| 1. The euphausiids and salps in the Prydz Bay regionEuphausia superba was mainly distributed in the area between64and67oS. Thedensity varied largely between stations in each cruise, and it changed by almost twoorders of magnitude between the minimum and maximum values. The Antarctic krill,which collected by high speed plankton sampler (HSPS) and Isacca-Kidd Mid-waterTrawl (IKMT), was occurred in all cruises from1999/2000to2009/2010, except for2007/2008. The inter-annual variation of density was large in these years, and themaximum average density of krill, sampled by HSPS was1442.3ind/1000m3or582.6g/1000m3(1999/2000), and the minimum value was58.2ind/1000m3or19.5g/1000m3(2005/2006), respectively, and79.7ind/1000m3or27.9g/1000m3(2001/2002), and1.4ind/1000m3or1.0g/1000m3(2008/2009) for krill collected byIKMT, respectively. The density of krill sampled by IKMT was significant lower thanHSPS, moreover, the maximum and minimum values of krill collected by HSPS andIKMT presented in different years, which were largely caused by the sampling nets,time, location and methods.The population structure of E. superba showed significant variation on the timeseries. The large proportion of juvenile (>10%) occurred in2001/2002,2004/2005and2009/2010populations, indicating the good recruitment in these years. And therecruitment was bad in other years. The3DF and3EF dominated in the2002/2003,2008/2009and2009/2010populations, indicating that the krill had started to spawn.Krill was collected from mid-January to mid-February2003, late-January toearly-March2009and late-December in2009, respectively, which may be thespawning time. In2001/2002and2004/2005seasons, the2F and3AF had a largenumber and the mated females was only a small part in these populations, indicatingthat the populations were under developing periods. The sampling times were almostfrom late-January to mid-February, which indicated that the spawning times were later than this time in these years. The individuals of2F and3AF also had a largeproportion in2005/2006, while3EF also occurred in the population, indicating thepopulation had started to spawn. The maturity stages of larvae were low in1999/2000and2004/2005, and high in2001/2002.Based on the relationship between body length and eye diameter of E. superba,we found that: The growth condition of krill was best in2002/2003and bad in1999/2000. In other years, the krill were under the normal growth condition. Thegrowth condition had correlation with the melting time of sea ice: the good growthcondition was found in2002/2003with early melting time, and bad conditionoccurred in1999/2000with late melting time.The occurrence frequency of salps in Prydz Bay was very low. Two species ofsalps were found in this region.2001/2002,2004/2005and2009/2010seasons, thesalp was Salpa thompsoni and it was Ihlea racovitzai in2002/2003,2005/2006,2007/2008and2008/2009, which presented mainly at the edge of Amery ice shelf.The average value peaked in2002/2003, when it was124.0ind/1000m3, while itwas lowest in2008/2009and2009/2010, when it was2.1and2.2ind/1000m3,respectively. The abundance decreased with the latitude increasing.2. The euphausiids and salps in the Southern Yellow SeaThe results of investigations from September2006to August2007indicated that:The E. pacifica peaked in spring (May) and autumn (October). The adults distributedwidely in the Southern Yellow Sea when the water temperature was low in winter andspring. And the population was presented mainly at the YSBCW area, when the watertemperature was up to20°C in summer and autumn. The larvae occurred in the openare in May, September and December, while it concentrated in the neritic in March,June and August. The larvae dominated in the populations during May and June, andthe adults had a large part in other months. The distribution of E. pacifica related tothe water temperature and they preferred to the waters with temperature ranging from8to16°C in the Southern Yellow Sea. S. fusiformis occurred largely in the Southern Yellow Sea from December2006,and the populations dominated by aggregate forms in each month. The distributionand abundance of both aggregate and solitary forms presented significant seasonalvariation in the Southern Yellow Sea. S. fusiformis was mainly distributed in the openarea in most months, and extended to the coastal area only in June. The bloom of S.fusiformis occurred in May2007, when the abundance of both aggregate and solitaryforms was high,79.7and5.8ind/m3, respectively. The average abundance ofaggregate forms was higher in June, when it was122.8ind/m3, while it decreasedslightly to5.0ind/m3for solitary forms.The diel vertical migration (DVM) of S. fusiformis varied between seasons andregions. At station S1-4, the aggregate forms in December exhibited irregular DVMbehavior in the upper50m, but never reached to the bottom layer (50–70m). Theyconcentrated in the surface layer from noon to sunset, and then migrated to the deeperlayer (10–30m). The solitary forms in this month were too scarce to analyze. In Mayand June, both aggregate and solitary forms showed significant reverse DVMbehavior. They migrated upward to the surface water during daytime and downwardto the bottom at night. At station S3-3, the aggregate forms in December alsoexhibited irregular DVM, which migrated downward at night and reached to thebottom at06:00. And they dominated in the upper20m during daytime. In May, theDVM was not obvious, and both forms concentrated in20–30m layer duringdaytime and mainly distributed in0–20m layer.The average body length of aggregate forms was largest in April (7.85mm) andsmallest in June (3.45mm). For solitary forms, it was largest in December (19.28mm), followed by April (14.24mm), and lowest in May (7.13mm). The developingstage of aggregate forms dominated in their populations in all six months, rangingfrom43.3%(April)–92.2%(March). The newly fertilized (0–7mm) of solitaryforms had high proportion in May, while the immature (15–25mm) and mature (≥25mm) individuals dominated in their populations of December and August. 3. The interaction between euphausiids and salpsIn the Prydz Bay, E. superba and salps generally displayed pronounced spatialsegregation in most years other than2004/2005, when they overlapped in theirdistribution. The spatial segregation was significant between E. superba and S.thompsoni in2001/2002and2009/2010. When the density of S. thompsoni was high,the density of E. superba was low in next year, which related to the sea ice condition.In the Southern Yellow Sea, the E. pacifica and S. fusiformis overlapped indistribution in all months. In May, the negative correlation was significant betweenthe abundance of E. pacifica and S. fusiformis.
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