1. ROLE OF HEADLANDS IN LARVAL DISPERSAL Tim Chaffey, Satoshi Mitarai Preliminary results and research plan

2. BACKGROUND Topographic eddies may be important in determining habitat connectivity –Eddies can retain larvae for time scales comparable with their PLD High local recruitment is observed in island wake eddies (e.g., Swearer et al, 1999) –But, such clear pattern will not be observed in coastal eddies where currents are less persistent in direction (Graham & Largier, 1997) Filament formation may be important in offshore transport of larvae (Haidvogel, 1991) –Offshore filaments present an obstacle to nearshore settlement in PLD. Few notable studies (Largier, 2003) –Geostrophic size & flow time scale considered

3. GOAL OF THIS STUDY Estimate the role of coastal headland eddies on larval dispersal using idealized ROMS simulations –Do headlands create a consistent connectivity or a stochastic connectivity? –If there is a consistent connectivity, does it remain constant under different wind regimes? –Is there a critical headland amplitude/width? –How important is headland spacing? –Describe the physics of filament formation and eddy recirculation around headlands?

4. HEADLAND DESIGN Gaussian-shape headland in idealized simulations –Three parameters 2. Width (w) (twice the std of Gaussian function) 1. Amplitude (a) 3. Domain size (d) = distance between headlands a = 10, 20 & 40 km w = 20 km d = 256 km

5. Model Setup Wind field taken from buoy measurements –All runs use July wind field (upwelling period) –Wind field comprised of a mean and pertubation component Pressure gradient determined using dynamic height data from CalCOFI July survey. Bathymetry –Same shelf slope as previous work –Isobaths follow irregular coastline

6. SST EVOLUTION

7. Small headland (a = 10 km)Large headland (a = 40 km)

8. LARVAL DISPERSAL Small headland (a = 10 km)Large headland (a = 40 km) Red dots = settlement (PLD = 20 to 40 days)

9. ONLY SETTLERS Small headland (a = 10 km)Large headland (a = 40 km) More turbulent particle motion Increased offshore transport Red dots = settlement (PLD = 20 to 40 days) Limited settlement near headland

10. CONNECTIVITY DIAGRAM Headland North South North

11. SAMPLE CONNECTIVITY (Connectivity is normalized so that summation becomes unity) Significant retention Headland is not strong sink Longer travel distance (than straight coastline) Headland is strong sink

12. ANOTHER REALIZATION Looks similar to the previous one…

13. AND ANOTHER Connectivity seems to be consistent interannually Some variations for intermediate size, though

14. TOTAL PARTICLE SETTLEMENT Small headland (a = 10 km)Large headland (a = 40 km) Center of Headland Peak settlement on north flank of headland Enhanced settlement to north and south of headland Limited settlement on the headland Enhanced settlement to north and south of headland

15. (POSSIBLE) PHYSICAL EXPLANATION H Small headland (a = 10 km)Large headland (a = 40 km) Wind stress Water accumulation H Headland eddies Pressure Additional pressure reduces larval displacement & create retention zone Headland eddies bring larvae offshore, leading to longer travel & headland settlement

16. COMBINED MEAN SURFACE CURRENTS Small headland (a = 10 km)Large headland (a = 40 km)

17. MONTHLY EOF ANALYSIS OF SURFACE CURRENTS FOR 10 KM HEADLAND

18. MONTHLY EOF ANALYSIS OF SURFACE CURRENTS FOR 40 KM HEADLANDS

19. SUMMARY (1) The role of head land in larval dispersal highly depends on the size (i.e., nearly opposite effect) When small (~ 10 km) –Create retention zone around them, leading to significant number of self recruitments –Not a strong source or sink When large (~ 40 km) –Makes flow field more turbulent, resulting in longer travel distance (than straight coast line) –Strong sink (i.e., accumulates settlers from upstream)

20. SUMMARY (2) Ensemble mean characterized by: – filament formation at headland –strong near shore alongshore flow –weak offshore alongshore flow EOF analysis shows approximately 40% of monthly variance in first mode. –the first mode is not spatially coupled month to month. –find eddy circulation structures in the first mode

21. DISCUSSION (1) Critical size would be Rossby radius –When the headland size is comparable to Rossby radius, eddies are greatly affected by headland, resulting in enhanced turbulence In reality, these two types co-exist, perhaps affecting each other –Interactions may be more important for small headland case (e.g., make it more turbulent?) Which one is more significant? –Consistency around headland or stochasticity driven by coastal circulations (straight coastline case)?

22. DISCUSSION (2) Can we support the simulation results with biological data (e.g., otoliths)? –Pick two types of habitats in central coast; i) around small headland and ii) large headland –Estimate dispersal scale using otoliths data (e.g., Siegel et al, 2003) –And see if there is significant difference between estimated dispersal scale Same thing happens in “realistic” simulations? –Collaboration with Georgia Tech, UCLA, SIO, OSU?

23. FUTURE PLANS Amplitude (km) Width (km) Retention regime Turbulent regime Examine winter (weak upwelling) case Examine different life histories (PLD, vertical behaviors) Change headland parameters –Clarify role of headland size (see diagram below) –Reduce domain size to see headland interactions Do more realizations & obtain statistics Change wind parameter to reflect wind around headlands

24. Future Plans (2) Using many realizations can we quantify relationship between variable topographies and bathymetries to predict larvae settlement patterns.

25. MEAN CURRENTS FOR SMALL HEADLAND

26. MEAN CURRENTS FOR LARGE HEADLAND