1. Chapter 6
Aquatic Life Zones

2. Major Factors in Aquatic Ecosystems
Temperature
decreases with depth
affects dissolved gases, rates of chemical reactions, & where organisms can live
Light (solar radiation)
essential for photosynthesis
Nutrient availability
limiting macronutrients: Phosphorus & Nitrogen
limiting micronutrients include Iron
essential for growth of phytoplankton
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3. Major Factors in Aquatic Ecosystems
Dissolved carbon dioxide
essential for growth of phytoplankton
varies with temperature, producers, & consumers
Dissolved oxygen
essential for respiration of organisms
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4. Properties of Water liquid over wide temperature range
high heat content
only natural substance on Earth that can be found in all 3 states: solid, liquid, and gas
dissolves a wide variety of compounds
high surface tension, high wetting ability, strong capillary action
maximum density at 4º C
expands when freezes
hydrogen bonding determines many of unique properties
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5. Saltwater Ecosystems Oceans cover 71% of Earth’s surface
ocean currents distribute solar energy (heat)
reservoir for CO2
regulates temperature of troposphere
habitat for plants & animals
critical food source for humans
communal dumping ground
Fig. 6–21
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6. Ocean Life Zones defined by amount of solar radiation
zones (in order of declining solar radiation):
euphotic zone (lots of light – photosynthesis)
bathyal zone (some light – twilight)
abyssal zone (darkness)
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8. Coastal Zones Extend from high–tide mark to edge of continental shelf
Entirely within the euphotic zone & include estuaries, wetlands, barrier islands, & coral reefs
Nutrient–rich
High primary productivity: sunlight + nutrients from land, upwelling, & ocean currents
Sites of most commercial fisheries
(see Fig. 6–22)
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10. Estuary
Where salt water mixes with freshwater from land, generally at mouth of a river
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11. Coastal Wetland
Area of coastal land covered all or part of the year with salt water

12. Estuaries & Coastal Wetlands
Importance:
Nutrient-rich
High primary productivity
Nurseries for fish & other aquatic animals
Breeding areas for waterfowl & shorebirds
Filter water pollutants
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13. Estuaries & Coastal Wetlands
Human Impacts:
World has lost over half of its estuaries & coastal wetlands
Percentage lost in U.S. higher; most lost to coastal development
Degradation due to urban runoff, sewage effluent, sediment & chemical runoff from agricultural lands
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14. Think About It
40% of the world’s population live along coasts or within 62 miles of a coast
13 of 19 megacities (pop. >10 million) are in coastal zones
By 2030, at least 6.3 billion people will live in or near coastal areas

15. Barrier Islands
Long, low offshore islands of sand that run parallel to the shore
Importance
Protect mainland from storms
Shelter bays, estuaries, & wetlands
Recreation & residential areas
Fig. 6–26
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16. Where do we have barrier islands near us?

20. Avalon
Stone Harbor

21. Barrier Islands Human Impacts: Development
destroys dunes & dune vegetation
causes beach erosion
destroys or degrades wildlife habitat, like nesting birds
Protection
jetties & seawalls
beach replenishment
replanting dune vegetation
controlling development
© Brooks/Cole Publishing Company / ITP

22. Barrier Islands are Dynamic
After a hurricane in 1933, the U.S. Army Corps of Engineers constructed two jetties
Assateague Island has changed dramatically since the construction

23. Human Efforts to Stop Erosion
Jetties, seawalls, and beach replenishment are usually just temporary fixes

24. Coral Reefs What Are Coral Reefs?
located in coastal zones of tropical oceans
formed by mutualism between polyps & algae
polyps secrete hard limestone deposits that remain when polyps die
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25. Coral Reefs Importance:
high biodiversity, like “tropical rain forests of ocean”
protect coastlines from storms & high waves
nurseries for many fish species
disappearing
Fig. 6–29

26. Coral Reefs Vulnerability: slow growing easily disturbed
thrive only in clear water
Human Impacts:
sediment runoff & effluent
increased UV radiation
fishing with cyanide & dynamite
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27. Coral Reef Distribution

28. Nutrients in Lakes

29. Nutrients in Lakes Oligotrophic – poorly nourished
oligo (small, little, few)
trophe (nutrients, food)
Deep
Clear water
Very little life
Low productivity
High in oxygen

32. Nutrients in Lakes Eutrophic – well-nourished eu (good, well)
trophe (nutrients, food)
Shallow
Murky water
Lots of algae
High productivity
Low in oxygen

35. Nutrients in Lakes Mesotrophic – in between oligotrophic and eutrophic
mesos (middle, intermediate)
trophe (nutrients, food)

36. Nutrients in Lakes

37. DEAD ZONE As more algae and plants grow, others die.
This dead organic matter becomes food for bacteria that decompose it.
With more food available, the bacteria increase in number and use up the dissolved oxygen in the water.
When the dissolved oxygen content decreases, many fish and aquatic insects cannot survive.
This results in a dead area.

39. Runoff
Video