live in all types of water and all latitudes and longitudes of the world.
Diatoms are divided into marine and fresh water diatoms. Marine diatoms
can be benthic(live on ocean floor) or planktic, which spend their lives,
including their reproductive period suspended in the water column. There
are also some neritic, which are afloat during their vegetative state,
but their spores fall to the bottom where they wait through unfavorable
conditions. The ability to float is essential for the existence of planktonic
diatoms, and their structure has been modified for this function. In regions
where there is substantial variation in water temperature from winter to
summer, some species of diatoms have adopted winter and summer forms. The
summer forms have a larger surface area to help them float in the warmer
water, which is less dense.
There are several chemical and physical factors which affect the distribution
of diatoms, these factors include the density, salinity, and temperature
of the water. Water density is an important factor in the flotation of
diatoms. The density of the water is affected by the temperature. Diatoms
experience their best development at specific depths because the temperature,
and therefore density of the water is enough to keep them afloat. Warm
water diatoms are better developed at lower levels than cold water diatoms
because of the difference in density.