Effects of acclimatization on metabolic plasticity of Eodiaptomus japonicus (Copepoda: Calanoida) determined using an optical oxygen meter

Abstract

Physiological adaptation may considerably improve aquatic organism survival when subjected to environmental threats in a variable environment. To clarify the metabolic plasticity of the freshwater copepod Eodiaptomus japonicus from Lake Biwa (Japan), respiration rates (R) of the copepod were determined over a temperature range of 8-30°C after acclimatizations at 15 and 25°C using an optical oxygen meter. R increased exponentially from 8 to 28°C and deviated from the exponential phase at 30°C for both acclimatizations with no significant differences, indicating the same metabolic plasticity to changing temperature as occurred in situ. Furthermore, R for copepodites was always high at high temperature, regardless of body weight. Therefore, it is possible to evaluate the metabolic costs of wild populations using the respiration rate temperature equation formulated in this study. Net growth efficiencies (K2) calculated from respiration losses in this study and growth rates in a previous study of food effects showed low K2 in the food-limited animals at high temperature, implying that high metabolic costs at higher temperatures induce decreasing growth rates in food-limited environments. Hence, the E. japonicus population that suffers from food shortage in Lake Biwa is probably threatened by temperature increase due to global warming.