The dynamics of specific rates of increase of Gracilaria verrucosa (Huds.) Papenf. f. procerrima (Esp.) Ag. were studied in terms of morphometric parameters (diameter, length, and number of branches of all orders) of the thalli. The thalli of Gracilaria were exposed to long-term cultivation in the winter-spring period under flow conditions with scaled-up water temperatures from 6 to 17 °C and light intensity 90 and 160 µE·m^-2·s^-1. It was revealed that water temperature is the main factor affecting growth and formation of the thallus. At water temperature changes from 6 to 17 °C and light intensity 90 µE·m^-2·s^-1 the specific rate of increase of the thalli is 0.001-0.021 day^-1. Under such conditions, branches of the 1–2 orders became thicker by 1.5 times; their number increased by two and seven times, accordingly. Branches of the third order demonstrate the most intensive increase of their number: 45 times. At higher levels of illumination the diameter of the stem increased more than twice, the diameter of the branches of the third order – by two-to-four times. Number of branches of the first order did not change; branches of the second and third orders increased in number by three and six times, accordingly. Under such a regime, the cultivating plants become strongly covered by epiphytes, resulting in a decrease with increases in specific rates from 0.007 to 0.002 day^-1.

Keywords: Gracilaria verrucosa, morphometry, bushing out, temperature, illumination, specific rate of increase

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