| In the Yellow Sea of China, large scale green tides have broken out for four consecutive years from 2007 to 2010. The main causative species of green alga was identified as Ulva prolifera. The original source of this seaweed was suspected to be from the south of the Yellow Sea (Jiangsu open-sea) as revealed by satellite images. The floating biomass drifted with water current northward and flourished in nearshore waters around Qingdao, some reports showed that the Porphyra cultivation areas and aquaculture ponds along Jiangsu coasts as the original source of the bloom forming alga. For tracking the origin and development mechanism of bloom, it is significant to clearfy the occurrence of the component species of the green tides, distribution and the characteristic of development. In April of 2009, "Investigation of green tide algae in Jiangsu sea area" was started in Jiangsu province. From April 2009 to March 2010, we investigated 6 populations and 27 sites (32-34°N119-122°E), the field survey including offshore, islands, seacoast, estuaries, aquaculture ponds and Porphyra cultivation areas totally about 50,000 km2 were covered. The component species, the distribution and the relationships between the tide-occurrence and environmental factors were investigated systematic in the present study.We used morphological methods or in combination with molecular biology methods to identify the species appear in survey area. The results showed that component of green algae were no less than 10 species, of which Ulva prolifera and U. linza were the dominant species, and U. intestinalis and U. compressa were common species. The morphological characteristics of main species, especially U. prolifera varied complicatedly to different habitats and growth season. In the past study about seaweeds distribution showed that the U. prolifera distributed along the costal area in south of Yangtze River, the U. linza growed along the Yellow sea and Bohai sea from Shandong biland to Liaoning province. There were no reports about the taxonomic study of green alga from Haizhouwan to the Yangtze River. Until the Ulva sp. population appeard in this area, which caused the bloom in Yellow sea, it was attracted vast attention. Several researchers have suggested that green tides are formed by an Ulva linza-procera-prolifera (LPP) complex instead of individual species. Furthermore, we found 4 atypical samples of Ulva sp. by using the morphological methods. We think there must be some relationships between them. The molecular and crossing test studies have shown that some closely related species could be interfertile and even appear as variants. After systematically comparing the morphological characteristics with previous taxonomic criteria, we believe that the morphological diversity of Ulva sp. is due to succession in response to environmental change.We investigated the biomass of Ulva sp., water temperature and the number of reproductive cells between the Porphyra cultivation areas and aquaculture ponds monthly. According the results, we consider that the groups in aquaculture ponds and Porphyra cultivation areas had major biomass and showed the similar succession with the fixed-growth populations. There is no direct evidence by the survey can be demonstrated that the thallus-segments from cultivations had relation with the origin of the green tides. Overall analysis of temperature, seawater transparency, the development scale of green alga and propagule number, we believe that the green tides occurred in Yellow sea were mainly composed of U. prolifera, which can only developed on the edge of the turbid area (dozens of kilometers away from the coast) and under certain water temperature. The young filamentous thallus begin to appear when the water temperature reached 13℃, assemble together at 17℃, and vanish soon above 25℃. The results indicated an independent succession of the green tides. |
PDF Full Text Request