Strong turbulence benefits toxic and colonial cyanobacteria in water: A potential way of climate change impact on the expansion of Harmful Algal Blooms

Abstract

Extreme natural events such as typhoons can amplify the effect of hydrodynamics on the lake ecosystems. Here we presented data on the effect of typhoons on algal cell size based on field observation. Then turbulence simulation systems were used to decipher the response of natural phytoplankton communities to a range of turbulence regimes (linked to typhoon-induced turbulence intensity) under laboratory conditions. Turbulence intensities of 6.17 × 10−3, 1.10 × 10−2 and 1.80 × 10−2 m2/s3 benefited algal growth and triggered abrupt switches from unicellular Chlorella dominated to colonial Microcystis dominance, and the abundance of colonial algae depended on the turbulence intensity. Under the influence of elevated turbulence, Microcystis dominated biomass increased by 2.60–6.58 times compared with that of Chlorella. At a given phytoplankton density and community composition, we observed a significant increase in extracellular microcystins (MCs) and a 47.5-fold increase in intracellular MCs with intensified turbulent mixing, suggesting that the damage of algal cells concomitantly the stimulation of toxin-producing Microcystis. Our results confirmed that the formation of large colonial algal cells, enhancement of the succession of algal species, and most importantly, the induction of toxin-producing Microcystis, were the active adaption strategy when phytoplankton were impacted by strong turbulence. The result implies that the ongoing climates changes and typhoon events are likely to contribute to undesirable outcomes concerning phytoplankton populations.