Cecie Starr
Christine Evers
Lisa Starr
www.cengage.com/biology/starr
Chapter 43
The Biosphere
(Sections 43.10 - 43.14)
Albia Dugger • Miami Dade College
43.10 Tundra
• Low-growing, cold-tolerant plants have only a brief growing
season on two types of tundra
• arctic tundra
• Highest-latitude Northern biome, where low, cold-tolerant
plants survive with only a brief growing season
• alpine tundra
• Biome of low-growing, wind-tolerant plants adapted to
high-altitude conditions
Arctic Tundra
• Arctic tundra forms between the polar ice cap and belts of
boreal forests in the Northern Hemisphere
• Snow covers arctic tundra up to nine months of the year;
lichens and shallow-rooted plants grow quickly during a brief
summer under nearly continuous sunlight
• Food webs include voles, arctic hares, caribou, arctic foxes,
wolves, and brown bears; many migratory birds nest here in
the summer
Locations of Arctic Tundra
Arctic Tundra (cont.)
• Only the surface layer of soil thaws during summer – below
that lies permafrost up to 500 meters (1,600 feet) thick
• Permafrost prevents drainage; and cool, anaerobic conditions
slow decay, so organic remains build up
• permafrost
• Continually frozen soil layer that lies beneath arctic tundra
and prevents water from draining
Arctic Tundra in Summer
Alpine Tundra
• Alpine tundra occurs at high altitudes throughout the world
• There is no permafrost, but some patches of snow persist in
shaded areas, even in summer
• Alpine soil is well drained, but nutrient-poor, resulting in low
primary productivity
• Grasses, heaths, and small-leafed shrubs withstand strong
winds that discourage the growth of trees
Alpine Tundra
Key Concepts
• Land Biomes
• A biome consists of geographically separated regions that
have a similar climate and soils, and so support similar
types of vegetation
• Biomes include deserts, grasslands, chaparral, various
types of forests, and tundra
43.11Freshwater Ecosystems
• Gradients in light penetration, temperature, and dissolved
gases affect the distribution of life in aquatic habitats – which
include coasts, oceans, and freshwater ecosystems
• Freshwater ecosystems include lakes, streams, and rivers
Lakes
• A lake is a body of standing fresh water
• If sufficiently deep, a lake will have zones that differ in
physical characteristics and species composition
• Nearest shore is the littoral zone, where sunlight penetrates to
the lake bottom and aquatic plants are primary producers
• Open waters include an upper, well-lit limnetic zone, and a
profundal zone where light does not penetrate
Lake Zonation
Lake Zonation
Littoral zone
limit of effective
light penetration
Fig. 43.24, p. 738
Food Webs
• Primary producers in the limnetic zone are phytoplankton, a
group of photosynthetic microorganisms that includes green
algae, diatoms, and cyanobacteria
• Phytoplankton are food for zooplankton, which are tiny
consumers such as copepods
• In the profundal zone, there is not enough light for
photosynthesis – consumers here depend on debris that drifts
down feeds detritivores and decomposers
Nutrients and Succession in Lakes
• Lake habitats undergo succession over time:
• A new lake is oligotrophic: deep, clear, and nutrient-poor, with
low primary productivity
• Over time, the lake becomes eutrophic – enriched with
nutrients that allow producers to grow – and productivity rises
An Oligotrophic Lake
Seasonal Changes in Lakes
• Temperate zone lakes undergo seasonal changes that affect
primary productivity:
• In ice-covered lakes, the densest (4°C) water is at the
bottom, and ice floats at the top
• In spring, oxygen-rich surface water moves down and
nutrient-rich water from the lake’s depths moves up –
primary productivity increases
• In summer, a lake has three layers, with a thermocline that
prevents mixing – primary productivity declines
• In autumn, a fall overturn again exchanges surface and
bottom waters – low light limits primary productivity
Season Changes in a Temperate Lake
Season Changes in a Temperate Lake
Fig. 43.26a, p. 739
Season Changes in a Temperate Lake
A Winter. Ice covers the
thin layer of slightly
warmer water just
below it. Densest
(4°C) water is at
bottom. Winds do not
affect water under the
ice, so there is little
circulation.
ice
water between 0°C and 4°C
water at 4°C
Fig. 43.26a, p. 739
Season Changes in a Temperate Lake
Fig. 43.26b, p. 739
Season Changes in a Temperate Lake
B Spring. Ice thaws.
Upper water warms to
4°C and sinks. Winds
blow across the lake
causing currents that
help overturn water,
bringing nutrients up
from the bottom.
wind
overturn
Fig. 43.26b, p. 739
Season Changes in a Temperate Lake
Fig. 43.26c, p. 739
Season Changes in a Temperate Lake
C Summer. Sun warms
the upper water, which
floats on a thermocline,
a layer across which
temperature changes
abruptly. Waters above
and below the
thermocline do not mix.
wind
thermocline
Fig. 43.26c, p. 739
Season Changes in a Temperate Lake
Fig. 43.26d, p. 739
Season Changes in a Temperate Lake
D Fall. Upper water
cools and sinks, thus
causing the thermocline
to disappear. Vertical
currents can now mix
waters that remained
separate during summer.
wind
overturn
Fig. 43.26d, p. 739
Streams and Rivers
• Streams are flowing bodies of water that start as freshwater
springs or seeps, flow downslope, and merge into rivers
• Rainfall, snowmelt, geography, altitude, and shade cast by
plants affect flow volume and temperature
• Water moving at different speeds contains different solutes
and differs in temperature, so the species composition of a
river varies along its length
Importance of Dissolved Oxygen
• Dissolved oxygen content is one of the most important factors
affecting aquatic organisms
• More oxygen dissolves in cooler, fast-flowing water than in
warmer, still water
• When water temperature increases or water becomes
stagnant, aquatic species with high oxygen needs suffocate
Variations in Dissolved Oxygen
• Smoothly flowing water (left), holds less oxygen than water
that mixes with air as it runs over rocks (right)
Key Concepts
• Freshwater Ecosystems
• Lakes have gradients of light and temperature
• They undergo succession, changing over time
• In temperate zones, their waters mix in response to
seasonal changes in temperature
• Rivers vary along their length in their properties, and in the
organisms they contain
ANIMATION: Lake zonation
43.12 Coastal Ecosystems
• Near the coasts of continents and islands, concentrations of
nutrients support highly productive aquatic ecosystems
• An enclosed coastal region where seawater mixes with fresh
water from rivers and streams is called an estuary
• estuary
• A highly productive ecosystem where nutrient-rich water
from a river mixes with seawater
Estuaries
• Estuaries are marine nurseries; many larval and juvenile
invertebrates and fishes live in them
• Detrital food chains predominate
• Primary producers include algae and other phytoplankton,
along with plants that tolerate submergence at high tide
Estuary: South Carolina Salt Marsh
Mangrove Wetlands
• Nutrient-rich mangrove wetlands are found on sheltered tidal
flats along tropical coasts
• Mangroves are salt-tolerant woody plants with prop roots that
extend out from the trunk
• Specialized cells at the surface of some roots allow gas
exchange
Florida Mangrove Wetlands
The Intertidal (Littoral) Zone
• Organisms that live along ocean shores are adapted to
withstand the force of the waves and repeated tidal changes
• Many species are underwater during high tide, but are
exposed to the air when the tide is low
• A shoreline is divided into three littoral zones (upper, mid, and
lower) with progressively greater species diversity
Vertical Zonation in the Intertidal Zone
• Tide height varies
with the lunar cycle
as a result of the
position of the
moon and Earth
Vertical
Zonation in
the Intertidal
Zone
intertidal zone’s
upper littoral;
submerged only
at highest tide
of lunar cycle
midlittoral;
submerged at
each highest
regular tide and
exposed at
lowest tide
lower littoral;
exposed only
at low tide of
lunar cycle
Fig. 43.29, p. 740
Rocky and Sandy Shores
• Rocky shores
• Waves prevent detritus from piling up
• Algae on rocks are producers in grazing food chains
• Sandy shores
• Waves continually rearrange loose sediments and
discourage algae growth
• Detrital food chains start with organic debris from land or
offshore
Animation: Rocky Intertidal Zones
43.13 Coral Reefs
• Coral reefs are wave-resistant formations that consist
primarily of calcium carbonate secreted by coral polyps
• Reef-forming corals live mainly in shallow, clear, warm waters
between latitudes 25° north and 25° south
• coral reef
• Highly diverse marine ecosystem centered around reefs
built by living corals that secrete calcium carbonate
Coral Reefs (cont.)
• A healthy reef is home to living corals and many other
species, including about a quarter of all marine fish species
• Australia’s Great Barrier Reef is 2,500 kilometers (1,550
miles) long; 600,000 years old; and supports about 500 coral
species, 3,000 fish species, 1,000 kinds of mollusks, and 40
kinds of sea snakes
A Healthy Coral Reef
Coral Bleaching
• Photosynthetic dinoflagellates (symbionts) live inside tissues
of all reef-building corals and provide the coral polyp with
oxygen and sugars – and color
• When stressed, coral polyps expel the dinoflagellates, turning
the coral white (coral bleaching)
• coral bleaching
• A coral expels its photosynthetic dinoflagellate symbionts
in response to stress and becomes colorless
• With prolonged stress, the coral dies, leaving only
bleached hard parts behind
Coral Bleaching
ANIMATION: Three Types of Reefs
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43.14 The Open Ocean
• The ocean is divided into two regions, the pelagic province
and the benthic province
• pelagic province
• The ocean’s open waters
• Includes water over continental shelves and offshore
• benthic province
• The ocean’s bottom; sediments and rocks
Oceanic Zones
water of the open
ocean
air at ocean
surface
water
over continental
shelf
continental
shelf
Pelagic
Province
0
200
1,000
2,000
4,000
11,000
depth (meters)
deep-sea
trenches
Oceanic
Zones
Fig. 43.32, p. 742
The Pelagic Province
• As in fresh water, gradients of light and temperature affect the
distribution of marine life
• In upper, bright waters, phytoplankton are the primary
producers, and grazing food chains predominate
• Some light may penetrate as far as 1,000 meters (more than
a half mile) beneath the sea surface
• Below that, organisms live in continual darkness, and organic
material from above is the basis of detrital food chains
The Benthic Province
• On the ocean bottom, species richness is greatest on
continental shelves at the edges of continents, around
seamounts, and at hydrothermal vents
• seamount
• An undersea mountain
• hydrothermal vent
• Place where hot, mineral-rich water streams out from an
underwater opening in Earth’s crust
Seamounts
• Seamounts may be 1,000 meters or more tall, but are still
below the sea surface
• Seamounts attract large numbers of fishes, which attract
commercial fishing vessels
• Trawling (fishing technique in which a large net is dragged
along the bottom) strips entire areas bare of life, and
suffocates filter-feeders in adjacent areas
Seamounts off Alaska
Seamounts
• Seamounts are home to
many marine
invertebrates, such as
this flytrap anemone
• Like islands, many
species that evolved
around seamounts are
found nowhere else
Hydrothermal Vents
• At hydrothermal vents, mineral-rich seawater heated by
geothermal energy spews out from an opening on the ocean
floor and forms extensive deposits
• Chemoautotrophic bacteria and archaeans are the primary
producers for food webs that include diverse invertebrates,
including large numbers of tube worms
Hydrothermal Vent Community
Key Concepts
• Coastal and Marine Ecosystems
• Productivity is high in coastal wetlands, on coral reefs, and
in the ocean’s upper, sunlit water
• Life also thrives in the ocean’s deeper, darker waters and
on the sea floor, especially on undersea mountains and at
hydrothermal vents
Effects of El Niño (revisited)
• Marine biologist Rita Caldwell discovered that an El Niño can
increase the number of cases of cholera
• The rise in surface temperature causes a rise in abundance of
the phytoplankton that copepods feed on – and copepods
carry the cholera bacterium, Vibrio cholerae
• Caldwell advised Bangladeshi women to filter water through
sari cloth, which cut cholera outbreaks by half
Rita Caldwell and Filtered Water
ANIMATION: Oceanic zones
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ANIMATION: Coastal Upwelling
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