72 LIFE IN THE WATER
ECOLOGY 73
Life in the Oceans
OCEANIC
ZONES
T
he first marine species emerged more than one billion years ago.
Since then, life in the oceans has become pr ogressively more
complex. Today, it is a very diverse environment. The ocean can be
divided into horizontal regions that correspond to polar, temperate, and
tropical ecosystems and into vertically separated zones, or layers, that
correspond to different depths. The deepest layer, the hadal zone, is the
least understood. Some parts of the ocean have their own particular, or
endemic, species.
Geographic Zones
Marine communities are distributed unevenly. They
follow horizontal patterns that are arranged into
polar, temperate, and tropical ecosystems. Climate and
food availability are the principal factors that determine
where the communities are located and the biodiversity
they possess. Even though there is life at all depths, most
of it is found in those zones in which the pressure,
temperature, and illumination are favorable. A boundary
between masses of water with different temperature and
salinity characteristics forms a barrier that is as effective
as mountains on the Earth’s surface. Below a certain
depth, however, these barriers diminish, and conditions
are more stable and uniform. Consequently, organisms
living in the abyssal zone have very wide distributions.
ENDEMIC
SPECIES
These species are
unique to particular
geographic areas.
They are found
nowhere else.
For example, the
porcupine fish
Diodon hystrix is
endemic to the
tropical waters of
the western Atlantic
Ocean.
CHANGES IN TEMPERATURE
Global warming is a phenomenon affecting the distribution of
many species. For example, warm-water fish have now been
found in cold ocean zones.
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PHOTIC ZONE
Because sunlight can
penetrate this zone,
photosynthesis is possible.
It is the warmest layer of
the ocean and the
richest in nutrients.
Phytoplankton, which
form the base of the food
chain in many parts of the
ocean, live here. The depth
of this zone is variable; it
depends on the turbidity
of the water.
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OLIGOPHOTIC
Extending to a depth of
1,600 feet (500 meters),
this zone is also known
as the penumbral zone. It
receives enough light for
animals to see during the
day. It is the location
where the constant
struggle between
predator and prey
occurs.
EQUATORIAL
SUBTROPICAL
TROPICAL
TEMPERATE
POLAR AND
SUBPOLAR
UNDERWATER EXPLORATION
Present-day technology allows crewed and
remote-controlled submersibles to carry out
detailed research at great depths. In 2006, the
China Ocean Mineral Resources R&D Association
(COMRA) began to test a crewed vehicle that can dive
to 23,000 feet (7,000 meters). As technology imprves,
next-generation submersibles will no longer depend on
ballast and flotation tanks. Deep Flight II, designed by
the American engineer Graham Hawkes, will
use inverted wings to generate
“negative lift” for rapid descent.
TRIESTE
The bathyscaphe
Trieste from the United
States reached a depth
of 35,810 feet (10,916
meters) in the
Challenger Deep of the
Marianas Trench.
This record
still stands.
Bioluminescence
Known as cold light, it is pr oduced by a
chemical reaction in specialized cells called
photocytes that exist in certain organisms. The light
that is produced is generally greenish-blue and can
serve as a form of communication to attract
potential mates, to frighten away other
organisms, or as camouflage from enemies.
This feature is very
common among
deep-ocean
LUMINOUS
fish, squid,
LURE
bacteria, and
The light
jellyfish. It is
attracts prey to
also found in
the deep-sea
various terrestrial
predator.
organisms such as
fireflies.
HYDROSTATIC
PRESSURE
The weight of the water
column. It varies with water
density and
depth. During
a descent, the
hydrostatic
pressure
increases
quickly.
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APHOTIC
This zone can extend
between 650 and 13,000
feet (200 and 4,000
meters), depending on the
time of year and the
turbidity of the water.
There is too little sunlight
for photosynthesis, and
the resulting lack of food
is the main problem for
the animals that live at
this depth.
4
DEADLY JAW
This weapon
helps this hunter
survive 3,300
feet (1,000
meters) under
water.
BEARD
This structure may
also produce light
for attracting prey.
ABYSSAL
Located between 13,000
and 26,000 feet (3,000
and 6,000 meters), this
zone is characterized by
cold conditions, a
scarcity of nutrients,
and total darkness.
Some of the animals
that live there are very
large, and some have a
monstrous appearance.
DEEPSEA ANGLER
Linophryne arborifera
It has a luminous lure attached to its head
and a branching beard that also gives off
light to attract prey. The male is smaller
than the female, and it lives off the
female as a parasite.
DIMENSIONS
5
HADAL
This very cold zone with
very high hydrostatic
pressure extends below
20,000 feet (6,000
meters). It is associated
with deep-ocean
trenches and accounts
for less than 2% of the
area of the ocean floor.
WEIGHT
10.5 ounces (300 grams)
3.9 inches (10 cm)
IN DARKNESS
A few fish species
live at depths below
8,200 feet (2,500
meters). They are
known as abyssal
fish, and they have
peculiar facial
features, such as
large heads, sharp
teeth, and
photospheres that
glow in the
darkness.