Lecture 7 - Tropical Ecosystems Flashcards
When have corals been present since?
The Ordovician period.
What corals are reefs dominated by?
Scleractinian corals (hard, reef-forming, stony corals that lay down skeleton)
How old is the Great Barrier Reef?
0.5 million years old
What are the two classes of corals?
- Hermatypic (reef-building)
- Ahermatypic (non reef-building)
How do cnidarians feed?
Catch food with nematocysts in tentacles and pass to the central mouth.
Describe coral growth.
The polyp constantly moves upwards, secreting a calcium carbonate skeleton behind it.
How many dinoflagellate cells are there per unit squared of a coral?
1 million
What are zooxanthellae?
Unicellular dinoflagellates taken up by the coral and hosted in the surface tissue
Describe the role of zooxanthellae.
- Fix CO2
- Provide up to 90% of energy to coral in return for protection and nutrients.
Where are corals found?
30 degrees North and South
What are some requirements for corals?
- Require clear water less than 50m, to ensure photosynthesis is possible
- Temperatures 18-36 degrees
- Full salinity water (33-35ppt)
- Hard substrate
What is the optimum temperature for corals?
26-28 degrees
Why is coral biomass low at the West Coast of Southern Africa?
Very intense upwelling, giving cold water and thus low coral density.
How do corals reproduce?
Asexually by budding.
How do corals disperse long distances?
By planulae via sexual reproduction.
Release buoyant eggs and sperm.
Give the three sexual categories of corals.
- Gonochoric (male or female)
- Simultaneous hermaphrodites (produce both eggs and sperm)
- Sequential hermaphrodites (produce eggs for a while, and then sperm)
Give the four stage life cycle of corals.
1) 1-3 day larval stage
2) settlement to hard rock
3) Metamorphosis and secretion of the basal plate
4) Zooxanthellae acquisition
Describe the work of Charles Darwin.
Wrote a book on reefs before Origin of Species; noticed that not all corals were the same, and could form different structures.
Name and describe three different coral reefs.
- Fringing reefs; corals growing on the edge of an island.
- Barrier reefs; lagoon between reef and edge of the island.
- Atoll; rings of corals growing out of the depths.
When do corals form fringing reefs?
On young land masses, where corals establish themselves on the edges of islands
When do barrier reefs form?
When islands sink back into the sea, and coral continues to grow upwards forming sand-filled lagoons
When are atolls formed?
When islands sink below the sea altogether.
What is the typical net growth rate of coral?
3mm per year
How much do individual corals grow per year?
20cm per year
