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Coastal, Marine and Island Specific Biodiversity Management in ESA-IO Coastal States
(Agreement n°RSO/FED/022-995)
Impact of the 3rd Global Coral Bleaching Event on the
Western Indian Ocean in 2016
Mishal Gudka, David Obura, Jelvas Mwaura, Sean Porter, Saleh Yahya and Randall Mabwa
May 2018
Da
Impact of the 3rd Global Coral Bleaching Event on the Western
Indian Ocean in 2016
Edited by
Mishal Gudka, David Obura, Jelvas Mwaura, Sean Porter, Saleh Yahya and
Randall Mabwa
This report was developed under the scientific coordination of CORDIO East
Africa, with the support of the Indian Ocean Commission, through its
Biodiversity Project funded by the European Union.
Citation : Mishal Gudka, David Obura, Jelvas Mwaura, Sean Porter, Saleh Yahya
and Randall Mabwa (2018). Impact of the 3rd Global Coral Bleaching Event on the
Western Indian Ocean in 2016. Global Coral Reef Monitoring Network
(GCRMN)/Indian Ocean Commission. pp. 67
Funding was provided by the European Union through the Indian Ocean
Commission’s Biodiversity Project
Maps were produced from open source country and coral reef layers by James
Mbugua, CORDIO East Africa. The designation of geographical entities in this
report, and the presentation of the material, do not imply the expression of any
opinion whatsoever concerning the legal status of any country, territory, or area,
or of its authorities, or concerning the delimitation of frontiers or boundaries.
Impact of the 3rd Global Coral Bleaching Event on the Western Indian Ocean in 2016
Executive Summary
The third global coral bleaching event started in the North Pacific in the summer of 2014, and
continued for a record 3 years, only dissipating in 2017. It affected the Western Indian Ocean
(WIO) between January and May 2016, and was the strongest bleaching event to occur in the
region since 1998.
The main objective of this report is to provide updated information on the status of coral reefs
in the region after the 2016 mass coral bleaching event. Secondary objectives are to a) update
the national and regional databases on coral reef health, and b) strengthen coral reef
monitoring networks in the region.
This assessment was based on the approach used for the 2017 GCRMN WIO coral reef status
report. Post-bleaching data were collected at long-term monitoring sites in September and
October 2017 in four countries: Tanzania, Kenya, Madagascar and Comoros. In addition, data
were gathered from various organizations, researchers, institutions and programmes across
the region that had conducted their own post-bleaching surveys. The analysis included 153
reef sites from 6 countries with both pre-bleaching (June 2016 and earlier) and post-bleaching
(July 2016 and later) data.
In 2016 thermal stress was nearly equivalent to that experienced in 1998. Overall, hard coral
cover in the region declined by 20% and fleshy algae cover increased by almost 35% following
bleaching in 2016. This is a significant acute loss in living coral, and represents a similar,
although not quite as dramatic step-change in benthic composition to what happened after
the 1998 event (25% loss of coral cover, 2.5 times increase in algae). Seychelles was the worst
hit country, followed by Madagascar. Parts of Mauritius, Kenya and Tanzania were also badly
impacted, while Comoros showed only slight impact. The increase in fleshy algae post-
bleaching has closed the gap between hard coral and fleshy algae cover on a regional scale,
with reefs in some countries experiencing a shift to greater dominance by algae rather than
corals.
Nevertheless, some two thirds of corals that bleached in 2016 recovered, implying a degree of
resistance to thermal stress which enabled recovery. This is a significant positive message: that
resistance to bleaching may be higher than it was in 1998 when thermal stress was broadly
similar but mortality was higher. However the amount of mortality indicates resistance is still
not enough to withstand warming completely.
The monitoring response to the 2016 bleaching event across the region was low, with a lack
of effort to undertake nationwide post-bleaching surveys in most countries. With bleaching
projected to become more frequent and intense in the future, it is vital that governments
develop national responses to prepare and respond effectively in the future. Reefs in the
region have shown the ability to recover from bleaching events, however with the likely future
increases in thermal stress it will become much more challenging for reefs to resist and recover
unassisted. Therefore drastic improvements to management strategies and policies must be
made at local, national and regional scales.
Summary of results from data submitted for this report showing the total number of sites from each
country, the number of sites with coral and algae data used in comparisons between pre- and post-
bleaching periods and the percent change (%) and the post-bleaching cover levels (in parentheses) for
coral and fleshy algae.
Country
# sites
% change (post
% cover)
Observations/interpretation
total
data for both periods
coral
algae
coral
algae
Comoros
9
5
0
5%
(62%)
-
Low impact of bleaching: post-bleaching
(2017) coral cover high (55%), fleshy
algae low
Kenya
30
21
21
0%
(24%)
9%
(36%)
Lamu (north) most affected region with
51% loss in coral cover at 2 sites
Fleshy algae cover higher than coral
cover post-bleaching
Madagascar
41
41
40
-13%
(46%)
56%
(14%)
Only data from west coast, most severe
impacts in northwest.
Relatively high coral cover and low fleshy
algae post-bleaching
Mauritius
5
5
5
~ 0%
(35%)
~ 0%
(7%)
Single site reported, from Anse La Raie
Lagoon.
Seychelles
50
43
32
-50%
(17%)
~45%
(42%)
Inner Islands more severely impacted
than Outer Islands (60% loss vs. 17%,
respectively)
Maximum mortality of 80% at North
Island.
4 sites with no impact or positive gain in
the Inner Islands (NW Mahe and Cerf
Island)
South Africa
5
5
0
~0%
(20%)
<5%
(21%)
Negligible bleaching and no mortality
Tanzania
25
16
16
-10%
(39%)
25%
(15%)
Lower mortality compared to bleaching
indicates substantial recovery and
survival of corals.
Highest impacts on west coast of Unguja
Island
REGIONAL
160
131
114
-20%
(33%)
~35%
(26%)
Approximately 20% decline in coral cover
across 131 sites in 6 countries and 35%
increases in fleshy algae cover across 114
sites in 5 countries
Impact of the 3rd Global Coral Bleaching Event on the Western Indian Ocean in 2016
Table of Contents
1. Regional Chapters ...................................................................................................... 1
1.1 Introduction ................................................................................................................. 1
1.2 Methodology ................................................................................................................ 5
1.3 Regional Results ........................................................................................................... 9
1.4 Discussion ................................................................................................................... 12
1.5 Recommendations ....................................................................................................... 15
1.6 References .................................................................................................................. 17
1.7 Annex ................................................................................................................................ 18
2. National Chapters .................................................................................................... 20
2.1 Comoros ...................................................................................................................... 20
2.2 Kenya .......................................................................................................................... 25
2.3 Madagascar ................................................................................................................. 32
2.4 Mauritius .................................................................................................................... 40
2.5 Seychelles ................................................................................................................... 45
2.6 South Africa ................................................................................................................ 52
2.7 Tanzania ...................................................................................................................... 62
Impact of the 3rd Global Coral Bleaching Event on the Western Indian Ocean in 2016
1. Regional Chapters
1.1 Introduction
The status of coral reefs in the Western Indian Ocean region was most recently updated in a
regional report of the Global Coral Reef Monitoring Network (GCRMN) published in 2017
(Obura et. al 2017). It included data recorded up to 2015. But several factors made an update
in 2017 necessary. First, the 3rd Global Coral Bleaching event, which extended from 2014 to
2017 had a significant presence in the region during 2016 (see fig. 1.1.3). This event was not
captured in the quantitative records of reef cover in the 2017 report, though the progression
of the event was covered in a dedicated chapter (Gudka & Obura, 2017). Second, many
countries in the region have had limited resources for coral reef monitoring since 2012, which
was visible in the 2017 report as a significant gap in recent data records. Thus, obtaining a
new, updated data record as soon as possible following the 2016 coral bleaching event was
seen as a high priority, to strengthen the value of the long-term datasets into the future.
Figure 1.1.1. All monitoring sites from across the WIO for which data were included in this analysis.
The Indian Ocean Commissions' Biodiversity Project, funded by the European Union, is aimed
at strengthening national and regional capacities in the management of biodiversity and
coastal ecosystems to contribute to the conservation and sustainable use of resources
(promotion of bio-sustainable applications). It thus approved a 'post-bleaching assessment' of
coral reef health to be undertaken, to strengthen national and regional capacities for
management of coral reef ecosystems.
2
The objectives of the project were to:
support sampling at long-term monitoring sites in the Biodiversity Projects beneficiary
countries (Comoros, Kenya, Madagascar, Mauritius, Seychelles, Tanzania) to plug the gap
in monitoring since 2012 and document the full impact of the 2016 bleaching event;
update the national and regional databases on coral reef health and report on it in an
update to the 2017 GCRMN report;
further strengthen capacity and standards for monitoring in the regional and national coral
reef networks, including involvement of the non-beneficiary countries (Mozambique,
South Africa, France).
1.1.1 Recent status of coral reefs in the Western Indian Ocean
The regional report on coral reef health, updated to 2015, found that coral reefs in the WIO
underwent a step-change as a result of the global bleaching event in 1998. Coral cover declined
by 25% and algal cover increased 2.5 times. While many reefs that were heavily impacted by
bleaching in 1998 did show some recovery, particularly in Kenya and the Seychelles, other
reefs failed to recover, and some reefs that escaped that event still showed significant decline.
In the intervening period there was a significant increase in general pressures from human
population and economic growth, with increased fisheries, coastal development and pollution
throughout the region. At the same time, minor bleaching events affected different locations
at different times, with significant events in 2005 and 2010 (McClanahan et al., 2011; Souter
& Linden, 2005). Overall, the picture is of a reef system struggling to recover from a major
acute stress (in 1998) while increasing chronic stresses chip away at its resilience. With algal
populations approaching the same cover as hard corals, it is possible that the reefs may be
approaching a threshold beyond which dominance by hard corals becomes less and less likely,
particularly if a major stress event induces significant coral mortality from which the coral
community cannot repopulate.
Coming into the bleaching event of 2016, the regional report speculated that a second step-
decline in reef health in the WIO may be possible. Thermal stress in the global event in 2015-
17 appeared to be greater than the 1998 event, and with coral and algal levels more or less
equivalent, the fear was that further suppressing coral cover may result in a permanent shift
whereby algal cover exceeds coral cover and causes a continuous downward spiral of coral
cover.
1.1.2 Progression of the 2016 bleaching event in the WIO
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
1
. It continued for a record 3 years, only
dissipating globally in 2017.
1
http://www.noaanews.noaa.gov/stories2015/100815-noaa-declares-third-ever-global-
coral- bleaching-event.html. Accessed 20 November 2016.
3
The climatic conditions in the WIO in 2016 were comparable to those experienced in 1998.
Between 1981 and 2017, the two highest mean sea surface temperatures were recorded in
1998 and 2016, with 2016 the only year where mean temperature exceeded 29.5°C (fig. 1.1.2).
Interestingly, the trend seems to indicate a bleaching threshold at 29°C, as both the major
bleaching events of 1998 and 2016, and the less extreme events in 2005 and 2010 occurred
when this value was surpassed.
Figure 1.1.2. Remotely sensed mean daily sea surface temperature (°C) for the Western Indian Ocean from 1981
– 2017 with trendline (blue line) and 29°C bleaching threshold (red line). Data from NOAA High Resolution SST
AVHRR provided by the NOAA OAR ESRL, available at http://las.incois.gov.in/las/.
Figure 1.1.3. NOAA Coral Reef Watch 5km Satellite Coral Bleaching Heat Stress Monitoring in the WIO for the 15th
of each month from January to June 2016. SST anomaly, hotspot and degree-heating-weeks (DHW) are shown.
4
The year began very hot, with sea-surface
temperatures (SST) 1-2°C above long-term
averages (yellow and orange colors) in
Mozambique, Tanzania and Seychelles (fig.
1.1.3). Thermal stress is present in January,
shown by the hotspot and DHW readings, and
builds to a peak in April as can be seen by the
‘hotter’ red and yellow colours and then
dissipates by June. Moderate DHW levels can
be seen in the Mozambique Channel and on
the East African coast in March and April,
whilst very high DHW and hotspot build up are
present east of Madagascar, around Reunion
and Mauritius. A strong hotspot is also present
over Seychelles. In March and April, hot
conditions begin moving northwards, leaving
some cool areas in the south and by May there
are some cool spots in the Northern
Mozambique Channel and north of
Madagascar.
Observations of coral bleaching during the
event were recorded through an online
reporting system set up by CORDIO and
partners in early 2016. Submissions were
based on visual estimates of bleaching at reef
sites by observers and were split into five
broad bleaching categories (none (<1% of
coral cover), low (1-10%), medium (10-50%), high (50-90%), extreme (>90%)). The results were
compiled in the regional GCRMN report (Gudka & Obura, 2017) and have been summarized
here for the six countries included in this analysis (fig. 1.1.4). Overall, bleaching increased until
April, when more than half of all reports were of high or extreme bleaching levels (fig. 1.1.4,
bottom). Of all the bleaching reports received from all WIO countries, 30% were of high or
extreme bleaching, but mortality levels were much lower (fig. 1.3.7, Gudka & Obura, 2017).
1.1.1 Justification for this study
While these bleaching reports give an important indication of bleaching levels, they are biased
towards bleaching, as few observers make the effort to report the absence of bleaching. Hence
the need for the quantitative post-bleaching assessment contained in this report; to provide
an unbiased estimate of the impact of the 2016 bleaching event on coral reefs of the WIO, and
to update and strengthen the national and regional coral reef monitoring programmes to
provide quality data on the health of coral reefs.
Figure 1.1.4. Breakdown of coral bleaching and mortality
observations for six countries in the Western Indian
Ocean in 2016 - top) coral bleaching from January-May
(n=300) and mortality from May-December 2016
(n=153); bottom) monthly breakdown of bleaching
observations (Jan; n=18, Feb; n=40, Mar; n=75, Apr;
n=103, May; n=64, Jun; n=33). Categories represent the
severity of bleaching/mortality reported as percentage of
coral cover bleached/dead at a site.
5
1.2 Methodology
1.2.1 Overall approach
The 2017/18 post bleaching assessment was based on the approach used for the 2017 GCRMN
WIO coral status report. We sought to extend the datasets compiled for that process (which
included data up to 2015 and early 2016), by adding more recent survey data from late 2016
and 2017, as well as data from new sources.
1.2.2 Data collection and management
As with the 2017 GCRMN WIO coral status report, CORDIO played the role of the regional
coordinator and led planning, data collection, analysis and report writing, under the auspices
of the GCRMN and coral reef networks for the WIO, and the regional Coral Reef Task Force.
Data for the assessment was collected through two channels. Funding provided by the
Biodiversity Project was used to organize field surveys to collect post-bleaching data in
September and October 2017 in four of the project’s beneficiary countries; Tanzania, Kenya,
Madagascar and Comoros. Surveys were organized by National Coordinators in each country,
who led teams to collect benthic, fish, coral condition and recruit data at a number of long-
term monitoring sites. Long-term monitoring sites were selected to maintain consistency in
time-series datasets, with a priority for sites that had not yet been monitored after the 2016
bleaching event. As most sites with historical data in the Seychelles had already been surveyed
post-bleaching, additional surveys were not funded. Unfortunately, due to logistical and
administrative challenges, post-bleaching surveys could not be organized in Mauritius during
the project implementation phase.
In addition to the above surveys, data were gathered from various organizations, researchers,
institutions and programmes across the region, through the coral reef networks/Coral Reef
Task Force for the WIO. Calls for data were made by email, during a webinar about the project
on the Reef Resilience platform in July 2017 (http://www.reefresilience.org/western-indian-
ocean-post-bleaching-assessment-training/), and at a special session held at the WIOMSA
Scientific Symposium on the 2nd of November 2017. A data sheet template was provided for
contributors to compile their data, and a Data Sharing Agreement was signed. Data were only
requested at a site-summary level (i.e. mean values at site levels) to encourage sharing and
collaboration. No raw-data were requested. Efforts were also made to include WIO countries
that are not beneficiaries of the Biodiversity Project, i.e. Mozambique, France and South
Africa, and data were obtained from South Africa.
Data cleaning, handling, management and compilation was mainly done using R studio.
Overall, we obtained data from 33 monitoring programmes or individuals, comprising 862
surveys of corals and 729 surveys of algae, from 153 locations across 6 countries (Table 1.2.1).
Table 1.2.1. Summary of data collected from the Western Indian Ocean for the post-bleaching assessment
Coral
Fleshy Algae
Countries
6
5
Locations/Sites/Stations
153
131
Site surveys
862
729
Start Year
1992
1992
End Year
2017
2017
Years surveyed
26
26
6
Some bleaching figures presented in this report were used in the 2017 GCRMN WIO coral
status report and have been referenced accordingly. The bleaching data were collected using
methods of varying levels (visual estimates, quantitative quadrats and transects) and
submitted to CORDIO during the 2016 bleaching dataset via an online form and emails. The
full list of data contributors is provided in the annex (Section 1.7).
Data contributors:
Organisations:
AIDE Comoros, Kenya Marine and Fisheries Research Institute, Kenya Wildlife Service, AROCHA
Kenya, CORDIO, EAWS, WWF, Blue Ventures, Frontier Madagascar, Madagascar Research and
Conservation Institute (MRCI), WCS Madagascar, Reef Conservation, Seychelles National Parks
Authority, Global Vision International, Seychelles Islands Foundation (SIF), Island Conservation
Society (ICS), Green Islands Foundation (GIF), Marine Conservation Society Seychelles,
Oceanographic Research Institute (ORI) South Africa, South African National Biodiversity
Institute (SANBI) Institute of Marine Sciences University of Dar es Salaam, Tanga Coelacanth
Marine Park, Chumbe Island Coral Park (CHICOP).
Individuals:
Ahamada S., Freed. S, Madi Bamdou M., Maharavo J., Mouhhidine J., Nicet J.B, Ali Ussi.
Fieldwork teams:
Madagascar: Ihando Andrainjafy (National Coordinator), RANDRIANANDRASANA José,
RADONIRINA Lebely, ZAKANDRAINY Andriamanjato, ANDRIALOVANIRINA Nicolas, Lope Jean
Charles, BAKARY Gisèle, Zavatra Jean Baptiste, Rajesy Farcy.
Kenya: Mwaura Jelvas (National Coordinator), Josephine Mutiso, Albert Gamoe, Joseph
Kilonzo, Peter Musembi.
Tanzania: Saleh Yahya (National Coordinator), January Ndagala, Ali M. Ussi, Mohammed S.
Mohammed, Hassan Kalombo.
Comoros: Mmadi Ahamada (National Coordinator), Nassur Ahamada Mdroimana, Rachad
Mourid, Zamil Mannfou, Jaffar Mouhidine, Adfaon Mchinda, Mouchtadi Madi Bounou
South Africa: Sean Porter (National Coordinator), Kerry Sink, Michael Schleyer, David Pearton,
Camilla Floros, Mari-Lise Franken, Stuart Laing.
1.2.3 Analysis
The main objective of the post-bleaching assessment was to quantify the impact of the
bleaching event in 2016 on coral cover in the form of direct mortality, and corresponding
changes in algal cover. Benthic cover data collected using different GCRMN-approved methods
were used in the analysis (Obura et. al., 2017). To ensure consistency in reporting on the status
of coral reefs in the WIO region, figures and graphical representations are akin to the 2017
WIO GCRMN coral reef status report.
Bleaching has direct impacts on living coral, and the knock-on or longer-term consequences of
coral mortality are changes in algal cover, coral recruitment and fish population structures.
Because of the short timeframe of this assessment in relation to the bleaching in 2016, and
the principal data collected by teams in the region (Obura et. al., 2017), it was decided that
hard coral cover and fleshy algal cover were the most appropriate variables for analysis and
presentation. Coral recruitment and fish populations were not analysed because of the time-
lag for impacts to manifest, the number of other factors apart from bleaching that could affect
7
them, and the paucity and quality of datasets. Due to differences in how various algal
communities are measured and defined by different monitoring programmes, turf,
filamentous, macro and Halimeda were combined into a single variable called fleshy algae.
This was also done to align with other recent regional reports on coral health.
Comparisons of coral and fleshy algae cover across the bleaching event, was done in two ways.
First, we compiled the long-term data to look at trends across the 'break' in 2016. Where this
break is provided in the data, we portray two lines - one up to June 2016 (pre-bleaching) and
the other from July 2016 onwards into 2017 (post-bleaching). Second, to focus on the effect
of coral mortality, we use data from sites in the period 2012 - June 2016 (pre-bleaching) paired
with data from July 2016-2017 (post-bleaching). Because our sampling focused on long-term
monitoring sites, many of which had not been sampled for several years (see Obura et al. 2017)
the wide pre-bleaching window of 2012-June 2016 was necessary to enable analysis of
sufficient samples (sites). We assumed that any mortality from this period to July 2016
onwards was due to the bleaching event, though there could have been other causes of coral
mortality. For each site, we selected the most recent date in the pre-bleaching and post-
bleaching windows for analysis.
To improve the reliability of results, several quality control measures were applied to filter the
data before analysis. Firstly, only data collected using GCRMN methods were included in the
analysis, and data were aggregated to the broadest, most basic level to cater for issues arising
from the combination of data collected via different methods and levels. Additionally, only
sites with both pre- and post-bleaching data were used in the analysis, to increase the accuracy
of comparisons before and after the 2016 bleaching event. Comparisons between hard coral
and fleshy algae were made only using sites where both variables were measured.
Analysis was done at national and regional levels. For both mean coral and fleshy algae (for
those countries where data were available) cover, trends over time were traced together with
a 95% confidence interval (fig. 1.2.1a), with the break in time series before/after bleaching in
2016 shown by different lines. The difference between ‘pre-bleaching’ (2012 - June 2016) and
‘post-bleaching’ (July 2016 – 2017) periods is shown by column graphs (mean ± s.e), using the
most recent value at each monitoring site for each period (fig. 1.2.1b). The graphical
representation is based on the GCRMN WIO 2017 report.
8
a b
Figure 1.2.1. Illustration of the analyses presented in this report: a) Trend in mean cover of live coral (blue, open
circles) and macro algae (green, closed circles) before (solid lines) and after (dotted lines) the bleaching event b)
national mean coral and algae cover before and after (response) the bleaching event. Data from Tanzania.
Due to the nature of this analysis, compiling data from different programmes that use different
methods, different levels of expertise and different levels of identification, there are
limitations to the analysis and results. Secondly, inconsistency in monitoring effort at sites
across years means that trends shown in the graphs may reflect sampling artifacts, rather than
real changes in coral reef health. The long temporal gaps between monitoring at sites,
especially in recent years, makes pre- and post-bleaching comparisons less accurate. There
were also no coherent nation-wide monitoring responses to the bleaching event, so data are
mainly from ad hoc responses or NGO monitoring programmes. For the regional results,
unequal representation of samples from countries biases the results. For some countries, such
as Mauritius and Comoros, the number of sites included is very small, due to lack of
participation and monitoring, and is not representative of historical monitoring in the
countries. Also, data from Mozambique, South Africa and France were not included in the
overall regional analysis.
An issue we identified as significant, and that monitoring programmes need to address is the
repeated monitoring of precisely the same locations from one year to another. Some sites
have very patchy corals, and different observers working in different years may simply be
placing transects in different locations, resulting in high variance in the data that don't reflect
real changes in the water. Greater standardization and reliability of methods is essential to
improve future reliability.
1.2.4 Data archiving and access
The efforts undertaken by CORDIO during the 2017 GCRMN regional reporting process,
brought together historical coral reef (benthic and fish) data into central regional datasets for
the first time. This post-bleaching assessment has updated the datasets with data from 2016
and 2017. The next steps to continue efforts to increase data sharing and availability, are to
make these datasets publicly available with the permission of all the data contributors on a
secure data repository, and visible through portals such as Ocean Biographic Information
9
System (OBIS). However, some kind of data citation and sharing-agreement must be
developed to facilitate this process.
1.3 Regional Results
1.3.1 Introduction
This section presents the regional results of the post-bleaching assessment using summary
benthic data submitted from six countries; Comoros, Kenya, Madagascar, Mauritius,
Seychelles and Tanzania. Only sites with both pre-bleaching (earlier than July 2016) and post-
bleaching (later than June 2016) data were used. The analysis included a total of 153 sites,
with Seychelles having the greatest number of samples with 43 sites and Mauritius the least
number of sites, with 5.
1.3.2 Coral cover
The trend in mean hard coral cover between 1992 and 2017 for most of the countries is very
erratic, largely as a result of inconsistency in sites sampled from year to year (fig. 1.3.1). The
mean cover of coral initially declines between 1992 and 2006 from about 40% to 20-30%, then
shows an improvement till 2015, returning to 40%. It then declines again, which can be directly
attributed to the 2016 bleaching event. Kenya, Madagascar and Seychelles show recoveries in
hard coral cover from the 1998 bleaching event up to 2016, but Comoros, Mauritius and
Tanzania show no apparent trend. For all countries except Tanzania, hard coral cover
decreased after the 2016 bleaching event. In 2017, Comoros and Madagascar had the highest
coral cover at over 45%, Tanzania and Mauritius were close to the regional mean at 35%, and
Seychelles and Kenya had the lowest coral cover of below 30%.
Figure 1.3.1. Mean hard coral cover across all 6 countries with data in the WIO (colored lines with symbols), the
regional mean with 95% confidence limits around the mean (black line and grey shading) and a linear regression
line on the regional mean (grey dashed line, y = 0.480x + 24.367).
The number and consistency of monitoring sites through the years has varied greatly among
countries (fig. 1.3.2). Kenya and Seychelles have consistent and large-scale monitoring effort
over time. Madagascar has shown a strong response to the bleaching event with a large
increase in samples in 2016 and 2017, while Tanzania has gaps in monitoring for some years,
and Comoros and Mauritius have very sporadic samples. It should be noted that sites
monitored in the past (see Obura et. al., 2017) but that were not sampled after the 2016
10
bleaching event have not been included in this analysis, so there are a significant number of
coral reef monitoring sites in all six countries that are excluded from this analysis. The fact that
these sites have not been monitored is a further sign of the challenge of maintaining regular
and reliable monitoring programmes in the region (Obura, 2013).
The scatterplots (fig. 1.3.2) show that up to early 2016, Seychelles, Comoros, Kenya and
Madagascar all show an increase in coral cover. Mauritius and Tanzania show a very slight
decline in coral cover.
Figure 1.3.2. Hard coral cover by country for the period 1992-2017 (excluding sites without both pre-bleaching
and post-bleaching data). Individual site records (blue open circles), the mean and 95% confidence interval (dark
blue line and grey shading) and linear regression (red line) are shown.
1.3.3 Fleshy algae
Fleshy algae and hard coral cover were both measured in five of the six countries. Fleshy algae
was declining from a peak of close to 40% in 2004, but began an upward trend in 2013, which
continued through the 2016 bleaching event into 2017 (fig. 1.3.3). These trends complement
the overall change in coral cover, including the clear break and decline in hard corals between
the pre- and post-bleaching periods.
A pattern is discernible and follows that reported in the latest regional reef monitoring report
(Obura et al. 2017), that coral and fleshy algal covers reversed in dominance after the 1998
bleaching event, then from 2006 corals recovered and became more dominant again. Now
from the 2016 event the same flip may be happening but from a starting point where the gap
is much smaller than in 1998. It will take a few years to see if coral cover increases and fleshy
algae declines again.
11
Figure 1.3.3. Regional average of hard coral (blue line, open circles) and fleshy algae (green line, closed circles)
cover pre- and post-bleaching (mean and 95% confidence interval) (n = 131). Post-bleaching period is from July
2016 onwards and is represented by a dotted line, and pre-bleaching is a solid line.
Looking at the relationship between fleshy algae and hard coral in each country individually,
algae abundance is relatively low in Madagascar, Mauritius and Tanzania in 2017 at under 20%,
whilst Kenya and Seychelles both have algae levels greater than hard coral, at over 40% (fig.
1.3.4).
Figure 1.3.4. Trends in fleshy algae (green line, closed circles) and hard coral cover (blue line, open-circles) in
countries where algal cover was collected. The shaded areas represent the 95% confidence interval and mean.
Only countries with hard coral cover and fleshy algae data were included in the analysis.
12
1.3.4 Coral/algal interactions
Just before the bleaching event in 2016, the
hard-coral cover for five countries in the
WIO stood at 40 ± 2% (mean ± se) after
which it fell by 20% to 32 ± 1.8% due to the
bleaching event (fig. 1.3.5). During the same
period, fleshy algae cover increased by
approximately 34% from 19 ± 2% to 26 ±
2%.
1.4 Discussion
The WIO was affected by the 3rd global coral
bleaching event in the regional summer of
2016 as El Niño conditions reached record
levels. This event was in many ways
equivalent to the 1998 event in the WIO in
the amount of heat stress (fig. 1.1.2), with
the 3rd and 4th most severe thermal stress
events happening in 2010 and 2005,
respectively.
Mass bleaching took place across all the countries of the WIO between January and May 2016,
and bleaching persisted at several reefs for months after conditions had cooled (Gudka &
Obura, 2017). Aggregating across 131 survey sites from 6 countries, hard coral cover declined
from 41 ± 1.9% (mean ± se) to 33 ± 1.8%, a drop of 20%. For 114 survey sites from 5 countries,
fleshy algae cover increased by ~35% from 19 ± 2% to 26 ± 2%. The comparable responses in
1998 of hard coral and algae were 25% and 150% respectively.
Thus, although bleaching was widespread, the subsequent coral mortality was not as extensive
as the bleaching, and was less than mortality in 1998. This recovery from bleaching and lower
mortality implies a degree of resistance to bleaching, which enabled corals to survive the high
thermal stress and recover. This is a significant positive message; that resistance to bleaching
may be higher than it was in 1998. However, the amount of mortality indicates it is still not
enough to resist warming completely, and the increase in algal cover to a higher level than
after the 1998 event is cause for concern (Obura et. al. 2017).
The measure of coral mortality reported here is more precise than the estimate provided by
visual observations of bleaching (Gudka & Obura, 2017). The visual observation method
enabled us to state that "10% of sites experienced high or extreme mortality (>50%) after
bleaching” (and about 20% of sites experienced moderate mortality), which corresponds to
the quantitative value of 20% mortality reported here.
Coral mortality among countries was heterogeneous. Seychelles was the worst-hit country
(Table 1.4.1), while Madagascar also experienced a sharp decline in coral cover. Comoros and
Kenya showed very low impacts, while Mauritius and Tanzania were relatively unaffected.
Following the bleaching event, reefs in Madagascar, Comoros and Mauritius had some of the
highest coral cover levels in the region, with moderate levels in Tanzania, and low levels in
Kenya and Seychelles. Because one third of sites reported here were from the Seychelles, the
Figure 1.3.5. Hard coral and fleshy algae mean cover and
standard error for pre-bleaching and post-bleaching
(response) periods for all sites where both variables were
reported. Pre-bleaching data are from 2012- June 2016
and post-bleaching (response) data are from July 2016 –
2017 (n = 114).
13
overall mortality level of 20% may slightly overestimate the average mortality across the
region.
Table 1.4.1 Summary of results from data submitted for this report showing the total number of sites from each
country, the number of sites with coral and algae data used in comparisons between pre- and post-bleaching
periods and the percent change (%) and the post-bleaching cover levels (in parentheses) for coral and fleshy algae.
Country
# sites
% change (post
% cover)
Observations/interpretation
total
data for both periods
coral
algae
coral
algae
Comoros
9
5
0
5%
(62%)
-
Low impact of bleaching: post-bleaching
(2017) coral cover high (55%), fleshy algae
low
Kenya
30
21
21
0%
(24%)
9%
(36%)
Lamu (north) most affected region with 51%
loss in coral cover at 2 sites
Fleshy algae cover higher than coral cover
post-bleaching
Madagascar
41
41
40
-13%
(46%)
56%
(14%)
Only data from west coast, most severe
impacts in northwest.
Relatively high coral cover and low fleshy
algae post-bleaching
Mauritius
5
5
5
~ 0%
(35%)
~ 0%
(7%)
Single site reported, from Anse La Raie
Lagoon.
Seychelles
50
43
32
-50%
(17%)
~45%
(42%)
Inner Islands more severely impacted than
Outer Islands (60% loss vs. 17%,
respectively)
Maximum mortality of 80% at North Island.
4 sites with no impact or positive gain in the
Inner Islands (NW Mahe and Cerf Island)
South Africa
5
5
0
~0%
(20%)
<5%
(21%)
Negligible bleaching and no mortality
Tanzania
25
16
16
-10%
(39%)
25%
(15%)
Lower mortality compared to bleaching
indicates substantial recovery and survival
of corals.
Highest impacts on west coast of Unguja
Island
REGIONAL
160
131
114
-20%
(33%)
~35%
(26%)
Approximately 20% decline in coral cover
across 131 sites in 6 countries and 35%
increases in fleshy algae cover across 114
sites in 5 countries
In the ten years preceding the bleaching event, there was an upward trend in regional hard
coral cover, reflecting recovery from the 1998 bleaching event. But this has now reversed as a
result of the 2016 bleaching event. The trajectory of coral cover at country levels shows high
levels of variation (fig. 1.3.1), with many peaks and troughs due to localized changes in reef
health as well as sampling inconsistencies. With this degree of variation, and particularly the
changing and irregularity of monitoring sites being measured and reported, it is difficult to
make strong conclusions.
The increase in fleshy algae post-bleaching, has closed the gap between hard coral and fleshy
algae cover on a regional scale. Seychelles and Kenya now have on average higher levels of
algae than coral cover, indicating that they may be close to experiencing a phase-shift to more
algal dominated reef systems (Hughes et. al. 2007; McManus et. al. 2004). Alternatively, low
algal abundance in Madagascar, coupled with the high coral cover indicates that these reefs
are in a healthier state.
14
Aggregation of data to the regional level, as we have done here, involves many challenges.
Unequal, limited and non-representation of data from countries restricted our ability to make
a comprehensive assessment of the region. It is impractical to acquire all relevant data from
each country, but it is important that participation and data sharing increase over time, to
improve the power and accuracy of results.
An important outcome from this and previous regional initiatives, is demonstration of the
erratic monitoring effort over time in some countries. Seychelles and Kenya have shown the
most consistent monitoring, but other countries have large gaps, leading to years where no
data are available (and see Obura, 2013). After the 1998 bleaching event, there was an
increase in effort and establishment of new monitoring programmes over a period of several
years (Obura et. al., 2017). One of the goals of this project was to ensure the gap in monitoring
after the 2016 bleaching event was shortened in beneficiary countries. However more stable
funding for monitoring is needed from internal resources within countries and programmes.
To match the expanded effort that occurred after the 1998 event, WIO countries and their
partners need to invest in monitoring within the next one or two years and ensure the
variation in sites being regularly monitored is reduced.
Most of the monitoring reported here was headed by NGOs and other monitoring
programmes, rather than national institutions, with the exception of Kenya Wildlife Service.
Given the importance of coral reefs to national economies and livelihoods, and that major
bleaching events will repeat at greater frequency (van Hooidonk et al., 2016, Hughes et al.,
2018), it is vital that governments develop national responses to bleaching events to allow
them to prepare and respond effectively. This will involve the ability to mobilize funding to
carry out consistent and emergency monitoring, and to use this information to manage reefs
to maximize their sustainability and find ways to adapt users and economic sectors to the
changing status of coral reefs.
This project has allowed the first update to the WIO benthic dataset since it was developed
during the 2017 GCRMN reporting process. It has also helped promote networking and
partnerships between researchers in the region and is continuing to stimulate the process of
data sharing and collaborations. It is important for institutions and researchers to maintain
this effort so the WIO coral reef science community can continue to move towards an open-
data science approach.
Reefs in the region have shown the ability to recover from bleaching events in the past (Obura
et. al., 2017), for example in Seychelles and Kenya, however with bleaching projected to
become more frequent and intense (Hughes et. al., 2018), it will become much more
challenging for reefs to recover unassisted. It is notable that East African reefs figure
prominently in a very recent analysis of which of the world’s reefs face the most promising
climate futures (Beyer et al. 2018). The coasts of Tanzania, Kenya, south Somalia, northwest
Madagascar and Comoros appear to have favourable futures, so if well managed could both
persist in reasonable health and be key source reefs for other reef areas that will face greater
climate threats. Therefore, drastic improvements to management strategies and policies must
be made soon at local, national and regional scales.
15
1.5 Recommendations
Based on the current state of the coral reefs in the region, and their response to the coral
bleaching of 2016, as well as long-term trends, the following recommendations are made:
Monitoring and understanding coral reef health
1) Coral reef monitoring should be more strongly supported at key long-term sites, as well as
expanded to include more sites and other parameters. Therefore, it is essential that
countries re-evaluate their funding strategies and sources, and prioritize monitoring of
these key resources.
2) Establish contingency funds to enable responsive monitoring to particular events.
3) Establish national coral bleaching response plans to include preparation, funding,
monitoring and communications (awareness creation) capacity. This will allow national
research institutions to respond more effectively to future coral bleaching.
4) Invest in efforts to develop or trial existing databases for improved storage and access of
coral reef and other marine biodiversity data. Support training of technical staff in general
principals of data management as well as in database use.
5) Continue to collate historical coral reef health data into a central, safe database for secure
storage and ease of access at national and regional levels. To support this, a system to
share metadata on coral reefs will make it easier to share information among organisations
and foster greater collaboration.
6) Identify regional strategies to source and allocate funding for consistent and continued
coral reef monitoring through the GCRMN and the Nairobi Convention’s Coral Reef Task
Force.
7) Standardize coral reef monitoring methodologies and site selection between countries and
programmes so that monitoring at long-term sites is maintained and prioritized.
Maintaining and improving the health of coral reefs
8) Promote management strategies that help to control fleshy algae on reefs. These may be
through fisheries, to protect herbivore populations and the role of herbivory, water quality
management, to minimize fertilization of algae, or other measures.
9) Improve coral reef management effectiveness and increase the scale of management
measures.
10) Mitigate controllable and avoidable local threats to coral reefs as much as possible through
smart management strategies.
11) Control and regulate nearshore and coastal activities that can be damaging to nearby coral
reefs e.g. dredging, illegal extraction, pollution, agricultural run-off etc.
16
12) Trials of restoration interventions for conserving and repairing coral reefs need to be
supported, with transparent evaluations of effectiveness and success based on area
impacted and cost.
Policy and research
13) Targeted research on the differential response of reefs to thermal stress and coral
bleaching should be undertaken, to identify if there are resilient reefs (bleaching refuges),
and what can be done to protect such sites and to promote seeding of other reefs.
14) Research to understand the long-term effects of the 2016 bleaching event on coral
recruitment and fish populations at badly impacted sites.
15) Coral reefs sustain many important business sectors, including tourism and fisheries, and
are among the most valuable ecosystems providing services and food to the poor. Better
understanding their value can be achieved through understanding them as key assets in
supporting the Sustainable Development Goals, and this can elevate their importance in
national and regional policy circles for protection and management.
17
1.6 References
1. Beyer H.L., Kennedy E.V., Beger M., Chen C.A., Cinner J.E., Darling E.S., Eakin C.M., Gates R.D.,
Heron S.F., Knowlton N., Obura D.O., Palumbi S.R., possingham H.P., Puotinen M., Runting R.K.,
Skirving W.J., Spalding M., Wilson K.A., Wood S., Veron J.E., & Hoegh-Guldberg O. (2018) Risk-
sensitive planning for conserving coral reefs under rapid climate change. Conservation Letters,
109, e12587.
2. Gudka M, Obura D (2017). The 2016 coral bleaching event in the Western Indian Ocean – overview
in Coral reef status report for the Western Indian Ocean (2017) Obura D., Gudka M., Abdou Rabi
F., Bijoux J., Freed S., Gian S.B., Maharavo J., Mwaura J., Porter S., Sola E., Wickel J., Yahya S. and
Ahamada S. (pp. 26-37). Global Coral Reef Monitoring Network (GCRMN)/International Coral Reef
Initiative (ICRI). Indian Ocean Commission (IOC).
3. Hughes T.P, Rodrigues M.J, Bellwood D.R, Ceccarelli D, Hoegh-Guldberg O, McCook L,
Moltschaniwskyj N, Pratchett M.S, Steneck R.S, Willis B (2007). Phase Shifts, Herbivory, and the
Resilience of Coral Reefs to Climate Change. Current Biology, 17(4), 360-365.
https://doi.org/10.1016/j.cub.2006.12.049.
4. Hughes, T. P., Anderson, K. D., Connolly, S. R., Heron, S. F., Kerry, J. T., Lough, J. M., et al. (2018).
Spatial and temporal patterns of mass bleaching of corals in the Anthropocene. Science,
359(6371), 80–83. http://doi.org/10.1126/science.aan8048.
5. McClanahan, T. I. M., Maina, J. M., & Muthiga, N. A. (2011). Associations between climate stress
and coral reef diversity in the western Indian Ocean. Global Change Biology, 17(6), 2023-2032.
6. McManus J.W, Polsenberg J.F (2004). Coral–algal phase shifts on coral reefs: Ecological and
environmental aspects, Progress in Oceanography, 60(2), 263-279
7. Obura D., Gudka M., Abdou Rabi F., Bijoux J., Freed S., Gian S.B., Maharavo J., Mwaura J., Porter
S., Sola E., Wickel J., Yahya S. and Ahamada S. (2017). Coral reef status report for the Western
Indian Ocean (2017). Global Coral Reef Monitoring Network (GCRMN)/International Coral Reef
Initiative (ICRI). Indian Ocean Commission (IOC). pp 144
8. Obura, D. (2013). Review of coral reef monitoring activities in the southwest Indian Ocean.
http://www.commissionoceanindien.org/fileadmin/resources/ISLANDSpdf/Review_of_coral_ree
f_monitoring_activities.pdf
9. Souter, D., & Linden, O. (2005). Coral reef degradation in the Indian Ocean: Status report 2005.
10. van Hooidonk, R., Maynard, J., Tamelander, J., Gove, J., Ahmadia, G., Raymundo, L., et al. (2016).
Local-scale projections of coral reef futures and implications of the Paris Agreement. Scientific
Reports, 1–8. http://doi.org/10.1038/srep39666
18
1.7 Annex
2016 bleaching data contributors to CORDIO
Organization
Observers
African Impact
Connie, Celeste Alex Botha, Karin
Albion Fisheries Research Centre, Mauritius
Vikash Munbodhe
andBeyond
Mnemba Island Dive and Conservation Team
AROCHA Kenya
Peter Musembi
Blue Ventures – Comoros
Sarah Freed
Blue Ventures
Abigail Leadbeater, Katrina Dewar
Cerf Island Conservation Programme
Savinien Leblond
Chumbe Island Coral Park (CHICOP)
Enock Kayagambe, Ulli Kloiber
Comoros CRMN
Jaffar mouhhidine, Mathieu, Mouchtadi Mmadi
CORDIO EA
David Obura, Melita Samoilys, Mishal Gudka
Cousine Island
Nina, Paul Anstey
COWI Tanzania
Matthew Richmond, Reinar Odsgaard
Divine Diving
Oscar Domingo Celades
Fisheries Protection Service
Sylvain Lisette
Frontier/MIMP
Chris Roberts
GVI Seychelles
Anna Koester, Chris Mason-Parker
ICS Alphonse
Ariadna Fernandez
IMS – SUZA
Ali M. Ussi
IOC Biodiversity program
Regional CRTF, Said Ahamada
Islands Conservation Society
Dr Joanna K Bluemel, Mr Peter Holden
Kasa Divers/Friends of Maziwe
Kerstin Erler
Kenya Marine and Fisheries Research
Institute
Jelvas Mwaura
Kenya Wildlife Service
Jillo Katello Wato
Lagon Bleu
Yann
Madagascar Coral Reef
Network/IOC/MAREX
Madagascar Coral Reef Network
Mafia Island Diving Ltd
Danielle Keates and David von Helldorff, Ivon
Sebastian
Marine Conservation Society Seychelles
Dr David Rowat
marinecultures.org
Christian Vaterlaus, Thomas Sacchi
Masoala Marine Park
Jean Baptiste Zavatra
Mauritian Wildlife Foundation
Reshad Jhangeer-Khan
Mauritius Oceanography Institute
Bacha Gian Suraj and others
Nature Seychelles
Louise Malaise
One Ocean, the Zanzibar dive centre
Oceanographic Research Institute
Sean Porter
Reef Conservation
Celine Miternique, Emma, Natalie Summers
Reef Doctor
Apolline Mercier
South African National Biodiversity Institute
Kerry Sink
SAM Program / California Polytechnic State
University / California Sea Grant
Jennifer O'Leary
Scuba Do Zanzibar
Tammy Holter
19
Organization
Observers
Seychelles Islands Foundation
April J Burt, Karen Chong-Seng
Shoals Rodrigues
Jovani Raffin and Rebecca Claus
SIREME
David Obura, Lionel Bigot
Sokoine University of Agriculture
Dr. Nsajigwa Mbije
Sound Ocean Ltd
Jason Rubens
Tanga Coelacanth Marine Park
January Ndagala
Tanga Tourism Network Association
Sibylle Riedmiller
Tanikely National Park
Farcy Rajesy
Ten Degrees South
Isobel Pring
UMAMA
Zamil Maanfou
Vrije Universiteit Brussel (VUB)
Filip Huyghe
WCS Madagascar
Komeno Roberto, Emily, Julien Leblond, Jean-
Benoit Nicet
WiseOceans
Georgina, Hannah Harries, Krishna Ashok, Jo
Eames
Young reSearchers Organisation
Madagascar
Danny Kornelio Ravelojaona
Other
Alan Sutton
Jan Robinson
Patrick Harbeland
Rob miller
Impact of the 3rd Global Coral Bleaching Event on the Western Indian Ocean in 2016
Data contributors: The data presented in this report remains the property of the organisations and individuals who
collected them.
2. National Chapters
2.1 Comoros
Data contributors: AIDE Comoros, Ahamada. S, Freed. S, Madi Bamdou. M, Maharavo. J,
Mouhhidine J., Nicet J.B.
Coordination and data collection: Mmadi Ahamada (National Coordinator), Nassur Ahamada
Mdroimana, Rachad Mourid, Zamil Mannfou, Jaffar Mouhidine, Adfaon Mchinda, Mouchtadi
Madi Bounou
2.1.1 Background to the 2016 bleaching event
Figure 2.1.1. Coral reef monitoring stations in Comoros for which data were included in this study.
2.1.1.1 History of coral bleaching events in the Comoros
The Comorian islands of Grande Comore, Moheli and Anjouan were affected by the first global
bleaching event in 1998 with bleaching reported at between 10-50% across various sites and
mortality estimated at 50% thereafter (Quod & Bigot, 2000). At Moheli Island mortality of hard
corals was recorded at 45% overall and 15% at Mitsamiouli reef (Ahamada et al., 2004). A
decline in coral cover over the period between 1998/99 to 2002 was reported, with low to
negligible recovery rates (Quod & Bigot, 2000). Live hard coral cover by the year 2002 had
dropped to approximately 40%, down from averages of about 76%, one year before the 1998
global bleaching event (Ahamada et al., 2004).
21
2.1.1.2 Progression of the 2016 coral bleaching event
Figure 2.1.2. National Oceanic and Atmospheric Administration (NOAA) Coral Reef Watch satellite bleaching
products, showing the bleaching related climatic conditions present at a remote monitoring station in Comoros.
Remote sensing of sea-surface temperature around the Comoros showed milder conditions
than experienced in most other WIO countries. Bleaching stress started to pick-up from mid-
March 2016, with less than a month in alert level 1 in April and only reached a maximum of 5
degree-heating-weeks (fig. 2.1.2).
Bleaching was observed at several monitoring sites as early as November 2015. An average of
over 40% of corals were bleached across seven sites surveyed in April 2016 with some signs of
early-mortality at all sites (fig. 2.1.3). Stress had completely dissipated by early May.
Figure 2.1.3. Coral bleaching and associated mortality recorded at seven sites in the Comoros in 2016. Categories
represent the severity of bleaching and associated mortality reported as a percentage of coral colonies at a site.
(Freed et.al, 2017)
22
2.1.2 Results
In total, data from 9 sites (Bambao, Bimbini,
Itsandra, Mea, Mitsamiouli, Moroni,
Nkandzoni, Sambia and Wani) across the
islands Anjouan, Grande Comore and
Moheli were assessed between 1999 and
2017.
After the 1998 bleaching event, the mean
coral cover was around 33% in 1999, and
this slowly increased to 55% in 2007 (fig.
2.1.4). Coral cover declined between 2007
and 2011, mainly due to some bleaching in
2010, to a low of just under 30%, but then
recovered once more to over 55% by 2015.
After the bleaching event in 2016, coral
cover was slightly lower than in 2015, at
55% in 2017.
For nine sites monitored in 2017, average
fleshy algae abundance was lower than 5%,
with six of these sites having no algae. At
the five sites with data immediately pre-
bleaching (i.e. 2012-2015) and post-
bleaching, mean coral cover was
equivalent, at 59 ± 4.4% and 62 ± 8.3% (mean ± se) respectively (fig. 2.1.5a).
a
b
Figure 2.1.5 Pre and post-bleaching (response) mean hard coral cover (with standard error bars) a) for all
Comoros reef sites (n=5) b) for Grande Comore, Moheli and Anjouan sites (Grande Comore n=2, Moheli n=2,
Anjouan n=1). Pre-bleaching data are from 2015 and ‘response’ data are from September 2017. Only sites with
data for both periods were included in the analysis.
When comparing the impact of the bleaching across the 3 islands, reefs on Grande Comore
showed a 30% increase in live hard coral cover from 57 ± 13.5% (pre-bleaching) to 73 ± 15%
(post-bleaching) (fig. 2.1.5b). In Moheli there was close to a 20% decline in hard coral cover
Figure 2.1.4. Trends in hard coral cover on Comorian reefs
before and after the 2016 bleaching event (national mean
(dark bold line) split into historical pre-bleaching data (purple
line, open-circles) and post-bleaching data from July 2016
onwards (blue line, open-squares), 95% confidence limit
(grey shaded area), individual monitoring stations (faded
background lines)). Only stations with data for both periods
were included in the analysis (n=9).
23
(60 ± 1.0% to 49 ± 13.5%) and at one site in Anjouan, there was a rise in hard coral cover by
just over 5% (61% to 65%).
2.1.3 Discussion
Even after the bleaching event, Comoros coral reefs retain moderate to high coral cover, with
close to 55% on average in 2017. Mortality due to bleaching in 2016 was low as there was no
significant change in coral cover after the bleaching event, and several sites showed increases
in coral cover. This was despite significant bleaching being observed at a number of sites at
the peak of the event, therefore it seems that there was substantial recovery rather than
mortality. This was likely due to the fact that temperatures had subsided by early May,
truncating the period of thermal stress endured by the corals, allowing for greater recovery
and survival. Reef sites at Moheli seem to have been the most badly impacted.
An important finding is that of the 9 sites surveyed in 2017, there were very low levels of fleshy
algae, and high levels of bare substrate. This will provide good conditions for recovery by
potentially increasing larval settlement and survival rates. Management measures should aim
to maintain this low-algal level through maintaining herbivory on reefs and ensuring low
nutrient run-off.
Unfortunately, due to intermittent monitoring efforts, especially recently, the number of sites
and years included in the analysis was low thereby limiting the overall conclusions that can be
made. There were only 10 time points over the 19-year period of analysis.
Although reefs around Comoros appear to be in a healthy, resilient state post-bleaching,
authorities should be proactive in their management and conservation efforts, including
increased monitoring, as pressures will undoubtedly continue to rise through climate change,
over-fishing, pollution and erosion from land-based activities.
2.1.4 Recommendations
Maintaining and improving the health of coral reefs
1) Maintain the current healthy state of reefs with respect to low algal cover. For this, the
importance of fisheries management to ensure herbivory is maintained may be important.
Monitor herbivore populations and put in place measures to ensure they remain at healthy
levels and are protected from over-fishing.
2) Address and minimize local threats – sedimentation and pollution from sand harvesting,
agricultural run-off and coastal/urban developments should be controlled and reduced
through improved planning, soil conservation and legislation.
Monitoring and understanding coral reef health
3) Ensure consistent annual monitoring is carried out at key long-term reef sites to track likely
changes in coral reef health.
4) Bleaching monitoring – develop national and organizational level bleaching response plans
to help prepare for future events.
24
2.1.5 References
1. Ahamada, S., Bijoux, J., Bigot, L., Cauvin, B., Kooonjul, M., Maharavo, J., Pierre-Louis, R. (2004).
Status of the coral reefs of the south west Indian Ocean island states. Status of coral reefs of the
world, 1, 189-212.
2. Freed S., Abdou Rabi F., Ahamada Mroimana N. (2017). Comoros national chapter In Coral reef
status report for the Western Indian Ocean (2017) Obura D., Gudka M., Abdou Rabi F., Bijoux J.,
Freed S., Gian S.B., Maharavo J., Mwaura J., Porter S., Sola E., Wickel J., Yahya S. and Ahamada S.
(pp. 53-59). Global Coral Reef Monitoring Network (GCRMN)/International Coral Reef Initiative
(ICRI). Indian Ocean Commission (IOC)
3. Quod, J. P., & Bigot, L. (2000). Coral bleaching in the Indian Ocean islands: Ecological consequences
and recovery in Madagascar, Comoros, Mayotte and Reunion. Coral reef degradation in the Indian
Ocean, 108-113.
Impact of the 3rd Global Coral Bleaching Event on the Western Indian Ocean in 2016
Affiliations: 1 KMFRI, 2 KWS
Data contributors and acknowledgements:
The data presented in this report remains the property of the organisations and individuals who collected them.
Fieldwork team: Mwaura Jelvas (National Coordinator), Josephine Mutiso, Albert Gamoe, Joseph Kilonzo, Peter Musembi
2.2 Kenya
Authors: Mwaura. J1, Gamoe. A2, Mutiso. J1, Mussembi. P1
Data contributors: Kenya Marine and Fisheries Research Institute (KMFRI), Kenya Wildlife
Service (KWS), AROCHA Kenya, CORDIO, EAWS, WWF
2.2.1 Background to the 2016 bleaching event
Figure 2.2.1. Coral reef monitoring sites in Kenya for which data were included in this study.
2.2.1.1 History of coral bleaching events in Kenya
Kenya’s coral reefs rank among the richest and most valuable ecosystems in the entire
Western Indian Ocean, harbouring a diverse array of marine organisms, and providing critical
ecosystems services such as fisheries, tourism and coastal protection (Obura et al., 2017). The
estimated value of Kenya's marine ecosystems is around US$ 2.5 billion per year (some 4% of
its GDP), of which 70% is from tourism, which is highly dependent on coral reefs.
However, just like in many reef regions worldwide, the future of coral reefs in Kenya is under
imminent threat from climate change and its associated impacts (McClanahan, 2000; Obura,
2005; Hoegh-Guldberg et al., 2009). The 1997/98 worldwide bleaching event greatly impacted
26
Kenya, with some reefs losing 50% to 90% of living corals (Obura, 1999; Wilkinson et al., 1999;
Goreau et al., 2000). Overall, coral cover declined to around 10% after this major bleaching
event (McClanahan et al., 2002). Recovery of reefs from 1998 to date has been moderate and
patchy (Obura, 2002), with some reefs showing no recovery (Muthiga et al., 2008). Other
milder bleaching events have been noted in 1987 and 1994 (McClanahan et al., 2001), and
more recently in 2002, 2005 and 2010.
2.2.1.2 Progression of the 2016 coral bleaching event
Thermal stress measured by satellite began to develop in March with the sun overhead and
the calming of monsoon winds, and subsequently increased but only to mild levels (fig.2.2.2).
At the end of April sea-surface temperatures (SST) reached 31°C and Degree-Heating-Weeks
(DHW) reached 3.5. Thermal stress had dissipated by mid-May. Kenya was one of only two
countries in the region to not experience stress constituting alert level 1 or 2.
Figure 2.2.2. National Oceanic and Atmospheric Administration (NOAA) Coral Reef Watch satellite bleaching
products, showing the bleaching related climatic conditions present at a remote monitoring station in Kenya.
The severity of coral bleaching in 2016 was relatively low but varied among locations, with
less than 10% of reefs showing high or extreme bleaching between January and May (fig.
2.2.3a). Reefs in Malindi and Shimoni, which are dominated by the bleaching susceptible coral
genera Acropora and Pocillopora, had the highest number of bleached and recently dead
colonies (Mwaura et. al., 2017). Bleaching peaked in April and May with the only reports of
extreme and high bleaching (fig. 2.2.3b). Subsequent mortality of corals was limited, with only
10% of reports indicating medium level mortality between May and September.
27
a
b
Figure 2.2.3. Breakdown of observations collected in Kenya in 2016 for a) coral bleaching (n=22) from Jan-
May and mortality (n=26) from May-September 2016 and b) bleaching each month (Feb; n=1, Mar; n=4, Apr;
n=6, May; n=11, Jun; n=15). Categories represent the severity of bleaching/mortality reported as percentage
of coral cover bleached/dead at a site.
2.2.2 Results
In total the analysis included data
from 30 sites in 8 areas (Shimoni,
Kisite, Diani-Chale, Mombasa, Kilifi,
Watamu, Malindi and Lamu)
between 2001 and 2017.
From 2001 and 2017, mean coral
cover increased progressively from
below 5% to approximately 31% by
2013 (fig. 2.2.4). Coral cover settles
at between 25-27% after the 2016
bleaching event.
At sites for which algal cover was
measured alongside coral cover,
algal cover shows a steady decline
from around 60% in 2001 to about
30% between 2013-15 and stays at
about the same level in 2017 (fig.
2.2.5).
Figure 2.2.4 Trends in hard coral cover on Kenyan coral reef
sites before and after the 2016 bleaching event (national
mean (dark bold line) split into historical pre-bleaching data
(purple line, open-circles) and post-bleaching data from July
2016 onwards (blue line, open-squares), 95% confidence
limit (grey shaded area), individual monitoring stations
(faded background lines)). Only stations with data for both
periods were included in the analysis (n=30).
28
Figure 2.2.5. Trends in fleshy algae (green line, closed circles) and hard coral cover (blue line, open-circles) in
Kenya before (solid line) and after (dotted line) the 2016 bleaching event. Shaded areas represent the 95%
confidence limit. Only stations with data for both periods and with both fleshy algae and hard coral cover were
included in the analysis (n=30). The post-bleaching period is from July 2016 onwards.
At a national level, a comparison of coral and fleshy algae cover for sites with data before
(2012-June 2016) and after (since July 2016) the bleaching event showed live hard coral cover
remained at around 24%, and a nominal (but not significant) increase in fleshy algae cover
from 33 ± 4.6% (mean ± se) to 36 ± 4.8% (fig. 2.2.6a).
a
b
Figure 2.2.6 Pre- and post-bleaching (response) mean cover (with standard error bars) for a) hard coral and
fleshy algae for all Kenyan reef sites with both fleshy-algae and hard coral cover data (n=21) and b) hard coral
for no-take and other management zones (n=13 no-take zone, n=8 other). Pre-bleaching data are from 2012-
June 2016 and ‘response’ data are from July 2016 -2017. Only sites with data for both periods were included
in the analysis.
29
When comparing the impact of the bleaching on reefs within no-take zones (protected areas)
and other zones (marine reserves, community conservation areas and open access areas),
there were no significant differences between them. Nevertheless, coral cover within no-take
zones increased slightly from 21 ± 2.7% (mean ± se) (pre-bleaching) to 23 ± 2.7% (post-
bleaching), but decreased in the other zones, from 30 ± 5.9% to 26 ± 2.7% (fig. 2.2.6b).
There were varying levels of coral mortality between different areas of the coast in 2016, with
sites around Lamu in the north and Mombasa the only two regions to experience substantial
declines of 51% and 10% respectively (Table 2.2.1). Reef sites in Watamu and Kilifi showed no
change in coral cover, whilst Shimoni and Malindi showed positive changes.
Table 2.2.1. Average percentage change in live hard coral cover across all sites for six Kenyan regions,
comparing coral cover before (2012-June 2016) and after (July 2016 – 2017) the bleaching event.
Area
Percentage change
in coral cover
Pre-bleaching
mean coral cover ± sd
Post-bleaching
mean coral cover ± sd
Number
of sites
Lamu
-51
39 ± 24.7
19 ± 2.8
2
Mombasa
-10
29 ± 2.6
26 ± 9.1
4
Watamu
0
19 ± 10.2
19 ± 9.2
5
Kilifi
0
18
18
1
Shimoni
14
28 ± 15.7
32 ± 3.6
4
Malindi
35
17 ± 13.1
23 ± 11.6
5
2.2.3 Discussion
Overall, Kenya escaped from the 2016 bleaching event relatively lightly compared to other
countries in the region and also compared to the severe impacts felt in the country from the
first global bleaching event in 1998. This may be due to its northern location and therefore
later onset of warm conditions as the sun moves north which coincided with an early switch
in the monsoon winds, resulting in a shorter period of heat stress compared to more southern
locations. Additionally, while widespread bleaching was reported across the country between
January and May 2016, the lack of coral mortality suggests stress was not so severe, and that
there is potentially strong resilience in the coral population. However, not all sites were
unaffected, with 6 sites experiencing significant losses in coral: Pezali Rock and Majongooni
in Lamu, Nyali and Starfish in Mombasa Marine Park and Reserve, Coral Gardens in Watamu
and Wasini CCA in Shimoni. While reefs in no-take areas coped with the bleaching event
better than reefs in other management regimes, the result is not conclusive enough to
determine if they have higher resilience.
Although our results showed no change in coral cover after the bleaching event, this may be
slightly misleading as bleaching surveys undertaken did show some mortality at sites. The
resolution of our analysis and methods were not able to capture this subtle change in coral
cover, highlighting the need for greater and more consistent monitoring at sites.
Despite a declining trend over time, fleshy algae cover in Kenya is high, compared to other
countries. At 35%, algal cover is currently greater than hard coral cover in Kenya, which is
about 20%. The difference in levels had been decreasing over time, but there are now signs
30
that the gap could widen once again, indicating that Kenyan reefs could be on the verge of a
phase-shift towards a permanently algal dominated state. It is therefore imperative that the
relevant authorities put in place policy and management measures that reverse this trend
and improve resilience to maintain coral reef functioning and service provision.
2.2.4 Recommendations
In order to strengthen the conservation of coral reefs in Kenya it is important that a number
of measures are implemented at various levels:
Monitoring and understanding coral reef health
1) National research institutions to organize regular and country-wide annual monitoring
at long-term coral reef sites to track changes in habitat characteristics, biota and
ecological processes as well as natural threats, such as coral diseases and outbreaks
of the crown-of-thorns starfish.
2) Establish effective national coral bleaching response plans with the capacity to include
preparation, funding, monitoring and communications (awareness creation).
Individual research programmes, NGOs and others can develop their own tailored
coral bleaching response plans to help them prepare for future bleaching events.
Maintaining and improving the health of coral reefs
3) Improve local management of coral reefs to enhance resilience and recovery
potential. Specific emphasis should be placed on reversing the sudden increase in algal
cover, to facilitate coral recovery.
4) Increase areas of coral reefs under no-take management regimes – either through co-
management solutions with communities or government protected areas.
5) Support trials of restoration interventions for conserving and repairing coral reefs with
transparent evaluations of effectiveness and success based on area impacted and
cost.
Policy and research
6) Targeted research on coral reef ecology, especially on factors enhancing or delaying
the recovery of coral reefs from large-scale impacts should be encouraged. Such
studies are useful in identifying nodes of reef resilience for conservation of reefs under
climate change.
7) Improved control and regulation of coastal and near-shore activities that can cause
damage to coral reefs e.g. dredging, coastal development, agricultural run-off, waste
disposal.
8) Regular monitoring of water quality specifically near coastal towns, agricultural farms
and industries.
31
2.2.5 References
1. Goreau, T., McClanahan, T., Hayes, R., & Strong, A. L. (2000). Conservation of coral reefs after the
1998 global bleaching event. Conservation Biology, 14(1), 5-15.
2. Hoegh-Guldberg, O., Hoegh-Guldberg, H., Veron, J. E. N., Green, A., Gomez, E. D., Ambariyanto,
A., & Hansen, L. (2009). The Coral Triangle and climate change: ecosystems, people and societies
at risk.
3. McClanahan, T. R. (2000). Bleaching damage and recovery potential of Maldivian coral
reefs. Marine Pollution Bulletin, 40(7), 587-597.
4. McClanahan, T., Muthiga, N., & Mangi, S. (2001). Coral and algal changes after the 1998 coral
bleaching: interaction with reef management and herbivores on Kenyan reefs. Coral reefs, 19(4),
380-391.
5. McClanahan, T.R., Maina, J. and Pet-Soede, L. (2002) Effects of the1998 coral mortality event on
Kenyan coral reefs and fisheries. Ambio 31, 543-550.
6. Mwaura J., Karisa J., Said O. M., Olendo M., Katello J., Onganda H., Nyunja J., Ambae R., Murage
D., Mussembi S., Obura D., Kamula J., Ngisiange N., Katua S. (2017) Kenya national chapter In Coral
reef status report for the Western Indian Ocean (2017) Obura D., Gudka M., Abdou Rabi F., Bijoux
J., Freed S., Gian S.B., Maharavo J., Mwaura J., Porter S., Sola E., Wickel J., Yahya S. and Ahamada
S. (pp. 60-69). Global Coral Reef Monitoring Network (GCRMN)/International Coral Reef Initiative
(ICRI). Indian Ocean Commission (IOC).
7. Muthiga, N. A., Costa, A., Motta, H., Muhando, C. A., Mwaipopo, R., & Schleyer, M. (2008). Status
of coral reefs in East Africa: Kenya, Tanzania, Mozambique and South Africa.
8. Obura, D.O. 1999. Status report - Kenya. In: Linden, O. & Sporrong, N. (eds.) Coral reef degradation
in the India Ocean. Status reports and project presentations 1999. CORDIO/SAREC Marine Science
Program, pp. 33- 36
9. Obura, D. (2002). Status of coral reefs in Eastern Africa: Kenya, Tanzania, Mozambique and South
Africa.
10. Obura, D. O. (2005). Resilience and climate change: lessons from coral reefs and bleaching in the
Western Indian Ocean. Estuarine, Coastal and Shelf Science, 63(3), 353-372.
11. Obura, D. et al. 2017. Reviving the Western Indian Ocean Economy: Actions for a Sustainable
Future. WWF International, Gland, Switzerland. 64 pp.
12. Wilkinson, C. R., Lindén, O., Cesar, H. S., Hodgson, G., Rubens, J., & Strong, A. E. (1999). Ecological
and socioeconomic impacts of 1998 coral mortality in the Indian Ocean: An ENSO impact and a
warning of future change? Ambio, 28(2), 188.
Impact of the 3rd Global Coral Bleaching Event on the Western Indian Ocean in 2016
Data contributors: The data presented in this report remains the property of the organisations and individuals who collected
them.
2.3 Madagascar
Data contributors: Blue Ventures, Frontier Madagascar, Madagascar Research and
Conservation Institute (MRCI), WCS Madagascar.
Coordination and data collection: Ihando Andrainjafy (National Coordinator),
RANDRIANANDRASANA José, RADONIRINA Lebely, ZAKANDRAINY Andriamanjato,
ANDRIALOVANIRINA Nicolas, Lope Jean Charles, BAKARY Gisèle, Zavatra Jean Baptiste, Rajesy
Farcy.
2.3.1 Background to the 2016 bleaching event
Figure 2.3.1. Coral reef monitoring stations in Madagascar for which data were included in this study.
2.3.1.1 History of coral bleaching events in Madagascar
During the first global bleaching event in 1998, Madagascar experienced a 2°C sea-surface
temperature rise above the threshold and seasonal average (Webster & McMahon, 2002).
Coral bleaching and subsequent mortality were reported in a few areas such as the Southwest
region of Toliara (Ahamada et al., 2002) and in some sites mortality rates were as high as 80
– 90% (McClanahan & Obura, 1998; Souter et al., 2000).
Despite this, in general, reefs around Madagascar were less affected by this event compared
to coral reefs in other countries in the Western Indian Ocean (Ahamada et al., 2002).
33
2.3.1.2 Progression of the 2016 coral bleaching event
Figure 2.3.2. National Oceanic and Atmospheric Administration (NOAA) Coral Reef Watch satellite bleaching
products, showing the bleaching related climatic conditions present at remote monitoring stations in
Southwestern (top) and Northwestern Madagascar (bottom).
From sea-surface temperatures recorded by satellite from fixed stations in SW and NW
Madagascar, both started to experience thermal stress in December, with the NW showing
more severe conditions and a faster rise in January (fig. 2.3.2). At the end of January, thermal
stress peaked in the north and remained around 8 DHW into May, only reaching alert level 2
for about 2 weeks in April. By contrast, thermal stress in the SW continued to rise from
January to April, with alert level 2 conditions persisting for 2 months and reaching a peak of
15 DHW in April-May. Sea-surface temperatures in both regions were generally above the
bleaching-threshold of 30oC from January to mid-April 2018, but with short phases below the
threshold in both cases.
Coral bleaching in 2016 was widespread in Madagascar, with almost 40% of reefs
experiencing bleaching of more than half their coral cover between the months of January
34
and May (fig. 2.3.3a). Bleaching was reported as early as mid-January in the SW, and this soon
spread to all parts with reports from the LMMAs in the east and NW as well. Bleaching was
prevalent through to June (fig. 2.3.3b). Bleaching surveys conducted in May 2016 in the NW
showed varying bleaching levels across genera, and high levels of bleaching at some sites
(Maharavo et al., 2017).
a
b
Figure 2.3.3. Breakdown of observations collected in Madagascar in 2016 of a) coral bleaching (n=86) from
Jan-May and mortality (n=61) from May-December 2016 and b) coral bleaching each month (Jan; n=2, Feb;
n=5, Mar; n=23, Apr; n=31, May; n=25, Jun; n=3). Categories represent the severity of bleaching/mortality
reported as a percentage of coral cover bleached/dead at a site.
2.3.2 Results
In total, data from 41 sites from
Soriake and Andavadoaka in the SW
and Nosy Komba, Nosy Be and Ankarea
in the NW, between 2005 and 2017,
were included in this analysis.
In the initial years (2005-2013) data are
only for 3 sites in Andavadoaka (fig.
2.3.4). In 2005, the mean coral cover
was approximately 31%, and this
increased to approximately 55% by
2012. However, this was followed by a
sharp decline in coral cover in 2013. In
2014, the addition of four sites from
Nosy Be meant mean coral cover
increased to around 43%.
The addition of pre-bleaching data
from 32 sites in 2016 from three more
areas on the west coast gives a pre-
bleaching coral cover level of just over
50%. The increase in coral cover
between pre- and post-bleaching 2016
and the difference between post-2016
Figure 2.3.4 Trend in hard coral cover on Madagascar coral
reef sites before and after the 2016 bleaching event
(national mean (dark bold line) split into historical pre-
bleaching data (purple line, open-circles) and post-
bleaching data from July 2016 onwards (blue line, open-
squares), 95% confidence limit (grey shaded area),
individual monitoring stations (faded background lines)).
Only stations with data for both periods were included in
the analysis (n=41).
35
and 2017 values is due to differences in sites represented. However, the final value for coral
cover in 2017 is at a value lower than the 2016 pre-bleaching level, at approximately 45% in
2017 (fig. 2.3.4).
At sites for which algal cover was measured alongside coral cover, fleshy algae cover shows a
decreasing trend between 2005 and 2016 from over 50% to less than 10%. In 2017, after the
bleaching event, there looks to be little difference in fleshy algae cover compared to 2016
pre-bleaching values (fig. 2.3.5).
Figure 2.3.5 Trends in fleshy algae (green line, closed circles) and hard coral cover (blue line, open-circles) in
Madagascar before (solid line) and after (dotted line) the 2016 bleaching event. Shaded areas represent the 95%
confidence limit. Only stations with data for both periods and with both fleshy algae and hard coral cover were
included in the analysis (n=40). The post-bleaching period is from July 2016 onwards.
When comparing national coral and algae cover levels before (2012 – June 2016) and after
the bleaching event, only sites with data for both periods and with both fleshy algae and hard
coral cover were included in the analysis (fig. 2.3.6). There was a 13% decrease in live hard
coral cover from 53 ± 3.6% (mean ± se) to 46 ± 2.8%. A complementary increase in fleshy
algae abundance over the same period occurred, with mean cover increasing from the pre-
bleaching period (9 ± 2.5%) to the post-bleaching period (14 ± 2.4%).
36
Figure 2.3.6. Hard coral and fleshy algae cover for pre-bleaching and post-bleaching (response) years: mean
and standard error of all Madagascar reef sites (n=40). Pre-bleaching data are from 2012-June 2016 and
‘response’ data are from July 2016 -2017. Only sites with data for both periods and with both fleshy-algae and
hard coral cover were included in the analysis.
Comparing the changes in hard coral cover in various areas on the west coast of Madagascar,
Nosy Be, Nosy Komba and Ankarea in the NW lost about 20-40% coral cover, while
Andavadoaka, and Soariake in the SW and Ankivonjy in the NW maintained about the same
level of coral cover (fig. 2.3.7).
Figure 2.3.7. Mean hard coral cover for pre-bleaching and post-bleaching (response) years, for no-take and
other management zones (with standard error bars). Pre-bleaching data are from 2012-June 2016 and
‘response’ data are from July 2016 -2017. Only stations with data for both periods were included in the
analysis. Sites are ordered from South to North. (Soariake; n=11, Andavadoaka; n=3, Ankivonjy; n=8, Nosy
Komba; n=3, Nosy Be; n=4, Ankarea; n=12).
In late 2017 Baie de Ranobe and Nosy Ve Anakao in Toliara (SW) and four sites in Nosy Be
(NW) were surveyed. Both the southwest areas had hard coral cover around 35% and fleshy
algae cover around 40%, and at the four sites in Nosy Be, hard coral was at 40% and fleshy
algae at 5%.
37
2.3.3 Discussion
The results presented here suggest that the 2016 bleaching event had a noticeable impact on
the coral cover of the reefs on the west coast of Madagascar, however this impact was more
severely felt in the NW of the island. It is important to note that sites reported here are
exclusively from the west coast of Madagascar, so conclusions don't apply to the east coast.
Across all sites, Madagascar had a relatively high coral cover compared to other countries in
the region, with over 50%. However, with the bleaching event this has declined to
approximately 45%, a change of almost 10% in living coral, although this is still relatively good.
Pre-bleaching, sites in the NW had significantly higher coral cover than sites in the SW, but
there is more parity between them now. Fortunately, fleshy algae cover after the event
remains quite low at under 15%, indicating that reefs are not in any immediate danger of
experiencing a phase-shift.
The SW coast of Madagascar is identified as a 'climate hotspot' - among the top 10 or 20
marine sites showing the highest rates of warming and associated climate change (Pecl et al.,
2017). Bleaching is reported there on an annual basis, in some years with high mortality, in
other years with low mortality. In 2016, sites at Andavadoaka in the SW experienced
significant bleaching during peak stress in March and April, but seemingly recovered very well
as there was no significant mortality post-bleaching. This was in spite of the SW experiencing
much harsher bleaching conditions than the NW (fig. 2.3.2). It is likely that the SW reefs are
more resistant to thermal stress than their counterparts in the north, due to high levels of
exposure in the past, and resulting acclimatization or adaptation to these conditions.
However, they may still suffer high mortality if conditions get too severe, and it may be that
the rapid dissipation in bleaching stress from mid-April onwards, due to a sharp and
significant drop in SST, helped prevent the reefs crossing their threshold into a high-mortality
phase. In the NW, bleaching conditions began as early as December but did not become as
extreme as in the SW, continuing at moderate level to mid-May. Nevertheless, conditions
were sufficiently severe to cause significant mortality of corals.
Apart from the sites analyzed in this chapter, other reefs from across Madagascar were
affected by moderate to high bleaching including at Toliara, Nosy Valiha, Bay de Ranobe and
others (Maharavo et al., 2017).
Madagascar’s reefs are unique biodiversity hotspots and have previously been defined by
high amounts of live coral cover. However, over the last 20 years, coral cover began to decline
relatively rapidly (Maharavo et al., 2017), and this trend has continued at some sites due to
the bleaching in 2016. These areas could now be at risk of permanent degradation if recovery
is restricted by local factors or repeat severe bleaching events in the future. The long-term
future of Madagascar's reefs is therefore uncertain, particularly as the rate of degradation is
expected to accelerate in coming years, making it as important as ever that significant
investment is made to monitor and manage these vital economic and ecological resources.
38
2.3.4 Recommendations
Maintaining and improving the health of coral reefs
1) Improve management measures with an aim to minimize avoidable local threats and
damage as much as possible. Strategies should be adaptive, with decisions being science-
driven as much as possible and human intervention should be trialed where cost-effective
and appropriate.
Monitoring and understanding coral reef health
2) Monitoring of coral reef health should be carried out by all reef stakeholders including
NGOs, marine park authorities, universities, research programmes, individual researchers
etc. with consistency in sites, methods and frequency. It is key to maintain monitoring at
long-term monitoring sites, ensuring any new research programmes do the same.
3) Increase monitoring and reporting focus of reefs on the east coast of Madagascar.
4) Establish effective coral bleaching response plans to include preparation, funding,
monitoring and communications (awareness creation) strategies. Individual research
programmes, NGOs and others can develop their own tailored coral bleaching response
plans to help them prepare for future bleaching events.
5) Data storage - ensure that a central repository is used to securely store coral reef health
data including historical data making it easily accessible for reporting for management
and policy.
Policy and research
6) Social resilience building – develop measures to increase the adaptability and resilience
of Madagascar's public to the consequences of changes in the ecosystem services these
resources provide.
7) Undertake studies to assess the bleaching vulnerability, susceptibility and resistance of
various coral populations in the southwest and northwest.
39
2.3.5 References
1) Ahamada, S., Bigot, L., Bijoux, J., Maharavo, J., Meunier, S., Moyne-Picard, M., & Paupiah, N.
(2002). Status of coral reefs in the south west Indian Ocean island node: Comoros, Madagascar,
Mauritius, Reunion and Seychelles. Status of coral reefs of the world, 79-100.
2) Maharavo, J., Andrianjafy, I., Rasolomaharavo, A. – Madagascar chapter, Coral reef status report
for the Western Indian Ocean (2017) Obura D., Gudka M., Abdou Rabi F., Bijoux J., Freed S., Gian
S.B., Maharavo J., Mwaura J., Porter S., Sola E., Wickel J., Yahya S. and Ahamada S. (pp. 70-77).
Global Coral Reef Monitoring Network (GCRMN)/International Coral Reef Initiative (ICRI). Indian
Ocean Commission (IOC).
3) McClanahan, T., & Obura, D., (1998) Monitoring, training and assessment of the coral reefs of the
Masoala Peninsular. Wildlife Conservation Society.
4) Pecl, G. T., Araujo, M. B., Bell, J., Blanchard, J., Bonebrake, T. C., Chen, I., Clark, T. D., Colwell, R.
K., Danielsen, F., Evengard, B., Robinson, S. et al (2017). Biodiversity redistribution under climate
change: Impacts on ecosystems and human well-being. Science, 355 (6332), 1-9.
5) Souter, D., Obura, D., & Linden, O. (2000). Coral reef degradation in the Indian Ocean. Status
report.
6) Webster, F. J., & McMahon, K. (2002). An assessment of coral reefs in northwest
Madagascar. Coral reef degradation in the Indian ocean: Status report, 190-201.
Impact of the 3rd Global Coral Bleaching Event on the Western Indian Ocean in 2016
Data contributors: The data presented in this report remains the property of the organisations and individuals who collected
them.
2.4 Mauritius
Data contributors: Reef Conservation
2.4.1 Background to the 2016 bleaching event
Figure 2.4.1. Coral reef monitoring stations in Republic of Mauritius for which data were included in this study.
2.4.1.1 History of coral bleaching events in Mauritius
Mauritius was least affected by the 1998 global bleaching event among the countries in the
WIO, as the reefs suffered comparatively low mortalities (Wilkinson et al., 1999; Quod, 1999).
A 1.5°C sea-surface temperature anomaly was recorded that caused bleaching of up to 85%
in places (Spencer et al., 2000). However, the substantial recovery from bleaching was
attributed to high resilience at some of the reefs (Turner, 1999; Obura, 2005) and mixing of
deeper cooler waters caused by the tropical cyclone Anacelle (Quod, 1999).
Since 1998 low recovery rates have been noted with minor bleaching events occurring
through the period to 2016 (Obura, 2005; Bacha Gian et al., 2017).
41
2.4.1.2 Progression of the 2016 coral bleaching event
Figure 2.4.2. National Oceanic and Atmospheric Administration (NOAA) Coral Reef Watch satellite bleaching
products, showing the bleaching-related climatic conditions at a site on the north shore of Mauritius island.
According to remote satellite monitoring in Northern Mauritius, bleaching stress began to
accumulate as early as mid-December 2015 and started building rapidly towards the end of
February 2016 (fig. 2.4.2). Alert level 2 was reached just before April and continued for almost
2 months till the end of May, when thermal stress peaked at a region high of 16 degree-
heating weeks. After this, temperatures dropped, and thermal stress dissipated completely.
Bleaching was widespread across Mauritius Island, with over 40% of coral cover partially
bleached (Bacha Gian et. al., 2017). All sites had some degree of bleaching, with the most
affected sites such as Belle Mare, Flic en Flac and Ile aux Benitiers having more than 65% of
corals affected, whilst Blue Bay, Bel Ombre and Mon Choisy had less than 15% bleaching
(Bacha Gian et. al., 2017).
42
Overall, approximately 35% of observations reported severe bleaching (greater than 50%
coral cover bleached) between January and May 2016 (fig. 2.4.3a). Recorded bleaching
mirrored the climatic conditions closely, with severe bleaching peaking in March and April
and then declining (fig. 2.4.3b).
a
b
Figure 2.4.3. Breakdown of observations collected in Mauritius in 2016 of a) coral bleaching (n=66) from
Jan-May and mortality (n=1) from May-September 2016 and b) bleaching each month (Feb; n=17, Mar;
n=27, Apr; n=19, May; n=3, Jun; n=5). Categories represent the severity of bleaching/mortality reported
as percentage of coral cover bleached/dead at a site.
2.4.2 Results
In total, data from 5 sites in Anse La
Raie Lagoon in the North of Mauritius
Island between 2013 and 2017 were
included in the analysis, as other sites
in the national coral reef monitoring
network (ref to GCRMN chapter, 2017)
have not been monitored after the
bleaching event.
Overall, cover of hard coral in Anse La
Raie has stayed approximately the
same from 2013 to 2017, without any
visible impact of the 2016 bleaching
event. Prior to the bleaching event,
values of 32-45% were recorded,
though there is no significant
difference between these (fig. 2.4.4).
A measurement of hard coral cover of
45% immediately after the event in late
2016 is not likely to reflect a true
increase in coral cover and follows the
same pattern as in prior years. The
hard-coral cover in 2017 was 35%.
Figure 2.4.4. Trends in hard coral cover on Mauritius coral
reef sites before and after the 2016 bleaching event (national
mean (dark bold line) split into historical pre-bleaching data
(purple line, open-circles) and post-bleaching data from July
2016 onwards (blue line, open-squares), 95% confidence
limit (grey shaded area), individual monitoring stations
(faded background lines)). Only stations with data for both
periods were included in the analysis (n=5).
43
The fleshy algae data recorded from the same sites shows a reciprocal pattern to hard coral
cover, and also cannot be interpreted in relation to impacts of the 2016 bleaching event (fig.
2.4.5).
Figure 2.4.5. Trends in fleshy algae (green line, closed circles) and hard coral cover (blue line, open-circles) in
Mauritius before (solid line) and after (dotted line) the 2016 bleaching event. Shaded areas represent the 95%
confidence limit. Only stations with data for both periods and with both fleshy-algae and hard coral cover were
included in the analysis (n=5). The post-bleaching period is from July 2016 onwards.
2.4.3 Discussion
Overall the results suggest that there was no change in hard coral cover as a result of the
bleaching event in Anse La Raie Lagoon. Given the very strong bleaching conditions remotely
measured through satellites for Northern Mauritius, and high levels of bleaching measured at
these sites in the early-part of the year, this result is quite surprising. Other studies of
bleaching on Rodrigues Island found that reefs around the island were not as fortunate with
widespread bleaching and possibly some of the worst coral mortality in the region (Klaus,
2016; F. Jouval pers. comm.).
Unfortunately, data from survey sites in only a single area were submitted for this report.
Given that there were several reports of strong bleaching at sites across Mauritius in the early
part of 2016, it is likely that mortality on both Mauritius and Rodrigues islands was significant
and needs to be documented as soon as possible.
2.4.4 Recommendations
The following recommendations can be made from this report:
1) Greater standardization of the monitoring programme at Anse La Raie Lagoon is needed,
to ensure that change measured from year to year can be reliably attributed to relevant
causes.
2) Revitalization of the national Coral reef monitoring network is needed, to ensure data
are collected regularly and reliably, and contributed into regional reporting processes.
44
2.4.5 References
1. Bacha Gian. S., Munbodhe V., Soogun N., Raffin J. Mauritius national chapter, GCRMN (2017).
Coral Reef Status Report for the Western Indian Ocean. (2017). Obura D., Gudka M., Abdou
Rabi F., Bijoux J., Freed S., Gian S.B., Maharavo J., Mwaura J., Porter S., Sola E., Wickel J., Yahya
S. and Ahamada S. (pp. 78-87). Global Coral Reef Monitoring Network (GCRMN)/International
Coral Reef Initiative (ICRI). Indian Ocean Commission (IOC).
2. Klaus, R. (2016). Assessing the impact of the 2015-2016 coral bleaching in Rodrigues, Republic
of Mauritius [Abstract]. Symposium at the Western Indian Ocean Marine Science Association.
3. Obura, D. O. (2005). Resilience and climate change: lessons from coral reefs and bleaching in
the Western Indian Ocean. Estuarine, Coastal and Shelf Science, 63(3), 353-372.
4. Quod, J. P. (1999). Consequences of the 1998 coral bleaching event for the islands of the
western Indian Ocean. http://hdl.handle.net/1834/492
5. Spencer, T., Teleki, K. A., Bradshaw, C., & Spalding, M. D. (2000). Coral bleaching in the
southern Seychelles during the 1997–1998 Indian Ocean warm event. Marine Pollution
Bulletin, 40(7), 569-586.
6. Turner, J., (1999). Status report Mauritius. In: Linden, O., Sporrong, N. (Eds.), Coral Reef
Degradation in the Indian Ocean. Status Reports and Project Presentations 1999. CORDIO,
Kalmar, pp. 60–62.
7. Wilkinson, C. R., Lindén, O., Cesar, H. S., Hodgson, G., Rubens, J., & Strong, A. E. (1999).
Ecological and socioeconomic impacts of 1998 coral mortality in the Indian Ocean: An ENSO
impact and a warning of future change? Ambio, 28(2), 188.
Impact of the 3rd Global Coral Bleaching Event on the Western Indian Ocean in 2016
Data contributors: The data presented in this report remains the property of the organisations and individuals who collected
them.
2.5 Seychelles
Data contributors: Seychelles National Parks Authority (SNPA), Global Vision International
(GVI), Seychelles Islands Foundation (SIF), Island Conservation Society (ICS), Green Islands
Foundation (GIF), Marine Conservation Society Seychelles.
2.5.1 Background to the 2016 bleaching event
Figure 2.5.1. Coral reef monitoring stations in Seychelles for which data were included in this study.
2.5.1.1 History of coral bleaching events in the Seychelles
The Inner Islands of the Seychelles were particularly badly affected by the first global
bleaching event in 1998. The granitic islands of Mahé and Praslin lost on average between 75-
90% of live coral cover (Amia, 2014; Harris et al., 2014). Shallow water over the extensive
banks surrounding the Inner Islands generally heats to very high temperatures during the
local summer, and temperatures were exacerbated by the extreme conditions in 1998. The
Outer Islands of the Seychelles are generally atolls or islands surrounded by deep waters, thus
experience less heating and have refuge habitats for corals living in cooler, deeper water.
However, they were also significantly affected by bleaching (Engelhardt et. al., 2002; Graham
et al., 2007).
46
2.5.1.2 Progression of the 2016 coral bleaching event
Figure 2.5.2. National Oceanic and Atmospheric Administration (NOAA) Coral Reef Watch satellite bleaching
products, showing the bleaching related climatic conditions present at a remote monitoring station in Seychelles.
Sea-surface temperatures recorded by satellite from a fixed station in the Seychelles show
extreme thermal stress building up from December 2015 to May 2016 (fig. 2.5.2.). Bleaching
warning and alert level 1 were reached early in January, then intensified in late March. SST
reached its highest value in April, well above the SST threshold for bleaching, and the
bleaching alert level reached the maximum value of 2 at the beginning of April. Thermal stress
peaked at 12 Degree Heating Weeks for 3 weeks in late April/early May.
The first reports of coral bleaching were made in early January at Aldabra Atoll. As the
temperatures rose in March and April, more sites across several Outer Islands became
affected by bleaching, including Providence and St. Pierre, and by early April, bleaching was
reported from Alphonse and Desroches in the Amirantes (Bijoux et. al., 2017). The level of
bleaching varied between and within island sites, with the west-side of Alphonse being the
most affected.
In the Inner Islands, several sites were impacted. On the northwest coast of Mahé, Pocillopora
and Acropora showed first signs of bleaching at all depths (Bijoux et. al., 2017). By early
August 2016 some corals were still showing signs of bleaching despite sea temperatures
having returned to normal since May (Bijoux et. al., 2017). Extensive coral mortality was
observed from May onwards.
47
a
b
Figure 2.5.3. Breakdown of observations in the Seychelles in 2016 of a) coral bleaching from January-May
(n=49) and mortality from May-September 2016 (n=22); b) bleaching each month (Jan; n=11, Feb; n=3, Mar;
n=1, Apr; n=25, May; n=9, Jun; n=6). Categories represent the severity of bleaching/mortality reported as
percentage of coral cover bleached/dead at a site.
Overall, during the peak bleaching months (Jan-May) approximately 65% of sites reported
severe bleaching levels (greater than 50% of coral cover bleached), with just over 30% of sites
reporting severe mortality from May onwards (fig. 2.5.3a). The monthly progression of
bleaching (fig. 2.5.3b) mirrored the increasing thermal stress.
2.5.2 Results
In total, data from 50 sites from 6 islands
(North, Mahe, Alphonse, Aldabra,
Desroches and Cerf) between 1999 and
2017 were included in this analysis.
In 1999, just after the 1998 bleaching
event, the mean coral cover was 24%,
and after an initial decline till 2006, this
steadily increased to approximately 37%
just before the bleaching event in 2016
(fig. 2.5.4). Sites surveyed after the
bleaching event during late 2016 and
early 2017 had a mean cover between
18 and 27% (see fig. 2.5.4). The
downward slope in the graph linking
post-bleaching sites measured in 2016
and 2017 is because different sites were
reported, it does not reflect a further
decline in coral cover.
At sites for which algal cover was
measured alongside coral cover, fleshy
algal cover increased drastically from
2015 to 2016 (before the bleaching
event), which may be an artifact of sampling, but did not change significantly after the
Figure 2.5.4. Trends in hard coral cover on Seychelles islands’
reefs before and after the 2016 bleaching event (national
mean (dark bold line) split into historical pre-bleaching data
(purple line, open-circles) and post-bleaching data from July
2016 onwards (blue line, open-squares), 95% confidence
limit (grey shaded area), individual monitoring stations
(faded background lines)). Only stations with data for both
periods were included in the analysis (n=50).
48
bleaching event (fig. 2.5.5). For these sites, a greater decline in coral cover was recorded from
over 30% pre-bleaching to between 8 – 20% after.
Figure 2.5.5 Trends in fleshy algae (green line, closed circles) and hard coral cover (blue line, open-circles) in the
Seychelles before (solid line) and after (dotted line) the 2016 bleaching event. Shaded areas represent the 95%
confidence limit. Only stations with data for both periods and with both fleshy-algae and hard coral cover were
included in the analysis (n=32). The post-bleaching period begins in July 2016.
At a national level, a comparison of coral and fleshy algae cover before (2012-June 2016) and
after (since July 2016) the bleaching event showed that there has been a 50% decrease in live
hard coral cover from 34 ± 2.8% (mean ± se) to 17 ± 2.2% (fig. 2.5.6a). In response to that
there has been an approximately 45% increase in fleshy algae abundance over the same
period with mean cover changing from 29 ± 4.3% pre-bleaching to 42 ± 3.8% post-bleaching.
a
b
Figure 2.5.6. Pre- and post-bleaching (response) mean (with standard error bars) for a) hard coral and fleshy
algae cover of all Seychelles’ reef sites with both fleshy-algae and hard coral cover data (n=32), and b) hard
coral cover for Inner and Outer Island reef sites in Seychelles (n=14 Outer, n=29 Inner). Pre-bleaching data are
from 2012-June 2016 and ‘response’ data are from July 2016-2017. Only sites with data for both periods were
included in the analysis.
49
When comparing the Inner and Outer Islands, there has been an almost 60% decline in live
hard coral cover from 33 ± 3.1% to 13 ± 1.2% in the Inner Islands, compared to a 17% decline
in the Outer Islands (44 ± 5.8% to 37 ± 5.6%) (fig. 2.5.6b).
Almost all Seychelles islands experienced high levels of coral mortality in 2016, with sites
around North Island being the most affected with an 81% decline in living hard coral on
average, and sites around Aldabra, Desroches and the northwest of Mahe losing over half of
their live coral (Table 2.5.1).
Table 2.5.1. Average percentage change in live hard coral cover for six Seychelles islands, across all sites analyzed
at each Island, comparing coral cover before (1996 -June 2016) and after (July 2016 – 2017) the bleaching event.
Island
Percentage
change in live
coral cover
Pre-bleaching
mean coral cover
± sd
Post-bleaching
mean coral
cover ± sd
Number of
sites
North
-81
43 ± 26.3
8 ± 4.9
5
Aldabra
-55
24 ± 9.2
11 ± 4.2
2
Desroches
-54
44 ± 43.9
20 ± 6.9
3
Mahe (NW)
-53
31 ± 13.6
15 ± 6.3
24
Alphonse
-13
54 ± 9
47 ± 19.3
6
Cerf
32
37 ± 12.5
49 ± 13.7
3
2.5.3 Discussion
Seychelles was once again one of the worst hit countries in the WIO by a regional bleaching
event. Across all sites there was a 50% decrease in live hard coral cover, and an almost
equivalent increase in fleshy algae abundance over the same period. However, although very
high, mortality in 2016 was not as high as in 1998 (Turner et al., 2000). This is despite the fact
that the 2016 El Niño was longer lasting and more extensive than the 1997-1998 episode.
Another pattern that mirrored the 1998 bleaching event was that the Inner Islands were more
severely impacted than the Outer Islands, with some sites losing over 80% of their live hard
coral cover. This is likely in part due to the warmer conditions experienced over the shallow
banks surrounding the Inner Islands resulting in greater thermal stress.
Despite this, some sites experienced only minor, if any, bleaching-related mortality in 2016.
Corsaire Reef in northwest Mahe was the only site from this area that showed a positive
change in coral cover, and the three sites on Cerf Island appeared to escape relatively
undamaged. Other sites with only minor impact of bleaching were found around the island of
Praslin at the Baie Ste Anne jetty and at Chauve Souris, within the Curieuse Marine National
Park (Bijoux et. al., 2017). The reasons for low bleaching at these sites are not clear, however
high resistance to bleaching at the Baie Ste Anne jetty has been reported in other years
between the 1998 and 2016 events (Grimsditch & Salm, 2005; Souter & Linden, 2005).
After two major bleaching events 18 years apart, and a number of smaller more localized
bleaching events in between, the corals of the Seychelles could be more acclimated and
resilient to hot conditions. It is also significant that coral cover returned to pre-1998 levels
over the 18 years, suggesting that if managed well, and given enough time, the reefs could
have the potential to naturally respond and recover from the 2016 bleaching event. However,
the rapidly changing climate is expected to cause more frequent and severe bleaching events
50
at shorter intervals in the future (van Hooidonk et al., 2016; Hughes et al., 2018), and it is
therefore likely that the reefs will not have the luxury of 18 years to recover before the next
major bleaching event. Additionally, in 2016 there has been a large step-increase in fleshy
algae, which could hinder the ability of corals to recover. It is therefore imperative that coral
reef health is closely tracked, and management measures are enhanced promptly to provide
the necessary support for reefs to recover.
2.5.4 Recommendations
In order to strengthen the conservation of coral reefs in the Seychelles the following measures
should be implemented at various levels:
Monitoring and understanding coral reef health:
1) Monitoring of coral reef health should be carried out by all reef stakeholders including
NGOs, marine park authorities, universities, research programmes, individual researchers
etc. with consistency in sites, methods and frequency.
2) Establish effective coral bleaching response plans on each island with sufficient capacity
(including preparation, funding, monitoring and communications/awareness creation).
Individual research programmes, NGOs and others can develop their own tailored coral
bleaching response plans to help them prepare for future bleaching events.
3) Collate all historical coral reef health data into a central, safe database for secure storage
and ease of access so the baseline and change in health of Seychelles coral reefs is clear.
To support this, a system to share metadata on coral reefs will make it easier to share
information among organisations and foster greater collaboration.
Maintaining and improving the health of coral reefs
4) Improve local management of coral reefs to enhance resilience and recovery potential.
Specific emphasis should be placed on reversing the sudden increase in algal cover, to
facilitate coral recovery.
5) Trials of restoration interventions for conserving and repairing coral reefs need to be
supported, with transparent evaluations of effectiveness and success based on area
impacted and cost.
6) Identify naturally resilient coral reef areas that can act as climate refuges and larval
sources, to ensure they are well protected through appropriate management measures.
Policy and research
7) Develop a policy for the conservation of coral reefs. This should be drafted and discussed
with all stakeholders and be in line with the Seychelles Sustainable Development Strategy
(SSDS) and the National Biodiversity Strategy and Action Plan (NBSAP).
8) Targeted research on coral reef ecology and resilience, especially on factors enhancing or
delaying the resistance and recovery of coral reefs from large-scale impacts should be
encouraged along with active collaboration among organisations (government, NGOs,
CBOs, academia) at the local and international level.
9) Many of the recommendations require joint action by government and non-government
actors, in a coordinated network. This can be done through the Seychelles National Coral
Reef Network (SNCRN), if strengthened through e.g. a national coral reef policy, and
51
supported through the emerging Marine Spatial Planning initiative to maintain the natural
capital of the Seychelles.
2.5.5 References
1. Amia, H. (2014, July 14). Seychelles coral reefs just beginning to show signs of recovery, say
researchers. Seychelles News Agency. Retrieved from http://www.seychellesnewsagency.com/
2. Bijoux J., Thérésine P., Mason-Parker C., Burt A., Pierre-Andre A., Anna K., Jennifer A., Nicholas G.,
Shaun W., Rodney Q., Isabelle R., Dainise Q., Mariliana L., Joanna B., Elke T., Arjan d.G., Aurélie D.,
Richard J., Jan R., Phillip H., Savi L., Josep N., Ariadna F., Christopher N. (2017) – Seychelles chapter
– WIO GCRMN report Obura D., Gudka M., Abdou Rabi F., Bijoux J., Freed S., Gian S.B., Maharavo
J., Mwaura J., Porter S., Sola E., Wickel J., Yahya S. and Ahamada S. (pp. 109-121). Global Coral
Reef Monitoring Network (GCRMN)/International Coral Reef Initiative (ICRI). Indian Ocean
Commission (IOC).
3. Engelhardt, U., Russell, M., & Wendling, B. (2002). Coral communities around the Seychelles
Islands 1998–2002. Coral Reef Degradation in the Indian Ocean, 212. Souter, D., Obura, D., &
Linden, O. (2000). Seychelles Chapter in Coral reef degradation in the Indian Ocean. Status report.
208-231
4. Grimsditch, G.D. and Salm, R.V. (2005). Coral Reef Resilience and Resistance to Bleaching. IUCN,
Gland, Switzerland.
5. Graham, N. A., Wilson, S. K., Jennings, S., Polunin, N. V., Robinson, J. A. N., Bijoux, J. P., & Daw, T.
M. (2007). Lag effects in the impacts of mass coral bleaching on coral reef fish, fisheries, and
ecosystems. Conservation biology, 21(5), 1291-1300.
6. Harris, A., Wilson, S., Graham, N., & Sheppard, C. (2014). Scleractinian coral communities of the
inner Seychelles 10 years after the 1998 mortality event. Aquatic Conservation: Marine and
Freshwater Ecosystems, 24(5), 667-679.
7. Hughes, T. P., Anderson, K. D., Connolly, S. R., Heron, S. F., Kerry, J. T., Lough, J. M., et al. (2018).
Spatial and temporal patterns of mass bleaching of corals in the Anthropocene. Science,
359(6371), 80–83. http://doi.org/10.1126/science.aan8048
8. Souter, D., & Linden, O. (2005). Coral reef degradation in the Indian Ocean: Status report 2005.
9. Turner, J., Klaus, R., & Engelhardt, U. (2000). The reefs of the granitic islands of the
Seychelles. Coral reef degradation in the Indian Ocean. Status report.
10. van Hooidonk, R., Maynard, J., Tamelander, J., Gove, J., Ahmadia, G., Raymundo, L., et al. (2016).
Local-scale projections of coral reef futures and implications of the Paris Agreement. Scientific
Reports, 1–8. http://doi.org/10.1038/srep39666
Impact of the 3rd Global Coral Bleaching Event on the Western Indian Ocean in 2016
Contributors and acknowledgments: Camilla Floros1, Mari-Lise Franken2 and Stuart Laing1 contributed in the
field and to project logistics. Larry Oellermann of the South African Association for Marine Biological Research
(SAAMBR) is thanked for his support. The Ford Wildlife Foundation is acknowledged for their contribution of a
4-x-4 vehicle. Financial support was provided by the Department of Economic Development, Tourism and
Environmental Affairs, the South African National Biodiversity Institute and SAAMBR.
Affiliations: 1Oceanographic Research Institute; 2South African National Biodiversity Institute
2.6 South Africa
Authors: Sean N. Porter1, Michael H. Schleyer1, Kerry J. Sink2 and David J. Pearton1
2.6.1 Background to the 2016 bleaching event
2.6.6.1 History of coral bleaching events in South Africa
During the largest mass coral bleaching and mortality event that impacted much of the Western
Indian Ocean (WIO) in 1998 (Goreau et al., 2000; Wilkinson, 2000), only negligible coral bleaching was
recorded on South African reefs (Schleyer & Celliers, 2000). While some reefs in the WIO experienced
more than 90% mortality due to bleaching (Wilkinson et al., 1999), less than 1% of the hard corals
bleached in South Africa (Schleyer & Celliers, 2000; Jordan & Samways, 2001). This was mostly due to
bleaching in widely spaced colonies of the hard coral genus Montipora (Schleyer & Celliers, 2000). No
bleaching was recorded in the following year in 1999 (Celliers & Schleyer, 2002). Subsequently, Floros
et al., (2004) recorded an increase in bleaching across the coral community of between 5-10% in 2000-
2001. Montipora spp. were again detected as being the most commonly bleached genus. The
bleaching was associated with increased sea temperatures characterized by high seasonal peaks, as
well as high radiation levels during the summer months of 2000 (Celliers & Schleyer, 2002).
During this period (2000), Celliers & Schleyer (2002) measured similar levels of bleaching of the total
living cover of up to 12% at Sodwana Bay. This was largely restricted to Two-mile Reef with the other
reefs in the Central Complex either showing no bleaching or levels of ~1%. They found that the
majority of hard corals that bleached belonged to the genera Montipora and Alveopora, and that an
encrusting sponge Suberites kelleri was also found to bleach. Of the coral colonies that manifested
bleaching, 47% were completely white whilst 44% were partially bleached. No whole colony mortality
was ever recorded but partial mortality was detected in 9% of bleached corals. Bleaching was also
inconsistent among colonies of the same species of Montipora, as colonies displayed variable levels
of bleaching across the two reefs where bleaching was detected (Celliers & Schleyer, 2002).
Bleaching was not documented again in South Africa until 2005, when the bleaching response index
across all hard coral taxa was as high as 40 during a warm-water anomaly in the southern Indian
Ocean (McClanahan et al., 2007). Montipora spp. were again found to show the highest incidences of
bleaching, with bleaching response indexes of up to 65. Ruiz Sebastian et al. (2009) recorded
bleaching responses across the coral community during this time, ranging from 11 at Nine-mile Reef
in the Central Complex to 30 at Timm’s Tridacna, Saxon Reef in the Northern Complex. Generally,
deeper sites suffered less from bleaching (Ruiz Sebastian et al., 2009). Since then, only negligible
levels of bleaching have been recorded up until 2016, when bleaching of 9.4% of the coral cover
occurred on Two-mile Reef (Porter, 2017).
53
Over the last twenty years, bleaching-induced mortality on South African reefs has been minimal and,
as such, the cover of hard coral has remained relatively consistent for the past decade (Porter &
Schleyer, 2017) (fig. 2.6.1). The high latitude of these coral reefs in South Africa has provided them
some protection from bleaching in the past (Celliers & Schleyer, 2002). The reefs are also located in
relatively deep water that is naturally turbulent and experience periodic upwelling events which help
to cool the surface waters where corals reside (Celliers & Schleyer, 2002; Riegl & Piller, 2003).
However, the characteristically clear water of this region can exacerbate bleaching (Celliers &
Schleyer, 2002; Porter et al., 2017).
Figure 2.6.1. Trend in hard coral cover at Nine-mile Reef, Sodwana Bay, South Africa over the past 20 years (Porter &
Schleyer, 2017). No bleaching has been recorded at the monitoring site although several colonies showed signs of paling
in March 2016.
2.6.6.2 Assessing the impact of the 2016 coral bleaching event
The impact of the 2016 coral bleaching event on South African reefs and the subsequent response in
the coral community was assessed by the Oceanographic Research Institute (ORI) and the South
African National Biodiversity Institute (SANBI) using different, but complementary methods. ORI
surveys were undertaken along 10-m transects using the line-intercept method to estimate the
percentage coral cover bleached at five sites haphazardly selected on Two-mile Reef in the Central
Reef Complex (fig. 2.6.2). These surveys were repeated at the same five sites in December 2015 (pre-
bleaching), May 2016 (peak-bleaching) and September 2016 (post-bleaching response) to assess the
progression and response of corals during this anomalously warm period.
SANBI conducted bleaching surveys of hard coral colonies in late April 2016 to assess peak-bleaching
levels, using a bleaching index derived by McClanahan (2004). This method allows for taxon- and site-
specific bleaching indices to be calculated, as well as the determination of the proportion of hard
coral colonies bleached relative to the total number of hard coral colonies assessed. These surveys
were conducted at twelve sites situated across all three reef complexes (fig. 2.6.2).
In total, 1 822 line-intercept points and 3 554 hard coral colonies were assessed by ORI and SANBI
respectively. The data utilized in this report were derived from routine monitoring projects conducted
independently by both organisations.
54
Figure 2.6.2. Monitoring sites used to assess levels of coral bleaching in South Africa.
2.6.6.3 Progression of the 2016 coral bleaching event
During the 2015-2016 warming event, average monthly subtidal (18 m) temperatures at Nine-mile
Reef rose from 24.1°C in October 2015 to 25.4°C in December 2015, before peaking in March 2016 at
27.4°C. During this period, a maximum temperature of 29.0°C was sustained for ~9 consecutive hours
in March 2016 (fig. 2.6.3). NOAA regional sea-surface temperature warnings prompted a “bleaching
watch” in January 2016 with temperatures peaking in February and again in March for several weeks
at ~28°C; these triggered two separate “bleaching warnings” for a week in February and for most of
March (fig. 2.6.4). Subsequent to March 2016, temperatures decreased at a faster rate than they rose
before March.
55
The first indications of bleaching were observed during December 2015, when 3.6 ± 2.8% of the coral
cover manifested paling on Two-mile Reef. Four genera (Acropora, Pocillopora, Montipora and
Astreopora) were found to be affected with minor paling at this stage. Full bleaching developed
several months later, with 14–56% (Ave. ± SD = 39.0 ± 11.3%) of hard corals assessed at sites with
some degree of either paling (25.7 ± 6.6%) or bleaching (13.4 ± 6.9%) across sites in the three reef
complexes (fig. 2.6.5a). Bleaching indices at sites ranged from 3.5–18.3 (Ave. ± SD = 11.5 ± 4.0). During
this period, 4.1–17.5% (Ave. ± SD = 9.4 ± 5.9%) of the total coral cover at all sites on Two-mile Reef
manifested either paling or bleaching (fig. 2.6.5b)
Figure 2.6.3. Hourly water temperatures at the Nine-mile Reef long-term monitoring site, Sodwana Bay from September
2015 to December 2016. The red line indicates the temperature threshold at which bleaching is known to occur on local
reefs (Celliers & Schleyer, 2002). The green line indicates the long-term average temperature at the monitoring site (Porter
& Schleyer, 2017).
Figure 2.6.4. National Oceanic and Atmospheric Administration (NOAA) Coral Reef Watch satellite bleaching products,
showing the bleaching-related climatic conditions at Sodwana Bay, South Africa.
56
Of the coral genera that exhibited some form of heat stress during peak bleaching, Montipora was by
far the most commonly bleached genus, comprising 63% of the bleached coral cover on Two-mile
Reef, followed by Favia (10%) and Pocillopora (7%). When corals were bleached, 49% of this coral
cover was pale but not white, whilst the remaining 51% were white. In the case of Montipora, some
of the paling colonies exhibited a fluorescing blue colour. Mortality during peak bleaching averaged
0.3 ± 0.6% of coral colonies assessed, was restricted to only three sites, and reached a maximum of
2.3% at a site.
Figure 2.6.5 Observations of coral bleaching (including paling) and associated mortality recorded in South Africa in April-
May 2016 during peak bleaching as A) a percentage of hard coral colonies (n = 12) and as B) a percentage of total coral
cover (n = 5). Categories represent the severity of bleaching/mortality reported as a result of bleaching at a site.
During the period of peak bleaching, spatial and depth-related patterns in bleaching prevalence were
evident in the region. The bleaching index at sites declined significantly with latitude, as sites in the
Southern Complex exhibited lower bleaching indices than sites in the Northern Complex (fig. 2.6.6).
Similarly, bleaching indices manifested a decreasing trend with depth, although the relationship was
not significant (fig. 2.6.7).
By late September 2016, some corals were still showing signs of paling despite sea temperatures
having returned to normal for over two months (fig. 2.6.3).
57
Figure 2.6.6. Bleaching index versus latitude at twelve sites situated across all three reef complexes in South Africa during
late April 2016, based on records of a total of 3554 hard coral colonies. A positive and significant relationship (r2 = 0.52; p
< 0.01) was found between bleaching index and decreasing latitude.
Figure 2.6.7. Bleaching index versus depth for twelve sites situated across all three reef complexes in South Africa during
late April 2016, based on a total of 3554 hard coral colonies. A negative but non-significant relationship (r2 = 0.14; p =
0.24) was found between bleaching index and increasing depth.
58
2.6.2 Results
During peak-bleaching, 4.6% of the coral cover on Two-mile Reef in the Central Reef Complex was
bleached, whilst 4.8% was pale (fig. 2.6.8). The post-bleaching recovery survey revealed that the
condition of the corals was on par with pre-bleaching levels, with <5% of the total coral cover
manifesting only paling, but no signs of bleaching or recent mortality (fig 2.6.8). Average (±SD) total
coral cover during the pre-bleaching period was 49.3 ± 9.7% and negligibly more (54.2 ± 10.3%) during
the post-bleaching assessment (fig. 2.6.9). Similarly, the cover of fleshy algae differed little from pre-
(18.8 ± 10.2%) and post-bleaching (21.4 ± 3.2%) levels (fig. 2.6.9).
Figure 2.6.8. Condition of the coral cover assessed prior to bleaching, during peak-bleaching and several months later
after post-bleaching recovery on Two-mile Reef, Sodwana Bay (n = 5).
Figure 2.6.9. Mean ± SD percentage coral and algal cover in the pre-bleaching and post-bleaching (response) periods at
five sites on Two-mile Reef, Sodwana Bay. Pre-bleaching data are from December 2015 and ‘response’ data are from
September 2016. Only sites with data for both periods were included in the analysis.
The average cover of hard coral on Two-mile Reef during the pre-bleaching survey was found to
approximate 20%, in line with the ~20% cover that has persisted over the last decade at the Nine-
mile long-term monitoring site. It, too, changed by only a small percentage between the pre- (19.3 ±
5.2%) and post-bleaching (16.9 ± 3.8%) periods (Table 2.6.1). No material decrease in coral cover and
concomitant increase in fleshy algae cover could therefore be detected as a result of the 2015-2016
coral bleaching event.
59
Table 2.6.1. Average percentage change in coral cover at five Sodwana Bay sites on Two-mile Reef in the Central Complex,
comparing coral cover before and after the bleaching event.
Site
Percentage change
in total coral cover
Percentage change in
hard coral cover
Arches
-18.0
0.6
Chain
21.2
-5.4
Coral Gardens
-1.8
-11.4
Eden
22.3
4.8
Simons Cave
0.8
-0.3
Ave ± SD
4.9 ± 17
-2.3 ± 6.2
2.6.3 Discussion
As in previous bleaching events and periods of warming, South African coral reefs were only negligibly
affected relative to more northern countries in the region. Importantly, no bleaching-related
mortality was recorded in post-bleaching recovery surveys on Two-mile Reef in the Central Complex.
Furthermore, there was no material change in the cover of total coral, hard coral or fleshy algae. The
negligible change measured probably reflects the naturally high within-site variation in coral and
other living cover that could not be accounted for in the follow-up survey, despite sampling at the
same sites.
The levels of bleaching varied among sites and this was largely attributable to the interaction of
latitude and depth. Shallow sites in the north were generally more affected than deep sites in the
south, which was previously noted by Ruiz Sebastian et al. (2009), who also found that deeper sites
generally had less bleaching. The latitudinal gradient in bleaching indices is likely to be a function of
the decreasing trend in sea-surface temperature with increasing latitude that characterizes the region
(Porter et al., 2017).
The South African coral reefs have remained healthy over the last two decades and they have not
experienced significant levels of bleaching in recorded history. The most severe bleaching event
probably occurred in 2000, when 12% of the total living cover manifested some degree of bleaching
(Celliers & Schleyer, 2002). Evidence in this report suggests that the 2016 bleaching event was
therefore less severe than that experienced in 2000. This despite the fact that the 2015-2016 El Niño,
on a global scale, was longer in duration and more extensive than the 1997-1998 episode that caused
widespread mortality to coral communities in the western Indian Ocean (Goreau et al., 2000; Jacox
et al., 2016; Zhai, 2016).
2.6.4 Recommendations
In order to maintain and enhance the conservation and proactive management of coral reefs in South
Africa, it is important that several attributes be acknowledged, and new measures implemented at
various levels:
1) South Africa’s coral reefs should be acknowledged as nationally important natural barometers in
indicating climate change.
60
2) A multi-disciplinary Centre of Excellence, with specialist skills in coral reef ecology, climate science
and monitoring, should be identified and supported with consistent and adequate funding to
conduct bleaching monitoring and general reef health assessments.
3) Research proposals aimed at investigating the potential effects of climate change on these
marginal coral reefs should be prioritized and given adequate funding.
4) Coral reef monitoring should be conducted routinely and on an annual basis, and not just during
periods of El Niño or during other threats. Fixed transects should be used to reduce natural
variation to enhance precision for detecting temporal changes.
5) Management should ensure that anthropogenic stressors and disturbances on coral reefs are kept
to a minimum to maintain and enhance coral reef resilience in the face of anticipated future
warming events.
6) The role of the Maputaland and St Lucia Marine Reserves in the iSimangaliso Wetland Park, in
climate adaptation and mitigation, should be recognized (Simard et al., 2016). The high levels of
protection and world heritage site status must be maintained for the climate mitigation and
adaptation benefits of this globally important MPA to be secured into the future (Roberts et al.,
2017).
7) Coral monitoring and the development of a bleaching response plan must be incorporated into
the National Adaptation Plan as outlined in South Africa’s Intended Nationally Determined
Contribution submitted to the United Nations Framework Convention on Climate Change
(UNFCCC).
8) The prioritization of mitigation interventions that significantly contribute to a peak, plateau and
decline greenhouse gas emission trajectory in accordance with South Africa’s Intended Nationally
Determined Contribution and the National Climate Change Response: White Paper. In particular,
interventions within the energy, transport and industrial sectors.
2.6.5 References
1. Celliers, L. and Schleyer, M.H., 2002. Coral bleaching on high-latitude marginal reefs at Sodwana Bay,
South Africa. Marine Pollution Bulletin 44: 1380–1387.
2. Floros, C.D., Samways, M.J. and Armstrong, B., 2004. Taxonomic patterns of bleaching within a South
African coral assemblage. Biodiversity and Conservation 13: 1175–1194.
3. Goreau, T., McClanahan, T., Hayes, R. & Strong, A., 2000. Conservation of coral reefs after the 1998
coral bleaching event. Conservation Biology 14: 5–15.
4. Jacox, M.G., Hazen, E.L., Zaba, K.D., Rudnick, D.L., Edwards, C.A., Moore, A.M. & Bograd, S.J., 2016.
Impacts of the 2015–2016 El Niño on the California Current System: Early assessment and comparison
to past events. Geophysical Research Letters 43: 7072–7080.
5. Jordan, I.E. and Samways, M.J., 2001. Recent changes in coral assemblages of a South African coral
reef, with recommendations for long-term monitoring. Biodiversity and Conservation 10: 1027–1037.
61
6. McClanahan T.R., 2004. The relationship between bleaching and mortality of common corals. Marine
Biology 144: 1239–1245.
7. McClanahan, T.R., Ateweberhan, M., Graham, N.A.J., Wilson, S.K., Sebastian, C.R., Guillaume, M.M. &
Bruggemann, J.H., 2007. Western Indian Ocean coral communities: bleaching responses and
susceptibility to extinction. Marine Ecology Progress Series 337: 1–13.
8. Porter, S.N., 2017. South Africa. In D. Obura, M. Gudka, F. Abdou Rabi, S. Bacha Gian, J. Bijoux, S. Freed,
J. Maharavo, J. Mwaura, S. Porter, E. Sola, J. Wickel, S. Yahya & S. Ahamada (Eds.). Coral reef status
report for the Western Indian Ocean. Indian Ocean Commission, Mauritius. ISBN: 978-99949-0-400-6.
9. Porter, S.N., Branch GM., & Sink K.J., 2017. Changes in shallow reef community composition along
environmental gradients on the East African coast. Marine Biology 164: 101.
10. Porter, S.N. and Schleyer, M.H., 2017. Long-term dynamics of a high-latitude coral reef community at
Sodwana Bay, South Africa. Coral Reefs 36: 369–382.
11. Riegl, B. and Piller, W.E., 2003. Possible refugia for reefs in times of environmental stress. International
Journal of Earth Science 92: 520–531.
12. Roberts, C.M., O’Leary, B.C., McCauley, D.J., Cury, P.M., Duarte, C.M., Lubchenco, J., Pauly, D., Sáenz-
Arroyo, A., Sumaila, U.R., Wilson, R.W. & Worm, B., 2017. Marine reserves can mitigate and promote
adaptation to climate change. Proceedings of the National Academy of Sciences 114: 6167–6175.
13. Ruiz Sebastián, C.R., Sink, K.J., McClanahan, T.R. & Cowan, D.A., 2009. Bleaching response of corals and
their Symbiodinium communities in southern Africa. Marine Biology 156: 2049–2062.
14. Schleyer, M.H. and Celliers, L., 2000. The status of South African coral reefs. In: Souter, D., Obura, D.,
Linden, O. (Eds.), Coral Reef Degradation in the Indian Ocean: Status Report 2000. CORDIO, Stockholm,
pp. 49–50.
15. Simard, F., Laffoley, D. & Baxter, J.M., 2016. Marine protected areas and climate change: adaptation
and mitigation synergies, opportunities and challenges. Gland, Switzerland: IUCN, 52 pp.
16. Wilkinson, C., Linden, L., Caesar, H., Hodgson, G., Rubens, J. & Strong A.E., 1999. Ecological and
socioeconomic impacts of the 1998 coral mortality in the Indian Ocean: An ENSO impact and a warning
of future change? Ambio 28: 188–196.
17. Wilkinson C. (ed.) (2000) Status of coral reefs of the world: 2000. Australian Institute for Marine
Science, Townsville, 363 pp.
18. Zhai, P., Yu, R., Guo, Y., Li, Q., Ren, X., Wang, Y., Xu, W., Liu, Y. & Ding, Y., 2016. The strong El Niño of
2015/16 and its dominant impacts on global and China's climate. Journal of Meteorological Research
30: 283–297.
Impact of the 3rd Global Coral Bleaching Event on the Western Indian Ocean in 2016
Affiliations: 1Institute of Marine Sciences; University of Dar es Salaam
Fieldwork team: Saleh Yahya (National Coordinator), January Ndagala, Ali M. Ussi, Mohammed S.
Mohammed, Hassan Kalombo.
2.7 Tanzania
Author: Saleh Yahya1
Data contributors: Institute of Marine Sciences University of Dar es Salaam, Tanga Coelacanth
Marine Park, Chumbe Island Coral Park (CHICOP), Ali M Ussi
2.7.1 Background to the 2016 bleaching event
Figure 2.7.1. Coral reef monitoring stations in Tanzania for which data were included in this post-bleaching study.
2.7.1.1 History of coral bleaching events in Tanzania
Coral reefs in Tanzania were severely impacted by the first global bleaching event in 1998, losing up
to 90% of hard coral cover in places (Obura, 2002; Wagner, 2004). Impacts were felt more on reef
flats than on deeper reef slopes.
Sites around Pemba such as on Misali Island lost up to 70% of hard coral cover. Reefs around Unguja
Island were also impacted, with losses of 24% of hard coral cover at Chumbe and Kwale reefs,
approximately 30% at Chole Bay, and about 50% at Kitanga, Taa and Chanjale reefs (Muhando and
Mohammed, 2002). There was over 80% loss of coral cover in various sites at Mafia, over 65% loss in
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Mnazi Bay and between 10-75% in Tanga (McClanahan et al., 2007). Reefs in Songo Songo were the
only sites not to experience significant losses (McClanahan et al., 2007).
2.7.1.2 Progression of the 2016 coral bleaching event
Figure 2.7.2. National Oceanic and Atmospheric Administration (NOAA) Coral Reef Watch satellite bleaching products,
showing the bleaching related climatic conditions present at a remote satellite monitoring station in Tanzania.
In 2016, thermal stress began to accumulate relatively late, in mid-March, and peaked in early April
at 6 degree-heating-weeks and alert level 1 (fig. 2.7.2). In mid-March to early April 2016, at the peak
of coral bleaching, water temperatures repeatedly reached 31°C. After the first week of May
bleaching stress had subsided completely.
Coral bleaching started in February 2016 and increased through till June (fig.2.7.3b). Peak bleaching
occurred during late March and into April. Bleaching of 80–90% was observed on some reefs, such as
Sinda reef off Dar es Salaam and northern Chumbe reef, Zanzibar (Yahya et al., 2017).
a
b
Figure 2.7.3. Breakdown of observations collected in Tanzania in 2016 - a) coral bleaching (n=64) from Jan-May and
mortality (n=18) from May-September 2016 and b) monthly breakdown of bleaching observations (Jan; n=3, Feb;
n=12, Mar; n=20, Apr; n=20, May; n=9, Jun; n=4). Categories represent the severity of bleaching/mortality reported
as percentage of coral cover bleached/dead at a site.
64
Over 40% of reports from January to May indicated that there was severe bleaching (greater than
50% of coral cover bleached) (fig. 2.7.3a).
The effects of bleaching varied between species and growth forms, with the most affected corals at
most sites being Acropora, Fungia, Pocillopora, Porites and the faviids. On Chumbe reef in Zanzibar,
branching and table Acropora suffered significant mortality (Yahya et. al., 2017).
2.7.2 Results
In total, the analysis included data from 25
sites from 5 areas spread across the whole
Tanzanian coast – Mtwara, Songo Songo,
Mafia, Tanga and Zanzibar – between 1996
and 2017. Across all sites between 1992 and
2016, there is no long-term trend in hard
coral cover, with mean cover varying
between 30% and 55%, although temporary
downward blips are shown in 1998/9 and
2010 corresponding to bleaching events (fig.
2.7.4).
Even after the bleaching event in 2016, no
major change in coral cover is clear, with
coral cover remaining around 40% in 2017.
The difference between 2016 post-
bleaching and 2017 values (an apparent
increase) is due to different sites
represented rather than any actual
recovery. For sites where both coral and
fleshy algal cover were recorded, there has
been an overall trend of increasing algal
cover (and variability) from 1992 to 2017
(fig. 2.7.5). Levels of algal cover post-
bleaching range between 15-20% and are significantly higher than the means in 2011 and 2015.
Figure 2.7.4. Trends in hard coral cover on Tanzanian
coral reef sites before and after the 2016 bleaching event
(national mean (dark bold line) split into historical pre-
bleaching data (purple line, open-circles) and post-
bleaching data from July 2016 onwards (blue line, open-
squares), 95% confidence limit (grey shaded area),
individual monitoring stations (faded background lines)).
Only stations with data for both periods were included in
the analysis (n=25).
65
Figure 2.7.5. Trends in fleshy algae (green line, closed circles) and hard coral cover (blue line, open-circles) in Tanzania
before (solid line) and after (dotted line) the 2016 bleaching event. Shaded areas represent the 95% confidence limit.
Only stations with data for both periods and with both fleshy-algae and hard coral cover were included in the analysis
(n=24). The post-bleaching period is from July 2016 onwards.
Overall, from sites where pre- (2012 to June 2016) and post-bleaching (since July 2016) data for both
coral and algal cover are available, there was an average decrease in live hard coral cover by almost
10% from 44 ± 4.7% (mean ± se) to 39 ± 4.2%, and a corresponding increase in fleshy algae cover,
from 12 ± 4% to 15 ± 3.9% (fig. 2.7.6a).
a
b
Figure 2.7.6. Pre- and post-bleaching (response) mean (with standard error bars) a) hard coral and fleshy algae cover
of all Tanzanian reef sites with both fleshy-algae and hard coral cover data (n=16) b) hard coral cover for the various
regions in Tanzania arranged from North to South (Tanga; n=4, Zanzibar; n=4, Mafia; n=3, Songo Songo; n=5). Pre-
bleaching data is from 2012-June 2016 and ‘response’ data is from July 2016 -2017. Only sites with data for both periods
and were included in the analysis.
Comparing the change in coral cover at different areas in Tanzania after the bleaching event, we find
that coral reefs in Zanzibar were the worst affected, with a 52% decrease in coral cover (56± 9.6%
66
pre-bleaching to 27 ± 4.3%, post-bleaching). Tanga recorded a minor decline (from 40 ± 10.1% to 38
± 7.8%), as did Mafia Island (from 35 ± 9.5% to 34 ± 8.8%). Songo Songo showed an increase in coral
cover (pre-bleaching 42 ± 8.6% to post-bleaching 54 ± 7.3%) (fig. 2.7.6b).
2.7.3 Discussion
The 2016 bleaching event had a lower than anticipated impact on Tanzania’s reefs. Bleaching reports
during January and May indicate that several sites experienced high levels of bleaching, but the lower
levels of mortality points towards substantial recovery and survival of bleached corals. This may be
due to resistance gained from surviving previous bleaching events, together with the early onset of
the southeast monsoon that helped cool temperatures allowing bleached corals to recover. However,
the lack of available data for a number of sites between 2011 and 2016 makes it difficult to make a
precise assessment of the overall effect of the bleaching event on hard coral and algal cover.
Nevertheless, some areas were significantly affected, particularly on the west coast of Unguja Island,
Zanzibar. Once again, Acropora was the most susceptible to bleaching and mortality, especially on
the shallow reefs of Chumbe. This could be important for any in-situ coral nurseries and restoration
projects that plan to use this fast-growing genus. Interestingly, sites in Songo Songo were relatively
unaffected by the bleaching, as occurred in 1998. The lack of bleaching and mortality from the 1998
event was attributed to screening by 'green water' from the Rufiji delta (Obura, 2005), which may
provide stable protection for coral reefs in this area.
National hard coral cover remains at close to 40% even after the bleaching event, which is moderate
relative to other countries in the region. Fleshy algae levels are moderate at under 20% but have
shown an upward trend over several years. In the shallower reef flats, where most of the bleaching
mortality occurred, there was a significant increase in turf algae. Unpublished data (S. Yahya 2017)
shows a possible change in structure of fish assemblages, with an increase in herbivore species, likely
due to the increase in turf algae. The abundance of these grazers may also explain the insignificant
increase in fleshy algae, and the importance of herbivory in suppressing algal growth.
The long-term history of high coral mortality (in 1998), recovery to near pre-bleaching conditions for
most sites and resistance of some sites to renewed bleaching is an indicator of some degree of
resilience against climate change (e.g. McClanahan et al., 1999, 2009) and should be a priority for
future conservation actions.
2.7.4 Recommendations
Based on the current state of the coral reefs in Tanzania, and their response to the coral bleaching of
2016, as well as long-term trends, the following recommendations are made:
Monitoring and understanding coral reef health
1) Coral reef monitoring should be continued, supported and expanded to include more sites and
other parameters, particularly coral bleaching and disease.
2) Establish effective national coral bleaching response plans with the capacity, to include
preparation, funding, monitoring and communications/awareness creation. Individual research
programmes, NGOs and others can develop their own tailored coral bleaching response plans to
help them prepare for future bleaching events.
67
3) Collate all historical coral reef health data into a central, safe database for secure storage and ease
of access. To support this, a system to share metadata on coral reefs will make it easier to share
information among organisations and foster greater collaboration.
Maintaining and improving the health of coral reefs
4) The role of herbivory in maintaining low cover of fleshy algae may be important on Tanzanian reefs
and managing fisheries to protect herbivore populations should be considered.
Policy and research
5) Targeted research on the differential response of Tanzanian reefs to thermal stress and coral
bleaching should be undertaken, to identify if there are resilient reefs (bleaching refuges), and
what can be done to protect such sites and to promote seeding of other reefs.
2.7.5 References
1. Jiddawi, N.S. and Öhman, M.C. (2002). Marine Fisheries in Tanzania. Ambio, 7-8, 518-527.
2. McClanahan, T. R., Ateweberhan, M., Muhando, C. A., Maina, J., & Mohammed, M. S. (2007). Effects of
climate and seawater temperature variation on coral bleaching and mortality. Ecological Monographs,
77(4), 503-525.
3. McClanahan, T.R., Muthiga, N.A., Kamukuru, A.T., Machano, H., and Kiambo, R.W. (1999). The effects of
marine parks and fishing on coral reefs of northern Tanzania. Biological Conservation, 89(2), 161-182.