Diatoms:
My research centers around this basic struggle between the cytoplasm and frustrule. By understanding the interplay between these two parts of the diatom, I am creating a new way of thinking about diatom sinking speeds and their significance in ocean communities. By using a combination of size measurements from SEM photography and sinking speed measurements from a highly controlled water column, I can better understand what factors cause a diatom to sink or float. |
Diatoms are one of the strangest and most common forms of life in the
ocean. Diatoms are a type of phytoplankton, a group of very small
plant-like organisms that live by floating in the ocean. They are
plant-like because they photosynthesize sunlight, but unlike
terrestrial plants their light absorbing pigments are brown, not
green. This means that diatoms are distantly related to giant kelp
and other brown algae. If you look under a microscope at almost any
bit of seawater, you'll see plenty of brownish circular or
banana-shaped spots- these are most likely diatoms. In fact, diatoms
are so common and well-shaped that in the 19th century diatoms were
used to test the quality of microscope lenses.
The unique and strange feature of diatoms is that they live in a glass
house. Diatoms encase themselves in an outer cell wall called a
frustrule which is composed of silica, or glass. These glass
frustrules provide diatoms with structure and defense, but they are
also extremely beautiful. Some high magnification pictures of diatom
frustrules are shown to the right. The frustrules are riddled with
pores, spikes, spines, and other features that can be less than a
micrometer in size. These features are sculptured by the diatoms
As floating phytoplankton, diatoms are faced with a classic question-
do I sink or do I float? The beautiful frustrules are intimately tied
to this question. The frustrule is a heavy glass structure, so it is
constantly pulling the diatom downward. When the diatom wants to
float or just hang out where it is, it has to pump light-weight ions
into its inner cytoplasm to make itself lighter and counter the weight
of the frustrule. There is a constant battle in the diatom between
its cytoplasm and frustrule- if the diatom just wants to chill out,
the frustrule wins and the diatom sinks. To stay in one place, the
diatom has to use its cytoplasm to hold up the entire weight of the
frustrule. This is like lifting weights at the gym, it takes energy.