Seasonal variations in the vertical distribution and buoyancy of Microcystis aeruginosa Kütz. emend. Elenkin in Rostherne Mere, England

Abstract

Distribution and buoyancy studies in Rostherne Mere (depth : 30m) show that the life-cycle of Microcystis is intimately related to the cycle of thermal stratification : colonies overwinter on the bottom muds, but migrate to the epilimnion in summer, returning again in late autumn or winter .

Sinking movements of phytoplankton indicated by a simple trapping method

“…It is likely that these algae, though physiologically inactive, had lost their buoyancy. Autumnal reductions in buoyancy, possibly as a result of enzymatic weakening of the gas-vacuole membranes (Walsby, 1971), have been observed in previous years in this and other meres (Reynolds, 1973b;Reynolds & Rogers, 1976). …”

Algal sedimentation in relation to phytoplankton periodicity in Rostherne Mere

“…The areal equivalent of the vernal diatom maxima (units cm-3) are calculated from equation (1), thus: P = C x 13.7 × 100 (1) where C is the concentration of algal units ml-1 of integrated 4.5 m column samples. During summer, the isothermal depth can never exceed that of the epilimnion, typically less than 8 m (Grimshaw & Hudson, 1970;Reynolds & Rogers, 1976). The areal equivalents of algal concentrations are approximated from equation (2): P=Cx 8.0 × 100 (2) With the exception of those for Nitzschia, the areal catches of the diatom species are apparently overestimated by factors of 2-20 for the commoner forms, and increasing to 330 in the case of Melosira varians.…”

The Effect of Temperature on Recovery of Buoyancy by Microcystis

“…Sedimentation of Microcystis populations is associated with declining water temperature (see data of Renolds & Rogers, 1976;Rother & Fay, 1977;Takamura et al, 1984), but temperature changes have not previously been shown to cause loss of buoyancy. In this paper direct evidence is presented for light-mediated regulation of buoyancy in a natural population of Microcystis and for the involvement of low temperature in the seasonal loss of buoyancy.…”