Phytoplankton DynamicsPhytoplankton Dynamics

Primary Productivity (g C/mPrimary Productivity (g C/m22/yr)/yr)

Gross (total) production = total C fixedGross (total) production = total C fixed

Net production = C remaining after Net production = C remaining after respirationrespiration

Standing crop = biomass present at a Standing crop = biomass present at a point in point in time time

Factors Affecting Primary Factors Affecting Primary ProductionProduction

1.1. LightLight

2.2. NutrientsNutrients

3.3. Loss out of the photic zone due to Loss out of the photic zone due to sinking or mixingsinking or mixing

4.4. GrazingGrazing

1. Light1. Light

Light penetration – affected byLight penetration – affected by– Angle of incidenceAngle of incidence– Surface reflectionSurface reflection– Suspended particlesSuspended particles– Adsorption by the water itselfAdsorption by the water itself

Water absorption of lightWater absorption of light

DDCC = = Compensation Compensation depthdepth

At DAt DCC ---- ----

primary production primary production (P) = respiration (P) = respiration (R) in each algal (R) in each algal cell cell

IIC C = Compensation = Compensation light intensitylight intensity

2. Nutrients2. Nutrients

• Nutrients = essential elements needed Nutrients = essential elements needed for cell maintenance and growthfor cell maintenance and growth

N, P, Si, Ca, K, etc.N, P, Si, Ca, K, etc.

• N and P in ocean water about 10,000 x N and P in ocean water about 10,000 x less than on land (“ocean desert”)less than on land (“ocean desert”)

• Redfield ratio C:N:P 105:16:1Redfield ratio C:N:P 105:16:1

same in seawater and pp cellsame in seawater and pp cell

• Body form of pp adapted for nutrient Body form of pp adapted for nutrient uptakeuptake

• Rate of uptake is concentration Rate of uptake is concentration dependentdependent

low nutrient specieslow nutrient species – very efficient – very efficient at nutrient uptake in low concentrations, at nutrient uptake in low concentrations, but rate saturates out at high but rate saturates out at high concentrationsconcentrations

high nutrient specieshigh nutrient species – less efficient – less efficient uptake at low concentrations, but can uptake at low concentrations, but can exploit high concentrationsexploit high concentrations

3. Loss out of the photic 3. Loss out of the photic zonezone• SinkingSinking• Water turbulence mixes plankton Water turbulence mixes plankton

deeper into the water columndeeper into the water column

DDMM = mixing depth = mixing depth

Vertical mixing can take plankton Vertical mixing can take plankton below the compensation depthbelow the compensation depth

DDCC = compensation depth, = compensation depth,

(P = R in each pp cell)(P = R in each pp cell)

DDCR CR = critical depth, = critical depth,

(P = R in whole pp (P = R in whole pp population)population)

DDMM < D < DCRCR P PWW > R > RWW

DDMM > D > DCRCR P PWW < R < RWW

4. Grazing4. Grazing

• Copepods can have extremely high Copepods can have extremely high grazing ratesgrazing rates

GR < PGR < PWW

GR = PGR = PWW

GR > PGR > PWW

WinterWinter

SpringSpring

SummerSummer

FallFall

DDCRCR moves up in the water column moves up in the water column – photic zone smaller– photic zone smaller

What happens in late What happens in late spring/early summer?spring/early summer?

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

Spring Spring Summer Summer

FallFall

Magnitude of fall Magnitude of fall bloombloom

-- timing, when -- timing, when DDMM falls below falls below

DDCRCR

Idealized ChartIdealized Chart

Why are the Why are the polar oceans polar oceans different?different?

Light in Light in springspring

No No thermoclinethermocline

Grazing?Grazing?

Why are the Why are the tropical tropical oceans oceans different?different?

Permanent Permanent thermoclinethermocline

Nutrients Nutrients always lowalways low

Blips?Blips?

What’s What’s different different between the between the Atlantic and Atlantic and Pacific? Pacific?

Copepod life Copepod life history – history –

lag timelag time

Coast vs. Open OceanCoast vs. Open Ocean

• Coast receives nutrients from landCoast receives nutrients from land• Upwelling Upwelling • Shallow water depth – bottom Shallow water depth – bottom

shallower than the Dshallower than the DCRCR

• Thermocline not as well developed Thermocline not as well developed or persistentor persistent

• Turbidity of water Turbidity of water can can counteract counteract other factorsother factors