Wildlife
Climatology
The Expedition
Peoples Of The North
The Global Issues
The "Making Of"
PLANKTON: The Oceans' Most Abundant Food Source
Caroline Underwood Writes from Pond Inlet, Baffin Island
The Bowhead Whale, Balaena Mysticetus
PLANKTON: The Oceans’ Most Abundant Food Source
Is the polar bear a marine mammal or a land mammal?
Thick-Billed Murre, Uria lomvia
by
Isabelle Deslandes, Ship's doctor
The word plankton, from the original Greek, means “to wander.” Plankton includes all the marine organisms that depend on water currents and flows for movement, for example, krill, copepods and jellyfish. This characteristic distinguishes them from the nekton, which control their own locomotion, such as fish, octopuses and marine mammals.
Thousands of species of plankton exist, and they are divided into two groups: The plant form is called phytoplankton, and the animal form, zooplankton.
Phytoplankton,
the plant form
Phytoplankton are rather like unicellular microscopic algae. Their populations
are distributed along the surface of oceans easily penetrated by sunlight.
The right intensity of light, temperature conditions and plentiful food source
encourage the rapid proliferation of plankton. Phytoplankton make up the base
of the oceanic food chain and form the majority of the biomass of our seas.
By photosynthesis, this minute marine plant form transforms water and carbon
dioxide into sugar molecules and the oxygen that is so indispensable for life.
The central parts of the oceans are not rich in phytoplankton. However, high population densities of these organisms are found in active seas--areas around coastal waters, along continental shelves, on great shoals and nearby reefs. Such ocean topographies generate underwater currents that bring to the surface high quantities of mineral salts essential for the plankton’s development.
Zooplankton,
the animal form
Zooplankton, unlike phytoplankton, do not require direct light for their development.
Thus high populations of these small marine organisms can be found at great
ocean depths, often reaching 1,000 metres. Since they are not in active control
of their own locomotion, zooplankton have developed various ways to stay afloat.
Such evolutionary adaptations as cilias, appendices, bubbles, floaters and
flat morphologies help keep them suspended in the water.
Plankton feed the smallest crustacean to the largest of whales. Various shellfish, sponges and corals also eat them. At dusk, most members of the zooplankton family migrate to the surface of the oceans to feed, where they, in turn, are preyed on by large numbers of fish and squids. Krill, larval stages of many fish, shellfish and even jellyfish are classified as zooplankton, but 90% of this group of organisms are composed of the herbivorous copepods. This is the species of zooplankton that we are sampling during our expedition.
Plankton and climate change
As we reach the end of our mission, these copepods, well preserved in ethanol,
will be used for molecular or DNA analysis. Along with various measurements
such as water salinity and water temperature (elements that can be useful
in studying climate change), scientists hope to study how plankton populations
are influenced by the physical environment. In the long run, such information
could be useful in explaining or even predicting the impact of climatic changes
on the oceans’ biomass.
Useful links
http://www.sciencephoto.com/html_press_archive/011001.html
http://biology.rwc.uc.edu/HomePage/BWS/planktonkey/phytozoo.html
http://huey.colorado.edu/LTER/images/pictures/lakes/plankton/R.html
http://www.nos.noaa.gov/nosgallery/welcome.html
http://www.oceanlight.com/search/dosearch.php?ss=tunicate
http://life.bio.sunysb.edu/marinebio/plankton.html
http://www.gcrio.org/ASPEN/epnews/fall95/plankton.html
