Scaling and Modeling of Larval Settlement

Satoshi Mitarai

Oct. 19, 2005

GOAL OF “FLOW”

• Assess larval dispersal scales using idealized simulations of California Current

• Develop simple modeling to establish source-destination relationships– Without fluid dynamics simulations, which are

time consuming

WHAT’S NEW?

• Weak upwelling case is added

• Larval dispersal scales are quantified

• A simple model to establish source-destination relationships is proposed– Accounts for spatial scales properly

TEMPERATURE FIELD(TOP VIEW)

Strong upwelling Weak upwelling

Summer Winter

MEAN TEMPERATURE FIELD(SUMMER)

Simulation CalCOFI

Shows reasonable agreement with CalCOFI data

(Averaged over 6 realizations)

MEAN TEMPERATURE FIELD(WINTER)

Simulation CalCOFI

Shows a good agreement with CalCOFI data

(Averaged over 6 realizations)

LARVAL TRAJECTORIESSummer Winter

Eddies sweep larvae into “packet” which stays together thru much of pelagic stage

LAGRANGIAN STATISTICS

3.4 / 4.340 / 484.2 / 4.6Poulain et al

(1998)

4.3 / 4.532 / 382.9 / 3.5Swenson et al

(2001)

1.6 / 1.829 / 296.9 / 5.7Winter

Simulations

3.1 / 4.131 / 353.7 / 3.7Summer

Simulations

Diffusivity

Zonal / Merid

Length Scale

Zonal / Merid

Time scale

Zonal / MeridData Set

Winter shows more correlation in time

& less diffusivity

LARVAL TRANSPORT& SETTLEMENT

Summer Winter

More settlers are observed in winter

ONLY SETTLERSSummer Winter

ALONGSHORE DISPERSAL KERNEL

Summer Winter

Gaussian fitting

More alongshore travel distance in summer

(Obtained from 6 realizations)

AVG = -122 km, STD = 103 km AVG = -80 km, STD = 92 km

CROSS-SHORE DISPERSAL KERNEL

Lognormal fitting

Summer Winter

More offshore travel distance in summerSettlers move out nearshore habitat before settle

(Obtained from 6 realizations)

ARRIVAL DIAGRAMSummer

15 days

21 days

43 km

64 km

Using variogram …

Winter

CONNECTIVITY MATRIXSummer Winter

48 km 53 km

SUMMARY

• Travel distance & survivability shows difference between summer & winter– More travel distance in summer

– Lower survivability in summer

• Settlement scales do not show much difference between summer & winter– Arrival length ~ 50 km

– Arrival time ~ a few weeks

– Connectivity length ~ 50 km

CONNECTIVITY MATRIX MODELDiffusion model Spiky kernel model

Neither one accounts for spatial structures

A NEW MODEL FOR CONNECTIVITY MATRIX

• Idea: model settlement events as a summation of “settlement packets”– Number

– Size

– Source locations

– Travel distance

Rossby radius (~50 km)

Randomly (uniform distribution)

Randomly (dispersal kernel)

• Determine # of settlement packets N = (T/t) (L/l) f (D/l)

NUMBER OF SETTLEMENT PACKETS

T: Larval release duration t: Lagrangian correlation time L: domain size l: Rossby radius f: survivabilityD: standard deviation of dispersal kernel

Total # of released packets

# of settlement events per packet

MODEL PREDICTIONSSummer Winter

Accounts for spatial structures

DIFFUSION LIMIT

Packet model

1 season 6 seasons 12 seasons 120 seasons

1 season 6 seasons 12 seasons Diffusion

Flow simulation Diffusion model

NEXT STEPS

• Use proposed model in F3 model

• Investigate effect of larval behavior– Preliminary study has been already done

• Investigate effect of coastal topography

LAGRANGIAN STATISTICS

3.4 / 4.340 / 484.2 / 4.6Poulain et al

(1998)

4.3 / 4.532 / 382.9 / 3.5Swenson et al

(2001)

1.6 / 1.829 / 296.9 / 5.7Winter

Simulations

3.1 / 4.131 / 353.7 / 3.7Summer

Simulations

Diffusivity

Zonal / Merid

Length Scale

Zonal / Merid

Time scale

Zonal / MeridData Set

Simulations: 6 realizations, 6000 particles

Swenson et al (2001): late spring to early fall, 1985-1990, 124 drifters, 18N-40N

Poulain et al (1998): early spring to late fall, 1985-1986, 29 drifters, 18N-36N