Effects of experimentally induced cyanobacterial blooms on crustacean zooplankton communities

Abstract

SUMMARY 1. Large in situ enclosures were used to study the effects of experimentally induced cyanobacterial blooms on zooplankton communities. A combination of N and P was added to shallow (2 m) and deep enclosures (5 m) with the goal of reducing the TN : TP ratio to a low level (∼5 : 1) to promote cyanobacterial growth. After nutrient additions, high biomass of cyanobacteria developed rapidly in shallow enclosures reaching levels only observed during bloom events in eutrophic lakes. 2. In the shallow enclosures, particulate phosphorus (PP) was on average 35% higher in comparison with deep enclosures, suggesting that depth plays a key role in P uptake by algae. Phytoplankton communities in both deep and shallow enclosures were dominated by three cyanobacteria species –Aphanizomenon flos‐aquae, Anabaena flos‐aquae and Microcystis aeruginosa– which accounted for up to 70% of total phytoplankton biomass. However, the absolute biomass of the three species was much higher in shallow enclosures, especially Aphanizomenon flos‐aquae. The three cyanobacteria species responded in contrasting ways to nutrient manipulation because of their different physiology. 3. Standardised concentrations of the hepatotoxic microcystin‐LR increased as a result of nutrient manipulations by a factor of four in the treated enclosures. Increased biomass of inedible and toxin producing cyanobacteria was associated with a decline in Daphnia pulicaria biomass caused by a reduction in the number of individuals with a body length of >1 mm. Zooplankton biomass did not decline at moderate cyanobacteria biomass, but when cyanobacteria reached high biomass large cladocerans were reduced. 4. Our results demonstrate that zooplankton communities can be negatively affected by cyanobacterial blooms and therefore the potential to use herbivory to reduce algal blooms in such eutrophic lakes appears limited.

Variation in the growth ofMicrocystis aeruginosadepending on colony size and position in colonies

“…Bloom-forming cyanobacteria generally exist as massive or filamentous colonies. Among the many features associated with large colonial forms of cyanobacteria include quick vertical migration (Kromkamp and Walsby, 1990), effective uptake of phosphorus (Shen and Song, 2007), protection from ultraviolet radiation (Sommaruga et al, 2009) and invulnerability to grazers (Ghadouani et al, 2003;Yang et al, 2008). These features are closely related to the ecological advantages of bloom-forming cyanobacteria over unicellular species in water ecosystems.…”

Influence of Daphnia infochemicals on functional traits of Microcystis strains (Cyanobacteria)

“…There is contrasting evidence in the literature on the extent to which grazing by zooplankton can control the development of cyanobacterial blooms. For instance, the effect of Daphnia, a key grazer in standing waters, on Microcystis biomass is debated, as Microcystis may strongly suppress the growth of Daphnia (Ghadouani et al, 2003), while other studies have provided evidence that Daphnia may suppress developing Microcystis blooms depending on initial conditions and history (Christoffersen et al, 1993;Sarnelle, 2007). Probably, environmental conditions are also important for the outcome of these interactions.…”

Short-term dynamics of cladocerans in a eutrophic shallow lake during a shift in the phytoplankton dominance

“…Cyanobacteria are widely considered low quality food for zooplankton, particularly for Daphnia sp., due to their filamentous or colonial structure, nutritional inadequacy and toxin production (e.g., Arnold, 1971;Haney, 1987;Lampert, 1987;Reinikainen et al, 1994;Gulati and DeMott, 1996;Repka, 1996Repka, , 1997DeMott, 1999;DeMott et al, 2001;Rohrlack et al, 2001;Ghadouani et al, 2003). In particular, the main cyanobacteria species recorded in Lake Vela during the study period (A. flosaquae), have been reported as toxic species, able to produce toxins (e.g.…”