Department of Ecology and Institute of Hydrobiology, Jinan University, 510632, Guangzhou, China.
Ecotoxicology. 2020 Aug;29(6):771-779. doi: 10.1007/s10646-020-02220-5. Epub 2020 May 8.
Many cyanobacterial species co-occur commonly in a freshwater ecosystem and can be consumed simultaneously by zooplankton. Both Microcystis aeruginosa and Cylindrospermopsis raciborskii are the dominant species and coexist in eutrophic tropical waters, and they together are assumed to have exert a stronger effect on the life history traits of cladocerans than a single cyanobacterial species. In the present study, we tested the hypothesis with life-history experiments of Daphnia sienesis, a large cladoceran species in tropics. In the experiments, M. aeruginosa and C. raciborskii were used as a mixture of food with Chlorella pyrenoidosa for the experimental animals. D. sienesis showed excellent growth and survival on sole diets of C. pyrenoidosa (CP). By contrast, Daphnia's growth decreased significantly and reproduction was completely inhibited when cyanobacteria comprised 100% of the food offered. The supplementation of C. pyrenoidosa into cyanobacterial diets significantly decreased their harmful effects on Daphnia, who improved the life history traits with the reduction of cyanobacterial percentage in mixed foods, irrespective of cyanobacterial species. Compared with the cultures of D. sienesis fed with a single cyanobacteria species, the animals in the treatments fed both M.aeruginosa-FACHB469 (F469) and C. raciborskii N8 (N8) had a lower growth rate in all the proportion of C. pyrenoidosa (25% CP, 50% CP or 75% CP). The strongest synergistic inhibition by the two cyanobacterial strains was found in the treatments with the 25% CP (i.e., 25% CP + 37.5% F469 + 37.5% N8), and no animal survived to maturity and reproduced. Thus, the simultaneous exposure to the two cyanobacterial species should be taken into account in assessing the ecological risks of cyanobacterial blooms, since multiple cyanobacterial coexistence can result in strong synergistic inhibition on growth and reproduction of zooplankton.
许多蓝藻物种共同存在于淡水生态系统中，并且可以被浮游动物同时食用。铜绿微囊藻和席藻都是优势物种，共同存在于富营养化的热带水域，并且它们一起对桡足类动物的生活史特征的影响被认为比单一的蓝藻物种更强。在本研究中，我们用热带地区的大型桡足类动物——大型溞（Daphnia sienesis）的生活史实验来检验这一假说。在实验中，铜绿微囊藻和席藻与小球藻（Chlorella pyrenoidosa）一起作为实验动物的混合食物。大型溞在单独以小球藻为食的情况下生长和存活情况良好（CP）。相比之下，当蓝藻占所提供食物的 100%时，大型溞的生长显著下降，繁殖完全受到抑制。将小球藻添加到蓝藻食物中，显著降低了蓝藻对大型溞的有害影响，而无论混合食物中蓝藻的比例如何，大型溞的生活史特征都得到了改善。与单一蓝藻物种培养相比，在同时投喂铜绿微囊藻-FACHB469（F469）和席藻 N8（N8）的处理组中，在所有小球藻比例（25% CP、50% CP 或 75% CP）下，动物的生长速度都较低。在含有 25% CP（即 25% CP+37.5% F469+37.5% N8）的处理组中，两种蓝藻菌株的协同抑制作用最强，没有动物能够成熟和繁殖。因此，在评估蓝藻水华的生态风险时，应考虑到两种蓝藻同时暴露的情况，因为多种蓝藻共存会导致浮游动物生长和繁殖的强烈协同抑制作用。
