Diet and respiration of the small planktonic marine copepod Oithona nana

The functional responses of Oithona nana (Giesbr.) to various phytoplankton and zooplankton food species are described. The food species were divided into three size categories, the seasonal abundances of which were measured in Loch Turnaig, a Scottish sea loch in 1977. The seasonal variations in feeding rates in the sea for each size class were derived. The seasonal variation in respiration rate of O. nana was measured, and metabolic requirements were claculated as between 6 and 40% of the food material estimated as being eaten. O. nana differs from other common copepods in having a wide food-particle size spectrum and a low metabolic rate. It is suggested that these adaptations constitute the strategy whereby O. nana maintains its population levels throughout the year.