Zooplankton Feeding on the Nuisance Flagellate Gonyostomum semen

Abstract

The large bloom-forming flagellate Gonyostomum semen has been hypothesized to be inedible to naturally occurring zooplankton due to its large cell size and ejection of long slimy threads (trichocysts) induced by physical stimulation. In a grazing experiment using radiolabelled algae and zooplankton collected from lakes with recurring blooms of G. semen and lakes that rarely experience blooms, we found that Eudiaptomus gracilis and Holopedium gibberum fed on G. semen at high rates, whereas Daphnia cristata and Ceriodaphnia spp. did not. Grazing rates of E. gracilis were similar between bloom-lakes and lakes with low biomass of G. semen, indicating that the ability to feed on G. semen was not a result of local adaptation. The high grazing rates of two of the taxa in our experiment imply that some of the nutrients and energy taken up by G. semen can be transferred directly to higher trophic levels, although the predominance of small cladocerans during blooms may limit the importance of G. semen as a food resource. Based on grazing rates and previous observations on abundances of E. gracilis and H. gibberum, we conclude that there is a potential for grazer control of G. semen and discuss why blooms of G. semen still occur.

The occurrence and spread of Gonyostomum semen (Ehr.) Diesing (Raphidophyceae) in Norwegian lakes

“…It is therefore likely that both temperature and other factors are controlling the growth and inhibiting success of G. semen. Previous studies suggest that the presence of and grazing from certain zooplankton might influence the occurrence and growth success of G. semen (Hansson, 1996;Findlay et al, 2005;Lebret et al, 2012a;Johansson et al, 2013b), However, we did not have data for this in our study.…”

“…During bloom periods, lower biomass of zooplankton food resources are observed (such as small chrysophytes and chlorophytes) and the assembly of zooplankton taxa differ between bloom and non-bloom lakes (Johansson et al, 2013a). Only some species of zooplankton are known to feed on G. semen ( Lebret et al, 2012a;Johansson et al, 2013b), and negative correlations are found both between large biomasses of G. semen and the amount of certain zooplankton grazers such as Daphnia (Bjørndalen, 1982;Findlay et al, 2005) and between Daphnia and G. semen recruitment rate from cysts (Hansson, 1996). Also G. semen causes problems when sampling with nets, caused by the slime ejected from the trichocysts at cell disturbance, and drinking waters may be affected by clogging of filters (Bjørnd-alen, 1982;Hongve et al, 1988;Berge, 1991;).…”

Gonyostomum semen(Ehr.) Diesing bloom formation in nine lakes of Polesie region (Central–Eastern Poland)

“…There was a supposition that due to its large size and presence of trichocysts the alga is inedible (Havens, 1989;Lebret et al 2012) but some researchers suggested that large zooplankton species may have a negative effect on alga abundance (Cronberg et al, 1988;Findlay et al, 2005). Two experimental studies (Lebret et al, 2012;Johansson et al, 2013) proved that some large species (like Daphnia magna and Eudiaptomus gracilis) could feed on the alga. Together with the fact that G. semen cyst recruitment is inhibited by the presence of Cladocera (Hansson, 2000) it is possible that the structure of zooplankton in lakes plays a role in the alga bloom forming.…”

An experimental study on the influence of the bloom-forming alga Gonyostomum semen (Raphidophyceae) on cladoceran species Daphnia magna

“…This mode of action was proposed by Cronberg et al (1988) to be a defence mechanism against grazers. Nevertheless, recent experimental studies revealed that G. semen cells may be grazed by some rotifers (Asplanchna priodonta), cladocerans (Daphnia magna, D. pulicaria, Holopedium gibberum) or copepods (Diaptomus oregonensis, Eudiaptomus gracilis) (Williamson et al, 1996;Lebret et al, 2012;Johansson et al, 2013;Björnerås, 2014). As reported by Hagman et al (2015), in lakes with high Gonyostomum biomass, bathers often suffered from skin irritation and itching after contact with lake water.…”

“…Rengefors et al (2008) reported that G. semen caused cell lysis of small phytoplankton flagellates, what suggests that it can be harmful for other freshwater organisms. Some field studies focused on the impact of G. semen blooms on phytoplankton, zooplankton, benthic invertebrates and fish (Trigal et al, 2011;Angeler and Johnson, 2013;Johansson et al, 2013), but there is no evidence that this species may negatively affect zooplankton in a direct way. To fulfill this gap, we designed an experimental study with the aim to test the influence of G. semen biomass on zooplankton using D. magna as a model organism.…”