PATTERNS IN PELAGIC AND BENTHIC NANOFLAGELLATE DENSITIES IN THE COASTAL UPWELLING SYSTEM ALONG THE BANC-DARGUIN, MAURITANIA

We studied spatial variation in abundance of marine benthic and pelagic heterotrophic nanoflagellates in relation to abundances of autotrophic flagellates, bacteria and cyanobacteria in an upwelling area off the Banc d'Arguin, Mauritania. There was enormous spatial variation in densities. In the sediments these ranged from 8-219 x 10(3) cm-3 for heterotrophic flagellates. Maximum values are in the range of those for temperate shallow marine bottoms. Low densities (< 20 X 10(3)) were confined to the deep stations (> 1000 m). Over the shelf (10-100 m depth) densities were high but related to grain size rather than to concurrent upwelling phenomena or to the abundance of benthic macrofauna. Pelagic flagellate abundance appeared to be more indicative of contemporary hydrographic conditions, most obvious by an increase in the ratio heterotrophic/autotrophic nanoflagellates away from the area of most intense upwelling.