Distributions And Hatching Characteristics Of Zooplankton Resting Eggs In Baisha Bay, Shantou City And Guishan Island, Zhuhai City

The physicochemical parameters of the different marine ecological types,zooplankton community structure, distribution and hatching success of zooplanktonresting eggs in the sediments were investigated by in situ survey and the enclosureexperiments in Baisha Bay, Nanao, Shantou City and Guishan Island, Zhuhai City.The main results were included as following:1. In Baisha Bay, the dominant species of zooplankton were Paracalanusparvus, Paracalanus gracilis sp. nov., Oithona brevicornis, Oithona rigida,Corycaeus sp., Microsetella norvegica, Euterpina acutifrons and Tintinnopsis radix,while the dominant species in Guishan Island were Euterpina acutifrons, Oncaeavenusta, Oithona nana, Oithona rigida and Paracalanus parvus.2. In Baisha Bay, the highest average contents of TN, TP and TOC werein surface sediments of fish culture area (1666mg/Kg,3245mg/Kg,1.49%),while the lowest average contents of TN and TP were in the Gracilarialemaneiformis culture area (1000mg/Kg,679mg/Kg), and the lowest averagecontent of TOC showed in the control area (0.98%). The potential ecological risk of heavy metals was at a low level in the investigated areas. The pollutionof Pb was heavier and its accumulating coefficients reached the middle pollution level which was ranged1-3in the sediments. The risk indices of fish and shellfish culture area (30.2and28.9) were higher than those of control area and Gracilaria lemaneiformis culture area (27.1and20.4), respectively.In Guishan Island, the highest content of TN was in the surface sediments offishing boats docked area, S11(5900mg/Kg), while the highest contents of TP andTOC was in the culture area, S8(2212mg/Kg,1.79%). The contents of TN, TP and TOC at S3(600mg/Kg,204mg/Kg,0.79%) were the lowest, which was far awayfrom the culture area. The potential ecological risk of heavy metals was at a low levelin the investigated areas. The pollution of Cu, Pb and Zn was heavier and theiraccumulating coefficients were more than1. The risk indices of culture area and thehuman living adjacent areas were higher (53.05) than that of other areas in GuishanIsland.3. In Baisha Bay, the potential recruitment of eggs into the planktonic populationfrom surface sediments in autumn (October2012) was higher (9.44×105ind./m3) thanthat in winter (February2012)(5.55×105ind./m3). The abundances of resting eggs atcontrol area and Gracilaria lemaneiformis culture area were higher than that of thefish culture area and shellfish culture area. In vertical distribution study, the potentialrecruitment of copepod eggs was higher in the0-4cm layer, and the potentialrecruitment of rotifer eggs was highest in the6-8cm layer.In Guishan Island, the potential recruitment of zooplankton eggs into theplanktonic population from surface sediments in the two islands junction area (4.9×106ind./m3) was more than that in culture area and the human living adjacent areas(9.44×105ind./m3). The number of resting eggs from surface sediments were variousin different seasons. During summer and autumn (8-11months), there was adecreasing tendency in the potential recruitment of resting eggs in surface sediments,but an increasing tendency in winter.4. Statistic analysis showed that in Baisha Bay and Guishan Island the abundanceof the resting eggs in sediments was negatively correlated to depth of water. In BaishaBay, the abundance and distribution of resting eggs in surface sediments was mainlyaffected by aquaculture and human activities, however in Guishan Island, it wasmainly influenced by the changes in erosion of rocks.5. Heavy metals(Cu, Zn, Cd), temperature, salinity and pH had a large impact onthe resting eggs hatching. With the increasing of concentration and exposuring time ofCu, Zn and Cd, the number of nauplii hatched from resting eggs reduced and themortality of resting eggs increased. As the increasing of temperature, salinity, pH, thenauplii number hatched from resting eggs increased. It is unsuitable for nauplii hatching when the temperature was higher than25℃, salinity was above30‰andpH was above8.6. The research of resting eggs hatching from surface sediments in GuishanIsland found that the number of nauplii hatched from resting eggs under longrefrigerated time (10months) was more than that under short refrigerated time (twoweeks). The results of in situ germination experiments in seawater showed that thenauplii could be hatched from resting eggs in0.5m,1m and2m water depth, but theamount significantly reduced with deeper water depth and lower illuminationintensity.