Plankton

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Plankton
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• Marine life 3 categories
• Benthos bottom dwellers sponges, crabs
• Nekton strong swimmers- whales, fish, squid
• Plankton animal/plants that drift in water. The
  have little control over their movement.
• Includes diatoms, dinoflagellates, larvae,
  jellyfish, bacteria.

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What physical factors are plankton subject to?

1. Waves
2. Tides
3. Currents

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• Plankton classified by
• Size
• Habitat
• Taxonomy

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Size

• Picoplankton (.2-2 µm) bacterioplankton
• Nanoplankton (2 - 20 µm) protozoans
• Microplankton (20-200 µm) diatoms, eggs, larvae
• Macroplankton (200-2,000 µm) some eggs, juvenile
  fish
• Megaplankton (gt 2,000 µm) includes jellyfish,
  ctenophores, Mola mola

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Habitat

• Holoplankton- spends entire lifecycle as plankton
• Ex. Jellyfish, diatoms, copepods
• Meroplankton- spend part of lifecycle as plankton
• Ex. fish and crab larvae, eggs

lobster
snail
fish
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Habitat

• Pleuston- organisms that float passively at the
  seas surface
• Ex. Physalia, Velella
• Neuston organisms that inhabit the uppermost
  few mm of the surface water
• Ex. bacteria, protozoa, larvae light intensity
  too high for phytoplankton

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Taxonomy
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Phytoplankton- restricted to the euphotic zone
where light is available for photosynthesis.

• Blooms
• High nutrients
• Upwelling
• Seasonal conditions

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Some important types of phytoplankton

• Diatoms temperate and polar waters, silica case
  or shell
• Dinoflagellates tropical and subtropical
  waters.... also summer in temperate
• Coccolithophores tropical, calcium carbonate
  shells or "tests"
• Silicoflagellates silica internal skeleton...
  found world wide, particularly in Antarctic
• Cyanobacteria (blue-green algae) not true algae,
  often in brackish nearshore waters and warm water
  gyres
• Green Algae not common except in lagoons and
  estuaries

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Some important types of zooplankton

• Crustaceans Copepods
• Krill
• Cladocera
• Mysids
• Ostracods
• Jellies
• Coelenterates (True jellies, Man-of-wars,
  By-the-wind-sailors)
• Ctenophores (comb jellies)
• Urochordates (salps and larvacea)
• Worms (Arrow worms, polychaetes)
• Pteropods (planktonic snails)

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Chaetognath
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Copepod
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Fish larvae
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Jelly-like house
Okiopleura
Marine snow
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Marine snow
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Zooplankton larvae, copepods. Some produce oil
to help them float. Smaller population size than
the phytoplanktoton. Zooplankton population size
increases after phytoplankton size increases.
zooplankton
phytoplankton
Winter Spring Summer Fall
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• Nutritional modes of zooplankton
• Herbivores feed primarily on phytoplankton
• Carnivores feed primarily on other zooplankton
  (animals)
• Detrivores feed primarily on dead organic matter
  (detritus) 
• Omnivores feed on mixed diet of plants and
  animals and detritus

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Diurnal vertical migration
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Vertical Migration
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Diel vertical Migration
Each species has its own preferred day and night
depth range, which may vary with lifecycle.

• Nocturnal Migration
• single daily ascent near sunset
• Twilight migration (crepuscular period)
• two ascents and two descents
• Reverse migration
• rise during day and descend at night

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• Advantages for Diurnal vertical migration
• An antipredator strategy less visual to
  predators
• Zooplankton migrate to the surface at night and
  below during the day to the mesopelagic zone.
  Copepods avoid euphasiids which avoid
  chaetognaths.

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Advantages for DVM

• 1. Energy conservation
• Encounter new feeding areas
• Get genetic mixing of populations
• Hastens transfer of organic material produced in
  the euphotic zone to the deep sea

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• Plankton Patchiness
• Zooplankton not distributed uniformly or randomly
• Aggregated into patches of variable size
• Difficult to detect with plankton nets
• - Nets average the catch over the length of
  the tow
• May explain enormous variability in catches from
  net tows at close distances apart

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• Causes of Patchiness
• Aggregations around phytoplankton
• - If phytoplankton occurs in patches, grazers
  will be drawn to food
• - Similar process that led to phytoplankton
  patches will form zooplankton patches
• Grazing holes
• Physical process
• - Langmuir Cells
• - Internal waves

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• Accumulation of Plankton in Langmuir Cells
• Buoyant particles and upward-swimming zooplankton
  will accumulate over downwelling zones

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Deep sea scattering layer Composite echogram of
hydroacoustic data showing a distinct krill
scattering layer. Black line represents surface
tracking of a blue whale feeding
patchiness