Area VII: Global Change
VIIC: Loss of Biodiversity
11-1 Human impacts on terrestrial biodiversity
Humans have degraded much of the
Earth
most temperate and tropical ecosystems
(except deserts) have been disturbed by
humans
 in U.S. 95% of virgin forests have been cut,
and 98% of tallgrass prairie has
disappeared
 biodiversity has intrinsic (existence) and
extrinsic (instrumental, use) value

Fig. 11-2 Factors affecting biodiversity
Biodiversity
Increase Factors
Decrease Factors
•Middle stages of
succession
•Extreme environmental conditions
•Moderate environmental
disturbance
•Large environmental
disturbance
•Small changes in
environmental conditions
•Intense environmental stress
•Physically diverse habitat
•Severe shortages of
key resources
•Evolution
•Nonnative species
introduction
•Geographic isolation
Fig. 11-3 Human affects on biodiversity
Human Population
Size and resource use
Human Activities
Agriculture, industry, economic
production and consumption, recreation
Direct Effects
Degradation and destruction
of natural ecosystems
Changes in number and
distribution of species
Alteration of natural chemical
cycles and energy flows
Pollution of air, water,
and soil
Indirect Effects
Loss of
Climate
biodiversity
change
Fig. 11-4 Future of biodiversity
Arctic Circle
60°
EUROPE
NORTH
AMERICA
30°N
Tropic of Cancer
Pacific
Ocean
0° 150° 120° 90°
Tropic of Capricorn
ASIA
Atlantic
Ocean
AFRICA
30°W
SOUTH
AMERICA
0°
Pacific
Ocean
60°E 90°
150°
Indian
AUSTRALIA
Ocean
30°S
Antarctic Circle
60°
ANTARCTICA
Critical and endangered
Projected Status of Biodiversity
1998–2018
Threatened
Stable or intact
13-2 Human impacts on aquatic biodiversity
Humans threats to aquatic
biodiversity

~75% of the commercially valuable marine
fish species are either overfished or fished
to their sustainable limits
overfishing leads to commercial extinction
 big fish of commercially valuable species are
becoming scarce
 during the last 45 years, the abundance of
large, open-ocean dwelling fish has plummeted
by 90%

13-2 Human impacts on aquatic biodiversity

overfishing, cont.
230 populations of marine fish suffered an 83%
drop in breeding population size from known
historic levels
 destruction of habitat can prevent recovery
 the fishing industry has begun to take fastergrowing varieties at lower trophic levels
 because of the fishing methods, almost 33% of
the fish caught are bycatch (dead or dying
unwanted fish thrown overboard)

Fig. 13-2 Marine biodiversity
Fig. 13-3 Freshwater biodiversity
12-2 Importance of Wild Species
Wild species have value

If species evolve, then why does it matter
that some go extinct? What’s the big deal?
evolution takes a long time
 species are useful to us
 economic value
 ecological value
 genetic value
 aesthetic value
 medicinal value
 recreational value
 photography, bird watching, ecotourism
 some benefits have not yet been identified

12-1 Species Extinction
There are three types of species
extinction
local extinction: species no longer found
in one area but present in others
 ecological extinction: species can no
longer play its ecological role because so
few are left
 biological extinction: species is no longer
found anywhere on Earth

Fig. 12-2 Some extinct species
12-1 Species Extinction
Species are classified according to
their risk

species heading toward biological
extinction are either endangered or
threatened
endangered species: species has few
remaining individuals and could become
extinct over all or most(?) of its range
 threatened species: species is abundant, but
declining numbers make it likely to become
endangered in the near future
 the first species to go tend to be
economically valuable ones

Fig. 12-3a Some endangered species
Grizzly bear
(threatened)
Kirtland's
warbler
White top
pitcher plant
Arabian oryx
(Middle East)
African elephant
(Africa)
Mojave desert
tortoise
(threatened)
Swallowtail
butterfly
Humpback
chub
Golden lion
tamarin
(Brazil)
Siberian tiger
(Siberia)
Fig. 12-3b Some endangered species
West Virginia
Giant panda
spring salamander (China)
Mountain gorilla
(Africa)
Pine barrens
tree frog (male)
Whooping
crane
Knowlton
cactus
Swamp
pink
Hawksbill sea
turtle
Blue whale
El Segundo
blue butterfly
Fig. 12-3c Some endangered species
Florida
manatee
Northern spotted Gray wolf
owl (threatened)
Florida panther Bannerman's
turaco (Africa)
Devil's hole
pupfish
Black-footed
Snow leopard Symphonia
(Central Asia) (Madagascar) ferret
Ghost bat
(Australia)
California
condor
Black lace
cactus
Utah prairie dog
(threatened)
Black rhinocerosOahu tree
snail
(Africa)
12-1 Species Extinction

International Union for Conservation of
Nature and Natural Resources (IUCN-in
your book “World Conservation Union”) is a
leading authority on species conservation

IUCN categories as seen on Wikipedia:
Fig. 12-4 Characteristics of prone species
Fig. 12-5 Percent of species at risk by type
Percent of species at risk-IUCN Red List 07
Percent of birds at risk-IUCN(?) Red List 08
12-1 Species Extinction
Biologists try to estimate extinction
rates
recall the terms background extinction
and mass extinction
 estimating current extinction rate is difficult
for several reasons

1. extinction takes a while
 2. we have not identified every species
 3. we know little about species we have
identified

12-1 Species Extinction

IUCN monitors species (such as changes
in number or distribution) so that patterns
can be detected


category of every species ideally re-assessed
every 5 years (Wikipedia)
species-area relationship can be used to
estimate extinction rates

based on observations of the correlation
between number of species and the size of an
area where they are found
Number of species per unit area
12-1 Species Extinction
Humans are increasing the extinction
rate

the extinction rate has increased since the
arrival of humans
1,000 to 10,000 times higher
 extinction rate of 0.1% to 1% per year
 number of species going extinct (based on
these percentages) depends on number of
species in the world

12-1 Species Extinction

extinction rate of 0.1% to 1% per year
might be conservative
1. rate likely to increase this century
 2. some areas (hot spots) have much higher
extinction rates
 3. we limit speciation by degrading biologically
diverse environments (?)


the rate could be too high because it is
based on inadequate data and sampling

either way, more research is needed
13-2 Human impacts on aquatic biodiversity

fish are more threatened with extinction by
humans than any other group of species

freshwater species are disappearing 5x faster
than land animals
Fig. 13-4 Mean trophic levels of fish catch
12-3 Extinction Threats-Habitat Loss
Habitat loss and degradation are the
greatest threats to species
12-3 Extinction Threats-Habitat Loss

secondary factors:
habitat destruction and fragmentation
 major habitat disturbance factors:
 agriculture
 commercial development
 water development
 outdoor recreation
 livestock grazing
 and pollution
 invasive species
 pollution
 overharvesting

Fig. 12-7a Effect of habitat loss
Range 100 years ago
Range today
(about 2,300 left)
Indian Tiger
Fig. 12-7b Effect of habitat loss
Range in 1700
Range today
(about 2,400 left)
Black Rhino
Fig. 12-7c Effect of habitat loss
Probable range 1600
Range today
(300,000 left)
African Elephant
Fig. 12-7d Effect of habitat loss
Former range
Range today
(34,000–54,000 left)
Asian or Indian Elephant
12-3 Extinction Threats-Habitat Loss

loss of terrestrial species is greatest in:
1. tropical forests (deforestation)
 2. wetlands (filling)
 3. grasslands (plowing)
 4. islands
 (island biogeography can help us
understand the effects of habitat
fragmentation)

12-3 Extinction Threats-Habitat Loss

birds are in decline
70% of bird species are declining in numbers
 causes:
 1. habitat loss and fragmentation
 2. nonnative species (cats, rats, snakes,
mongooses, other birds)
 3. pet trade (parrots)
 4. human structures (fishing lines, phone
lines, buildings, etc.)
 5. pollution

Fig. 12-8 Threatened U.S. songbirds
Cerulean warbler
Florida scrub jay
Sprague’s pipit
Bichnell’s thrush
California gnatcatcher Kirtland’s warbler
Blacked-capped vireo
Golden-cheeked
warbler
Henslow’s sparrow
Bachman’s warbler
13-2 Human impacts on aquatic biodiversity

aquatic species are also threatened
~50% of world’s coastal wetlands were lost in
the last century
 coral reefs are severely damaged, mostly by
human activities
 >33% of mangrove swamps have disappeared
because of clearing for development, crops,
and aquaculture
 dredging and trawling are destroying many
bottom habitats
 scientists signed a statement to urge the UN
to ban bottom trawling on the high seas

12-4 Extinction Threats-Nonnative species
Nonnative species can be beneficial,
detrimental, or both
we use nonnative species for food,
medicine, enjoyment (pets)
 nonnative species can displace or cause
the extinction of native species

no predators
 introduce new diseases
 grow faster
 result: they decrease biodiversity

Fig. 12-9a Deliberately introduced species
Purple looselife
European starling
African honeybee
(“Killer bee”)
Marine toad
Water hyacinth
Japanese beetle
Nutria
Salt cedar
(Tamarisk)
Hydrilla
European wild boar
(Feral pig)
Fig. 12-9b Accidently introduced species
Sea lamprey
(attached to lake trout)
Argentina fire ant
Brown tree snake
Eurasian muffle
Common pigeon
(Rock dove)
Formosan termite
Zebra mussel
Asian long-horned
beetle
Asian tiger mosquito
Gypsy moth larvae
Fig. 12-11 Argentina fire ant range
1918
2000
12-4 Extinction Threats-Nonnative species

prevention is the best way to reduce threats
from invasive species

difficulties:
 small
 hard to detect
 breed rapidly
Fig. 12-12 Invaders and ecosystems
13-2 Human impacts on aquatic biodiversity

nonnative species are an increasing threat
to marine and freshwater biodiversity

nonnative aquatic species arrive in ship ballast
water
 can be lessened by requiring ships to:
 discharge ballast water and replace it
with saltwater at sea before entering
ports,
 sterilize ballast water, or
 pump nitrogen into it
13-2 Human impacts on aquatic biodiversity

nonnative species are an increasing threat
to marine and freshwater biodiversity

case study: purple loosestrife is a perennial
plant that has invaded wetlands and greatly
reduced biodiversity
 two natural predators of loosestrife have
been introduced from Europe where
loosestrife is native
 it will take time to determine whether this
biological control approach works without
the predators becoming pests
Fig. 13-5 Distribution of purple loosestrife
12-5 Extinction Threats-Poaching
Poaching is highly profitable
huge profits and few penalties encourage
poaching (illegal killing or taking of wildlife)
 hunting (for food) can threaten wild species
when it is done for export as opposed to
subsistence


increasing due to:
 (1) increasing population
 (2) accessibility to forests
 (3) restaurant demand
 (4) high profits
12-6 Other Extinction Threats
Killing predators, acquiring exotic
pets and plants, and climate change
and pollution affect ecosystems

predators are killed because they bother us
or cause economic losses
Carolina parakeet (eat fruit)
 elephants (trample)
 coyotes, wolves, bobcats (eat livestock or
poultry, popular game, or fish in farms)
 prairie dogs (make holes (not predator))

11-2 Conservation Biology
Humans have degraded much of the
Earth
conservation biology aims to analyze and
protect Earth’s biodiversity
 bioinformatics is the applied science of
managing, analyzing, and communicating
biological information

species cataloging
 DNA analysis
 species ranges

Fig. 11-5 Protecting biodiversity
The Species Approach
Goal
Protect species from
premature extinction
Strategies
• Identify
endangered
species
• Protect their critical
habitats
Tactics
• Legally protect
endangered species
• Manage habitat
• Propagate endangered
species in captivity
• Reintroduce species into
suitable habitats
The Ecosystem Approach
Goal
Protect populations of
species in their natural
habitats
Strategy
Preserve sufficient areas
of habitats in different
biomes and aquatic
systems
Tactics
• Protect habitat areas
through private purchase or
government action
• Eliminate or reduce
populations of alien species
from protected areas
• Manage protected areas to
sustain native species
• Restore degraded
ecosystems
12-8 Protecting Wild Species: Sanctuary
Wildlife refuges can help protect
species
wildlife refuges set aside land for species
 gene banks (or seed banks), botanical
gardens, farms, zoos, and aquariums can
help preserve species

important for education
 minimize need for wild species (farms)
 limited effectiveness

Fig. 12-15 Major migratory flyways
12-9 Reconciliation Ecology
Reconciliation ecology is a new form
of conservation

reconciliation ecology involves inventing,
establishing, and maintaining new habitats
for species conservation in the areas where
humans live and work
Fig. 12-16 Preventing premature extinction
12-7 Protecting Wild Species: Legal
Treaties and laws can help protect
species

international treaties

1975 Convention on International Trade in
Endangered Species (CITES)
 protects many species from commercial
trade
 limited effectiveness
 enforcement is difficult
 enforcement varies
 allows exemptions
12-7 Protecting Wild Species: Legal
Treaties and laws can help protect
species

international treaties

Convention on Biological Diversity 1992
 signatory nations agree to inventory
biodiversity and develop a plan to protect it
 U.S. has not ratified it
 no enforcement
12-7 Protecting Wild Species: Legal

national laws
Lacey Act of 1900
 requires federal permit to transport live or
dead wild animals across state borders
 Endangered Species Act of 1973 (ESA)
 identifies and legally protects endangered
species (currently about 1260 species)
 NMFS and USFWS list species
 forbids sale and purchase of any product
made from endangered species (including
foreign species)
 forbids federal agencies from harming
endangered species or their habitats

12-7 Protecting Wild Species: Legal

national laws, cont.

Endangered Species Act of 1973, cont.
 requires protection of critical habitat
 some habitats have not been protected
due to political pressure and lack of
funds
 controversial
 private versus public property rights issues
 examples
 two types of freedoms: protection from
others, do what you want without
government interference
12-7 Protecting Wild Species: Legal

national laws, cont.

Endangered Species Act of 1973, cont.
 applies to private land
 steep fines and imprisonment for
violations
 incentives for private land owners
 habitat conservation plans (HCPs) can
help
 safe harbor agreements
 voluntary candidate conservation
agreements
12-7 Protecting Wild Species: Legal

national laws, cont.

Endangered Species Act of 1973, cont.
 The National Academy of Sciences
recommended three major changes in order
to make the ESA more scientifically sound
and effective
 1. greatly increase funding to implement
the act
 2. develop recovery plans more quickly
 3. when a species is first listed, establish
a core of its survival habitat that could
support the species for 25–50 years
Fig. 12-14 Biodiversity hot spots in U.S.
13-3 Protecting and Sustaining Marine Bio.
Protection of marine life is difficult

protecting marine biodiversity is difficult:
coastal development
 large inputs of sediment, nutrients, and
pollution
 damage not visible to most people
 lack of knowledge about ocean; view that
ocean is inexhaustible
 most of the ocean is outside the legal
jurisdiction of any country (resulting in tragedy
of the commons)

Fig. 13-6 Threatened marine mammals
13-3 Protecting and Sustaining Marine Bio.
Laws, treaties, and education can
help

three sea turtle species are endangered
loss of onshore habitat
 taking of eggs
 used as food, medicine, jewelry, etc.
 unintentional catching
 1000’s globally from long-line fishing
 1000’s from U.S. shrimp trawling
 reduced by turtle exclusion devices since
1989

Fig. 13-7 Major species of sea turtles
13-3 Protecting and Sustaining Marine Bio.
Laws, treaties, and education can
help
Convention on International Trade in
Endangered Species (1975) (CITES)
 Global Treaty on Migratory Species (1979)
 U.S. Marine Mammal Protection Act (1972)
 U.S. Endangered Species Act (1973)
 U.S. Whale Conservation and Protection
Act (1976)
 International Convention on Biological
Diversity (1995)

Fig. 13-8a Toothed whales
Fig. 13-8b Baleen whales
13-3 Protecting and Sustaining Marine Bio.
Some countries want to overturn the
1970 whaling ban

International Whaling Commission (IWC)
est. 1946 (now has 49 member nations)
established quotes for whaling
 did not work because
 quotas based on inadequate data or
ignored
 no powers of enforcement


U.S. banned all commercial whaling and
imports of whale products in 1970
13-3 Protecting and Sustaining Marine Bio.
Some countries want to overturn the
1970 whaling ban

U.S. and many nonwhaling countries in
IWC imposed a moratorium on commercial
whaling in 1986
42.5 k killed in 1970, 1.2 k in 2004
 Japan, Norway, and Iceland still hunt whales
 traditional
 “moratorium based on emotion, not science”
 why not if there are over 1 M whales?

13-3 Protecting and Sustaining Marine Bio.
Some countries want to overturn the
1970 whaling ban

some conservationists disagree
 “whales are peaceful”
 “whales are intelligent”
 “whales are sensitive”
 “whales are social”
 inaccuracy of estimates
 limited whaling will open the door to
approval and weaker laws
13-3 Protecting and Sustaining Marine Bio.
Some marine sanctuaries exist but
not many

national control of oceans
sovereignty to 12 miles offshore (U.N. Law of
the Sea)
 jurisdiction to 200 miles offshore (Exclusive
Economic Zone (EEZ))

not much of that area (36% of ocean
surface and 90% of fish stocks) is protected
 IUCN has helped establish marine
protected areas (MPAs) since 1986

13-3 Protecting and Sustaining Marine Bio.
Other solutions

integrated coastal management


zone land and sea portions of an entire coastal
area
reconciliation ecology
13-5 Protecting, Sustaining, and Restoring Wetlands
Coastal and inland wetlands are
important reservoirs of aquatic
biodiversity; they provide ecological
and economic services

a law that requires a permit to fill or deposit
dredges into wetlands has cut wetland loss
by 80% between 1969 and 2002
13-5 Protecting, Sustaining, and Restoring Wetlands

a study by the National Academy of
Sciences found that mitigation banking, the
destruction of a wetland as long as an
equal area of the same type is created or
restored, does not work very well; these
projects often fail to meet the standards set
for them
Fig. 13-10
Solutions
Protecting Wetlands
Legally protect existing wetlands
Steer development away from existing wetlands
Use mitigation banking only as a last resort
Require creation and evaluation of a new wetland before
destroying an existing wetland
Restore degraded wetlands
Try to prevent and control invasions by nonnative species
13-5 Protecting, Sustaining, and Restoring Wetlands

case study: Everglades
natural Everglades are half their original size
and are drying out, leaving them vulnerable to
fire and invasion by nonnative species
 Everglades NP was set up in the lower part of
the Everglades, but water did not flow into it
and human activity caused disturbances
 90% of the wading birds are gone, and
other vertebrates are reduced in number by
75–95%
 Florida Bay has become saltier and warmer
 loss of water flow and input from crop fields
and cities have caused large algal blooms
 harm coral reefs, tourist industry

13-5 Protecting, Sustaining, and Restoring Wetlands

case study: Everglades, cont.

the U.S. Army Corp of Engineers has begun a
restoration project funded by the state and the
federal government to restore the river and
flow of water to the Everglades; goals:
 restore curving flow of more than half of the
Kissimmee River
 remove 250 miles of canals and levees
south of Lake Okeechobee
 buy 93 square miles of farmland and allow it
to flood to create artificial marshes
 create a network of artificial marshes
13-5 Protecting, Sustaining, and Restoring Wetlands

case study: Everglades, cont.

project goals, cont.
 create 18 large reservoirs to ensure water
for south Florida’s present and future
population and the lower Everglades
 build new canals, reservoirs, and pumping
stations to capture and return to the
Everglades 80% of the water flowing out to
sea
Fig. 13-11
Kissimm
ee
River
Channeliz
ed)
Unchanneliz
( ed)
(
FLORID
A
Fort
Myers
GULF
OF
MEXIC
O
Lake
Okeechob
ee
West
Palm
Beac
h
Naple
s
Fort
Lauderda
le
Agricultural
area
Treatment
marsh
Water
conservation
Can
area
al
Everglad
es
National
Park
FLORID
A
Area
of
detail
Florida
Bay
20
0
0
20
40
Mia
mi
ATLANTI
C
OCEAN
Key
Largo
40
60 miles
60 kilometers
13-6 Protecting, Sustaining, and Restoring Lakes and Rivers
invasions by nonnative species have
upset the ecological functioning of
the Great Lakes for decades
at least 162 nonnative species have
invaded the Great Lakes since the 1920s
 sea lampreys have depleted a number of
the sport fish species in the lakes

13-6 Protecting, Sustaining, and Restoring Lakes and Rivers
nonnative species in Great Lakes,
cont.

zebra mussels were brought into the lakes
in ballast water
very aggressive pests (no known natural
enemies)
 displaced native mussel species
 clogged pipes and piers
 fouled beaches
 spread to other parts of the U.S.

13-6 Protecting, Sustaining, and Restoring Lakes and Rivers
rivers/streams are important
ecological and economic resources
degraded by overfishing, pollution, dams,
and water withdrawal
 case study: salmon in Columbia River


salmon are migratory fish that breed in the
upper reaches of the river and its tributaries
 need free flowing water to return, spawn,
and lay eggs where they hatched
 benefit nearby forest as fertilizer as bears
eat and discard carcasses on the forest
floor
 trees grow up to 3x faster along streams
13-6 Protecting, Sustaining, and Restoring Lakes and Rivers

case study: Columbia River, cont.

threats to salmon:
 many dams on Columbia River
 overfishing in the Pacific Ocean
 destruction of spawning grounds by
sediment and lack of trees (makes water too
warm for eggs)
 water withdrawal
 release of farm raised salmon (could
decrease genetic diversity)
 result: 94% drop of wild Pacific salmon, and
nine species of Pacific Northwest salmon
are endangered or threatened
Fig. 13-13
Fig. 13-14
Human
capture
Fish change
form
Fish enter
rivers
and head for
spawning
areas
To
hatchery
Salmon
processi
ng
plant
In the fall spawning salmon
deposit eggs in gravel nests
and die
Modifi
ed
Life
Cycle Eggs are taken from
Grow to
maturity
in Pacific
Ocean
Norm
in 1-2 years
Fry hatch in the
spring...
al
Life
Cycle
Grow to smolt
and enter the
ocean...
Fingerlings migrate
downstream
adult
females and fertilized
with
sperm “milked” from
males
Eggs and young are
cared for in the
hatchery
And grow in the
stream
for 1-2 years
Fingerlings
are released into
river
13-6 Protecting, Sustaining, and Restoring Lakes and Rivers

case study: Columbia River, cont.

solutions:
 The Northwest Power Act was passed in
1980; goals:
 meeting electricity needs of the region
 restoring salmon, other fish populations
 these two goals often conflict
 people are working together to try to solve
the conflicts in this large-scale reconciliation
project
 critics say that the wild salmon populations
are stable in Alaska, so we should not worry
about the wild salmon of the Pacific
Northwest
Fig. 13-15
Solutions
Rebuilding Salmon Populations
Building upstream hatcheries
Releasing juvenile salmon from hatcheries to underpopulated streams
Releasing extra water from dams to wash juvenile salmon downstream
Building fish ladders so adult salmon can bypass dams during upstream
migration
Using trucks and barges to transport salmon around dams
Reducing silt runoff from logging roads above salmon spawning streams
Banning dams from some stream areas
13-6 Protecting, Sustaining, and Restoring Lakes and Rivers

sustainable management of freshwater fish
involves encouraging populations of
commercial/sport fish species, preventing
overfishing, and reducing or eliminating
less desirable fish populations
1. regulate fishing seasons and the number
and size of fish taken
 2. improve habitats, breed genetically resistant
fish varieties, and use judicious amounts of
antibiotics and disinfectants to control
predators, parasites, and diseases are
methods suggested
 3. some individuals have worked to restore

13-6 Protecting, Sustaining, and Restoring Lakes and Rivers

the National Wild and Scenic Rivers Act
was passed in 1968 to protect rivers and
river segments with outstanding scenic,
recreational, geological, wildlife, historical,
or cultural values

Congress established a three-tiered
classification scheme
 wild rivers are relatively inaccessible; they
are not permitted to be widened,
straightened, dredged, filled, or dammed
 scenic rivers are free from dams, mostly
undeveloped, of great scenic value, and
accessible in some places by roads
13-6 Protecting, Sustaining, and Restoring Lakes and Rivers

the National Wild and Scenic Rivers Act,
cont.
classification, cont.
 recreational rivers are readily accessible
by roads and may have some dams or
development along their shores
 only 0.2% of the 3.5 million miles of rivers are
protected under the Act, and 17% of the total
river length has dams and reservoirs on them
 environmentalists want to add 1,500 additional
river segments for a total of 2% of the total
river systems; there is opposition

13-6 Protecting, Sustaining, and Restoring Lakes and Rivers

threats to aquatic biodiversity are real and
growing

we must greatly increase research and expand
efforts to protect and restore aquatic
biodiversity and promote integrated ecological
management
Fig. 13-12
Natural Capital
Ecological Services of Rivers
•Deliver nutrients to sea to help sustain coastal fisheries
•Deposit silt that maintains details
•Purify water
•Renew and renourish wetlands
•Provide habitats for wildlife