Relationships between geotaxis/phototaxis and diel vertical migration in autotrophic dinoflagellates

Marine dinoflagellate diel vertical migrations are often conceptuallyexplained by a species' geotactic and phototactic preferences,but actual simultaneous measurements are rare. Newly collectedsimultaneous measurements on Heterocapsa (Cachonina) illdefina(Herman and Sweeney) and Gymnodinium breve (Davis) are combinedwith similar literature information on Amphidinium carterae(Hulbert), Peridinium faeroense (Paulsen) and Prorocentrum micans(Ehrenberg) to explore several examples of the actual relationshipsbetween diel vertical migration and geotaxis/phototaxis. Amphidiniumcarterae does not migrate, but it exhibits a negative geotaxisthat may counter a small sinking velocity. The four other speciesall exhibit diel vertical migrations that yield surface aggregationsduring daylight, but the associated combinations of geotaxisand phototaxis precision (which is strongest when every cellin a population exhibits the same response to a stimulus andweakest when the response is random) and sign [which is positive(negative) when motion is toward (away from) the stimulus] aredifferent in each case. These different taxis combinations maybe related to species-specific sensor structure and/or placement.Furthermore, variations in the different biochemical pools overa species' cell cycle may contribute to structural/mechanicalchanges that influence how a given sensory array functions ata given time. If so, this coupling may be an important linkin the growth optimization mechanisms and occasional bloom successesof different autotrophic dinoflagellate species under varyingenvironmental conditions.