ENVM3115 Lecture 6: ENVM3115 WEEK 6- Part 2
1 Jun 2018
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Climate change and coral reefs
What does this mean for all reefs?
4 potential problems
• Temperature
• Increased c02 in the water
• Increased storm activity
• Sea level rise
Storms and cyclones
• Breakage of corals and other fragile organisms
• Increased competition with algae
• Disturbance of recruitment
Sea level rise
Results for reefs not obvious but the following are possible:
• Inundation of land will bring more harmful runoff from land to reefs
• Changes in the amount of light reaching corals so some
• Reefs may drown, some could bleach less due to less light
Temperature
• Coral bleaching – warm and cold
• Growth changes
• Reproductive changes
• Recruitment changes
▪ As temperature rises, you would expect growth to increase until an optimum
temperature is passed.
▪ Multiple new studies showing calcification drops of around 20% in the last 3 decades
Combined effects of different drivers
What is bleaching and what does it do to corals?
Coral gets:
• Carbon from zooxanthellae (energy)
• Glycerol that helps make fats
• Help with making skeleton
Zooxanthellae get:
• Protection – safe place to live
• Nutrients from the coral (nitrogen and phosphorus)
What is coral bleaching?
• Zooxanthellae provide corals with their brown colour
• Coral bleaching involves the loss of most of the zooxanthellae
Bleaching
• No reports in scientific literature before 1979
• High sea water temperatures trigger wide spread symbiotic dysfunction – results in
bleaching. • Effect enhanced by high light and low flow conditions
• Many major periods of mass bleaching since 1979 • Mass coral bleaching and
mortality are increasing
• 1998 worst year world-wide (16% of all corals died worldwide) before 2016.
• 2002 worst bleaching on the GBR before 2016
• 2005 very high mortality in Caribbean
• 2010 big bleaching through Asia
• And then 2016 and 2017
Bleaching events do not affect all reefs in a region to the same degree or even all corals in a
reef patch.
Investigating why some reefs/patches/coral bleach more than others is an important part of
understanding and managing reefs.
When sea surface temperatures exceed the bleaching threshold temperature for a reef for long
enough, a bleaching event takes place
The intervals between bleaching events across the globe have decreased substantially since
the 1980s. The median period between bleaching events is now six years.
One reason for this is that temperatures in La Niña conditions (when we expect lower
temperatures) are now higher than those of El Niño conditions in the 1980s
Coral bleaching – not always fatal but there may be longer term effects
Document Summary
4 potential problems: temperature, sea level rise. Storms and cyclones: breakage of corals and other fragile organisms, disturbance of recruitment. Results for reefs not obvious but the following are possible: Inundation of land will bring more harmful runoff from land to reefs: changes in the amount of light reaching corals so some, reefs may drown, some could bleach less due to less light. Coral gets: carbon from zooxanthellae (energy, glycerol that helps make fats, help with making skeleton. Zooxanthellae get: protection safe place to live, nutrients from the coral (nitrogen and phosphorus) What is coral bleaching: zooxanthellae provide corals with their brown colour, coral bleaching involves the loss of most of the zooxanthellae. Bleaching events do not affect all reefs in a region to the same degree or even all corals in a reef patch. Investigating why some reefs/patches/coral bleach more than others is an important part of understanding and managing reefs.
