Effects of Zooplankton Extracts on the Production of Paralytic Shellfish Toxins by <i>Gymnodinium catenatum</i> and <i>Alexandrium pacificum</i>

Abstract

The presence of zooplankton in marine ecosystems is an important factor affecting toxin production in dinoflagellates. However, whether the production of paralytic shellfish toxins (PSTs) by Gymnodinium catenatum and Alexandrium pacificum is affected by substances produced by zooplankton is not yet fully understood. This study assessed the effects of zooplankton extracts on cell abundance, pigment concentration and composition, chlorophyll-a-specific primary production (Chl-a SP), and PST production in G. catenatum and A. pacificum, isolated from Korean coastal waters. In addition, a novel group of hydroxybenzoate PSTs known as GC toxins, which lack commercial reference standards, was evaluated. No significant differences were observed in cell abundance, pigment composition, or Chl-a SP in the experimental group of G. catenatum strains exposed to zooplankton extracts compared to the control group. However, the production of PSTs, including GC toxins, was significantly enhanced when the strain was exposed to extracts of Calanus finmarchicus. Meanwhile, in the A. pacificum strain, some experimental groups showed significant differences in cell abundance and pigment composition, while Chl-a SP significantly decreased in all experimental groups. In addition, PST production was stimulated by the addition of C. finmarchicus extracts. No GC toxins were detected in the A. pacificum strain. This study demonstrated that substances derived from C. finmarchicus enhance the production of PSTs in G. catenatum and A. pacificum. Our findings will improve the current understanding of the occurrence and development mechanisms of PSTs in marine ecosystems and contribute to developing strategies to efficiently secure standard reference toxin products using toxic dinoflagellates.