The ever-lasting green tides: What can we do？

Abstract

Macroalgal blooms (Green tides) are occurring more frequently in many regions of the world because of the combined effects of increasingly intense human activity and climate change. In the last decade, the world's largest Ulva prolifera green tide has become a recurrent phenomenon, appearing every summer in the southern Yellow Sea, China. Green tides can hurt coastal tourism and eradicate aquaculture and artisanal fishing. Eutrophication in nearshore waters is the ultimate explanation for the explosive growth of the macroalgal biomass, but the specific course of each nearshore green tide is often complex and requires in-depth and extensive research to develop effective mitigation strategies. Researchers have undertaken extensive studies on the prevention, control and mitigation of large-scale green algal blooms, and felicitated the utilization of green tide harmful biomass through bio-refining, bioconversion and other measures. However, due to the large-scale and trans-regional nature of the green tide, the government's administrative coordination measures are also essential for effective control. Nevertheless, it is becoming increasingly urgent to prevent and control the bloom at the early stage, and efficiently salvage and use these valuable raw materials.

Keywords: Developed coastal area; Eutrophication; Green tides.

Fig. 1

Distribution of green tides worldwide since 1980. The most frequently attacked coastal areas are densely populated areas. “1–2” marks the world's largest green tide. 1, China (Shandong); 2, China (Jiangsu); 3, Korea; 4, Japan; 5. USA (Guam Island); 6, Australia; 7, New-Zealand; 8, Hawaii; 9, USA (Washington); 10, USA (Oregon); 11, USA (California); 12, Mexico; 13, Cuba; 14, USA (Massachusetts); 15, USA (Connecticut); 16, USA (North Carolinas); 17, USA (Florida); 18, Venezuela; 19, Martinique; 20,Brazil; 21,Senegal; 22, Great-Britain; 23. Ireland; 24, Norway; 25, Denmark; 26, the Netherlands; 27, France; 28, Italy; 29, Tunisia; 30, South Africa; 31, Tanzania; 32, India. Population data is retrieved from the LandScan Program [16]. Green arrows show areas where green tides have broken out repeatedly. The color of the rectangle indicates the density of the population. All labeled areas are according to reports in peer-reviewed papers or issued by government agencies with credibility. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Fig. 2

Illustration of the formation, prevention, treatment, and utilization strategies of the Ulva prolifera bloom. Nutrient enrichment pathways are shown via river runoff, storm water runoff (Urban Runoff and Residential Runoff), and atmospheric precipitation and demonstrate the effects of anthropogenic nutrient enrichment on Ulva (Enteromorpha) prolifera bloom and associated consequences, e.g., oxygen depletion of bottom waters (O₂↓). a. Methyl hexanoate is used for U. pertusa spore settlement [17]; b. sodium benzoate is used for U. prolifera antifouling [18]; and c. hymenialdisine is used for U. prolifera spore settlement [19]. In 2008, a fertilizer production line was built in China that can process 10,000 metric tons fresh U. prolifera per day (BMSG™, www.bmsg.com).