Immobilized Isochrysis galbana (Haptophyta) for long-term storage and applications for feed and water quality control in clam (Meretrix lusoria) cultures

The marine microalga Isochrysis galbana was cultivated and entrapped in alginate beads for long-term storage. The entrapped cells were alive and maintained their physiological activities after one year of storage in absolute darkness at 4degreesC without a liquid medium. The number of cells in the beads increased more than 32 times when they were subsequently re-cultured in an aqueous medium for five weeks, showing that they had remained alive during storage. TEM observations showed that the entrapped cells reduced their cell covering and pyrenoid size compared with the normal free-living cells after long-term storage. The algal beads were also applied to feed and water quality control in clam cultures' leading to a marked decrease in ammonium concentrations. Algal cells escaped from the beads provided a food source for the clams. This might reduce the cost of clam culture compared to traditional culture methods. Therefore, immobilized l. galbana can be used for long-term preservation of algal stock in the laboratory and applied practically to clam cultures.