2016 Volume 63 Issue 2 Pages 55-65
Cell counts of marine phytoplankton in formaldehyde, formaldehyde–glutaraldehyde, and acid Lugol’s iodine fixatives were carried out for natural seawater samples, which were stored at room- and cooled-storage temperature for 3, 6, and 12 months and were concentrated with the Utermöhl method. The number of species in the taxonomic groups identified for the 3 and 6 months samples of 0.1–1％ formaldehyde increased, mainly due to diatoms at the cooled storage temperature. The loss rates of the dominant diatoms (Leptocylindrus danicus and Pseudo-nitzschia complex) in the acid 1％ Lugol’s iodine fixatives under the room temperature storage for 3 months was almost the same (87–100％) as those in the cooled temperature storage, but were 1.5–2 times as high as those in 0.1％ formaldehyde or the mixtures of 0.1％ formaldehyde and 0.025％ glutaraldehyde in cooled temperature storage. Cooled-storage temperature could decrease the loss rate of diatoms in 0.01–1％ formaldehyde. The abundance of the Pseudo-nitzschia seriata complex in 0.01％formaldehyde-0.025％glutaraldehyde was lower than that in 0.1％formaldehyde-0.025％glutaraldehyde (P < 0.03). The loss rate of the cell numbers of diatoms (Leptocylindrus danicus and Pseudo-nitzschia complex) in 0.1％formaldehyde (0.1％formaldehyde-0.025％glutaraldehyde) at cooled storage after 12 months was as low as 19％ (25％) on average. The loss rates of Gephyrocapsa oceanica in formaldehyde fixatives for 3 months were insensitive to the storage temperature, the concentrations of formaldehyde, and the addition of glutaraldehyde. The adoption of 0.1％ formaldehyde and cooled storage could keep the preserved phytoplankton in good condition and even minimize risk management of chemically hazardous materials as well as improve working environments for counting.
