EFFECT OF DENSITY ON LARVAL DEVELOPMENT AND FEMALE PRODUCTIVITY OF TISBE-HOLOTHURIAE (COPEPODA, HARPACTICOIDA) UNDER LABORATORY CONDITIONS

The harpacticoid copepod Tisbe holothuriae has been cultivated in the Helgoland laboratory for more than 20 years. The effects of density on the larval development and the female productivity were studied by co mparing two culture systems: (1) enclosed system, and (2) running-wate r system. In both systems, a nutritious mixed diet of Dunaliella terti olecta, Skeletonema costatum, and granulated Mytilus edulis was offere d. Larval mortality, larval development and female productivity are fo und to be significantly dependent on both the population density and s pecificity of the culture system. Increasing density causes higher lar val mortality, longer larval development time, and a reduction in fema le productivity. In comparison with the enclosed system, the running-w ater system shows decisive advantages: larval mortality is about 20 % lower, the rate of larval development is about two days shorter, and t here is a very high rate of nauplii production. The sex ratio exhibits high variations, but in general, there is no clear relationship betwe en sex ratio and population density. Nevertheless, when reared in the running-water system, a relatively high percentage of females (> 45 %) was found at lower densities.