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Coral Reefs: Effects of climate change on the UK’s largest reef system Charles Sheppard
1. What are coral reefs?
Built by corals
<1% of the ocean, 50% of marine
species
Many Nations are built of them entirely or in
part (including BIOT)
Coral reefs feed about billion people
They protect 1,000’s of miles of shoreline
2. Britain’s greatest marine diversity is in the Chagos Archipelago (BIOT) What and where is it?
Developing network of giant MPAs
BIOT was one of the six founding ‘Big Ocean Network’ members
Critical for numerous reasons to Indian Ocean generally:
Biologically
Economically
Aesthetically
For Indian Ocean people
Effectively Lost Reefs (%)
Reefs at Critical Stage (%)
Reefs at Threatened Stage (%)
Reefs at Low Threat level (%)
What has been happening to reefs?
Local disturbances:
•Sewage / nutrient runoff
•Overfishing (and destructive
fishing)
•Sedimentation
•Construction
disturbance
Why?
plus
The global triplet:
•Warming
•Acidification
•Sea level rise
Let’s look at what caused it
0
10
20
30
40
50
60
70
80
1975 1980 1985 1990 1995 2000 2005 2010 2015
% c
ora
l co
ver
Year
Coral cover on ocean reefs, Chagos
5 m 10 m
15 m 20 m
25 m
Dashed lines initially because of the long interval: unlikely to have been smooth in reality
-3
-2
-1
0
1
2
3
1975 1980 1985 1990 1995 2000 2005 2010 2015
Stan
dar
dis
ed D
ep
artu
re
Multivariate ENSO Index
0
10
20
30
40
50
60
70
80
1975 1980 1985 1990 1995 2000 2005 2010 2015
% c
ora
l co
ver
Year
Coral cover on ocean reefs, Chagos
5 m 10 m
15 m 20 m
25 m
Dashed lines initially because of the long interval: unlikely to have been smooth in reality
-3
-2
-1
0
1
2
3
1975 1980 1985 1990 1995 2000 2005 2010 2015
Stan
dar
dis
ed D
ep
artu
re
Multivariate ENSO Index
0
10
20
30
40
50
60
70
80
1975 1980 1985 1990 1995 2000 2005 2010 2015
% c
ora
l co
ver
Year
Coral cover on ocean reefs, Chagos
5 m 10 m
15 m 20 m
25 m
Dashed lines initially because of the long interval: unlikely to have been smooth in reality
0
10
20
30
40
50
60
70
80
1975 1980 1985 1990 1995 2000 2005 2010 2015
% c
ora
l co
ver
Year
Coral cover on ocean reefs, Chagos
5 m 10 m 15 m 20 m 25 m
Dashed lines initially because of the long interval: unlikely to have been smooth in reality
1979. Chagos was in great condition
0
10
20
30
40
50
60
70
80
1975 1980 1985 1990 1995 2000 2005 2010 2015
% c
ora
l co
ver
Year
Coral cover on ocean reefs, Chagos
5 m 10 m 15 m 20 m 25 m
Dashed lines initially because of the long interval: unlikely to have been smooth in reality
1996. Shortly before the wipe-out
1999. Immediately after the first observed mortality
0
10
20
30
40
50
60
70
80
1975 1980 1985 1990 1995 2000 2005 2010 2015
% c
ora
l co
ver
Year
Coral cover on ocean reefs, Chagos
5 m 10 m 15 m 20 m 25 m
Dashed lines initially because of the long interval: unlikely to have been smooth in reality
2001. 3 years after 1998 mortality
0
10
20
30
40
50
60
70
80
1975 1980 1985 1990 1995 2000 2005 2010 2015
% c
ora
l co
ver
Year
Coral cover on ocean reefs, Chagos
5 m 10 m 15 m 20 m 25 m
Dashed lines initially because of the long interval: unlikely to have been smooth in reality
0
10
20
30
40
50
60
70
80
1975 1980 1985 1990 1995 2000 2005 2010 2015
% c
ora
l co
ver
Year
Coral cover on ocean reefs, Chagos
5 m 10 m 15 m 20 m 25 m
Dashed lines initially because of the long interval: unlikely to have been smooth in reality
2006. April. Recovery well underway
0
10
20
30
40
50
60
70
80
1975 1980 1985 1990 1995 2000 2005 2010 2015
% c
ora
l co
ver
Year
Coral cover on ocean reefs, Chagos
5 m 10 m 15 m 20 m 25 m
Dashed lines initially because of the long interval: unlikely to have been smooth in reality
2012. April. Healthy reef again
2015. April. Warm… not yet critical
0
10
20
30
40
50
60
70
80
1975 1980 1985 1990 1995 2000 2005 2010 2015
% c
ora
l co
ver
Year
Coral cover on ocean reefs, Chagos
5 m 10 m 15 m 20 m 25 m
Dashed lines initially because of the long interval: unlikely to have been smooth in reality
0
10
20
30
40
50
60
70
80
1975 1980 1985 1990 1995 2000 2005 2010 2015
% c
ora
l co
ver
Year
Coral cover on ocean reefs, Chagos
5 m 10 m 15 m 20 m 25 m
Dashed lines initially because of the long interval: unlikely to have been smooth in reality
2015. May. Bleaching started
2017. April. Massive mortality
0
10
20
30
40
50
60
70
80
1975 1980 1985 1990 1995 2000 2005 2010 2015
% c
ora
l co
ver
Year
Coral cover on ocean reefs, Chagos
5 m 10 m 15 m 20 m 25 m
Dashed lines initially because of the long interval: unlikely to have been smooth in reality
Another strong climate change indicator is rainfall:
1,000
1,500
2,000
2,500
3,000
3,500
4,000
4,500
5,000
1950 1960 1970 1980 1990 2000 2010 2020
mm
rai
n p
er y
ear
Total annual rain in Diego Garcia
-50
0
50
100
150
200
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
Ch
ange
in r
ain
fall
mm
Month
Diego Garcia, change in monthly rainfall 1950-2016
Significance goes beyond local events Rising rainfall here = decreasing rain in Africa = increased food shortages Some of the best data sets come from BIOT
Significance of this reef story: • Britain’s most diverse marine system, which is of global consequence, is in trouble
• It is used to see how a reef really works, without local impacts
• Fills huge global hole for climate system monitoring
• Insurance policy for the Indian Ocean
• Predictions?
Major funding (chronologically): UK Gov: BIOT, MoD, OTEP, ODA, FCO, DFiD, DEFRA, US Navy, Bertarelli Foundation. Data: Charles Sheppard, Anne Sheppard, 2016 coral cover data: Dr Ronan Roche Video 2015: Living Oceans Foundation Photos, video 2017: Anne Sheppard
Summarised from: Sheppard C, Sheppard A, Mogg A, Bayley D, Dempsey A, Roche R, Turner J, Purkis S. 2017. Coral Bleaching and mortality in the Chagos Archipelago. Atoll Research Bulletin 613: 1-28.
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