Planktonic Ciliate Community In Different Areas In The Southern Ocean

The present study investigated the spatial distribution of planktonic ciliates in Prydz Bay,Amundsen Sea and seas near Antarctic Peninsula in the Southern Ocean.We compared ciliate distribution patterns in different areas in Antarctic waters.Our results revealed ciliate distributions in different water masses?Summer Surface Water,Winter Water and Circumpolar Deep Water?,and tintinnid communities in Antarctic Zone,Polar Front and Subantarctic Zone.Meanwhile,we discussed the relationships between the tintinnids and the environment factors.Generally,our study roughly depicted a planktonic ciliates distribution structure in the Southern Ocean.Planktonic ciliates are important microzooplanktons in pelagic ecosystems.The previous studies in Antarctic waters have only investigated the ciliate assemblages in different habitats without considering the water masses.Here,we reported the characteristics of ciliate assemblages in different water masses in open waters near Prydz Bay?East Antarctica?during austral summer.Three water masses were identified according to temperature and salinity:Summer Surface Water?SSW?,Winter Water?WW?and Circumpolar Deep Water?CDW?.Summer Surface Water was further divided into SSW_{Chl a>3}?in vivo chlorophyll a>3?and SSW_{Chl a<3}?in vivo chlorophyll a<3?.Ciliate abundance and biomass in water masses decreased in the order SSW?>649?559 ind./L,>4.96?4.98?g C/L?>WW?228?222 ind./L,1.44?1.35?g C/L?>CDW?94?90 ind./L,0.29?0.33?g C/L?.Summer Surface Water _{Chl a>3} had a higher proportion?38.2%?of tintinnids to the total ciliate abundance and larger aloricate ciliates?ciliates in the 10-20?m size class were<15%of the total aloricate ciliate abundance?than in other water masses.Winter Water had a higher proportion?>30%?of Southern Ocean endemic tintinnid species in total tintinnid abundance than in other water masses.Each water mass had the following indigenous tintinnid species:SSW,Salpingella sp.,Codonellopsis gaussi;WW,Salpingella costata,S.faurei,Cymatocylis convallaria forma drygalskii and Cy.vanhoeffeni.Laackmanniella naviculaefera and Cy.convallaria forma cristallina were present at high abundance in both WW and SSW_{Chl a>3}.Upwelling caused discontinuity of the ciliate distribution.Our results will help predict the spatial and temporal variations of ciliate assemblages and other plankton according to the dynamics of water masses in Antarctic waters.Most of previous studies in Amundsen Sea were in a relatively small latitude range with little information about tintinnid species composition and distribution.In the present study,we firstly investigated the tintinnid assemblages from Antarctic Zone?AZ?northward through Polar Front?PF?to Subantarctic Zone?SAZ?.A total of 17tintinnid species in 7 genera were collected and 16 of them were identified.Nine of them were Southern Ocean endemic species which mainly inhabited in AZ near Antarctic continent with abundance proportion exceeding 60%in total tintinnid.According to tintinnid abundance distribution,tintinnid species were attributed to four groups:Group I including Acanthostomella norvegica,Codonellopsis glacialis,Cd.pusilla and Cymatocylis antarctica mainly occurred in the north boundary of PF;Group II including Cymatocylis convallaria forma calyciformis,unidentified species and Amphorellopsis quinquealata mainly inhabited in PF;Group III including S.costata,Cy.vanhoeffeni,Cy.convallaria forma cristallina,Cy.convallaria forma drygalskii,Cy.convallaria,Cd.gaussi and L.naviculaefera mainly occurred in AZ near Antarctic continent;Group IV including Salpingella sp.inhabited in all zones.We found a new type?Group II?of tintinnid distribution characteristic in Polar Front and large lorica-oral-diameter?LOD?primarily inhabited in AZ.Meanwhile,we figured out distribution ranges of the tintinnid assemblages from AZ to PF and how the different assemblages mixed in PF.Our study could act as a typical example for a better understanding of tintinnid assemblages from Antarctic continent to Antarctic Circumpolar Current in Antarctic waters.Average abundance and biomass of planktonic ciliate in seas near Antarctic Peninsula were 636?936 ind./L and 2.57?3.56?g C/L,respectively.High values of ciliate abundance and biomass were mainly in the upper 50 m,but there was an obvious subsidence in Transect 2.Average abundance and biomass of tintinnid were 18 ind./L and 0.29?g C/L,respectively.Tintinnid distribution patterns varied considerably in different transects.Tintinnid mainly occurred from surface to 300 m layer in the south of Transect 1.Tintinnid sank from surface in the north to 200 m in the south of Transect2,while tintinnid in Transect 3 was on the contrary.In Transects 5 and 6,tintinnid mainly distributed in the surface layer.Aloricate ciliates were dominated in ciliate communities in study area,which determined total ciliates distribution pattern.Sixteen tintinnid species belong to 6 genera were identified,including 6 Southern Ocean endemic species.Neritic genus Tintinnopsis was occurred around Antarctic Peninsula.Sothern Ocean endemic species,which tended occurred in cold water,were dominant in this area.Cy.convallaria forma cristallina and Cy.convallaria were the most abundant species,their average abundances?maximum abundances?were 4.20?74?ind./L and 4.15?63?ind./L.In Principle Components Analysis,the first principle component was closely related to temperature,which had great influence on Southern Ocean endemic species,especially for Cy.convallaria forma cristallina and Cy.convallaria forma drygalskii.Cd.balechi,Cy.convallaria and L.naviculaefera had strongly negative correlations to total nitrogen,nitrate and silicate.The present study investigated planktonic ciliates in a relative complex habitat from Bransfield Strait,Weddell-Scotia confluence area to the South Orkney Islands,and figured out ciliate distribution situations in this area which provided valuable information for further study.