LARVAL TRANSPORT

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LARVAL TRANSPORT
Eileen E. Hofmann Center for Coastal Physical
Oceanography Old Dominion University

• Potential for Spread
• Rate of Spread

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Outline of Presentation

• Can it happen example of transport
• Conditions that affect larval survival
• Environmental conditions climate change
• How fast/far can transport occur
• Suggestions for consideration by panel

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• Distance of 1700 km
• Larval life of about six
• to eight months
• Krill populations at
• South Georgia not
• self-sustaining
• South Georgia system
• dependent on an
• upstream source

Fach et al. (2002, MEPS)
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Sea ice extent determines winter survival
Food Availability
Sea Ice Concentration and Extent
Fach et al. (2002, MEPS)
Environmental Conditions Affect Larval Survival
Fach et al. (2002, MEPS)
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• Larval transport happens over large scales
• Environmental control on survival during
  transport
• Importance of knowing what sustains larvae
• as they are moved from spawning area
• Larval transport can sustain populations far
  removed
• from the initial spawning area
• Implication Distribution of the
  adults/population is
• larger than the distribution
  of the brood
• stock

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Conditions that Affect LarvalTransport in
Chesapeake Bay

• Temperature
• Timing of Food Availability
• Food Quantity
• Food Quality
• Food Composition

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Dekshenieks et al. (1993, JSR)
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Longest larval times occur in northern bays
Dekshenieks et al. (1993, JSR)
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Early bloom extends larval time
Summer bloom shortens larval time
Fall bloom extends larval time
Spring and fall blooms provide optimal conditions
Dekshenieks et al. (1993, JSR)
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Ratio of neutral lipid to polar lipid is
important in determining successful metamorphosis

Bocheneck et al. (2000, JSR))
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High protein diet results in unsuccessful metamorp
hosis at all egg sizes and respiration rates
Low protein diet results in successful
metamorphosis at essentially all egg sizes and
respiration rates
Bochenek et al. (2001, JSR)
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Short-term fluctuations in food supply can
have large effects on larval survival
Bocheneck et al. (2000, JSR)
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Potomac River
Used environmental data sets from the EPA
monitoring stations
Oyster data available from a nearby reef
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Predicted Salinity Change for Chesapeake Bay
from the Hadley Center Climate Model
Amount of Salinity Decrease
Najjar et al. (2000, LO)
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Potomac River Future
Potomac River becomes less saline with a warming
climate
Potomac River - Present
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Potomac River - Present
Potomac River - Future
Overall oyster biomass decreases with
climate warming
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York River
Used the EPA monitoring data sets for
environmental conditions
Used oyster data sets from nearby reef
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York River - Future
Becomes less saline with a warming climate
York River - Present
York River - Present

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York River - Present
Some reduction in oyster biomass but still an
increasing trend with climate warming
York River Future
Implication is that oyster populations in
southern Chesapeake Bay may provide larvae for
the entire Bay if climate warming occurs
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How Far Can Larvae BeTransported?

• Larval life span of 20 days and a current
• velocity of 10 cm/s 173 km
• Larval life span of 25 days and a current
  velocity of 10 cm/s 216 km
• Larval life span of 20 days and a current
  velocity of 5 cm/s 86 km
• Chesapeake Bay is about 250 km in length

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Summary

• Larvae are transported from spawning areas over
  large distances
• Environmental conditions are important in
  determining larval survival
• Climate warming is an issue to consider because
  it will alter the habitat and possible source
  regions for larvae

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Considerations

• Oysters are transplanted world wide on purpose
• Number of oyster species have been moved
  culture and wild populations
• No cases where transplanted oysters have
  out-competed native populations
• Implication Oysters are not good invaders

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• Why are oysters not good invaders?
• High rates or reproduction
• Do not seem to be selective feeders
• Suggestion Evolved to fit a particular type of
  habitat and are not able to exploit a range of
  habitats

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Models of Invading Species

• Traveling wave model (black plague)
• Propagation model (leap frog seeds)
• Wave model slower than dispersion rate
• Propagation model not applicable as currently
  formulated
• Suggestion Need new modeling approach that uses
  hydrodynamically driven transfer functions and
  includes biology of species of interest

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What Needed?

• Long-term monitoring of the habitat that includes
  measurements of food quantity as well as quality
• Development of a schematic circulation pattern
  for Chesapeake Bay from models and measurements
• Studies of the basic biology of the species
  within the context of its environment
• Development of modeling approaches that include
  the life history of the species and its
  environment
• Focus on post-settlement population as well as
  larvae