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?

• Waves
• Tides
• 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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Life cycle of a squid

• Squid experience benthic, planktonic, and
  nektonic stages
• Squid are considered meroplankton (opposite
  holoplankton)

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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

Neuston net
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Taxonomy
Zooplankton
Phytoplankton
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Importance of Phytoplankton
Phytoplankton is the base of the food chain.
Phytoplankton population decline causes
zooplankton and apex predators to decline .
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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
• Cniderian (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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Importance of krill in Antarctic food web
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Chaetognath
Copepod
Crab larvae
jellies
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Fish larvae
Queen Trigger fish Egg to Juv.
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tunicate
Jelly-like house
Oikopleura
Marine snow
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Marine Snow
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Marine Snow
A major component of marine snow is fecal pellets
Base of Florida Escarpment covered with marine
snow. Octocorals attach to steep sides and under
ledges to avoid burial.
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Marine Snow
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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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Vertical Zonation of Zooplankton

• Epipelagic upper 200-300 m water column high
  diversity, mostly small and transparent
  organisms many herbivores
• Mesopelagic 300 1000 m larger than
  epipelagic relatives large forms of gelatinous
  zooplankton (jellyfish, appendicularians) due to
  lack of wave action some larger species (krill)
  partly herbivorous with nightly migration into
  epipelagic regimes many species with black or
  red color and big eyes (why?) 
• Oxygen Minimum Zone 400 800 m depth,
  accumulation of fecal material due to density
  gradient, attract high bacterial growth, which in
  turn attracts many bacterial and larger grazers
  strong respiration reduces O2 content from 4-6 mg
  l-1 to lt 2 mg l-1
• Bathypelagic 1000 3000 m depth, many dark red
  colored, smaller eyes
• Abyssopelagic gt 3000 m depth, low diversity and
  low abundance
• Demersal or epibenthic live near or temporarily
  on the seafloor mostly crustaceans (shrimp and
  mysids) and fish

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Diurnal vertical migration
Organisms within the deep scattering layer
undertake a daily migration to hide in deep,
darker waters during daytime
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Diurnal 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

• 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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Langmuir Cells
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Langmuir Cells
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Internal Waves

• Underwater waves propagated along the thermocline
• Generated by overflow over rough topography
• Much greater amplitude than surface waves

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Satellite image of internal wave
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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
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Inquiry

• Where do plankton aggregate?
• What is the difference between holoplankton and
  meroplankton?
• What is marine snow composed of?
• What is the connection between the deep sea
  scattering layer and DVM?
• Why arent phytoplankton found in neuston?