Methods of preservation for marine samples

Samples should in generally be preserved by more than one method; one optimal for morphological study of the taxon, the other optimal for genetic study. The various methods of preservation and fixation have advantages and disadvantages as discussed below and illustrated in the matrix of treatments versus objectives of study. Particularly for genetic studies, tissues from targeted organs should be preserved if the size of the specimen permits.

Dry specimens: Dead collected material of hard bodied taxa such as corals, mollusks and bryozoans can often be identified to species level, or to genus level with diatoms and foramiferans. Dead collected material of most other taxa is not usually retained.

Ethanol preservation: used for general anatomy and short gene sequences for many taxa. Fluids from specimen dilute the ethanol which needs to reach a final concentration of 70% or above. Concentrations of 95% or above are preferred for DNA sequencing, but concentrations above 80% can harden tissued beyond usefulness for anatomy. With large specimens, injection of the ethanol and initial refrigeration increase effectiveness at stopping decay.

Buffered formalin: Formalin is used to fix fine anatomical detail for histological studies and to preserve gross morphology with some soft bodied taxa. Formalin typically prevents extraction of DNA, especially long sequences. Specimens are sometimes stored in Bouin's solution which contains formalin, but also contains picric acid, which is explosive when dry.

Gluteraldehyde: Better fixative than formalin in some situations, but can't be used for long-term storage.

Hydantoin: promising alternative to formalin or ethanol in some situations; needs further investigation.

Freezing (-80°C): Effective for DNA preservation; susceptible to power failures.

Liquid nitrogen: Best for DNA preservation, genomics, proteomics, cell culture; dangerous because of extreme temperatures.

Freeze-drying: Used for DNA preservation; cost-effectiveness relative to freezing should be investigated.

Other preparations, such as Davidson's solution or RNA later, might be appropriate for particular taxa and analyses.