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creatures of the deep sea
must develop a number of unique
adaptations
in order to survive the extreme
conditions
but there are two pathways that almost
all deep sea life must choose from
whether to live on the bottom or to
brave the expansive open ocean
of the mid-water zone
creatures that adapt to life in the
mid-water zone
are known as pelagic or creatures that
evolve to be well suited to an existence
on or near the sea floor are known as
benthic or demersal
these two groups could not be more
different
but which is a more effective way of
life
first let's take a look at the demersal
creatures of the deep
the bottom feeders clinging to rocky
seamounts
and burrowing into the mud
we will begin our investigation in the
shallows
and follow the ever deepening sea floor
down to the far
depths of the ocean the diversity of
organisms that are adapted to life near
the bottom
is immense and far greater than that of
pelagic organisms
life thrives on every part of the ocean
floor
from near shore ecosystems all the way
to the abyss
but the deeper you go the stranger they
become
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most common are the demersal creatures
of coral reefs
making use of these hot spots of food
and shelter
as a place to live and as important
spawning grounds
the diversity here allows for some
complex communities to form
symbiosis can occur and creatures work
together to ensure they have the best
chances of survival
but follow the slope of the sea floor to
a depth of just 200 meters
and life already appears different
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cold water corals cling to the edge of
the continental shelf
where the shallows end and the deep sea
widens into a dark expanse
below
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sponges line the rocky precipice making
use of the abundant food that drifts
past on the unhindered currents
they are filter feeders drawing water
into their bodies through tiny holes
called
incurrent pores and taking up tiny
particles from the water
as food
following the continental slope
downwards we come to the abyssal plain
at around four thousand to six thousand
meters deep
there is no light here beneath the
bathypelagic zone
however the benthic organisms here have
a number of advantages
over their pelagic counterparts in a way
they experience an easier existence
they do not have to swim to keep from
sinking as they can simply rest on the
bottom
so they waste less energy than creatures
that must constantly move
in order to remain buoyant furthermore
down on the abyssal plain food comes to
you
anything that sinks will end up here
dead animals shells and excrement
organic matter that only briefly passes
through the midwater zones
settles here at its final destination
this easier life explains why a greater
abundance and diversity of organisms
is found in the deep sea benthos
compared with the open ocean
but an easier existence in the benthos
and near bottom
also allows organisms to develop more
muscular bodies
than is possible in the bathi pelagic
consequently more food and more muscle
allows organisms here to lead a more
active lifestyle
this is a huge advantage as the bottom
of the deep sea is a remarkably large
habitat
it encompasses eighty percent of the sea
floor
and sixty percent of the surface of the
earth
an expanse of deep sediment and soft mud
shrimps and worms burrow into the
sediment where they live
heavily armoured for unlike their
pelagic cousins
they can afford this extra protection as
staying afloat is not a problem
these burrowers are examples of infauna
creatures that live within the sediment
while organisms that reside on top
are called epifauna organisms here
play an entirely different role in the
deep sea ecosystem
compared with pelagic life here
their decomposers assimilating dead
organic material into their biomass
and thus providing nutrients to larger
predators in the food web
in the process they maintain the energy
flow
and cycle the sunken nutrients that
would otherwise go to waste
crinoids are abundant here as
stalked filter-feeding echinoderms they
too help cycle nutrients through the
ecosystem
but what's remarkable about these
creatures is the fact that they are
ancient appearing in the fossil record
as far back as the ordovician period
480 million years ago
specimens found alive today do not
appear
vastly different from their ancestors
and this shows that the benthic zone of
the ocean is a
stable habitat wherein life is able to
thrive
the diversity of fish found here is also
a testament to this
many of them appear to have an elongated
body form
like the rattail fish halosaurs and
chimera
this particular adaptation is thought to
be so common because a longer body
allows for a longer lateral line which
provides the fish with enhanced
sensory perception these are the lines
seen running along the body of this
chimera
a tool it uses to detect minute water
motions caused by prey
here on the sea floor sediment of the
abyssal plain
life is abundant but limited
there are many creatures that simply
cannot survive here
due to the absence of any solid surface
to which they can attach themselves
but rising abruptly out of the sea floor
there are towering geological landforms
formed by volcanic activity
under sea mountains known as seamounts
these are biological hot spots that
support a dazzling array of marine life
the biological richness of seamounts is
due to their shape
the steep slopes allow nutrients to be
carried upwards from the abyssal plain
below
causing an upwelling of food for
creatures of all
forms most common are the cold water
reefs
coral gardens that don't need to rely on
sunlight for nutrients
due to this supply of food from the deep
they can be found six thousand meters or
twenty thousand feet
deep and are well established
with some having been growing for 40 000
years or more on the rocky ridges
seamounts provide the vital ingredients
needed for a stable community to form
but they are not the only of such places
at expansive brine pools life
clings to the edges mussels crabs and
their predators
rely on the production of nutrients from
chemosynthetic bacteria
converting dissolved chemicals in the
brine
the deep sea equivalent to
photosynthesis
chemosynthesis occurs also at
hydrothermal
vents another island of productivity for
benthic
life to thrive the vents are found on
rocky surfaces
where new ocean floor is being formed by
sea
floor spreading sea water seeps through
cracks in the new sea floor
and comes back out at the vents
superheated
up to 350 degrees c
and yet life 2 is found 8
000 meters down at the very bottom of
the ocean
life finds a way the benthic
lifestyle of minimal energy use and
abundant sunken food
allows the deepest living fish the
mariana snailfish
to survive here in the mariana trench
as blind elongate fish they use a
well-developed sense of smell
to locate their prey benthic pollicate
worms
that are abundant even here due to their
incredible adaptability to the
extremities
overall demersal life is abundant
and diverse in the deep sea due to the
benefits of living near the sea floor
and making use of the conditions and
resources found there
creatures can waste less energy on
swimming
and so can afford to develop such
adaptations
as armor and larger muscles it is an
entirely different way of life compared
with that of pelagic creatures
and demonstrates the fascinating
adaptability of life
to vastly differing habitats that
comprise
a single ecosystem
check out the brand new deepsea hub over
on our website for more facts and
footage about the deep sea
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you