Only 7 to 10 days without wind driven vertical mixing were required in spring to start the first
growth pulse, despite of a still very unstable water column (sometimes inverse thermal stratification).
Mainly flagellates and Stephanodiscus hantzschii increased their biomass and achieved net
growth rates of 0.1 and up to 0.65 d–1 respectively. During such a phase the mixing depth was always
smaller than the euphotic depth. Later on, at the start of the spring bloom (= last growth pulse in
spring before the clear water stage), the intensity of vertical mixing as well as the mixing depth
were markedly reduced due to an increase in heat input and low wind. Then flagellates dominated
(contribution up to 75.5% of the areal biomass reaching 60 g fresh weight m–2) and the growth rate
rose to a maximum of 0.65 d–1.