278 CHAPTER 11 The Ocean and Fisheries
- Describe and distinguish among the four main
ocean life zones.
T
he immense marine environment is sub -
divided into several zones (Figure 11.4):
s The intertidal zone (between low and
high tides)
s The benthic (ocean floor) environment
s The two provinces—neritic and oceanic—of the
pelagic (ocean water) environmentThe neritic province is that part of the pelagic environment
from the shore to where the water reaches a depth of 200
m (650 ft). It overlies the continental shelf. The oceanic prov-
ince is that part of the pelagic environment where the water
depth is greater than 200 m, beyond the continental shelf.
The Intertidal Zone: Transition
Between Land and Ocean
Although high levels of light, nutrients, and
oxygen make the intertidal zone a biologi-
cally productive habitat, it is a stressful one.
On sandy intertidal beaches, inhabitants must
contend with a constantly shifting environ-
ment that threatens to engulf them and gives
them little protection against wave action. Consequently,
most sand-dwelling organisms are active burrowers. They
usually lack adaptations to survive drying out or exposure
because they follow the tides up and down the beach.
Rocky shores provide fine anchorage for seaweeds
and marine animals, but these organisms are exposed to
wave action when submerged during high tides and ex-
posed to temperature changes and drying out when in
contact with the air during low tides (Figure 11.5).
A rocky-shore inhabitant generally has some way
of sealing in moisture, perhaps by closing its shell (if it
has one), and a means of anchoring itself to the rocks.
For example, mussels have tough, threadlike anchors
secreted by a gland in the foot, and barnacles secrete
a tightly bonding glue that hardens underwater. Rocky-
shore intertidal algae usually have thick, gummy coats,
which dry out slowly when exposed to air, and flexible
bodies not easily broken by wave action. Some
organisms hide in burrows or under rocks
or crevices at low tide. Some small crabs run
about the splash line, following it up and down
the beach.The Benthic Environment
Most of the benthic environment consists of
sediments (mainly sand and mud) where manyintertidal zone
The area of shoreline
between low and high
tides.
benthic
environment The
ocean floor, which
extends from the
intertidal zone to the
deep-ocean trenches.suspecting that weather shifts during La Niña might al-
ter migratory patterns of flu-carrying birds, including
their stopovers and interactions with other species.- What is the global ocean, and how does it
affect Earth’s environment? - How are the Coriolis effect, prevailing winds,
and surface–ocean currents related? - What is the El Niño–Southern Oscillation
(ENSO)? What are some of its global effects?
Like ENSO, La Niña affects weather patterns around
the world, but its effects are more difficult to predict. In
the contiguous United States, La Niña typically causes
wetter-than-usual winters in the Pacific Northwest,
warmer weather in the Southeast, and drought condi-
tions in the Southwest. Drought and a warmer-than-av-
erage winter in much of the United States in 2011–2012
are attributed in part to La Niña’s effects. Atlantic hur-
ricanes are stronger and more numerous than usual dur-
ing a La Niña event.
Scientists have recently determined that flu pandem-
ics are more likely to occur after La Niña events. They
are considering a link between the two phenomena,
Major Ocean Life Zones
LEARNING OBJECTIVE