Plankton and Oceanic Food Webs

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Plankton and Oceanic Food Webs

• Coastal Marine Biology
• Feb 2007

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Basic Plankton Vocabulary

• Plankton vs. Nekton
• Phytoplankton vs. Zooplankton
• Classification based upon size
• Megaplankton (above 2mm) macro- (0.2 to 2mm)
  Micro- (20 microns-0.2mm) nano- (2 to 20
  microns)
• Holoplankton vs. Meroplankton
• Entire lives vs. part of life cycle (larvae)

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Diatoms and DinoflagellatesDominant
Phytoplankton Groups

• These two groups are the major 1o producers
• Diatoms (eukaryotic algae 100K species)
• Cell wall made of silica
• No visible means of locomotion
• Unicellular, some form chains or colonies
• As diatoms divide by binary fission, their cells
  get smaller
• Dinoflagellates (flagellated protists)
• Possess two flagellae (used for some locomotion)
• Plates of cellulose
• Half are producers
• Usually solitary rarely form chains
• Dont get smaller as they divide
• Some species can produce toxins released into sea
  water
• Can cause Red Tides toxins may accumulate in
  shellfish and poison other organisms and humans
• Other minor constituents of the phytoplankton
• Blue green algae (cyanobacteria)
• Coccolithophores (in tropics)

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How do phytoplankton stay afloat?

• Plankton tend to be more dense than sea water
• Phytoplankton should sink below photic zone
• Zooplankton would sink below where their food is
  at
• Both groups are weak swimmers unable to cope with
  winds and currents
• How do they do it?

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Decrease overweight /or increase the surface of
resistance

• Decrease density
• Alter body fluids so that they are less dense
• Replace heavy chemical ions with lighter ones
• Employ liquids that are less dense than water
  (fats, oils)
• Fats serve a dual purpose food reserves and
  floatation
• Changes in surface of resistance
• Stay small!
• Smaller organisms have greater surface
  areavolume ratio
• Change the shape of the body
• Flattened body shapes or appendages
• Various spine and body projections (common in
  diatoms, crustaceans)

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Dominant Zooplankton

• Extremely diverse group
• Host of larval and adult forms representing most
  animal phyla
• Jellyfish, ctenophores, worms, mollusks,
  arthropods (most abundant)
• Dominant group Copepods (14k species 70 of
  zooplank)
• Small (1-5mm) holoplanktonic crustaceans
  separate sexes
• Some herbivorous some carnivorous
• Swim weakly with jerking movement
• Large antennae to slow rate of sinking
• Use sight and smell
• Graze on phytoplankton by using their legs like
  paddles to draw water towards their mouth
  (filtering them) or grabbing them with their
  appendages
• Graze on the aquatic pastures of phytoplankton
  and provide the vital link between the primary
  production of phytoplankton and the larger
  oceanic organisms
• Live only a few weeks

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Coral life cycle
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Primary Productivity Vocabulary

• Gross primary productivity
• Total amount of organic material (sugars)
  produced from inorganic carbon (CO2)
• Expressed in grams carbon/m2/yr
• Net Primary Productivity
• Amount of total production that is left after
  losses to respiration, metabolism, and waste
• Not available to support other trophic levels
• NPP GPP E used by producers
• Standing Crop
• Total amount of plant biomass present in a given
  volume of water at a given time
• Varies greatly across seasons and years

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Differences between GPP and NPP
Sun
Photosynthesis
Energy lost and unavailable to consumers
Respiration
Gross primary production
Net primary production (energy available
to consumers)
Growth and reproduction
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How do you measure primary productivity?

• Freshwater/Marine System
• Light/dark bottle technique
• C14 uptake
• Terrestrial vegetation
• Harvest techniques measure weight increase of net
  production.
• Changes in biomass over time
• Other techniques approach gross production and
  respiration through measurement of exchange of
  gases, especially CO2. These include
• Enclosure studies, involving measurements of CO2
  exchange in plastic enclosures of parts of
  ecosystems
• Remote sensing (using satellites)
• Indirect Chlorophyll a measurements

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Factors affecting primary productivity in the
oceans

• Light
• How much light is available depends on many
  factors including absorption of light by water,
  the wavelength of the light, angle of incidence,
  transparency of the water, amount of light
  reflected, latitude, and season of year
• Nutrients (the major limiting factor)
• Major inorganic nutrients required by
  phytoplankton include nitrogen (nitrate)
  phosphorus (phosphate)
• Occur in small amounts in sea water
• Used up very quickly in photic zone
• Untapped reservoir exists below the photic zone
• Need mixing of water to tap this reservoir
• Wind
• Upwelling

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Productivity across seasons in different seas

• Tropical seas
• Upper waters are well lit year round sharp angle
  of incidence so light penetrates well
• Water becomes thermally stratified so little if
  any mixing of nutrients (extremely nutrient poor)
• Few phytoplankton in water
• Results in low but constant productivity
• Temperate seas
• Amount of light and nutrients varies seasonally
• Peak in spring, lesser peak in fall, and low
  productivity in summer and winter
• Low light in winter higher nuts in spring
  (bloom), in summer less nutrients b/c water is
  thermally stratefied (low nutrients)
• Polar seas
• Productivity is restricted to a single short
  period in the polar summer (July or Aug)
  nutrients in these areas are not limiting (light
  is)
• Coastal Waters
• Inshore waters have an abundant supply of
  nutrients from land
• Shallow water means phytoplankton are rarely
  below compensation depth
• No thermocline so abundant mixing of nutrients
• Production limited to upper 5-10m b/c water is
  less clear

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Energy flows through food webs

• 1st and 2nd laws of thermodynamics
• Not all of the energy of one trophic level is
  passed onto the next level
• Not all of the energy of phytoplankton is passed
  on to the primary consumers
• Some energy is converted into heat b/c organisms
  must use energy themselves, wastes, etc
• Only about 10-20 of the energy present at one
  trophic level is passed to the next
• The other 90-80 is converted into heat which is
  not available to do cellular work
• B/c each level has less available energy than the
  level before it, there is a limit on the number
  of levels that can exist
• Fewer top carnivores than herbivores
• Many larger marine organisms with large energy
  demands eat low on the food chain b/c there is
  more biomass in plankton
• Whale sharks (largest fish) and blue whales
  (largest mammal) do this

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Sun
Producers (rooted plants)
Producers (phytoplankton)
Primary consumers (zooplankton)
Secondary consumer (fish)
Dissolved chemicals
Tertiary consumer (turtle)
Sediment
Decomposers (bacteria and fungi)
Fig. 4.11, p. 78
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Generalized Food Web of the Antarctic
Note Arrows Go in direction Of energy flow
Food chain Vs Food web?
Be sure you can come up with a typical food web
in the marine environment!!!!!
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Energy Flows and Matter Cycles in Ecosystems
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Tertiary consumers (human)
Decomposers
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Secondary consumers (perch)
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Primary consumers (zooplankton)
1,000
10,000 Usable energy Available at Each tropic
level (in kilocalories)
Producers (phytoplankton)
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Top carnivores
Decomposers/detritivores
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Carnivores
5,060
383
Herbivores
3,368
Producers
20,810
Fig. 4.21, p. 85
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Feeding Strategies

• Filtering Food
• Some swim vs. some are sessile
• Whales, whale sharks, copepods, corals, barnicles
• Benthic feeders (deposit feeders)
• Any plankton missed dies, sinks, and joins the
  rain of faecal matter and dead material that
  falls onto the ocean floor
• Ocean floor is littered with organic matter which
  is broken down by bacteria (which themselves
  become food)
• Fine sediment, detritus, and living animals
  create a grainy soup
• Scoop up mouthfuls of sand and extract food
• Ex. Sea cucumbers, marine worms, etc
• Grazing
• Predation (the arms race!)

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Compensation Depth

• Less light as one goes deeper
• Longer wavelengths of light are first to go
• At some depth (the CD), the light energy
  available is just sufficient to fix sugars at a
  rate equal the rate at which the plant uses the
  sugars
• If the plant goes deeper RespirationgtPhotosynthes
  is
• Net loss of energy
• Above this depth PSgtRespiration net gain of
  energy
• CD varies geographically b/c depends on clarity
  of water
• The clearer the water, the deeper light
  penetrates
• Deeper in clear open ocean waters and shallower
  in inshore waters
• Phytoplankton thus only exist in the upper 200m
  of the water column where light penetrates