Nucleic acids and protein content in ontogenetically migrating copepods in the Oyashio region as influenced by development stage and depth distribution

We investigated individual DNA, RNA and protein (PRO) content of the ontogenetically migrating copepods Neocalanus cristatus, N. plumchrus and Eucalanus bungii collected from surface layers; of the northwestern Pacific Ocean during the spring phytoplankton bloom and mesopelagic depths during winter. RNA:DNA and RNA:PRO ratios for dormant and adult stages residing at mesopelagic depths were significantly lower than those for animals collected from the surface layers. Compiling the values of all species and stages together, log-transformed individual content of RNA (logRNA) was significantly correlated with log-transformed individual contents of DNA (logDNA) and protein (logPRO) in both layers. While logRNA:logDNA and logRNA:logPRO ratios were significantly lower for specimens residing at mesopelagic depths, the difference of the logRNA:logPRO ratio was not clear for some specimens appearing in the surface layer. These results indicate that in these ontogenetically migrating copepods, RNA to DNA decreases considerably during dormant and adult stages residing at mesopelagic depths. We propose the RNA:DNA ratio as a biochemical indicator for dormancy of ontogenetically migrating copepods.