Intra- and infra-specific morphological variation in selected coccolithophore species in the equatorial and subequatorial Pacific Ocean

The ecological preferences of morphological groups within major coccolithophore taxa were studied in surface water samples from the equatorial and subequatorial Pacific Ocean. Emiliania huxleyi was subdivided into three morphological groups: Type A, Type C, and variety corona. The most probable factors limiting the occurrence of E. huxleyi Types A and C were high temperatures and low nutrient concentrations, respectively. E. huxleyi var. corona had an affinity for oligotrophic conditions. Calcidiscus leptoporus ssp. small was adapted to fertile waters. Umbilicosphaera foliosa and Umbilicosphaera sibogae preferred mesotrophic upwelling waters and stratified marginal waters surrounding the upwelling front, respectively. Among the three Umbellosphaera tenuis morphotypes observed in this study (Types I, III, and IV), only Type I was found in very warm tropical surface. Both Types III and IV were found in subtropical waters, and Type III differed from Type IV in that its distribution was constrained to hemi-pelagic waters. Habitat segregation among the morphotypes of major taxa indicates that the observed global distributions of these major taxa are, in fact, combinations of discrete morphological groups.