Abstract
The toxic effects of the typically noxious bloom-forming dinoflagellate Karenia mikimotoi were studied using the allelopathic experimental system under controlled laboratory conditions. The potency of intact cell suspensions with whole cells, cell-free culture filtrate in different growth phases, and lysed cells with ultrasonication were compared, and the growth and reproduction of the marine rotifer Brachionus plicatilis were used as endpoints to evaluate toxic differences. The intact cell suspension resulted the most significant growth inhibition, including lethality, on the growth of B. plicatilis (p < 0.05). Lysed culture medium treated with ultrasonication and the cell-free culture filtrates at either the exponential or stationary phase exhibited limited negative impacts compared to the control according to changes in the population growth rate (r) and survival rate (p > 0.05). Reproduction presented a similar tendency to change, and the number of eggs produced per individual, as well as spawning period decreased in the whole cell and lysed cell suspensions. The key parameters in the lift table include the net reproductive rate (R0) and the intrinsic rate of increase (rm), which were more sensitive to treatment and were significantly suppressed compared to that of the control. The addition of the ROS inhibitor N-acetylcysteine (NAC) could not change the growth or reproduction patterns. Moreover, substantial hemolytic toxicity was found in the treatment of the intact cell suspension (p < 0.05), while limited toxicity was found in other treatments compared to that of the control. K. mikimotoi was speculated to secrete allelopathic substances onto the cell surface, and direct cell contact was necessary for allelopathic toxicity in B. plicatilis. Reactive oxygen species (ROS)-independent hemolytic toxicity was assumed to be the explanation for what was observed.
Highlights
Harmful algal blooms (HABs), which are known for causing severe damage to the marine ecological environment and marine economy as well as to public health, are increasing in frequency, magnitude, and duration worldwide [1]
No significant difference was observed in Groups C and E compared with the control
Thisexert result indicated that the culture filtrates without microalgal cells at either exponential or effect plateau phases had little effect on the growth of B. plicatilis
Summary
Harmful algal blooms (HABs), which are known for causing severe damage to the marine ecological environment and marine economy as well as to public health, are increasing in frequency, magnitude, and duration worldwide [1]. It is calculated that there are more than 100 toxic or harmful marine phytoplankton species, among which dinoflagellates are well known as the major HAB-causing species. Karenia mikimotoi is one of the common HAB-causing dinoflagellate species that is widely distributed in temperate and tropical shallow waters and possesses the unique feature of fish poison [2]. Two different allelopathy pathways have been reported: one was toxin mediated and the other was toxin-independent, and the toxic-allelopathic pathway was more common in the natural environment compared with allelopathic interactions. It has been reported that K. mikimotoi exert noxious impacts on other species of phytoplankton [18] through the allelopathic pathway, but whether the pathway was toxin-dependent or toxin-independent or whether this allelopathic effect was species-dependent, was not well clarified
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