1. ROLE OF HEADLAND IN LARVAL DISPERSAL Satoshi Mitarai Preliminary results and research plan (Maybe for the next F3 meeting)

2. BACKGROUND Topographic eddies may be important in determining habitat connectivity –Eddies can retain eddies 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) Few notable studies (Largier, 2003) –Geostrophic size & flow time scale to be considered

3. GOAL OF THIS STUDY Estimate the role of coastal headland eddies on larval dispersal using idealized ROMS simulations –By comparing the obtained results with straight coastline case –Are there any critical sizes?

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

5. SST EVOLUTION

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

7. ONLY SETTLERS Small headland (a = 10 km)Large headland (a = 40 km) More turbulent & offshore transport Red dots = settlement (PLD = 20 to 40 days)

8. 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

9. ANOTHER REALIZATION Looks similar to the previous one…

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

11. (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

12. SUMMARY 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)

13. 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)?

14. 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 UCLA, SIO, OSU?

15. FUTURE PLANS (TIM’S WORK) Tim will work on these Amplitude (km) Width (km) Retention regime Turbulent regime Examine winter (weak upwelling) case Change headland parameters –Clarify role of headland size (see diagram below) –Reduce domain size to see headland interactions Do more realizations & obtain statistics