| Antarctic krill is the main food source of many Antarctic creatures,such as whales,seals,fish and birds,and is called the key species in the Antarctic ecosystem.At the same time,as one of the main sources of animal protein in the world,it has important commercial value and nutritional value,and is the key fishery resource in China.Parasites in the digestive tract of Antarctic krill and their parasitic relationship widely exist in nature.The change of infection intensity and abundance of parasites greatly affects the physiological conditions of Antarctic krill,such as health level,reproductive capacity,growth rate and body size,which leads to the change of population density.Moreover,Antarctic krill,as a low-level consumer in the Antarctic marine ecosystem,the change of its population density plays an important role in regulating and controlling the dynamic changes of the whole ecosystem.Therefore,it is of great ecological significance and guiding role for sustainable development of resources to study Antarctic krill parasites and explore the infection mechanism of parasites.In view of this,this study is based on the fact that the waters of the East Pole are located at 65.2104°S and 145.3198°E,in February 2019;64.793°S,152.10375°E,65.9499°S,147.70315°E;65.8848°S,144.557°E;65.8815°S and 144.5165°E krill were collected by trawl(NET-8).Ten krill were randomly selected from each station,totaling 50 krill.Taking Antarctic krill and its intestinal parasitic gregarines as the research object,the infection rate and infection intensity of gregarines in Antarctic krill were statistically analyzed.The generalized linear model(GLM)method was used to reveal the significant relationship between the number of gregarines in Antarctic krill and the sampling site,body length,weight,sex,sexual maturity and intestinal width.Combined with the eating patterns of Antarctic krill,sampling depth,water mass in the sampling area and the characteristics of slope flow,the physiological changes of Antarctic krill in the southeast pole and the corresponding living environment differences were analyzed.This study can provide reference for further understanding the infection mechanism of gregarines in Antarctic krill,in order to provide scientific data for the effective management and rational development of its resources.The main research results are as follows:(1)The sampling site,body length,sex and sexual maturity,δ13C and δ15N values,niche overlap rate and area,sampling depth(oxygen consumption rate,light intensity)and slope flow of Antarctic krill have a significant relationship with the number distribution of gregarines parasitic in Antarctic krill intestines,but have nothing to do with the weight,average intestinal width and water mass of Antarctic krill.(2)According to morphological identification,the parasite in this paper is gregarines,including immature gamonts and mature gamonts.A total of 57,383 gregarines were detected in all stations,and 47 Antarctic krill were parasitized,with an infection rate of 94%.The distribution of gregarines in Antarctic krill is characterized by high infection rate,wide prevalence and high infection intensity.According to the total number of gregarines in each site,the order is T32 > T24 > T31 > T18 > T33.(3)According to the average body length of Antarctic krill,the order of each station is T24 > T31 > T18 > T32 > T33.The longer the body length of Antarctic krill is,the more gregarines there are.(4)The Antarctic krill in this sample is divided into two parts: male and female,which are divided into 2BF,2CF,2DF,3AF,3BF,3CF and 3DF according to sexual maturity.2BM,2CM,3AM.According to the average abundance of gregarines in each maturity stage,the order is 3BF > 3CF > 2d F > 3d F > 2BM > 3AF > 2CF > 2BF >2CM > 3AM.According to the number of Antarctic krill samples in each maturity stage,the order is 3BF > 2CF = 3CF > 2d F > 2BM > 2CM > 3AF > 2BF = 3d F > 3AM.The total number of gregarines in female Antarctic krill is higher than that in male Antarctic krill.The higher the degree of sexual maturity,the greater the gregarines content in the body.(5)According to δ13C value and δ15N value,the order is T32 > T18 > T24 >T31 > T33;T32 > T31 > T24 > T18 > T33.The abundance of gregarines in Antarctic krill increased with the increase of δ13C and δ15N,showing a positive correlation.(6)The niche area of Antarctic krill samples in this study is T18(SEA = 4.877,SEAc = 5.487,TA = 9.398)> T31(SEA = 2.969,SEAc = 3.340,TA = 5.345)> T33(sea=2.352)TA=3.863)>T24(SEA=1.550,SEAc=1.744,TA=2.458)>T32(SEA=0.688,SEAc=0.774,TA=1.351).The niche overlap between T18 station and T24,T32and T33 is 8.5%,13.5%and 9.1%,respectively.The overlap rate between T24 and T31sites is 21.9%.The overlap rate between T24 and T32 sites is 0.2%.There is overlap space between all sites,with the minimum value of 0.2%and the maximum value of13.5%.Site T32 has the smallest niche area and the largest total number of gregarines,but this site only overlaps with one site with the smallest overlap rate,so it is necessary to comprehensively consider the influence of various values of niche on gregarines distribution.(7)Sampling depth affects the distribution of gregarines among stations,and the stations are ranked according to the sampling depth: T32 < T24 < T18 < T31 < T33.With the increase of sampling depth,the dissolved oxygen concentration and light intensity in water samples decreased,the dissolved oxygen decreased,the oxygen consumption rate of Antarctic krill decreased,and the total amount of gregarines in the site decreased.(8)Antarctic krill and gregarines are distributed around the South Pole,and their distribution is influenced by ocean circulation,sea ice dynamics,phytoplankton species and their abundance,etc.The sampling site is close to the Antarctic shelf area,and the distribution of gregarines in Antarctic krill is affected by the Antarctic Slope Current.(9)There are three types of water masses in the sampling waters from the sea surface to the depth below 300 m,which are Antarctic Summer Surface Water,Winter Water and Circumpolar Deep Water.The water masses in the sampling depth are winter water,and the water masses have no effect on the distribution difference of gregarines.(10)The reasons that affect the distribution difference of gregarines are mainly divided into biological factors and abiotic factors.The result is never the result of a single factor but the interaction of many factors.It can only be said that a certain reason accounts for a larger proportion in the process of influence.For parasites,especially this single-host parasite,the physiological change of krill is the main reason for the distribution difference of gregarines compared with the difference of rings. |
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