Algicidal effects on Heterocapsa circularisquama and ecological response of microbial communities by thiazolidinedione derivative TD49 in mesocosm

Abstract

To assess the algicidal effects on Heterocapsa circularisquama and the response of microbial communities by the thiazolidinedione derivative (TD49), we conducted exposure experiments (control, blank, 0.2, 0.4, 0.6, and 1.0 &micro M TD49) in mesocosm enclosure (1,300 L). As the significantly decreasing of TD49 concentration in seawater, the toxicity of TD49 may have less persistence in marine ecosystem. The biomass of H. circularisquama were decreased by 84% within 2 days at over 0.4 &micro M TD49. The chlorophyll a also reduced dependence on TD49 concentration. Moreover, the concentrations of pH and dissolved oxygen also reduced following the decrease in target H.circularisquama. As the phytoplankton composition, diatoms and cryptophyta in the TD49 treatments were more rapidly increased than control, especially the small pennate diatoms. Heterotrophic bacteria (HB) increased completely contrary to reduction of H. circularisquama, and heterotrophic nano-flagellates (HNFs) grew after HB increasing. Ciliates biomass remained relatively low in TD49 treatments compared to control, whereas aloricate ciliate gradually increased at the end of the experimental period, even with high TD49 concentrations, implying that these ciliates were inhibited or promoted by TD49 concentration gradients. In conclusion, TD49 was an effective agent to reduce for H. circularisquama blooms, and it directly or indirectly affected the microbial communities including the phytoplankton.