Abstract
Blooms of the ichthyotoxic dinoflagellate Cochlodinium polykrikoides are responsible for massive fish mortality events in Korean coastal waters (KCW). They have been consistently present in southern KCW over the last two decades, but they were not observed in 2016, unlike in the previous years. Despite extensive studies, the cause of this absence of this dinoflagellate bloom remains largely unknown. Thus, we compared physico-chemical and biological data from along the Tongyeong coast between 2016 and the previous four years (2012–2015). The averages of water temperature and salinity in August, 2016 were significantly (p < 0.001) different from those in the previous years. The amount of Changjiang River discharge, which can affect the environmental conditions in the southern Korean coastal area via ocean currents, was larger than in the previous years, resulting in a reduction in the salinity level in August when blooms of C. polykrikoides usually occurred. Moreover, compared to previous years, in 2016, there was a weak expansion of C. polykrikoides blooms in the Goheung-Oenarodo area where C. polykrikoides blooms were annually initiated in KCW. Lastly, the strong winds from the typhoon Lionrock may also have contributed to the early termination of this dinoflagellate bloom. Together with these findings, the combination of these environmental conditions in 2016, unlike in previous years, may have inhibited the formation of C. polykrikoides blooms along the Tongyeong coast.
Highlights
Harmful algal blooms (HABs) are a growing environmental problem globally and have serious impacts on public health, aquatic organisms, and aquaculture industries [1,2,3]
We aimed to elucidate a potential factor that can lead to a sporadic pattern of annual blooms of C. polykrikoides along the Tongyeong coast, where C. polykrikoides blooms annually occur in southern Korean coastal waters (KCW)
Recent studies [13,15,28] provide genetic evidence that is suggestive of this long-distance transfer using microsatellite markers and ribotype-specific real-time PCR. These findings suggest that the cell accumulation by hydrographically south-to-north flow from the East Changjiang River discharge at Datong (China) Sea (ECS) linked with the Tsushima Warm Current (TWC) can play an important role in bloom initiation in southern KCW
Summary
Harmful algal blooms (HABs) are a growing environmental problem globally and have serious impacts on public health, aquatic organisms, and aquaculture industries [1,2,3]. Massive blooms of C. polykrikoides, which covered wide areas along the south and east coasts at high densities, reoccurred in 2013 From these dinoflagellate blooms were continuously generated in 2014–2015 but disappeared again in 2016 [12]. Physiochemical factors (e.g., temperature, salinity inorganic nutrients, etc.) can play a key role in the formation and termination of this dinoflagellate bloom in KCW [17]. It is unclear which factor is capable of leading to this sporadic annual pattern of the C. polykrikoides bloom in KCW.
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