Download Diatom forms gametes (auxospore)

GROWTH & REPRODUCTION
Diatom life-cycle
Asexual phase
 Cell divides into two copies of
Sexual phase
 Diatom forms gametes (auxospore)
itself, one of which is the same
that fuse to become a specialized
size as the mother cell, the other
cell which swells to the maximum
of which is slightly smaller.
(original) size for the species.
 Gradual reduction in size occurs
 Life-cycle continues from one to
several years.
 Enters the sexual phase for
original size preservation or by a
trigger from the environment.
 Then divides asexually and
initiates the asexual phase of the
life-cycle again.
 Do these changes in the life cycle in a diatom (one species),
impose changes in the size of valves?
 Do these changes in the size of valves of a diatom, make it
difficult to recognize the species?
 Whatever occur in the
sizes of the valves of diatoms, each
species is unique and can be recognized on the basis of its
valves alone.
 Note: reduction in the diatomsize during the life-cycle
(asexual phase). Length
reduces faster than width
Diatom distribution and Ecology
1.
2.
Diatoms constitute a major component of the marine (open sea)
phytoplankton, living only in the upper 200 m of the surface water.
Autotrophic and form the basis of food chains in many aqueous
ecosystem.
Distribution of diatoms frustules in the surface
sediments of the Indian and Pacific Oceans, in
millions per gram of sediments, from Brasier
(1980).
Antarctic
3.
Inhabit all aquatic environments. They occur in the body of the water
as plankton or on the bottom where they may be attached to plants or
rocks or sand particles, or may be free living and able to move between
particles of the substratum.
4.
In general, members of both classes (Centric and Pennate) may be
found in either fresh or salt water, though Centric forms tend to
predominate in marine habitats, while Pennate diatoms are more
typical of freshwater environments.
5.
Can achieve very high cell densities in nature. In the same time, cell
density can be decreased by reducing the concentration of heavy ions
(K+, Na+, Cl-).
6.
To maintain bouyancy, many species have elaborate spines that
increase the cell's effective surface area, and consequently decrease the
settling rate. The spines promote turbulence, thus reducing the width of
the boundary layer, and promoting nutrient exchange.
Diatoms and dissolution
Diatoms are so resistant to
dissolution than any other
shells.
High deposition of diatoms
forms DIATOMITE beds in
the geologic history.
GEOLOGIC RECORD AND EVOLUTION
Centrate diatoms started first in Lower Cretaceous, then pinnate
diatom evolved to dominate only at the beginning of Miocene age.
The oldest certain fossil diatoms are Lower Cretaceous in age.
Diatoms probably had a much longer history than this; there are
reports of Precambrian and Triassic fossils that might be diatoms
or diatom relatives. However, definite fossil diatoms older than
the Cretaceous are not known. An older report of diatoms from the
Upper Jurassic is now doubted by experts, since silica
recrystallizes under pressure. So, any older diatom fossils may
have been destroyed.
Most diatom fossils known are from Eocene and Miocene rocks,
such as the marine diatoms rich by Actinoptychus heliopelta and
Sceptroneis caduceus.
Actinoptychus heliopelta
Sceptroneis caduceus
At areas of seasonal changes (lakes and oceans), diatom
deposits occur in layers which correspond to annual cycles,
which can be used to observe changes over many years,
providing information about past climatic changes.
APPLICATIONS AND
IMPORTANCE OF DIATOMS
1. About 20 to 25% of all organic carbon fixation on the planet
(transformation of carbon dioxide and water into sugars,
using light energy) is carried out by diatoms.
2. Diatoms cover a vast area of oceans, so they are major
players in the global carbon balance.
3. Important in fresh water primary productivity, although
they have more competition in the freshwater environment.
4. Diatoms contain chlorophyll, thus they are a major source of
atmospheric oxygen.
5. Form the basis of food chains for zooplankton in any a
aqueous ecosystem.
6. Diatomacous rocks are widely used in commerce as:
cleansers, paints, filtering agents, abrasives and many
toothpastes.
7. Because each species of diatoms tends to have distinct
requirements for temperature, salinity, acidity, oxygen,
mineral concentration and disturbances, they are
frequently used to evaluate the river health (water and
habitat quality).
8. See rest of the applications in Brasier, 1980.