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Many estuarine and coastal planktonic copepods depend on the hatching of benthic resting eggs for recruitment of nauplii to the water column population. The potential effects of two organochlorine pesticides, hexchloriobinzene (HCH) and dichlorodiphenyltrichloroethane (DDT), on the recruitment of Acartia pacifica nauplii from benthic resting eggs in the seabed of Xiamen Bay were experimentally investigated. The abundance of A. pacifica nauplii hatched from the sediment significantly decreased with the increase of pesticide concentration. Trimmed Spearman-Karber analysis gave sediment 96-h LC_{50} values were 84.81 ng/g for HCH, and 157.94 ng/g for DDT. The median AI (AI_{50}) was -0.77, which suggested that the combined effect of HCH and DDT showed a weak effect than individual effects. There was a positive relationship between mortality and exposure time in DDT treatment, while the relationship was not significant in HCH treatment. The results suggest that organochlorine pesticides can reduce recruitment of A. pacifica nauplii from benthic resting eggs to planktonic population. [ABSTRACT FROM AUTHOR]

The seasonal variations in diel production pattern, and egg hatching time of the copepod Centropages tenuiremis in Xiamen waters, China, were investigated between January and June of 2003. The results show that in the winter–spring (January to early May) the adult females tended to lay subitaneous eggs at night, while in the beginning of summer (late May–June) they tended to lay diapause eggs as well as subitaneous eggs during the daytime. The egg hatching time negatively correlated with water temperature. These results, combined with the fact that C. tenuiremis migrates vertically in Xiamen waters, may explain the reproductive strategy of this dominant species in winter–spring. [ABSTRACT FROM AUTHOR]

The respiration and the isoenzymes of subitaneous and diapause eggs of Centropages tenuiremis in Xiamen waters of China were investigated. The results demonstrated that the average oxygen consumption of subitaneous eggs was lower than that of diapause eggs during the pre-diapause stage. The character of respiration in diapause eggs was as follows: the oxygen consumption quickly rose after spawning, and reached a maximal value, then gradually declined to a lower value that was maintained at a lower value (∼20% of the maximal value), the low value of oxygen consumption in diapause eggs was lower than that in subitaneous eggs at the same temperature (∼70%). The experimental results also indicated that among subitaneous, diapause and pre-diapause eggs of Centropages tenuiremis, the pre-diapause eggs were the most sensitive to temperature, the diapause eggs were the most insensitive; the sensitivity of subitaneous eggs to temperature was intermediate. The results also showed that there are obvious differences of isozyme patterns in malate dehydrogenase (MDH), sorbitol dehydrogenase (SDH), superoxide dismutase (SOD) and esterase (EST) between subitaneous eggs and pre-diapause eggs, and the characteristic enzyme bands for pre-diapause eggs were shown to be as follows: MDH61, MDH81, SDH41, SDH60, SOD97, EST48, EST59 and EST61; for subitaneous eggs: MDH59, SDH70 and EST93. [ABSTRACT FROM AUTHOR]

The egg production rate (EPR) and the effects of environmental variations on diapause induction in the copepod Centropages tenuiremis in Xiamen waters were studied in 2002 and 2003. The EPR ranged from 7.33 ± 8.14 (on 18 February 2003) to 91.08 ± 20.61 (on 6 June 2003) eggs female−1day−1 (mean ± 95% confidence limits), and displayed a significant seasonal pattern. Before the period of maximum egg production, EPR increased with seawater temperature and chlorophyll a concentration; but after the maximum, no significant relationship was found between EPR and chlorophyll a concentration, and there was a negative linear relationship between EPR and temperature. Seawater temperature and photoperiod, respectively, played a primary role in the switch to diapause egg production by the females as shown by single-factor probit analysis. However, the difference in effect between the two factors was demonstrated by binary logistic multivariate analysis. These results suggest that this copepod rapidly increases subitaneous EPR by taking full advantage of conditions in favorable seasons (winter and spring). Subitaneous EPR decreases and there is a switch to the production of diapause eggs that survive in the bottom sediments during unfavorable seasons (summer and autumn) in Xiamen waters. [ABSTRACT FROM AUTHOR]