Life in a Moving Fluid (Steve Vogel) Two Kinds of Flow: Laminar flow – fluid particles move more or less parallel to each other in a smooth path Turbulent flow – fluid particles move in a highly irregular manner even if the fluid as a whole is moving in a single direction 1

FLOW Which will happen and why? 2

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Reynolds number (R e ) describes the nature of the flow regime when a solid (organism) and liquid encounter one another R e = σ l v/ μ σ = density of fluid l = length (size) solid v = velocity of solid μ = viscosity of fluid R e =F I F I = inertial forces F V F V = viscous forces Inertia? 5

In nature: Small = slowLarge = fast Small creatures live in world dominated by viscous forces Large creatures affected most by inertial phenomena 6

Typical Reynolds Numbers ReReReRe Large whale swimming at 10 m/s 300,000,000 Tuna swimming at same speed 30,000,000 Duck flying at 20 m/s 300,000 Dragonfly going 7 m/s 30,000 Copepod in a pulse of 20 cm/s 300 Flight of smallest insects 30 Invertebrate larva,, 0.3 mm long, moving at 1 mm/s 0.3 Sea urchin sperm advancing the species at 0.2 mm/s

Plankton – most have a density that is greater than seawater What happens? 8

SR = W 1 - W 2 (R)(V W ) SR = sinking rate W 1 = density of organism W 2 = density of seawater (W 1 -W 2 = overweight) (W 1 -W 2 = overweight) R = surface of resistance V W = viscosity of water Sinking rate equation Two solutions W 1 -W 2 = organism overweight, reduce density 9

Reduction of overweight Make body fluids less dense than seawater Make body fluids less dense than seawater Osmotic problem – Solutions: Osmotic problem – Solutions: –Replace heavy ions with lighter ones –Replace normal body salts with NH 4 Cl –Replace heavy Cl with SO 4 10

Reduction of overweight Incorporate less dense liquids – oils and fats – in tissues – Copepods – oil droplets – Diatoms - vacuoles Decrease overall density by incorporating gas gas bags bubbles 11

Incorporate gas-filled floats in body Portuguese man-o-war, Janthina 12

13 BUT – if overweight can’t be reduced ?

SR = W 1 - W 2 (R)(V W ) SR = sinking rate W 1 = density of organism W 2 = density of seawater (W 1 -W 2 = overweight) (W 1 -W 2 = overweight) R = surface of resistance V W = viscosity of water Sinking rate equation Two solutions W 1 -W 2 = organism overweight, reduce density #2 - Increase R - surface of resistance 14

Increase Surface of Resistance Why is plankton small? 15

Why small is important Surface area increases as a square of liner dimension Volume increases as a cube 16

Change shape of body - flatten body, feathery projections Develop spines, body projections – Lots of surface area, little mass 17

Water motion and buoyancy 18

Langmuir Cells Heating-cooling diurnal cycle, counter – rotating helical cells localized vertical movement, scale of meters Effect – vertical mixing, horizontal differences Vertically mix zooplankton, horiz. Patches 2 zones: chaotic regions that help to spread plankton and locally coherent regions (patches), that do not mix with the chaotic regions and which persist for long periods of time. 19

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Nekton – also have adaptations for buoyancy Make body fluids less dense - Fish – swim bladders Lay down lipid layer – in enlarged liver (sharks), throughout body (mackerel), subcutaneous lipid layer (marine mammals) Pectoral fins, flippers, heterocercal tail 21

Drag – loss of momentum in movement through a fluid Skin friction – results from stickiness of water – Proportionally more important at low R e Pressure drag – results because dynamic pressure to separate flow at front end is not counter balanced by an opposite pressure at rear end – Proportionally more important at high R e 22

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Adaptations to reduce drag Change body shape 24

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Reduce frontal area and streamline shape – to minimize skin friction Long tapering tail- reduces pressure drag by recapturing energy as fluid closes in rear 26

What is “streamlined?” 27

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Speedo LZR Racer Reduces skin drag Compresses body 30

Adaptations to reduce drag Minor adaptations: Eliminate protuberances – eyes, pectoral fins, etc. recessed into depressions Surface roughness – overcome viscosity at high velocities 31

Mucus, compliant skins, scales, riblets and roughness polymers found in mucus decrease the pressure gradient, channel water molecules in direction of flow Compliant surfaces equalising and distributing pressure pulses Small longitudinal ridges on rows of scales on fish can reduce shear stress in the boundary a rough surface increases the shear stress in the boundary layer and makes it thinner. 32

The function of the roughness on the sword of a swordfish is probably to reduce the total drag by generating premature turbulence and by boundary layer thinning, despite an increased friction over the surface of the sword. 33

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Phytoplankton Dynamics Primary Productivity (g C/m 2 /yr) Gross (total) production = total C fixed Net production = C remaining after respiration Standing crop = biomass present at a point in time 35

Factors Affecting Primary Production 1.Light 2.Nutrients 3.Loss out of the photic zone due to sinking or mixing 4.Grazing 36

1. Light Light penetration – affected by – Angle of incidence – Surface reflection – Suspended particles – Adsorption by the water itself 37

Water absorption of light 38

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D C = Compensation depth At D C ---- primary production (P) = respiration (R) in each algal cell I C = Compensation light intensity 40

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2. Nutrients Nutrients = essential elements needed for cell maintenance and growth N, P, Si, Ca, K, etc. N and P in ocean water about 10,000 x less than on land (“ocean desert”) Redfield ratio C:N:P 105:16:1 same in seawater and pp cell 42

Body form of pp adapted for nutrient uptake Rate of uptake is concentration dependent low nutrient species – very efficient at nutrient uptake in low concentrations, but rate saturates out at high concentrations high nutrient species – less efficient uptake at low concentrations, but can exploit high concentrations 43

3. Loss out of the photic zone Sinking Water turbulence mixes plankton deeper into the water column D M = mixing depth Vertical mixing can take plankton below the compensation depth 44

D C = compensation depth, (P = R in each pp cell) (P = R in each pp cell) D CR = critical depth, (P = R in whole pp population) (P = R in whole pp population) D M R W D M R W D M > D CR P W D CR P W < R W 45

4. Grazing Copepods can have extremely high grazing rates GR < P W GR = P W GR > P W 46

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WinterSpringSummerFall 48

D CR moves up in the water column – photic zone smaller 49

What happens in late spring/early summer? 50

Zooplankton – grow and reproduce in spring, GR?? 51

Spring  Summer Fall Magnitude of fall bloom -- timing, when D M falls below D CR -- timing, when D M falls below D CR 52

Idealized Chart 53

Why are the polar oceans different? Light in spring No thermocline Grazing? 54

Why are the tropical oceans different? Permanent thermocline Nutrients always low Blips? 55

What’s different between the Atlantic and Pacific? Copepod life history – lag time lag time 56

Coast vs. Open Ocean Coast receives nutrients from land Upwelling Shallow water depth – bottom shallower than the D CR Thermocline not as well developed or persistent Turbidity of water can counteract other factors 57