Investigation of the decline of Ulva prolifera in the Subei Shoal and Qingdao based on physiological changes
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Investigation of the decline of Ulva prolifera in the Subei Shoal and Qingdao based on physiological changes* HAO Ya1, GUAN Chen1, ZHAO Xinyu1, QU Tongfei1, TANG Xuexi1, 2, **, WANG Ying1, 2, ** 1
College of Marine Life Sciences, Ocean University of China, Qingdao 266100, China
2
Laboratory for Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China
Received Mar. 30, 2020; accepted in principle Apr. 27, 2020; accepted for publication May 24, 2020 © Chinese Society for Oceanology and Limnology, Science Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract It has been a scientific consensus that Ulva prolifera green tide that break out annually between May and August in the recent decade off eastern coast of Yellow Sea. To investigate the ecological mechanism of the decline of U. prolifera green tide, we compared the physiological characteristics of U. prolifera samples collected in three stages of the green tide in Subei Shoal north Jiangsu, the initiation point, on May 10 (early, the initiation), July 10 (middle, the outbreak), and in Taipingjiao, Qingdao on August 10 (late, the decline). Compared to the early samples, the middle, and late samples showed a lower chlorophyll content and photosynthetic efficiency at a higher lipid peroxidation level. The middle and later samples had fewer chloroplasts in the cells of U. prolifera than those in the early samples. In addition, the cells of U. prolifera sampled in the late stage showed ruptured and deformed cell walls. Differences in physiological function were reflected in the growth rate. Both the middle and late U. prolifera samples presented negative growth rates. Correlation analysis results show that the rising temperature was mainly responsible for the local decline of U. prolifera green tide. The high light-intensity that could induce the photoinhibition was also an important factor for the decline. Therefore, U. prolifera population that remained in the Subei Shoal and those that northward drifted to Qingdao experienced the same decline processes: rising temperature and continuous high light conditions in the late phase of green tide reduced the photosynthetic capacity and destroyed the antioxidant system of the thallus, which lead to decrease of biomass. The only difference is that the temperature in the Subei Shoal rose earlier than that in Qingdao; thus, U. prolifera remaining in the Subei Shoal went disappeared first. Keyword: Ulva prolifera; green tide; decline process; photoinhibition; lipid peroxidation
1 INTRODUCTION Since 2007, Yellow Sea green tide occurred in coastal China almost every year, and large-scale green tides caused considerable negative impact on offshore aquaculture, shipping, and tourism, resulting in many economic losses (Liu et al., 2009; Hu et al., 2010; Pang et al., 2010; Zhang et al., 2014, 2019). Ulva prolifera has been identified as the causative macroalgal species based on morphological taxonomy and molecular biology techniques (Shen et al.
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