• 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

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Example of life cycle for species with larvae

Most larvae bear little resemblance to adults

Sea star Phoronid worm Octopus Snail

Din

ner

A

dults

Larv

ae

Mussel Crab Lobster Tuna

Most seafood species have larvae

Most fouling organisms have larvae

(Oceanographers are always looking for better ways to keepbarnacle 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

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• 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

What influences larval transport?

• Biological Processes– Development Mode– Pelagic Larval Duration – Response to Environment – Larval Behavior

• Physical Processes– Currents, turbulence– Upwelling

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!

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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

Ave

rage

num

ber

of e

ggs

prod

uced

per

fem

ale

per

seas

on

Plankto-trophic

Lecitho-trophic

Brooders

Thorson 1950

Development rate depends on temperature

Scheltema 1967

25.2 oC

17.5 oC

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Pfeiffer-Hoyt & McManus 2005

10 days

20 days

Barnacle development rate

For feeding larvae, development rate also depends on temperature & food availability

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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 Rep

• If Rep>1, Inertia dominates.

• If Rep<1, viscosity dominates.

• Plankton with Rep1 feel like they’re swimming in molasses.

Rep=

inertiaviscosity

=upd

νup =swimming velocity (cm/s)

d=diameter (cm)

ν =kinematic viscosity (≈ 0.01 cm2 /s)

Swimming velocity scales with body size

Most Invertebrate Larvaeu 1 mm/s to 1 cm/s

Fish Larvaeu 1 to 20 cm/s

From Huntley & Zhou 2004

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

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)

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.

Note the direction arrows

Halpin et al. 2004

Point Conception

WA

OR

CA

Primary production in California Current is strongly dependent on upwelling

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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

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CA

OR

WA

1

2

1. Oregon Coast 2. Central California Coast

-Weak, intermittent upwelling -Strong, steady upwelling

-High invertebrate recruitment -Low invertebrate recruitment

Connolly et al. 2001

Barnacle

MusselBarnacle

Barnacle

California Oregon

California Oregon

California Oregon

California Oregon2 years of recruitmentdata

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