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

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.

Green and golden seaweed tides on the rise

“…These patches were subsequently driven inshore by winds, hitting a 140 km stretch of coastline, which included Qingdao. The species responsible, Ulva prolifera, was subsequently shown to proliferate rapidly by sporulation of cells of fragmented thalli; these grew into new thalli by attaching to the parent thallus, with 1-2-mm diameter fragments having the highest sporulation rate 18 .…”

“…Thus, in favourable topographical and hydrological environments, free-floating macroalgae are likely to continue to proliferate and maintain the eutrophic state that is favourable for their perpetuation. The occurrence and magnitude of green tides often vary both annually and seasonally, hence the planning of mitigation measures will require interdisciplinary investigation of the life-cycle strategies of the species involved in relation to the physical and chemical setting of the environment: topography, circulation, wind patterns and the nutrient regime, exemplified by the work done on the Yellow Sea green tides 3,[15][16][17][18][19][20][28][29][30] . An obvious mitigation target would be the overwintering and early spring growing stages.…”

“…Furthermore, life cycles also need to be studied in situ. The ability to produce new thalli on the surface of the parent thallus 18 suggests the absence of chemical deterrents, which are known to exist for the thallus surface of other Ulva species 45,46 . In the case of Sargassum, the factors necessary for large-scale spring regeneration of thalli require elucidation, as well as hindcasting for the factors that allowed the 2011 Sargassum event.…”

The yellow sea green tides were dominated by one species, Ulva (Enteromorpha) prolifera, from 2007 to 2011

“…First, there are at least five tubular Ulva species along the north coast of China (Figure 1), but the green tides were unialgally composed. U. prolifera exhibits reproductive diversity and excellent ability in enduring adverse conditions, such as extreme hyper salinity and desiccation [35][36][37], which may help them drift a long distance on the sea surface. ESTs have been sequenced and annotated [38,39], but the functions of the annotated genes have not been validated and species-specific genes cannot be annotated.…”

Effects of Environmental Factors on Zoospore Release and Early Growth of the Green Tide Alga Cladophora albida

“…arctirum (Bast et al, 2009;Xu et al, 2013), ( ) Cladophora monteagneana (Kamermans et al, 1998;Na et al, 2016). 2008 (Gao et al, 2010;Zhang et al, 2016 . Vertical bars indicate standard errors (n=3 replicates).…”