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?
Updates Online
The latest references for topics covered in this section can be found at
the book companion website. Log in to the book’s e-resources page at
www.thomsonedu.com to access InfoTrac articles.



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InfoTrac: Down the bayou: a marine biologist, a community,
and the resolve to preserve an ocean's bounty. Taylor Sisk.
Earth Island Journal, Autumn 2006 v21 i3 p27(6).
InfoTrac: A scourge of the '70s returns to Great Lakes. The
Christian Science Monitor, March 30, 2006 p14.
InfoTrac: The fate of the ocean. Julia Whitty. Mother Jones,
March-April 2006 v31 i2 p32(15).
National Oceanic and Atmospheric Administration: Fisheries
Amazon Conservation Association: Amazon Rivers Project
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. 6-1a, p. 126
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
Ocean hemisphere
Land–ocean hemisphere
Fig. 6-2, p. 127
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
Natural Capital
Marine Ecosystems
Economic
Services
Ecological
Services
Climate moderation
Food
CO2 absorption
Animal and pet
feed
Nutrient cycling
Waste treatment
Reduced storm
impact (mangroves,
barrier islands,
coastal wetlands)
Habitats and
nursery areas
Pharmaceuticals
Harbors and
transportation routes
Coastal habitats for
humans
Recreation
Employment
Genetic
resources and
biodiversity
Oil and natural gas
Scientific
information
Building materials
Minerals
Fig. 6-4, p. 129
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
Sun
Euphotic Zone
Photosynthesis
Estuarine
Zone
Continental
shelf
Open
Sea
Sea level
Bathyal Zone
Abyssal
Zone
Darkness
High tide Coastal
Zone
Low tide
Fig. 6-5, p. 130
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
Herring gulls
Peregrine falcon
Snowy
Egret
Cordgrass
Short-billed
Dowitcher
Marsh
Periwinkle
Phytoplankton
Smelt
Soft-shelled
clam
Zooplankton and
small crustaceans
Clamworm
Bacteria
Producer to
primary
consumer
Primary to
secondary
consumer
Secondary to
higher-level
consumer
All consumers
and producers
to decomposers
Fig. 6-7a, p. 131
Fig. 6-7b, p. 131
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
Rocky Shore Beach
Hermit crab
Sea star
Shore crab
High tide
Periwinkle
Sea urchin
Anemone
Mussel
Low tide
Sculpin
Barnacles
Kelp
Sea lettuce
Monterey flatworm
Nudibranch
Fig. 6-9, p. 132
Barrier Beach
Beach flea
Peanut worm
Blue crab
Tiger
Beetle
Clam
Dwarf
Olive
High tide
Sandpiper
Low tide
Silversides
Mole
Shrimp
White sand
macoma
Sand dollar
Ghost
Shrimp
Moon
snail
Fig. 6-9, p. 132
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
Ocean
Beach
Intensive
recreation,
no building
Primary
Dune
Trough
Secondary
Dune
No direct
No direct
Limited
passage
passage
recreation
or building and walkways or building
Back Dune
Most suitable
for development
Bay or
Lagoon
Intensive
recreation
Grasses
or shrubs
Bay shore
No filling
Taller shrubs
Taller shrubs and trees
Fig. 6-10, p. 133
Threats to
Coral Reefs:
Increasing
Stresses
 Biologically
diverse and
productive coral
reefs are being
stressed by
human activities.
Figure 6-11
Gray reef shark
Green sea
turtle
Sea nettle
Fairy basslet
Blue
tangs
Parrot fish
Sergeant major
Hard corals Algae
Brittle star Banded coral
shrimp
Phytoplankton
Symbiotic
algae
Zooplankton
Coney
Blackcap basslet
Sponges
Moray
eel
Bacteria
Producer to Primary to
primary
secondary
consumer
consumer
Secondary to
higher-level
consumer
All consumer
and producers
to decomposers
Fig. 6-11, p. 134
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
Natural Capital Degradation
Marine Ecosystems
Half of coastal wetlands lost
to agriculture and urban
development
Over one-third of mangrove
forests lost to agriculture,
development, and
aquaculture shrimp farms
Beaches eroding because of
coastal development and
rising sea level
Ocean bottom habitats
degraded by dredging and
trawler fishing
At least 20% of coral reefs
severely damaged and 30–
50% more threatened
Fig. 6-13, p. 136
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
Natural Capital
Freshwater Systems
Ecological
Services
Economic
Services
Climate moderation
Food
Nutrient cycling
Drinking water
Waste treatment
Irrigation water
Flood control
Hydroelectricity
Groundwater
recharge
Transportation
corridors
Habitats for many
species
Recreation
Genetic resources
and biodiversity
Employment
Scientific
information
Fig. 6-14, p. 136
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
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.
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.


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