Temporal Dynamic Distributions of Coccolithophorids in Water Column on Continental Shelf Break of the Southern East China Sea

This study is to quantify the dynamic distribution of coccolithophorid assemblages at a single site (25o42.3­ÝN, 122o28.8­ÝE) on the shelf-break of the southern East China Sea where the internal tide is conspicuous. Particle samples from six water-depths at 0, 20, 30, 50, 70 and 100 m were filtered at 12:00, 18:00 and 21:00 Nov. 12 and 00:00 Nov. 13, 1995 and investigated. The biomasses of coccolithophorid ranged from 78.6 x 102 to 444.0 x 102 cells l-1. The lowest biomass was recorded at 100 m at 18:00 and 00:00, while the largest one occurred at 30 m at 21:00. During the monitoring period, light-cycle, growth and herbivore feeding showed little influence on the vertical distribution of coccolithophorids. To unravel the effects of internal tide on the distribution pattern of coccolithophorids, a triangular coordinate diagram was constructed following Okada (Utrecht Micropaleontology Bulletin 30, 271-285, 1983) and Winter et al. (Coccolithophores, 161-177, 1994) to categorize the coccolithophorid assemblages into three groups. The triangular diagrams show that the floral compositions of the surface water were relatively static, while that of the water column between 20 and 100 m displayed complicated dynamics in corresponding to tidal currents and concomitant temperature variations. It is evident that the internal tide caused strong effects on the vertical distribution of coccolithophorids in the study area.