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Chapter 6
Major Ecosystems of the World
Lecture Outline:
I. Earth’s Major Biomes
A. A biome is a large, relatively distinct terrestrial region with a similar climate, soil,
plants, and animals
i. It encompasses many interacting ecosystems
ii. It is considered the next level of ecological organization above those of
community, ecosystem, and landscape
B. Tundra (arctic tundra): cold boggy plains of the far north
i. Tundra is a treeless biome consisting of boggy plains covered by lichens and
small plants such as mosses
1. It has harsh, cold winters and extremely short summers
2. It is characterized by little precipitation (4-10 inches/yr), permafrost,
low species richness, and low primary productivity
ii. Animal life includes lemmings, voles, weasels, arctic foxes, snowshoe hairs,
ptarmigan, snowy owls, and musk oxen
C. Boreal forests (taiga): conifer forests of the north
i. Boreal forest is a region of coniferous forest (such as pine, spruce, and fir) in
the Northern Hemisphere; located just south of the tundra
1. It has extremely cold, severe winters
2. It is characterized by little precipitation (20 inches/year),
acidic/mineral poor soil, ponds, lakes, and cone-bearing evergreens
ii. Animal life includes caribous, wolves, bears, moose, rodents, rabbits, lynx,
sable and mink
D. Temperate rain forest: lush temperate forests
i. Temperate rain forest occurs on the northwest coast of North America,
southeastern Australia and southern South America, and consists mostly of
large evergreen trees, mosses, lichens, and ferns
1. Seasonal fluctuation is narrow; winters are mild and summers are cool
2. It is characterized by high precipitation (50 inches/year), dense fog,
high species richness, and high primary productivity
ii. Animal life includes squirrels, wood rats, mule deer, elk, birds, and several
amphibian and reptile species
E. Temperate deciduous forest: broad-leaved trees that shed their leaves
i. Temperate deciduous forest occurs in temperate areas with a moderate amount
of precipitation
1. It has wide seasonal fluctuation with hot summers and cold winters
2. It is characterized by moderate precipitation (30 – 60 inches/year), rich
top soil, and broad-leaf hardwood trees that lose their foliage annually
ii. Animal life includes large mammals (puma, wolves, bison, deer, bears) and
many small mammals and birds
F. Grasslands (tallgrass prairies): temperate seas of grass
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i. Temperate grasslands contain a profusion of grasses and other herbaceous
flowering plants and few trees
1. It has wide seasonal fluctuation with hot summers and cold winters
2. It is characterized by moderate precipitation (10-30 inches/yr) and a
mineral rich top layer of soil ideal for agriculture
ii. Animal life includes grazing mammals such as pronghorn elk and bison,
wolves, coyotes, prairie dogs, foxes, ferrets, birds of prey, grouse, reptiles,
and insects
Chaparral (mediterranean climates): thickets of evergreen shrubs and small trees
i. Chaparral is a hilly temperate biome located around the Mediterranean Sea
as well as in the North American southwest, southwestern and southern
Australia, central Chile, and southwestern South Africa
1. It has mild winters with abundant rainfall combined and dry summers;
files are common during summer months
2. It is characterized by low precipitation (mostly in winter),dense growth
of evergreen shrubs, small trees, and thin, unfertile soil
ii. Animal life includes mule deer, wood rats, chipmunks, lizards, and many
species of birds
Deserts: arid life zones
i. Deserts are dry areas found in both temperate (cold deserts) and subtropical
regions (warm deserts) usually with sparse plant cover of cacti, yuccas, Joshua
trees and sagebrushes
1. The low water vapor content of the desert atmosphere results n daily
temperature extremes of heat and cold;
2. They are characterized by low precipitation (less than 10 inches/yr),
very little plant life, low species richness, and soil low in organic
material but high in mineral content
ii. Animal life includes small mammals, insects amphibians, and reptiles (most
are desert adapted)
Savanna: tropical grasslands
i. Savannas are tropical grasslands with widely scattered trees or clumps of trees
1. They usually occur in areas of low and/or seasonal rainfall with
prolonged dry periods, temperature varies little throughout the year,
and seasons are regulated by precipitation
2. Annual precipitation is moderate (30-60 inches/yr), soil is low in
nutrient minerals, both trees and grasses have fire-adapted features and
protection against herbivores
ii. Animal life includes hoofed mammals (antelope, giraffe, zebra elephants),
large predators (lions and hyenas), many bird species, and cattle (present
rangeland grazing is leading to desertification of savannas)
Tropical rain forests: lush equatorial forests
i. Tropical rain forests are lush, species-rich forest biomes that occur where the
climate is warm and moist throughout the year
1. They are found in Central and South America, Africa, and Southeast
Asia and are typically home to evergreen flowering plants, epiphytes,
tall trees, and three distinct layers of vegetation
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2. It is characterized by high annual precipitation (80 – 180 inches/yr),
ancient, highly weathered mineral-poor soil, high productivity, and
high species richness
ii. Animal life includes an enormous array of insects, reptiles, amphibians, birds,
and mammals (sloths and monkeys)
K. Vertical zonation: the distribution of vegetation on mountains
i. The cooler temperatures at higher elevations of a mountain produce a series of
ecosystems similar to the biomes encountered when going toward the North
Pole (deciduous/temperate forest, subalpine coniferous/boreal forest,
alpine/arctic tundra)
ii. Types of organisms living on the mountain change as the temperature changes
II. Aquatic Ecosystems
A. Determinants of species composition in aquatic ecosystems include salinity, dissolved
oxygen, light, temperature, pH, and presences or absence of waves and currents
B. Aquatic ecosystems contain three main ecological categories of organisms
i. Free-floating plankton
1. Phytoplankton are free-floating photosynthetic algae and
cyanobacteria that form the base of most aquatic food webs
2. Zooplankton are nonphotosynthetic organisms that include protozoa,
crustaceans, and the larval stages of many animals
ii. Strongly swimming nekton (fishes, turtles, whales)
iii. Bottom-dwelling benthos (sponges, oysters, barnacles, worms, clams, sea
cucumbers, crawfish, insect larvae, brittle stars)
C. Freshwater ecosystems (occupy only about 2% of Earth’s surface)
i. Rivers and streams: flowing-water ecosystems
1. The concept of a river system as a single ecosystem with a gradient in
physical features from headwaters to mouth is known as the river
continuum concept
2. This gradient results in predictable changes in the organism inhabiting
different parts of the river system
ii. Lakes and ponds: standing-water ecosystems
1. A large lake has three zones
a. The littoral zone is a shallow-water area along the shore of a
lake or pond where light reaches the bottom; it is the most
productive section of the lake
b. The limnetic zone is the open water beyond the littoral zone; it
extends down as far as sunlight penetrates to permit
photosynthesis
c. The profundal zone is beneath the limnetic zone; light does not
penetrate effectively to this depth (no plants or algae found
here)
iii. Thermal stratification and turnover in temperate lakes
1. Thermal stratification is the marked layering of large temperate lakes
caused by how far light penetrates it, causing temperature to change
sharply with depth
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2.
Falling temperatures in fall, and rising temperatures in spring cause
turnover, a mixing of the layers of lake water
iv. Marshes and swamps: freshwater wetlands
1. Grasslike plants dominate in marshes, while woody trees and/or shrubs
dominate in swamps
2. Wetlands are valued wildlife habitat for migratory birds, beaver, otters,
muskrats, and game fishes
3. They provide natural flood control and serve as groundwater
recharging areas
D. Estuaries: where fresh and salt water meet
i. Estuaries are among the most fertile ecosystems in the world
ii. Temperate estuaries usually contain salt marshes which are important in
preventing flood damage during storm surges
iii. Mangrove forests are the tropical equivalent of salt marshes; they cover nearly
70% of tropical coastlines
1. Mangroves are breeding ground and nurseries for several
commercially important fishes, shellfish, and birds
2. They also help prevent coastal erosion and provide a barrier against
the ocean during storms/hurricanes
E. Marine ecosystems
i. The intertidal zone is the area of shore line between low and high tides
ii. The benthic environment: seagrass beds, kelp forests, and coral reefs
1. The benthic environment consists of sediments (mostly sand and mud)
where many animals burrow
2. Shallow benthic communities are particularly productive
a. Seagrass beds are flowering plants adapted to complete
submersion in salty ocean water; they are areas of high primary
productivity and help stabilize sediments, reducing surface
erosion
b. Kelp forests provide habitats for many marine animals; the
diversity of life supported by kelp forests rivals that found in
coral reefs
c. Coral reefs are found in warm shallow seawater; they consist
of colonies of millions of tiny coral animals, which require
light for zooxanthellae (the symbiotic algae that live and
photosynthesize in their tissues)
i. Coral reefs are ecologically important because they
provide a habitat for many kinds of marine organisms
and protect coastlines from shoreline erosion
ii. There are three main types of coral reefs
1. Fringing reefs are directly attached to the shore
of a volcanic island or continent
2. Atolls are circular coral reefs that surround a
central lagoon of quiet water
3. Barrier reefs are separated from nearby land by
a lagoon of open water
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iii. Various human activities cause serious threats to the
health of coral reefs (runoff, overfishing, disease, etc.)
3. Deeper parts of the benthic environment are divided into three zones
a. Bathyal benthic zone – 200m to 4000m
b. Abyssal benthic zone – 4000m to 6000m
c. Hadal benthic zone – 6000m to the bottom of the deepest
trenches
iii. The pelagic environment: the vast marine system
1. The pelagic environment consists of all of the ocean water, from the
shoreline down to the deepest ocean trenches
a. The upper reaches of the pelagic environment comprise the
euphotic zone
b. The euphotic zone spans from the surface to 150m deep
2. The two main divisions of the pelagic environment are the neritic and
oceanic provinces
a. The part of the pelagic environment that overlies the ocean
floor from the shoreline to a depth of 200m is referred to as the
neritic province
b. The part of the pelagic environment that overlies the ocean
floor at depths greater than 200m is referred to as the oceanic
province
iv. A national marine sanctuary is a marine ecosystem set aside to minimize
human impacts and protect unique natural resources and historical sites
1. The U.S. has 14 national marine sanctuaries along the Atlantic,
Pacific, and Gulf of Mexico coasts
2. They include kelp forests, coral reefs, fishing grounds, deep submarine
canyons and shipwrecks
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Answers to Thinking About the Environment
End of Chapter Questions:
1. Offer a possible reason why the tundra has such a low species richness.
Ans: The limited precipitation in combination with low temperatures, flat topography (surface
features), and the permafrost. Few species have specialized to this environment. Another reason
for low species richness may be the short growing season which results in low primary
productivity.
2. Relate the tundra’s temperature and precipitation to its biotic characteristics.
Ans: Animals that occur on the tundra must be able to survive the long harsh winters and cold
temperatures or migrate seasonally. Mosquitoes, blackflies, and deerflies survive the winter as
eggs or pupae, and adults occur in great numbers during summer. Caribou and dozens of birds
species migrate north in summer. Although precipitation is low soil is usually waterlogged
because permafrost interferes with drainage. Plant species are then limited to those that can
survive waterlogged conditions and extreme cold.
3. Describe representative organisms of the forest biomes discussed in the text: boreal forest,
temperate deciduous forest, temperate rain forest, and tropical rain forest.
Ans: Black and white spruces, balsam fir, eastern larch, and other conifers (cone-bearing
evergreens) dominate the boreal forest. Conifers have many drought-resistant adaptations, such
as needlelike leaves with a minimal surface area for water loss. Such an adaptation lets conifers
withstand the “drought” of the northern winter months when roots cannot absorb water because
the ground is frozen. Being evergreen, conifers resume photosynthesis as soon as warmer
temperatures return. Animals in the boreal forest include; caribou, which migrate from the tundra
in the summer, wolves, bears, moose, lynx, sable, and mink. Most species of birds are abundant
in the summer but migrate to warmer climates for winter.
The temperate deciduous forest is dominated by broad-leaved hardwood trees, such as oak,
hickory, maple, and beech, that lose their foliage annually. The trees of the temperate deciduous
forest form a dense canopy that overlies saplings and shrubs.
Temperate deciduous forests originally contained a variety of large mammals, such as puma,
wolves, and bison, which are now absent, plus deer, bears, and many small mammals and birds.
The dominant plants in the North American temperate rain forest are large evergreen trees such
as western hemlock, Douglas fir, western red cedar, Sitka spruce, and western arborvitae.
Temperate rain forests are rich in epiphytic vegetation—smaller plants that grow on the trunks
and branches of large trees. Epiphytes in this biome are mainly mosses, club mosses, lichens, and
ferns, all of which also carpet the ground. Deciduous shrubs such as vine maple grow wherever a
break in the overlying canopy occurs. Squirrels, wood rats, mule deer, elk, numerous bird
species, and several species of amphibians and reptiles are common temperate rainforest animals.
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No single species dominates the tropical rain forest. The trees of tropical rain forests are typically
evergreen flowering plants. Their roots are often shallow and concentrated near the surface in a
mat. The root mat catches and absorbs almost all nutrient minerals released from leaves and litter
by decay processes. Swollen bases or braces called buttresses hold the trees upright and aid in
the extensive distribution of the shallow roots. Little light penetrates to the understory, and many
plants living there are adapted to climb already established host trees. Not counting bacteria and
other soil-dwelling organisms, about 90% of tropical rainforest organisms live in the upper
canopy. Rainforest animals include the most abundant and varied insects, reptiles, birds and
amphibians on Earth. Most rainforest mammals, such as sloths and monkeys, live only in the
trees and rarely climb to the ground.
4. In which biome do you live? If your biome does not match the description given in this book,
how do you explain the discrepancy?
Ans: Answers will vary
5. Which biomes are best suited for agriculture? Explain why each of the biomes you did not
specify is less suitable for agriculture.
Ans: The biomes most suited for agriculture are temperate deciduous forest and grasslands.
Tundra is not suitable for agriculture because it is to cold and has water logged soil. Boreal forest
is not suitable because it has a short growing season and mineral poor soil. Chaparral and
savanna biomes have evolved with fire and need frequent fires to release nutrients back into the
soil. Desert biomes are too dry for most agricultural products. Tropical rain forest are not good
for agriculture because little organic matter accumulates in the soil.
6. What human activities are harmful to deserts? to grasslands? to forests?
Ans: Off-road vehicles damage desert vegetation, which sometimes takes years to recover. When
the top layer of desert soil is disturbed, erosion occurs more readily, and less vegetation grows to
support native animals. In some savanna grasslands, severe overgrazing and harvesting of trees
for firewood have converted savanna to desert, a process called desertification. In all forests
overharvesting leads to deforestation and lost of species habitat.
7. Which biome do you think is in greatest immediate danger from human activities? Why?
Ans: Answers will vary
8. What would happen to the organisms in a river with a fast current if a dam were built? Explain
your answer.
Ans: In streams with fast currents, the inhabitants may have adaptations such as hooks or suckers
to attach themselves to rocks so that they are not swept away. A dam causes water to back up,
flooding large areas of land and forming a reservoir, which destroys terrestrial habitat. Below the
dam, the once-powerful river is often reduced to a relative trickle, which alters water
temperature, sediment transport, and delta replenishment and prevents fish migrations. The
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organisms that are adapted for fast currents will be out competed by species better suited for the
new conditions.
9. Explain the role of freshwater wetlands in water purification.
Ans: One of freshwater wetlands most important roles is to help cleanse water by trapping and
holding pollutants in the flooded soil. Wetlands also provide natural flood control because they
are holding areas for excess water when rivers flood their banks. The floodwater stored in
wetlands then drains slowly back into the rivers, providing a steady flow of water throughout the
year. Wetlands serve as groundwater recharging areas.
10. If you were to find yourself on a boat in the Chesapeake Bay, what aquatic ecosystem would
you be in? What ecosystem would you be in if you were in the middle of Everglades National
Park?
Ans: The Chesapeake Bay is an estuary- A coastal body of water, partly surrounded by land,
with access to the open ocean and a large supply of fresh water from a river. Everglades National
Park is a salt marsh- shallow wetlands dominated by salt-tolerant grasses.
11. Which aquatic ecosystem is often compared to a tropical rain forest? Why?
Ans: Coral reef ecosystems are the most diverse of all marine environments. They contain
thousands of species of fishes and invertebrates, such as giant clams, snails, sea urchins, sea
stars, sponges, flatworms, brittle stars, sea fans, shrimp, and spiny lobsters. The Great Barrier
Reef occupies only 0.1% of the ocean's surface, but 8% of the world's fish species live there. The
multitude of relationships and interactions that occur at coral reefs is comparable only to tropical
rain forests among terrestrial ecosystems.
12. Explain how coral reefs are vulnerable to human activities.
Ans: Globally, many coral reefs are at risk. In some areas, silt washing downstream from
clearcut inland forests has smothered reefs under a layer of sediment. In addition to pollution
from coastal runoff, overfishing, fishing with dynamite or cyanide, disease, and coral bleaching
are serious threats. Land reclamation, tourism, oil spills, boat groundings, anchor draggings,
hurricane damage, ocean dumping, and the mining of corals for building material also take a toll.
13. What is the largest marine environment, and what are some of its features?
Ans: The oceanic province is the largest marine environment, comprising about 75% of the
ocean's water; the oceanic province is the open ocean that does not overlie the continental shelf.
Most of the oceanic province is loosely described as the “deep sea.” All but the surface waters of
the oceanic province have cold temperatures, high hydrostatic pressure, and an absence of
sunlight. These environmental conditions are uniform throughout the year.
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14. Briefly discuss two major human-caused problems in the ocean.
Ans: Answers may include any two of the following: Coastal and marine ecosystems receive
pollution from land, from rivers emptying into the ocean, and from atmospheric contaminants
that enter the ocean via precipitation. Disease-causing viruses and bacteria from human sewage
contaminate seafood, such as shellfish, and pose an increasing threat to public health. Millions of
tons of trash, including plastic, fishing nets, and packaging materials, find their way into coastal
and marine ecosystems. Less visible contaminants of the ocean include fertilizers, pesticides,
heavy metals, and synthetic chemicals from agriculture and industry. Offshore mining and oil
drilling pollute the neritic province with oil and other contaminants. Millions of ships dump oily
ballast and other wastes overboard in the neritic and oceanic provinces. Fishing is highly
mechanized, and new technologies detect and remove every single fish in a targeted area of the
ocean.
15. A 2003 study reports that in recent years tropical ocean waters have become saltier, whereas
polar ocean waters have become less salty. What do you think is a possible explanation for these
changes?
Ans: Answers will vary.
16. In modeling the Chesapeake Bay system, scientists consider the following health indicators
for the bay, which are organized into three categories. Pick two human-caused problems and
explain how each affects the biotic and abiotic components of the Chesapeake Bay system.
Ans: Answers may include two of the following:
Nutrient pollution (most often nitrogen), empties into the bay from agricultural runoff, sewage
treatment plants, electric power companies, and motor vehicles. Most of this pollution remains in
the bay, causing excessive algal growth that results in a much lower level of dissolved oxygen in
the water. Oxygen-deprived water suffocates oysters, crabs, and other aquatic organisms.
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Sediment pollution can alter water circulation patterns, if freshwater flow into the estuary is
blocked or limited salinity in the Bay will increase. Excess sediment can suffocate benthic
organisms and destroy marshes which are nurseries for many fish species.
Toxicant pollution may not alter any of the abiotic aspects of the Chesapeake Bay but it will
affect all aspects of the biotic ecosystem. Persistent toxicants biomagnify as they go from low
trophic levels (planton) to higher trophic levels (shellfish and finfish).
Overfishing disrupts the balance of producers, consumers, and decomposers. For example, if to
many algae eating fish are removed algae populations can over grow causing decreased
dissolved oxygen levels in the water. Oxygen-deprived water suffocates oysters, crabs, and other
aquatic organisms.
Unsound land use can alter water flow patterns, water circulation and salinity. This will affects
all of the biotic communities by adding or removing habitat.
Answers to Review Questions
Earth’s Major Biomes (p. 129)
1. What is a biome? What two climate factors are most important in determining an area's
characteristic biome?
Ans: A biome is a large, relatively distinct terrestrial region with a similar climate soil, plants,
and animals, regardless of where it occurs in the world. Near the poles, temperature is generally
the overriding climate factor, whereas in temperate and tropical regions, precipitation becomes
more significant than temperature
2. What climate and soil factors produce each of the major terrestrial biomes?
Ans: Tundra is found in areas where winters are long and summers short. There is little
precipitation (10 to 25cm per year) with most of it falling during the summer months. Most
tundra soils are geologically young because they formed when glaciers retreated after the last Ice
Age. In the boreal forest winters are extremely cold and severe, although not as harsh as in the
tundra.
Boreal forest receives little precipitation, perhaps 50 cm per year, and its soil is typically acidic
and mineral-poor, with a deep layer of partly decomposed pine and spruce needles at the surface.
In temperate rain forests winters are mild and summers are cool. Annual precipitation in this
biome is high, more than 127 cm per year, and is augmented by condensation of water from
dense coastal fogs. Temperate rain forest has relatively nutrient-poor soil, although its organic
content may be high.
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Temperate deciduous forest, which occurs in temperate areas where precipitation ranges from
about 75 to 150 cm annually. Typically, the soil of a temperate deciduous forest consists of a
topsoil rich in organic material and a deep, clay-rich lower layer.
Grasslands have hot summers and cold winters with annual precipitation averages 25 to 75 cm.
Grassland soil has considerable organic material because the aerial portions of many grasses die
off each winter and contribute to the organic content of the soil, whereas the roots and rhizomes
(underground stems) survive.
Chaparral biomes have mild winters with abundant rain and dry summers. Chaparral soil is thin
and often not fertile.
Deserts are dry areas found in doth temperate and subtropical regions. The low water vapor
content of the desert atmosphere results in daily temperature extremes of heat and cold, and a
major change in temperature occurs in a single 24-hour period. Generally, less than 25 cm of rain
fall per year. As a result of sparse vegetation, desert soil is low in organic material but is often
high in mineral content.
In savanna biomes temperature varies little throughout the year seasons are regulated by
precipitation, not by temperature as they are in temperate grasslands. Annual precipitation is 76
to 150 cm. Savanna soil is somewhat low in essential nutrient minerals.
Tropical rain forests climate is warm and moist, the annual precipitation of a tropical rain forest
is typically from 200 to 450 cm. Tropical rain forest commonly occurs in areas with ancient,
highly weathered, mineral-poor soil.
3. How does vegetation change with increasing elevation and latitude?
Ans: Similar ecosystems are encountered in climbing a mountain (increasing elevation) and
traveling to the North Pole (increasing latitude). This elevation-latitude similarity occurs because
the temperature drops as one climbs a mountain, just as it does when one travels north.
Aquatic Ecosystems (p. 143)
1. What environmental factors are most important in determining the kinds of organisms found
in aquatic environments?
Ans: In aquatic ecosystems, important environmental factors include salinity, amount of
dissolved oxygen, and availability of light for photosynthesis.
2. How do you distinguish between freshwater wetlands and estuaries? Between flowing-water
and standing-water ecosystems?
Ans: Freshwater wetlands are lands that shallow fresh water covers for at least part of the year;
wetlands have a characteristic soil and water-tolerant vegetation. An estuary is a coastal body of
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water, partly surrounded by land, with access to the open ocean and a large supply of fresh water
from a river. A flowing-water ecosystem is a freshwater ecosystem such as a river or stream in
which the water flows in a current. A standing-water ecosystem is a body of fresh water that is
surrounded by land and that does not flow (a lake or a pond).
3. What are the four main marine environments?
Ans: Four important marine environments are the intertidal zone, benthic environment, neritic
province, and oceanic province.
4. Which marine environment is transitional between land and ocean?
Ans: The intertidal zone is the area of shoreline between low and high tides.
5. How do the neritic and oceanic provinces differ?
Ans: The pelagic environment consists of all of the ocean water, from the shoreline down to the
deepest ocean trenches. The two main divisions of the pelagic environment are the neritic and
oceanic provinces. The neritic province is the part of the pelagic environment that overlies the
ocean floor from the shoreline to a depth of 200 m. The oceanic province is the part of the
pelagic environment that overlies the ocean floor at depths greater than 200 m.
6. What are four purposes of national marine sanctuaries?
Ans: The National Oceanic and Atmospheric Administration (NOAA) administers the
sanctuaries for multiple purposes, including conservation, recreation, education, mining,
scientific research, ship salvaging, and commercial fishing.
Interaction of Life Zones and Humans (p. 145)
1. How did the Florida Everglades get so degraded?
Ans: Two problems have led to the degradation of the everglades, it receives too little water, and
the water it receives is polluted with nutrient minerals from agricultural runoff.
2. What are some of the challenges associated with restoration of the Florida Everglades?
Ans: one major challenge is supplying clean, fresh water to the Everglades and to the fastgrowing population of South Florida. Other questions remain about how best to restore a more
natural water flow, repel invasions of foreign species, and reestablish native species.
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