Reproductive Biology Of Schmackeria Poplesia And Its Use In Ecotoxicological Study Of Bis(Tributyltin) Oxide

Tributyltin(TBT) is one of the most toxic organotin type and has been used extensively. Tributyltin is so effective as a biocide and its toxicity is non-specific. It has a high bioaccumulation factor and a persistence that poses a great problem to the marine environment. Crustacean zooplankton such as copepods form the keystone link between primary producers and fish stocks, making it critical to understand their responses to toxic pollutants in marine. In this paper, we established a multi-generation cultivation system for colanoid copepod Schmackeria poplesia, and investigated the responses of S. poplesia to bis(tributyltin) oxide (TBTO). The main conclusions as follows:1. To produce copepods in large quantity and nutritional, developmental and genetic uniformity, experiments were carried out to manipulate and control egg production in females. Results showed that Isochrysis galbana was a more efficacious diet, and a 2:1 mixed diet of I. galbana and Phaeodactylum tricornutum in a density of 5×104 cells ml-1 was recommended in multi-generation culturing system and life-cycle toxicity tests. In addition, by starvation and reintroduction of food as well as timed collection, the production of copepods can be well controlled.2. The female reproductive system of S. poplesia consists of a single ovary with two diverticula, and we established a classification system of four ganad maturation stages. During a spawning cycle, distinct modifications of the gonad morphology were observed, while the ovary did not change, neither in size nor in cytological composition. Environmental factors such as temperature and salinity can significantly affect the development and reproduction of S. poplesia. At higher salinities, the survival increased, and the development was delayed. While at higher temperatures, the survival decreased and the development was advanced. So we should make invariable conditions in the exposed tests for reproducible work.3. The acute exposure test revealed that S. poplesia was very sensitive for TBTO exposure. The 96h-LC50 value for females was 0.42μgTBTO l-1, and no sex-specific differences were observed. The effects of temperature, salinity, food concentration and copepod density were detected for TBTO exposures. The results shows that increase in temperature increased the toxicity of TBTO, but the effect of salinity was more complex. Low salinity and high salinity increased mortality of S. poplesia. In addition, food concentration and copepod density have significant effects on the mortality of copepods. Therefore, the eco-toxicity tests should be conducted at a range of environmentally realistic regimes, as this will enhance the sensitivity of the test and improve the safety margin in line with the precautionary principle.4. Life-cycle exposure tests are essential method for risk assessment. The survival, development and reproduction of S. poplesia are affected when exposed to TBTO for three generations. The results indicate that nauplii are more sensitive than copepodites, and the survival of copepods exposed to 5 ngTBTO l-1 was decrease. The female-to-male ratio in F1 and F2 generations exposed to 20 ngTBTO l-1 concentration were significantly reduced. The first egg sac for females and the fecundity was not affected, while in higher TBTO concentration treatments, there were some females couldn't produce egg sacs or aborted. Histological examinations suggest that the exposure to TBTO block the posterior end of the diverticula and inhibit the production of egg sacs. A full explanation of the effect of TBTO on copepods requires further investigation.5. A modified Euler-Lotka equation was used to calculate a population-level endpoint, the intrinsic rate of natural increase, from individual life-table endpoints, i.e. mortality rate, time of release of first brood, sex ratio, the fraction of ovigerous females among all females as well as the number of nauplii per ovigerous female. The intrinsic rate of natural increase of S. poplesia was significantly decrease when expose to TBTO concentrations higher than 20 ngTBTO l-1. Compared with individual life-table endpoints, the population effects the relatively weak. While a more sensitive end-point does not necessary have to be more ecologically relevant than a less sensitive endpoint. The results of colony exposure tests reveal a similar phenomenon that the population exposed to higher than 20 ngTBTO l-1 concentrations decline. The results from the present study demonstrate that ecologically relevant toxicity data on population dynamics can be gained from a relatively short and cost-effective full life-cycle toxicity test, which can improve the assessment of ecosystem risk of chemicals.These results show that the colanoid copepod Schmackeria poplesia is sensible for toxic pollutants such as TBTO, and is a promising species for use in ecotoxicology test. The full life-cycle toxicity test combined with the study of population growth rate structure can indicate the toxicity of pollutants more effectively.