Predatory feeding behavior of an Antarctic marine copepod, Euchaeta antarctica

Abstract

During the austral summer, fall and winter, feeding rates of Euchaeta antarctica were measured in the laboratory. Measurements were taken over 24 hours in the dark on a mixing device at the ambient temperature using lively prey and predators in good condition with intact first antennae. Under these conditions, I found that no feeding occurred during winter so the following characterizes summertime feeding behavior. Adult females of Euchaeta antarctica are exclusive carnivores, exhibiting highest feeding rates on prey having a prosome length of 1200 ?m. The size of these preferred prey was 65% the length of the second basipodal segment of the maxilliped, the main appendage used in prey capture by E. antarctica. These prey, juvenile stages of Metridia gerlachei, also were the most abundant prey available in the plankton. The mean saturation ingestion rate of the adult female on their preferred prey of 18.7 Melridia/female/d is 8.8% its body weight, of which 17.3% is respired. A three-week starvation period caused less than a 1.5 fold increase in the feeding rate. Maximum volume effectively searched by this predatory copepod was 2.4 liters/day. Fecal pellets were produced at a constant rate of 0.697 pellets/hour; this rate was not influenced by the level of gut fullness. In order to produce one fecal pellet, E. antarctica must ingest 1.63 prey of the preferred size. Assuming that the rate of egestion is equal to the rate of ingestion, prey were ingested at a rate of 1.14/h. Many of the field-caught copepods evacuated 3-5 pellets which converts to 5-8 copepod prey ingested. This in situ meal more than adequately covers their daily respiratory costs. Smaller predators. CIV and CV E. antarctica, exhibited higher rates on smaller prey while males did not feed at all. The younger and potentially faster growing stage CIV consumed a higher proportion of their body weight per day than did the older mature predators; they were able to meet their metabolic costs on large and small prey. Older stages may not be able to obtain enough food to meet their metabolic needs during the late summer when prey availability is limited; they cease feeding and go into the overwintering state.