Cryptophytes of Lake Shira (Khakassia, Russia): explosive growth during breakdown of meromixis

We conducted a monitoring study on the dynamics of the abundance, biomass, and vertical distribution of the cryptophyte population in meromictic saline Lake Shira (90.11 E, 54.30 N) in the periods of stable meromixis (2012–2014), meromixis breakdown and mixing of the entire water column (2015–2016), and the subsequent reestablishment of meromixis (2017–2021). When stable stratification was broken down, cryptophyte biomass increased sharply: from 0.1 to 6 g m−2 on average in the water column (to 4500 cells ml−1 in the vertical maximum). The shape of the vertical distribution of cryptophytes has also changed. Changes in the abundance of cryptophytes caused by the breakdown of meromixis have largely endured after it was reestablished. Such a considerable increase of cryptophyte biomass did not correlate with the corresponding parameters of other components of the Lake mixolimnion ecosystem, whose biomass changed by a factor of no more than two. The explosive growth of cryptophyte abundance can be explained by a decrease in the trophic pressure of zooplankton—copepods and rotifers.