Study On The Diversity And Distribution Of The Pico-Chlorophyta And The Pico-Haptophyta In The East China Sea

The Chlorophyta and the Haptophyta are the important primary producers of marine ecosystem, play an important role in the material circulation and energy flow. But the knowledge of their diversity and distribution is very limited. In this study, we used molecular approaches,18S rRNA clone library and fluorescent in situ hybridization associated with tyramide signal amplification (FISH-TSA) to investigate the diversity of Chlorophyta and Haptophyta and the distributions of major components of the photosynthetic picoeukaryotes in the East China Sea. The main results are as below:(1) We chose8samples from6stations in the East China Sea and the source area of the Kuroshio in the West Pacific to construct the18S rRNA clone libraries for Chlorophyta and Prymnesiophyceae.The Chlorophyta had a high diversity in all the samples and we got336Chlorophyta sequences which could be classified into35operational taxonomic unit (OTU). The sequences fall into5groups:Pyramimonadales, Mamiellophyceae, Prasino-Clade VII, Prasino-Clade IX and Trebouxiophyceae. The phylogenetic analysis showed the sequences all fall into the known evolutionary branch. The Micromonas Clade A and Ostreococcus Clade B were the dominate groups of the Chlorophyta in the East China Sea, the Micromonas Clade B._.4contain sequences only from stations in the continental shelf. An Ostreococcus OTU and a reference sequence from the Red Sea formed a new evolutionary branch, could be a new Ostreococcus clade.We got554Prymnesiophyceae sequences which divided into58OTU. The sequences fall into6groups:Phaeocystales, Prymnesiales, Hapto-Clade D, Hapto-Clade E, Zygodiscales and Syracosphaerales. Phylogenetic analysis showed the sequences fall into the known evolutionary branches and a new evolutionary branch. The sequences of this branch all came from the West Pacific libraries suggest this branch could be a new Haptophyta group that mainly distributed in the oligotrophic waters. The Hapto-Clade D was thought to be widely distributed in the oligotrophic waters, but our results showed the Hapto-Clade D could also existed in the mesotrophic or even the eutrophic waters.(2) We investigated the temporal and spatial variations of the major components of photosynthetic picoeukaryotes (PPEs) in spring and fall in the East China Sea.Results suggested the pico-Chlorophyta and the pico-Haptophyta were the major components of the PPEs which account for44.8-100%of the total cell abundance in the spring and fall cruises. The max abundance of PPEs in the spring cruise was36364cells mL-1, significantly higher than that of the fall cruise which was18715cells mL-1. In the fall cruise, the PPEs showed a patchy distribution along the estuary-continental shelf-open sea, while it was mainly distributed at the Changjiang estuary area and the pico-Haptophyta mainly distributed at the surface layer of continental shelf in the spring cruise.