2. What are larvae?
How biology affects larval transport
How physics affect larval transport
Upwelling and larval transport in the California Current

3. Holoplankton: Plankton that are free-swimming for their entire life cycle.
Goals: Eat, avoid being eaten, reproduce
Meroplankton: A planktonic life stage (“larvae”) of organisms that are strong swimmers or live on the bottom as adults. Microscopic, ~0.1 to ~5 mm
Goals: Develop, avoid being eaten, find habitat

4. Example of life cycle for species with larvae

5. Most larvae bear little resemblance to adults
Sea star
Phoronid worm
Octopus
Snail

6. Most seafood species have larvae
Mussel Crab Lobster Tuna
Dinner Adults Larvae

7. Most fouling organisms have larvae
Barnacle life cycle
Feeding Non-feeding
(Oceanographers are always looking for better ways to keep
barnacle larvae from settling on their boats and instruments!)

8. What makes larval ecology so important
What makes larval ecology so important? ~70% of benthic invertebrates have planktonic larvae
Population dynamics
Ecologically important (population limited by supply)
Edible species (valuable +$)
Fouling organisms and invasive species (costly -$)
Biogeography --
geographic distributions
range expansions
Conservation --
Identify “source” and “sink” populations
design of marine reserves

9. Larval Transport: Horizontal movement of larvae from one point to another
Larval Dispersal: Spread of larvae from spawning sites to wherever they die or settle
Settlement: When a larva metamorphoses and adopts a benthic lifestyle
Recruitment: Defined by when we first observe the “new recruit” in the population

10. What influences larval transport?
Biological Processes
Development Mode
Pelagic Larval Duration
Response to Environment
Larval Behavior
Physical Processes
Currents, turbulence
Upwelling

11. Two potential development modes
Planktotrophic larvae
Feed on other plankton, usually phytoplankton
Female produces many small embryos with a long pelagic larval duration (PLD).
Lecithotrophic larvae
Do not feed on other plankton. Instead they consume yolk that is added to the embryo.
Female produces fewer, larger embryos with shorter PLD.

12. Sea slug (Alderia willowi) switches seasonally from plantotrophic to lecithotrophic larvae
Planktotrophic eggs
Adult
Lecithotrophic eggs
P. J. Krug

13. Feeding larvae tend to be in the plankton longer and disperse farther than non-feeding larvae
This is about half the earth’s diameter!
This is about half a mile!
Shanks et al. 2003

14. An extreme example -- this Pacific snail can remain in the larval stage for 4.5 years!
If average current speed is 20 cm/s, this thing can travel 28,000 km, or 2/3 the distance around Earth, before settling!
Strathmann and Strathmann 2007

15. Comparable odds ratios
1 in 176,000,000
1 in 3,000,000
1 in 20,000
1 in 10
Comparable odds ratios
Average number of eggs produced per female per season
Brooders
Lecitho-
trophic
Plankto-
trophic
Thorson 1950

16. Development rate depends on temperature
25.2 oC
17.5 oC
Scheltema 1967

17. For feeding larvae, development rate also depends on temperature & food availability
10 days
20 days
Barnacle development rate
Development is fraction of progress towards becoming a cyprid
Pfeiffer-Hoyt & McManus 2005

18. Behavior affects distance and direction of transport
 SINK
 SWIM
 SWIM
 SINK

19. Particle Reynolds Number
Inertia: an object in motion tends to stay in motion (tendency for gliding)
Viscosity: “stickiness” of a fluid, like friction (inhibits gliding)
Reynolds number: ratio of inertial forces to viscous forces

20. Particle Reynolds Number Rep
If Rep>1, Inertia dominates.
If Rep<1, viscosity dominates.
Plankton with Rep1 feel like they’re swimming in molasses.

21. Swimming velocity scales with body size
Most Invertebrate Larvae
u  1 mm/s to 1 cm/s
Fish Larvae
u  1 to 20 cm/s
From Huntley & Zhou 2004

22. Reynolds number scales with body size
Most larvae are <0.1 cm long and have Rep<1.
Some exceptions include large crustacean larvae, fish larvae
At Rep<1,
Net velocity = flow + behavior
Inertia
Viscosity
Mann & Lazier, after Okubo 1987

23. Horizontal advection
x = (Ucurrent + Uswim) t
[distance] = [distance/time] x [time]
Ucurrent  1 to 100 cm/s
Uswim  0.01 to 1 cm/s
**Currents dominate horizontal advection
Vertical advection
z = (Wcurrent + Wswim/sink) t
[distance] = [distance/time] x [time]
Typical Wcurrent  1 to 10 cm/s, but average = 0
Typical Wswim/sink  0.01 to 1 cm/s
**Behavior dominates vertical advection
Diffusion
(Random motion due to turbulent mixing)

24. Larval Transport: Focus in on California Current, Oregon upwelling zone

25. Upwelling in California Current has big effect on dispersal of rocky shore species
Mussels and barnacles form patches in intertidal zones and stay attached to rock after settlement.

26. Note the direction arrows

28. WA OR
Point
Conception CA
Halpin et al. 2004

29. Primary production in California Current is strongly dependent on upwelling
Temperature Chlorophyll
MBARI data from August (peak upwelling season)

30. Separation of coastal jet can be seen in Chl A mapWA OR
S. Calif.
Point
Conception CA
San Diego

31. 2. Central California Coast1 2
1. Oregon Coast
2. Central California Coast
-Weak, intermittent upwelling
-Strong, steady upwelling
-High invertebrate recruitment
-Low invertebrate recruitment

32. Barnacle Mussel California  Oregon California  Oregon 2 years of
recruitment
data
California  Oregon
California  Oregon
Connolly et al. 2001

33. Central California example - barnacle data
Counted barnacle larvae
# to 1984
#63, to 1984
Roughgarden et al. 1988

34. Upwelling transports larvae offshore
Roughgarden et al. 1988

35. Central California example - barnacle recruitment peaks during relaxation events
Farrell et al. 1991

36. Oregon region:
-Seasonal upwelling, weak/intermittent in summer
-coastal jet remains near coast
-upwelling increases production
-upwelling doesn’t prevent larvae from getting to shore
-upwelling positively affects recruitment of feeding larvae
California region:
-continuous upwelling, strong in summer
-upwelling pushes coastal jet and larvae offshore
-nearshore production may be lower
-relaxation events are important for recruitment