What are larvae? How biology affects larval transport How physics affect larval transport

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?~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 • Planktotrophiclarvae • Feed on other plankton, usually phytoplankton • Female produces many small embryos with a long pelagic larval duration (PLD). • Lecithotrophiclarvae • 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 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 Pfeiffer-Hoyt & McManus 2005

18. Behavior affects distance and direction of transport  SWIM  SINK  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 1cm/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 1cm/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 map WA OR S. Calif. Point Conception CA San Diego

31. 1 2

32. Barnacle Barnacle 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 #67 - 1969 to 1984 #63,70 - 1982 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