Abstract
The mixotrophic dinoflagellate Akashiwo sanguinea frequently forms harmful algal blooms around the world and has caused massive deaths of shellfish, finfish and birds, yet its toxic mechanism is still unclear. In this study, toxic effects of A. sanguinea on co-culturing phytoplankton and zooplankton were investigated. The results showed that sonicated cultures of A. sanguinea JX13 and JX14, isolated from the Pearl River Estuary, had a significant lethal effect on the rotifer Brachionus plicatilis, with the highest mortality rate of 80%. The highest inhibition rates of A. sanguinea cultures JX13 (90%) and JX14 (80%) on R. salina were much higher than that of AS2 (20%). Toxicity varied with the growth stage, during which A. sanguinea cells in the exponential stage showed the highest toxicity (40%), while A. sanguinea filtrate had the highest toxicity (10%) in the decline stage. The action mode of A. sanguinea toxicity on plankton was explored through an osmotic membrane culture device. It was found that A. sanguinea JX13 displayed an inhibitory effect on coexisting phytoplankton, whether they had contact or not, but the inhibition rate increased by 25% with contact. A lethal effect of A. sanguinea JX13 on rotifer Brachionus plicatilis was observed only in contact treatment. This study suggests that direct contact is the key action mode to trigger the release of toxins and induce toxic effects of A. sanguinea on co-occurring plankton.
Highlights
Published: 30 December 2021Akashiwo sanguinea is a mixotrophic dinoflagellate that adapts to wide ranges of temperature (10–30 ◦ C) and salinity (5–40) [1], utilizes various forms of N sources, including urea, ammonia and nitrate [2], and forms cysts under unfavorable conditions [3]
In the non-contact coculture treatment of A. sanguinea JX13 and B. plicatilis, there was was no significant difference observed in relative concentrations of both species at 48 h no(psignificant difference observed in relative concentrations of both species at 48ofhJX13
Results are expressed in triplicate ± standard deviation (SD)
Summary
Akashiwo sanguinea is a mixotrophic dinoflagellate that adapts to wide ranges of temperature (10–30 ◦ C) and salinity (5–40) [1], utilizes various forms of N sources, including urea, ammonia and nitrate [2], and forms cysts under unfavorable conditions [3] In recent decades, this species has formed harmful algal blooms (HABs) in coastal waters worldwide, including in Australia [4], North America [5], Europe [6], South America [7] and Asia [8,9], resulting in a large number of deaths of fish, shellfish and birds [7,10]. A total of more than 30 recorded A. sanguinea blooms have occurred in four major sea areas of China, with a total affected area of 2098 km , causing huge economic losses and ecological hazards [12]
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