Studies On The Wave-specific Influence Of Visible And Ultraviolet Light On Activities Of Calanus Sinicus

Calanus sinicus is the dominant species in the Yellow sea and East China Sea, It is one of the key zooplankton species in the Marine Ecosystem Dynamics Research in Yellow Sea and East China Sea. It is regarded as one of the most important zooplankton species in the shelf waters by virtue of its enormous abundance, large body size and its significant role in the conversion of primary production to higher trophic levels. Some of its activities, such as the diel vertical migration, grazing at night and laying eggs in the dawn, are supposed to be related with the diel light cycle. In this research, experiments in the lab and field were carried out to study the phototaxis of C. sinicus to visible light and ultraviolet-B (UV-B, 280-315 nm) radiation, the influence of light spectra and intensity on the grazing acticity, egg production rate and egg hatching rate. The followings are the main results. 1. Phototaxis of C. sinicus The sensitivity of C. sinicus depends on the former light environment (light history). After reared in lab for a period of time, C. sinicus tends to move toward the blue-green light (488.3 and 509.2 nm) and yellow light (576.8 nm) of higher intensities, but backward the yellow light (594.9 nm) of lower intensities and full spectra white light of higher intensities. No significant trend was observed for other spectral light. In situ experiments, however, revealed that C. sinicus responded positively to green light (509.2 nm), yellow light (594.9 nm) and full spectra white light. Furthermore, it behaved weakly negative phototaxis with the spectra of 449.9, 576.8 and 631.2 nm. No obvious phototaxis was found with other spectra. When UV-B intensity was higher than 10 μW/cm2, C. siniucs behaved negatively to UV-B; but no phototaxis was found when UV-B intensity was lower than 5 μw/cm2. 2. Lethal effect of UV-B on C. sinicus C. sinicus is safe with a UV-B intensity lower than 100 μw/cm2. Higher death rate was found with increasing UV-B intensity. When UV-B intensity was 300 μW/cm2, 97.78% of the individuals would die in 4 hours. With linear regression method, we got the lethal time of 50% (LT50) of the C. sinicus individuals. The LT50 of C. sinicus under 200, 300, 500 μW/cm2 UV-B are 30.47, 2.86, 1.96 hours, respectively. 3. Effects of different intensities white light on the egg production rates (EPR, ind·female-1·d-1) of C. sinicus The egg production cycles of C. sinicus was devided into three stages: beginning, fastigium and telophase. The length of the egg production cycles was 7 to 9 days. The EPR is highest when the light intensity was 1.58 mW/cm2. Lower EPR was found with both lower and higher intensities. The EPR under 2.53 mW/cm2 white light is lower than those under dark condition and 0.78, 1.58 mW/cm2 white light. This result is well correlated with the phenomenon that C. sinicus always spawn in the dawn. 4. Effects of different white light intensities on the egg hatching rates (EHR) of C. sinicus The hatching rates of eggs laid by C. sinicus was influenced by the white light intensities. But at the beginning of egg production cycle, there was no significant difference in the hatching rate. The hatching rates under intensities lower than 1.78 mW/cm2 kept steadily higher than that under 2.53 mW/cm2 white light, which was not only the lowest one but also kept descending in the whole egg production cycle process. 5. Effects of different intensities spectra visible light and UV-B on the ingestionof C. sinicus Yellow light can enhance the ingestion of C. sinicus. For other spectra, the effects on ingestion of C. sinicus were unconspicuous. UV-B with intensity more than 100 μw/cm2 restrains C. sinicus grazing at a rate over 50%.