GCRMN_COI_2017-Western Indian Ocean Reef Status

Coral reef status report for the Western Indian Ocean (2017)
Global Coral Reef Monitoring Network
zooxanthellae present zooxanthellae expelled algae-covered skeleton
Figure 1.3.1 Stages of coral bleaching. (Source Marshall, P. and Schuttenberg, H. 2006. A Reef
Manager’s Guide to Coral Bleaching. GBRMPA, Australia).
The Western Indian Ocean (WIO) has already experienced an extreme bleaching event in
1998, as well as less severe events in 1983, 2005, 2007 and 2010. The 1998 bleaching
event occurred as a result of abnormally high summer temperatures, combined with strong
positive phases of the El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD),
which led to extreme sea water temperatures. The event caused extensive bleaching of
about 90% of corals in the Seychelles and more than 50% in many other locations. As a
consequence, coral mortality varied between 50-80% at a site level, and accounted for a
total loss of 16% of healthy reefs in the region (Wilkinson 2000).
In October 2015, the National Oceanic and Atmospheric Administration (NOAA) declared
the current event, which began in the North Pacific in summer 2014, as the third global
coral bleaching event after those in 1998 and 2010 3 .
1.3.2 The 2016 event
The last three years have been among the hottest ever recorded globally, with each successive
year outdoing the record set in the previous one (fig. 1.3.2a). Both the Indian Ocean Dipole
and El Niño indices (fig. 2, right) were positive at the end of 2015 and into 2016, though the
IOD was declining at the time that bleaching started in the WIO in January-February. In late
2015, the El Niño index exceeded the previous record of 3.0 set in 1997-98. The combination
of record hot conditions for 2014-2016 and the in-phase high positive values for both Pacific
and Indian Ocean dipoles, made for very high bleaching risk in the WIO. This continued the
strong bleaching conditions already reported for the Caribbean and Pacific in 2015, and cooccurring
in the Great Barrier Reef in 2016.
3 http://www.noaanews.noaa.gov/stories2015/100815-noaa-declares-third-ever-global-coralbleaching-event.html.
Accessed 20 November 2016.
Affiliation: CORDIO East Africa.
Contributors & acknowledgements: we would like to acknowledge Tammy Holter (Scuba- Do Diving, Zanzibar)
and Ulli Kloiber (Chumbe Island Coral Park) for developing the online reporting form for coral bleaching for the
Western Indian Ocean. The full list of contributors to this online form is listed in section 1.3.7.
REGIONAL CHAPTERS
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