The seasonal dynamics of catalase activity of two related species of brown macroalgae, Cystoseira crinita (Desf.) Bory (1832) and Fucus vesiculosus L. (1753) was studied. In general, catalase activity (CA) in C. crinita was several times higher than in F. vesiculosus. The maximum values of CA in C. crinita were observed in November and the minimum ones in September. For F. vesiculosus, the maximum CA was found in January and the minimum in April. Abrupt changes in water temperature significantly affected the catalase activity in C. crinita and F. vesiculosus. In both species of algae, a similar seasonal trend in the change of CA was noted: two periods of adaptation adjustment associated with sharp changes in the temperature regime (spring and autumn) were distinguished. In spring, with a rapid increase in the temperature of the water masses, catalase inactivation occurred, whereas during summer to winter transition, accompanied by a sharp water cooling, catalase activity increases. Stabilization of the CA values of the studied macroalgae in the absence of sharp temperature variability was observed. However, this period of “stationary state” varies in time: in Cystoseira crinita it lasts from May to August, and in Fucus vesiculosus it lasts from May to December.
