What are larvae? How biology affects larval transport How physics affect larval transport Upwelling...
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Transcript of What are larvae? How biology affects larval transport How physics affect larval transport Upwelling...
• 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