Week 6 Lecture Notes - Oct. 4

(Outlines were collected and a quiz was given.)

 

Aquatic ecosystems found in the tropics

Increase diversity of tropics, because of additional habitats not found inland.

Rivers
Largest by volume river is Amazon.

16% of all river water flows through its delta which is 200 miles wide.

Andes – what happens in the mountains affects the river and ocean.

What happens upstream affects the downstream regions.

Deforestation on a mountain increases

• Erosion
• Silt in rivers which smothers fish and eggs, ends up in ocean.
• Sunlight on the river – therefore warms the water.

Warmer water holds less oxygen, therefore kills fish (cooler water holds more oxygen).

Delta = Where the river flows into the sea.

Wet dry season in the tropics, therefore there is an annual flood cycle.

Flooding -
Disperses sediment which fertilizes the floodplain = The land adjacent to a river that floods when the river is high.

Usually a floodplain has fertile soil since this is where the sediment is deposited.


Riverine ecosystems
The river channel itself.

The river carries sediment = the soil material carried by a river – may be sand, clay, silt (mud).

This sediment is deposited in various places. 

Too much in the river is bad – it smothers fish eggs, predators can’t see to hunt, reduces light that penetrates into the water.  As we will see, coral reefs need sunlight.

Riparian edge = the land along the edge of a river, formed by the sediment being deposited.

A buffer of vegetation protects the water from silt running off the land.

Oxbow lake = a lake formed when a stream cuts a new channel which cuts off and isolates a bend.

Sandbar = a landform in a body of water created from a deposit of sand.  (See figures from book)

Goes through the stages of succession also:

1. First it forms.
2. Plant seeds blow in or wash in and colonize the sand bar.
3. This stabilizes the sandbar.
4. Forms a community of vegetation, more sand accumulates, and eventually becomes an island.

Mangroves = trees that are ecologically restricted to tropical tidal areas.

• Grow along coasts where salt water intrudes into fresh.
• 34 species of trees throughout the world live in mangroves.
• Neotropics have only 8 species (see those listed in the paper).
• They form pure or low species rich stands
• Reproduce by viviparity (live birth) rather than seeds = making new plants from off-shoots.
• Aerial roots
• Tolerate high salt water.
• Protect the interior from hurricanes.

Coral reefs (ch. 11 neotropics, ch 12 trop eco) – a colony of coral polyps

• Confined to waters >20C (68F).
• Grow 1 to 3 cm (0.39 to 1.2 in) per year, and
• Grow vertically 1 to 25 cm (0.39 to 9.8 in) per year
• Grow only at depths shallower than 150 m (490 ft) because of their need for sunlight

What is a coral?  An animal like jellyfish & sea anemones, housed in a calcium carbonate shell that it creates.  Has tentacles to capture food.  Live in colonies that we see as coral reef.

Where are the plants in a coral reef? 

Zooxanthellae = Microscopic plants live among the coral, photosynthesizing.  The coral relies on the plants for nutrients and oxygen.  The plants rely on the coral for shelter.

See slides.

The coral reef builds on itself, the living part is the top layer.

Why are coral reefs important?

• High species richness.
• Home for 25% of all marine species, yet occupy 0.1% of the world’s ocean surface.
• FISH!  FOOD FOR PEOPLE.
• Protect the shoreline from pounding waves.

What damages coral reefs?

1. Runoff from the land, therefore deforestation
2. Pollution
3. Silt
• This smothers the algae and the coral
• Makes the water turbid
• Algae can’t photosynthesize and the coral dies
4. Overfishing & harvest aquarium fish
• almost no food fish of reproductive age remain on Haiti's reefs
5. Climate changes – if sea levels rise, it will be too deep for them, the algae need sunlight.