Effects of food concentration on egg production and feeding rates of the cyclopoid copepod Oithona davisae

Experiments to determine egg production and feeding rates of Oithona davisae were carried out under controlled laboratory conditions. From copepodite IV stage on, the animals were fed the heterotrophic dinoflagellate Oxyrrhis marina in a wide range of concentrations (from 10 µg C L −1 to 286 µg C L −1 ), and adult females were daily monitored to study different aspects of their fecundity. Both clutch and egg‐production rate increased with food concentration, with values from 8 to 20 eggs for the clutch size, and from 1.8 eggs to 6.3 eggs female −1 d −1 for the egg production. In addition, to assess the efficiency of conversion of food intake into egg mass, two feeding experiments were conducted. Maximum weight‐specific ingestion rates (≈ 80% body C d −1 ) and the egg‐production efficiency (16%) were lower than those reported for free‐spawning calanoid copepods. The fact that satiating food concentrations for feeding and egg production of adult females of Oithona davisae were rather low suggests an adaptation to exploit oligotrophic environments, and might explain the ecological success of the genus in situations when food becomes limiting for other groups of copepods.