Coral bleachhing

Question 1

What are corals

Answer 1

• most primary reef-building corals are calcifying anthozoans
• Anthozoa is a class of 6000 species (within cnidaria). They only exist as polyps , never medusa
• True “stony” corals are in the order scleritina

Question 2

What do corals create

Answer 2

Coral reefs - hyper diverse marine environments, they only cover 1% of the sea floor yet hold 1/4 of all marine species

Question 3

Biology of scleritinian corals

Answer 3

Scleratinian reef corals form an aragonite corallum (colonial skeleton) composed of individual cuplike coralites around and under each polyp

Question 4

corallum

Answer 4

the entire skeleton of a compound coral

Question 5

How does coral growth occur

Answer 5

• Growth occurs on top of previous calcification.

- Growth in some acopora corals can be >100mm annually

Question 6

How large can coral colonies get

Answer 6

• Large coral colonies can reach several M in height and tons in weight.
• The living tissue however is typically <1mm thick on surface

Question 7

What controls the rate of growth/calcification

Answer 7

Growth is controlled by function of specific calciloblastic tissue (has a direct role in crystal formation)
- Growth is also controlled by photosynthetic contributions of symbiotic zooxanthellae

Question 8

what is a zooxantehllae

Answer 8

In this case it is a coral containing an algal symbiont.

Question 9

what is typical of (hermatypic) scleritinian corals

Answer 9

they are typical of shallow seas and almost all are zooxanthellae

Question 10

What are hermatypic corals

Answer 10

Hermatypic corals are those corals in the order Scleractinia which build reefs by depositing hard calcareous material for their skeletons, forming the stony framework of the reef. Corals that do not contribute to coral reef development are referred to as ahermatypic (non-reef-building) species

Question 11

What are the most common zooxanthellae relationship

Answer 11

• Most scleritinian corals have a symbiotic relationship with dinoflagellates of the genus symbiodinum

Question 12

how many types of symbiodinum are there

Answer 12

> 100 genotypes of symbiodinum , some are widely distributed whilst others are specific to species or environments

Question 13

where are zooxanthellae located

Answer 13

zooxanthellae are inra-cellular and located within host gastrodermal cells

Question 14

how many zooxanthellae are typically within an individual

Answer 14

• 1-3 or more per cell

- typically 1500000 symbiont cells per cm^2

Question 15

What are the three functions of zooxanthellae

Answer 15

• influence calcification process
• Provide nutritional material to their hosts
• take up host waste products

Question 16

How does light affect calcification rates

Answer 16

• light, photosynthesis and calcification are intimately linked
• A cloudy day can reduce carbonate deposition by 50%
• Carbonate production is 3x higher at daytime compared to night

Question 17

How does the zooxanthellae provide nutrition for the coral

Answer 17

• Carbon fixed by photosynthesis is translocated to the host in the form of amino and fatty acids, glucose and glycerol

Question 18

What is the ratio of photosynthesis to respiration

Answer 18

In some conditions photosynthesis to respiration ratio (P:R) can be >1. I.E. all metabolic requiremnts met by photosynthesis

• symbiosis is autotrophic (in this case)
• This varies substantially with light, depth ,season ,habitat etc.

Question 19

Are corals autotrophic

Answer 19

No , most corals also feed heterotrophically, this significantly increases both tissue growth and calcification rates

feed on planktonic prey

Question 20

How do corals deal with their waste products

Answer 20

• Zooxanthellae take up phospherous and nitrogen from their hosts
• They transform these into organic compounds and transfer them back to host
• Ammonium and nitrate are potentially toxis to corals, zooxanthellae act as “metabollic kidneys”

Question 21

what is the main benefit of the symbiotic zooxanthellae relationship

Answer 21

Allows reef-building corals to survive in nutrient poor shallow tropical waters

Question 22

Reef corals are intolerant to the following types of environmental change

Answer 22

• reduced salinity
• prolonged low tides
• disease
• pollution
• temperature extremes (KEY)
• High light levels

Question 23

What are coral stress responses

Answer 23

At threshold levels
- increased mucous secretion and polyp withdrawal (no longer active)

Beyond physiological thresholds
-zooxanthellae symbionts are expelled (bleaching)

Question 24

What is coral bleaching

Answer 24

• A complex reaction based on physiology, biochemistry and traits from both partners
• Most obvious forms of bleaching result in host appearing transparent (this is through revealing the aragonite skeleton underneath)

Question 25

Not all coral bleaching is worrying and can reflect seasonal variation , what is this called

Answer 25

cyclical changes are called physiological bleaching

Question 26

How does severe bleaching affect corals

Answer 26

- Typically a loss of 60-90% of symbiont cells - Usually accompanied by a loss of host tissue biomass - bleaching is significant injury to the coral , not just loss of photosynthesis

Question 27

How does temperature affect bleaching

Answer 27

- Most reefs are sensitive to small increases in temp - Just 1-2 degree celcius increase above summer highs can induce bleaching -El ninos generate wide swathes of such conditions , 30-32 degrees widespread in the tropics

Question 28

What happens when the corals release the zooxanthellaes

Answer 28

-Without the algae (symbiont) , the coral loses its major source of food , turns white/transparent and becomes more susceptible to disease.

Question 29

Examples of previous mass bleaching events

Answer 29

- Super el nino (1998) , caused coral mortality across the tropics. Unprecedented in global scope. - Coral coverage was reduced >90% in many parts of the indian ocean - similar patterns in pacific + caribbean - 16% of the worlds shallow water reefs were lost

Question 30

The role of climate change in coral bleaching

Answer 30

climate change interacts with natural processes and variation to increase the severity and extent of bleaching events

Question 31

How does coral bleaching effect reef ecosystem services

Answer 31

- Many species entirely dependant on healthy corals for habitat and food - Coral cover and topgraphic complexity especially important to fish

Question 32

Example of bleaching effect on reef species composition

Answer 32

Example: Pratchett et al. (2008) Effects of coral bleachng, 1998 on species richness - Most species declined/died out - Species which suffered the most were coralivores and coral dwellers - Herbivores tend to do well as bleached coral gets colonised by macroalgae

Question 33

When did NOAA declare the 3rd ever global bleaching event

Answer 33

2015 - NOAA declared 3rd ever global bleaching event - > 1/2 of japans coral reef died - severe effects predicted globally - As the year progressed predictions worsened significantly - covered most of the tropics and pretty much everywhere else

Question 34

The 2016 bleaching event and the great barrier reef

Answer 34

- 1000km of the reef was affected - Northern areas hit hardest , 95% of reefs between cairns and papau new guinea showed bleaching - southern and central regions protected by cooler weather form cyclone winston

Question 35

What was special about the bleaching of the great barrier reef

Answer 35

first bleaching event that played out on social media

Question 36

According to Terry hughes what was the extent of damage to the reef

Answer 36

``` Northern = 26% mortality North = 67% mortality Central = 6% mortality South = 1% mortality ```

Question 37

How does the future look for bleaching events

Answer 37

- Projected increase in sea suraface temps (1.2/2 -5/10 degree increase by 2100) will increase bleaching events significantly - Surface aragonite is going to decrease , this will reduce calcium deposition preventing coral regeneration - prediction suggest future seas will be unable to support corals

Question 38

How does aragonite concentration affect corals

Answer 38

There is a critical concentration of aragonite below which calcifying organisms such as corals cannot function

Question 39

What is the problem with saying the great barrier reef "died"

Answer 39

Russel Bainard , chief scientist at NOAA there is increasing concern that overstatement of the environmental situations that our planet faces causes people to lose hope and thus reduces efforts to fix the problem. -only 22% of the reef died , a large proportion of the public think 100% perished

Question 40

Summary

Answer 40

- Coral reefs are dependant on symbiotic relationship with zooxanthellae - many stressors can lead to it breaking down - temperature is primary driver of bleaching

Question 41

Coral reefs prognosis

Answer 41

- Tropical reef systems are transitioning to a new era in which the interval between bleaching events is too small to allow full coral regeneration - median return times between events is no 6 years (decreased since 1980s) - Annual bleaching may become the norm