Calcareous nannoplankton in the surface sediments of the East China Sea and its environmental implications

Calcareous nannoplankton flora in the surface sediments of the East China Sea has been investigated many times based on isolated sample collections since 1980. In the present study, 73 surface sediment samples recovered from the East China Sea, extending from the estuaries to the Okinawa Trough (about 10-2000 m in depth of water), were chosen to investigate the floral distributional pattern and to discuss in greater detail the controlling factors. Thirty-nine species were identified under polarized microscope and SEM. In general, nannoplankton abundance and diversity increase progressively with the increase of depth. In estuaries and the inner shelf nannoplankton are extremely rare. The 50 m isobath is a sharp boundary for the development of calcareous nannoplankton. Another low floral concentration is encountered at the edge of the outer shelf where Pleistocene relict sediments outcrop. The nannoflora displays a scattered distributional pattern in the Okinawa Trough. Nannoplankton of larger sizes is mainly encountered beyond the 100 m isobath.