Seasonal variation of dominant free-floating <i>Ulva</i> species in the Rudong coastal area, China: Differences of ecological adaptability to temperature and irradiance

Abstract

In this paper, species compositions and seasonal variations of free-floating <i>Ulva</i> species at Rudong coastal area were investigated during 2009-2011. Based on the sequences analysis of nuclear-encoded ITS and 5S rDNA spacer regions, dominant species of the floating <i>Ulva</i> population at the early stage of the green tide were <i>U. compressa</i>, <i>U.flexuosa</i>, and <i>U. linza</i>, respectively. <i>U. prolifera</i> first appeared in the middle of May and dominated the floating community until June each year. The effects of environmental factors on the growth of four <i>Ulva</i> species were examined in laboratory culture at different combinations of irradiance and temperature. The results showed that the highest growth rate of <i>U. prolifera</i> was 41.8%, which was much higher than the other three <i>Ulva</i> species. Meanwhile, the strong adaptability and tolerance of <i>U. prolifera</i> to extreme conditions also help it survive and bloom in the Yellow Sea.