1. 4.5 Aquatic Ecosystems

2. Conditions Underwater
What factors affect life in aquatic ecosystems?

3. Conditions Underwater
What factors affect life in aquatic ecosystems?
Aquatic organisms are affected primarily by
water’s depth
Temperature
Flow
amount of dissolved nutrients. PH

4. Water Depth
Water depth strongly influences aquatic life because sunlight penetrates only a relatively short distance through water.

5. Light in Aquatic Ecosystems
Divided into 2 zones: photic and aphotic

6. Water Depth
Photosynthetic algae, called phytoplankton, live in the photic zone.
Zooplankton—tiny free-floating animals—eat phytoplankton. This is the first step in many aquatic food webs.

7. Light in Aquatic Ecosystems
Photic Zone
Aphotic Zone
The photic zone is the region where light is able to penetrate
Producers can live here
Photosynthesis happens here
The aphotic zone is the region where light is NOT able to penetrate
Producers cannot live here because photosynthesis cannot occur
Chemosynthesis occurs instead

8. Water Depth
Many aquatic organisms live on, or in, rocks and sediments on the bottoms of lakes, streams, and oceans.
These organisms are called the benthos, and their habitat is the benthic zone.
When the water is shallow enough for the benthic zone to be within the photic zone, algae and rooted aquatic plants can grow.
When the benthic zone is below the photic zone, chemosynthetic autotrophs are the only primary producers.

9. Temperature and Currents
Aquatic habitats are warmer near the equator and colder near the poles.
Temperature in aquatic habitats also often varies with depth. The deepest parts of lakes and oceans are usually colder than surface waters.
Currents in lakes and oceans can dramatically affect water temperature because they can carry water that is significantly warmer or cooler than would be typical for any given latitude, depth, or distance from shore.

10. Nutrient Availability
Organisms need certain substances to live, such as oxygen, nitrogen, potassium, and phosphorus.
The amount of dissolved gases in seawater depends on the type of life forms (plans and animals) that are present.
Lots of plants = Lots of Oxygen
Few plants = Lots of carbon dioxide

11. Nutrients in Aquatic Ecosystems
Plants need nutrients to live:
Phosphorous
Nitrogen
These nutrients are found in animal feces, which sinks to the bottom of the ocean
The majority of nitrogen and phosphorous nutrients are found in the deep and only come to top during upwelling

12. Freshwater Ecosystems
What are the major categories of freshwater ecosystems?

13. Freshwater Ecosystems
What are the major categories of freshwater ecosystems?
Freshwater ecosystems can be divided into three main categories: rivers and streams, lakes and ponds, and freshwater wetlands (marshes and swamps)
Defined by relatively shallow water and damp soil.

14. Estuaries
Why are estuaries so important?

15. Estuaries Why are estuaries so important?
Estuaries serve as spawning and nursery grounds for many ecologically and commercially important fish and shellfish species including bluefish, striped bass, shrimp, and crabs.
An estuary is a special kind of wetland, formed where a river (fresh water) meets the sea (salt water).
Estuaries contain a mixture of fresh water and salt water, and are affected by the rise and fall of ocean tides.
Many are shallow, which means that enough sunlight reaches the benthos to power photosynthesis.

16. Salinity Changes in the Ocean
If there is more evaporation (drying) than precipitation (rain) then the salinity increases.
Since salt is not evaporated into the atmosphere.
If there is more precipitation (rain) than evaporation (drying) then the salinity decreases.

17. Salinity Chnages
The thawing of large icebergs (made of frozen fresh water and lacking any salt) will decrease the salinity while the actual freezing of seawater will increase the salinity temporarily

18. Marine Ecosystems
How do ecologists usually classify marine ecosystems?
Ecologists typically divide the ocean into zones based on depth and distance from shore.

19. Marine Ecosystems
How do ecologists usually classify marine ecosystems?

20. Marine Ecosystems
Ecologists typically divide the ocean into zones based on depth and distance from shore.
Starting with the shallowest and closest to land, marine ecosystems include the intertidal zone, the coastal ocean, and the open ocean.

21. Marine Ecosystems
This diagram shows the different zones in an ocean.

22. Intertidal Zone
Organisms in the intertidal zone are submerged in seawater at high tide and exposed to air and sunlight at low tide.
These organisms are subjected to regular and extreme changes in temperature and are often battered by waves and currents.

23. Coastal Ocean
The coastal ocean extends from the low-tide mark to the outer edge of the continental shelf—the relatively shallow border that surrounds the continents.

24. Coastal Ocean
Water in the coastal ocean is brightly lit, and is often supplied with nutrients by freshwater runoff from land. As a result, coastal oceans tend to be highly productive.
Kelp forests and coral reefs are two important coastal communities.

25. Examples:

26. Jill made the table below during her research on aquatic zones and living organisms.
Characteristics of Aquatic Zones:
Intertidal
Air, sun and water exposure; crashing waves
Neritic
Water depth less than 200 m; lots of sunlight; warm water
Benthic
Very deep water; no light; cold water except near thermal vents that emit heat and chemicals.

27. Based on Jill’s observations, which conclusion could you draw?
A. Organisms in the intertidal zone must be able to withstand very cold water. B. There are no producers in the benthic zone that rely on photosynthesis. C. Organisms in the benthic zone must be able to tolerate large amounts of oxygen. D. The warm water and abundant sunlight in the nertic zone limits the plankton population.

28. Answer: B

29. The pH of the water in several lakes in Norway and Sweden had decreased to below 5.0 due to an increase in acid rain. Which of the following is most likely to happen in these lakes? 
A. the decline of several fish populations.
B. an increase in numbers of fish
C. an increase in the amount of primary producers
D. increased predator-prey relationships

30. Answer: A.
the decline of several fish populations Fish are sensitive to changes in pH and would experience a decrease in numbers if a shift in the pH of the water occurred.

31. Why are there so few aquatic plants and phytoplankton that live at the bottom zones in the ocean?
A. The ocean floor contains many decomposers.
B. Most sunlight is absorbed before reaching these levels. 
C. Water is a limiting factor.
D. The temperature in these zones is extremely low.

32. Answer: B.
Most sunlight is absorbed before reaching these levels. Plants and phytoplankton are primary producers that rely on the sun to carry out photosynthesis. The bottom zones of the ocean have little to no light.