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Lagrangian description of 2-D marine larval dispersal kernels. Karen Pehrson Edwards, Jon Hare, Cisco Werner, Harvey Seim Ocean Sciences, Feb. 2006. Outline. Background: Dispersal Kernels Model Region: The South Atlantic Bight Methods: Lagrangian Particle Tracking

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lagrangian description of 2 d marine larval dispersal kernels

Lagrangian description of 2-D marine larval dispersal kernels

Karen Pehrson Edwards, Jon Hare, Cisco Werner, Harvey Seim

Ocean Sciences, Feb. 2006

outline
Outline
  • Background: Dispersal Kernels
  • Model Region: The South Atlantic Bight
  • Methods: Lagrangian Particle Tracking
  • Results: Quantifying the dispersal kernels
  • Next steps

Provided by Harvey Walsh, NOAA Beaufort

dispersal kernels

1D dispersal kernel -Passive, Mean Flow- Diffusion

Dispersal Kernels
  • A dispersal curve, or dispersal kernel (probability density function), the probability that a larva will settle at a given distance from its release location.

Cowen et al. (2002)

  • Factors affecting dispersal include:
    • Physical factors:
      • Advection & diffusion
      • Intermittent/ episodic events,
      • interannual variability,
      • long-term modulations
    • Biological factors:
      • Spawning time & location
      • Larval behavior
      • Along-trajectory mortality
      • Larval condition and the ability to respond to cues for suitable habitat.

Cowen et al. (2002), Mora & Sale (2002)

Provided by Harvey Walsh, NOAA Beaufort

understanding larval dispersal provides important information about
Understanding larval dispersal provides important information about:
  • Population connectivity
  • Population persistence or sustainability
  • Effectiveness and design of management strategies such as MPAs

Cowen et al, 2002

slide5
Question: what is the relative importance of the following factors on larval dispersal and population connectivity?
  • time of release,
  • location of release,
  • larval duration,
  • larval behavior, and
  • larval dispersion
  • Focusing on a case study in the South Atlantic Bight
the south atlantic bight

Cape Hatteras

NC

SC

GA

Cape Canaveral

FL

The South Atlantic Bight

Gulf Stream

the south atlantic bight7
The South Atlantic Bight

Inner Shelf (<15-20m):

  • River runoff
  • Atmospheric fluxes and tides

Mid- Shelf (20-40m):

  • Winds
  • Tides and Gulf Stream

Outer- Shelf (>40m):

  • Gulf Stream

http://www.skio.peachnet.edu/

Lee et al. 1991

methods lagrangian particle tracking model
Methods: Lagrangian Particle Tracking Model
  • 3D long-term monthly mean circulation fields (Blanton et al., 2003)
  • Plus the M2 tide
  • and turbulent random kick (providing larval dispersion).
  • 300 particles released in each model run.
results grnms dispersal
Results: GRNMS Dispersal
  • Monthly releases
  • Mid-depth releases
  • 30d passive
  • Principal Component Analysis (PCA) defines the dispersal kernel.
larval behavior
Larval Behavior

Resulting mean dispersal for each behavior:

Simple Model Behaviors

larval behavior13
Larval Behavior

Dispersal for particles released at 60m isobath:

Mid-depth

Shallow

Deep

physics
Physics

Tracks of drifters released at GRNMS

  • Model 2002-2004 to look at interannual variability
modeling specific species

www.martinreefs.com/pages/species_index/species_common.html

Adult Black Sea Bass Species Occurrence

Hare et al., 1999

http://map.mapwise.com/safmc MARMAP survey

Modeling specific species
dispersal in the sab
Dispersal in the SAB
  • Dominant factors: Time and Location of Release
    • with strong seasonal modulation
  • Behavioral Implications
    • Adult behavior (spawning time & location):
      • most important factor in quantifying dispersal with spawning in (apparently) retentive inner- to mid-shelf
    • Larval behavior: smaller effects possibly due to
      • Weak vertical structure on inner-shelf
      • Long-term (average) flow fields don’t account for transient features.
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