Chapter 14 149
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ESTUARIES
Chapter Outline
PHYSICAL CHARACTERISTICS OF
ESTUARIES
Types of Estuaries
Salinity and Mixing Patterns
Salt Wedge Estuary
Maintaining Osmotic Balance
Osmoconformers
Osmoregulators
Remaining Stationary in a Changing
Environment
Estuaries as Nurseries
Animals of the Mud Flats
Seagrass Meadows
Seagrass Productivity
Seagrass Food Webs
Seagrass Meadows as Habitat
Mangrove Communities
Distribution of Mangrove Plants
Mangrove Root Systems
Mangal Productivity
Mangroves as Habitat
LAGOONS
Chapter Objectives
• Describe the general characteristics of estuaries and their mixing patterns.
• Identify the major adaptations of life to living in an estuary.
Key Terms
estuary
embayment
coastal plain estuary
bar-built estuary
tidal overmixing
positive estuary
pseudofeces
osmoregulators
osmoconformers
Chapter Summary
1. Estuaries form in embayments where freshwater from rivers and streams mix with
2. The mixing of nutrients from freshwater and seawater that occurs in estuaries, along
with plentiful sunlight, makes these areas some of the most productive in the marine
3. Animals that live in estuaries must be able to adapt to changing salinity. Remaining
4. Because estuaries are highly productive and relatively protected from wave action,
they make good nurseries for the juveniles and young of many species. Estuaries
support a variety of distinct communities that include oyster reefs, mud flats, sea
Chapter 14 151
Chapter Outline
I. Physical Characteristics of Estuaries
A. Types of estuaries.
B. Salinity and mixing patterns.
1. Salt-wedge estuary.
C. Temperature.
II. Estuarine Productivity
III. Life in an Estuary
A. Maintaining osmotic balance.
1. Osmoconformers.
IV. Estuarine Communities
A. Oyster reefs.
B. Mud flats.
1. Mud-flat food webs.
V. Wetlands
A. Salt marsh communities.
1. Ecology and the marine environment: predation regulates benthic population size.
B. Mangrove communities.
1. Distribution of mangrove plants.
VI. Lagoons
152 Estuaries
Suggestions for Presenting the Material
1. A field trip to a local wetland can provide an invaluable learning opportunity for recognizing
firsthand the local organisms and observing their behavioral responses to tidal change.
2. How many acres of wetlands have been lost in your state? Have students research and
3. Use Google Earth to view representative wetland habitats (e.g., Chesapeake Bay, MD;
4. Have students create a concept map using estuarine communities as the starting point that
Classroom Discussion Ideas
1. What ecological role do bacteria play in estuarine habitats?
2. What human activities can decrease the species richness and diversity found in a
temperate salt marsh?
3. What is considered the base of the estuarine food chain? How is this different from
strictly terrestrial ecosystems?
4. In a salt-wedge estuary, how does invertebrate species diversity change over a tidal
cycle from the mouth of a river to the ocean?
Videos, Animations, and Websites
Videos
Estuaries Video Gallery.
Government site with short clips detailing estuary expeditions, science, and research.
Animations
Classifying Estuaries by Water Circulation. (NOAA)
Classifying Estuaries by Geology. (NOAA)
A series of animations on different types of estuaries by geology.
Websites
National Wildlife Federation’s Wetland Information.
Teacher’s Domain: Intertidal Zone.
Background information on eastern seaboard salt marsh ecosystems, and a short video
segment from the NOVA episode, “The Sea Behind the Dunes.”
Restore America’s Estuaries.
National organization dedicated to preserving the country’s network of estuaries
Dead Zones—Teach Ocean Science.
A site with figures and animations detailing the issue of dead zones within estuaries
using case studies.
Suggested Answers to End of Chapter Questions
Multiple Choice
1. b. uniform
2. c. salinity
Matching
1. d.
6. e.
Short Answer
1. What are the distinguishing characteristics of an estuary?
The distinguishing characteristics of an estuary are: regions where freshwater
2. What is a salt-wedge estuary, and how does it differ from other types of estuaries?
A salt-wedge estuary forms at the mouth of a river flowing into seawater. The
3. What factor(s) contributes to the productivity of estuaries?
Estuarine productivity is influenced by both the amount and the quality of
4. What adaptations have evolved in mangroves that help them survive in their habitat?
Adaptations of mangroves that help them survive in their habitat include: shallow,
5. Explain how organisms that are osmoconformers survive in estuaries.
6. Explain how fiddler crabs are well adapted to life in the salt marsh.
Fiddler crabs are well adapted to life in the salt marsh because they can withstand
7. Describe the process of succession in a salt marsh.
Marsh succession proceeds in the following sequence. First, marsh plants trap
8. Compare a lagoon with an estuary.
Lagoons are partially isolated from the ocean by sand or other sediments, whereas
9. Sketch a chart that traces energy flow in a mud flat.
10. What important roles do wetlands play?
Important roles of wetlands include: habitat for shorebirds and migratory birds,
Thinking Critically
1. Why is it difficult for burrowing animals that exchange gas through their skin to
survive in mud flats?
Mud flats typically consist of a shallow layer of oxygenated sediment overlaying
2. Predict what effect agricultural runoff would have on a neighboring estuary.
Agricultural runoff is usually high in nutrients, which can cause eutrophication in
3. To control flooding, a series of dams is constructed along a river that feeds a large
estuary. What effect do you think the dams will have on the estuary’s productivity?
Upstream dams trap sediments and organic matter that normally would be
4. What effect would a hurricane likely have on the animal life in an estuary? Explain
your answer.
A hurricane could cause a number of different effects on animal life in an estuary.
Hurricane flooding can smother estuarine vegetation under a thick layer of
Suggested InfoTrac® Articles
“Salt Marshes under Siege.” Bertness, B., R. Sillman, and R. Jeffries. American Scientist,
(2004).