Summer and winter distribution and malformation of coccolithophores in the East China Sea

A quantitative scanning electron microscope study of coccolithophores was sampled during the summer and winter from the surface waters over the continental shelf of the East China Sea (ECS) was conducted. In all, only ten coccolithophorid taxa were observed during the investigation periods. Emiliania huxleyi (Lohmann) Hay et Mohler and Gephyrocapsa oceanica Kamptner were predominant among the coccolithophorid flora during both seasons. E. huxleyi increased its relative abundance seaward, while G. oceanica concentrated in inner shelf area. These two species accounted for over half of the coccolithophores in the middle shelf of the ECS. These dominant taxa are eurythermal, occurring in patchy and “bull‘s-eyes” distributions in both the summer and winter, respectively. Special emphasis has been paid to the overall distribution and intra-species frequency of malformed cells of the two dominant species, as well as other minor species. Malformed cells occurred so frequently in both seasons that the frequency amounted to as much as 80% in both dominant species. The malformation was manifested largely by corroded defects. A comparison of the malformed distribution with the hydrological and nutrient parameters suggests that the malformation was caused mainly by a deficiency of nitrate in the ambient waters.