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Sustaining Aquatic Biodiversity
Chapter 11
11-1 What Are the Major Threats to
Aquatic Biodiversity?
 Concept 11-1 Aquatic species are threatened
by habitat loss, invasive species, pollution,
climate change, and overexploitation, all made
worse by the growth of the human population.
We Have Much to Learn about
Aquatic Biodiversity
 We know fairly little about the biodiversity of the
world’s marine and freshwater systems.
• The greatest marine biodiversity occurs in coral
reefs, estuaries and the deep ocean floor.
• Biodiversity is higher near the coast and bottom
because of habitat and food source variety.
Human Activities Are Destroying and
Degrading Aquatic Habitats
 Just remember H.I.P.P.C.O.!!
 Habitat destruction
• 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.
• We have destroyed more than 1/3 of the world’s
mangrove forests for shipping lanes.
• Freshwater aquatic zones are also affected
• Dams and excessive water withdrawal from rivers/lakes
Invasive Species, Population Growth, and
Pollution Can Reduce Aquatic Biodiversity
 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 Population lives on or
near a coastal zone and 80% of ocean water.
 Pollution comes from land-based human activities.
• Nitrates and phosphates mainly from fertilizers enter water
• Leads to eutrophication
• Toxic pollutants from industrial and urban areas
Climate Change Is a Growing Threat
 Climate change as a result of global warming will
cause sea levels to rise and aquatic biodiversity to
be threatened.
• Water too warm for coral reefs
• Swamp some low-lying islands
• Drown many highly productive coastal wetlands
Overfishing and Extinction:
Gone Fishing, Fish Gone
 Overfishing
• About 75% of the world’s commercially valuable
marine fish species are overfished or fished near their
sustainable limits.
• Big fish are becoming scarce.
• Smaller fish are next.
• Commercial extinction
– so few exist that it is no
longer profitable to continue
• Bycatch – organisms caught unintentionally in nets
• We throw away 30% of the fish we catch.
Major Commercial Fishing Methods Used to
Harvest Various Marine Species
Trawler damage
11-2 How Can We Protect and Sustain
Marine Biodiversity?
 Concept 11-2 We can help to sustain marine
biodiversity by using laws and economic
incentives to protect species, setting aside
marine reserves to protect ecosystems, and
using community-based integrated coastal
management.
Legal Protection of Some Endangered and
Threatened Marine Species
 Why is it hard to protect marine biodiversity?
• Human ecological footprint and fishprint are
expanding
• Much of the damage in the ocean is not visible
• The oceans are incorrectly viewed as an
inexhaustible resource
• Most of the ocean lies outside the legal jurisdiction
of any country
Legal Protection of Some Endangered and
Threatened Marine Species
 Laws, international treaties, and education can help
reduce the extinction of marine species.
• CITIES, ESA, etc.
 Since 1989 the U.S. government has required
shrimp trawlers to use turtle exclusion devices.
• Sea turtle tourism brings in almost three times as much
money as the sale of turtle products.
• “Dolphin Safe” tuna
Case Study:
Protecting Whales: A Success Story… So Far
 International Whaling
Commission (IWC)
 After many of the world’s whale
species were overharvested,
commercial whaling was
banned in 1986.
• Annual harvest dropped from
42,000 to 1,300
 Whale populations have
rebounded so much that some
countries are contemplating
hunting again.
Marine Sanctuaries Protect
Ecosystems and Species
 Exclusive economic zones
• A country’s offshore fishing zone extends 200 miles
from the shore
• This area is under their jurisdiction and is their responsibility
 High seas – beyond legal jurisdiction
• Difficult to monitor and enforce international treaties
Establishing a Global Network of Marine Reserves:
An Ecosystem Approach
 Marine reserves areas of the ocean that are closed to
commercial fishing, dredging, mining and waste disposal
• Less harmful activities allowed
• E.g., recreational boating and shipping
 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 30%,
reproduction triples, and species
diversity increases by 25%.
 Integrated Coastal Management – conservation efforts
and methods need to customized to the specific
region/ecosystem being protected.
11-3 How Should We Manage and
Sustain Marine Fisheries?
 Concept 11-3 Sustaining marine fisheries will
require improved monitoring of fish populations,
cooperative fisheries management among
communities and nations, reduction of fishing
subsidies, and careful consumer choices in
seafood markets.
11-3 How Should We Manage and
Sustain Marine Fisheries?
 Maximum sustained yield (MSY)
• The maximum that can be harvested without
causing a population drop
 Optimum sustained yield (OSY)
• Recalculates MSY taking into account the interactions
with other species and allows for more room for error.