Plankton include a wide variety of living
organisms that range from tiny bacterioplankton to gelatinous animals like
jellyfish. For most part, these organisms spend their lives drifting on ocean
currents since they are unable to swim against ocean currents. As a result,
they move with the currents. They are vast and diverse and thus make up a
great majority of the living biomass in the ocean.
Types of Plankton
Phytoplankton - Live closer
to the water surface and include various prokaryotes (autotrophs) and
Zooplankton - Zooplankton
includes metazoa and protozoa that survive by feeding on other plankton
Bacterioplankton - These
are bacteria and archaea that are responsible for breaking down organic
material in the ocean
Virioplankton - Studies have identified
a group of viruses (virioplankton) to be a dynamic component of plankton. They
are divided into bacteriophage (majority) and eukaryotic viruses.
bacteriophage, these viruses infect and reproduce by infecting bacteria in
order to grow and thrive. However, to a lesser extent, they are capable of
producing their own food. In their environment, virioplankton play an important
role of regulating carbon as well as recycling nutrients.
* The word plankton is derived from the Greek
word "Planktos" meaning drifter/wanderer.
While most are too small to be seen
with the naked eye, some like the Blue-bottles jellyfish and Moon jellyfish
can be seen without the aid of a microscope. Also, it's possible
to see tiny plankton move around a sample of water collected from oceans and
These types can also be viewed more easily by using a
stereo/dissecting microscope. This simply involves placing a concentrated
sample (concentration may be achieved using a centrifuge) on a plastic slide
and mounting on the microscope to observe any plankton that may be present. For
many others that are too small to be seen with the naked eye, other techniques can
Microplankton under the Microscope
Microplankton include phytoplankton and
zooplankton that measure between 20 and 200 micrometers. This includes a
variety of ciliates (protistan).
For this technique, the ciliates in seawater sample
were preserved using acid Lugol's fixative.
Add 37 percent formaldehyde
to 250 ml of the sample (in acid Lugol) and allow to stand overnight. This
allows for fixation of organism
Use glass fixation system
to filter 100 mm of the sample. Filtration is achieved by using a 25mm, 8
micrometer black polycarbonate filters that has a 10 micrometer nylon backing
filter at low pressure - Using this process will result in an even distribution
Place the filters on a
plain paper to allow the residuals water to wick away for about 30 seconds - Avoid
Spread a drop of immersion
oil (Cargille Series A) on a glass slide to produce an even layer
Carefully separate the
polycarbonate membrane from the backing filter and place it on the immersion
Add another drop of
immersion oil on the membrane with the sample and cover with a cover slip
Mount and view under the
microscope (inverted compound microscope)
Using this technique, students can identify a
number of organisms including dinoflagellates, diatoms as well as other ciliates.
An Epi-fluorescence microscope refers to a
fluorescence microscope where the specimen is illuminated from above. The
arrangement of the optical components of the microscope is such that the
objective serves as the source of light and also collects light from the specimen.
Using this technique, it is possible to observe a number of plankton including
bacteria, phytoplankton and zooplankton.
Bacteria Microscopy (Epi-fluorescence
membrane; pore size (0.2 micrometer) and 2.5 mm diameter
Glass filter holder
Vacuum source (about 25cm
37 percent formaldehyde
Acridine Orange stock
(with high pressure mercury burner)
Using formaldehyde, fix the
sample immediately - This involves adding formaldehyde (37 percent) in to 250
ml of the sample.
Using free-particle water,
moisten the filter unit and place the supporting filter (1.2um) and black membrane
(0.2um) on top.
Using ultra pure water,
rinse the filter unit funnel and place it on the filters (clamp to fasten)
Pour a small amount of the
sample on the membrane filter and add the Acridine Orange to stain
After one minute, gently
filter the mixture at maximum vacuum (100mmHg). This prevents damage to the
cells in the sample
Spread a drop of immersion
oil on a clean glass slide and place the filter on the slide
Place another drop of
immersion oil on the membrane and cover using a cover slip
View the slide under the
microscope and try counting the number of bacteria present
Under the microscope, the cells will appear to
shine giving off orange and green colours.
Phytoplankton Under the Microscope (Epi-fluorescence Microscope)
Water sample with phytoplankton
Use Lugol's solution to fix
Add the mixture into a
sedimentation chamber (fill to the top)
Allow the chamber to
vibrate in a dark area (away from light)
Having removed excess
volume, mount the chamber using a cover slip
View under inverted
Some of the phytoplankton that may be viewed
under the microscope include green algae, diatoms and dinoflagellates among
If the sample is
concentrated, dilute using tap water and mix thoroughly
Using a volumetric pipette
(wide-mouth pipette), obtain 1 mL of the sample and add it into a
Place on the microscope and
try counting the number of organisms present
When viewed under the microscope, the sample may
reveal such zooplankton as microcrustaceans (e.g. cladoceran).
Planktons: Life and Characteristics
Phytoplankton may be described as free-floating
microscopic plants. This is because they are tiny organisms that are capable of
using carbon dioxide and sunlight to produce their own food.
Like other plans
that grow on land, phytoplankton have chlorophyll in their cells used for
photosynthesis. This allows them to trap sunlight, which is then converted to
chemical energy in the presence of carbon dioxide.
Phytoplankton are very diverse and exist as both
prokaryotic (e.g. cyanobacteria) and eukaryotic (algae) forms. This is a big
advantage given that phytoplankton are the primary producers in aquatic bodies.
However, some phytoplankton like sapromixotrophs and phagomixotrophs are
classified as mixotrophs because they are not only capable of producing their
own food through photosynthesis, but also obtain nutrients from organic
material present in their environment.
Importance (Aquatic Environments)
As the primary producer, phytoplankton plays a
very important role in the aquatic food web. By feeding other plankton like
zooplankton as well as other small fish, phytoplankton make it possible to feed
other bigger aquatic organism like whales. Therefore, in the absence of
phytoplankton, other higher aquatic organisms would be highly affected and even
Apart from their importance in the aquatic food
web, phytoplankton also play a very important role in the carbon cycle. As
earlier mentioned, phytoplankton use carbon dioxide for photosynthesis in order
to produce food (chemical energy). In the process, some of the carbon is stored
in phytoplankton when they die and settle at the bottom of the sea.
Any change in the growth and amount of these
organisms therefore has a direct impact on global atmospheric carbon-dioxide
gas and thus on the temperature. Because they carry some of the carbon to the
bottom of the ocean when they die, phytoplankton also contribute to the
formation of oil.
* While phytoplankton are important, they can
cause diseases and even kill both marine life and people. Some of the species
have been shown to produce dangerous bio-toxins that result in red tides and
algal blooms. When consumed, these toxins can cause serious illnesses and even
Zooplankton are a variety of minuscule animals with
limited swimming abilities. As such, they are incapable of swimming against the
current and thus go where the current takes them.
Unlike phytoplankton that are
capable of manufacturing their own food, zooplankton survive by feeding on
phytoplankton since they lack chlorophyll. The different types of
zooplankton can be grouped on the basis of size and how they develop.
Size - Based on size, zooplanktons are
Picoplankton - Picoplankton are the
smallest zooplankton that measuring less than 2 micrometers. Examples of
picoplankton include Synechococcus, picoeukaryotes and Prochlorococcus.
Nanoplankton - Nanoplankton may range
between 2 and 20 micrometers and include such zooplankton as Pyrrophyta,
Xanthophyta and Chrysophyta.
Microplankton - Microplankton measure
between 20 and 200 micrometers and include certain small copepods
Mesoplankton - Mesoplankton range
between 0.2 to 20 mm in size and include euphausids and some larval fish
Macroplankton - Measuring between 20 and
200 mm, examples of macroplankton include larger crustaceans and jellyfish
Megaplankton - Megaplankton are over
200 mm in size and include larger jellyfish
Development stage - Apart from size,
zooplankton are also classified on the basis of development stage. The two main
groups based on development include:
Meroplankton -Meroplankton include zooplankton that are in
their larval stage. Later in their development, meroplankton change to such
animal as fish, insects and worms among others
Holoplankton - Whereas meroplankton change to
other animals, such holoplankton as copepods, pteropods and siphonophores
remain zooplankton for the rest of their life
Importance (in Aquatic Environment)
Like phytoplankton, zooplankton also play an important role in the aquatic food web. By feeding primarily on phytoplankton (algae), zooplankton prevent algae from growing out of control.
As already mentioned, changes in the growth of phytoplankton has a direct impact on the global carbon cycle. Therefore, by consuming phytoplankton, zooplankton also play an important role in the regulation process.
Zooplankton are also important food sources for various organisms including planktivorous fish. As such, they play an important role in aquatic food web given that their absence would affect the rest of organisms above them in the food chain.
Bacterioplankton are also a group of plankton.
They are primarily prokaryotic, which means that they lack a membrane bound
nucleus as well as a number of other organelles.
Some of the bacterioplankton
like the blue-green algae are primary producers (they can synthesis their own
food through photosynthesis) while others such as various heterotrophic
flagellates are primary consumers and survive by consuming organism material present
in their environment.
Bacterioplankton has been associated with the uptake of
phosphorous in water thereby playing an important role of controlling
eutrophication, which can result from high phosphorous concentration.
* Eutrophication refers to excessive amounts of
nutrients and given minerals in water that can affect oxygen concentration.
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