What are larvae? How biology affects larval transport How physics affect larval transport Upwelling and larval transport in the California Current
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
Most larvae bear little resemblance to adults Sea star Phoronid worm Octopus Snail
Dinner Adults Larvae Mussel Crab Lobster Tuna Most seafood species have larvae
Most fouling organisms have larvae (Oceanographers are always looking for better ways to keep barnacle larvae from settling on their boats and instruments!) Barnacle life cycle Feeding Non-feeding
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
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
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.
P. J. Krug Adult Planktotrophic eggs Lecithotrophic eggs Sea slug (Alderia willowi) switches seasonally from plantotrophic to lecithotrophic larvae
Shanks et al. 2003 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!
An extreme example -- this Pacific snail can remain in the larval stage for 4.5 years! Strathmann and Strathmann 2007 If average current speed is 20 cm/s, this thing can travel 28,000 km, or 2/3 the distance around Earth, before settling!
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 Plankto- trophic Lecitho- trophic Brooders Thorson 1950
Development rate depends on temperature Scheltema 1967 25.2 o C 17.5 o C
Pfeiffer-Hoyt & McManus 2005 10 days 20 days Barnacle development rate For feeding larvae, development rate also depends on temperature & food availability
Behavior affects distance and direction of transport SINK SWIM SINK SWIM
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
Particle Reynolds Number Re p If Re p >1, Inertia dominates. If Re p <1, viscosity dominates. Plankton with Re p 1 feel like they’re swimming in molasses.
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
Reynolds number scales with body size Most larvae are <0.1 cm long and have Re p <1. Some exceptions include large crustacean larvae, fish larvae At Re p <1, Net velocity = flow + behavior Inertia Viscosity Mann & Lazier, after Okubo 1987
Horizontal advection x = (U current + U swim ) t [distance]= [distance/time] x [time] U current 1 to 100 cm/s U swim 0.01 to 1 cm/s **Currents dominate horizontal advection Vertical advection z = (W current + W swim/sink ) t [distance]= [distance/time] x [time] Typical W current 1 to 10 cm/s, but average = 0 Typical W swim/sink 0.01 to 1 cm/s **Behavior dominates vertical advection Diffusion (Random motion due to turbulent mixing)
Larval Transport: Focus in on California Current, Oregon upwelling zone
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.
Primary production in California Current is strongly dependent on upwelling Temperature Chlorophyll MBARI data from August (peak upwelling season)
Point Conception San Diego S. Calif. Separation of coastal jet can be seen in Chl A map CA OR WA
1 2 1. Oregon Coast2. Central California Coast -Weak, intermittent upwelling-Strong, steady upwelling -High invertebrate recruitment-Low invertebrate recruitment
Connolly et al. 2001 Barnacle MusselBarnacle California Oregon 2 years of recruitment data
Central California example - barnacle data Roughgarden et al. 1988 Counted barnacle larvae #67 - 1969 to 1984 #63,70 - 1982 to 1984
Upwelling transports larvae offshore Roughgarden et al. 1988
Central California example - barnacle recruitment peaks during relaxation events Farrell et al. 1991
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