Dynamic Surface L6 Flashcards
What is a reef?
A biologically influenced carbonate accumulation which possessed topographic relief during its growth.
Are all reefs built by corals - how do we know this?
No - corals are absent from many pre Caenozoic examples
What is the geological time scale of tabulate and rugose corals and what did they secrete?
Ordovician-Permian range
Calcite
What order to modern corals belong to?
Scleractinia
What do modern corals secrete?
Aragonite
When did modern corals arise?
The Mid Triassic
What do shallow water Scleractinia contain as a part of a symbiotic relationship and what do they need to survive?
Xooxanthellae - photosynthetic dinoflagellates
Need light to survive (the photic zone)
What type of modern corals are vulnerable to ocean acidification and why?
Deep, cold water corals are more vulnerable to ocean acidification than tropical corals as deep ocean water has a lower pH
When did the stromatolites first appear?
The Archean
How did stromatolites form reefs?
Stromatolites form algal mats that colonise sediment surfaces which can build up large structures
When do rugose and tabulate corals first appear?
Ordovician
When do stromatoporoids first appear?
Ordovician
What do stromatoporoids secrete?
Calcite
When did the stromatoporoids become extinct?
Devonian
When do rudists first appear and what order to they belong to?
Rudists are bivalves and first appear in the Cretaceous
What are skeletal/framework reefs?
Living colonies that form topographic highs, usually forming at the edge of continental margins and isolated platforms
What are 4 types of skeletal/framework reefs?
Fringing reef
Barrier reef
Submerged shelf-edge reef
Atoll reef
Where are fringing reefs found?
Fringing reefs are attached to continents and exist in the intertidal zone
Where are barrier reefs found?
Barrier reefs are separated from land by an area of shallow water
Where are submerged shelf-edge reefs found?
Found on continental shelf edges
What is an atoll reef?
A reef located on sea mounts and isolated platforms
What is the difference between a reef mound and a skeletal reef?
Reef mounds don’t have a living framework unlike skeletal reefs
How is a reef mound formed?
Calcareous material (algal remains, coral remains etc) is swept together by currents and tides into heaps which are held together by algal mats.
When have reef mounds been frequent in geological history?
At times of high sea level
What organisms have dominated frame-built reefs throughout Earth’s history?
Corals
Stromatolites
Stromatoporoids
Algaes
What organisms primarily form reef mounds?
Bryozoans
Sponges
Crinoids
What type of organisms form mud mounds?
Microbial mats
What do rugose corals secrete?
Calcite
Are rugose corals colonial or solitary
Solitary
Are tabulate corals colonial or solitary?
Colonial
What to tabulate corals secrete?
Calcite
Why are stromatoporoid reefs able to deflect wave energy so effectively?
Due to their rounded dome structure
Why does the back reef area contain more delicate organisms not found elsewhere on the reef?
The reef front protects the back reef against wave action
What are 5 destructive processes that affect reefs?
Physical
Biological
Sedimentation
Cementation
Rising temperature
How do physical processes damage reefs?
Wave action breaks off pieces of the reef and carries them to environments where growth is not possible e.g. tsunamis
How do biological processes damage reefs?
Invasive species such as starfish and sea urchins destroy reefs by extracting coral polyps destroying huge areas of reef rapidly
How do rising sea temperatures destroy reefs?
Warm water causes corals to spew out zooxanthellae causing coral bleaching
How does sedimentation destroy reefs?
Flash flooding can wash terrestrial clastic sediment down onto reef communities causing corals to die due to indigestion
How is cementation essential to reefs?
Modern reefs are strengthened and stuck together by chemical precipitates forming in areas of high rate of evaporation, concentration of sea water and safe spaces where micrite can precipitate.
What is the growth rate of modern scleractinians in m/yr?
9-15m/1000years
What water depth do modern scleractinians live in?
<100m
What is the optimum temperature for modern scleractinians?
25-29 degrees Celsius
What is the optimum salinity for modern scleractinians?
36 parts per thousand
Why is an excess of nutrients hazardous to modern scleractinians?
An excess of nutrients increases the planktonic population rapidly, causing light from the sun to be blocked.
What are some characteristics of corals found at the reef front?
Robust
Large surface area
