Cyanobacteria Blooms:

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Cyanobacteria Blooms Effects on Aquatic
Ecosystems
Karl E. Havens University of Florida /
IFAS Department of Fisheries and Aquatic Sciences
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Outline

• What kind of algae form these blooms?
• How does bloom occurrence vary seasonally?
• How does it vary with trophic state?
• What factors trigger onset and collapse of
  blooms?
• What are the ecosystem impacts?
• What are the key data gaps / research needs?

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Data from Lake George, Florida provided by Ed
Phlips (University of Florida)
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Zohary, T. et al. 1995. Cyanobacteria-phytoplankto
n dynamics in a hypereutrophic African lake.
Water Science Technology 32 103-104.
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Downing, J.A., S.B. Watson and E. McCauley. 2001.
Predicting cyanobacteria dominance in lakes.
Canadian Journal of Fisheries and Aquatic
Sciences 581905-1908.
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Havens, K.E., R.T. James, T.L. East and V.H.
Smith. 2003. NP ratios, light limitation, And
cyanobacterial dominance in a subtropical lake
impacted by non-point source nutrient Pollution.
Environmental Pollution 122 379-390.
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Lathrop, R.C., S.R. Carpenter, C.A. Stow, P.A.
Soranno and J.C. Panuska. 1998. Phosphorus
loading reductions needed to control blue-green
algal blooms in Lake Mendota. Canadian Journal of
Fisheries and Aquatic Sciences 55 1169-1178.
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Soranno, P.A. 1997. Factors affecting the timing
of surface scums and epilimnetic blooms of
blue-green algae in a eutrophic lake. Canadian
Journal of Fisheries and Aquatic Sciences 54
1965-1975.
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Onset of blooms

• Increased water temperature
• Stable water column (species dependent)
• Reduced flow / continuous low flow (rivers)
• Depletion of nitrate nitrogen relative to ammonia
• Low DINSRP ratio
• Elevated pH, depletion of free carbon dioxide
• Selective grazing by zooplankton on edible
  algae
• High availability of soluble P or sediment source

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Bloom collapse

• Decreased solar radiation (cloudy days)
• Input of turbid or colored water
• Increased water flow
• Enhanced grazing by certain fish
• Increased turbulence (species specific)
• Input of water high in herbicides from the
  watershed

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EVENT
RESPONSE
IMPACT

• Light limitation plants, epiphyton, benthic
  algae, phytoplankton

Reduced Transparency

• Sub-lethal and lethal impacts
• to fish populations

Elevated pH
BLOOM FORMATION

• Altered competitive interactions
• among phytoplankton

Reduced CO2

• Allelopathy, sub-lethal and lethal toxic
  effects on fish, zooplankton,
  macro-invertebrates, wading birds, other aquatic
  vertebrates

Toxin Production
Increased Algal Size

• Impacts on zooplankton grazing and food web
  efficiency

Hypoxia / Anoxia
BLOOM COLLAPSE

• Fish kills, sub-lethal and lethal impacts on
  other biota

Ammonia
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Biological Effects 1. Plants / Alternative States
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Alternative
States
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Biological Effects 2. Zooplankton / Food Webs
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Effects on grazing zooplankton

• Mechanical interference
• Toxic effects
• P limitation at high CP ratios

Results in

• Reduced growth rates
• Reduced fecundity
• Reduced longevity
• Increased mortality
• Large Daphnia most sensitive
• Food web effects

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Size
Zooplankton
Phytoplankton
Nutrients
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Trophic effects on fish

• Fish biomass correlated with TP and Chl a
• Changes in fish community structure with
  eutrophication
• Loss of piscivores, increased omnivores
• Studies focused in temperate regions where main
  effect may be loss of cold water hypolimnetic
  refuge in summer due to anoxia
• No major changes in fish community structure
  noted in Florida lakes (Bachmann et al. 1996)
  with increased TP and Chl a

Bachmann et al. 1996. Relations between trophic
state indicators and fish in Florida (USA)
lakes. Canadian Journal of Fisheries and Aquatic
Sciences 53 842-855.
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Biological Effects 3. Benthic Communities
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Palmer, M.A., A.P. Covich, S. Lake et al. 2000.
Linkages between aquatic sediment biota And life
above sediments as potential drivers of
biodiversity and ecological processes. BioScience
50 1062-1075.
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Biological Effects 4. Impacts of Cyanobacterial
Toxins
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Neurotoxins
Chemical Structure Alkaloid. Mode of Action
Neuromuscular block, e.g. block of sodium
pump. Symptoms Convulsions, muscle
cramps, respiratory distress, heart
failure death in as little as minutes very
fast death factor. Occurrence Relatively rare
compared to hepato- toxins, fortunately.
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Anatoxin-a
One of the first cyanobacterial neurotoxins
described very fast death factor, Gorham 1964.
Associated Species Anabaena flos-aquae,
Oscillatoria formosa, Aphanizomenon flos-aquae
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Hepatotoxins
Chemical Structure cyclic complex
peptides Mode of Action inhibition of protein
synthesis and disruption of cytoskeleton
in hepatocyte (liver) cells Symptoms liver
cancer and chronic problems associated with
gastro-intestinal tract Occurrence relatively
common in lakes with dense blooms of
Microcystis or Cylindrospermopsis
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Microcystin
One of the first cyanotoxins described, fast
death factor (Bishop et al. 1959). Cyclic
peptide, over 50 variants discovered so far.
Specific modes of action necrosis the liver,
death from hemorrhagic shock. Inhibition of
protein synthesis, DNA damage. Possible tumor
promotion.
Associated species Microcystis aeruginosa
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Cylindrospermopsin
Alkaloid tricyclic guanidinyl hydroxymethyluraci
l (Ohtani et al. 1992). Associated with now
famous Palm Island, Australia Intoxication of
148 people in 1979 (Bourke et al. 1983).
Specific mode of action cytotoxicity, lesions,
necrosis, hepato-enteritis. Possibly related to
suppression of glutathione levels (Runnegar et
al. 1994).
Associated Species Cylindrospermopsis raciborski
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Some Documented Effects of Cyanobacterial Toxins

• Suppression of zooplankton grazing (Gilbert 1990)
• Allelopathy on other phytoplankton (Suikkanen et
  al. 2004)
• Hepatotoxic effects on fish (Ernst et al. 2001)
• Renal failure in fish (Kotak et al. 1996)
• Inhibition of fish gill Na/K-ATPase activity
  (Bury et al. 1998)
• Accumulation in copepod body tissues and fecal
  pellets and potential for accumulation in higher
  trophic levels in plankton and benthos
  (Lehtiniemi et al. 2002)
• Accumulation in crayfish tissues and potential
  for transfer to higher trophic levels (Liras et
  al. 1998)
• Mass mortality of ducks reported during a
  Microcystis bloom in Japan (Matsunaga et al. 1999)

Most results from controlled lab experiments
and toxic effects occurred at high doses of toxins
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Estimates of summer internal P loading by
vertical migration of cyanobacteria

• 2.3 mgP/m2/day (Barbiero and Welch 1992)
• 2.5 mgP/m2/day (Pettersson et al. 1993)
• 2.2 to 3.6 mg/m2/day (Barbiero and Kann 1994)
• 2.0 mgP/m2/day (Head et al. 1999)
• Head et al. (1999) conclude that following
  reduction of external phosphorus loading,
  utilization of such internal phosphorus sources
  may delay expected reductions of bloom-forming
  cyanobacterial communities, and consequently
  improvements in other aspects of water quality.

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Unresolved questions / research focus areas

• What physical, chemical and biological factors
  determine level of toxin production during a
  bloom?
• What are the community level impacts of toxic
  cyanobacterial blooms?
• What impacts do changes in food web structure and
  function during cyanobacterial dominance have on
  fish?
• To what extent does dominance by vertically
  migrating cyanobacteria lengthen response time of
  aquatic ecosystems to nutrient load reduction?