Responses of a tropical micro-crustacean, Daphnia lumholtzi, upon exposures to dissolved toxins and living cells of cyanobacteria

10 AM Tuesday, 17th November, 2020 - CARE meeting room (B7, 1st floor)

Thi-My-Chi Vo^a, Ba-Trung Bui^b,c, Claudia Wiegand^d, Khuong V. Dinh^e,f, Thanh-Son Dao^g*

^aInstitute of Research and Development, Duy Tan University, Da Nang, Vietnam.

^bInstitute for Environment and Resources, VNU-HCM, 142 To Hien Thanh St., Dist. 10, Hochiminh City, Vietnam

^cAquatic Ecology & Water Quality Management Group, Department of Environmental Sciences, Wageningen University, P.O. Box 47, 6700 AA Wageningen, The Netherlands

^dUniversity Rennes 1, UMR 6553 ECOBIO, Campus de Beaulieu, 35042 Rennes Cedex, France

^eSchool of Biological Science, Washington State University, Pullman, WA, U.S.A.

^fDepartment of Fisheries Biology, Nha Trang University, Nha Trang City, Vietnam

^gHochiminh City University of Technology, VNU-HCM, 268 Ly Thuong Kiet St., Dist. 10, Hochiminh City, Vietnam

* Corresponding author Email address: dao.son@hcmut.edu.vn (T.S. Dao)

The mass development and expansion of cyanobacteria release cyanotoxins in the aquatic environment and cause serious problems for grazers such as micro-zooplankton. In contrast to aquatic ecosystems in temperate regions, impacts of cyanobacteria and their toxins on tropical micro-crustaceans are relatively understudied. In this study, acute and chronic effects of pure microcystin-LR (MC-LR), a crude extract of water bloom sample with a dominance of Microcystis aeruginosa containing microcystins (MCE) and living cells of Cylindrospermopsis curvispora were tested on a tropical micro-crustacean, Daphnia lumholtzi. The 24h– and 48h–LC50 values for MC-LR ranged from 247 – 299, and 331 – 409 µg MCE L-1, respectively. Exposures to 1 – 25 µg MCE L-1 decreased survival, fecundity, and reproduction of D. lumholtzi. The impacts of C. curvispora cells on life-history traits of D. lumholtzi were density-dependent and more severe than the impacts of dissolved microcystins. It could be that the adverse effects of C. curvispora on D. lumholtzi are linked to a combination of potential toxic metabolites, mal-nutrients, feeding and swimming interference. Daphnia lumholtzi used in this study is more sensitive to microcystins compared to Daphnia species from temperate regions. Therefore, we highly suggest using D. lumholtzi as a model species for toxicity testing and monitoring on water quality, particularly in tropical countries.

Keywords: acute lethal concentration, clutch size, Cylindrospermopsis curvispora, microcystins, reproduction, survival proportion