Hello marine biology students.
In this video we're going to talk about cells
that are able to do all of the functions of
multicellular organisms while still being
single-celled.
We're going to talk about protists and fungi.
[Intro Music]
While all of the multicellular 
organisms in the oceans are eukaryotic, there
are many types of unicellular eukaryotic organisms
as well.
These unicellular eukaryotic organisms have
great diversity in their shapes, behavior,
and means of acquiring energy.
Photosynthetic unicellular eukaryotes are
called phytoplankton.
One type of phytoplankton that we are going
to discuss are the diatoms.
As I had mentioned, they are photosynthetic
and they're a yellowish brownish color.
When we look at their photosynthetic pigments,
we see that they have chlorophylls a and c
and carotenoids.
Most land plants have chlorophylls a and b.
These diatoms have a shell made out of silica
and that shell is called a frustule.
Diatoms are among the most important primary
producers on Earth.
They perform a significant amount of photosynthesis
that's occurring on the planet, because so
much of the surface of the planet is covered
with ocean.
While diatoms are not the only phytoplankton,
in certain parts of the ocean they are the
most abundant and most important.
These diatoms are mostly solitary and unicellular,
however some can be colonial.
Here we see a diagram of what a typical diatom
looks like.
There are two ends of the frustule, a larger
valve and a smaller valve, or the upper and
lower frustule and I often think of these
as looking a lot like a petri dish with a
lid.
Those two interlocking plates are held together
and within there we have the cytoplasm and
the chloroplasts and the nucleus and the other
cellular structures of the diatom’s cell.
Remember, these diatoms are unicellular and
eukaryotic.
Now around half of the 12,000 known species
of diatoms are marine and most of the marine
diatoms are planktonic.
You will occasionally find diatoms in freshwater
environments as well as rivers and lakes and
ponds.
As diatoms perform photosynthesis and generate
excess photosynthetic product, they end up
storing that excess energy in the form of
oil as opposed to, say, starch or other carbohydrates,
and this oil aids in buoyancy.
A phytoplankton wants to ensure that it remains
floating in the surface so it can receive
the amount of Sun that it needs to continue
photosynthesizing.
When we look at the silica frustule of a diatom,
there are tiny pores within their shell and
this allows gases and nutrients to exchange
with the seawater through diffusion.
Some diatoms produce a toxin known as domoic
acid, and when these certain species of diatoms
are in bloom, that toxin can accumulate in
the tissues of organisms that eat diatoms,
such as shellfish and small fish.
When larger organisms eat those smaller ones
they can become ill or even die from the accumulated
toxin.
If this occurs to a human we call it amnesic
shellfish poisoning and it's not always fatal
but it can be, especially if untreated.
Since diatoms are unicellular, they mainly
reproduce
by cellular division.
This is a form of asexual reproduction and
in this type of reproduction the two halves
of the frustules separate and each cell then
generates a smaller frustule within whichever
frustule was there.
This means that one of the diatoms will end
up being the same size as the original parent,
but one of the diatoms will be smaller.
When that smaller diatom divides, one of its
offspring will be that smaller size and then
one of them will be even smaller.
After cell division, the cell must secrete
the other half of the frustule, and because
of this, diatoms get smaller each time they
reproduce, or at least half of the offspring
will always be smaller than that original
parent cell.
As these divisions continue, the population
of these diatoms get smaller and smaller until
they reach a critical level.
At that point, the diatoms need to restore
to their normal size by reproducing sexually,
where an egg and a sperm meet, and the resulting
cell, known as an auxospore, grows to the
size of a large diatom and then the process
of asexual reproduction can begin again.
So, here we see a diagram of diatom reproduction.
That one diatom will split into two, each
of those will then replace the smaller internal
frustule and in that way the diatoms as a
population get smaller and smaller until sexual
reproduction occurs.
The formation of that auxospore will then
allow that diatom to grow to full size again
before it starts another series of divisions.
As diatoms die, which they regularly do, their
silica frustule will sink and settle down
on the sea floor.
Diatoms contribute to biogeous sediments on
the sea floor below them, and we call a sediment
that is made primarily of diatom frustules,
we call it a diatomaceous ooze.
Now these layers of sediment will settle and
eventually become rock.
If this area of the seabed ends up being uplifted,
the sediments from these ancient seabeds would
be called diatomaceous earth.
Now, diatomaceous earth is actually used in
a variety of industrial processes by humans.
These silica-based sediments have been used
as a form of insect repellent for gardening,
they have been used in pool filters, they've
been used for beer clarification, and they've
even been used as mild abrasives in toothpaste.
This useful material came from these phytoplankton.
The next category of phytoplankton that I'd
like to discuss are marine dinoflagellates.
So this is another very abundant category
of phytoplankton.
Like the diatoms, most dinoflagellates are
photosynthetic, although some are able to
ingest particles.
The defining characteristics of dinoflagellates
is that they have two flagella that are in
grooves around their body.
Each species has a particular shape and that
is reinforced by plates of cellulose.
Some of these dinoflagellates are bioluminescent
and when they are blooming they can end up
causing waves and the surface of the water
to glow a bright blue color during the evening.
Here we see a microscopic image and also an
artist's impression of what these dinoflagellates
look like, and the groove around their theca
is where these flagella will be found.
A specific type of dinoflagellate known as
a zooxanthellae are important dinoflagellates
that live in a symbiotic relationship with
reef corals, some sea anemones, and other
organisms as well.
The hosts provide protection to the zooxanthellae
and the zooxanthellae in turn provide photosynthetic
products to the hosts.
In fact, many of these host organisms have
little or no growth without zooxanthellae.
Now, you may have heard of a situation called
coral bleaching.
Coral bleaching is when these reef corals
released the zooxanthellae symbiotes that
they had held inside of them out into the
water.
Now this can definitely impact, even kill
some corals, so preventing coral bleaching,
preventing this loss or expulsion of zooxanthellae
is important.
It's not known exactly what causes coral bleaching,
but it does seem to be tied to increasing
temperatures in certain regions.
Diatoms and dinoflagellates can go through
periods of rapid growth known as blooms.
This is usually a result of high levels of
nutrients
in the water.
This can come from upwelling or runoff or
pollution.
These blooms can be harmful 
to marine organisms and even to humans at
times.
This is because toxins can accumulate in marine
organisms which are consuming these algae,
And also, following an algae bloom, once that
algae have died off, the bacteria in the water
begin to break them down.
They can end up using the oxygen that's in
the water, and so you can end up with very
low levels of dissolved oxygen in water after
an algal bloom.
Some species can reproduce in large numbers
and produce what's called red tides.
These red tides can change the color of the
water sometimes and depending on the species
of the algae these could be considered a harmful
algal bloom.
A particular dinoflagellate that has been
known to bloom is from the genus Pfiesteria.
Pfiesteria is a dinoflagellate that produces
very serious toxins and can cause massive
fish kills can also harm shellfish and impair
the nervous systems of humans.
There are a few more groups of phytoplankton
I would like to discuss.
Next we have the silicoflagellates.
As their name suggests silicoflagellates have
a shell made out of silica and they have flagella
of two varying lengths.
You can see this star shape internal skeleton
in this micrograph.
Another type of phytoplankton are the cocolithophores.
Cocolithophorids have calcium carbonate shells,
so these ornate shells of calcium carbonate
plates.
And as you can see from this micrograph, each
cocolithophore has several of these plates.
As these cocolithophores die, these calcium
carbonate plates sink and settle to the bottom,
performing another type of biogenous sediment.
In fact, as these calcium carbonate plates
collect and settle they form what we call
chalk.
And so, chalk deposits that are harvested,
whether for writing implements for a chalkboard
or whether it's used for a drywall, these
are usually from ancient marine sediments
that had accumulations of cocolithophore plates.
A famous example would be the White Cliffs
of Dover in the UK.
These white cliff sides are marine sediments
that were made from cocolithophores.
We've spent some time talking about photosynthetic
microorganisms, now we're going to talk about
some microorganisms that act much more like
animals, even though they are unicellular.
The first of these that we'll discuss are
the Foraminiferans or forams for short.
Forams are exclusively marine, non-photosynthetic,
meaning they are heterotrophs or they have
to consume food, thus making them animal-like.
They have shells of calcium carbonate.
Of these forams, many of them are benthic,
however some can be planktonic.
Forams can end up being important contributors
of calcareous materials on coral reefs or
sandy beaches.
Pseudopods or cytoplasmic extensions, they
extend through pores in the shell where they
are used to capture minute food particles,
such as phytoplankton or detritus in the water.
Here we can see some photos of some forams,
with the first being a planktonic example
with its pseudopods extending from its test,
versus a cluster of red colored benthic foraminifera
as well.
Like the diatoms and the cocolithophores,
foraminifera can contribute to biogenous marine
sediments and we call these foraminiferan
ooze.
Limestone 
is often uplifted marine sediments that had
been formed by foraminifera in the past.
The field of paleoclimatology 
often uses foraminifera shells or tests to
answer questions of water column temperature
from the distant past.
The orientation or direction in which the
planktonic foraminifera shells coil can give
paleoclimatologists information about past
temperatures.
Isotope testing can also be done on these
calcium carbonate tests to see which isotopes
of oxygen were used in making these structures.
Another animal like planktonic member are
the radiolarians.
Radiolarians 
in a lot of ways are very similar to foraminifera,
but they are described as being star-shaped.
They usually have a circular central body
with rays extending outwards they are very
round and circular unlike foraminifera, radioalarian’s
tests are made out of silica, like the diatoms.
Yet like forams, they use pseudopods that
extend through the pores in their shell and
they use these pseudopods to capture minute
food particles such as phytoplankton and detritus.
Another unicellular protist are the ciliates.
So ciliates have hair-like cilia for moving
and for feeding.
Most live as solitary cells, but some end
up building shells made out of organic debris
or sometimes even sand.
Many of these ciliates live on hard substrates,
yet some can be planktonic.
We're almost at the end of our discussion
of unicellular marine organisms.
And so, the last category I'd like to talk
about are fungi.
Fungi are abundant and ubiquitous on land,
but it turns out that they are not as common
in the marine environment.
Like some of the protists we've talked about
so far, fungi are eukaryotic
and most of them are multicellular.
They are heterotrophic, meaning they must
consume organic molecules in order to get
energy and of the at least 1500 species of
marine fungi, most of them are microscopic.
Like bacteria, many fungi break down dead
organic matter into detritus.
Another place that you'll find marine fungi
is in the form of lichen that can be found
usually in wave-splashed areas of rocky shores.
A lichen is a symbiosis between fungi and
cyanobacteria or fungi and a form of algae
and we call this symbiosis lichen.
Marine lichens often live in wave splash areas
of rocky shores and other hard substrates.
I would like to end this video by drawing
your attention to an important table that
is in our textbook in chapter 5.
This table highlights the characteristics
of the major marine microbes, providing information
about their distinguishing features whether
they are photosynthetic and which photosynthetic
pigments are present, where they get their
food, how they store their energy, if they
have a cell wall and what it's composed of,
and also the role that it plays in their associated
ecosystems.
There's a lot of information here and it's
far too small to see on this slide, but I
definitely encourage you to look at this table
in the textbook as it does a great job of
summarizing the information from this presentation.
So that finishes our discussion on protists
and fungi.
Now, before our next video I would like you
to think “What does it take for something
to be a plant?”
All right, see you in the next video.
