Egg production and energy storage in relation to feeding conditions in the subantarctic calanoid copepod Drepanopus pectinatus:: an experimental study of reproductive strategy

The egg production and the hatching success of Drepanopus pectinatus (Brady, 1883) was examined in relation to food availability. The spawning frequency did not change in relation to the concentration of phytoplankton with an interval time of 7.6 d between 2 broods. At least 1 egg sac was produced per female in almost all cases (> 93 %) independent of the food level. The subsequent recruitment of breeding females was strongly influenced by feeding conditions: only 22 to 50 % of the starved females completed 3 successive breeding cycles, while 100% of the fed females did. The number of eggs per was also affected by the concentration of food, with a mean of 12 eggs per sac in starved females and 19.4 eggs per sac in fed females independent of the food level. Brood sizes increased significantly in the fourth breeding cycle to 35.3 eggs per sac in females fed a concentration of 1180 pg protein 1(-1). Egg-hatching time was constant, with an average of 6.7 d. To evaluate the relative roles of reproduction and of accumulation of energy reserves, we compared the production of eggs and the changes in the organic composition of females in various limiting food conditions. Brood size was influenced by both immediate and past trophic conditions, with the number of eggs per sac varying from 10.1 to 12.8. The content of the eggs was constant: 122 ng of protein and 234 ng of Lipids. In females, protein content was a good indicator of immediate feeding conditions, while lipids, dominated by wax esters, reflected both immediate and past feeding conditions. A low level of egg production was maintained throughout periods of nutritional Limitation or starvation. Subsequently, food was used to reduce the consumption of the energy reserves of females before being invested in reproduction, as observed at high food concentration.