Temporal And Spatial Distributions Of Green Algae Micro-propagules In The Coastal Waters Of The South Yellow Sea

Large-scale green tide of Ulva prolifera occurred consecutively since 2007becoming a regular ecological disaster in the Yellow Sea,China.This world's largest green tide caused serious marine ecological issues as well as social economy problems,especially in 2008 when it hit the coast of Qingdao for the first time.In order to clarify the annual variation in green macroalgal micro-propagules of Qingdao coast,the influence of the main environmental factors,evaluate the effect of the large-scale green tide on micro-propagule community and function in the coastal waters of Qingdao,and the temporal and spatial distribution of green macroalgae attached on the Pyropia rafts and micro-propagules in water in Subei shoal,a year-round survey was conducted in the coastal waters of Qingdao from March 2016 to March 2017 and monthly investigation was conducted in Subei shoal in spring of 2017.The main results are as follows:1.The abundance and species composition of micro-propagules in coastal waters of Qingdao showed evident tempo-spatial variations.Seasonal variation of the abundance showed a consistent bi-peak pattern,in which the values were highest at spring,and reached a minor peak in fall.The average densities of micro-propagule at Zhanqiao,Yiyu,Olympic and Shilaoren were 308,79,360,93 inds L^-1,respectively.There were six green macroalgal species identified,including 4 ulvoid species?Ulva.linza,Ulva.prolifera,Ulva.compressa and Ulva.pertusa?,an unclassified Ulva sp.and one Blidingia sp.In general,U.linza was the most abundant species with an average proportion of 54.4%.U.prolifera were abundant from July to September.The other three species,U.pertusa,U.compressa and Blidingia sp.,were relatively rare,and the average proportions were lower than 10%.2.An evident shift on species composition was observed in summer when the large-scale floating biomass of U.prolifera approached the coasts of Qingdao.The dominant species of propagule changed from U.linza to U.prolifera.Detection of the‘floating'type of U.prolifera in summer,a unique strain responsible for the green tide in Yellow Sea,supported that large-scale floating U.prolifera biomass could affect local micro-propagule community.There were,however,no‘floating'U.prolifera propagules detected in the following winter,indicating that influence from the large-scale green tide was transient,and it has not leave prolonged seeds in Qingdao coastal waters.3.The abundance of green macroalgae attached on the Pyropia rafts and micro-propagules in the water of Subei Shoal showed an obvious seasonal variation and a rising tend in spring.There were four green macroalgal species identified,including U.linza,U.prolifera,Blidingia sp.and an unclassified Ulva sp.In general,Blidingia sp.was the most abundant species with an average proportion of 48.1%.The highest abundance of micro-propagules in water was observed in May(276 inds L^-1 in average).Compared with the results of the previous studies,the abundance of green macroalgae attached on the Pyropia rafts and micro-propagules was significantly reduced in the same period.