Dinoflagellate cyst counts from water samples along a land-sea transect off Cape Blanc NW Africa (Maria S. Merian cruise MSM79)

Résumé

Dinoflagellate cyst counts obtained in water samples collected along a shelf break-offshore transect in the upwelling region off Cape Blanc (NW Africa) are presented. Data was collected in November 2018 during the cruise Maria S. Merian MSM 79. New data on organic-walled and calcareous dinoflagellate cysts were obtained within and between the nepheloid layers to investigate their distribution, dispersal and accumulation patterns. The main objectives were to find out how far cysts can be advected offshore and assess the role of nepheloid layers on the lateral transport of dinoflagellate cysts.Water samples (36 samples) were collected at 11 stations by in-situ pump (ISP) filtering (fraction >10 μm) and processed on board immediately after recovery. For this, the polycarbonate filters were washed in previously filtered tap water (0.1 μm) to remove all particles from the filter. The sample was then sonicated and sieved over a 20 μm high precision metal sieve (Storck-Veco). Material was further concentrated by centrifugation (5 min at 3500 rpm) and transferred to Eppendorf tubes. The final volumes were adjusted to 1 ml and depending on the amount of organic content a known volume of material was transferred to a microscope slide embedded in glycerine jelly and covered with a coverslip. Slides were observed under a Zeiss Axioskop R5111 light microscope at x400 and x1000 magnifications, and all dinoflagellate cysts were identified and counted at the lowest possible taxonomic level.