Reduction of recruitment of Acartia pacifica nauplii from benthic resting eggs due to organochlorine pesticides

Many estuarine and coastal planktonic copepods depend on the hatching of benthic resting eggs for recruitment ofnauplii to the water column population. The potential effects of two organochlorine pesticides, hexchloriobinzene （HCH） and dichlorodiphenyltrichloroethane （DDT）, on the recruitment of A ccu＇tla 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 LC50 values were 84.81 ng/g for HCH, and 157.94 ng/g for DDT. The median AI （Al50） was -0.77, which suggested that the combined effect of riCH 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.

A potential source of recruitment of Acartia pacifica nauplii: viable benthic resting eggs

Many estuarine and coastal planktonic copepods depend on the hatching of benthic resting eggs for recruitment of nauplii to the water column population. The distribution and abundance of viable resting eggs of Acartia pacifica in the Xiamen Bay were determined by the presence of nauplii in the laboratory. The number of viable eggs var/ed temporally and spatially. The maximum number (9.2×10^4m^-2) of viable eggs was in summer. In spring the average abundance of viable eggs was 5.6×10^4 m^-2. The abundances of viable eggs in fall and winter were similar, respectively 2.7×10^4 and 3.3×10^4m^-2, which were the lowest in the year. The numbers of viable eggs inside the stations of the Xiamen Bay were higher than those outside the stations. The viable eggs were found at all depths (0-10 cm),although not in every station. The maximum number did not necessarily occur in the uppermost centimeter of the sediments but often occurred several centimeters below the water-sediment interface. The accumulation of viable eggs in the seabed of a subtropical bay constitutes a potential source of recruitment of nauplii into the pelagic population.

Heavy metal exposure reduces hatching success of Acartia pacifica resting eggs in the sediment

The potential effects of three heavy metals （Cu, Pb, and Cd） on hatching success ofAcartia pacifica resting eggs in the sediment of Xiamen Bay were experimentally investigated. The number ofA. pacifica nauplii hatched from the sediment sharply decreased with the increase of metal concentration and exposure time from 3 to 30 d. An increase of the Cu concentration from 34.8 to 348 mg/kg, reduced the number of hatched nauplii by 46.6%-100%. An increase of the Pb concentration from 75.2 to 752 mg/kg, reduced the number of hatched nauplii by 21.4%-78.9%. An increase of the Cd concentration from 0.68 to 6.8 mg/kg, reduced the number of hatched nauplii by 31.6%-94.7%. The number of nauplii also significantly decreased with the increase of mixed-metal concentration and exposure time in the mixed-metal test. Trimmed Spearman-Karber analysis gave sediment metal 72-h LC50 values of 1.25 mmol Cu/kg, 1.73 mmol Pb/kg, and 0.054 mmol Cd/kg, which suggested that Cd was the most toxic to A. pacifica resting eggs in the three tested metals. The results indicate that heavy metals with higher concentrations can reduce recruitment of A. pacifica nauplii from benthic resting eggs to planktonic population.

Reduction of hydrocarbon contamination on viability of Acartia pacifica benthic resting eggs

The potential effect of hydrocarbon contamination on the hatching success of benthic resting eggs of Acartia pacifica in Xiamen Bay was investigated experimentally. The number of nauplii emerging from the sediment samples decreased with increasing Fuel Oil #0 concentration. The estimated rate of mortality increased markedly with the increase of Fuel Oil #0 concentration. Successive fuel Oil #0 concentrations from 50 mg/kg to 5000 mg/kg reduced the number of hatched nauplii by 3.8% -100%. The mortality of A. pacifica resting eggs due to Fuel Oil #0 contamination did not significantly increase as time progressed at each concentration level. The LC50 values of resting eggs, changing from 237.12 to 279.59 mg/kg, remained at an almost stable level in two months. The number of A. pacifica nauplii that hatched from the sediment at 10℃ was higher than those from the sediment at 30℃, which indicates that the toxicity of Fuel Oil #0 on A. pacifica resting eggs increases with increasing temperature.

STUDY ON MIXIS POTENTIAL OF ROTIFER RESTING EGGS ( BRACHIONUS PLICATILIS ) WITH DIFFERENT COLLECTION TIMES AND DIFFERENT PRESERVATION PERIODS

The present study investigated the possible changes in the mixis potential of rotifer resting eggs produced by a single stock of Brachionus plicatilis and collected and preserved annually from 1985-1998. Several clones derived from each batch of resting eggs were cultured under the same conditions for 21 days. The percentage of clones appearing resting eggs and the average yield of resting eggs produced from each clone were recorded and statistically analyzed to find the differences between the mixis potential of those resting egg batches. Results showed that different batches of resting eggs had different mictic levels among their descendent clones; but no regular relationship was found between the mixis potential of resting eggs and their collection times/preservation periods. Several internal and external factors that might affect the mixis potential of resting eggs were discussed.

Resting Stages of Crustaceans in the Crimean Hypersaline Lakes(Ukraine) and Their Ecological Role

1 Introduction A presence of resting stages in various aquatic organisms is a long-known phenomenon as a mechanism of species adaptation to exist in unstable aquatic habitats,surviving adverse conditions in the"sleeping"state(Radzikowski,2013).Bank of resting stages of planktonic organisms is an important component of the plankton community,without which we cannot understand community dynamics(Brendonck and De Meester,2003).

Cambrian Fossil Embryos from Western Hunan,South China

The exquisitely preserved fossil embryos of Markuelia recovered from the limestones of the Middle Cambrian Haoqiao Formation and Upper Cambrian Bitiao formation in western Hunan, South China are described and illustrated in detail for the first time. A new species Markuelia elegans sp. nov. is established based mainly on embryos from the Upper Cambrian. A few of animal＇s resting eggs, which are comparable with those of the Ediacaran Doushantuo Formation, have been also found in the Upper Cambrian of western Hunan. The membrane of one egg from the uppermost Cambrian has been replaced by pyrite and the overgrowth of the pyrite crystals exhibits a unique inorganic pattern termed herein ＇Pseudoembryo＇. The taphonomic setting in deeper water with possible strong reducing conditions promoted the excellent preservation for the Markuelia specimens. The study of Markuelia provides not only constraint on the anatomy, affinity, embryonic development and phylogenetic significance of this wormlike animal and but also opens a new window onto the evolution and development of the earliest animals.

Effects of sexual reproduction of the inferior competitor Brachionus calyciflorus on its fitness against Brachionus angularis

Sexual reproduction adversely affects the population growth of cyclic parthenogenetic animals. The density-dependent sexual reproduction of a superior competitor could mediate the coexistence. However, the cost of sex may make the inferior competitor more vulnerable. To investigate the effect of sexual reproduction on the inferior competitor, we experimentally paired the competition of one Brachionus angularis clone against three Brachionus ealyciflorus clones. One of the B. calyciflorus clones showed a low propensity for sexual reproduction, while the other two showed high propensities. The results show that all B. calyciflorus clones were excluded in the competition for resources at low food level. The increased food level promoted the competition persistence, but the clones did not show a clear pattern. Both the cumulative population density and resting egg production increased with the food level. The cumulative population density decreased with the mixis investment, while the resting egg production increased with the mixis investment. A trade-off between the population growth and sexual reproduction was observed in this research. The results indicate that although higher mixis investment resulted in a lower population density, it would not determinately accelerate the exclusion process of the inferior competitor. On the contrary, higher mixis investment promoted resting egg production before being excluded and thus promised a long- term benefit. In conclusion, our results suggest that mixis investment, to some extent, favored the excluded inferior competitor under fierce competition or some other adverse conditions.