Changes of Bacterial Population in the Nursery Tanks for the Forced Cultivation of Makonbu Laminaria japonica

Abstract

Conditions for the forced cultivation of makonbu in the nursery tanks which were examined in this study were as follows; Zoospores of makonbu were collected by cremona strings (culture bed), and were reared until grown up to visible size of sporophytes in aerated tanks containing enriched seawater (culture medium) for two months at 10-13°C and 12-16h light exposure per day. The culture medium was renewed every week after initial 12-13 days' incubation.
Changes of bacterial population in the culture medium and on the culture bed of the makonbu nursery tanks were examined for 40 days cultivation. Number of viable cells in the culture medium increased from 10² to 10⁶cells/ml after 12 days. During this period, the predominant Alterornonas and Vibrio (the decomposers of macromolecular organic substrates) were replaced by terrestrial or marine pseudomonads which were non-decomposers of macromolecular organic substrates. In the following two weeks, the number of viable cells decreased to 10⁴cells/ml, but the same groups of bacteria maintained their dominance. At the end of the experiment (40 days), viable cells increased again, and alginate and laminarin decomposers, such as the populations of marine pseudomonads, Flavobacterium and Alcaligenes increased.
On the culture bed, number of viable cells increased from 10² to 10⁸cells/g after 20 days and maintained the same level throughout the following periods. Changes of bacterial flora on the culture bed resembled with these of culture medium, but occurred about one week later.