Species Diversity, Abundance And Distribution Of Medusae In Taiwan Strait And The Waters Off Eastern Taiwan

Based on the data from the survey of 908 (2006-2007) in Taiwan Strait and the data from cooperation Survey of subtropical circulation between China and Janpan(1995-1997)in the waters off eastern Taiwan,using several statistical methods and ecology analysis tools,the species composition,temporal and spatial variation of abundance and biodiversity characteristic are described , and the effect of environmental factors on the Medusae community were discussed by analying diversity index.The brief results of this study are described as following:1. 189 Medusae species were identified in Taiwan Strait,in which ,121 are Hydrozoans,54 are Siphonophores,7 are Scyphozoans,and 7 are Ctenophore,including 20 new species and 4 new records in Taiwan strait. The seasonal variations of species in number follows the order of summer > spring> winter> autumn with the number105,104,91 and 84,higher species number occurred in the southern part of the strait. While 88 Medusae species were recorded in the waters off eastern Taiwan,including 48 Siphonophores,35 Hydrozoans,2 Scyphozoans and 3 Ctenophore. The seasonal variations of species in number follows the order of summer > winter> spring> autumn with the number71,50,48 and 34,higher species number occurred in offshore.2. Reference to the data before,according to distribution and the seasonal variation of abundance of Medusae and the adaptability of Medusae to the different habitat,the Medusae species in Taiwan strait were classified into four ecological groups: neritic warm-temperate,neritic warm-water,oceanic eurythermal warm-water and oceanic tropical species.Whihe the Medusae species in the waters off eastern Taiwan were classified into different four ecological groups: neritic warm-water,oceanic eurythermal warm-water,oceanic tropical and oceanic deep-water species.3. Four curise of Medusae abundance in Taiwan Strait exhibited obvious seasonal change with the mean abundance of 12.65 ind*m-3: high in the summer,followed by spring and autumn,low in winter. The horizontal distribution of abundance in nearshore was larger than in offshore.While the Medusae abundance in the waters off eastern Taiwan also showed an apparent seasonal change with the mean abundance of 0.81 ind*m-3,highest in summer and lowest in autumn. The different from result in the Taiwan Strait,the horizontal distribution of abundance in nearshore was smaller than in offshore.4. The most dominant species,together they contributed to 80% of the numerical total of Medusae in Taiwan Strait were Diphyes chamissoni and Lensia subtiloides(Siphonophorae) , Liriope tetraphylla and Aglaura hemistoma (Hydromedusae). While there are evlenve most dominant species of Medusae in the waters off eastern Taiwan with contributing to 82.22% of the numerical total of Medusae:Abylopsis eschscholtzi,Chelophyes contorta,Bassia bassensi,Eudoxoides mitra,Abyla tetragona,Eudoxoides spiralis,Chelophyes appendiculata Lensia subtilis and Diphyes bojani (Siphonophorae),Rhopalonema velatum and Aglaura hemistoma (Hydromedusae).The dominat species of Medusae exhibited apparent seasonal succession,and different dominant species showed different seasonal distribution patterns.5. The dynamics of Medusae diversity and the cause were analyzed. In Taiwan Strait the biodiversity showed that it was higher in south than north and was higher in spring(2.17) and winter(1.96) than in autumn(1.68) and summer(1.52). While it was higher offshore than nearshore and higher in in summer(3.59) and winter(3.54) than in spring(3.35) and autumn(2.95). They all found that the number of species was closely correlated with H′value,while the abundance was not correlated with it significantly. Moreover,the distribution of species diversity is associated with main environmental factor in Taiwan Strait such as water temperature and salinity,which are results of the seasonal changes of water system.6. Compared to the result in Taiwan Strait ,the species composition,temporal and spatial variation of abundance and biodiversity characteristic of Medusae in the waters off eastern Taiwan are all shown that they have more tropical oceanic properties. 7. Distribution and the seasonal variation of abundance of fish egg and larvaes are discussed. All of their abundance peaked in spring,and got the second highest in summer,and the lowest in winter,which is different from Medusae's. The high abundance of fish egg and larvaes was mostly found at the edges of the concentrated region of Medusa,it showed that there was a negative correlationbetween fish egg and larvaes and Medusae in distribution pattern. This result not only reflects their predation and food competition,but also provide the scientific information to fisheries management.