Saccharina japonica showing the highest capacity of 0.10 pH increase within the aquaculture area, followed by Gracilariopsis lemaneiformis (Delta pH = 0.04) and Porphyra haitanensis (Delta pH = 0.03). The ranges of pH variability within seaweed farms spanned 0.14-0.30 unit during the monitoring, showing intense fluctuations which may also help marine organisms adapt to enhanced pH temporal variations in the future ocean. Deficit in pCO(2) in waters in seaweed farms relative to control waters averaged 58.7 +/- 15.9 mu atm, ranging from 27.3 to 113.9 mu atm across farms. However, Delta pH did not significantly differ between day and night. Dissolved oxygen and Omega(arag) were also elevated in surface waters at all seaweed farms, which are benefit for the survival of calcifying organisms. Seaweed farming, which unlike natural seaweed forests, is scalable and is not dependent on suitable substrate or light availability, could serve as a low-cost adaptation strategy to ocean acidification and deoxygenation and provide important refugia from ocean acidification. (C) 2021 Elsevier B.V. All rights reserved.