| Nanoflagellates and ciliates, the key intermediates between the ‘microbial’ andthe ‘classical’ pathway, play an important role in nutrient and carbon cycling inpelagic systems. However, their role during jellyfish bloom remains unexplored. Weinvestigated the changes of the community structure and distribution of planktonicnanoflagellates and ciliates based on samples collected from the12transects in theYellow Sea and East China Sea in April and August of2011. The nanoflagellates andciliates were studied using DAPI epifluorescence microscopy and the quantitativeprotargol stain, respectively. The potential relationship between the nano-andmicrozooplankton and the jellyfish (Rhopilema esculentum Kishinouye) occurrence insummer was discussed.Our study showed that the abundance of nanoflagellates was high in the coastalarea and decreased towards the offshore area. The high abundance was likelyattributed to the distribution of high value of nutrients in this area, which wasinfluenced by Changjiang River diluted water, and was extended to the offshore areaalong the transect L with the extension of the influences of the Changjiang Riverdiluted water in summer. Vertically, nanoflagellates were mainly distributed in thesurface and near the bottom layers of water. Compared with those in spring (604±405cells/ml,19.98±17.68g C/L), the total abundance and biomass of nanoflagellatesslightly increased in summer (779±866cells/ml,20.26±20.53g C/L), with thecontribution of heterotrophic nanoflagellates increased from28%in spring to37%insummer.Among the51ciliate taxa identified,35taxa of aloricate ciliates belonging to19genera contributed to95%of total ciliate abundance, and tintinnids (12genera,16taxa) contributed to the rest. Different from that of nanoflagellates, the abundance ofciliates increased from the inshore to offshore area. Vertically, ciliates in the surfacelayer contributed up to80%of the total abundance and abruptly decreased below the30m depth. Statistical analyses showed that the species number was significantlypositively correlated with temperature and negatively with salinity and water depth.The distribution of ciliate community was consistent with the water mass, with anobvious change from spring to summer. We indicate that the change in the pattern oftemperature, salinity and Chl a affected by different water mass in spring and summerwas the major factors resulting in the distribution of ciliates in the Yellow Sea and East China Sea. Compared to those in spring (4258±4151cells/L and12.43±24.36gC/L), the overall ciliate abundance and biomass (4812±5953cells/L and16.90±29.90g C/L) slightly increased in summer. The ciliate abundance at transects where therewas no jellyfish observed increased by about100%-200%from spring to summer,while certain transects such as transect I got a sharp increase by10times in ciliateabundance. By contrast, at transects where jellyfish occurred there was a tendency ofciliate decrease in abundance, and consequently resulted in the increase ofnanoflagellates. Our study indicates that jellyfish as top predators may cause directand indirect changes to nano-and microzooplankton through cascading effects. Theobvious decrease of ciliates at the transects E、G and PN was likely attributed to thepredation pressure from increasing jellyfish.In addition, the quantitative protargol stain (QPS) method yielded a highertaxonomic resolution and higher abundance for ciliates than the traditional Uterm hlmethod. For example, the ciliate abundance detected from the Changjiang Riverestuary was almost5times higher than previously reported. We indicated that thetraditional Uterm hl method would underestimate the abundance of small ciliates,especially the nano-ciliates which contributed to about39%and57%of the totalciliate abundance in spring and summer, respectively. The QPS method could providemore details about species-abundance information via taxa identification andclassification with much higher taxonomic resolution. |
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