AME 27:249-259 (2002)  -  doi:10.3354/ame027249

Spatial distribution of ciliates, copepod nauplii and eggs, Engraulis japonicus post-larvae and microzooplankton herbivorous activity in the Yellow Sea, China

Wuchang Zhang1,*, Kuidong Xu2, Ruijing Wan3, Guangtao Zhang1, Tianxiang Meng3, Tian Xiao1, Rong Wang1, Song Sun1, Joong Ki Choi2

1Department of Marine Ecology, Institute of Oceanography, Chinese Academy of Sciences, 266071 Qingdao, PR China
2Regional Research Center for Coastal Environments of Yellow Sea, Inha University, Inchon 402-751, Korea
3Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, 106 Nanjing Road, 266071 Qingdao, PR China

ABSTRACT: The abundance of anchovy Engraulis japonicus larvae, >20 μm ciliates, copepod eggs and nauplii, and microzooplankton herbivorous activity were studied in the Yellow Sea in June 2000. Anchovy juveniles and larvae were found in only 6 of the 19 stations sampled. The ciliate communities were dominated by 2 species: Laboea strobila and Strombidium compressum. In the surface waters, the abundance of L. strobila ranged between 0 and 560 ind. l-1. S. compressum only appeared at Stns 15 to 18 (20 to 3300 ind. l-1). L. strobila was found mainly in the top 20 m. The abundance of L. strobila was less than 50 ind. l-1 in waters deeper than 25 m. S. compressum showed subsurface abundance peaks at the salinity abnormality. Tintinnids occurred occasionally with abundance lower than 100 ind. l-1. The total ciliate abundance fell in the range of 40 to 3420 ind. l-1. The ciliate biomass in the surface water and the water column ranged between 0.15 and 6.76 μg C l-1 and 0.4 and 134.4 mg C m-2, respectively. In the surface waters, the abundance of copepod eggs and nauplii ranged from 0.3 to 3.1 and 1.1 to 15.6 ind. l-1, respectively. The average abundance of copepod eggs and nauplii in 4 depth (0, 5, 10 and 20 m) fell in the range of 0.2 to 2.8 and 1.0 to 29.4 ind. l-1, respectively. As a food item of the E. japonicus post-larvae, the abundance of copepod nauplii and eggs appeared to be low. The abundance peaks of ciliate and E. japonicus post-larvae coincided. Although not found in the gut of E. japonicus post-larvae, aloricate ciliates might be ingested by first-feeding anchovy larvae, preventing initial starvation and prolonging the time to irreversible starvation. On the basis of dilution experiments with positive microzooplankton grazing rates, microzooplankton grazed at rates of 0 to 0.61 d-1. Grazing pressure of microzooplankton on chlorophyll a standing stock (Pi) and potential chlorophyll a primary production (P p) were 17 to 46% and 35 to 109% d-1, respectively.

KEY WORDS: Ciliate · Engraulis japonicus · Microzooplankton · Dilution incubation

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