Lagrangian Description of Marine Larval Dispersal Kernels

1. Lagrangian Description of Marine Larval Dispersal Kernels www.martinreefs.com/pages/species_index/species_common.html Larval Behaviors near-surface fixed-depth mid-depth passive fixed-depth above bottom Mid-depth Shallow Deep Cape Hatteras NC SC GA Cape Canaveral FL • Inner Shelf (<15-20m): • River runoff • Atmospheric fluxes and tides • Mid- Shelf (20-40m): • Winds • Tides and Gulf Stream • Outer- Shelf (>40m): • Gulf Stream Lee et al. 1991 www.skio.peachnet.edu Karen Pehrson Edwards1*, Jon Hare2, Cisco Werner1 1Department of Marine Sciences, University of North Carolina-Chapel Hill 2NOAA NMFS NEFSC, Narragansett Laboratory Introduction Individual based models (IBMs) track the characteristics of individual organisms over time and can be used to make global population-level statements. One natural application of spatially-explicit IBMs is the quantitative, Lagrangian, description of the post-spawn dispersal phase of individuals, where planktonic larvae are entrained in oceanic circulation fields with limited control over their trajectories. Quantitative measures of connectivity can be expressed through dispersal curves or dispersal kernels, the probability that a larva will settle at a given distance from its release location. • Lagrangian Particle Tracking Model • Lagrangian Particle Model: using a realistic, highly resolved circulation model for the shelf region • the 3D long-term monthly mean circulation fields (including wind-driven and baroclinic) • plus the M2 tide • and turbulent random kick (providing larval dispersion). • 300 particles released in each model run. • Fully factorial modeling approach for the 5 factors tested, resulting in 1,620 model runs: Results Using MANOVA (1620 model runs) quantify the relative importance of each factor: Larval Behavior These behaviors were chosen in order to sample the entire water column and represent the maximum effect of larval behavior. On the inner-shelf, in shallow water, the top & bottom Ekman layers may merge and the water column may move largely as a slab. • Research Questions • As part of a larger effort in the development of Marine Protected Areas (MPAs) on the southeastern U.S. continental shelf, we use Lagrangian methods to construct dispersal kernels of a target fishery species, black sea bass, and quantify the important factors in determining the dispersal kernel. • 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 Model domain with the 5 release locations shown with white diamonds. Larval behavior more important for particles released in deeper water. The Region The southeast U.S. continental shelf extends from Cape Hatteras, North Carolina, to Cape Canaveral, Florida. The coast is permeated with rivers and tidal inlets, particularly from middle South Carolina to northern Florida. Results • Conclusions • 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. • Seasonal Dispersal Kernels • Particles released at GRNMS • Monthly releases summarized by Season • Mid-depth releases • 30d passive SEUSCS.30% of the bottom is rocky-reefs which support more than 70% of the offshore fisheries in the region. Shown are Gray’s Reef National Marine Sanctuary () and the SABSOON towers (). • Future Directions • Target Species: Black Sea Bass • Important fishery species • Currently overfished Compass plot shows the mean distance and direction of the monthly releases. Physical Oceanography Model successful recruitment to juvenile stage Combine adult and larval behavior with realistic physics (including interannual variability) Seasonal Signal: generally southward transport in the winter months; northward transport in the summer months; Spring and Fall are transition months with smaller mean dispersal that is generally on-shore from GRNMS. Acknowledgements This work was supported through a contract from the Center for Coastal Fisheries and Habitat Research to UNC-CH from funds provided by the Office of National Marine Sanctuaries (NOAA NOS) in support of research at GRNMS and SEACOOS. *email: kpedwards@unc.edu