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Harmful algal blooms: mechanisms, monitoring, and prevention in a rapidly changing world
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Toxic and allelopathic effects of Alexandrium leei (Dinophyceae) tested with zooplankton (Rotifer and Artemia), fish (Oryzias melastigma) and phytoplankton (Akashiwo sanguinea)
Wednesday 9th @ 1030-1050, Multifunction Hall
Li-Xia Shang* , Institute of Oceanology, Chinese Academy of Sciences
Yang-Bing Xu, Fisheries College, Ocean University of China
Danielle Saunders,
Zhang-Xi Hu, Institute of Oceanology, Chinese Academy of Sciences
Po Teen Lim, University of Malaya
Chui Pin Liaw, University of Malaya
Ying-Zhong Tang, Institute of Oceanology, Chinese Academy of Sciences
Presenter Email: lxshang@qd.ac.cn |
| Many dinoflagellates form harmful algal blooms and produce phytotoxins, which may cause massive losses in aquaculture and fisheies, serious deleterious impacts on ecosystems, tourism and recreational activities, and even human illness. The genus Alexandrium is well known for including many species that produce paralytic shellfish toxins (PST) and these toxins have sometimes been implicated in association with fish killing. Non-PST based ichthyotoxicity has also been reported from PST-producing species as well as from A. monilatum, a non-PST producing species. Alexandrium leei, with a distribution spanning the tropical waters of South East Asia to the temperate waters of North East Asia, has been reported to be non-toxic, containing low level of PST for a Vietnamese strain, but highly toxic to fingerlings for a Singapore strain. This study reports the toxic and allelopathic effects of a strain of A. leei isolated from Malaysia on zooplankton (Rotifer and Artemia), fish (Oryzias melastigma) and phytoplankton (Akashiwo sanguinea), as well as the potential mechanisms of the toxicity and allelopathy. The toxicity of A. leei was dependent on target animals (size), as the most and least potent toxicity was observed in Rotifer and fish bioassays. The initial culture of A. leei exhibited to be dramatically more potent in toxicity (per cell) than did the equivalent doses of intracellular (extracted by f/2 medium after ultrasonic disruption) and extracellular (cell-free culture medium) fractions. The toxic activity of A. leei (3000 cells/mL) also depended on the growth stages of culture, with the culture at stationary growth stage being more potent than that of the cultures at early and late-exponential phases, while the minimum mortalities of Rotifer were observed when exposed to the culture at late-exponential phase for both the extracellular and intracellular fractions. Survivals of animals exposed to cultures and cell-free culture medium were significantly decreased with the increase of A. leei cell density up to 3000 cells/mL. The toxicity of initial culture, cell-free culture medium, and the intracellular fraction were all dependent on cell density in a manner of linear relationship between the mortality of animals and the logarithm of cell density. The allelopathic effects of A. leei culture on the target Akashiwo sanguinea included loss of motility, deformation of cell morphology and cell mortality at higher dosage. These results together indicate that the Malaysia isolate of A. leei has potent toxicity to zooplankton, fish and allelopathy to other microalgae, which may pose threat to aquaculture industry and fisheries. |
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