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Climate Change Induced Coral Bleaching
and Algal Phase Shift in Reefs of the Gulf
of Mannar, India
J. Joyson Joe Jeevamani, B. Kamalakannan, N. Arun Nagendran
and S. Chandrasekaran
1 Introduction
Coral reefs are the most diverse and complex of all marine ecosystems which
normally flourish in tropical and semitropical regions of the world where water
temperatures range between 16 and 30 °C. Coral reefs are most productive and
provide various goods and ecological services (Moberg and Folke 1999) to human
as well as marine biota. On other hand, throughout the world, there are many
threats to existing coral reefs. Global warming, over fishing, mining, sedimenta-
tion, pollution, and diseases all threaten the viability and health of coral reefs.
Coral bleaching is considered one of the biggest threats to coral reefs which
accompanies coral mortalities (Brown 1997; Glynn 1993). Bleaching is a natural
phenomenon in which the symbiotic intracellular algae (zooxanthellae) of reef-
building corals is expelled under stressful environmental conditions causing corals
to lose their color. Such conditions are now more frequent due to global warming
(Donner et al. 2005; Hoegh-Guldberg et al. 2007). Global warming and associated
increases in sea surface temperatures (SSTs) are now projected to be very likely in
the coming decades (IPCC 2007; Phinney et al. 2006). Incidence of coral
bleaching reports, primarily due to SST rise, has increased considerably since the
early 1980s (Glynn 1993; Hoegh-Guldberg 1999; Hoegh-Guldberg et al. 2007;
Hughes et al. 2003). More often, mass coral mortality due to bleaching is followed
by an invasion of macro algae which ultimately results in shifted algal dominated
system (Done 1992). Such shift from coral reefs to high cover of macro algae is
J. Joyson Joe Jeevamani
Department of Botany, Thiagarajar College, Madurai 625009, India
N. Arun Nagendran
Department of Zoology, Thiagarajar College, Madurai 625009, India
B. Kamalakannan S. Chandrasekaran (&)
Department of Plant Sciences, School of Biological Sciences, Madurai Kamaraj University,
Madurai 625021, India
e-mail: invasionecology@gmail.com
S. Nautiyal et al. (eds.), Knowledge Systems of Societies for Adaptation and Mitigation
of Impacts of Climate Change, Environmental Science and Engineering,
DOI: 10.1007/978-3-642-36143-2_6, ÓSpringer-Verlag Berlin Heidelberg 2013
87
referred as ‘coral-algal phase shift’. Regional scale studies are highly necessary to
investigate the process of coral-algal phase shift after the bleaching phenomenon.
Reefs of India also experienced severe bleaching events in 1998 and 2002.
Increase in SST appears to be the main stress for these events (Arthur 2000;
Kumaraguru et al. 2003). The present study reports algal phase shift after a
bleaching event in 2010 in reefs of the Gulf of Mannar (GoM), India.
2 Materials and Methods
Visual observations of the bleaching event were observed during April 2010 in
reefs of Kurusadai Island (9°150N; 79°120E) at Gulf of Mannar, Southeast coast of
India (Fig. 1). Bleaching occurred in both massive and branching forms of corals.
Photographic records were taken at first and bleached coral cover was estimated
using transects. Totally, 10 transects, each of 5 m in length, were laid on selected
bleached locations at a depth range from 0.25 to 2 m. Transects were marked using
a Geographical Position System (GPS) device and revisited periodically at least
once in a month from April to July 2010. Biophysical status of coral reefs were
assessed based on observation of live coral cover, bleached coral (massive and
branching forms), algal mat cover (algal turfs, macro-algal cover) and sand/coral
rubble. SST was measured in situ using mercury bulb thermometer. To correlate
SST with bleaching, satellite SST dataset obtained from National Oceanic and
Atmospheric Administration’s Coral Reef Watch (NOAA/CRW) satellite
bleaching alert (SBA) system (http://coralreefwatch.noaa.gov) specifically derived
for the Gulf of Mannar region from January 2001 to October 2010 was used (Gang
Liu, ‘‘personal communication’’). The SST data is based on the NOAA 0.5°
(approximately 50 km) resolution using Advanced Very High Resolution Radi-
ometer (AVHRR) with weekly twice time interval. The data was subjected to
appropriate statistical analyses.
3 Results and Discussion
Results show that both massive (Porites sp.) and branching (Acropora sp.) corals
have been affected during the bleaching event of 2010 (Plate 1). Around 57 % of
corals were found to be bleached in Kurusadai Island during April to June 2010.
Porites species were affected more compared to Acropora species. SST results
shown that mean SST of the Gulf is 28.7 °C in 2010 with a maximum temperature
of 31 °C in May and minimum temperature of 27.0 °C in February (Fig. 2).
Sudden increase of temperature was observed (Fig. 2) from 29.9 to above 30.9 °C
in April (16th week) and the existence of high temperature (up to 31 °C) for
7 weeks (April to May). Anomalies of mean SST for these weeks were also shows
a great increase range from +1 to 2.2 °C (Fig. 3) relative to the 1950–1979 base
88 J. Joyson Joe Jeevamani et al.
periods. Prolonged existence of inexperienced increased SST for nearly 50 days
caused the corals to bleach. Decadal mean SST of Gulf of Mannar varied from
28.2 to 28.7 °C with a maximum temperature of 31.2 °C in 2002 and minimum
temperature of 25.7 °C in 2004 (Fig. 4). The mean SST of the Gulf of Mannar has
been growing at 0.02 °C per decade along with 0.1 °C increase per decade in
minimum SST temperature.
Observation in July 2010 indicates that recovery was also rapid as that of
bleaching. Nearly 15 % of bleached corals were found to have recovered.
Recovery patterns differed between the two forms of corals. Recovery process is
fast and effective in massive (Porites) rather than branching forms (Acropora). The
increase in live coral cover (from 11.23 to 44.87 %) was mainly contributed by
massive corals (Table 1). Significant recovery of branching corals was not
observed. As a consequence, these corals were overgrown by algal mats (Sar-
gassum sp., Turbinaria sp., Ulva sp., Caulerpa sp., Kappaphycus alvarezii) or
algal turfs (Plate 1e and f) which increased the algal assemblage in branching
forms from 10.9 to 18.36 %.
Fig. 1 Map of the Gulf of Mannar (GoM) Biosphere Reserve showing Kurusadai Island and
study site
Climate Change Induced Coral Bleaching and Algal Phase Shift in Reefs 89
Similar to 1998 and 2002, the bleaching event in 2010 is driven by the
increased effect of SST which was also recorded in other parts of world during the
summer season (Harrison et al. 2011). Our results of this SST anomaly were also
correlated with the prediction of McWilliams et al. (2005) who stated that max-
imum bleaching extent and intensity will occur at regional SST anomalies of less
than +1 °C level. In our study, the mortality rate was high and recruitment rate was
low in branch coral forms rather than in the massive and encrusting coral forms.
Similar results were also reported earlier, which demonstrated that scleractinia
corals with branching colony morphologies generally suffer higher rates of mor-
tality than species with massive and encrusting morphologies (Hoegh-Guldberg
and Salvat 1995; Jokiel and Coles 1990; Marshall and Baird 2000; McClanahan
y = -0.007x + 28.902
R2= 0.0052
26.5
27
27.5
28
28.5
29
29.5
30
30.5
31
31.5
0 2 4 6 8 101214161820222426283032343638404244
Weeks (Januar
y
- October , 2010)
Mean SST (°C)
Fig. 2 Weekly mean SST occurred in Gulf of Mannar in the year 2010
y = 0.0146x + 0.4478
R2= 0.0757
-1
-0.5
0
0.5
1
1.5
2
2.5
0
2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48
Weeks (January - October, 2010)
SST anomaly ( C)
o
Fig. 3 Weekly mean SST anomaly occurred in Gulf of Mannar in the year 2010
90 J. Joyson Joe Jeevamani et al.
and Maina 2003). Bleaching incidence, caused by global warming, has resulted in
replacement of hardier coral species by less hardy corals (Glynn and De Weerdt
1991) and corals by macro algae (Shulman and Robertson 1996). Our results
synchronize with the above reported changes. Bleaching has significantly induced
occurrence of phase-shift from coral to algae in the study site as previously
observed in other regions of the world (Aronson et al. 2002,2004; Hughes 1994).
Baker et al. (2008) suggested that changes in coral community structure following
y = 0.0994x - 173.09
R2= 0.6348
y = 0.0199x - 11.487
R2= 0.1448
y = - 0.0212x + 73.231
R2= 0.04
25
26
27
28
29
30
31
32
2000 2002 2004 2006 2008 2010 2012
Year
SST (
oC)
Mean Minimum
Mean SST
Mean maximum
Fig. 4 Average minimum, maximum and mean SST at Gulf of Mannar for 2001–2010
Table 1 Status of coral life forms after bleaching event on April 2010 and during recovery on
July 2010 in Kurusadai Island, Gulf of Mannar, India
S. No. Life forms
a
April 2010 July 2010 t—test
b
Mean (SE) Cover (%) Mean (SE) Cover (%) t value P
c
(n =10)(n =10)
1. BMC 2.25 (0.24) 45.10 0.57 (0.06) 11.43 6.57 <0.05
2. BBC 0.59 (0.06) 11.74 0.16 (0.02) 3.16 7.26 <0.05
3. AMC 0.40 (0.04) 7.95 0.44 (0.04) 9.05 6.14 <0.05
4. ABC 0.55 (0.06) 10.90 0.92 (0.10) 18.36 3.59 <0.05
5. LC 0.56 (0.06) 11.23 2.23 (0.23) 44.87 8.08 <0.05
6. SA 0.65 (0.07) 13.08 0.66 (0.07) 13.13 1.00 0.922
a
BMC Bleached massive type corals, BBC Bleached branching type corals, AMC Algal
assemblage over massive type corals, ABC Algal assemblage over branching type corals, LC Live
coral, SA Sand area
b
Paired t—test
c
Bold faced values are highly significant
Climate Change Induced Coral Bleaching and Algal Phase Shift in Reefs 91
bleaching can take two forms, viz., changes in the relative abundance of coral
surviving zooxanthellae and changes in the dominance of non-coral taxa associ-
ated with reef assemblages. When bleaching long lasts with pronounced effect,
coral-algal phase shift results and can lead to fundamental differences in the
structure of reef communities. So it is inferred from this study that if increase in
SST continues into the future, it will definitely impact the coral communities in the
Gulf of Mannar and, thereby, affect the unsubstituted ecosystem services obtained
from them.
Plate 1 a Bleaching in massive corals (Porites sp.). bRecovered massive corals. cBleaching in
branching corals (Acropora sp.). dAlgal turfs over bleached Acropora corals. eand fAlgal phase
shift dominated in branching coral forms
92 J. Joyson Joe Jeevamani et al.
4 Conclusion
Existence of shift from coral dominance to algal dominance, following a bleaching
incident in reefs of Gulf of Mannar is clear from the study. Once these commu-
nities have shifted, it will require a long time to return to their original status. Coral
reefs of the Gulf of Mannar are already under serious threats like pollution, sed-
imentation, destructive fishing practices, biological invasion (Chandrasekaran
et al. 2008; Kamalakannan et al. 2010), etc. Now coral-algal phase shift is also
adding stress to the environment. Immediate mitigation measures have to be taken
in order to protect the enriched coral diversity of Gulf of Mannar from recent
climate change.
Acknowledgments We are thankful to the UGC and CSIR, New Delhi for the financial assis-
tance to carry out this work. We also thank the Forest Department, Government of Tamil Nadu
for providing permission and their encouragement to carry out this work. We are thankful to Mr.
M. R. Anbarasan, Madurai for his valuable help in data mining.
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