Ecology of Subarctic Populations of Cyclops Bicuspidatus Thomasi Forbes and Diaptomus Ashlandi Marsh (Copepoda)

Abstract

[Factors influencing the life history, feeding and reproduction of Cyclops bicuspidatus thomasi and Diaptomus ashlandi in Yellowknife Bay in the Canadian subarctic were studied between August 1975 and November 1976. The former species emerged as copepodid IV from the overwintering stage in June and completed its life cycle in 60 days. Temperature reduced the developmental rate but food supply was not limiting. Although algae were abundant in the environment, <30 cells/animal occurred in the guts of nauplius III to copepodid III. Only the smallest species, Cyclotella glomerata, was usually eaten, with other algae being rejected because of their length. Almost all specimens ingested large quantities of finely divided (<1 μm) detritus. Only 35-55% of carnivorous copepodid IV-VI contained material in their guts. Rotifers were most frequently ingested and copepodid VI fed throughout the reproductive phase. Changing daylength, measured 2 and 4 weeks earlier, accounted for 34 and 68% of variation in the percentage of females with eggs and clutch size respectively. Food supply was second in importance (24-25%) with temperature being of little significance. Variation in the sex ratio could not be adequately explained by daylength, temperature, or food. D. ashlandi required 5 months to complete its life cycle, emerging from the overwintering phase in April as nauplius II. Temperature and possibly photoperiod affected development but food supply was unimportant. Up to 60 algal cells occurred in the gut of copepodid IV-VI with several species (C. glomerata, Synedra acus var. radians, Chrysolykos gracilis, Dinobryon divergens) being ingested. Size selection restricted consumption of most other species. Changing daylength accounted for up to 79% of the variation in the percentage of females with eggs and 67% in the clutch size. Temperature also significantly affected both parameters, with food supply being of little importance. Changes in sex ratio were independent of daylength, food and temperature., Factors influencing the life history, feeding and reproduction of Cyclops bicuspidatus thomasi and Diaptomus ashlandi in Yellowknife Bay in the Canadian subarctic were studied between August 1975 and November 1976. The former species emerged as copepodid IV from the overwintering stage in June and completed its life cycle in 60 days. Temperature reduced the developmental rate but food supply was not limiting. Although algae were abundant in the environment, <30 cells/animal occurred in the guts of nauplius III to copepodid III. Only the smallest species, Cyclotella glomerata, was usually eaten, with other algae being rejected because of their length. Almost all specimens ingested large quantities of finely divided (<1 μm) detritus. Only 35-55% of carnivorous copepodid IV-VI contained material in their guts. Rotifers were most frequently ingested and copepodid VI fed throughout the reproductive phase. Changing daylength, measured 2 and 4 weeks earlier, accounted for 34 and 68% of variation in the percentage of females with eggs and clutch size respectively. Food supply was second in importance (24-25%) with temperature being of little significance. Variation in the sex ratio could not be adequately explained by daylength, temperature, or food. D. ashlandi required 5 months to complete its life cycle, emerging from the overwintering phase in April as nauplius II. Temperature and possibly photoperiod affected development but food supply was unimportant. Up to 60 algal cells occurred in the gut of copepodid IV-VI with several species (C. glomerata, Synedra acus var. radians, Chrysolykos gracilis, Dinobryon divergens) being ingested. Size selection restricted consumption of most other species. Changing daylength accounted for up to 79% of the variation in the percentage of females with eggs and 67% in the clutch size. Temperature also significantly affected both parameters, with food supply being of little importance. Changes in sex ratio were independent of daylength, food and temperature.]