Transcript Ch10Pres - Leornian.org

Ocean Studies
Introduction to Oceanography
American Meteorological Society
Chapter 10
Life in the Ocean
© AMS
Case in Point
– For nearly 500 years the cod fishery was the basis of
the economy of Newfoundland and other parts of
Atlantic Canada.
– Natural fluctuations in cod populations meant periods
of low catches but fish stocks always recovered.
– This changed after the middle of the 20th century
when fishers began using huge factory trawlers to fish
intensively for cod on the offshore banks, in waters
beyond the limits of Canada’s national jurisdiction.
• Some 40,000 people lost their jobs in Newfoundland where
many small coastal villages depended entirely on the cod
fishery for employment.
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Case in Point
– Cod population declined, no sign of recovery,
numbers continue to decrease
• The ecosystem that formerly supported cod stocks was
altered in such a way as to favor other fish and even lobsters
in place of cod.
• It is unclear if the fish stock and the ecosystem that sustained
it for centuries can be restored.
– The impact of the decline in cod stocks on the fishing
industry in northwestern Europe is expected to be
serious with the loss of many thousands of jobs and
devastation of fishing communities—comparable to
what happened earlier in Newfoundland.
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Life in the Ocean
• Driving Question:
– How have the large and diverse populations
of marine organisms adapted to
environmental conditions in the ocean?
© AMS
Life in the Ocean
• In this chapter, we examine:
– Various flora and fauna, marine habitats, and
some of the ways marine organisms have
adapted to the diverse environmental
conditions in the ocean
– Marine plant and animal life at the boundaries
of the ocean including organisms living in the
intertidal zone, wetlands and estuaries, the
deep-sea floor, and coral reefs
© AMS
Marine Habitats
– The ocean contains about 99.5% of Earth’s
potentially inhabited living space.
– Living organisms inhabit all parts of the
ocean, even extreme environments such as
Arctic and Antarctic sea ice and hydrothermal
vents on the sea floor.
• Including estuaries, coral reefs, polar oceans, and
deep-sea trenches
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Marine Habitats
• OCEANIC LIFE ZONES
– Defines marine habitats in terms of distance from
shore and depth
– Open ocean waters constitute the pelagic zone.
• Pelagic organisms include plankton (passive floaters or
weak swimmers such as copepods,
• larval fish, and jellyfish) and nekton (strong swimmers
including most fish, squid, turtles, and marine mammals)
– The environment of the sea floor at all depths is
called the benthic zone.
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• Benthic organisms live either on the ocean bottom or within
sediment deposits.
• Include attached, burrowing, and mobile organisms, such as
sea stars, crabs, worms, clams, sea cucumbers, sea
anemones, urchins, snails, and barnacles
Marine Habitats
• OCEANIC LIFE ZONES
– The area along the shore between high- and
low-tide lines is the intertidal zone.
• Home to ecosystems such as salt marshes and
mangrove swamps
– The area seaward from the shore, across the
continental shelf, to the shelf break at a water
depth of 120 to 200 m (390 to 650 ft) forms
the neritic zone.
• Commonly referred to as the coastal zone
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Marine Habitats
Life zones in the ocean
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Marine Habitats
• OCEANIC LIFE ZONES
– Oceanic life zones are also defined in terms of
nutrient supply and productivity.
– Nutrient-poor waters having low primary production
are described as oligotrophic.
• Waters are exceptionally clear and appear luminous blue in
sunlight due to the lack of organisms and suspended
particles.
– Nutrient-rich waters having high primary productivity
are described as eutrophic
• Excessive amounts of nutrients promotes an unusually
abundant growth of phytoplankton (an algal bloom), which
die, sink to the bottom, and deplete waters of dissolved
oxygen as they decompose.
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Marine Habitats
• PLANKTON IN THE PELAGIC ZONE
– Phytoplankton are slightly denser than seawater and
would gradually sink below the sunlit photic zone
were it not for characteristics that counteract the
tendency to sink.
• Species have different shapes
• This adaptation significantly slows sinking, especially in less
dense, warm waters, and allows them to remain in the photic
zone above the pycnocline.
• The complex shapes and spiny structures of zooplanktonic
organisms also increase their surface area to volume ratio,
thereby adding to their buoyancy.
– Some large planktonic animals have gelatinous
bodies, consisting of 95% to 98% water, and are
almost neutrally buoyant.
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Marine Habitats
Although microscopic in size,
diatoms can be beautiful and
occur in a variety of shapes
that provide them with
© AMS
buoyancy in the ocean.
The bane of
swimmers in the
Chesapeake Bay,
the stinging sea
nettle, Chrysaora
quiquecirrha.
Marine Habitats
• NEKTON IN THE PELAGIC ZONE
– Larger, free-swimming pelagic animals, collectively
called nekton, include fish of all sizes, squid, sea
turtles, and marine mammals.
– Many adaptations for buoyancy are found in nektonic
organisms
• Gas bladders
– Many fishes have gas-filled swim bladders that control
buoyancy and regulate the amount of gas in the bladder
through a connection to the gut.
© AMS
– Most pelagic fish rely on active swimming to maintain
their level in the ocean and obtain food.
Life Strategies and Adaptations
• VERTICAL MIGRATION
– The photic zone is a dangerous place for marine
organisms because predators can easily see them.
– Many types of zooplankton avoid this threat by daily
vertical migration.
• Each day at dusk, they come to the surface zone to feed on
phytoplankton. As daylight comes, they return to the relative
safety of darker, deep waters.
• Typically over a vertical distance of about 200 m (650 ft),
require expenditure of enormous amounts of energy.
• Vertical migration also plays a role in the carbon cycle in that
carbon consumed by zooplankton feeding on phytoplankton
near the surface at night is transported to deeper water as
the animals respire during their return to depth at dawn.
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Life Strategies and Adaptations
• LIGHT AND VISION
– Near the ocean surface, light is abundant and
predators have no problem locating prey.
– The most common adaptation is adaptive
coloration or camouflage where the animal’s
color pattern closely matches its background
substrate.
• Many fish exhibit countershading, that is, their
dorsal side (or back) is a dark color, making it
difficult for predators above to see them against
the dark, deep water.
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Life Strategies and Adaptations
• LIGHT AND VISION
– Marine animals that rely on sight to locate their prey
in the dim light of the twilight zone have large,
sensitive eyes.
• The deeper in the twilight zone, the dimmer is the light, and
the larger are the eyes of predators living there.
– Below the twilight zone, in the greatest depths of the
ocean, light is absent and vision is not useful for
locating prey.
• Many marine animals emit light, a phenomenon known as
bioluminescence.
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Life Strategies and Adaptations
• LIGHT AND VISION
– Bioluminescence is
mainly a marine
phenomenon and is
thought to have
evolved a number of
different times
because it is a
characteristic of a
broad array of
organisms.
© AMS
Bioluminescence is a property of
a wide variety of marine
organisms such as the jellyfish
Aequorea aequorea pictured
here.
Life Strategies and Adaptations
• LIGHT AND VISION
– Marine animals use light emission to attract
mates or prey, frighten or confuse predators,
or to disguise themselves.
– Short bursts of bioluminescent light
apparently are especially effective at
disorienting prey.
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Life Strategies and Adaptations
• SOUND
– Many marine animals have evolved ways of
sensing the vibrations produced by other
organisms moving through the water.
– Seawater is essentially transparent to sound.
– Many marine mammals, including whales,
routinely communicate over great distances,
even the width of an ocean basin.
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Life Strategies and Adaptations
• FEEDING STRATEGIES
– The general name for
marine animals equipped
with features that strain
food particles out of large
volumes of water is filter
feeder.
• Mostly eat food items
trapped in their feeding
structures; they are not
selective
– Some planktonic
organisms, such as the
planktonic snails called
pteropods produce a large
sticky net of mucus, which
functions much like a
spider web to trap small
water-borne organisms and
© AMS
other food particles.
This humpback whale
feeds by straining water
and trapping food in the
baleen plates in its mouth
Life at the Ocean’s Edge
– After the pelagic zone, the next largest environment
for marine life is the benthic zone, the sea floor at all
depths, from the intertidal zone to the deep ocean.
• Marine organisms that live in the benthic zone collectively are
called benthos.
– Three basic life strategies characterize the benthic
zone:
• Organisms may live attached to a firm surface
– Seaweed, sea grasses, barnacles, mussels, clams, oysters,
corals, and anemones
• Construct burrows or tunnels or simply dig into sediment
deposits
• Move freely on the sea floor
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Life at the Ocean’s Edge
• INTERTIDAL ZONE
– The area along the shore between low and high-tide
levels
• Waves, winds, and tidal currents continually disturb the
intertidal zone
– Some intertidal zones feature extensive mud flats.
• Often ideal habitats for submerged aquatic vegetation, salt
marshes, and many forms of benthic animals
– Seaweeds are important components of the intertidal
zone and provide habitat for animals.
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Life at the Ocean’s Edge
• INTERTIDAL ZONE
– Animals are distributed in the intertidal zone
according to their tolerance for drying and changes in
temperature and salinity.
– Highly mobile animals, such as crabs, move up and
down with the changing water levels as the tide floods
and ebbs.
– Animals such as barnacles and mussels attach
themselves to hard surfaces and can shut their shells
completely, thereby retaining enough seawater inside
to survive until they are covered again by the flood
tide.
© AMS
Life at the Ocean’s Edge
• INTERTIDAL ZONE
– Tide pool: a volume of
water left behind in a rock
basin or other intertidal
depression by an ebbing
tide
– Harbor species that have
evolved to deal with wide
fluctuations in
environmental conditions;
these organisms include
certain algae, sea
anemones, starfish, snails,
small crustaceans,
barnacles, mussels, and
© AMS
fish
Life at the Ocean’s Edge
• SEA GRASS BEDS AND SALT MARSHES
– On mud flats and other soft-bottomed habitats the
most important plants are sea grasses, also known as
submerged aquatic vegetation (SAV).
• These are angiosperms, flowering and seed bearing vascular
plants with true roots.
– Sea grass beds are highly productive with some
rivaling the primary production of intensively
developed agricultural land in the amount of carbon
fixed.
• Export large amounts of organic matter to nearby coastal
waters
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Life at the Ocean’s Edge
© AMS
A sunlit sea grass meadow in the Florida Keys
National Marine Sanctuary. Sea grasses are also
known as submerged aquatic vegetation.
Life at the Ocean’s Edge
• SEA GRASS BEDS AND
SALT MARSHES
– Salt marshes commonly
occur along sheltered
shorelines and are
ecologically similar to sea
grass beds in estuaries.
– Home to abundant marine
life, and are refuges for
waterfowl and other wildlife
– Transition zones between
marine and terrestrial
ecosystems
© AMS
The edge of a salt marsh meeting oak
and other higher ground flora on
Daniel Island, SC
Life at the Ocean’s Edge
– Mangrove swamps:
consist of tropical plant
species including trees
that grow in low
marshy areas and can
tolerate salt water
flooding of their roots
and lower stems
– Compete successfully
with local marsh
grasses
© AMS
Red mangroves are
common in Florida.
Mangroves roots serve as
critical habitat for many
species and nutrient filters
Life at the Ocean’s Edge
• KELP FORESTS
– Kelp forests grow where
waters are cool and
nutrient-rich.
– Kelp includes various
species of brown algae that
grow to enormous size.
– Strong waves easily
destroy kelp beds and
huge amounts of detached
kelp wash onto beaches
following storms.
– Kelp forests support a rich
community of animals that
lives below its canopy
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Life at the Ocean’s Edge
• CORAL REEFS
– Carbonate-secreting colonial animals are the primary
builders of coral-reef frameworks.
– Open coral structures are bound together by layers of
calcareous algae.
– Grow along coastlines or cap extinct undersea
volcanoes
– Consist of thin veneers of living organisms growing on
older layers of dead coral or volcanic rock
– Corals are found in all ocean basins, but large reefs
occur only in tropical waters, between about 30° N
and 30° S.
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Life at the Ocean’s Edge
© AMS
The Great Barrier Reef extends for 2,000
kilometers along the northeastern coast of
Australia. It is not a single reef, but a vast
maze of reefs, passages, and coral cays
Life at the Ocean’s Edge
• CORAL REEFS
– Most corals cannot tolerate prolonged exposure to
either very low or high water temperatures or to large
fluctuations in temperature.
– Even small changes in sea surface temperatures—
perhaps associated with large scale climate change—
threaten coral reefs.
– They also require clear water and are endangered by
sediment runoff from land, oil spills, and other forms
of water pollution.
– Each type of coral animal builds a characteristic
structure that is conspicuous on reef surfaces.
© AMS
Life at the Ocean’s Edge
• CORAL REEFS
– Individual coral animals,
called polyps capture tiny
plants and animals floating
in the waters flowing over
the reef.
– Reef-building corals also
obtain large amounts of
energy from microscopic
dinoflagellates called
zooxanthellae living within
the tissues of polyps.
© AMS
• Photosynthetic pigments
in zooxanthellae are
responsible for the bright
color of corals.
Coral polyps
Life at the Ocean’s Edge
• CORAL REEFS
– Without zooxanthellae, corals cannot flourish.
• Coral polyps have little pigmentation and appear nearly
transparent on the coral’s white skeleton, a condition known
as coral bleaching.
• A rise in SST of one to two Celsius degrees (2 to 4
Fahrenheit degrees) is sufficient to cause temporary
bleaching.
– Atoll: A series of coral reefs surrounding a lagoon that
remains after a volcanic island sinks beneath the
waves or erodes away
• Shaped like a ring or horseshoe and vary from 1 to 100 km
(0.6 to 60 mi) across
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Life at the Ocean’s Edge
Satellite image of an atoll in the western Pacific Ocean
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Life at the Ocean’s Edge
• CORAL REEFS
– Solitary corals and small coral reefs also live
in cold, deep water along continental shelf
breaks in some parts of the ocean
(ahermatypic corals).
• Cannot rely on zooxanthellae, so they depend
exclusively on trapping food directly from the water
using their stinging cells or nematocysts
• Provide excellent habitats for deepwater fishes
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Life at the Ocean’s Edge
Location of atolls and coral reefs in the world ocean.
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Life at the Ocean’s Edge
Darkblotched
rockfish nestled in
the branches of a
deep-sea
gorgonian soft
coral.
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Life at the Ocean’s Edge
• BENTHIC FEEDING HABITS
– Animals that live on or in soft-bottomed
habitats—whether in the intertidal zone,
shallow coastal areas, or in the deep sea—
are divided into two categories.
• Infauna inhabit sediment deposits.
• Epifauna live on the sea floor.
– Benthic animals living in muddy habitats
require specialized breathing structures.
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Life at the Ocean’s Edge
• LIFE ON THE DEEP-SEA FLOOR
– Many unusual creatures live on the deep-sea
floor.
– Communities of specialized animals have
evolved to live on the deep ocean bottom
near hydrothermal vents.
© AMS
This delicate sea lily
(crinoid), a member of
the phylum that
includes starfish, can
orient toward the
current to increase food
capture.
© AMS
Tube worms at a hydrothermal
vent on the floor of the Pacific
Ocean. Discovery of such
organisms launched a new
avenue of inquiry into our
understanding of biological
processes operating
in the deep ocean (especially
chemosynthesis).
Marine Animals
• FISHES
– Fish are cold blooded and hence are as warm or cold
as the surrounding water.
– Inhabit all parts of the ocean and possess special
adaptations for buoyancy, swimming, and life in the
dimly lit twilight zone as well as the greatest depths of
the ocean
– May be herbivorous, carnivorous, or omnivorous
– Two major groups of fishes: elasmobranchs (or
cartilaginous fishes) and teleosts (or bony fishes)
• Elasmobranchs or cartilaginous fishes include sharks,
skates, and rays and are considered to be more primitive.
© AMS
Marine Animals
• FISHES
– Their skeletons lack
true bones and consist
entirely of cartilage.
– There are over 800
species of
cartilaginous fishes.
– Reproductive
strategies favor
survival of their young.
© AMS
Marine Animals
• FISHES
– Teleosts (or bony fishes) have bony skeletons,
scales, and a flap covering their gills.
– Most have a swim bladder, a gas-filled structure that
can be inflated or deflated enabling the fish to adjust
its buoyancy with changes in water depth.
– Fishes living on or near the ocean bottom are called
demersal fishes and many of them are commercially
important, such as cod, halibut, haddock, and sole.
– Flatfishes are demersal fishes that have a special
coloration that camouflages them against the ocean
bottom.
© AMS
Marine Animals
• FISHES
– Many environmental factors influence the
reproductive success of bony fishes.
• Anadromous fishes spend most of their lives in cold regions
of the ocean, returning to the same river to breed when they
are sexually mature.
• Catadromous fishes are not as well known as anadromous
fishes; they breed in the open ocean, but spend their adult
lives in fresh water.
– Many species of fish reduce predation by swimming
together as organized groups, keeping a certain
distance between one another.
• This so-called schooling behavior is particularly
advantageous in the open ocean where hiding places are few
and far between.
© AMS
Marine Animals
Note the two eyes on one
side of the head of this
flounder photographed at an
ocean depth of more than
2600 m (8600 ft) off
the North Carolina coast
© AMS
School of northern
anchovies. Schooling is a
behavioral adaptation of
teleosts that may offer
protection from predators.
Marine Animals
• MARINE MAMMALS
– Warm blooded, air breathing animals that bear live
young, which they nurse
• Include whales, dolphins, seals, walrus, sea lions, and polar
bears
– The largest marine mammals, baleen whales, live
primarily in the open ocean where they filter
zooplankton from the water as they swim slowly with
their mouths open.
– Polar bears are unique to the Arctic and are the
region’s largest land predator.
• Inhabit the waters and coastal areas of Alaska, northern
Canada, northern Russia, Greenland, and Norway
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Marine Animals
• MARINE MAMMALS
– Pinnipeds, named for
their distinctive
swimming flippers,
include seals, sea
lions, and walruses.
• Many of them inhabit
coastal waters.
• Come ashore to breed,
give birth, and rear their
young
© AMS
Marine Animals
• MARINE REPTILES
– The few reptiles that live in the ocean fall into
three groups, the best known being sea
turtles.
• All sea turtles live in the ocean, but come ashore to
lay their eggs.
• Only a few hatchlings survive to adulthood.
© AMS
Marine Animals
• MARINE REPTILES
– Sea snakes are rare, occurring only in the tropical
Pacific and Indian Oceans, usually around reefs.
• Sea snakes are reptiles and must come to the surface to
breathe.
• Some species of sea snakes go ashore to reproduce and lay
eggs; others mate and bear live young without leaving the
sea.
– Marine iguanas are herbivores, feeding mostly on
seaweeds in the intertidal zone.
• Occur only in the Galápagos Islands in the equatorial Pacific
Ocean
• Having evolved from land lizards, they need a special
adaptation to deal with the large amount of salt water they
swallow while feeding.
© AMS
Marine Animals
• SEA BIRDS
– Carnivorous predators that occupy a high
trophic level in marine food webs
– No seabird can stay at sea for its entire life
• All of them must come ashore to breed and lay
eggs on a solid surface
– Where fishing grounds are exceptionally
productive, seabirds establish huge colonies
on rocky shores and cliffs, especially during
their breeding season.
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Marine Animals
Brown pelican in breeding colors
© AMS
Although ungainly on land, the
flightless penguin is an expert
swimmer. Shown here are Gentoo
Penguins (Pygoscelis papua),
largest of the “bush-tail” penguins.
They live on Antarctic islands
as well as the Antarctic Peninsula
Conclusions
– Marine plants and animals have evolved
many specialized adaptations involving
buoyancy, feeding, reproduction, and
protection from predators
– Marine plants and animals are distributed
nonuniformly in the ocean; their distribution is
controlled primarily by environmental factors
such as water temperature, salinity, light, and
availability of food
© AMS