Light, temperature and nitrogen as interacting factors affecting diel vertical migrations of dinoflagellates in culture

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Abstract
Diel vertical migrations of the marine dinoflagellates Gonyaulax polyedra Stein and Ceratium furca (Ehr.) Clap, et Lachm. were followed in a laboratory tube (2.02 m × 0.25 m) under a 12:12h light:dark cycle. The effects of temperature stratification, two levels of surface irradiance and nitrogen depletion on patterns of vertical migrations were examined. At temperatures between 22–26°C with small temperature gradients, both species migrated at a rate of 0.7 –1.0 m h−1. Steeper thermoclines (ca. 0.8°C 0.1 m−1) with temperatures below ca. 20°C caused a marked decrease in swimming speed which resulted in accumulations of cells in these thermocline regions. Under conditions of nutrient sufficiency both algae migrated into the surface layers at irradiance values of over 1000 μE m−2 s−1. Increasing nitrogen depletion caused the downward migration of both algae to commence progressively earlier in the day and before the end of the light period. The earlier downward migrations enabled a more complete descent through the thermocline. Nitrogen depleted cells of Gonyaulax continued to undertake vertical migrations but avoided high irradiances thus forming subsurface maxima at irradiance levels close to 150 μE m−2 s−1. Ceratium cells which exhausted both inorganic nitrogen and phosphorus ceased to migrate accompanied by a large change in cellular fluorescence.

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