Effect of temperature and food concentration on the relationship between growth and AARS activity in Paracartia grani nauplii

The in situ activity of the enzymes aminoacyl-tRNA synthetases (AARS) and the growth rates of naupliar stages of the planktonic marine copepod Paracartia grani were measured in the laboratory under different temperature and food concentrations. We assessed the effect of these parameters on growth and protein synthesis rates of P. grani nauplii. Growth and protein synthesis rates of P. grani nauplii depended on temperature and food concentration. AARS activity is valid as an index of somatic growth for P. grani nauplii when growth is not limited by food availability. However, the relationship between protein-specific AARS activity and nauplii growth varied according to food availability levels. The degradation of proteins during starvation and/or the ß-oxidation of fatty acids affected the relationship between specific AARS activity and growth rates. The results presented here add to previous studies showing that the AARS activity is a useful tool for estimating somatic growth of this and other key copepod species. Nevertheless, further research is required to elucidate the validity of AARS activity as a universal proxy for growth.

► Growth and protein synthesis rates of P. grani nauplii depended on temperature.
► Growth and protein synthesis rates of P. grani nauplii depended food concentration.
► AARS activity is valid as index of somatic growth for P. grani nauplii.
► The relationship between spAARS activity and nauplii growth varied with food amount.