Study Guide - Chapter 11 - Sustaining Aquatic Biodiversity
Core Case Study:
A Biological Roller Coaster Ride in Lake Victoria
is a large
shallow lake in East Africa in ecological trouble. In 1980 it contained 500 species of
(found no where else) cichlids, but today only 200 species survive.
The factors causing this loss
of biodiversity include:
1) introduction of Nile perch, a large predator, and 2) large algae
blooms from agricultural and urban runoff
Poverty has increased in the local population
due to mechanized fishing for Nile perch, which has put small-scale fishermen out of business,
and has caused local forests to be depleted of firewood, which is used to smoke the perch.
Now, the Nile perch is declining as its food supply diminishes. Anthropogenic changes that
occur without a clear understanding of the dynamics of large aquatic ecosystems threaten
another component of the world’s the biodiversity needed to sustain earth’s ecosystems.
What are the major threats to aquatic biodiversity?
Only 5% of the earth’s ocean has been explored and we know little about its biodiversity.
Scientist have observed that:
1) coral reefs, estuaries and the deep-ocean floor have the
greatest marine diversity, 2) biodiversity is higher near the coasts, and 3) because of
greater habitat and food variety, the ocean floor has more biodiversity than the ocean
Habitat loss and degradation are the greatest threats to marine and freshwater
Ocean fishes spawn in coral reefs, mangrove forests, coastal wetlands, and
Unfortunately, these are the areas with the greatest human activity, and coastal habitats
are disappearing 2-10 times quicker than tropical forests.
Dredging operations and fishing
boats that use trawls are degrading the ocean bottom.
In the United Nations, an agreement to
stop bottom trawling in the South Pacific has been reached, but enforcement will be difficult.
freshwater aquatic zones, dams and excessive water withdrawal from lakes and rivers disrupts
flow and habitats. Today 51% of freshwater fish species are threatened with premature
The deliberate or accidental introduction of harmful
displaces many native
species and disrupts ecosystem services. The Nature Conservancy has reported that 84% of
the world’s coastal waters are being colonized by invasive species, and bioinvaders are blamed
for 2/3 of the fish extinctions in the U.S. from 1900-2000.
Two major sources of these invaders
ship ballast water
and consumers, such as aquarium hobbyists that dump tanks into
nearby streams and lakes, a particularly bad problem in Florida.
We may be able to use
biological controls to fight some invasive species seems, but these programs could just
introduce another pest.
By 2020, 80% of the world population will live in gigantic cities along marine coastlines, and this