Environmental Factors Of Nitrogen, Phosphorus, Heavy Metals On Growth And Ingestion In Pseudodiaptomus Annandalei

Copepods play important rroles in the ocean. The change in ocean environmental conditions has great influences on the growth, development, ingestion and behaviors of the copepods and then influences on marine ecosystem. So it is important to investigate the effect of different environment conditions on copepods. Pseudodiaptomus annandalei, a species of copepod in the coast of southestern China, is used in this study. The growth, development and ingestion of the Pseudodiaptomus annandalei were investigated with Tetraselmis subcordiformis of different phosphorus and nitrogen contents as food. The toxicity effects of heavy metals on P. annandalei and the change of grazing rate of them under the presence of Cu2+, Zn2- and Cd2+ heavy metals were also studied. The research results were summarized as follows:(1) The growth rates of P. annandalei were (0.044±0.0034)/d and (0.034±0.005)/d when using Tetraselmis subcordiformis with low P content (C/P=197 or 375 in molar) as food. The growth rate was (0.104±0.040)/d when using Tetraselmis subcordiformis with high P content (C/P=78 in molar) as food. There was a close linear significant correlation between the growth rates and P contents in the copepodite. The ingestion rates of nauplius, copepodites and adults decreased significantly in low P condition compared with those under P-sufficiency, which changed from 790, 720 and 728 cells/(ind·h) in the P-sufficiency condition to 150-370, 695-703 and 648-733 cells/(ind·h) in the low P condition, respectively. It was concluded that the nutritional quality (C/P and C/N ratio) of algae was degraded in low P condition, which led to the significant impairment on the growth and ingestion of the Pseudodiaptomus annandalei. Therefore, the P-limitation in marine copepods was verified.(2) The growth rates of P. annandalei were (0.067±0.001)/d and (0.062±0.005)/d when using Tetraselmis subcordiformis with high N content (C/N=8.53 or 9.56 in molar) as food. The growth rates were reduced to (g=0.056±0.001)/d and (g=0.043±0.004) under N-dificiency (C/N=12.67 in molar). There was a close linear significant correlation between the growth rates and N contents in the copepodite. The ingestion rate of P. annandalei adults decreased significantly in normal N content condition compared with those under N-free condition, which changed from 811 cells/(ind·h) to 577 cells/(ind·h). It was concluded that the N-limitation led to the significant impairment on the growth and ingestion of the adults of P. annandalei. (3) The 96h median lethal concentrations of these three heavy metals to Pseudodiaptomus annandalei are 0.158mgL-1,0.894mgL-1, and 0.170mgL-1. The toxicity order of these three heavy metals is obtained as follows:Cu2+>Cd2+>Zn2+. It was found that the effect of heavy metals on the ingestion rates exhibited the order of Cd2+>Cu2+>Zn2+ in the acute toxicity experiment. However, this order was changed to Cu2+>Cd2+>Zn2+ and the ingestion rate of male adult was commonly lower than that of female adult in the chronic toxicity experiment.