Study On Waterbirds To Disperse Resting Eggs Of Zooplankton

Many plants and invertebrates rely on internal transport by animals for long‐distance dispersal.Waterbirds play an important role on dispersal by endozoochory for zooplankter resting eggs.Although some progress has been made in the study of the dispersal function of waterfowl,it is still in the preliminary stage as there is little evidence of dispersal and the research object is single.At present,the research is mainly focused on Europe and Africa,while the Asian region is still blank.This study first studied the ability of shorebirds to carry zooplankton resting eggs in the wetland of Chongming Dongtan,Shanghai.Then we analyzed the hatching mechanism of zooplankton resting eggs in heron feces.At last,by feeding experiment research,we studied the effects of intestinal alterations on the endozoochory ability for resting eggs of mallard.The results showed that migratory water birds could disperse the resting eggs of zooplankton,and the mechanism of the dispersal of the resting eggs of zooplankton by water birds and zooplankton was preliminarily explored.1.Carrying effect of shorebirds on small aquatic organisms in Chongming Dongtan wetlandIn order to identify and quantify dispersal capacity of zooplankton resting eggs by shorebirds through ectozoochory and endozoochory,we analyzed the presence and average abundance of resting eggs of zooplankton in the body surface and feces of water birds,but also the ability of waterbirds to carry phytoplankton and invertebrates to comprehensive analysis of waterbirds carrying capacity of aquatic organism.A total of 6322 phytoplankton from 5 taxa,287 adult invertebrates from 12 taxa and 20 resting eggs from 7 species were recovered from 746 samples.The results showed that bird species,bird weight,season and carrying location had significant effects on the abundance and presence of aquatic organisms in body surface samples.A total of 1003 phytoplankton from 5 taxa,280 adult aquatic organisms from 10 taxa and 103 resting eggs from 14 taxa were recovered from 520 fecal samples.The statistical results showed that there were significant differences in the abundance and presence of aquatic organisms in feces among different seasons,bird species and fecal sampling methods.Comparison of fecal and body surface samples showed that the abundance of adult phytoplankton and invertebrates in body surface samples was greater than that in fecal samples,while the abundance of resting eggs was less than that in fecal samples,but the two carrying modes were complementary.2.Study on hatching ability of resting eggs in feces of waterbirdTo study the number and type of dormant zooplankton eggs in the faeces of waterbirds and their hatching.In this study,resting eggs in heron feces were identified and counted.Meanwhile,the hatching rate of resting rotifer eggs in feces and sedimentary samples from the sampling area was studied,and the effects of temperature,light hours and salinity on the hatching rate of resting rotifer eggs were tested.A total of 249 Heron feces samples were collected from November to January in Fengxian,Shanghai,and 526 resting eggs were recovered,among which 363 dormant eggs of Brachionus accounted for the largest proportion.Statistical results showed that the abundance and hatching rate of resting eggs had no significant difference between different months,the experimental of salinity results show that salinity had a significant negative impact on resting eggs from faeces and sediments,sediments resting egg hatching rate significantly greater than in feces,temperature and light time experimental results showed that the light times,temperature and the interaction between them had no significant effect on resting eggs hatch.3.The influence of digestive tract traits on aquatic organisms in waterbirdsThe capacity of disperse is largely influenced by the action of the digestive tract.Omnivorous birds adjust their digestive tract morphology to seasonally variable diets.We performed feeding trials in waterfowl to clarify how changing digestive tract caused by changes in food composition affects dispersal potential.We subjected captive mallards to mimics of summer(animal‐based),winter(plant‐based)diets,and analyzed gut passage of resting eggs before and at 1,2 and 4 months after the treatment.The results showed that the increase of animal-based food in the diet of mallard ducks in a short period of time resulted in an increase in the size of small intestine and gizzard,and significantly affected the retention time of resting eggs in gut.Compared with the plant-based food mallards,the retrieval rate and hatching rate of the resting eggs after passing through the gut of the animal-based mallards were not significant.But the retention time in the digestive tract was significantly shorter.The analysis of the resting eggs in various parts of the digestive tract showed that the number of resting eggs in the digestive tract of the mallard was small after 3 hours of ingestion,most of which were distributed in the muscle stomach and small intestine,but no resting eggs were found in the Proventriculus.The results of this study demonstrate that the digestive tract of waterbirds is significantly changed under the change of food composition,which affects the maximum distance of resting egg long-distance dispersal by waterbirds.