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
How much limestone a year can coral reefs deposit?
4,200 tons of limestone per km per year
What are the two sources of coral erosion?
- Physical; e.g. hurricanes, storms, tidal effects.
- Grazing; parrotfish, urchins and boring by sponges and bivalves.
How much more surface area do corals provide compared to a seabed?
15% more
What percentage of marine species do coral reefs provide ecological niches for?
25%
How many reef building corals are there?
About 800
Give four theories for the coral triangle.
- Centre of origin; lots of new species evolving, and gradually spread away from centre.
- Centre of overlap; species evolving all over Pacific Ocean, but where species overlap we have the highest number of species.
- Centre of survival/refuge
- Centre of accumulation; diverse habitat, and over time species accumulate in the area.
How many species of fish can be found in the Coral Triangle?
2,000
What did studies show on the coral triangle?
- Older populations closer to the coral triangle
- Youngest populations found further away from the triangle
- Therefore is the centre of origin or refuge.
How much a year do coral reefs provide in ecosystem goods and services?
$375 billion per year
How many people rely on reefs for food and livelihoods?
500 million people.
Why are reefs important ecologically?
- Act as a buffer zone between land and sea, providing coastal protection from the power of the ocean.
- Play role in waste processing, through uptake of CO2 and removal of nutrients from the water.
If present rate of destruction continues, what percentage of the world’s reefs will be destroyed by 2050?
70%
What percent of the world’s coral reefs are threatened by human activities at the local level?
60%
When coupled with global threats, what percentage of the world’s reefs are threatened?
75%
What are the only true marine angiosperms?
Seagrasses
How long have seagrasses been around?
100 million years
Explain the role of seagrasses.
- Have a rhizome and root system
- Fix nitrogen and stabilise soft sediments.
Why are seagrasses so important?
Important for coastal protection, through stabilisation of mobile sediment.
What depth can seagrasses be found?
From intertidal to 10m
How many shoots per metre squared do seagrasses produce?
1,200
What are mangroves?
Trees or shrubs that form extensive mangals in high salinity waters.
Give the three types of mangrove.
- Riverine
- Tide-dominated
- Basin
How do mangroves obtain oxygen?
From lenticles in aerial / knee roots.
What are pneumatophore roots?
Roots that stick up out of the sand/mud.
Name the seagrass species that can excuse salt uptake by roots.
Avecinnia
Describe a method that seagrasses are adapted to cope with high salinities.
Excreting excess salt in bark or leaves.
How are mangroves adapted to cope with high temperatures?
Leaves are held at angles to the sun to avoid excess transpiration.
Can regulate temperature of the leaves.
