PRIMARY PRODUCTION AND DISTRIBUTION OF PHYTOPIGMENTS IN THE WATER COLUMN AND SEDIMENTS ON THE UPWELLING SHELF OFF THE MAURITANIAN COAST (NORTHWEST AFRICA)

In May 1988, water and sediments of the shelf area off the Banc d'Argu in were studied for plant pigments and organic carbon. Phytoplankton p rimary production was also measured and sedimentation of organic matte r was estimated using moored sediment traps. On the basis of simultane ous hydrographic measurements, two water types could be distinguished. Upwelling water covered the southern shelf and the outer part of the northern shelf. The other water type had more coastal characteristics and covered the inshore part of the northern transect. The distributio n of chlorophyll a and particulate organic carbon conformed with the d istribution of the two water types. A similarity analysis of the pigme nts from the sediment traps showed a difference in the composition of the algal material depositing from the two water types. The primary pr oduction was also found to be distinctly different, i.e. higher in the coastal water type. The pigments in the surface sediments did not ref lect the respective overlying water types due to the increasing accumu lation of pigments at the offshore stations of the northern transect. This accumulation seems to correspond with the progressive reduction o f the benthic respiratory activity in an offshore direction. Along the southern transect such a relation could not be established, i.e. pigm ent accumulation along the shelf edge was not apparent. Special attent ion was paid to the presence of specific seagrass pigments on the shel f. No evidence for a major influx of seagrass material was found.