Science 8
Fresh & Saltwater Systems
3.1-Diversity and Adaptations-Key
I can explain the diversity in water-based organisms and determine their adaptations.
Diversity in an ecosystem refers to the variety of species living in the area.
An ecosystem is any place on Earth where living things interact with other living and nonliving things.
Saltwater supports a larger diversity of living things than freshwater, for the oceans have a
greater number of different environments.
Freshwater Diversity
In freshwater
 Organisms may need to withstand cold temperatures (winter freeze-over) or low oxygen
conditions due to less water movement in lakes and ponds.
There are three zones (or layers)
1. Upper Zone:
 Lots of light, and many plants, insects, aquatic species.
2. Middle Zone:
 Low light and few plants.
 Phytoplankton is a large source of food.
3. Lowest Zone:
 No light or plants.
 Food is organic material that sinks down from the organisms above.
Saltwater Diversity
In moving water
Intertidal Zone-The shoreline of an ocean.
 A tough, changing environment.
 Organisms must be able to prevent dehydration when low tide draws all the water away
from them.
 Also these organisms must be able to resist the impact of waves or move to a hiding place
to avoid birds.
 Example: ____________________________
1
Science 8
Fresh & Saltwater Systems
In brackish water
Estuary- One of the most diverse and richest ecosystems.
 Areas where fresh and saltwater meet to form brackish water.
 Organisms must be able to withstand low to moderate levels of salt.
 Example: ____________________________
In warm water
Continental Shelf-Part of the continent that lies underwater directly off the shore.
 Water is warmer than in the ocean sea , and light goes through almost all the way to the
bottom.
 Example: ____________________________
In deep saltwater
The Oceanic zone: Deep ocean water past the continental shelf.
 Organisms must be able to find food in complete darkness.
 Example: ____________________________
It has three zones:
1. The upper part of the ocean (photic zone)
 This zone gets some sunlight so photosynthesis can occur and plants can grow there.
2. The middle part of the ocean (twilight zone)
 Some sunlight reaches this zone, but not enough for photosynthesis to occur.
3. The deepest part of the ocean (in figure included in the aphotic zone)
 It is very cold and completely dark.
 Water pressure is high.
 Fewer organisms than other zones.
2