MEPS 191:71-77 (1999)  -  doi:10.3354/meps191071

ABSTRACT: This study was specifically designed for sediment trap researchers and oceanographers working with organic material which is fixed in situ with formalin and analysed several months after collection. The effects of long-term formalin storage on phytopigment and DNA determinations were tested on seawater, algal cultures and trap material. DNA determinations in formalin-preserved samples were hampered by the use of specific flurochromes (i.e. Thiazole Orange and Hoechst). In contrast, the use of DABA (diaminobenzoic acid) reagent allowed these problems to be overcome, making DNA determination feasible in formalin-preserved samples without any interference. DNA concentrations measured in all samples did not change significantly with long-time formalin storage (up to 9 mo), indicating that, independently from the quantity and the source of genetic material, non significant DNA losses occurred. In contrast, chloropigment concentrations in formalin-preserved samples significantly decreased. The decreasing temporal pattern of chlorophyll a (chl a) concentrations in formalin-preserved algal culture and seawater samples was similar, suggesting that chl a degradation is independent from the initial pigment concentration. A possible explanation for the strong decrease in chl a concentrations is changes in its molecular structure. The recovery of total chloroplastic pigments in trap samples was higher than the recovery of chl a observed in algal cultures and seawater samples. Such discrepancy appears to be due to the different degradation rates of the phaeopigments after their fixation in the sediment traps.

KEY WORDS: Formalin · Trap samples · DNA · Phytopigments