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Plankton and Plankton Communities

Chapter 2

Plankton Fundamentals

Free floating

Chlorophyll – bearing

Greatest amount of photosynthesis in ocean

Oceanic productivity greater than terrestrial

Traps most of sun that enters ocean

Transfers energy to other organisms

No life in ocean without energy-fixing, minute planktonic organisms










Viroplankton – recently discovered in oceans


Size, see table 2.1 page 39

Captured by nets

Seven sizes

Net plankton – caught by nets





Can not be captured by nets ( too small ), centrifuge needed, micropore filters




Characteristics of zooplankton

Holoplankton – spend entire lives in plankton

Meroplankton – species that spend only part of their lives in plankton

Include large number of larvae of animals that as adults either live on the bottom or swim as nekton


Larger phytoplankton

Two groups



Smaller phytoplankton

Picoplankton is more important in productivity


Class Bacillariophyceae

Easily differentiated from dinoflagellates

Enclosed in unique glass " pillbox "

No visible means of locomotion

Two valve or frustules

Living part of diatom is in the box

Silicon dioxide ( glass )

Many designs species-specific

Pits, perforations

Popular among light microscopists, SEM fig 2.2

Occur singularly or in long chain fig. 2.4


Two halves: top and bottom

Secretes a valve a re-create a typical box

Average size decreases until becomes a auxospore ( some don not )

original size returns fig. 2.16

Domoic acid – toxic to other organism

Some diatoms are benthic



Second major group: class Dinophyceae

Two flagella for locomotion through water

Armored with carbohydrate cellulose fig. 2.3 and 2.4

Small organism having chromosomes

Usually found as a single organism and not in chains

Reproduce by fission

Do not change in size

Toxins released in water and may affect other organisms and cause mass mortality if 2-8 million cells / liter

Red tide

Zooxanthellae – nonmotile, symbionts in tissues of coral, sea anemones, giant clams

Noctiluca ( fig. 2.24 a ) – highly bioluminescent – light up boat wakes and beaches

Role as grazer


The smaller plankton

Collectively called nanoplankton

Important in oceanic food webs

Most important, just discovered

Prochlorophytes – very tiny, 0.8 – 0.6 um

Contributes 1/3 of chlorophyll a in open ocean

Estimated to contribute 1/3 – ½ of total ocean productivity

Resemble cyanobacteria, but smaller, have different pigments

Other important groups


Cyanobacteria ( blue-green algae ) fig. 2.4

Red Sea named from cyanobacteria


Recognized a a major source of primary production in many ocean areas.

Pelagic bacteria

Found in oceans

Most abundant near the surface

Exceeds biomass of phytoplankton

Usually found associated with POC

Particulate organic carbon

And on marine snow

Gelatinous zooplankton

Usually motile

Decrease with depth

Role – microbial loop in food web

The Zooplankton

Extremely diverse

Two groups

Net zooplankton


Nanozooplankton, picozooplankton

Important grazer

In the sea and coastal waters


Free-living planktonic are small

Swim weakly with jerky movements

Large antennae slows sinking rate

Readily recognized

Graze on phytoplankton

Filtering mechanism or anterior appendages fig. 2.6

Sexes are separate

Sperm transferred by spermatophores

Eggs in sack and attached to female body

Hatch as nauplius larvae

several stages then an adult, fig. 2.5

Affects the phytoplankton cycles in the sea


Other zooplankton

Kingdom Protista most important

Difficult to capture to study, fig. 2.7

Order Foraminiferida and class Radiolaria

Both very abundant

Form ooze over sea floor

Important consumers, fig. 2.7 p. 45

Phylum Cnidaria

Class: Scyphozoan - Jellyfish as a plankton, fig. 2.10, p. 46

Phylum Ctenophora

voracious carnivores, capture food with sticky tentacles or engulfing with oversized mouth fig. 2.11, p. 47

Planktonic nemerteans

deep water worms

Phylum Mollusca

Highly modified plankton mollusks

Pteropods and heteropods fig. 2.11e,f, p.47 and 2.24 d p. 53

Squids – powerful, fast swimmers, considered nekton




Flotation Mechanism

Density greater than seawater

Sinks in water column


Density of seawater




Organism’s shape

Equation: SR = W1 – W2 / ( R ) ( Vw )

Reduction of overweight

Alter composition of body fluid

Less dense than equal volume of seawater.

Avoid osmotic problems

Exclude heavy ions

Special gas-filled floats

Portuguese Man of war, fig. 2.25a,b, p. 53

Oils and fats

Food and buoyancy


Changes in surface of Resistance

General body size is small

Smaller organism, the greater the surface area relative to volume.

Far more surface area

Slow down in warmer water

Tropical plankton

Change the shape of the body

Fig. 2.26, p. 54

Developed various spines and body projections

Add resistance but little to the weight

Common in diatoms and radiolarians, foraminiferans, crustaceans

Water Movements

Buoyancy and water columns in the ocean

Surface water hot to cold

Leads to convection currents

Plankton moved by them

Langmuir convection cells

Wind speeds above 3 m/s

Few meters wide but hundreds long

Water diverges towards outside of cell

Converge and downwell for a short distance and move horizontally, meet water moving in same direction then rises to surface, completes the cycle fig. 2.7. P 55

Primary Production

Rate of formation of energy-rich organic compounds from inorganic compounds


6CO2 + 6H2O ΰ C6H12O6 + 6O2

Some by chemosynthetic bacteria

Gross primary production

Net production

Standing crop

water absorbs light

Depth at which respiration is used

Compensation depth

Compensation intensity

Water clarity and availability of nutrients


Measurement of Primary Productivity

Classical method

Light-dark bottle method

Winkler method – oxygen content

Net community photosynthesis\new production

14 C method

Equation, p. 57

Satellite imaging, fig. 2.28






Standing crop

Is the result of the difference between factors tending to increase the number of individuals

Reproduction and growth

Factors tending to decrease biomass or numbers

Death and sinking or lateral transport out of the sea

Difficult to measure

Method used


Other methods used

Measure ATP ( Holme-Hansen and Booth )

Factors Affecting Primary Productivity

Physical and chemical factors

Light and Nutrient supply



Extinction coefficient

Nutrients, figure 2.33 figure 2.34

Turbulence and Critical depth, fig. 2.35







Geographical Variations in Productivity

Temperate Seas fig. 2.36 p. 66

Spring bloom fig. 2.37 b p. 67

Tropical Seas

Thermal stratification fig. 2.36 p. 66

Polar Seas fig. 2.37 a, fig. 2.36 c

Productivity in Inshore and Coastal Waters

Receives considerable nutrient input phosphates and nitrates form land

Shallow water depth

Shallow waters rarely have persistent thermocline

Large amounts of terrigenous debris

Restricts depth of photic zone

5-10 m

Light absorbing debris

Offshore water 50 m

Inshore tropical water 10 x the productivity

Increased nutrient concentration






Vertical Migration

Puzzling phenomena of zooplankton

Separate from seasonal migration

Diel migration ( daily ) known for over 100 yrs.

Distance transversed daily 100-400 m

Human walk 25 miles to work and back

Not all zooplankton migrate

Light motivates diel, move away from the light

Sonar used to track the movement

Temperature a factor

Gather on bottom, place for predators

Four hypotheses why?

Seasonal Succession in Phytoplankton

Seasonal succession

Biological conditioning



The Marine Planktonic Food Web

Dominant producers

Diatoms and larger dinoflagellates


Top carnivores

Figure 2.44 p.85

Figure 2.45 p. 86

Spatial Distribution of Plankton




Eddies or rings

Coastal fronts

Chlorophyll maximum

Marine snow

The Major Plankton Biomes

Terms for Chapter 2 Test:  study these and you will do aok.

Winkler Method                standing crop          cyanbacteria

Languir convection cells     Red Tide               net production

dinoflagellates                  diatoms               gelatinous zooplankton

nauplius                          osmosis                radiolarians

k                                    limiting factors       DOC

microbial loop                  marine snow          eutrophic

extinction coefficient       domoic acid             hydrography

zooxanthellae                  geodesic dome       larval copepod

Portuguese man-of-war     copepods               Chaetognatha

compensation depth        auxospore               Ctenophores

phytoplankton and light intensities                nanozooplankton

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