Virginia Institute of Marine Science, College of William & Mary
Partnership between Educators and Researchers for
Enhancing Classroom Teaching
(GK-12 PERFECT)
Funding source:
National Science Foundation GK-12 grant no. DGE-0840804
Plankton Blooms in Chesapeake Bay:
Causes and Consequences
http://upload.wikimedia.org/wikipedia/commons/6/6e/Plankton_collage.jpg
http://earthobservatory.nasa.gov/Features/ChesapeakeBay/Images/chesapeake_amo_2004119.jpg
Plankton: Floating or weakly swimming organisms
that drift with ambient water movement
http://upload.wikimedia.org/wikipedia/commons/6/6e/Plankton_collage.jpg
What is a plankton bloom?
Cause of phytoplankton blooms:
Growth > Losses
Cause of phytoplankton blooms:
Growth > Losses
Growth:
O2
CH2O
H2O
(phytoplankton)
CO2
Cause of phytoplankton blooms:
Growth > Losses
Growth:
– Photosynthesis: the process of using light
energy to fix carbon and make organic matter
– Primary production: rate of photosynthesis of
all phytoplankton in an area
(amount of carbon fixed in a given time)
Cause of phytoplankton blooms:
Growth > Losses
Losses:
senescence &
sinking
grazing
flushing/
dilution
Cause of phytoplankton blooms:
Growth > Losses
Losses:
senescence &
sinking
grazing
flushing/
dilution
Cause of phytoplankton blooms:
Growth > Losses
Losses:
High
Growth
senescence &
sinking
grazing
flushing/
dilution
Low
Growth
http://hpl.umces.edu/~lzhong/estuary_coastal/estuary.htm
Direct controls of growth
• Nutrients
• Light
• Temperature
O2
CH2O
H2O
(phytoplankton)
CO2
Major Nutrients
• Nitrogen (NO3-, NO42-, & NH4+)
–Limiting in marine systems
• Phosphorus (PO43-)
–Limiting in freshwater systems
• Silica (SiO2)
–Important to diatoms
• Redfield ratio
106 : 15 : 16 : 1
C
Si
N P
[diatoms]
Direct controls of growth
• Nutrients
• Light
• Temperature
O2
CH2O
H2O
(phytoplankton)
CO2
Light
• Photosynthetically active radiation (PAR)
400 nm
700 nm
Light
Too much light can
reduce
photosynthesis
Rate of photosynthesis 
• Photoinhibition:
Light intensity 
Light
• Self-shading
Direct controls of growth
• Nutrients
• Light
• Temperature – influences rate of
biochemical reactions
Phytoplankton losses
• Senescence/sinking
• Grazing
• Flushing
US JGOFS
Senescence/sinking
• Phytoplankton cells “get old” and sink
– Nutrient limitation
• Further growth impossible after nutrient run out
• Unable to regulate buoyancy properly
– Disease
• Bacteria
• Viruses
– Aggregation
• Older cells may be more “sticky”
Phytoplankton losses
• Senescence/sinking
• Grazing
• Flushing
US JGOFS
Grazing
Many zooplankton eat phytoplankton
copepod
cladoceran
barnacle nauplius
Definitions
Top-down control: Control of the size of a
population from above (grazers/predators)
Bottom-up control: Control of the size of a
population from below (nutrients/food)
Grazing
Lag
Controls on zooplankton growth
• Individuals
– Temperature
– Food availability
• Population
– Predation
Lag
Phytoplankton losses
• Senescence/sinking
• Grazing High
Growth
• Flushing
Low
Growth
Chesapeake Bay - Spring Bloom
Onset of bloom:
Spring freshet (rainfall, snow melt)
Warming/high nutrient surface water
]Phytoplankton growth increases
Head
Mouth
NOT TO SCALE
Chesapeake Bay - Spring Bloom
Decline of bloom:
Increasing temperature
Increased food availability
]Zooplankton grazers increase, exert top-down control
Head
Mouth
NOT TO SCALE
Chesapeake Bay - Fall Bloom
Onset of bloom:
Breakdown of stratification (storms, cooler temperature)
High nutrient bottom water mixed up
Decrease in numbers of zooplankton grazers
]Phytoplankton growth increases
Head
Mouth
NOT TO SCALE
Chesapeake Bay - Fall Bloom
Decline of bloom:
Decreasing photoperiod
Nutrient limitation
Decreasing temperature
NASA: Ocean’s Green Machines
Consequences of blooms
• Phytoplankton blooms are natural
• Problems:
Human induced eutrophication ]
Relaxing of nutrient limitation]
Excessive phytoplankton growth ]
Consequences of blooms
Problems:
Human induced eutrophication ]
Relaxing of nutrient limitation]
Excessive phytoplankton growth ]
– Shading:
Block light to benthos (bad for submerged
aquatic vegetation)
Consequences of blooms
Problems:
Human induced eutrophication ]
Relaxing of nutrient limitation]
Excessive phytoplankton growth ]
– Excess organic matter production:
Respiration during bacterial decomposition can
deplete bottom water O2 (hypoxia/anoxia)
http://www.epa.gov/msbasin/images/eutro_550w.jpg
http://www.epa.gov/msbasin/images/eutro_550w.jpg
http://www.epa.gov/msbasin/images/eutro_550w.jpg
http://www.epa.gov/msbasin/images/eutro_550w.jpg
Consequences of blooms
Problems:
Human induced eutrophication ]
Removal of nutrient limitation]
Excessive phytoplankton growth ]
• Poor aesthetics
• Potentially poor
habitat for larger
animals
www.lifeinfreshwater.org.uk
Consequences of blooms
Problems:
Human induced eutrophication ]
Removal of nutrient limitation]
Excessive phytoplankton growth ]
– Harmful algal blooms (HABs)
Correlation between eutrophication/excess
nutrients and HAB occurrence
NASA: In the Zone
dinoflagellates
diatoms
copepod
cladoceran
barnacle nauplius