Abstract
The world’s largest macroalgal blooms caused by Ulva prolifera have occurred in the Yellow Sea for 11 consecutive years. The area covered by blooms has been approximately 500 km2 in previous years, while in 2017, the maximum area decreased significantly to 312 km2. In this study, we concluded that species competition between Ulva and Sargassum (fast rise of the golden tides), extreme high sea surface temperature and harvest for floating Ulva macroalgae were the three critical factors influencing the sharp reduction in covered area for blooms in 2017. In addition, analysis of annual variations of Pyropia aquaculture area in the Southern Yellow Sea over the past two decades revealed that a great expansion in “Sansha” regions was mainly responsible for the initial blooms in 2007, and that this expansion supported the great biomass of the blooms in following years. Based on these findings, we suggest comprehensive utilization of the macroalgal blooms is a feasible way to control them.
Highlights
Green tides, which are formed by rapid growth and vast accumulation of unattached green macroalgae, are associated with eutrophicated marine environments [1, 2]
The maximum coverage areas of the floating blooms were 650 km2, 2100 km2, 530 km2, 560 km2, 267 km2, 790 km2, 540 km2, 594 km2, 554 km2 and 312 km2, respectively, which were all observed in the Northern Yellow Sea in June and July of each year (Fig 2)
The satellite remote sensing method was used to track green tides back to 2004, and no evidence of floating Ulva macroalgae were observed in the Yellow Sea during 2004–2006 [10]
Summary
Green tides, which are formed by rapid growth and vast accumulation of unattached green macroalgae, are associated with eutrophicated marine environments [1, 2]. Over the past few decades, green tides have been increasing in severity, frequency, and geographic range, resulting in their becoming a growing concern worldwide [3,4,5,6]. The world’s largest green tide events, which are caused by Ulva prolifera, have occurred annually from 2007 to 2017 along the coast of the Yellow Sea, China, seriously affecting marine environments and ecological services functions [7, 8]. Green tides in the Yellow Sea are characterized by seasonal and annual occurrence, long distance transportation and large biomass. The work reported in previous studies has led to a much better understanding of green tides in the Yellow Sea, many questions have yet to be answered.
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