Hello marine biology students.
In this video we're going to talk about the
life that lives in the bottom levels of the
ocean.
[Intro Music]
While there are differences between the bathypelagic,
abyssopelagic, and hadopelagic, also known
as the deep sea, we're going to be focusing
on the similarities between these different
levels.
This includes, they are uniformly dark, uniformly
cold, uniform in their salinity, and water
chemistry, and high pressure.
So these are the three layers of the sea below
the mesopelagic.
For animals of the bathypelagic, abyssopelagic,
and hadopelagic, no countershading
is needed as no light is present.
Bioluminescence 
is also present in the upper portions of the
deep-sea, but its occurrence actually decreases
with increasing depth.
Bioluminescence is thought to be used for
courtship, communication and/or to attract
prey.
Unlike organisms in the mesopelagic, the photophores,
the structures that generate bioluminescence,
are normally located near or on the head,
as opposed to the ventral side of the body.
In animals of the deep-sea, their eyes are
small or maybe absent altogether.
Eyes are used only to detect bioluminescence.
These organisms also typically have pressure
resistant enzymes to allow their metabolism
to proceed, something that surface marine
organisms would not be able to do.
When we look at the fish of the bathypelagic,
abyssopelagic and hadopelagic, the fish are
similar to those in the mesopelagic that wouldn't
migrate, such as the absence of swim bladders,
flabby muscles, light and weak skeletons.
Typically their mouth will also be large,
with long pointed teeth.
They tend to have less developed nervous system
and circulatory systems as well, and this
may be because of lower nutrition availability.
Here we see a variety of the types of fish
that live in the deep sea, from different
types of angler fish to gulper eels and swallower
eels.
These organisms, in a lot of ways, look very
different from surface fish.
Some, like anglerfishes, possess a lure on
their head containing symbiotic bioluminescent
bacteria 
to attract prey.
Certain reproductive and lifestyle changes
are also found in these deep sea organisms.
One includes male parasitism.
This can be seen in the anglerfish, where
the male is much smaller than a female and
when a male comes in contact with a female
it will bite on to the female and end up dissolving
its face and lips and even brain, merging
into the female's circulatory system, and
in that way the male just becomes a pair of
gonads available for the female whenever she
needs to fertilize her eggs.
Some deep-sea fish will use chemical cues
and pheromones
to help attract the opposite sex and there
is a higher incidence of hermaphrodism
because with so few individuals in the area,
finding a member of the opposite sex may be
less likely than simply finding another member
of your same species.
There are organisms that not only live in
the water column above the sea floor, but
also on the sea floor itself.
The deep-sea benthos depends on food that
reaches the bottom from higher in the water
column.
Decomposing bacteria can be found in deep
sea sediments, but they decompose at a much
slower rate than bacteria at the surface,
because of the extreme pressure.
Many of the benthic organisms of the deep-sea
will be deposit feeders and they will mostly
be epifauna.
This is more dominant over suspension feeders
because there isn't a lot of food suspended
in the water, but it will slowly settle as
sediment over time.
In the deep sea there's also a wide variety
of Meiofauna.
These are the organisms that live between
the sediment grains in the sediments.
When we look at the deep-sea benthic fish,
they're actually typically larger and more
muscular then deep-sea pelagic fish.
They will often have an elongated shape 
and will usually be darkly pigmented.
They typically will have small eyes.
An interesting aspect of some of the deep-sea
benthos is a condition known as deep-sea gigantism.
This is where many organisms tend to be larger
than counterparts in shallower marine communities.
They tend to grow more slowly and have exceptionally
long life.
Of these marine organisms, many reproduce
late in life and have few large, but well-developed
eggs.
In fact, for some of these deep-sea organisms,
they will not reproduce until they've found
enough food to generate the reproductive cells.
And so, for some organisms, sexual maturity
does not onset until they've had their first
large meal.
This chart allows us to compare the fish in
different levels of the ocean from the epipelagic,
with the rapid swimmers with streamlined body,
the mesopelagic vertical migrators which will
be smaller but still have strong muscles,
the mesopelagic non migrators, which are going
to have weak and flabby muscles but are more
likely to have spines.
The deep-sea pelagic, which often lack any
sort of streamlining to their body, and then
the deep-sea bottom dwellers, which are going
to be back to having strong muscular bodies
and usually elongated in shape.
One last community to talk about in the deep
sea are those found at the deep sea hydrothermal
vents.
Here chemical-laden water escapes from cracks
in the sea floor, particularly around mid-ocean
ridges.
These are used by chemoautotrophic bacteria
as a form of primary production.
Most of these bacteria use hydrogen sulfide.
The bacteria feed many types of animals.
These deep sea hydrothermal vents can be oasis
in the otherwise nutrient-poor deep sea.
There are a few different types of hydrothermal
vents, including black smokers and white smokers
and they support bacteria that are the base
of a food chain of fishes, shrimps, clams,
crabs, snails, barnacles, sponges, and other
animals.
There's amazingly rich diversity at these
deep sea hydrothermal vents.
Many of the hydrothermal vents are dominated
by tube worms like this image pictured.
The main genus of these tube worms is Riftia.
And these tube worms harbor symbiotic chemoautotrophic
bacteria that manufacture organic matter from
hydrogen sulfide, and this in turn provides
nutrition to the mouthless worm.
So surprisingly, these worms do not have mouths
or digestive systems, but instead they have
means of bringing in the chemicals needed
by these chemoautotrophic bacteria to allow
them to generate organic matter.
And that completes our discussion about what's
at the bottom of the ocean.
Now, next week we're going to talk about what
resources we as humans get from the oceans,
so see you next week.
Bye.
