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Chapter 6
Aquatic Biodiversity
Chapter Overview Questions
 What
are the basic types of aquatic life zones
and what factors influence the kinds of life
they contain?
 What are the major types of saltwater life
zones, and how do human activities affect
them?
 What are the major types of freshwater life
zones, and how do human activities affect
them?
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
Fig. 6-1b, p. 126
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.
AQUATIC ENVIRONMENTS
 Saltwater
and freshwater aquatic life zones
cover almost three-fourths of the earth’s
surface
Figure 6-2
AQUATIC ENVIRONMENTS
Figure 6-3
What Kinds of Organisms Live in
Aquatic Life Zones?
 Aquatic
systems contain floating, drifting,
swimming, bottom-dwelling, and decomposer
organisms.

Plankton: important group of weakly swimming,
free-floating biota.
• Phytoplankton (plant), Zooplankton (animal),
Ultraplankton (photosynthetic bacteria)



Necton: fish, turtles, whales.
Benthos: bottom dwellers (barnacles, oysters).
Decomposers: breakdown organic compounds
(mostly bacteria).
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.
SALTWATER LIFE ZONES
 The
oceans that
occupy most of the
earth’s surface
provide many
ecological and
economic services.
Figure 6-4
The Coastal Zone:
Where Most of the Action Is
 The
coastal zone: the warm, nutrient-rich,
shallow water that extends from the high-tide
mark on land to the gently sloping, shallow
edge of the continental shelf.
 The coastal zone makes up less than 10% of
the world’s ocean area but contains 90% of
all marine species.


Provides numerous ecological and economic
services.
Subject to human disturbance.
The Coastal Zone
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
Fig. 6-6, p. 130
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
Mangrove Forests
 Are
found along
about 70% of
gently sloping
sandy and silty
coastlines in
tropical and
subtropical
regions.
Figure 6-8
Estuaries and Coastal Wetlands:
Centers of Productivity
 Estuaries
and coastal marshes provide
ecological and economic services.



Filter toxic pollutants, excess plant nutrients,
sediments, and other pollutants.
Reduce storm damage by absorbing waves
and storing excess water produced by storms
and tsunamis.
Provide food, habitats and nursery sites for
many aquatic 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.


Gravitational pull by moon and sun causes tides.
Intertidal Zone: area of shoreline between low
and high tides.
Rocky and Sandy Shores:
Living with the Tides
 Organisms
in
intertidal zone
develop specialized
niches to deal with
daily changes in:



Temperature
Salinity
Wave action
Figure 6-9
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
Threats to
Coral Reefs:
Increasing
Stresses
 Biologically
diverse and
productive coral
reefs are being
stressed by
human activities.
Figure 6-11
Natural Capital Degradation
Coral Reefs
Ocean warming
Soil erosion
Algae growth from fertilizer runoff
Mangrove destruction
Bleaching
Rising sea levels
Increased UV exposure
Damage from anchors
Damage from fishing and diving
Fig. 6-12, p. 135
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.
Effects of Human Activities on Marine
Systems: Red Alert
 Human
activities
are destroying or
degrading many
ecological and
economic services
provided by the
world’s coastal
areas.
Figure 6-13
FRESHWATER LIFE ZONES
 Freshwater
life zones
include:


Standing (lentic)
water such as lakes,
ponds, and inland
wetlands.
Flowing (lotic)
systems such as
streams and rivers.
Figure 6-14
Lakes: Water-Filled Depressions
 Lakes
are large natural bodies of standing
freshwater formed from precipitation, runoff,
and groundwater seepage consisting of:




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.


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?
Lakes: Water-Filled Depressions
Figure 6-15
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.
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
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.


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.




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