The Seasonal Growth Dynamics of Fucus distichus subsp. evanescens (C. Agardh) H.T. Powell, 1957 (Phaeophyceae: Fucales) in the Avacha Bay (Southeastern Kamchatka)

Resumo

The peculiarities of the linear growth and morphogenesis of the commercial brown alga Fucus distichus subsp. evanescens from the Avacha Bay (southeastern Kamchatka) were studied during the period from April 1 to October 7, 2017. Fucus plants were divided into five size groups (Groups 1 to 5) of five labeled plants each. The observations were conducted at spring ebb tides; we measured the length of dichotomous branches of each order regularly, one to two times per month, and determined their increase and the state of maturity of apical branches. During the period of our field observation, labeled plants formed from four to six new dichotomous branches. Moreover, the plants with only one dichotomy in April had a higher growth rate than those that had three to five dichotomous branches at the beginning of the studies. By the end of the observations, plants with one, two, three, four, and five dichotomous branches became bushes with seven, seven, eight, eight, and nine dichotomies, respectively. The absolute growth rate of the investigated plants of F. distichus subsp. evanescens varied from 23.2 to 36.7 mm per month with the maximum value of 2.33 mm per day recorded in June. Thus, Fucus displayed more active growth than previously believed. This allows us to consider these brown algae as a potential object for introduction to mariculture. Since Kamchatka representatives of the species can form several dichotomous branches during one vegetation season, the number of dichotomies is not an indicator of the age of algal plants, as was previously suggested.