Know Your Enemy: Biology, Physiology, Ecology, and Population Dynamics of Zebra Mussels

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Know Your Enemy Biology, Physiology, Ecology,
and Population Dynamics of Zebra Mussels
Robert F. McMahon Department of Biology The
University of Texas at Arlington Arlington, Texas
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• ZEBRA and QUAGGA MUSSELS
• Originally endemic to Europe
• Introduced to North America in 1986
• Discovered in eastern basin of Lake Erie in 1989
• Have since spread throughout US and Canadian
  drainage systems east of the Rocky Mountains
• Great Lakes drainage, the Mississippi River, and
  its eastern tributaries, lower Missouri River,
  Arkansas River and isolated lakes and rivers
• Quagga mussels recently found in Lake Mead, lower
  Colorado River, and lakes in southern California
• Zebra Mussel recently found in San Justo
  Reservoir, Central California
• Most costly aquatic macrofouling and ecological
  pest ever introduced to North American freshwaters

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DREISSENID SHELL MORPHOLOGY
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DREISSENID DISTRIBUTION IN NORTH AMERICA
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• DREISSENID BIOLOGY
• Essentially similar for zebra and quagga mussels
• Adults attach to hard substrata with byssal
  threads, forming thick layers (gt100,000 square
  meter)
• Are filter feeders (bacteria, algae and rotifers)
• Efficiently filter smaller particles (i.e.,
  bacteria lt 1 µm) than native unionid bivalves
  giving them a broader feeding niche
• Separate sexes, external fertilization, complex
  larval stages
• Planktonic veliger larva allows extensive
  dispersal
• Dispersal between water bodies via canals, pipes
  and other conduits
• Rapid growth, short life span, high fecundity
• Adults disperse on floating objects, and barge
  and boat hulls
• Upstream and downstream dispersal
• Overland dispersal on trailered boats and boat
  trailers
• Extensive dispersal power accounts rapid N.A.
  spread and macrofouling

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• FILTER FEEDING
• Zebra and quagga mussels both efficiently filter
  bacterioplankton (lt 1 µm)
• Large adults may filter gt2 L / Day
• Average 1.5 L / Day
• 1,500,000 L / Day at a density of 100,000 mussels
  / m2
• Results in rapid clarification of infested waters
• Removes phytoplankton resulting in starvation of
  unionid bivales
• Quagga mussels more efficient than zebra mussels
  at filtering bacteria
• Leads to eventual replacement of zebra mussels by
  quagga mussels

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Filtration Rates and Particle Size Retention
Particle Retention
Filtration Rates
Single Adult Mussel can Filter more than a Liter
of water per Day
More efficiently remove bacterio-plankton (lt1.0
µm) than other bivales
Griffiths, R. W., Schloesser, D. W., Leach, J.
H., and Kovalak, W. P. 1991. Distribution and
Dispersal of the Zebra Mussel in the Great Lakes
Region, Canadian Journal of Fisheries and
Aquatic Sciences 481381-1388.
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DREISSENID LIFE CYCLE

• External Fertilization
• Fecundity can be 100,000,000 eggs per adult
  female per year
• Trochophore (6-20 Hours)
• No shell ( 40 µm)
• Early Veliger (3-4 Days)
• D-shaped shell (40-100 µm)
• Late veliger (1-2 weeks)
• Umbonal shell (100-200 µm)
• Pediveliger (2-3 weeks)
• Develops foot settles (200-300 µm)
• Plantigrade (3-4 weeks)
• Byssal attachment transforms to mussel shape
  (250-300 µm)
• Juvenile (3-5 Weeks)
• Mussel-shaped shell (gt 300 µm)
• Spawn at low levels 10-16C
• Spawning maximized gt 18-24C
• Settle in three to five weeks

Umbonal Veliger
D-shaped Veliger
Pediveliger
Plantigrade
Juvenile
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DREISSENID LIFE CYCLE
Fertilization ? Trochophore
Early Veliger
Late Veliger
Pediveliger
Early Juvenile
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MUSSEL LARVAE IN PLANKTON SAMPLE
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DREISSENID POPULATION DYNAMICS

• Maximum age 3-5 years depending on population
• Maximum adult size 2.5 4.0 cm dependent on
  population
• Growth rate declines with increasing adult size
• Survival rate is low across year classes
• Adult growth rates and population density
  dependent on temperature and phytoplankton and
  bacterioplankton productivity
• High fecundity leads to development of massive
  populations within 3-5 years of initial
  introduction

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Population Growth Through Time
Lag period when slow increase in density prevents
discovery
Strayer, D. Malcom, H. 2006. Long-term
demography of a zebra mussel (Dreissena
polymorpha) population. Freshwater Biology 51
117-130.
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Vertical Distribution
Soulanges Canal (off St. Lawrence River, Quebec)
Canal is approximately 6 m (20 feet) deep
Ricciardi, A. and Whoriskey, F. 2004. Exotic
species replacement shifting dominance of
dreissenid mussels in the Soulanges Canal, upper
St. Lawrence River, Canada Journal of the North
American Benthological Society 23507514.
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Quagga Replacement of Zebra Mussels
Soulanges Canal (off St. Lawrence River, Quebec)
Ricciardi, A. and Whoriskey, F. 2004. Exotic
species replacement shifting dominance of
dreissenid mussels in the Soulanges Canal, upper
St. Lawrence River, Canada Journal of the North
American Benthological Society 23507514.
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Dreissenid Population Density Dynamics
Cyclic
Population Decline

• Common pattern for many invasives
• Not Common for Zebra Mussels
• Noted Examples
• Lake Erie
• Alpine Lakes in Europe
• Possible Causes
• Predators/Disease
• Food Limitation
• Strong overshoot of carrying capacity

• More Common
• Driven by dominance of strong year-classes
• Period is linked to lifespan of the dominant
  year-class (often 3 to 5 years)
• Cycles tend to dampen over time
• May be restarted with disturbance
• Hudson River population has shown this pattern

Equilibrial
Irregular

• Common Pattern
• Driving Mechanism are unclear
• Difficult for Predictions

• Best suited for making predictions
• Extrapolation
• Understanding long-term impacts
• Not Common

Strayer, D. Malcom, H. 2006. Long-term
demography of a zebra mussel (Dreissena
polymorpha) population. Freshwater Biology 51
117-130.
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Water Quality Factors Affecting Dreissenid Mussel
Distribution and Invasion

• pH Inhabit waters with pH gt 7.4 (basic)
• Salinity
• Do not spawn or successfully fertilize above 7
  ppt
• larvae do not develop at gt 8 ppt
• juveniles and adults do not survive gt 5 ppt (14
  SW)
• Turbidity and Suspended Solids
• Thrive in lower Ohio and Lower Mississippi Rivers
  at gt 80 NTU units
• Turbidity unlikely to be a factor in limiting
  distribution
• Organic Enrichment Does not generally limit
  distribution except when associated with hypoxic
  conditions - will accelerate growth
• Calcium ion Concentration Not found below 12-15
  mg/L Ca
• Total Hardness Not found below 25 mg/L Ca
• Alkalinity Not found below 20 mg/L Ca
• Phosphate Concentration Found as low as 0.001
  mg/L
• Nitrate Concentration Not found below 0.009 mg/L

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Water Quality Factors Affecting Dreissenid Mussel
Distribution and Invasion (Continued)

• Ambient Water Temperature
• Will not tolerate temperatures continuously above
  30C
• Can survive higher temperatures if temperatures
  fall below 30C during the evening
• Great mortality reported in the lower Mississippi
  River during mid-summer at 31C
• Do not reproduce well at lt16C, 12C required for
  spawning
• Oxygen Concentration
• Will not be successful in chronically hypoxic
  waters
• Does not extend into hypoxic hypolimnetic waters
  below thermocline
• Depth Distribution
• Adults not generally found above depths of 1 m
• Juveniles settle above 1 m but migrate into
  deeper waters by fall
• Maximum densities for zebra musses occur at 2-14
  m depth
• Maximum densities for quagga mussels can occur
  below 14 m

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Water Quality Factors Affecting Dreissenid Mussel
Distribution and Invasion (Continued)

• Potassium Ion
• Intolerant of waters with natural potassium
  concentrations gt 30 mg/L K
• Pollution
• Generally as tolerant of industrial and municipal
  water pollution as are native unionids and Asian
  clams
• Will not invade waters made chronically hypoxic
  by receipt of organic pollutants

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Hydrological Factors Affecting Zebra Mussel
Distribution and Invasion

• Rainfall
• Unlikely to invade watersheds with low rainfall
  limiting the number of permanent rivers and lakes
• Most successful in watersheds with high rainfall
  and large, stable, permanent bodies of water
• Flooding and Water Level Variation
• Will not be successful in rivers prone to
  extensive flooding and lakes with large annual
  level fluctuations
• Large stable rivers and lakes with reduced level
  fluctuations are most prone to invasion
• Calcium Content/Water Hardness/Alkalinity
• Generally not successful in very soft waters of
  low calcium content
• Can invade as low as 12-15 mg/L Ca
• Reach high densities above 20 mg/L Ca
• pH
• Will not invade waters below pH of 7.4
• Reach highest densities at pH gt 8.0
• Unlikely to be successful in waters receiving
  acid mine drainage

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Hydrological Factors Affecting Zebra Mussel
Distribution and Invasion (Continued)

• Size of Water Body
• Will be most successful in large, stable rivers
  and lakes
• Generally not found in lakes with surface areas
  less than 0.1 km
• Potassium Concentration
• Eliminated from waters gt 30 mg K/L
• Navigable Rivers
• Most likely to invade navigable freshwaters
• Adults are transported on hulls of barges and
  commercial vessels
• Availability of Hard Substrata
• Greatest densities in habitats with abundant hard
  substrata
• Can colonize sandy bottoms if solid objects
  (rocks, wood, clam shells) support initial
  attachment of colonizers
• Do not generally colonize muddy substrata
• Latitude
• Will not invade latitudes where water
  temperatures are generally too cold to reproduce
  or too warm to tolerate
• 55N - 25N in North America

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Thermal Tolerance

• Chronic upper thermal limits impacted by prior
  thermal history and season
• Incipient maximal upper thermal limit 30C
  (86F)
• Appear to have a limited capacity for thermal
  selection
• Thermally tolerant race may have been developed
  in the lower Mississippi River
• Thermal selection may be occurring in
  southwestern water bodies

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Selection For Thermal Tolerance

• Acute upper thermal limit determined after
  selection by exposure to increasing temperature
  at a rate of 1/10 min to progressively higher
  lethal temperatures.
• Acclimated to 25C prior to test
• Induced moralities of 52, 61, and 68 at 37,
  37.5, 37.3C, respectively
• Determine thermal tolerance after recovery
• Chronic thermal tolerance time determined after
  exposure to lethal temperature of 33C for 10 h
• Acclimated to 25C prior to test
• Induced mortality of 29
• Determined tolerance time after recovery

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Acute Respiratory Response to Progressive Hypoxia
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Mortality on Exposure to 5 Air O2 Saturation
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• Emersion Tolerance
• Summer emersion and desiccation (lt10 Days)
• Temperature and humidity dependent

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Tolerance of Prolonged Starvation in Zebra Mussels