Observations on the diel migration of marine dinoflagellates off the Baja California coast

Abstract

The vertical distribution of Gonyaulax polyedra, Ceratium furca, Gymnodinium sp., Ceratium dens, Gonyaulax digitale, Prorocentrum micans, Polykrikos kofoidii, and Peridinium depressum was followed during two 36 h time-series stations, off the Baja California coast. Water samples were taken at 6 h intervals, at 7 light penetration depths, for phytoplankton identification and for chemical and biological analysis. The results indicate that the dinoflagellates were able to perform vertical migration against the physical water movements, such as upwelling internal waves and wind mixing, that existed in the area during this study. Attempts to correlate the vertical dstribution of the dinoflagellates with the seawater density and nitrate distribution lead to the conclusion that even a weak density gradient acted as a barrier to the downward migration, and that nitrate assimilation in darkness was not required for their growth. Differences in the vertical distribution at 12.00 hrs of each species supports the hypothesis that migration is of a phototactic nature. A comparison of this study with previous ones on vertical migration in other areas suggests that a species should not be defined in general as a positive or negative phototactic organism, but that the direction of the migration is related to the light intensity at the sea surface.