This study evaluates the rarely observed phenomenon of the simultaneous occurrences of phytoplankton blooms, hypoxia, and upwelling along the Zhejiang coast in the East China Sea. Results show that the upwelling uplifted bottom water to 5–10 m below the surface. In the upwelling region, phytoplankton blooms (Chl a = 10.9 μg L⁻¹) occurred and hypoxia or low-oxygen appeared below the surface water. High concentrations of nitrate and phosphate were regenerated in the hypoxic regions, corresponding with mean values (± SD) of 16.9 (± 1.5) and 0.90 (± 0.14) μM, respectively. The upwelling expanded the region of hypoxic water, which nearly reached the surface, thereby increasing the threat to marine life. In addition to fluvial nutrients, the upwelling of water with high nutrient levels, especially phosphates, can enhance phytoplankton blooms. The results suggest that hypoxia can become more severe due to further decomposition of bloom-derived organic matter after blooms crash.

The dynamics of the aragonite saturation state (Ωarag) were investigated in the eutrophic coastal waters of Guanabara Bay (RJ-Brazil). Large phytoplankton blooms stimulated by a high nutrient enrichment promoted the production of organic matter with strong uptake of dissolved inorganic carbon (DIC) in surface waters, lowering the concentrations of dissolved carbon dioxide (CO2aq), and increasing the pH, Ωarag and carbonate ion (CO32−), especially during summer. The increase of Ωarag related to biological activity was also evident comparing the negative relationship between the Ωarag and the apparent utilization of oxygen (AOU), with a very close behavior between the slopes of the linear regression and the Redfield ratio. The lowest values of Ωarag were found at low-buffered waters in regions that receive direct discharges from domestic effluents and polluted rivers, with episodic evidences of corrosive waters (Ωarag<1). This study showed that the eutrophication controlled the variations of Ωarag in Guanabara Bay.

To evaluate the effect of rainfall intensity on phytoplankton blooms, a continuous monitoring system was deployed during 2015 in a hyper-eutrophic lagoon in Taiwan. Intensive rainfall occurs during the wet summer months, from May to September. Salinity in the lagoon was found to decrease with increasing intensity of rainfall. The magnitude of phytoplankton blooms also increased linearly with increasing rainfall intensity. The chlorophyll a concentration rose by an order of magnitude during the heaviest rainfall. Blooms may be fueled by nutrient enrichment caused by drainage or run-off water from surrounding areas that is channeled into the lagoon during rainfall events. During bloom periods, the rates of net primary production and ecosystem respiration were high. However, this ecosystem was autotrophic for most of the year. As extreme rainfall is predicted to increase, the results of this study imply that the frequency and magnitude of phytoplankton blooms may increase in the future.

This study was aimed to investigate the growth characteristics of Oxyrrhis marina and Chattonella marina in co-culture to provide experimental evidences for discussing successions of harmful algal blooms (HABs) and coastal biological communities. The colour changes of culture media of C. marina and growth characteristics of O. marina and C. marina in co-culture were analysed by the combined methods of macroobservation, microscopic examination and counting. In co-culture, the colours of culture media of C. marina had changed and their transparencies had increased with increasing elapsed incubation time after inoculated by O. marina under different initial cell densities. With the increase of the initial density of O. marina (0.17×104 cells/mL, 0.50×104 cells/mL and 0.64×104 cells/mL in C. marina culture media), the time required, that the populations of O. marina reached the stationary phases, was shorter i.e. 6d, 5d and 3d after inoculated by O. marina, respectively, and the death time of all cells of C. marina became shorter, i.e. 7d, 6d and 4d after inoculated by O. marina, respectively. During the 15 days culture period, all C. marina populations were evolved to O. marina populations. Residues of C. marina adhering to precipitates and chromatophores scattering in the culture media could strengthen the colour of culture media, C. marina populations were evolved to O. marina populations respectively within the concentrations designed in co-culture in this experiment. Disturbance feeding was one of the reasons for successions, and the results provide experimental evidences for discussing successions of red tides and coastal biological communities.