| The effects of salinity and Heterosigma akashiwo on survival, ingestion, reproduction, development, population dynamics and respiration of planktonic copepods Schmackeria poplesia (Copepoda: Calanoida) were studied in this paper.The results of survival, development, reproduction and population structure of S. poplesia in different salinity (10, 20, 30) indicated that: the survival of the nauplius of S. poplesia increased with growing salinity, but the S. poplesia in the lower salinity (10) can get the maximum innate capacity of increase (rm) and the minimum mean length of a generation (T). There may be a correlation between this result and the S. poplesia we used in this study because the copepod has been cultured in our lab for many generations.The results for ingestion of S. poplesia are listed below: Both the grazing rates (G, cells·ind-1·h-1) and filtering rates (F, ml·ind-1·h-1) were significantly affected by different algae and their concentrations (P<0.05).The grazing rates (G, cells·ind-1·h-1) of the copepod are correlated with food. G tended to increase in optimal range of food concentration, above which range, G decreased. But the filtering rates (F, ml·ind-1·h-1) always decreased with the increase of food concentration. The maximum G (4265.0 cells·ind-1·h-1) of S. poplesia for H. akashiwo appeared at 5.0×104cells·ml-1, and the maximum G (5410.3 cells·ind-1·h-1) of S. poplesia for Isochrysis galbana appeared at 10.0×104cells·ml-1. Furthermore, the F and G of S. poplesia for H. akashiwo is always lower than that of S. poplesia for I. galbana at the same concentration.The third part of this paper is the effect of different concentrations (1.25-20.0×104 cells·ml-1) of H. akashiwo on the respiration, survival, development, reproduction, population structure of S. poplesia. The results show that: when the H. akashiwo concentration is within 5.0×104～10.0×104 cells·ml-1, the copepod gets a higher survival rate and population density and rm. If the concentration is lower or higher than 5.0×104～10.0×104 cells·ml-1, all the three index of copepod decreased. The egg production increased with the increase of food concentration within 1.25×104～20.0×104 cells·ml-1. But the entire index we tested showed that as the food the I. galbana is better than the H. akashiwo. The respiration of S. poplesia was measured to tested how the copepod to response to the effect of H. akashiwo. The result showed that when the concentration of H. akashiwo was higher than 2.5×104cells·ml-1, the respiration of S. poplesia became lower and then kept constant with the increase of food ration.The fourth study was designed to test whether the H. akashiwo is nutritionally insufficient or toxic to the copepod S. poplesia. The population density and population structure were measured when the copepods were fed different food (H. akashiwo, I. galbana and mixture of H. akashiwo and I. galbana by 1:1, but in which the total food concentration was held constant). The results showed that the S. poplesia fed H. akashiwo can form stable population but the population density and rate of increase were lower than those fed the two other foods.In a fifth experiment designed to test if the H. akashiwo can affect the physiological salinity tolerance of S. poplesia, especially acute changes in salinity. The result show that the sensitivity of the nauplius of S. poplesia to acute changes in salinity increase with increasing food ration. But the copepodite of S. poplesia is not so sensitive when exposed to different concentrations of H. akashiwo.Hence, the H. akashiwo does harm to S. poplesia in physiology, development, reproduction and population, but all this effects are not deadly. At least these effects are nutritionally insufficient.
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