Sustaining Aquatic Biodiversity
1. Aquatic biodiversity refers to the composition of plants and animals in the fresh and salt waters of the planet.
The economic importance of aquatic diversity lies in the conservative estimate of the value of their ecological
services, which is $21 trillion a year. Additionally, at least 3.5 billion people depend on the seas for their
primary source of food and this number could double to 7 billion in 2025. Many medicines have been
developed from sea organisms: sponges, anemones, puffer fish, porcupine fish, seaweeds, etc. The waters are
used for extensive recreational activities, not to mention commercial transportation.
2. Human activities are undermining aquatic biodiversity by destroying and degrading coastal wetlands, coral
reefs, seagrass beds, kelp beds, mangroves, and the ocean bottom.
3. We can protect and sustain marine biodiversity by using laws, international treaties, and education. We must
identify and protect species that are endangered and/or threatened. This entails cleaning up aquatic
environments, as well as inventing fishing methods that do not destroy animals and birds inadvertently caught
in fishing nets. Poaching and illegal harvesting of marine creatures must also be eliminated. Public aquariums
can also educate the public about protecting marine animals and birds. Marine sanctuaries and coastal
management can protect aquatic environments as well as their creatures.
4. The world’s marine fisheries can be managed by setting catch limits below the maximum sustained yield
limits, by reducing/eliminating fishing subsidies, and by charging fees for fishing in publicly owned offshore
waters. Some areas can be protected from any kind of fishing; there should be more marine protected areas and
more integration of coastal management practices. Develop net-escape devices for fishing boats. Restriction of
coastal locations for fish farms, control of pollution, and decreasing the pollution of ship ballast water into the
sea will all protect marine fisheries. Multispecies management of large marine systems offers hope for
conserving marine resources and for renewing those resources.
5. Wetlands can be protected, sustained, and restored by government regulations that prevent wetland loss.
Destroyed wetlands can also be restored and adequately monitored for their protection. Development can be
kept away from wetland areas and control of nonnative species needs to be instituted to prevent invasion into
6. Freshwater fisheries, lakes, and rivers can be protected, sustained, and even restored by building and protecting
populations of desirable species, by prevention of overfishing, and by decreasing populations of less desirable
species. Laws can be enacted, and enforcers of these laws must be funded to protect scenic rivers; they should
be protected from development and dam construction projects.
Key Questions and Concepts
11-1 What are the major threats to aquatic biodiversity?
CORE CASE STUDY: The introduction of the large predatory Nile perch into Lake Victoria in East Africa
has led to the extinction of some 200 cichlid species. The lake was once home to about 500 endemic species. In
a short time, many have been driven to extinction, and many more are currently at risk. The introduction of the
Nile perch served to satisfy a market in Europe, but has had unforeseen consequences, such as changes in the
local economy and widespread deforestation.
We know very little about the earth’s aquatic biodiversity because there has been so little exploration of the
water on this “water planet.”
A. Three patterns of marine biodiversity are:
1. The greatest marine biodiversity occurs in coral reefs, estuaries, and on the deep-sea ocean floor.
2. Biodiversity is higher near the coasts because of great variety of producers, habitats, and nursery areas.
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3. Biodiversity is higher in the bottom region than in the surface region of the ocean.
B. The greatest threat to the biodiversity of oceans is loss and degradation of habitats.
1. Coral reefs, mangrove forests, and coastal wetlands are under great pressure from human activities.
2. Trawling and dredging are major threats to sea bottom habitats.
3. Dams and excessive water withdrawal are destroying freshwater habitats.
C. Harmful invasive species increasingly threaten marine biodiversity.
D. By 2020, 80% of the world’s population will live near coasts. Population growth and pollution have drastic
effects on ocean systems.
1. Pollutants such as nitrogen from fertilizers can cause algal blooms and eutrophication.
2. Toxic pollutants can kill some aquatic life forms.
SCIENCE FOCUS: Lake Wingra in Wisconsin receives excessive nutrients from runoff and is populated
by invasive species, including carp and purple loosestrife. The carp devour the algae that would normally
stabilize sediments on the lake bottom. Scientific experiments that involved excluding carp from a study
area showed that algae recolonized and the lake water became noticeably clearer. There is now an effort to
remove the carp from the rest of the lake to alleviate the effects of this invasive species.
E. Climate change threatens aquatic biodiversity and ecosystems services.
F. Overfishing can have drastic effects on biodiversity.
1. Modern industrial fishing can deplete 80% of target fish species in just 10–15 years.
2. Overfishing can lead to commercial extinction, which occurs when it is no longer profitable to continue
fishing the affected species.
3. Nearly one-third of annual fish catch consists of bycatch—non-target species that are thrown
4. Marine and freshwater fishes are threatened with extinction by human activities more than any other
group of species.
SCIENCE FOCUS: Mangroves provide important ecological services. They reduce the impacts of
storms and rising sea levels. Due to coastal development in Indonesia, about 70% of that nation’s
mangroves have been degraded or destroyed. There are now efforts to protect these areas. The economic
benefits and ecological services provided by mangroves should be considered in all coastal development
CASE STUDY: Industrial fishing dominates the global fishing industry. 75% of the world’s fisheries
are fished unsustainably. Trawler fishing extracts fish and shellfish from the ocean floor. Purse-seine
fishing is used to catch surface dwelling species. Longlining strings out thousands of baited hooks as
much as 80 miles long. Finally, drift netting involves massive nets that can lead to overfishing. In 1992,
the UN limited the size of driftnets that could be used in international waters, but compliance is
11-2 How can we protect and sustain marine biodiversity?
A. Protecting marine biodiversity is difficult because it is difficult to monitor the impact of the human
ecological footprint, oceans are unseen by most people, oceans are often thought to be inexhaustible
resources, and most of the ocean area lies outside of the jurisdiction of any nation.
CASE STUDY: Overharvesting of whale species has driven some commercially valuable species to the
brink of extinction. Blue whales were once numerous, but today only a small portion of their original
population remains. Despite protection, it is uncertain whether their population will make a comeback.
Several nations continue to harvest whales, and are attempting to overthrow bans on commercial whaling.
At the same time, some communities have prospered by offering whale watching excursions to tourists.
B. Biodiversity can be valuable to local communities that develop eco-tourism markets.
CASE STUDY: Six of the seven species of marine turtles are endangered. Leatherback turtles are being
heavily impacted by human activities. Fishing practices, pollution, and climate change all threaten their
survival. However, there has been progress. Some local communities are reducing their impacts on beaches
where turtles lay their eggs, Turtle Excluder Devices are now required on trawlers by the U.S. government,
and some communities are focusing on the economic advantages of protecting these species
C. A country’s offshore fishing zone extends 370 kilometers from its shores.
1. Ocean areas beyond these Exclusive Economic Zones, called the high seas, are difficult to monitor.
2. The World Conservation Union helped establish a global system of marine protected areas (MPAs).
3. There are about 4,000 MPAs, almost 200 in U.S. waters; however, most MPAs allow ecologically
harmful activities like trawling, dredging, and resource extraction.
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D. Scientists are advocating an ecosystems approach to sustaining marine biodiversity.
1. This would entail a network of protect marine reserves, closed to extractive activities.
2. Studies show that within as few as two years after establishing a reserve the fish are larger, reproduce
more often, and are in greater variety than previously.
3. Less that 1% of the world’s ocean area is closed to fishing in marine reserves.
E. Integrated coastal management is a community-based effort to develop and use coastal resources more
1. The idea is to find cost-effective, adaptable solutions to preserve biodiversity while meeting economic
and social needs.
11-3 How dhould ee manage and sustain marine fisheries?
A. One way to prevent overfishing is to develop better ways to protect fish populations. The maximum
sustained yield mathematical model is used, but indications are that it has hastened the collapse of most
commercially valuable stocks for several reasons.
B. Optimum sustained yield is a concept that takes into account interactions with other species and allows
more room for error. Another approach is multi-species management of a number of interaction species,
which accounts for competition and predator-prey interactions.
1. There has been limited management of several large marine systems, such as the Mediterranean Sea.
2. Many fisheries scientists and environmentalists are interested in using the precautionary principle for
management of fisheries and marine systems.
C. Some fishing communities regulate fish harvests on their own and others work with the government to
regulate them. Influx of large modern fishing boats and fleets has weakened the ability to regulate and
sustain local fisheries. Many community management systems are now co-managed, where community and
government work together to manage fisheries.
1. Central government sets quotas for various species and divides the quotas among communities.
2. Government may also limit fishing seasons and regulate gear to be used.
3. Each community then allocates its quota among members.
D. Government subsidies that are intended to keep businesses afloat can encourage overfishing.
E. Individual transfer rights (ITRs) are assigned to each fisherman, and these can then be bought, sold, or
leased like private property. This has resulted in some reduction of overfishing, but it is hard to enforce,
and wasteful bycatch has not been reduced.
F. Problems with the ITQ system are:
1. It transfers public ownership to private fishers, but still makes the public responsible for cost of
management and enforcement.
2. Small fishing vessels and companies may be squeezed out if they can’t afford to buy ITQs from others.
3. Fishing quotas are often set too high, so they leave 10–50% of the estimated MSY as a buffer to protect
the fishery from decline.
G. Individuals can help sustain aquatic diversity by demanding sustainably harvested seafood.
1. Labeling seafood would inform consumers.
11-4 How should we protect and sustain wetlands?
A. Coastal and inland wetlands are important reservoirs of aquatic biodiversity; they provide ecological and
1. Despite their value, the U.S. has lost more than half of its coastal and inland wetlands since 1900.
2. Wetland loss in the U.S. will get worse as global warming leads to rising sea levels, which will put many
coastal wetlands under water.
B. In the U.S., a federal permit is required to fill or deposit dredge material into many wetlands.
1. The U.S. federal policy is a zero net loss goal; mitigation banking allows destruction of some wetlands
as long as the same type of wetland is created elsewhere.
CASE STUDY: An ambitious restoration project is trying to undo the human damage in South Florida’s
Everglades. The natural Everglades is half its original size and is drying out, leaving it vulnerable to fire
and invasion by nonnative species. Everglades National Park was set up in the lower part of the Everglades,
but water didn’t flow into it and human activity caused disturbances. Ninety percent of the wading birds are
gone and other vertebrates are reduced in number by 75–95%. Florida Bay has become saltier and warmer
due to lack of water flow from the Everglades and the Kissimmee River. Loss of water flow and input from
crop fields and cities has caused large algal blooms on the bay.
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These blooms threaten coral reefs and hinder diving, fishing, and the tourist industry of the bay and the
Florida Keys. The U.S. Army Corp of Engineers has begun a restoration project funded by the state and the
federal government to restore the meandering river and flow of water to the Everglades. It has several
ambitious goals, which include restoring curving flow of more than half of the Kissimmee River, removing
250 miles of canals and levees south of Lake Okeechobee, buying 93 square miles of farmland and
allowing it to flood to create artificial marshes, creating a network of artificial marshes, creating 18 large
reservoirs to ensure water for south Florida’s present and future population and the lower Everglades, and
building new canals, reservoirs, and pumping stations to capture and return to the Everglades 80% of the
water flowing out to sea.
11-5 How can we protect and sustain freshwater lakes, rivers, and fisheries?
A. There are many threats to freshwater ecosystems, including habitat destruction, invasive species, and
CASE STUDY: Invasions by nonnative species have upset the ecological functioning of the Great Lakes
for decades, with more invaders coming. At least 162 nonnative species have invaded the Great Lakes since
the 1920s. Measures have been taken to control a number of these species. Sea lampreys are one of the
biggest threats and have depleted a number of the sport fish species in the lakes. Zebra mussels were
brought into the lakes in ballast and have become very aggressive pests since they have no known natural
enemies. They have displaced native mussel species, clogged pipes and piers, fouled beaches, and have
spread to other parts of the U.S. Quagga mussels invaded the Great Lakes in 1991 and Asian Carp may be
the next invader.
B. Rivers/streams are important ecological and economic resources, but they can be degraded by overfishing,
pollution, dams, and water withdrawal.
C. The Columbia River has been altered by 119 dams and withdrawal of water for agriculture.
D. To protect rivers and lakes from excess pollutants, watersheds need to be protected.
E. 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.
F. Congress established a three-tiered classification scheme:
1. Wild rivers are relatively inaccessible; they are not permitted to be widened, straightened, dredges,
filled or dammed.
2. Scenic rivers are free from dams, mostly undeveloped, of great scenic value, and accessible in some
places by roads.
3. Recreational rivers are readily accessible by roads and may have some dams or development along their
4. Only 0.2% of the 3.5 million miles of rivers are protected under the act.
G. Sustainable management of freshwater fish involves encouraging populations of commercial/sport fish
species, prevents overfishing, and reduces or eliminated less desirable fish populations.
11-6 What should our priorities be for sustaining biodiversity and ecosystem services?
A. There is evidence that the harmful effects of human activities on biodiversity can be reversed over the next
1. This must entail an ecosystem approach to protecting biodiversity.
Large Lecture Courses:
In what ways do our ordinary activities impact the aquatic environment? Explore this question with your
students, using a diagram of the hydrologic cycle for reference. Focus on households, the campus, and the
immediate environment. What activities lead to pollution or other alterations in these systems? What is the outcome
of such changes? Once you have exhausted the many effects of our mundane activities, begin to synthesize a list on
the board of ways that we could diminish our impact.
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Smaller Lecture Courses:
Assign your students to locate information on the web (the EPA is a good source) regarding water quality in
local streams, lakes, bays, etc. Each small group can take a particular body of water. Then, as a class, compare the
findings. Which waterways are cleanest? Which contain coliform bacteria? Now, looking at these waterways on a
map from Google Earth, stimulate the students to suggest reasons why the waters are either polluted or clean. Are
the local waters clean and well-managed?
Term Paper Research Topics
1. Food resources obtained from aquatic ecosystems
2. Resources (other than food) obtained from aquatic ecosystems
3. Damage caused by human activities in aquatic environments
4. Problems and solutions associated with overfishing
5. Strategies to protect marine environments
6. Ecological services of wetlands and wetland restoration projects
7. Wetlands protection
8. Prevention of beach erosion
9. Coastal cleanup strategies
10. Endangered species of the coast
11. What can be done to prevent coral bleaching?
1. What is the best way to manage coastal development to both provide protection and economic use of the
2. What is the value of wetland areas?
3. Is development of beachfront property for human recreation worth the potential danger from hazards
associated with the coastal environment?
4. Are developed countries exploiting the marine resources of developing countries?
5. Should the United States take a global leadership role in protecting marine ecosystems? Why or why not?
Activities and Projects
1. As a class field trip, visit a coastal area, managed lake, or wetland area. Invite a biologist/ecologist to explain
the processes taking place in the system. What specific methods are used to curb ecosystem damage in
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2. Invite a representative of an agency involved with aquatic system management to speak to the class about
issues regarding the agency’s impacts on the resource, the public’s benefit from the agency’s management, and
what the agency is doing to minimize the ecological impacts of their activities.
3. Consider the ecological problems that confront(ed) Lake Victoria in East Africa and the Great Lakes in the
United States. How are the factors that harm(ed) ecological diversity similar and how are they different? What
lessons can the United States learn from the devastation in Lake Victoria?
4. Are inland wetlands being drained and filled in your locale? Is there a nearby stream or river being subjected to
excessive levels of pollution? Is it feasible for you and your class to "adopt" one of these disturbed ecosystems
and help restore it to health?
5. Arrange a debate on the problems and alternatives of coastal zone management. Debate the proposition that we
should severely restrict engineering approaches to beach stabilization and adopt a "retreat from the beach"
strategy, emphasizing the preservation of coastal ecosystems and the ecosystem services they provide.
Attitudes and Values
1. Have you ever visited a developed seashore? How did you feel about the patterns of development? Do you
think this type of development should be allowed to continue?
2. What benefits do you receive from aquatic ecosystems where you live?
3. Where are the nearest locations in your area to go to observe aquatic ecosystems? What kinds of aquatic
ecosystems occur where you live?
4. What are your feelings toward aquatic ecosystems?
5. Do you feel that humans have the right to develop aquatic ecosystems in any way they wish? If not, what limits
do you see on human behavior toward aquatic ecosystems?
6. Do you use products that come from the ocean? Do the products you use result in destruction of, or the
continued sustainable use of, the ocean?
7. How do you feel when you see pictures of the beach erosion and economic loss following a hurricane?
Additional Video Resources
After the Storm (Documentary, free DVD or VHS)
Looks at watersheds and their importance in various parts of the U.S.
Blue Planet (Video Series from Discovery Channel, 2001)
Mammoth series, five years in the making, taking a look at the rich tapestry of life in the world's oceans.
Conserving America: The Wetlands (PBS, 1994)
A four-part series on American conservation of wetlands.
Planet Earth Series—Discovery Channel (TV Series)
Series contains excellent documentaries on major aquatic biomes.
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Ocean Oasis (Documentary, San Diego Natural History Museum, 2001)
Biodiversity in the Sea of Cortez, and the deserts of Baja.
We all Live Downstream (Documentary, 1991)
A look at pollution in the Mississippi River and the effects on human health.
Excellent information on a variety of aquatic issues.
Suggested Responses to Critical Thinking Questions
The following are examples of the material that should be contained in possible student answers to the end of
chapter Critical Thinking questions. They represent only a summary overview and serve to highlight the core
concepts that are addressed in the text. It should be anticipated that the students will provide more in-depth and
detailed responses to the questions depending on an individual instructor’s stated expectations.
1. Explain how introducing the Nile perch into Lake Victoria (Core Case Study) violated all four scientific
principles of sustainability.
The Nile Perch introduction into Lake Victoria violated all four principles of sustainability. Cichlids are
algae eaters whereas the perch are predatory carnivores, therefore the sun’s energy is not being utilized in
the most efficient way since the introduction of the perch. The biodiversity of the lake has been reduced
severely by the perch consuming and wiping out many of the cichlid species. The algae have increased due
to the lack of cichlids, and thus the nutrient recycling system in the lake has been detrimentally affected by
the perch. The lake has also been invaded by the water hyacinth, which has taken hold in this degraded
aquatic ecosystem. The perch numbers are now dropping because it has effectively eaten all of its available
food supplies, such as the cichlid. What is being seen is the typical “boom then bust” that is characteristic
of a population explosion and its aftermath.
2. What difference does it make that the introduction of the Nile perch into Lake Victoria (Core Case Study)
caused the extinction of more than 200 cichlid fish species? Explain.
The introduction of the Nile perch into Lake Victoria caused a massive disruption of the ecosystem of the
entire lake. The cichlid is intrinsically linked to many other parameters of maintaining a healthy, viable
aquatic ecosystem. Once the cichlid numbers decline this can cause the breakdown of the entire system.
3. What do you think are the three greatest threats to aquatic biodiversity? Why? Why are aquatic species
overall more vulnerable to premature extinction from human activities than terrestrial species are? Why is it
more difficult to identify and protect endangered marine species than to protect endangered species on
I think that three of the greatest threats to aquatic biodiversity are habitat destruction, increased pollution
from increasing population growth, and overharvesting. Aquatic species are more vulnerable to premature
extinction due to the delicate balance of marine and freshwater ecosystems. Small changes in pH or
temperature changes in the water can have a major affect on aquatic areas, for example, coral reefs and
fish-spawning grounds. Also, because we cannot actually “see” what is living under the surface of the
oceans, lakes, and seas, there is danger of harvesting species in numbers that exceed the maximum
sustainable yield. On the land, if you cut down a forest you can see that it has gone, but you cannot look
into the ocean and directly relate to the impact that overfishing is having as it is “hidden” from view. For
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this reason it is difficult to identify and monitor rare species in aquatic environments. Also, it is very
difficult to protect species that range over parts of the ocean that are not under the jurisdiction of any
4. Why do you think no-fishing marine reserves recover their biodiversity faster and more surely than do
areas where fishing is allowed but restricted?
The most obvious reason is that populations will grow faster when they are not being harvested from
outside of the system. There will always be predation, but harvesting adds another obstacle to the growth of
the population. Additionally, when fishing is allowed but restricted, it can be very difficult to monitor the
catch to make sure that it is in compliance with regulations.
5. Should fishers harvesting fish from a country’s publicly owned waters be required to pay the government
(taxpayers) fees for the fish they catch? Explain. If your livelihood depended on commercial fishing, would
you be for or against such fees?
I think that taking fish from publicly owned waters should be applicable for a tax or fee of some sort. The
money could be used for research and/or monitoring purposes. If I was a commercial fisherman I would
want my livelihood to continue. If charging fees meant that the fishing industry would become more
sustainable then I would be for it. The fees paid would be reflected in higher fish prices and may help
regulate the industry and keep fishing families who have been in the business for many generations from
going bankrupt or having to close their operations.
6. Why do you think that about half of all attempts to create new wetlands fail to replace lost wetlands? Give
three reasons why a constructed wetland might not provide the same level of ecological services as a
natural wetland. Do you agree with some ecologists’ argument that mitigation wetland banking should be
used only as a last resort? Explain.
Many attempts likely fail because of a flawed understanding of how to construct a complex ecosystem as
well as failure to follow up and monitor the progress of the restoration project. Constructed wetlands might
not provide the same level of ecological services as natural wetlands because the hydrology will not be the
same as the natural wetland, it is difficult to guide succession and direct what suite of species will
ultimately comprise the wetland, and the constructed wetland might not have the same substrate, such as
would allow water to seep into the water table or aquifer. Mitigation wetland banking should definitely be a
last resort. There are very few intact wetlands remaining, and they are very important ecologically. We are
not yet very effective at creating a landscape that will mimic the functions of an intact natural ecosystem,
so it is better to conserve the remaining wetlands where possible.
7. Do you think the plan for restoring Florida’s Everglades will succeed? Give three reasons why or why not.
No I do not believe the Everglades restoration project will work. The powerful political lobbying groups
will affect how elected state and federal officials view this issue, and the sugarcane and agriculture industry
will probably win out in the end. Secondly, a comprehensive plan has to be implemented about who gets
what in terms of the amount of water that is supplied to homes and industries, and how much they will have
to pay for it. Also, how much water gets redirected back into the Everglades ecosystem? This too has to be
established and followed through on. Third, a sustainable funding source must be established and
maintained for each step of the project in order for it to be successful. The money cannot come in fits and
starts depending on how much financial commitment there is from one year to the next.
8. Dams on some rivers provide inexpensive hydroelectric power, but they also disrupt aquatic ecosystems.
For example, production of hydroelectric power on the Columbia River has resulted in the degradation of
the river’s Pacific salmon population. Do you think the benefits of these dams justify the ecological damage
they cause? Explain. If you see this as a problem, describe a possible solution.
The disruption of ecosystem function for the generation of power is ill advised. We should direct our best
efforts toward energy conservation and toward developing technologies that have a minimal impact on the
100 Sustaining Aquatic Biodiversity
natural environment. It may be possible to direct some of the flow of a river toward turbines for electrical
generation, while at the same time allowing the aquatic ecosystem to continue to function.
9. Congratulations! You are in charge of protecting the world’s aquatic biodiversity and ecosystem services.
List the three most important points of your policy to accomplish this goal.
Monitor the health of the world’s aquatic ecosystems from a number of perspectives. One, perform a global
biodiversity inventory to be undertaken over several years, maybe even decades, and introduce measures to
protect vulnerable species. Second, conduct a thorough pollution monitoring and prevention program and
establish enforcement and monitoring measures to prevent further pollution of the aquatic ecosystems that
could lead to loss of biodiversity. Third, based on the results of the first two initiatives, global cooperation
and new legislation needs to be established to protect all aquatic life on earth.
10. List two questions that you would like to have answered as a result of reading this chapter.
Student answers will vary and provide a good starting point for class discussion.
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