Physical processes
in a mesophotic coral refuge
across bleaching events
Joanna Gyory1 · Tyler Smith1 · Laurent Cherubin2
1University
2University
of the Virgin Islands
of Miami
Shallow water
has
increased
Shallowtemperature
water temperature has
increased
in the
past decades
two decades inin
thethe
USVI USVI
in the past
two
120
100
Number of
Days at or
Above each
Temperature
80
60
• Computed daily average temperature
between July 1 and October 31
• Counted the number of days at or above
each temperature for each year
40
20
0
27.5
28.0
28.5
29.0
29.5
o
Temperature ( C)
30.0
30.5
1990
1991
1992
1993
1994
1995
1996
1997
1998
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
120
116
1996
100
Number of
Days at or
Above each
Temperature
80
60
40
26
20
0
0
27.5
28.0
28.5
29.0
29.5
o
Temperature ( C)
30.0
30.5
Shallow water temperature has increased
Shallow water temperature has increased
in the past
decades
in thetwo
past two
decades inin
the the
USVI USVI
120
100
Number of
Days at or
Above each
Temperature
80
60
40
20
0
27.5
28.0
28.5
29.0
29.5
o
Temperature ( C)
30.0
30.5
1990
1991
1992
1993
1994
1995
1996
1997
1998
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
Bleaching
Prevalence
Irradiance
Temperature
Potential for
heterotrophy
Photo by Robert Brewer
-2
-1
Photosynthetically Active Radiation (E m s )
0
10
30
Depth (m)
50
70
90
400
800
1200
1600
-2
-1
Photosynthetically Active Radiation (E m s )
0
400
800
1200
10
30
Depth (m)
50
70
90
22%
1600
-2
-1
Photosynthetically Active Radiation (E m s )
0
400
800
1200
10
22%
30
Depth (m)
50
70
90
9%
1600
-2
-1
Photosynthetically Active Radiation (E m s )
0
400
800
1200
10
22%
30
Depth (m)
9%
50
70
90
3%
1600
Irradiance
Temperature
Potential for
heterotrophy
Photo by Robert Brewer
Shallow
Mesophotic
0
Shallow
(9 m)
20
Mesophotic
(37 m)
40
Depth (m)
60
80
100
0
5
10
15
Distance along transect (Km)
20
30
Bleaching
threshold
29
Temperature
o
( C)
Shallow
28
27
Mesophotic
26
Jan
Feb Mar
Apr May
Jun
Jul
2007
Aug
Sep
Oct
Nov Dec
30
Bleaching
threshold
29
Temperature
o
( C)
28
Shallow
27
26
Mesophotic
25
Jan
Feb Mar
Apr May
Jun
Jul
2008
Aug Sep
Oct
Nov Dec
30
Bleaching
threshold
29
Temperature
o
( C)
28
Shallow
27
26
Winter
Mesophotic
Summer
25
Jan
Feb Mar
Apr May
Jun
Jul
Aug Sep
Oct
Nov Dec
2008
o
o
Temperature ( C)
26.5
27.5
0
27.0
10
10
20
20
30
30
Depth (m)
Depth (m)
26.0
0
Temperature ( C)
40
50
28.5
29.0
40
50
60
60
70
70
80
35.0 35.5 36.0 36.5 37.0 37.5 38.0
80
36.2
Salinity (PSU)
28.0
36.4
Salinity (PSU)
36.6
31
Shallow
30
Bleaching
threshold
29
Temperature
o
( C)
28
27
26
Mesophotic
25
Jan
Feb Mar
Apr May
Jun
Jul
2010
Aug
Sep
Oct
Nov Dec
30
Shallow
29
Temperature
o
( C)
Mesophotic
28
27
26
Jul 27
Jul 28
Jul 29
Jul 30
Jul 31
2010
Aug 1
Aug 2
Aug 3
Hurricane Earl
31
30
Shallow
29
Temperature
o
( C)
28
27
Mesophotic
26
25
Jan
Feb Mar
Apr May
Jun
Jul
2010
Aug
Sep
Oct
Nov Dec
31
Shallow
9m
30
Bleaching
threshold
29
Temperature
o
( C)
28
27
37 m
Mesophotic
26
25
Mar
Apr
May
Jun
Jul
Aug
2005
Sep
Oct
Nov
Dec
31
Shallow
9m
30
Bleaching
threshold
29
Temperature
o
( C)
28
37 m
Mesophotic
27
26
25
Mar
Apr
May
Jun
Jul
Aug
2005
Sep
Oct
Nov
Dec
Daily average temperature in a mesophotic reef
31
30
29
threshold
o
Temperature ( C)
Bleaching
2005
2010
2008
28
27
26
25
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Irradiance
Temperature
Potential for
heterotrophy
Photo by Robert Brewer
Backscatter strength above a mesophotic reef
140
120
Backscatter
(counts)
100
80
Mar
Apr
May
Jun
Jul
2005
Aug
Sep
Oct
Nov
-3
-3
Chlorophyll (mg m )
0.0
0.4
0.8
1.2
Chlorophyll (mg m )
1.6
0.0
0
0
20
20
40
40
60
60
80
80
100
100
0.4
0.8
1.2
1.6
Depth (m)
Nov-Mar
2006-2011
120
Apr-Oct
2006-2011
120
Backscatter strength above a mesophotic reef
Backscatter strength above a mesophotic reef
140
140
120
120
Backscatter
(counts)
Backscatter
(counts)
100
100
80
80
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
60
Mar
Nov
Apr
May
Jun
2005
Jul
Aug
Sep
Oct
Nov
2006
2005
2006
Backscatter strength above a mesophotic reef
Backscatter strength above a mesophotic reef
140
140
120
120
Backscatter
(counts)
Backscatter
(counts)
100
100
80
80
60
Mar
Apr
May
Jun
Jul
2007
2007
Aug
Sep
Oct
Nov
Mar
Apr
May
Jun
Jul
2008
2008
Aug
Sep
Oct
Nov
Conclusions
30
Bleaching
threshold
29
Temperature
o
( C)
• Seasonal stratification separates the environments of
shallow and mesophotic reefs
28
Shallow
27
26
Mesophotic
25
Jan
Feb Mar
Apr May
Jun
Jul
Aug Sep
Oct
Nov Dec
2008
31
9m
30
Bleaching
threshold
• Mesophotic corals have a different bleaching threshold
than shallow corals
29
Temperature
o
( C)
28
37 m
27
26
25
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
2005
31
Hurricane Earl
30
Temperature
o
( C)
• Hurricane mixing may increase temperature in the
mesophotic environment
Shallow
29
28
27
Mesophotic
26
25
Jan
Feb Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
2010
Backscatter strength above a mesophotic reef
• Hints that zooplankton delivery to mesophotic reefs is
enhanced during warmest months
140
120
Backscatter
(counts)
100
80
Mar
Apr
May
Jun
Jul
2005
Aug
Sep
Oct
Nov