I have kept a mass of semi-dried (4-6 hours within silica desiccator) Chaetoceros sp. at 4 degree C in the refrigerator for 1.5-2 months, and was able to reestablish the live culture of the species from those semi-dried refrigerated pellets. Please note, the pellet must not be full dried. In that case, re-culturing is impossible. However, I haven't analyzed the biochemical compositions, but the culture become regular like the previous after 2-3 consecutive subcultures.