Interspecific interactions between Noctiluca scintillans and Pseudo-nitzschia

Muyao Zhou, Yang Li, Shuwen Zhang*

Guangzhou Key Laboratory of Subtropical Biodiversity and Biomonitoring, Guangdong Provincial Key Laboratory of Healthy and Safe Aquaculture, School of Life Science, South China Normal University, Guangzhou, China

Noctiluca scintillans is a ubiquitous heterotrophic dinoflagellate and frequently causes red tide in coastal regions. Pseudo-nitzschia, a typical harmful algal bloom (HAB) species, is the main biological source of the neurotoxin domoic acid (DA) in the ocean. Pseudo-nitzschia is frequently the dominating group in the phytoplankton community during N. scintillans bloom, and sometimes forms mixed blooms with N. scintillans. However, their interspecific interactions have not been investigated till now. Therefore, we conducted laboratory experiments on N. scintillans and P. fukuyoi to determine whether ingestion of N. scintillans would increase Pseudo-nitzschia's cellular toxin production and how DA is accumulated and degraded by N. scintillans. Results showed that N. scintillans consumed toxic P. fukuyoi at a rate of 203±77 cells Noctiluca^-1 d^-1 and accumulated 67.94 ± 2.72 pg DA cell^-1 after one day of incubation. The DA content in N. scintillans cells decreased gradually with the length of starvation, but 5% of the accumulated DA remained in the cells despite the absence of food vacuoles after 3 days of starvation. This suggests that feeding P. fukuyoi with N. scintillans can attenuate the toxic effects of P. fukuyoi on the ecosystem. At the same time, part of DA still accumulated in N. scintillans, which continues to transport DA up the food chain. There was a mismatch between estimated and measured DA level in N. scintillans cells one day after ingestion of P. fukuyoi, indicating that N. scintillans may absorb part of dissolved DA. Furthermore, the cellular DA content of P. fukuyoi was higher when cultured with N. scintillans, but the difference was not statistically significant. This may be due to the short incubation period (24 h) and insufficient amount of induced toxin generated by P. fukuyoi to distinguish between the two groups This work sheds light on the interspecific impacts and successional mechanisms of HAB species, as well as the environmental behavior of their toxins.

Acknowledgment

This study was supported by the National Natural Science Foundation of China (41906117), and Funding by Science and Technology Projects of Guangzhou (202201010722).