7 The Water Column Plankton

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7 The Water ColumnPlankton

• Notes for Marine Biology Function, Biodiversity,
  Ecology
• by Jeffrey S. Levinton

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Plankton Definitions

• Plankton organisms living in the water column,
  too small to be able to swim counter to typical
  ocean currents

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Plankton Definitions

• Phytoplankton
• Zooplankton
• Mixoplankton (or mixotrophic)

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Plankton Definitions

• Holoplankton - permanent residents
• Meroplankton - temporary residents
• Neuston - associated with slick
• Pleuston - sticking up above water surface

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Plankton Definitions

• Size classes

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Vertical Position of Plankton - Factors

• Bulk density - regulated by ionic substitution,
  gas secretion, and release (cuttlefish, Nautilus)
• Swimming behavior
• Turbulence stirs plankton through the water column

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Vertical Position of Plankton - Factors

• Size of plankton - smaller plankton, low Reynolds
  number
• Low Re means there is a boundary layer around
  plankters body
• Smaller organisms denser than seawater sink with
  a constant velocity, proportional to organismal
  volume, although increases of spines etc. can
  slow sinking

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Phytoplankton
Diatoms

• Occur singly or form chains
• Size range of nanno to microplankton
• Encased in silica shell consisting of two valves
• Usually radially symmetrical
• Reproduce asexually by binary fission
• Also sexual reproduction
• Doubling once or twice per day usually

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(a) Diatoms
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Thalassiosira
Chaetoceros
Asterionella japonica
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Phytoplankton
Dinoflagellates

• Secrete organic test and have two flagellae
• Size range of nanno and microplankton
• Asexual and sexual reproduction
• Often some life history stages, benthic cysts
• Many species are heterotrophic
• Often abundant in tropics, mid-latitudes in
  summer
• A few species are the cause of red tides

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Peridinium
(b) Dinoflagellate
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Phytoplankton
Other Groups

• Cyanobacteria - abundant, nitrogen fixation
• Coccolithophores - unicellular, nannoplankton,
  spherical, and covered with calcium carbonate
  plates - coccoliths
• Silicoflagellates - unicellular, biflagellate,
  internal skeleton of silica scales, often in
  Antarctic, open ocean

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Cyanobacteria types
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Bloom of coccolithophores, near Newfoundland
Coccolithophore
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Silicoflagellate
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Phytoplankton
Other Groups

• Numerous other groups, including many flagellated
  types
• CRUCIAL POINTS ABOUT PHYTOPLANKTON
• DIVERSITY IN WATER COLUMN
• DIFFERENT NUTRIENT NEEDS OF VARIOUS GROUPS (e.g.,
  Fe, Si, Ca, P, N)
• DIFFERENT PROPERTIES SUCH AS BULK DENSITY,
  ABILITY TO SWIM

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Zooplankton
Crustacean zooplankton (Arthropods)

• External chitin skeleton
• Segmentation
• Paired jointed appendages (e.g., legs, antennae)
• Antennae, mandibles, and maxillae as head
  appendages
• Usually compound eyes
• Include copepods, krill, amphipods (crabs,
  lobsters, sowbugs - not in plankton)

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Zooplankton
Crustaceans - Copepods

• Largest group of crustaceans in zooplankton
• Range from lt1 - a few mm long
• Planktonic forms - Calanoida
• Long pair of antennae
• Swim mainly with aid of 5 pairs of thoracic
  appendages
• Lack compound eyes, medial naupliar eye
• Feed on phytoplankton or smaller zooplankton,
  depending on the species

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Zooplankton
Copepod Feeding
Low Reynolds number - viscosity dominates Feeding
current (green) generated by thoracic
appendages Maxilliped reaches out and grabs
particles entrained in current
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Zooplankton
Copepods
Females of different species with eggs
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Zooplankton
Crustaceans - Euphausids (Krill)

• Shrimplike, up to 5 cm long
• Abundant in Antarctic and in upwelling regions
• Main food of baleen whales in Antarctic
• Feed on phytoplankton and smaller zooplankton
• Feeding by means of group of appendages that form
  a basket - appendages have setae and smaller
  setules, hairs that capture particles

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Zooplankton
Gelatinous Zooplankton

• Jellies include a wide variety of distantly
  related groups, all have gelatinous material used
  for support (skeleton)

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Zooplankton
Gelatinous Zooplankton - Cnidaria

• Planktonic Cnidaria Scyphozoan jellyfish,
  Hydrozoan jellyfish (some meroplanktonic
  jellyfish stages), and siphonophores, specialized
  colonial and polymorphic cnidarians such as
  Portuguese man-of-war
• mainly carnivores, nematocysts - stinging cells -
  on tentacles

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Zooplankton
Cnidaria - Scyphozoan jellyfish
Note muscular bell and tentacles
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Zooplankton
Gelatinous Zooplankton - Cnidaria
By-the-wind-sailor Velella

• Porpita (ca. 10 cm wide) Physophora
• 
  (50 mm high)

Siphonophores
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Physalia physalis
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Zooplankton
Gelatinous Zooplankton - Ctenophores

• Known as comb jellies
• Microcarnivores - feed on smaller zooplankton,
  planktonic eggs, invertebrate larvae
• 8 rows of meridional plates, some have two long
  tentacles

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Zooplankton
Gelatinous Zooplankton - Ctenophores
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Zooplankton
Gelatinous Zooplankton - Salps

• Related to benthic sea squirts, but have
  incurrent and exit siphons on opposite ends of
  body
• Solitary or colonial (up to 2 m in length)
• Have a tail, typical of tunicate swimming larvae
• Small, only a few mm long
• Tail generates current through house, current is
  strained by fine fibers that trap food

Gelatinous Zooplankton - Larvacea
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Salps
Instructor recommend use of http//www.whoi.edu/c
ms/images/oceanus/salp_550_59911.jpg
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Zooplankton
Arrow worms

• Torpedo shaped, a few cm in length
• Rapid swimmers, carnivorous

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Zooplankton
Pteropods

• Holoplanktonic snails
• Swim by means of lateral projections from foot
• Suspension feed or are carnivorous, depending
  upon species

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Zooplankton
Planktonic polychaetes

• Have very well developed parapodia

Instructor Use, for example http//www.tmbl.gu.se
/staff/FredrikPleijel/03Tomopteris_helgolandica.jp
g
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Zooplankton
Protistan zooplankton - Foraminifera

• Secrete skeleton of calcium carbonate, sometimes
  with great ornamentation
• Common in plankton
• Size 1 mm to a few mm
• Contractile pseudopodia trap food particles
• Foram ooze - deep-sea sediment

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Zooplankton
Protistan zooplankton - Radiolaria

• Skeleton of silica, sometimes with great
  ornamentation, occurs singly and as colonies,
  depending on species
• Common in plankton
• Size 50 ?m to a few mm
• A membrane separates interior cell from exterior
  cytoplasm, which streams out something like
  foraminifera
• Radiolarian ooze - deeper than foram ooze

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Zooplankton
Protistan zooplankton - Ciliates

• Common in plankton, feed on bacteria, smaller
  phytoplankton, some mixotrophic
• Elongate, ranging from size from about 50 ?m to
  over 1 mm in length, covered with rows of cilia

Strombidium, 80??m long
Strombidium sp. Under UV light, ingested
chloroplasts in red
Photos by Diane Stoecker
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Phytoplankton and Microbial Diversity - Molecular
Techniques

• Problem of high diversity, enumeration in samples
• Important issue is function of cells e.g.,
  photosynthesis, nitrogen transformation
• Many plankton photosynthesizers and bacteria are
  morphologically difficult to identify
• Need other techniques to use probes to count
  different cell types

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Phytoplankton and Microbial Diversity - Molecular
Techniques

• First need to collect sample and sort by cell size

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Phytoplankton and Microbial Diversity - Molecular
Techniques

• Immunofluorescence develop antibodies to
  specific species, produce antibodies, tag
  antibodies with fluorescent dye, enumerate dyed
  cells by fluorescent reaction to uv light source
• Monoclonal antibodies allows more specific
  antigen-antibody reaction to specific proteins in
  cell

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Phytoplankton and Microbial Diversity - Molecular
Techniques
Example immunofluorescence staining targetted at
cell surface proteins of red tide dinoflagellate
Alexandrium tamarense (yellow)
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Phytoplankton and Microbial Diversity - Molecular
Techniques

• DNA analysis using Polymerase Chain Reaction
  (PCR)
• Primers (short chain nucleotides) from known DNA
  of a species can be used to bind to DNA of a cell
  and then can be amplified and identified, even
  quantified relative to other sequences
  (quantitative version of PCR)

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Phytoplankton and Microbial Diversity - Molecular
Techniques
PCR involves steps of breaking up DNA into chains
(denaturation), adding primers (annealing) and
nucleotides, and new DNA sequence is synthesized
(extension) through steps of heating and cooling
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Phytoplankton and Microbial Diversity - Molecular
Techniques

• High Throughput Sequencing - It is possible now
  to sequence entire genomes extreme example is
  shotgun sequencing, involving complete sequencing
  of an entire water sample of cells (See Hot
  Topics 7.1)

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Phytoplankton and Microbial Diversity - Molecular
Techniques

• Microarrays DNA sequences are extracted from an
  organism, and a library of sequences is recorded
  sequences are synthesized and put on a chip
  sample is added to chip and complementary
  sequences in sample binds to appropriate spots on
  chip.
• Allows for enumeration of known sequences in a
  water sample

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Phytoplankton and Microbial Diversity - Molecular
Techniques

• PCR study of nitrogen-transforming microbes.
  Allows relative abundance of different types
  (e.g., nitrogen-fixers denitrifiers) - see Ward,
  B. and OMullan 2002, references in text)
• PCR study of microbes as function of depth
  allows complete survey of known microbes in
  plankton as function of depth. Allows us to see
  when photosynthesizers stop with a given depth
  (e.g. survey of Pacific microbes with depth - see
  DeLong et al. 2006, references in text)

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The End