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Chapter 7
Aquatic Biodiversity
Euphotic zone- layer of water where
sunlight can penetrate
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What is the concentration of dissolved

O2 at the surface ? at 1000 m ?
What is the concentration of dissolved
CO2 at the surface? at 1000 m ?
Explain why dissolved O2 levels are so
high near the surface.
Explain why dissolved CO2 levels are
so low near the surface.
Explain why the O2 becomes less
concentrated and the CO2 becomes
more concentrated in deeper waters.
How would you expect this graph to
change at night ? Why ?
How should the pH change with depth
during the day ? Explain.
Graph page 146
Aquatic Life Zones
 Saltwater
or
Marine
 · Estuaries
 · Coastlines
 · Coral reefs
 · Coastal marshes
 · Mangrove
swamps
 · Ocean
 Freshwater
·
Lakes and ponds
 · Streams and
rivers
 · Inland wetlands
Core Case Study:
Why Should We Care About Coral
Reefs?
 Coral
reefs form in
clear, warm
coastal waters of
the tropics and
subtropics.

Formed by
massive colonies
of polyps.
Figure 6-1
Natural capital: a
healthy coral reef in
the Red Sea covered
by colorful algae
These diverse and
productive
ecosystems are being
damaged and
destroyed at an
alarming rate.
Fig. 6-1a, p. 126
Bleached Coral
Reef
That has lost most of
its algae because of
changes in the
environment (such
as cloudy water or too
warm temperatures).
With the algae gone,
the white limestone of
the coral skeleton
becomes visible. If the
environmental stress
is not removed and no
other alga species fill
the abandoned niche,
the corals die.
Fig. 6-1b, p. 126
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•
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Coral Reefs-built from accumulated
layers of calcium carbonate, CaCO3 laid
down by relatives of sea anemones.
1. Most of these organism require
warm shallow water
2. Many live in a symbiotic relationship
with green algae known as
zooxanthellae
3. A very diverse marine environment
4. The Great Barrier Reef off the coast
of Australia is one of the largest
Value of coral reefs
•
•
•
•
Provide valuable habitat
Provide humans with seafood
Pharmaceuticals
Recreation/tourism dollars
Human Impacts
• Covered with silt from inland logging
• In 1980’s coral bleaching occurred stressed
corals expelled zooxanthellae algae
• Thought to be related to warming of the seas.
Corals can recover because
• 1. Hold a secret reserve of algae
• 2. Can take on other algae species when one
species leaves
• 3. Seasonally lose up to 75% of algae
• Diving and snorkeling Overfishing
• Agricultural and industrial pollutants in runoff.
Core Case Study:
Why Should We Care About Coral
Reefs?
 Help
moderate atmospheric temperature by
removing CO2 from the atmosphere.
 Act as natural barriers that help protect 14%
of the world’s coastlines from erosion by
battering waves and storms.
 Provide habitats for a variety of marine
organisms.
Natural capital: the ocean planet. The salty oceans cover 71% of
the earth’s surface. About 97% of the earth’s water is in the
interconnected oceans, which cover 90% of the planet’s mostly
ocean hemisphere (left)
Ocean hemisphere
Land–ocean hemisphere
and 50% of its land–ocean hemisphere (right). Freshwater
systems cover less than 1% of the earth’s surface.
Fig. 6-2, p. 127
AQUATIC ENVIRONMENTS
Figure 6-3
Life in Layers
 Life
in most aquatic systems is found in
surface, middle, and bottom layers.
 Temperature, access to sunlight for
photosynthesis, dissolved oxygen content,
nutrient availability changes with depth.

Euphotic zone (upper layer in deep water
habitats): sunlight can penetrate.
The Coastal Zone
The Open Ocean
Life Zones
Euphotic Zone
1.Light
2. Dissolved Oxygen
3. Nutrients
upwellings
4.Organisms
Bathyal Zone
1.Light
2. Organisms
Abyssal Zone
1.Light
2.Oxygen
3. Nutrient levels
Figure 6-5
Marine Ecosystems
 Scientists
estimate
that marine systems
provide $21 trillion in
goods and services
per year – 70% more
than terrestrial
ecosystems.
Figure 6-4
Major Human Impacts
 Salt
Marshes, Mangrove Forests, Sea-grass
Meadows
Filled in for coastal development
Aquaculture of shrimp
 BeachesErosion
 Benthic Habitat
Bottom trawlers
 Coral Reefs
Ocean warming, pH changes associated
with global warming.

Estuaries and Coastal Wetlands:
Centers of Productivity
 Estuaries
include river
mouths, inlets, bays,
sounds, salt marshes
in temperate zones
and mangrove forests
in tropical zones.
Figure 6-7
Estuaries &Associated Coastal
Wetlands
 Located
at the mouth of rivers and streams
 Fresh and salt water mix
 Highest NPP of any ecosystem because
 · 1. Nutrient runoff from land
 · 2. Tides circulate nutrients and remove
wastes
 · 3. Light penetrates the shallow water
 · 4.Plant carry out photosynthesis and trap
detritus
 Organisms must deal with daily changes in
temperature and salinity.
Saltwater marshes
 Found
associated with temperate estuaries
 Dominated by salt tolerant grasses
 Important services
 · 1. Habitat
 · 2. Sediment and pollution trapping
 · 3. Storm buffering
 Most are being covered over for coastal
development
Mangrove Forests
 Are
found along
about 70% of
gently sloping
sandy and silty
coastlines in
tropical and
subtropical
regions.
Figure 6-8
Mangrove Forests-tropical
equivalent of saltwater marsh
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Network of roots of the mangrove trees are important
nurseries of many commercially important fish and
shellfish (shrimp)
Branches of mangrove trees provide important
habitat for nesting birds: pelicans, herons, egrets.
Roots stabilize submerged soil preventing coastal
erosion
Storm buffer
Being harmed by:
Logging
Coastal development
Intertidal Zone- between
high and low tide
·
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Organisms must contend with changing
levels of water
In rocky shoreline habitat, most organisms
are anchored in some way and have a
way to seal off their bodies to prevent
moisture loss when the tide goes out.
Most sandy beach organisms either burrow
in the sand or travel in and out with the
tide.
The importance of sea grass
 High
NPP make them important producers in
shallow water
 Roots stabilize sediments reducing erosion
 Provide food and habitat for many marine
species, sea turtles, manatees, ducks and
geese

Chinook salmon
and eelgrass
Kelps Beds
 Formed
from species of
marine algae
 Many are anchored to the
bottom and have air filled
bags to allow the upper part
of the plant to float to the top
 equivalent to the forest
biome on the land
 Kelp beds or forests provide
habitat and food for many
species
Rocky and Sandy Shores:
Living with the Tides
 Organisms
experiencing daily low and high
tides have evolved a number of ways to
survive under harsh and changing conditions.

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Gravitational pull by moon and sun causes tides.
Intertidal Zone: area of shoreline between low
and high tides.
Barrier Islands
 Low,
narrow, sandy islands that form offshore
from a coastline.
 Primary and secondary dunes on gently
sloping sandy barrier beaches protect land
from erosion by the sea.
Figure 6-10
Biological Zones in the Open Sea:
Light Rules
 Euphotic

Nutrient levels low, dissolved O2 high,
photosynthetic activity.
 Bathyal

zone: dimly lit middle layer.
No photosynthetic activity, zooplankton and fish
live there and migrate to euphotic zone to feed at
night.
 Abyssal

zone: brightly lit surface layer.
zone: dark bottom layer.
Very cold, little dissolved O2.
FRESHWATER LIFE ZONES
 Freshwater
life zones
include:
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Standing (lentic) water
such as lakes, ponds,
and inland wetlands.
Flowing (lotic) systems
such as streams and
rivers.
Ponds are generally
shallow and have only
one zone-light reaches
to the bottom
Figure 6-14
Lakes: Water-Filled Depressions
 Lakes
are large natural bodies of standing
freshwater formed from precipitation, runoff,
and groundwater seepage consisting of:
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Littoral zone (near shore, shallow, with rooted
plants).
Limnetic zone (open, offshore area, sunlit).
Profundal zone (deep, open water, too dark for
photosynthesis).
Benthic zone (bottom of lake, nourished by dead
matter).
Lakes: Water-Filled Depressions
 During
summer and winter in deep temperate
zone lakes the become stratified into
temperature layers and will overturn.

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This equalizes the temperature at all depths.
Oxygen is brought from the surface to the lake
bottom and nutrients from the bottom are brought
to the top.
 What
causes this overturning?
Sunlight
Green
frog
Painted
turtle
Blue-winged
teal
Muskrat
Pond
snail
Littoral zone
Limnetic zone
Diving
beetle
Plankton
Profundal zone
Benthic zone
Yellow
perch
Bloodworms
Northern
pike
Fig. 6-15, p. 137
Effects of Plant Nutrients on Lakes:
Too Much of a Good Thing
 Plant
nutrients from a lake’s environment
affect the types and numbers of organisms it
can support.
Figure 6-16
Effects of Plant Nutrients on Lakes:
Too Much of a Good Thing
 Plant
nutrients from a lake’s environment
affect the types and numbers of organisms it
can support.


Oligotrophic (poorly nourished) lake: Usually
newly formed lake with small supply of plant
nutrient input.
Eutrophic (well nourished) lake: Over time,
sediment, organic material, and inorganic
nutrients wash into lakes causing excessive plant
growth.
Effects of Plant Nutrients on Lakes:
Too Much of a Good Thing
 Cultural

eutrophication:
Human inputs of nutrients from the atmosphere
and urban and agricultural areas can accelerate
the eutrophication process.
Physical Properties of water
 Approaches
maximum density at 4oC
 At temperatures cooler than 4oC water
becomes less dense and it floats
 and freezes as temperatures drop to 0oC
 At temperatures greater than 4oC water
becomes less dense and it floats
Seasonal Overturn in Lakes
 Fall
Overturn Surface waters
 cool to 4oC (39oF)
 and descend to
 the bottom


Nutrients
Oxygen levels
 Spring
Overturn Surface waters
 warm to 4oC and
 descend through
 the colder less
 dense waters
 beneath.
Freshwater Streams and Rivers:
From the Mountains to the Oceans
 Water
flowing from mountains to the sea
creates different aquatic conditions and
habitats.
Figure 6-17
Rain and
snow
Lake Glacier
Rapids
Waterfall
Tributary
Flood plain Oxbow
lake
Salt marsh
Delta Deposited
sediment
Ocean
Source Zone
Transition Zone
Water
Sediment
Floodplain Zone
Fig. 6-17, p. 139
Case Study:
Dams, Wetlands, Hurricanes,
and New Orleans
 Dams
and levees have been built to control
water flows in New Orleans.
 Reduction in natural flow has destroyed
natural wetlands.
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
Causes city to lie below sea-level (up to 3
meters).
Global sea levels have risen almost 0.3 meters
since 1900.
Freshwater Inland Wetlands:
Vital Sponges
 Inland
wetlands
act like natural
sponges that
absorb and store
excess water
from storms and
provide a variety
of wildlife
habitats.
Figure 6-18
Freshwater Inland Wetlands:
Vital Sponges
 Filter
and degrade pollutants.
 Reduce flooding and erosion by absorbing
slowly releasing overflows.
 Help replenish stream flows during dry
periods.
 Help recharge ground aquifers.
 Provide economic resources and recreation.
Impacts of Human Activities on
Freshwater Systems

Dams, cities, farmlands, and filled-in wetlands alter
and degrade freshwater habitats.
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Dams, diversions and canals have fragmented about 40%
of the world’s 237 large rivers.
Flood control levees and dikes alter and destroy aquatic
habitats.
Cities and farmlands add pollutants and excess plant
nutrients to streams and rivers.
Many inland wetlands have been drained or filled for
agriculture or (sub)urban development.
Impacts of Human Activities on
Freshwater Systems
 These
wetlands
have been ditched
and drained for
cropland
conversion.
Figure 6-19