Effects of starvation on the respiration rate and motility of the copepod Limnocalanus macrurus in a mesocosm experiment

2nd International Aquatic Mesocosm Research Symposium - from local processes to cross-domain interactions, 12-16 April 2021, Heraklion, Crete, GreeceThe effect of starvation on Limnocalanus macrurus energy metabolism and behavioural response was studied in a short-term experiment during August-September 2019 at the mesocosm facilities of Finnish Environment Institute in Helsinki (SYKE). Planktonic copepods, such as Limnocalanus macrurus, are able to survive during unfavourable periods by using fat reserves in their bodies represented mainly by wax lipids. Throughout the entire period of the 11-day experiment the stomachs of L. macrurus remained empty and all the studied individuals had an oil sac to store lipids. During the experiment the total respiration rate of adult females decreased by 1.9 times from 0.91±0.13 to 0.47±0.08 μg O2 mg-1h-1 on day 11 while basal weight specific respiration rate remained on the quasi constant level (0.4±0.05 μg O2 mg-1h-1). The indicators of motion activity of copepods (total duration, distance and average swimming speed, frequency and duration of movements) decreased by about 60% during the experiment. Such a decrease in the activity of copepods during the experiment can be explained by the lack of “fast” energy source for muscle activity, which is usually replenished with the energy of food. Taking into account that L. macrurus is mostly a carnivorous species adapted to the consumption of heterotrophic food in summer, we assumed that the studied population, which consisted mostly of preoverwintering adults and late copepodite stages, was not feeding as in natural conditions. The observed trend in total respiration rate without effect of starvation on basal respiration indicates that large energy reserves of this species are saved and kept for the future spring reproduction (egg production), but not for everyday energy expenditures associated with fast metabolic processe