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Macroalgal biomass blooms, including those causing the green and golden tides, have been rising along Chinese coasts, resulting in considerable social impacts and economic losses. To understand the links between the ongoing climate changes (ocean warming and acidification) and algal tide formation, the effects of temperature (20 and 24 °C), pCO2 concentration (Partial Pressure of Carbon Dioxide, 410 ppm and 1000 ppm) and their interaction on the growth of Ulva prolifera and Ulva lactuca (green tide forming species), as well as Sargassum horneri (golden tide forming species) were investigated. The results indicate that the concurrent rises in temperature and pCO2 level significantly boosted the growth and nutrient uptake rates of U. lactuca. For U. prolifera, the heightened growth and photosynthetic efficiency under higher CO2 conditions are likely due to the increased availability of inorganic carbon. In contrast, S. horneri exhibited negligible responsiveness to the individual and combined effects of the increased temperature and CO2 concentration. These outcomes indicate that the progressive climate changes, characterized by ocean warming and acidification, are likely to escalate the incidence of green tides caused by Ulva species, whereas they are not anticipated to precipitate golden tides. [ABSTRACT FROM AUTHOR]

Macroalgae, playing a crucial role in coastal marine ecosystems, are subject to multiple environmental challenges due to tidal and seasonal alterations. In this work, we investigated the physiological responses of Pyropia yezoensis to ocean acidification (ambient CO2 (AC: 400 μatm) and elevated CO2 (HC: 1000 μatm)) under changing salinity (20, 30 psu) and light intensities (50, 100 μmol photons m−2 s−1) by measuring the growth, pigment content, chlorophyll fluorescence, and soluble sugar content. The key results are the following: (1) P. yezoensis exhibited better growth under normal salinity (30 psu) compared to hyposaline conditions (20 psu). (2) Intermediate light intensity increased phycoerythrin content, ultimately enhancing thalli growth without significant changes to the contents of chlorophyll a and carotenoids. (3) Ocean acidification alleviated hyposaline stress by enhancing pigment production in P. yezoensis only at a salinity of 20 psu, highlighting the complex interplay of these environmental factors. These findings indicate that higher light intensities and elevated pCO2 levels could mitigate the stress caused by low salinity. [ABSTRACT FROM AUTHOR]