Lecture 7

Question 1

What is a coral reef built from?

Answer 1

Built from the accumulated skeletons of calcium carbonate (CaCO3) secreting animals and plants

Question 2

Where are tropical coral reefs found?

Answer 2

Along Australian and Indonesian coastline

Near the warmer currents of oceanic gyres

Question 3

Problems of tropical surface waters

Answer 3

Stratified and nutrient-poor
Permanent thermocline
Strong pycnocline
Low biomass except in upwelling regions and coral reefs

Question 4

What is ahermatypic coral?

Answer 4

Soft coral
Not reef-building
Do not produce a rigid calcareous skeleton
Can produce sclerites (calcium carbonate needles)

Question 5

What is hermatypic coral? What is the dominant group?

Answer 5

Stony corals
Reef-building
Dominant group are Scleractinian coral
Produce massive skeletons of calcium carbonate

Question 6

Features of Scleractinian coral

Answer 6

CaCO3 skeleton produced by coral polyps
Solitary or colonial
Colonies formed by asexual division - all polyps genetically the same
Polyps connect into a single living surface (tissue layer) above the exoskeleton

Question 7

How do corals obtain the nutrients they need?

Answer 7

They have a symbiotic relationship with photosynthesising algae (zooxanthellae - dinoflagellates)
Holobiont = ecological unit of coral and it’s symbionts
Algae supplies up to 90% of energy required by tropical coral
Coral therefore requires well-lit marine environment
Nutrients cycled between coral polyp and symbiotic algae

Question 8

What genus are zooxanthellae in?

Answer 8

Symbiodinium

Question 9

Density of algae within corals

Answer 9

more than a million per cm squared of coral surface

Question 10

How else does coral obtain nutrients besides its symbiotic relationship with algae?

Answer 10

• Prey capture of zooplankton using stinging cells called cnidocytes
• Mesenterial filaments: tubes attached to the wall of the gut that are extruded through the mouth to digest food outside the body
• Mucus threads secreted over colony surface to capture passing plankton, then gathered into mouth (mucus is food source for benthic bacteria)

Question 11

How do symbionts affect calcification?

Answer 11

The skeletal growth of tropical coral with symbiotic algae is much faster than cold water due to symbionts
Calcification is 3x higher during the day when algae can photosynthesis

Question 12

Cold water coral features

Answer 12

Long-lived, slow growing and extremely fragile coral
Below 40m water depth they are most common, as there is no symbiotic relationship with photosynthetic algae
Host to specific bacteria

Question 13

What is ahermatypic cold water coral growth limited by?

Answer 13

Oxygen and food rather than water temperature and light

Question 14

What is coral bleaching?

Answer 14

Breakdown of symbiosis between algae and coral host

Coral will bleach if temperatures reach 1 degrees above average seasonal maxima

Question 15

When was the most extensive coral bleaching seen on the Great Barrier Reef?

Answer 15

February 1998

87% of inshore reefs saw bleaching occur

Question 16

What are important alternative energy sources for coral during bleaching?

Answer 16

• Capture of plankton
• Lipid reserves
• Night-time mesenterial feeding on neighbouring algal turfs

Question 17

How might coral adapt to shifts in thermal tolerance

Answer 17

Adaptive bleaching hypothesis

Shuffling the population of symbiotic algae to increase the threshold temperature of bleaching

Question 18

What is another coral reef builder besides hermatypic coral?

Answer 18

Crustose coralline algae
Order Corallinales, in Rhodophyta/red algae
Dominant reef-building genus is Porolithion
Acts like a mortar for the reef by forming an encrusting cement of Mg-rich CaCO3
Surface aids the settlement of coral recruits and other reef invertebrates

Question 19

What is another coral reef builder besides hermatypic coral and crustose coralline algae?

Answer 19

Halimeda
Calcareous green alga
95% of weight is CaCO3
Individual segments accumulate to form carbonate sediment on reefs

Question 20

What are the two types of coral reef erodes?

Answer 20

1. Bioeroders

2. Chemical eroders

Question 21

What are three examples of bioeroders?

Answer 21

Polychaetes (e.g. Christmas tree worms)
Crown of thorn starfish
Parrotfish (Scaridae)

Question 22

Features of parrotfish

Answer 22

Fused dental plants to form a beak
Have a pharyngeal jaw (second set of jaws within the throat)
Very long intestine, no stomach
Graze reef in large schools
Adult invests more than 5 tonnes a year of structural reef carbonate

Question 23

What is an example of a chemical eroder of coral?

Answer 23

Upwelling high CO2 (low pH) waters

Question 24

How does upwelling of high CO2 water erode coral?

Answer 24

Low pH water has low carbonate concentration
The rate of calcification for both coral and coralline algae is proportional to the carbonate concentration in seawater
The stability of calcium carbonate is dependent on the carbonate concentration in seawater, so a lower concentration of carbonate causes the dissolution of the CaCO3 skeleton of coral

Question 25

Where is it that reefs can occur?

Answer 25

Where calcification exceeds erosion

Question 26

What is the single species of coral which makes up most cold water coral reefs in the North Sea?

Answer 26

Lophelia pertusa