Marine plankton

•     Plankton overview

•     Phyto and Zoo Plankton

•     Plankton Adaptations

–   life in a dense and viscous medium

–   Reynolds number

–   Solutions to sinking

–   vertical migration

 

Marine planktonic lifestyle

•      primary producers:

–  microalgae

–  no indigestible support structures

•    herbivores are small

Phytoplankton      Zooplankton

•     Primary producers

 

•     Dependent upon surface waters

 

•     Primary and Secondary consumers

•     Dependent upon phytoplankton

Phytoplankton: Diatoms and dinoflagellates

Zooplankton

•    Holoplankton: all life cycle stages in plankton

–  Copepods

–  Ctenophores

–  Krill

–  Arrow worms (Chaetognaths)

 

 

Zooplankton

•     Meroplankton: larval stages in plankton

–   Crustaceans:

•   Barnacles, crabs

–   Molluscs:  snails

–   Polychaeta: worm larvae

–   Echinodermata

•   Sand dollar

 

 

Why is planktonic life so common?

Forces in a fluid

•     Viscous:  sticky layers

–   Movement in streamlines

•     Inertial:  tendency of a moving object to continue moving

–   Movement independent of fluid

Reynolds number: measure of inertial vs. viscous forces

Reynolds number

Re = V*L*rf / v 

 

V = Velocity

L = length of object

rf = density of fluid

v = viscosity

Reynolds number

•    In seawater

Re µ V*L             

 

•    The small, slow moving organisms live at low Re

–  viscous forces dominate

Sinking rates

•    Phytoplankton:       30 m/dy

 

•    Protozoans:                         30-350 m/dy

 

•    Copepods:              36-720 m/dy

 

How to reduce sinking

•         Sinking rate =

                        r1 - rf / R × v

 

r1 = density of object

rf  = density of water

r1 - rf = overweight

R = resistance

v = viscosity

Resistance: frictional drag

•    R, Resistance:  R µ SA

–  High if surface area high (for a given weight)

SA µ L2

VOL µ L3

VOL µ WEIGHT

Resistance: frictional drag

•    R, Resistance:  R µ SA

•    For size (holding shape constant): smaller size means

–  greater SA/VOL

–  greater SA/WEIGHT

Resistance: form drag

•   R, Resistance: R µ CA

CA = cross-section area

 

– Disk has high form resistance

– Long and thin has least form resistance

Adaptations: reduce sinking rate

                        r1 - rf / R × v

 

•    Density: reduce overweight

•    Resistance

•    Active swimming

Density: Reduction of overweight

1.       Replace heavy ions

–       Organisms maintain iso-osmotic state

–       Use lighter ions

•         Ctenophores: comb jellies

–       Replace S ions with Cl ions

•         Noctiluca: NH4CL isoosmotic

Density: Reduction of overweight

2.       gas filled floats

–       intracellular or special structures

•         Physalia Portugese Man of war

•         gas vacuoles (BG algae)

 

 

Density: Reduction of overweight

3.  Store low-density  liquids:  oils, fats, wax

 

•    Copepods: oil droplets under carapace

–  Floatation, energy storage.

 

Resistance

•    flattened body shape

–  bell of jellyfish

•    long arms, spines

–  Add surface, little weight

–  Echinoderm larva

–  Copepod appendages

 

Active swimming

•    Jellyfish: pulsing bell

•    flagellated phytoplankton 

•    Krill: appendages to swim up

 

Why migrate to deep water?

•    Diurnal vertical migration

–  100-400m

–  Like a human walking 25 miles daily

 

Why migrate to deep water?

•    Avoid predators? Visual hunters

•    Avoid light damage? UV radiation

•    Movement with Ekman transport