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Responses of cyanobacteria to herbivorous zooplankton across predator regimes: who mows the bloom?

Urrutia Cordero, Pablo LU ; Ekvall, Mattias LU and Hansson, Lars-Anders LU (2015) In Freshwater Biology 60(5). p.960-972
Abstract
1. The massive growth of large, toxic cyanobacteria in eutrophic waters has traditionally been explained by their evolution of defences to herbivorous zooplankton. These conclusions come mostly from studies using the large-bodied cladoceran Daphnia as a grazer model. In contrast, very little is known about the effects of other zooplankters such as copepods and small cladocerans that, unlike Daphnia, often coexist with cyanobacterial blooms and under high levels of fish predation. We performed a series of grazing experiments during a cyanobacterial bloom in a eutrophic lake, subject to decreasing predation on zooplankton (removal of cyprinid fish). We also used long-term observational data to analyse the response of cyanobacteria to changes... (More)
1. The massive growth of large, toxic cyanobacteria in eutrophic waters has traditionally been explained by their evolution of defences to herbivorous zooplankton. These conclusions come mostly from studies using the large-bodied cladoceran Daphnia as a grazer model. In contrast, very little is known about the effects of other zooplankters such as copepods and small cladocerans that, unlike Daphnia, often coexist with cyanobacterial blooms and under high levels of fish predation. We performed a series of grazing experiments during a cyanobacterial bloom in a eutrophic lake, subject to decreasing predation on zooplankton (removal of cyprinid fish). We also used long-term observational data to analyse the response of cyanobacteria to changes in abundance, body size and biomass of the naturally, coexisting zooplankton community across different predator regimes. A natural grazer community, dominated by selective herbivores like calanoid and cyclopoid copepods, positively affected cyanobacterial growth in early summer at low cyanobacterial densities. However, cyclopoid copepods and small cladocerans suppressed the growth of Anabaena, Microcystis and Planktothrix species under bloom conditions in late summer, with the exception of the highly toxic Microcystis botrys. Long-term observational data support the results from the grazing experiments regarding the potential capacity of the natural zooplankton community to suppress cyanobacterial growth, especially of the dominant taxon Microcystis (including the most toxic species, M.botrys). In particular, these results suggest that direct grazing may contribute significantly to the observed 72% decrease in Microcystis biomass through a 111% increase in abundance of cyclopoid copepods, and an 18% increase in body size of cyclopoid copepods and a 31% increase in body size of the generalist feeder Daphnia, during the biomanipulation. Together, these results suggest that, within the complex interactions brought about by trophic cascades, direct grazing by the coexisting zooplankton community is a strong driver regulating cyanobacterial growth in eutrophic lakes and that this can display contrasting effects, both seasonally and under different levels of fish predation. Importantly, we show that herbivory may be enhanced along a gradient of decreasing fish predation by the combined action of copepods (selective herbivores) and Daphnia (generalist herbivores). (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
copepods, cyanobacteria, herbivory, predation, zooplankton
in
Freshwater Biology
volume
60
issue
5
pages
960 - 972
publisher
Wiley-Blackwell
external identifiers
  • wos:000352571600010
  • scopus:84926318661
ISSN
0046-5070
DOI
10.1111/fwb.12555
language
English
LU publication?
yes
id
acfd4afe-c942-4b96-9951-5742488f5ce9 (old id 5402809)
date added to LUP
2015-05-19 13:42:44
date last changed
2017-10-29 03:56:20
@article{acfd4afe-c942-4b96-9951-5742488f5ce9,
  abstract     = {1. The massive growth of large, toxic cyanobacteria in eutrophic waters has traditionally been explained by their evolution of defences to herbivorous zooplankton. These conclusions come mostly from studies using the large-bodied cladoceran Daphnia as a grazer model. In contrast, very little is known about the effects of other zooplankters such as copepods and small cladocerans that, unlike Daphnia, often coexist with cyanobacterial blooms and under high levels of fish predation. We performed a series of grazing experiments during a cyanobacterial bloom in a eutrophic lake, subject to decreasing predation on zooplankton (removal of cyprinid fish). We also used long-term observational data to analyse the response of cyanobacteria to changes in abundance, body size and biomass of the naturally, coexisting zooplankton community across different predator regimes. A natural grazer community, dominated by selective herbivores like calanoid and cyclopoid copepods, positively affected cyanobacterial growth in early summer at low cyanobacterial densities. However, cyclopoid copepods and small cladocerans suppressed the growth of Anabaena, Microcystis and Planktothrix species under bloom conditions in late summer, with the exception of the highly toxic Microcystis botrys. Long-term observational data support the results from the grazing experiments regarding the potential capacity of the natural zooplankton community to suppress cyanobacterial growth, especially of the dominant taxon Microcystis (including the most toxic species, M.botrys). In particular, these results suggest that direct grazing may contribute significantly to the observed 72% decrease in Microcystis biomass through a 111% increase in abundance of cyclopoid copepods, and an 18% increase in body size of cyclopoid copepods and a 31% increase in body size of the generalist feeder Daphnia, during the biomanipulation. Together, these results suggest that, within the complex interactions brought about by trophic cascades, direct grazing by the coexisting zooplankton community is a strong driver regulating cyanobacterial growth in eutrophic lakes and that this can display contrasting effects, both seasonally and under different levels of fish predation. Importantly, we show that herbivory may be enhanced along a gradient of decreasing fish predation by the combined action of copepods (selective herbivores) and Daphnia (generalist herbivores).},
  author       = {Urrutia Cordero, Pablo and Ekvall, Mattias and Hansson, Lars-Anders},
  issn         = {0046-5070},
  keyword      = {copepods,cyanobacteria,herbivory,predation,zooplankton},
  language     = {eng},
  number       = {5},
  pages        = {960--972},
  publisher    = {Wiley-Blackwell},
  series       = {Freshwater Biology},
  title        = {Responses of cyanobacteria to herbivorous zooplankton across predator regimes: who mows the bloom?},
  url          = {http://dx.doi.org/10.1111/fwb.12555},
  volume       = {60},
  year         = {2015},
}