Grazing resistance allows bloom formation and may explain invasion success of Gonyostomum semen

Abstract

The nuisance alga Gonyostomum semen (Raphidophyceae) has expanded in the Nordic countries during the last decades and can dominate lake phytoplankton communities almost completely. A possible explanation to its dominance could be limited grazing by zooplankton. We investigated the potential grazing pressure on G. semen using an experimental approach supported by field data. We determined the grazing rate by cladocerans, calanoid copepods, and Chaoborus larvae to determine which were able to feed on G. semen. Only the large cladoceran Daphnia magna was able to feed successfully on G. semen. The large cell size of G. semen was likely a limiting factor for the filtering apparatus of smaller cladocerans. The copepod Eudiaptomus gracilis did not graze on G. semen, although the mechanism behind this selective feeding is still unknown. In addition to the experimental study, we quantified the zooplankton and phytoplankton communities in 40 lakes to determine the composition and abundance of the zooplankton communities co-occurring with G. semen, suggesting that large cladoceran species were not present in lakes where G. semen occurred. Hence, the growth of G. semen is not significantly controlled by grazing in natural systems, which likely facilitates bloom formation and invasion success of G. semen.

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.…”

Cyanophytes and chlorophytes versus raphidophytes in humic lakes with different catchment basins

“…Moreover, it is able to produce toxins, which can inhibit the development of other algae (Cronberg et al 1988;Reynolds 2006). The large size of cells and grazing avoidance strategies hamper the zooplankton pressure and favours the abundant occurrence of G. semen in brown water lakes (Rengefors et al 2008;Lebret et al 2012;Johansson et al 2013).…”