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 pelagi c heterotrophic nanoflagellates in relation to abundances of autotroph ic flagellates, bacteria and cyanobacteria in an upwelling area off th e Banc d'Arguin, Mauritania. There was enormous spatial variation in d ensities. In the sediments these ranged from 8-219 x 10(3) cm-3 for he terotrophic flagellates. Maximum values are in the range of those for temperate shallow marine bottoms. Low densities (< 20 X 10(3)) were co nfined to the deep stations (> 1000 m). Over the shelf (10-100 m depth ) densities were high but related to grain size rather than to concurr ent upwelling phenomena or to the abundance of benthic macrofauna. Pel agic flagellate abundance appeared to be more indicative of contempora ry hydrographic conditions, most obvious by an increase in the ratio h eterotrophic/autotrophic nanoflagellates away from the area of most in tense upwelling.