The Cyanobacterium Microcystis aeruginosa Is Nutritionally Inadequate, but Not Toxic, for the Freshwater Rotifer Brachionus calyciflorus

Primary Faculty Mentor’s Name

Emily K Prince

Proposal Track

Student

Session Format

Paper Presentation

Abstract

Toxic cyanobacterial blooms are a nuisance for freshwater recreation, and can be a major problem for drinking water supplies. For example, the freshwater cyanobacterium Microcystis aeruginosa is known to produce microcystins, compounds toxic to vertebrates. Its effects on zooplankton is less clear, but in one study microcystins were shown to inhibit the growth of some clones of the zooplanker Daphnia pulicaria, but not others. However, further research to clarify the effects of microcystins on zooplankton is needed. In this study, we attempted to decipher the effects of M. aeruginosa on the freshwater rotifer Brachionus calyciflorus. First, we fed B. calyciflorus either a toxic or non-toxic strain of M. aeruginosa alone or as part of a mixed diet. We determined the survival and egg production of rotifers on all diets. In a separate experiment, we fed rotifers a mixed diet and measured rotifer consumption rate of M. aeruginosa and a control food. We also measured the effect of rotifer grazing on M. aeruginosa cell number and photosynthetic efficiency. Overall, we found that grazing pressure from rotifers was stressful to M. aeruginosa, and resulted in decreased photosynthesis. We found that neither the toxic nor the non-toxic strain of M. aeruginosa was adequate for B. calyciflorus as a sole food. However, when M. aeruginosa was part of a mixed diet, rotifer survival and egg production increased significantly. Interestingly, rotifers actually consumed a higher proportion of M. aeruginosa than the control food, although it is unclear whether rotifers are able to select which algal cells to eat. Our results suggest that M. aeruginosa is nutritionally inadequate for B. calyciflorus, but that when the cyanobacterium is part of the phytoplankton community it can supplement rotifer diets. Additionally, our results suggest that microcystin is not toxic to B. calyciflorus. These results may have implications for whether zooplankton are able to control or terminate cyanobacterial blooms.

Keywords

Cyanobacteria, Toxin, Harmful algal bloom

Location

Room 1909

Presentation Year

2014

Start Date

11-15-2014 8:30 AM

End Date

11-15-2014 9:30 AM

Publication Type and Release Option

Presentation (Open Access)

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Nov 15th, 8:30 AM Nov 15th, 9:30 AM

The Cyanobacterium Microcystis aeruginosa Is Nutritionally Inadequate, but Not Toxic, for the Freshwater Rotifer Brachionus calyciflorus

Room 1909

Toxic cyanobacterial blooms are a nuisance for freshwater recreation, and can be a major problem for drinking water supplies. For example, the freshwater cyanobacterium Microcystis aeruginosa is known to produce microcystins, compounds toxic to vertebrates. Its effects on zooplankton is less clear, but in one study microcystins were shown to inhibit the growth of some clones of the zooplanker Daphnia pulicaria, but not others. However, further research to clarify the effects of microcystins on zooplankton is needed. In this study, we attempted to decipher the effects of M. aeruginosa on the freshwater rotifer Brachionus calyciflorus. First, we fed B. calyciflorus either a toxic or non-toxic strain of M. aeruginosa alone or as part of a mixed diet. We determined the survival and egg production of rotifers on all diets. In a separate experiment, we fed rotifers a mixed diet and measured rotifer consumption rate of M. aeruginosa and a control food. We also measured the effect of rotifer grazing on M. aeruginosa cell number and photosynthetic efficiency. Overall, we found that grazing pressure from rotifers was stressful to M. aeruginosa, and resulted in decreased photosynthesis. We found that neither the toxic nor the non-toxic strain of M. aeruginosa was adequate for B. calyciflorus as a sole food. However, when M. aeruginosa was part of a mixed diet, rotifer survival and egg production increased significantly. Interestingly, rotifers actually consumed a higher proportion of M. aeruginosa than the control food, although it is unclear whether rotifers are able to select which algal cells to eat. Our results suggest that M. aeruginosa is nutritionally inadequate for B. calyciflorus, but that when the cyanobacterium is part of the phytoplankton community it can supplement rotifer diets. Additionally, our results suggest that microcystin is not toxic to B. calyciflorus. These results may have implications for whether zooplankton are able to control or terminate cyanobacterial blooms.