Cryopreservation of marine microalgae and potential toxicity of cryoprotectants to the primary steps of the aquacultural food chain

Cryopreservation, a technique of high potential for culture collections, might offer a solution for reliable supply of microalgae in aquaculture units. Marine microalgae used in aquaculture were cryopreserved under 4, - 20 and - 80 degreesC using common cryoprotectants (methanol, dimethylsulfoxide (DMSO), propylene glycol and polyvinylpyrrolidone (PVP)) with promising results for Chlorella minutissima, Chlorella stigmatophora, Isochrysis galbana and Dunaliella tertiolecta. As cryoprotectants usually are toxic above certain concentrations and exposure time, and assuming that low amounts of cryoprotectants will remain in regenerated cultures, an experimental scheme was employed to explore the lower limits of safety for these algae and their primary consumers in hatchery food chains. Results showed that methanol was well tolerated by C. stigmatophora and D. tertiolecta up to a concentration of 1.6% (v/v) while I. galbana could not survive in culture at any concentration and C. minutissima exhibited some 30% of the control's yield at 0.2%. DMSO was highly tolerated up to 1.0% by all strains with the Chlorella strains surviving well up to 2%. Propylene glycol was not only tolerated up to 8% by Dunaliella but induced mixotrophic growth as well, while for Isochrysis it was lethal at any concentration. Among zooplanktonic consumers, brine shrimp Artemia nauplii could tolerate very high concentrations of the tested cryoprotectants, the rotifer Brachionus plicatilis was found sensitive to low amounts of PVP, while the nauplii of the shrimp Penaeus japonicus and the crab Eriocheir sinensis were in general very sensitive to all cryoprotectants and in several cases to much lower amounts than 1%. However, as long as the residues of cryoprotectants are kept below 1% in the regenerated cultures, there will be no problem with the animal consumers. (C) 2004 Elsevier B.V. All rights reserved.