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Plankton
is derived from the Greek language and means ‘wandering’. When
we think of organisms in the ocean that wander—can’t control
their motion against the current—we usually think of animals such
as jellyfish.
Jellyfish are zooplankton; zoo is Greek for animal.
But that’s only part of the story…
Plankton
can be divided into many groups, but the most common divisor is
between zooplankton and phytoplankton.
Phytoplankton are tiny, aquatic plants usually so
small they must be viewed with a microscope.
Phyto is Greek for a plant.
Plankton
can further be categorized to account for the tiniest living constituents in
the ocean, bacteria and viruses. Bacterio- and virioplankton belong
to the group encompassing the smallest planktonic organisms, the
picoplankton (1 picometer = 10-12 meters).
Bacteria and viruses may be enumerated in a number of ways, and some
examples are as follows. Both can be visualized under a microscope
using fluorescence: samples are treated with biological stains, and when
they are illuminated with light of a specific wavelength, the stained
components emit light of a longer wavelength (fluorescence). The
fluorescence is visible when a microscope is fitted with a set of filters
specific for the stain.
·
Bacteria rods visualized with multiple stains
These images
were collected
at different
magnifications.
Viruses = the smallest
green dots
(The big, round green dots are bacteria.)
Photo by Molecular Probes Inc.
Photo by Dr. Jed Fuhrman
Bacteria colonies grown on marine agar, which is
a culture medium for microorganisms derived from seaweed.
Bacterio- and
Virioplankton
Bacteria colonies can be counted when they are grown on media
(agar). A drawback to this method is most marine bacteria cannot be
grown in the laboratory; however, culturing bacteria can be useful to
answer some research questions.
Some colonies are circled.
Phytoplankton
have a marvelous diversity of forms. They
can be classified according to a number of
characteristics (for example, by morphology);
in coastal waters, they are often divided into 2
groups: diatoms and dinoflagellates.
Diatoms
have glass cell walls (called
frustules), which the cells form by
taking up dissolved silicate from
seawater.
Some diatom species have ‘setae’, which are spine-like projections.
The projections increase the cell’s surface area, thus increasing the cell’s
drag and reducing its sinking rate into deeper, darker waters that have
less sunlight. Individual cells may also form long chains to reduce
sinking rates.
Dinoflagellates
Dino is Greek for whirling; flagellum is Latin for a whip.
Dinoflagellates can ‘swim’ through the water—and stay in nutrient-rich
patches—using a pair of whip-like flagella.
Dinoflagellates
are capable of capturing energy in 1 of 3 ways:
Autotrophs perform photosynthesis to capture the sun’s energy and
transform it to food. In this regard, dinoflagellates are plant-like.
(auto- is G for self; troph is Greek for nourishment)
Heterotrophs cannot perform photosynthesis and must obtain
organic carbon, by eating other organisms or decayed marine biota, to
provide nutrition. In this regard, dinoflagellates are animal-like.
(hetero- is G for other; troph is Greek for nourishment)
Mixotrophs can both perform photosynthesis and take up dissolved
organic matter. Thus, in this regard, dinoflagellates are both plant-like
and animal-like.
(mixo- is Greek for mix; troph is Greek for nourishment)
In this image,
you can clearly
see the transverse
may
also be classified by their outer coatings:
grooves
(cingulums)
for the
flagella.
Dinoflagellates
Armored
dinoflagellates have an
outer,
protective coating
made of
cellulose.
Again, in this image, you
can clearly see the transverse
grooves (cingulums) for the
flagella.
Naked
dinoflagellates have
no
outer coating made
of cellulose.
Phytoplankton
Of the 5000 species of phytoplankton, about 300 species can occur in
‘blooms’ with concentrations high enough to color the water, including
the so-called ‘red tides’ and ‘brown tides’.
At least 90 of the bloom-forming species are harmful to humans or
animals. When filter feeders, such as oysters,
are present during toxic algal blooms, they
may concentrate algal toxins in their tissues,
and, in turn, when people eat the shellfish, they can contract illnesses
affecting the nervous or gastrointestinal system. Also, when the bloom
ends, phytoplankton cells die, then they sink to bottom waters and are
decomposed by bacteria. These aerobic bacteria use oxygen in the
water; sometimes the oxygen level is reduced so much that shellfish and
other bottom-dwelling organisms suffocate.
Numbers from Bowers et al. 2000
In September 2003, a toxic
dinoflagellate bloom
(Gymnodinium sp.) occurred
in Sarah Creek, which flows
into the York River, a tributary
to Chesapeake Bay. Algal
concentrations were great
enough to color the water.
Sarah creek is home to an oyster
farm run by the non-profit
Chesapeake Bay Foundation*.
As a result of the bloom,
approximately 650,000 oysters
died.
* http://www.cbf.org
The secchi disk is ~15 cm in diameter; the shadow in the
water is from a davit on the boat carrying the science party.
Photos by Dr. Rob Brumbaugh
Plankton (Greek for ‘wandering’) can be divided into 2 groups:
Phytoplankton
(phyto- G, ‘a plant’)
Zooplankton
(zoo- G, ‘an animal’)
can be divided into 2 groups
Diatoms
• glass-like shells
• some have setae (projections
that prevent sinking and grazing)
Dinoflagellates*
• move using
whip-like flagella
can be divided into 3 groups
autotrophs
mixotrophs
heterotrophs
(auto- G, ‘self’)
(mixo- G, ‘mix’) (hetero- G, ‘other’)
(troph G, ‘nourishment’)
• armored
• “naked”
* Dino- G, whirling; flagellum Latin, a whip
Bibliography
Bowers, H.A., Tengs T., Glasgow H.B. Jr., Burkholder J.M., Rublee P.A.,
and Oldach D.W. 2000. Development of real-time PCR assays for rapid
detection of Pfiesteria piscicida and related dinoflagellates. Applied and
Environmental Microbiology 66: 4641-4648.
Carlton, J.T. 1985. Transoceanic and interoceanic dispersal of coastal
marine organisms: the biology of ballast water. Oceanography and
Marine Biology Annual Review 23: 313-371.
Hallegraeff, G.M. 1993. A review of harmful algal blooms and their
apparent global increase. Phycologia 32: 79-99.