ИСТИНА

Different microbial communities inhabit a lot of marine invertebrates. The species composition and abundance of these epibiotic communities change during an annual cycle. A necessary component of all epibiotic communities living in the photic zone is oxygen-evolving phototrophic microorganisms (OPM): cyanobacteria and unicellular algae. The goal of our work was to reveal biomass dynamics of the epibiotic trichome cyanobacteria and the diatom algae inhabit hydroid Dynamena pumila in the White Sea during the summer period. The seasonal variability of the species composition and the abundance of the diatom algae and trichome cyanobacteria have been demonstrated on the apical internode of D. pumila during the summer months (June, August). The significance differences of mean values of the abundance (N) and biomass (B) were estimated by the Mann-Whitney test with using the program PAST. The values N and В of the diatom algae were observed 2,09±1,85 cell mm-2 and 0,130±0,115 µg С mm-2, respectively in June, while the values N and В were significantly lower (р<0,02) in August. Mean N and В values were 1,45±2,74 cell mm-2 and 0,091±0,170 µg С mm-2, respectively. The biomass of the diatom Cocconeis scutellum dominated in June and in August. Perhaps, the higher values of the diatom biomass in June can be explained by the older age of the young internode of the hydroid D. pumila. The biomass of the trichome cyanobacteria was significantly lower in June than in August unlike the diatom algae. The cyanobacteria N values varied from 53 to 292,50 cell mm-2 in June. Cyanobacteria density depends on the place of the localization on the shoots of the hydroid. The largest abundance of the cyanobacteria was observed at the points of the hydrothacae “fusion” with the steam of the shoot marked by shallow furrows. The mean values of N and В of cyanobacteria in June were 27,02±60,86 cell mm-2 and 0,54±1,23 µg С mm-2, respectively. The values of N and В were significantly higher (р<0,01) in August than in June. The mean values of N and В of cyanobacteria in August were 100,73±124,00 cell mm-2 and 2,03±2,44 µg С mm-2, respectively. The values of diatom and cyanobacteria biomass were approximately equal in June while the values of cyanobacterial biomass were significantly higher (р<0,01) than values of diatom biomass in August. We estimated the maximum value of primary production of the epibiotic OPM with calculated biomass of OPM and maximum specific rate of the growth of different size classes of OPM. According to the calculations the epibiotic OPM on the hydroid D. pumila can make a significant contribution to the processes of primary production in the coastal zone.