Ecological Studies Of Planktonic Ciliates In China Seas

Marine planktonic ciliates mainly include subclass Choreotrichia and Oligotrichia. They are unicellular and eukaryotic protists in the size range of 10-200μm. They are abundant and ubiquitous with average abundance 102-103 ind. L-1 in various marine habitats. As one of the major components of microzooplankton in the pelagic ecosystem, ciliates play a key role in the transfer of carbon and energy through microbial food web to classical food chain, acting as top-down consumer of, pico-, nano- plankton and other primary producers and as a food source for mesozooplankton (e.g. copepod).Ecological researches of planktonic ciliate in the coastal area of China seas are limited. Basic data of ciliate abundance and biomass is scarce in the South China Sea; those in the East China Sea are scattered. There is no research on the spatio-temporal variability of ciliate abundance and biomass during blooms and much less reports on grazing impact of ciliate. In this study, abundance, biomass and distribution of planktonic ciliate were investigated in the South China Sea and East China Sea. Influence of different water masses on distribution of ciliate abundance was studied in the East China Sea. Spatio-temporal variability of ciliate abundance and biomass during spring blooms was investigated in the Yellow Sea. In addition, incubations were carried out to study the grazing of microzooplankton on phytoplankton and nanoflagellate, the grazing of copepod (Calanus sinicus) on ciliate.Ciliate abundance and biomass in different seas In the northern South China Sea in October, 2007, ciliate abundance ranged from 0 to 5757 (on average 848±776) ind. L-1, of which dominant aloricate ciliates occupied 91.9±9%. The biomass of all ciliates was 0-2.09 (on average 1.2±1.54)μg C L-1, of which aloricate ciliates (on average 0.94±1.27μg C L-1) occupied 78.6μ23.8% to the total. Forty-nine species of tintinnids in 16 genera were identified. Genus Tintinnopsis was dominant in abundance. Ciliates mainly distributed near coastal shallow waters which was warm and less salty with more Chl a concentration. The maximum abundance of ciliate in the study was higher than those in other parts of China seas.In the Changjiang River Estuary and its adjacent sea, ciliate abundance ranged from 0 to 4163 (on average 718±571) ind. L-1 and the biomass ranged from 0.00 to 64.88 (on average 1.86±6.34)μg C L-1 in August 2006; the ciliate abundance ranged from 35 to 1155 (on average 358±235) ind. L-1 and the biomass ranged from 0.00 to 9.23 (on average 0.5±1.15)μg C L-1 in October 2006. Higher surface and integrated abundance and biomass of ciliate occurred in the coastal water in the eastern of Changjiang River mouth and Hangzhou Bay mouth in August. However, those occurring in the offshore in October were higher in the northern than in the southern part. The contribution of tintinnid to total biomass in October was slightly higher than in August. Influence of dissolved oxygen (DO) concentration on the vertical distribution of ciliate abundance and biomass was not significant.In the shelf areas of East China Sea, ciliate abundance and biomass ranged from 0 to 1795 (on average 208μ266) ind. L-1 and from 0 to 2.36 (on average 0.28μ0.35)μg C L-1, respectively, in autumn (11.19-12.23), 2006. Ciliate abundance and biomass were in the range of 0 to 22695 (on average 524μ1990) ind. L-1 and 0 to 10.87 (on average 0.47μ1.01)μg C L-1, respectively, in winter (2.22-3.11), 2007. In autumn, ciliate abundance and biomass in the outer and middle shelf were higher than in the inner shelf. However, in winter, more ciliates occurred in the middle shelf than in the outer and inner shelf. Aloricate ciliates were dominant in the abundance in both autumn and winter, but contribution of tintinnid to total biomass was higher than aloricate ciliate in autumn. Small ciliates (ESD 10-20μm) accounted for 63% and 82% in abundance in autumn and winter, respectively. In comparison with reports in the 1990s in East China Sea, no distinct variation on ecological distribution of planktonic ciliates was found.Distribution of ciliate abundance in relation to water massesIn the East China Sea, distribution of ciliate abundance was affected by different water masses. In August (summer) 2006, average surface ciliate abundance (972±746 ind. L-1) in the Changjiang Diluted Water (CDW) was higher than in the offshore Shelf Mixing Water (SMW) (475±345 ind. L-1) in the Changjiang River Estuary and its adjacent sea. Salinity variation had important effects on the spatial pattern of surface ciliate abundance in the SMW.In February-March (winter) 2007, average surface ciliate abundance in the SMW (452μ645 ind. L-1) was higher than in the Kuroshio Water (202±170 ind. L-1) and the Coastal Water (CoW) (209±307 ind. L-1) in the shelf area. Integrated ciliate abundance of 0-30 m in the SMW was not only significantly and negatively correlated with salinity, but also positively correlated with Chl a concentration.Ciliate distribution was characterized by increase of abundance close to the frontal areas. Most tintinnids identified as neritic species did not show discrimination of distribution between two water masses in the Changjiang River Estuary in summer. However, there were pronounced distribution zones of tintinnid species and some occasional species might indicate the intrusion route of Kuroshio Water on the continental shelf in winter.Variability of ciliate integrated biomass during spring blooms in the Yellow SeaCiliate and Myrionecta rubra abundance and biomass responded differently to various phytoplankton blooms.Ciliate integrated biomass at representative diatom bloom station in 2006 was higher than the maximum integrated biomass during blooms in 2007 and 2009. In 2007, diatom blooms at three stations (St. BM1, St. BM2 and St. BM3) were found. At St. BM1, maximum abundance of M. rubra was up to 2.9×105 ind. L-1. During the bloom of St. BM1 and St. BM2, M. rubra abundance and integrated biomass sharply decreased. Non-Myrionecta ciliates daily average integrated biomass decreased. Average integrated biomass of M. rubra was higher than ciliate during the bloom of St. BM1 and St. BM2, but during the bloom of St. BM3, integrated biomass of M. rubra with low abundance was lower than ciliate.In 2009, M. rubra abundance was low during the diatom bloom with Euglena sp. occurring in the maximum abundance 3.5×104 ind. L-1. Average integrated biomass of ciliate that was much higher than M. rubra increased at the end of bloom. During the dinoflagellate and diatom mixed bloom, average integrated biomass of M. rubra was higher than ciliate. Daily average integrated biomass of ciliate and M. rubra reached a peak on the fourth day and then declined.Grazing of microzooplankton on phytoplankton and nanoflagellateIn April 2007, phytoplankton growth rate (1.18 d-1) and microzooplankton grazing mortality rate (0.76 d-1) at bloom St. BM1-1 were higher than those at the post-bloom and non-bloom stations. Microzooplankton daily grazing impact on primary production at St. BM1-1 was lower than post-bloom and most of non-bloom stations. Average integrated biomass of ciliate and Gyrodinium sp. during the bloom were not higher than those at non-bloom stations. Therefore, the top-down control of microzooplankton on spring bloom might be not significant.In May 2007,ciliate abundance kept a proportional relationship with dilution factors after incubation in the dilution incubations while flagellate abundance increased in the more diluted series at both eutrophic and oligotrophic stations in the southern Yellow Sea. Microzooplankton grazing rate on flagellates was higher in the eutrophic water (1.01 d^-1) than in the oligotrophic water (0.42-0.44 d^-1). In the eutrophic water, most of the flagellate production (99%) was grazed by microzooplankton. In the oligotrophic water, only 72-73% of the flagellate production was grazed by microzooplankton. Grazing of Copepod on ciliateIn April 2009, clearance rates of ciliates and M. rubra by C. sinicus (155 ml copepod^-1d^-1, 252 ml copepod^-1d^-1) during the course of bloom (St. B20-29) were higher than those at the end of bloom (St. B20-85, 20 ml ind.^-1d^-1, 147 ml ind.^-1d^-1) and at non-bloom stations (St. B31, 98 ml ind.^-1d^-1, 79 ml ind.^-1d^-1), respectively. Daily grazing pressures on ciliate (83.3%) and M. rubra (94.6%) during the bloom (St. B20-29) were higher than those at non-bloom station (67.8%, 59.8%) and at the end of bloom (20.9%, 81.7%), respectively. Copepod grazing may be an important factor in the variability of ciliate biomass during the bloom.In May 2007, C. sinicus additions in the incubation significantly reduced ciliate abundance at the oligotrophic stations in the the southern Yellow Sea. Heterotrophic flagellates did not increase while Synechococcus abundance.increased significantly. Therefore, there was no trophic cascade along the copepod-ciliate-flagellate food chain. Ciliates might be the dominant grazers of Synechococcus.