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Chapter 8
Aquatic Biodiversity
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
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.
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).
Marine Ecosystems

The oceans that occupy
most of the earth’s
surface provide many
ecological and economic
services.
 Scientists estimate that
marine systems provide
$21 trillion in goods and
services per year – 70%
more than terrestrial
ecosystems.
Figure 6-4
The Coastal Zone

Warm, nutrient-rich,
shallow water that
extends from the
high-tide mark on
land to the gently
sloping, shallow
edge of the
continental shelf.
 Makes up less than
10% of the world’s
ocean area but
contains 90% of all
marine species.
Estuaries and Coastal Wetlands

Figure 6-7
Estuaries include river mouths,
inlets, bays, sounds, salt marshes
in temperate zones and mangrove
forests in tropical zones.
Estuaries and Coastal Wetlands
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.

Mangrove forests are found
along sandy and silty
coastlines in tropical and
subtropical regions.
Rocky and Sandy Shores

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
Coral Reefs
Formed by massive colonies of polyps.

Form in clear, warm coastal
waters of the tropics and
subtropics.
 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.
Threats to
Coral Reefs
 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
Effects of Human Activities on Marine Systems
 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.
Effects of Plant Nutrients on Lakes


Plant nutrients from a lake’s
environment affect the types and
numbers of organisms it can
support.
 Oligotrophic (Few nutrients)
newly formed or high mountain
lake
 Eutrophic (well nourished)
sediment, organic material,
and inorganic nutrients wash
into lakes causing excessive
plant growth.
Cultural eutrophication:
 Humans activities cause
acceleration
• Fertilizers & other chemicals
Freshwater Streams and Rivers
 Water
flowing from mountains to the sea
creates different aquatic conditions and
habitats.
Figure 6-17
Freshwater Inland Wetlands

Inland wetlands act like
natural 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.
Figure 6-18
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.
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.

These wetlands have
been ditched and
drained for cropland
conversion.