Characterization of the allelopathic effects and toxicity in an isolate of Cochlodinium
polykrikoides from Jiaozhou Bay, China
Zhang Xi Hu and Ying Zhong Tang
Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology,
Chinese Academy of Sciences, Qingdao, PR China. E-mail: yingzhong.tang@qdio.ac.cn
The toxic dinoflagellate, Cochlodinium polykrikoides, is one of the fastest expanding
species causing harmful algal blooms (HABs) in the past 30 years along the Chinese
coastline. Blooms caused by this species have caused catastrophic impacts to fisheries
and coastal ecosystems. During 1984-2014, numerous blooms of C. polykrikoides
over varying spatial scales and with different severity of deleterious effects were
reported in China's coastal waters, including Hong Kong, Guangdong, Zhejiang,
Shandong, Hebei, and Jiangsu. Blooms of this species have thus become a potentially
serious threat to aquaculture and fisheries, which have attracted great attention from
the HAB research community, local governments, and other stakeholders in China. In
2012, a small-scale bloom caused by this species was first reported in coastal water of
Qingdao, China, and subsequently, we established a clonal culture from Jiaozhou Bay,
proximate to the subsequent bloom area in 2014. Phylogenetic and morphological
analysis using partial sequences of the SSU rDNA and LSU rDNA, epi-fluorescence
microscopy, and scanning electron microscopy confirmed its identity as the East
Asian ribo-type of C. polykrikoides. We then examined allelopathic effects of a clone
of C. polykrikoides isolated from northeast coast of the USA (American/Malaysian
ribotype), which has been shown to have potent allelopathic effects and
ichthyotoxicity. We tested the effects of this clone on ten cultures of other
phytoplankton species, including Prorocentrum spp., Akashiwo sp., Karlodinium sp.,
Karenia sp., Scrippsiella sp., Heterosigma sp., and observed acute toxicity to two
model organisms, the rotifer Brachionus plicatilis and the brine shrimp, Artemia
salina. Our results demonstrated this isolate of C. polykrikoides had strong
allelopathic effects and toxicity against the tested target species, which suggests that C.
polykrikoides can use its toxicity to outcompete co-occurring phytoplankton and
reduce grazing pressure of zooplankton. This demonstrates the ability of C.
polykrikoides to use toxicity and allelopathy to form dense blooms in Chinese coastal
waters and other regions of the world.