Seasonal variance of salinity tolerance of a copepod Drepanopus bispinosus in an Antarctic littoral saline lake (Burton Lake)

In Burton Lake (an Antarctic littoral saline lake), as one of the overwinter species, the female Drepanopus bispinosus reach adult form in autumn. and early winter.For the subsequent life period of more than eight months, the animals experience such changing environment as increasing salinities from approximately 33 (in May) to 39 (in November). There is a considerable difference of salinity tolerance of female adults between summer and winter populations.Winter collected copepods survived lower salinities than summer collected copepods in this experiment. The upward shift in their salinity tolerance range is related to the development of field acclimation to salinity. Respiration rates of the summer animals showed a visible increase over those of winter copepods in simitar salinity and temperature conditions, thus supporting the above conclusion.

EFFECT OF ENVIRONMENTAL FACTORS ON POPULATION DYNAMECS OF DREPANOPUS BISPINOSUS IN BURTON LAKE, ANTARCTICA

The population dynamics of Drepanopus bispirosus (Calanoida: Copepoda) was studied throughout the year of December 1983 -January 1985 in Burton Lake, a littoral saline lake on Vestfold Hills,Antarctica, and the environmental factors of the lake were observed simultaneously. D. bispinosus is univoltine. Its population life cycle could be in 20-21 months and reproductive activity stays from winter to early summer. The adults (male and female) and nauplii mainly form the winter population. Adult females are instead of male and, copepodites are instead of nauplii in summer population. Then it consists of copepodites mainly in stages II-V from late summer through autumn. The density of population components considerably varies for their whole life time. Most of nauplii appearing in winter may not develop and transform into further stages under the restrictive conditions, such as low oxygen content and scarce food. Earlier stage copepodites of new generation appear largely in summer, when the lake is rich in oxygen content and phytoplankton. The adult females decrease markedly after their reproductive activities, as the sharp salinity diluting in early summer. This density variation of population compositions is mostly related with the changeof en-vironmental factors in the lake. The conception is supported by the data obtained from another saline lake on the Vestfold Hills.

THE STUDY OF ADAPTABILITY OF Drepanopus bispinosus TO TEMPERATURE AND SALINITY IN THE ANTARCTIC BURTON LAKE

The tolerance to temperautre and salinity of a Calanoida copepod: Drepanopus bispinosus from the Burton Lake in the Vestfold Hills, Antarctica, was tested in each season. The results obtained show that the copepod has a marked physiological property of tolerance to low temperature and high salinity, and this property could be strengthened after winter. The response to different temperature and salinity of the copepod evidently expressed the tardy characteristics contrasted with seasons. This means that for a long term in early winter(lower temperature and higher salinity) the animal still has higher tolerance to lower salinity and higher temperature; and it is opposite in early summer. These physiological features are possibly caused by natural acclimatization in the lake. The experimental data were processed and plotted by computer. The correlation of animal’s survival rate with the changes of temperature and salinity presented an approximately smooth surface of a three-degree elliptic sphere.