Sustaining Aquatic
Biodiversity
Core Case Study: A Biological Roller
Coaster Ride in Lake Victoria
 Lake
Victoria has lost their endemic fish
species to large introduced predatory fish.
Figure 12-1
Core Case Study: A Biological Roller
Coaster Ride in Lake Victoria
 Reasons
for Lake Victoria’s loss of
biodiversity:




Introduction of Nile perch.
Lake experienced algal blooms from nutrient
runoff.
Invasion of water hyacinth has blocked sunlight
and deprived oxygen.
Nile perch is in decline because it has eaten its
own food supply.
Three General Patterns of Marine
Biodiversity

The greatest marine biodiversity occurs in coral
reefs, estuaries, and the deep-ocean floor

Biodiversity is higher near coasts than in the open
sea because of the greater variety of producers and
habitats in coastal areas

Biodiversity is higher in the bottom region of the
ocean than in the surface region because of the
greater variety of habitats and food sources on the
ocean bottom
HUMAN IMPACTS ON AQUATIC
BIODIVERSITY
 Human
activities have destroyed, disrupted
or degraded a large proportion of the world’s
coastal, marine and freshwater ecosystems.



Approximately 20% of the world's coral reefs
have been destroyed.
During the past 100 years, sea levels have risen
10-25 centimeters.
We have destroyed more than 1/3 of the world’s
mangrove forests for shipping lanes.
Shrimp farms in
areas that were
once mangrove
forests
Additional ways humans
degrade our ocean
environment
HUMAN IMPACTS ON AQUATIC
BIODIVERSITY
 Area
of ocean before and after a trawler net,
acting like a giant plow, scraped it.
Figure 12-2
HUMAN IMPACTS ON AQUATIC
BIODIVERSITY
 Harmful
invasive species are an increasing
threat to marine and freshwater biodiversity.

Bioinvaders are blamed for about 2/3 of fish
extinctions in the U.S. between 1900-2000.
 Almost
half of the world’s people live on or
near a coastal zone and 80% of ocean water
pollution comes from land-based human
activities.
Asian Rice Eel
Population Growth and Pollution

Each year plastic items
dumped from ships and
left as litter on beaches
threaten marine life.
It’s just a plastic bag!
It can’t hurt anyone.
Sea turtle off the coast of Florida
What can you do to
make sure this does
not continue?
Overfishing and Extinction:
Gone Fishing, Fish Gone
 About
75% of the world’s commercially
valuable marine fish species are over fished
or fished near their sustainable limits.




Big fish are becoming scarce.
Smaller fish are next.
We throw away 30% of the fish we catch.
We needlessly kill sea mammals and birds.
Human impacts on marine biodiversity
•
•
•
•
•
•
•
•
Coral reef destruction
Sea level rising
Destruction of mangrove forests
Trawler nets destroying ocean floor
Invasive species
Coastal development
Trash
Overfishing
Industrial fish harvesting methods

Trawler fishing: dragging net along ocean floor

Purse-seine fishing: surround fish with net

Long-line fishing: 80 miles of fishing line with
thousands of baited hooks

Drift-net fishing: 80 miles of drifting nets below the
surface
Problems with industrial fish harvesting
methods

Trawler fishing: like clear-cutting forest; destroys
ocean floor; captures endangered seals and turtles

Purse-seine fishing: kills hundreds of dolphins

Long-line fishing: hooks endangered sea turtles,
albatross, pilot whales, sharks, dolphins

Drift-net fishing: kills non-target fish species and
marine mammals
Fish farming
in cage
Trawl flap
Trawler
fishing
Spotter airplane
Sonar
Purse-seine fishing
Trawl
lines
Trawl bag
Long line
fishing
Fish
school
Drift-net fishing
Float Buoy
Lines with
hooks
Deep sea
aquaculture cage
Fish caught
by gills
Fig. 12-A, p. 255
Trawler fishing
By-catch
Purse-seine fishing
Long-line fishing
Several countries
have banned the use
of drift nets or they
are carefully
monitoring the use of
drift nets
Drift-nets
catch and
kill
anything
caught in
its net
Why is it Difficult to Protect Aquatic
Biodiversity?
 Rapid
increasing human impacts, the
invisibility of problems, citizen unawareness,
and lack of legal jurisdiction hinder protection
of aquatic biodiversity.



Human ecological footprint is expanding.
Much of the damage to oceans is not visible to
most people.
Many people incorrectly view the oceans as an
inexhaustible resource.
PROTECTING AND SUSTAINING
MARINE BIODIVERSITY
 Laws,
international treaties, and education
can help reduce the premature extinction of
marine species.
 Since 1989 the U.S. government has
required offshore shrimp trawlers to use turtle
exclusion devices (TEDs).

Sea turtle tourism brings in almost three times as
much money as the sale of turtle products.
PROTECTING AND SUSTAINING
MARINE BIODIVERSITY
 Six
of the world’s
seven major turtle
species are
threatened or
endangered
because of human
activities.
Figure 12-4
Laws and international treaties protecting
marine biodiversity
 CITES
 Global
Treaty on Migratory Species
 Marine Mammal Protection Act
 ESA
 Whale Conservation and Protection Act
 International Convention on Biological
Diversity
Exclusive Economic Zone
PROTECTING AND SUSTAINING
MARINE BIODIVERSITY
 Fully
protected marine reserves make up less
than 0.3% of the world’s ocean area.

Studies show that fish populations double, size
grows by almost a third, reproduction triples and
species diversity increases by almost one fourth.
 Some
communities work together to develop
integrated plans for managing their coastal
areas.
Integrated Coastal Management
•
•
•
•
•
•
Fisheries scientists
Conservationists
Citizens
Business interests
Developers
Politicians
Competing for the same resource – identify shared problems and
goals and attempt to develop workable, cost-effective, and adaptable
solutions that preserve biodiversity and environmental quality while
meeting economic and social needs.
Solutions
Managing Fisheries
Fishery Regulations
Bycatch
Set catch limits well below the
maximum sustainable yield
Use wide-meshed nets to allow
escape of smaller fish
Improve monitoring and enforcement
of regulations
Economic Approaches
Use net escape devices for sea
birds and sea turtles
Sharply reduce or eliminate fishing
subsidies
Ban throwing edible and
marketable fish back into the sea
Aquaculture
Charge fees for harvesting fish and shellfish
from publicly owned offshore waters
Restrict coastal locations for fish
farms
Certify sustainable fisheries
Protected Areas
Control pollution more strictly
Establish no-fishing areas
Depend more on herbivorous fish
species
Establish more marine protected areas
Nonnative Invasions
Rely more on integrated coastal
management
Kill organisms in ship ballast water
Consumer Information
Label sustainably harvested fish
Publicize overfished and threatened species
Filter organisms from ship ballast
water
Dump ballast water far at sea and
replace with deep-sea water
Fig. 12-7, p. 261
Natural Capital
Ecological Services of Rivers
• Deliver nutrients to sea to help sustain
coastal fisheries
• Deposit silt that maintains deltas
• Purify water
• Renew and renourish wetlands
• Provide habitats for wildlife
Fig. 12-11, p. 267
The End