Lecture 6- Coral Reefs Flashcards
What is a coral reef?
-An ecological association of corals and other tropical organisms
What are coral reefs made of?
-corals secrete calcium carbonate= chemical that hardens the exoskeleton= that is responsible for the reef structure
In what latitudes can coral reefs occur?
30 S to 30 N
What is the primary network for the coral reef?
-coral -some coralline algae
What is a coral reef and coral community?
-reef= the landform, the rocky area -community= the wider interaction of the landform and the organisms living there (fish, predators etc)
How can the reef change the environment?
-by growing vertically and laterally
What are coral reefs composed of?
-variety of sediments, formed by the corals, have different species, they die and sediment can be transported
What is the far reef area?
-deeper area of the ocean, hard to penetrate the deep water, protected from wave breaking
What is the reef front?
-the waves start shoaling here, more shallow type corals
What is the reef crest?
-highest point on the reef, this is where the waves break , high wave energy,
What is the reef flat?
-largest part of the reef, flat bit
What is the lagoon?(back reef)
-basin or central area, low energy, only type of circulation are from waves that get over the reef crest -the reef is a circle sort of
Is there a relationship between the wave energy and the type of coral growing in that area?
-yes, affects its morphology -even the same species will look very different depending on where it is on the reef
What sort of coral is there on the lower reef slope (far reef)?
- not that much light= BRANCHING coral, not much wave energy so can be thinner -tries to get as much light as possible so almost flat sometimes (like a pancake)
What sort of coral is there on the upper reef slope?
-main change in coral is that it is more dense= response to increase in wave energy -shorter
What sort of coral is there on the reef flat?
-waves breaking, shallow water,= coral is compact, grows large laterally fue to lot of light
What sort of coral is there on the back reef?
-can become thin and branching
What sort of coral is there in the lagoon?
-= more branching and thinner -more light available and less wave energy
Where is the reef outer slope and what are its characteristics?
-Beneath the limit of waves and light -Generally very steep, extending from below the limit of reef growth often to the sea floor -Differences between reefs depend on length of the slope, which in turn is affected by the depth of sea floor the reefs are developed on.
What is the upper limit of the reef outer slope characterised by and how do these form?
over hangs and caverns -these are related to multiple sea level cycles and evolution of reef systems –when sea lower and reef is exposed because it is made of calcium carbonate= then wind and rain fall and interacts with water= slightly acidic= weathers down the rock= karstified, then sea becomes higher level= then these caves are flooded -coral re-establishes itself -this cycle occurs over long time periods 100ka -the morphology of reefs today is a result of this form habiatats
What are some examples of reefs with long reef slopes?
-Great Barrier Reef has some stepped outer slopes relating to lower sea level reefs —-e.g. Bikini Atoll outer slope descends to 3.6 ␣ 4.5 km at 46 and 36o respectively —–e.g. Mururoa Atoll outer slope averages 45o from 20 ␣ 500 m depth, then decreases to 30-35o in north & 15-25o in south. Difference related to wind direction.
What is the spur and groove zone?
-Reefward edge of outer slope often has grooves shallowing in a reefal direction -These grooves link into the active spur & groove zone -Major feature in moving water & sediment from the reef crest into deep water -drain water into the ocean –groove= troph
How long and deep can grooves be?
-often 15- 30 m long, 1 -3 m wide, 2- 4 m deep (Bikini Atoll)
What are spurs?
-Spurs occur between grooves and are where wave breaking is concentrated
