Arch. Hydrobiol.
Vol 129:1; pp. 67-87
Stuttgart, November 1993

Effects of short- and long-term freezing of chloropigments in cultured diatoms and bivalve

digestive gland and faeces as determined by standard fluorometry and HPLC

Abstract

Short-term freezing effects on chlorophyll-a type pigments in filtered samples of cultured diatoms, Thalassiosira weissflogii were examined following 24 hr of filter storage in liquid nitrogen (-196º C) , on dry ice (-79º C) and in a freezer at -20º C. Traces of chlorophyllide-a and chlorophyll-a allomers and epimers appeared in the extracts of all frozen algal samples following 1 day of storage. Relative amounts of chlorophyll-a derived products increased with an increase in storage temperature. Total pigment recoveries, however, were not significantly different (p > 0.40). The degradative effects of freezing chloropigments (chlorophyll-a types plus phaeopigments) in T. weissflogii and Mytilus edulis (blue mussel) digestive gland and faeces were examined in samples frozen on dry ice followed by storage at -20º C for periods up to 12 months. T. weissflogii extracts showed no losses, and only small changes in composition, of chlorophyll-a type pigments throughout the duration of storage. However, standard fluorometric measurements of chlorophyll-a type pigments in T. weissflogii extracts were higher than HPLC determinations by an average of 8.8 % (± 4.6 %). Although chloropigment composition in mussel faeces remained constant throughout 12 months of storage at -20º C, total amounts extracted following 1 week of storage increased by 40 - 50 %. Chloropigment concentration in mussel digestive gland samples changed little over 12 months of storage at -20º C, although there were significant transformations within the various chloropigment pools. There were no significant differences between methods in measurements of total chloropigments from either M. edulis digestive gland or faeces (p > 0.50). In all 3 sample types, the degradative effects of freezing were most pronounced within the first week of storage; thereafter, the rate of transformation decreased. In general, extracts containing a mix of chlorophyll-a type pigments and phaeopigments showed very good agreement between standard fluorometric and HPLC determinations of total chloropigment concentration.