Dynamic Surface L6

Question 1

What is a reef?

Answer 1

A biologically influenced carbonate accumulation which possessed topographic relief during its growth.

Question 2

Are all reefs built by corals - how do we know this?

Answer 2

No - corals are absent from many pre Caenozoic examples

Question 3

What is the geological time scale of tabulate and rugose corals and what did they secrete?

Answer 3

Ordovician-Permian range
Calcite

Question 4

What order to modern corals belong to?

Answer 4

Scleractinia

Question 5

What do modern corals secrete?

Answer 5

Aragonite

Question 6

When did modern corals arise?

Answer 6

The Mid Triassic

Question 7

What do shallow water Scleractinia contain as a part of a symbiotic relationship and what do they need to survive?

Answer 7

Xooxanthellae - photosynthetic dinoflagellates
Need light to survive (the photic zone)

Question 8

What type of modern corals are vulnerable to ocean acidification and why?

Answer 8

Deep, cold water corals are more vulnerable to ocean acidification than tropical corals as deep ocean water has a lower pH

Question 9

When did the stromatolites first appear?

Answer 9

The Archean

Question 10

How did stromatolites form reefs?

Answer 10

Stromatolites form algal mats that colonise sediment surfaces which can build up large structures

Question 11

When do rugose and tabulate corals first appear?

Answer 11

Ordovician

Question 12

When do stromatoporoids first appear?

Answer 12

Ordovician

Question 13

What do stromatoporoids secrete?

Answer 13

Calcite

Question 14

When did the stromatoporoids become extinct?

Answer 14

Devonian

Question 15

When do rudists first appear and what order to they belong to?

Answer 15

Rudists are bivalves and first appear in the Cretaceous

Question 16

What are skeletal/framework reefs?

Answer 16

Living colonies that form topographic highs, usually forming at the edge of continental margins and isolated platforms

Question 17

What are 4 types of skeletal/framework reefs?

Answer 17

Fringing reef
Barrier reef
Submerged shelf-edge reef
Atoll reef

Question 18

Where are fringing reefs found?

Answer 18

Fringing reefs are attached to continents and exist in the intertidal zone

Question 19

Where are barrier reefs found?

Answer 19

Barrier reefs are separated from land by an area of shallow water

Question 20

Where are submerged shelf-edge reefs found?

Answer 20

Found on continental shelf edges

Question 21

What is an atoll reef?

Answer 21

A reef located on sea mounts and isolated platforms

Question 22

What is the difference between a reef mound and a skeletal reef?

Answer 22

Reef mounds don’t have a living framework unlike skeletal reefs

Question 23

How is a reef mound formed?

Answer 23

Calcareous material (algal remains, coral remains etc) is swept together by currents and tides into heaps which are held together by algal mats.

Question 24

When have reef mounds been frequent in geological history?

Answer 24

At times of high sea level

Question 25

What organisms have dominated frame-built reefs throughout Earth's history?

Answer 25

Corals Stromatolites Stromatoporoids Algaes

Question 26

What organisms primarily form reef mounds?

Answer 26

Bryozoans Sponges Crinoids

Question 27

What type of organisms form mud mounds?

Answer 27

Microbial mats

Question 28

What do rugose corals secrete?

Answer 28

Calcite

Question 29

Are rugose corals colonial or solitary

Answer 29

Solitary

Question 30

Are tabulate corals colonial or solitary?

Answer 30

Colonial

Question 31

What to tabulate corals secrete?

Answer 31

Calcite

Question 32

Why are stromatoporoid reefs able to deflect wave energy so effectively?

Answer 32

Due to their rounded dome structure

Question 33

Why does the back reef area contain more delicate organisms not found elsewhere on the reef?

Answer 33

The reef front protects the back reef against wave action

Question 34

What are 5 destructive processes that affect reefs?

Answer 34

Physical Biological Sedimentation Cementation Rising temperature

Question 35

How do physical processes damage reefs?

Answer 35

Wave action breaks off pieces of the reef and carries them to environments where growth is not possible e.g. tsunamis

Question 36

How do biological processes damage reefs?

Answer 36

Invasive species such as starfish and sea urchins destroy reefs by extracting coral polyps destroying huge areas of reef rapidly

Question 37

How do rising sea temperatures destroy reefs?

Answer 37

Warm water causes corals to spew out zooxanthellae causing coral bleaching

Question 38

How does sedimentation destroy reefs?

Answer 38

Flash flooding can wash terrestrial clastic sediment down onto reef communities causing corals to die due to indigestion

Question 39

How is cementation essential to reefs?

Answer 39

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.

Question 40

What is the growth rate of modern scleractinians in m/yr?

Answer 40

9-15m/1000years

Question 41

What water depth do modern scleractinians live in?

Answer 41

<100m

Question 42

What is the optimum temperature for modern scleractinians?

Answer 42

25-29 degrees Celsius

Question 43

What is the optimum salinity for modern scleractinians?

Answer 43

36 parts per thousand

Question 44

Why is an excess of nutrients hazardous to modern scleractinians?

Answer 44

An excess of nutrients increases the planktonic population rapidly, causing light from the sun to be blocked.

Question 45

What are some characteristics of corals found at the reef front?

Answer 45

Robust Large surface area