EFFECT OF TEMPERATURE AND FOOD CONCENTRATION ON POSTEMBRYONIC DEVELOPMENT, EGG-PRODUCTION AND ADULT BODY-SIZE OF CALANOID COPEPOD EURYTEMORA-AFFINIS

Post-embryonic development time, egg production rate and adult body size of calanoid copepod Eurytemora affinis from Lake Ohnuma, Japan. were determined under six temperature-food conditions (10(3), 5 x 10(3), 10(4) and 5 x 10(4) cells ml-1 at 15-degrees-C, 5 x 10(4) cells ml-1 at 10 and 20-degrees-C) in the laboratory. The measured parameters varied with both temperature and food concentration. Development time from hatching to adult female was 9.2, 11.4 and 22.8 days at 20, 15 and 10-degrees-C respectively, at the highest food concentration. The males developed to adult at one to two days earlier than the females. An effect of food shortage on development time occurred at the lowest food concentration. This development time was 24.8 days even at 15-degrees-C, being twice as long as that at the highest food concentration. Prosome length of these food-limited females was approximately 75% of well-fed ones, which reduced by only 10% with increasing temperature from 10 to 20-degrees-C. Clutch size (C, eggs clutch-1) of well-fed individuals depended on prosome length of the adult female (L, mm), and was expressed as an equation: C = 65.2 L3.83. Clutch size of individuals reared at less than 10(4) cells ml-1, however, mostly laid below the estimated curve, especially at the lowest food concentration being only 10% of that at the highest food concentration. These results suggest that food availability is a more important factor affecting population growth of E. affinis in Lake Ohnuma than variation of temperature.