Nanoflagellates (mixotrophs, heterotrophs and autotrophs) in the oligotrophic eastern Mediterranean@en

The vertical distribution (0 to 100 m) and abundance of nanoflagellates were examined in the oligotrophic Aegean Sea (east Mediterranean) in early spring (south basin) and late summer (north and south basins) of 1997 in the framework of the MATER project (Mass Transfer and Ecosystem Response). Different trophic types of nanoflagellates (mixotrophic, heterotrophic, and phototrophic) were identified based on the possession of chloroplasts and the consumption of Fluorescently Labelled Minicells (FLM). Bacterial production (leucine method) was compared with bacterivory estimated from FLM consumption. We found that mixotrophic nanoflagellates played a small role as bacterivores relative to heterotrophic nanoflagellates and total bacterivory roughly balanced bacterial production. In early spring with cool (14.2°C) well-mixed water columns, flagellate concentrations were lowest, phototrophic flagellates were the dominant group and concentrations varied little with depth. Average concentrations of mixotrophs, heterotrophs and autotrophs were 0.07, 0.34, and 0.64 x 103 cells/ml, respectively. Bacterial production in the 0 to 100 m layer averaged about 0.74 µg C/l/d. Estimated nanoflagellate bacterivory from FLM ingestion accounted for 40% of bacterial production with mixotrophic nanoflagellates consuming 5% of bacterial production. In late summer, total nanoflagellate concentrations were higher. Average concentrations of mixotrophs, heterotrophs and autotrophs were 0.09, 1.14, and 0.66 x 103 cells/ml, respectively, in the southern basin and 0.09, 1.1, and 0.98 x 103 cells/ml, respectively, in the northern basin. In September, bacterial production for both basins roughly balanced estimated nanoflagellate consumption. Similar to the March estimates, mixotrophic nanoflagellates accounted for about 5% of nanoflagellate bacterivory. In a nutrient enrichment experiment in March, treatments including phosphorus resulted in increased bacterial production and reductions in identifiable mixotrophs.1997年，依托MATER项目（Mass Transfer and Ecosystem Response，MATER），研究团队针对东地中海贫营养化的爱琴海海域，分别于春季早期（南部海域）与夏末（南北部海域），调查了0至100米水深范围内微型鞭毛虫（nanoflagellates）的垂直分布特征与丰度。研究基于叶绿体携带情况与荧光标记微型细胞（Fluorescently Labelled Minicells，FLM）的摄食情况，对微型鞭毛虫的不同营养类型（混合营养型、异养型与自养型）进行了区分；同时将采用亮氨酸法（leucine method）测定的细菌生产力，与通过FLM摄食估算得到的细菌摄食水平进行了对比分析。结果显示，相较于异养型微型鞭毛虫，混合营养型微型鞭毛虫在细菌摄食者中所占比例极低；总细菌摄食总量大致与细菌生产力持平。春季早期水体温度较低（14.2℃）且混合均匀，微型鞭毛虫总浓度处于最低水平，自养型微型鞭毛虫为优势类群，其浓度随水深变化幅度极小。混合营养型、异养型与自养型微型鞭毛虫的平均浓度分别为0.07×10³、0.34×10³与0.64×10³个/毫升；0至100米水层的细菌生产力平均约为0.74 μg C/L/d。通过FLM摄食估算得到的微型鞭毛虫细菌摄食量约占细菌生产力的40%，其中混合营养型微型鞭毛虫的摄食量占细菌生产力的5%。夏末时节，微型鞭毛虫总浓度有所升高。南部海域混合营养型、异养型与自养型微型鞭毛虫的平均浓度分别为0.09×10³、1.14×10³与0.66×10³个/毫升；北部海域则分别为0.09×10³、1.1×10³与0.98×10³个/毫升。9月时，两个海域的细菌生产力大致与估算的微型鞭毛虫摄食量持平。与3月的估算结果类似，混合营养型微型鞭毛虫的细菌摄食量约占微型鞭毛虫总摄食量的5%。在3月开展的营养盐富集实验中，添加磷的实验组细菌生产力有所提升，同时可识别的混合营养型微型鞭毛虫数量出现下降。