Effects of nutrient limitations on three species of zooplankton

Nutrient imbalance—a mismatch in nutrient ratios between the available food supply and the demands of consumers—has the potential to be transported up food chains,exposing zooplankton to nutrient limitations.In this study,the response of Calanus sinicus（copepod）,Moina mongolica（cladocera）,and Brachionus plicatilis（rotifer） to nutrient-limited（no-limited,P-limited,and N-limited） food were evaluated from the perspective of growth,reproduction,and stoichiometric homoeostasis.The results indicated that the growth of three species was suppressed under nutrient-limited（especially P-limited） conditions.However,the effect of nutrient limitations on their reproduction was species-specific.For C.sinicus,the dietary UFA（unsaturated fatty acid） as a major phospholipid component affected their egg production and total FA supporting energy promoted the hatchability of eggs.Furthermore,excess carbon in the diet promoted egg production but reduced hatching success.For M.mongolica,nutritional（P and UFA） and energy（total FA） support affected their fecundity.B.plicatilis fecundity exhibited the same pattern of growth（no-limited〉N-limited〉P-limited）.In terms of stoichiometric homeostasis,B.plicatilis＇ s elemental compositions were less likely to be affected by nutrient limitations than M.mongolica.We suggest that the effects of nutrient imbalances could potentially become an evolutionary force affecting ecosystem structure and stability in eutrophic waters.

Photobehaviors ofthe calanoid copepod Calanus sinicus from the Yellow Sea to visible and UV-B radiation as a function of wavelength and intensity

The effects of wavelength-specific visible light, white light, and ultraviolet-B (UV-B, 280- 315 nm) on selected behaviors, grazing rate, spawning rate, and hatching rate of the marine copepod Calanus sinicus collected from the Yellow Sea were studied. Calanus sinicus placed in a partitioned experimental system responded positively phototaxis to blue-cyan and yellow light but negatively to orange light and UVB. No obvious dodge activity was found among C. sinicus irradiated with <0.005 mW/cm^2 UV-B. Under 0.20, 0.30 and 0.50 mW/cm^2 UV-B radiation, the lethal half times of individuals were 30.47, 2.86, and 1.96 h, respectively. Grazing of C. sinicus was restrained at >0.10 mW/cm^2 UV-B, whereas yellow-red light stimulated grazing. Egg production rate was highest at a white-light intensity of 1.58 mW/cm^2, with an average rate of 10.04 eggs/(female·d). These results are consistent with the observed phenomenon that C. sinicus in the Yellow Sea mostly spawn near dawn. Our results indicate that light intensity and spectrum are important factors affecting the diel vertical migration of C. sinicus under natural conditions in the Yellow Sea.