Research Article: A Strategy for the Proliferation of Ulva prolifera, Main Causative Species of Green Tides, with Formation of Sporangia by Fragmentation

Date Published: January 5, 2010

Publisher: Public Library of Science

Author(s): Shan Gao, Xiaoyuan Chen, Qianqian Yi, Guangce Wang, Guanghua Pan, Apeng Lin, Guang Peng, Wendy A. Peer.

Abstract: Ulva prolifera, a common green seaweed, is one of the causative species of green tides that occurred frequently along the shores of Qingdao in 2008 and had detrimental effects on the preparations for the 2008 Beijing Olympic Games sailing competition, since more than 30 percent of the area of the games was invaded. In view of the rapid accumulation of the vast biomass of floating U. prolifera in green tides, we investigated the formation of sporangia in disks of different diameters excised from U. prolifera, changes of the photosynthetic properties of cells during sporangia formation, and development of spores. The results suggested that disks less than 1.00 mm in diameter were optimal for the formation of sporangia, but there was a small amount of spore release in these. The highest percentage of area of spore release occurred in disks that were 2.50 mm in diameter. In contrast, sporangia were formed only at the cut edges of larger disks (3.00 mm, 3.50 mm, and 4.00 mm in diameter). Additionally, the majority of spores liberated from the disks appeared vigorous and developed successfully into new individuals. These results implied that fragments of the appropriate size from the U. prolifera thalli broken by a variety of factors via producing spores gave rise to the rapid proliferation of the seaweed under field conditions, which may be one of the most important factors to the rapid accumulation of the vast biomass of U. prolifera in the green tide that occurred in Qingdao, 2008.

Partial Text: Green tides are caused by very large accumulations of green macro-algae that occur under suitable conditions, in particular eutrophication [1]–[7]. In the summer of 2008, a large-scale green tide occurred in the Yellow Sea, especially along the shores of Qingdao (35°35′–37°09′N, 119°30′–121°00′E), China [8]. The results of satellite remote sensing monitoring showed that this green tide covered approximately 3800 km2[9]. It was speculated that around 20 million wet tonnes of the biomass of the green macro-algae was produced along the shores of Qingdao, and at least 1.5 million wet tonnes was salvaged (unpublished results). This green tide had a negative impact on recreational beaches, and it invaded more than 30% of the area of the 2008 Beijing Olympic Games sailing competition in Qingdao, seriously hindering the preparations for the Games [9]. Increasing attention has been paid to the event by the government of China and by many people all over the world.

Pulse amplitude-modulated chlorophyll fluorescence has the advantages that it is convenient, nonintrusive and rapid and has been a useful tool for assessing the macro-algal physiological state under different conditions [22], [25], [26]. The technique is widely used for measuring the influence of environmental stress on the physiological state of aquatic photosynthetic organisms [26], and it is attractive for making qualitative and even quantitative comparisons of photosynthetic properties of cells during differentiation and development. On the basis of the in vivo chlorophyll fluorescence yields of PS II determined by PAM fluorimetry, the photosynthetic parameters are calculated with established formulae [24], [27]. The most useful is Y (II), which represents the proportion of the light absorbed by chlorophyll in PS II that is used in photochemistry. Fv/Fm, another widely used parameter, provides information on the potential quantum efficiency of PS II, and is used as a sensitive indicator of photosynthetic performance of photosynthetic organisms [28]. The application of PAM fluorimetry in the formation of sporangia and the development of U. prolifera spores will help us to understand these processes.



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