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Chapter 7 Aquatic Ecosystems
Section 1 Key Terms
1. Wetland – land that is periodically underwater or whose soil contains a great deal of moisture
2. Plankton – mass of mostly microscopic organisms that float or drift freely in the waters of aquatic
environments
3. Nekton – all organisms that swim actively in open water, independent of currents
4. Benthos – organisms that live at the bottom of oceans or bodies of fresh water
5. Littoral zone – a shallow zone in a freshwater habitat where light reaches the bottom and nurtures
plants
6. Benthic zone – the bottom region of oceans and bodies of fresh water
7. Eutrophication – an increase in the amount of nutrients, such as nitrates from fertilizer, in a marine or
aquatic ecosystem
Section 1 Review Questions
1. List two factors that determine where an organism lives in an aquatic ecosystem. Answers may vary.
On sample answer are temperature and nutrients, others are sunlight, oxygen
2. Compare the littoral zone of a lake with the benthic zone of a lake. The littoral zone exists in shallow,
sunlit water, while the benthic zone occupies the dark bottom of a lake or pond
3. List two environmental functions that wetlands provide. How do these functions affect you?
Wetlands trap and filter pollutants, which improves water quality downstream. Wetlands also absorb
excess water and reduce the likelihood of a flood. Wetlands buffer shorelines against erosion.
Wetlands provide habitat for rare, threatened, and endangered species. The also provide recreational
areas for activities such as watching, hiking, canoeing, photography and painting.
4. Describe one threat against river ecosystems. Answers will vary. One threat is Sewage dumping.
Runoff from the land can put pesticides and other poisons into rivers. Dams alter the ecosystems in
and around a river. People take water from the rivers to use in homes and manufacturing.
5. A piece of garbage that is thrown into a stream may end up in a river or an ocean. What effects
might one piece of garbage have on an aquatic ecosystem? What effects might 100 pieces of
garbage have on an aquatic ecosystem? Answers will vary. In general, more garbage will have more
of a harmful effect on the ecosystem
6. Write a short paragraph that explains how fertilizing your yard and applying pesticides can affect the
health of a river ecosystem. Rain can wash fertilizers and pesticides off my yard and into a river.
Fertilizers can cause an increase in plant growth or and algal bloom. Pesticides can kill plants and
animals in the river.
Section 2 Key Terms
1. Estuary – an area where fresh water from rivers mixes with salt water form the ocean; the part of a
river where the tides meet the river current
2. Salt marsh – a maritime habitat characterized by grasses, sedges, and other plants that have adapted
to continual, periodic flooding; salt marshes are found primarily throughout the temperate and
subarctic regions
3. mangrove swamp – a tropical or subtropical marine swamp that is characterized by the abundance of
low to tall trees, especially mangrove trees.
4. Barrier island – a long ridge of sand or narrow island that lies parallel to the shore
5. Coral reef – a limestone ridge found in tropical climates and composed of coral fragments that are
deposited around organic remains
Section 2 Review Questions
1. Explain why estuaries are very productive ecosystem. Why are estuaries vulnerable to the effects of
pollution? Estuaries are very productive because they constantly receive nutrients from rivers and for
the ocean. Estuaries are vulnerable to pollution because ocean, lake, and river pollutants enter and
because dense human settlements surround most estuaries.
2. Compare salt marshes with mangrove swamps. Salt marshes are dominated by marsh grasses and
develop in estuaries, while mangrove swamps are dominated by mangrove trees and develop in
tropical and subtropical areas.
3. Describe two factors that can damage coral reefs. Water that is too hot or cold can damage reefs by
killing corals. Muddy water can kill the algae that live within corals.
4. List two ways in which animals of the oceans are threatened. Overfishing is destroying some fish
populations, and trawl nets can entangle and drown marine mammals, such as sea lions. Some ships
illegally discard fishing lines and nets into the ocean where they strangle and kill animals
5. Suppose that the sea level suddenly rose by 100 m. What would happen to the world’s coral reefs?
Explain. A 100 m rise in sea level would kill off most of the world’s coral reef ecosystems, because the
algae in coral s need water shallow enough to allow sufficient light through for photosynthesis.
6. Explain why cities are often built on estuaries. How would building a city on an estuary affect the
plants and animals living in the estuary? Cities are often built on estuaries because estuaries provide
protected harbors, access to the ocean and connection to a river. Building a city on an estuary would
reduce populations of many animals through fishing and pollution.