Most studies of energetics in marine filter feeders have focused on animals living in steady state food conditions. However, copepods experience highly variable access to food because of food patchiness and behavioural avoidance of predators. For small copepods this is especially important since they lack the potential of energy storage, e.g. in the form of lipids. After a period of food deprivation Acartia tonsa show a compensatory increase in ingestion rate, but only temporarily and on the time scale of the gut filling time. The copepods are able to compensate for the lacking input of food. On the other hand, longer periods of starvation (6-14h) induce elevated ingestion rates that lasts longer than gut filling time. Under these circumstances other energetic factors influence the ingestion rate. Consequently, the energetics of the copepods are highly variable in a patchy food environment.
The study showed that medium length periods of starvation (12-36h) had a depressing effect on egg production rate (EPR) in copepods. Individuals fed constantly at 500 microgC/l had an PR of 1.23 (0.19) eggs/female/d [mean (s.d.)]. After starvation at the onset of feeding the EPR of starved individuals covaried with the length of the previous starvation: 0.76 (0.15) for those starved 12h, 0.53 (0.01) for 24h, and 0.12 (0.03) for 36h. EPR increase linearly to the pre-starvation level and the length of time needed to reach this level was proportional to the length of the previous starvation period. A probable explanation is a gradual arrest of enzymatic processes during the period of starvation. Similarly, the respiration rate of all starved individuals was depressed to approximately 50% of that of constantly individuals: 0.5 vs. 0.96 nlO2/ind/min. Within approximately 3h the respiration rates increased to that of the constantly feeding individual. The most interesting result of the study was that the increase in respiration rate continued to levels above that of constantly feeding individuals within 12h at the onset of feeding after the starvation period. Excess energy was probably needed for building up the digestion and egg production apparata during the recuperation from starvation. The duration of these high levels of respiration was proportional to the length of the previous starvation period. In those starved 12h the respiration decreased to that of the constantly fed individuals after 8h, in those starved 24h after 20h, and in those starved 36h after 30h.