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

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