I. Types of pelagic oceanic food chains
A. Gyre-center, nutrient-poor
1. I'll use the food-chain framework of this section to introduce the
different types of plankton.
2. At the base are the photosynthetic autotrophs
(phytoplankton=single-celled); nannoplankton (20 - 200 microns).These are the most important
marine plants and these PHYTOPLANKTON produce 99% of the food for marine
(Often nannoplankton) = algae, one or
more flagella, no hard exoskeleton so don't sink so fast
some bioluminescent, tropics, temperate summers, centers of gyres in mid-latitudes. Can
also ingest organic matter as a food source which gives them a competitive advantage in these nutrient-poor environments.
1) Cause of red tides and paralytic
shellfish poisoning. During a red tide up to 2 million of them can be
found in a quart of seawater.
a) Produce water-soluble toxins, some of which kill shellfish and some
of which are just passed on to, and affect the human consumers in the form of PSP.
b) Are known to have caused 300 deaths world-wide.
c) Symptons akin to drunkeness
b. In temperate regions the nature of the phytoplankton population changes
with the season varying between diatoms during periods of high nutrients
and mixing intensities and dinoflagellates later during low-nutrient, low-mixing times.
c. Coccolithophores (relatives of diatoms)
= nannoplankton with calcite plates, warmer, nutrient-deficient tropical & temperate
waters where their extremely small size makes them very efficient producers and slow sinkers. (<.06mm
(.002in) in diam.) Their hard parts are the sediments that form chalk, such as makes up the
White Cliffs of Dover.
3. Next up the food chain are the microzooplankton which are unicellular, amoeba-like zooplankton (KINGDOM PROTISTA, eukaryotes). In the Linnean Classification
these are not in the Animal Kingdom, but since they are not primary producers, we will call them animals.
a. These protozoans (Phylum Protozoa) can also
be benthic & favor warmer, organic-rich water.
The commonest forms have calcareous (foraminifera) or siliceous (radiolarians,) exoskeletons from which they can extrude protoplasm to trap food (i.e., nannoplankton)
in the surrounding water.
4. Next macrozooplankton, which are dominated by the copepods
a. single most important zooplankton- bulk of animal mass in oceans,
b. tiny shrimp-like creatures (.5-5mm), limited vert. migr,
graze on phytoplankton
c. Largely responsible for deep
scattering layer (accumulations of organisms in a thin band extending horizontally along a density boundary or at
a preferred light intensity or food resource level, which are capable of partially
reflecting sound waves from depth sounders).
d. Members of: Phylum Arthropoda-jointed legs & external skeletons. Largest group of animals on Earth (includes the insects).
1) Class Crustacea - majority of all
5. Next megazooplankton
a. Euphasids or Krill (3-5 cm,
1) Also herbivorous
2) Dominant zooplankton at high latitudes and may be main food for baleen whales.
b. Chaetognath (arrow worms)-voracious
1) In some cases a specific species is found only in a certain water mass,
to the extent that they can used to identify the origin of the water in which found.
c. Various forms of what we normally group as jellyfish.
1) (Phylum Coelenterata or Cnidaria)
Organisms with a gut and tentacles at one end, meat-eaters
(predatory, although also feed on organic detritus),stinging cells in tentacles, some colonial forms = Portugues
Man-of-War (tentacles can be > 100 ft long).
2) Ctenophores (Phylum Ctenophora) -
"comb jellies", small (<few cms) and transparent, bioluminescent, plankton/nekton (i.e., entirely
pelagic), also meat-eating but have adhesive cells on their tentacles instead of stinging cells.
3) About 97% water so they cannot support their own body weight and have
no muscles or bones. Nor do they have a brain, heart or eyes.
a) Instead they have a network of nerve cells that help them move and
react to food and danger. They have simple sensors that tell them if they aremoving up or down (i.e.,
toward or away from the light).
4) Supremely successful group in all the oceans.
5) The Sea Wasp in Australia has a deadly sting that can kill a person
6) In some reginos of the oceans that are being
overfished by commercial fishermen, jellyfish have moved in and replaced the overexploited bony
7) Sea turtles, some fish and some sea birds will eat them.
= fish and other organisms that eat plankton
a. Stomias and lantern fish in the deep ocean
make-up most of these
= fish and other organisms that eat fish
a. Many mammals, squid, game fish and popular table fish