Use of RNA:DNA ratios for assessing secondary production of planktonic food webs effects of temperature, salinity, food and heavy metals /

by 1974- Speekmann, Christa Liane

Acartia tonsa is a dominant copepod in coastal waters and is an important link in the food web between microplankton and higher trophic levels. RNA:DNA ratios have been used to describe growth and nutritional condition of field collected copepods and to show strong correlation between group egg production and RNA:DNA ratios. A method was developed using a sensitive, nucleic acid fluorescent dye and automated microplate fluorometer to measure RNA, DNA and RNA:DNA ratio of individual A. tonsa. RNA, DNA, RNA:DNA ratios and egg production were all significantly higher in copepods fed Thalassiosira spp. compared to starved copepods. There was a general trend toward an increase in RNA:DNA ratios with increase in egg production, but due to the high degree of variation in both RNA:DNA ratios and egg production of individual copepods no significant correlation between RNA:DNA ratios and egg production was found. Significant differences in the RNA:DNA ratios between fed (7.2) and starved (3.4) copepods were found after 2 days. In the future this assay may be applied to other species of copepods sampled directly from the field, to provide an index of the health of planktonic food webs in nature.