STRUCTURE
OF THE
OCEAN
TIDAL ZONES
INTERTIDAL ZONE
• The intertidal area (also called the
littoral zone) is where the land and sea
meet, between the high and low tide
zones. This complex marine ecosystem
is found along coastlines worldwide. It
is rich in nutrients and oxygen and is
home to a variety of organisms.
NERITIC ZONE
• The neritic zone is the first 200 meters (656 feet) of ocean water, which includes the seashore and
most of the continental shelf. Most photosynthetic life (life that uses light energy to convert carbon
dioxide and water into food), such as phytoplankton, is found in this region.
• Zooplankton, which are the floating creatures ranging from microscopic diatoms to small fish and
shrimp, also live here. Many species of whales, like the gigantic blue and humpback whales, feed
almost entirely on the tiny zooplankton. These whales force seawater through baleen plates (combs of
bony material that form in the place of teeth) to filter out the tiny sea creatures. The largest of all
fish, the whale shark, lives off plankton alone!
NERITIC ZONE
• Fish are found everywhere in the ocean, the abundance of small organisms in the neritic zone
provides a plentiful source of food for larger animals. Great schools of tuna and mackerel feed on
squid, krill and small fish that gather where warm waters meet nutrient-rich cooler waters. The largest
example, the northern bluefin tuna, can grow to be more than 10 feet long and weigh over 1500lbs!
Most sharks are common near the surface as well, some feeding on schools of fish, while others,
including the basking and whale sharks, eat plankton.
OCEANIC ZONE
• The oceanic zone extends from 200 meters (656 feet) out and includes all areas all
the way down to the bottom of the ocean, which can be thousands of meters deep.
BENTHIC ZONE
• The benthic zone of the ocean is varied. There are mountains,
trenches, volcanoes, flat muddy areas, sandy areas and rocky
areas. There is a wide variety of life that makes its home on the
ocean floor. Some organisms live in the mud, some crawl or swim
along the bottom and some anchor themselves to the ocean floor.
OCEAN LIFE
•All life in the ocean is
divided into three main
groups. They
are plankton, nekton,
and benthos.
•Plankton are all of the creatures in the sea that
drift and float and rely on the tides to move them
from place to place.
•Not all plankton are microscopic. They are
either phytoplankton (microscopic plants) or
zooplankton (jellyfish, copepods, arrow worms).
•Many animals rely on plankton for their
existence.
NEKTON
•Nekton are all of the animals in the ocean that
are able to swim on their own, without the help of
the tides. This includes over 20,000 types of fish
in the sea. These animals range in size from
sharks which 50 feet in length to fish which are
less than an inch long.
•Most nekton have streamlined bodies to help
them swim more efficiently.
•Some nekton can travel at remarkable speeds.
The sailfish can swim up to 30 miles an hour.
•Many nektonic animals are able to swim vast
distances. For example, the eel can travel
thousands of miles.
BENTHOS
•Benthos are animals
which live at the
bottom of the sea.
•Examples of
benthonic animals are
sea snails, clams,
sponges, sea lilies, and
starfish.