Coral reef ecosystems are among the most biologi-
cally diverse and complex marine ecosystems worldwide.
In addition to their biological and ecological impor-
tance, coral reefs support major economic and physical
functions (e.g. food production, tourism, biotechnology
development and coast protection) that are essential for
many countries (Costanza et al. 1997). This is particularly
true in the Pacific Ocean where coral reefs sustain local
economy of several Pacific Islands and Territories (Chin
et al. 2011). Unfortunately, the frequency and severity of
natural (e.g. cyclone, outbreaks of predators, particularly
the starfish Acanthaster planci – COTS: crown-of-thorns
startfish) and anthropogenic perturbations (e.g. pesticide
pollution, rising sea-water temperature, overfishing) on
coral reefs greatly increased worldwide over the last three
decades. For example, coral reefs currently have to face
one of the strongest El Nino, with 93 % of the Great Bar-
rier Reef in Australia that bleached under the effect of
high temperatures lasting several months in 2016 (http://
www.coralcoe.org.au/). As a consequence of those per-
turbations, coral reefs suffered unprecedented changes
of community assemblages, relocation, decline and ulti-
mately mortality (e.g. Salvat 1980, Wilkinson & Salvat
2012, Lecchini et al. 2012, 2013, Galzin et al. 2016).
Thus, today 20 % of coral reefs are already dead, 25 %
are in great immediate threat, and another 25 % will be
threatened by 2050 due to the effects of coastal develop-
ment, over-fishing and multiple factors associated with
global climate change (Chin et al. 2011). In this context
of increasing degradation of coral reefs, ecological sur-
veys are needed to document changes in reef communi-
ties (i.e. “long term monitoring” – Adjeroud et al. 2005,
Wilkinson & Salvat 2012).
In the South Pacific region, the “Polynesia Mana”
monitoring network was set up in 1992 by the Criobe
research centre (http://observatoire.criobe.pf/) with the
goal to assess the effects of natural and/or anthropogenic
perturbations on coral assemblages on the reef slopes at
both local scale (between sites around an island separated
from few meters to kilometres – e.g. different sites around
Moorea Island) and regional scale (between islands and
archipelagos, separated by up to hundreds of kilometres
– e.g. between Tahiti, Tonga, Niue) (e.g. Adjeroud et al.
2005, Galzin et al. 2016). In 2013, Polynesia Mana was
implemented in Western Samoa. Despite some stud-
ies have been performed in American Samoa (e.g. Craig
2001, Wilson 2012), almost nothing was known on the
current state of Western Samoa coral reefs (Tiitii 2015).
The present study aimed to provide the first data on
the evolution of the coral cover on the Western Samoa
in order to appraise how coral reefs might be impacted
across time by some anthropogenic and/or natural distur-
MATERIALS AND METHODS
Some underwater visual surveys were conducted in May 2013
and May 2015, on the outer slope of the reef on the North coast
of Upolu island, Western Samoa (13°48’354 S; 172°01’915 W),
between 10 m and 13 m depth using the photo quadrat method.
This site is one of the most diversity at Upolu Island and it is
monitored by Fisheries & Environment departments at Samoa
(Tiitii 2015). Two stainless stakes were permanently driven into
the substrate and separated by 20 m. During the surveys, a stain-
VIE ET MILIEU - LIFE AND ENVIRONMENT, 2016, 66 (2): 155-157
FIRST REPORT OF A DRAMATIC RAPID LOSS OF LIVING CORAL
ON THE NORTH COAST OF WESTERN SAMOA
C. BERTHE1,2, Y. CHANCERELLE1,2, D. LECCHINI1,3,*, L. HEDOUIN1,2
1 USR 3278 CNRS-EPHE-UPVD, CRIOBE, Paris Sciences Lettres, 98729 Moorea, French Polynesia
2 Laboratoire d’Excellence “”CORAIL” 98729 Moorea, French Polynesia
3 IRCP, Institute for Pacific Coral Reef, 98729 Moorea, French Polynesia
* Corresponding author: firstname.lastname@example.org
ABSTRACT. – Some coral reefs are threatened around the world due to the effects of coastal
development, over-fishing and multiple factors associated with global climate change. In 2013,
a monitoring programme was implemented in Western Samoa to document changes in reef com-
munities and the impacts of natural and anthropogenic disturbances. Underwater visual surveys
reported the first data on coral cover on the north coast of Western Samoa. Between 2013 and
2015, all living coral genera (Acropora, Leptoria, Montipora, Platygyra, Pocillopora) dropped
from 42 % to 0 %. The interaction of crown-of-thorns startfish outbreak in 2010-2014 and
unusually high temperature in 2015 could have acted as a deathly combination for the coral
reefs in Western Samoa.
POLYNESIA MANA NETWORK
156 C. BERTHE, Y. CHANCERELLE, D. LECCHINI, L. HEDOUIN
Vie Milieu, 2016, 66 (2)
less cable was stretched between the two stakes, and 20 metal
markers were used to indicate where a quadrat would be posi-
tioned. The quadrat consisted of a 1 m² metallic frame subdivid-
ed into 81 squares with strings. A photograph of the quadrat was
taken at each position, i.e. 20 positions, with a Nikonos camera
(V Body camera equipped with a Nikon D300s/14 mm Nikkor
lens, flashes; Fig. 1). Living coral colonies were distinguished
at the genus level (Acropora, Leptoria, Montipora, Platygyra,
Pocillopora) and coral cover values were obtained as the ratio
of the number of points (string crosses) under which a living
colony was identified to the total number of points (81) of the
quadrat. Thus, living coral covers were compared between the
The living coral cover percentage on the outer slope
of the reef on the North coast of Upolu island, Western
Samoa was of 42 ± 6.7 % (mean ± SD) in May 2013
(Fig. 2). Among the five main coral genera, the covers of
Acropora and Montipora were, respectively, 36 ± 5.1 %
and 5 ± 1.3 %, while the three other coral genus (Leptoria,
Pocillopora, Platygera) displayed a cover lower than 1 %
in 2013. All coral genera dropped to 0 % in 2015 (Fig. 2).
Our study reported an unusual coral loss. Within two
years, all living corals died, dropping from 42 % to 0 % of
living coral cover (Fig. 2). Kayal et al. (2012) reported a
coral loss on Moorea reefs (French Polynesia) from 40 %
in 2005 to 5 % in 2010 due to COTS and tropical cyclone
Oli. Alevison & Porter (2014) underlined a loss of 76 %
of stony corals in the Caribbean reefs in 26 years. The
dramatic coral loss observed in the present work is likely
due to the A. planci outbreak that occurred from 2010 to
2014 in Western Samoa (Tiitii 2015). A. planci consumes
all coral genera, but shows preferences for Acropora
species (Pratchett 2007), which was the main genus on
Fig 1. – Example of a photo-
quadrat (1 m²) of coral reefs in
Western Samoa outer reefs in
2013 and 2015.
Fig. 2. – Monitoring of living
coral cover (total coral cover and
five coral genus: Acropora, Lep-
toria, Montipora, Platygera,
Pocillopora) in May 2013 and
May 2015 at Western Samoa.
Values are mean ± SD percentage
of the total living coral cover and
of the five coral genera, comput-
ed on the 20 photo-quadrats.
DEGRADATION OF SAMOA’ CORAL REEFS 157
Vie Milieu, 2016, 66 (2)
Western Samoa reefs (Fig. 2). Causes of A. planci out-
break still remain uncertain, but abundance of resources
(i.e. living corals) could be one explanation in those reefs
(Kayal et al. 2012). However, other stressors may have
acted simultaneously with COTS to worsen coral decline.
The January-May 2015 period was reported as an unusual
warm period worldwide and bleaching events have been
reported in Western Samoa (Tiitii 2015). High sea tem-
perature is known to make corals expel their symbiotic
zooxanthellae and thus bleached (Lesser 2011). The tem-
perature has to drop quickly so that algae can recolonize
corals before they die. During mass bleaching events, the
rate of coral mortality is highly variable depending on the
geographic areas and on the period the sea temperature
stays high. For example, the 1997-1998 bleaching event
led to a coral mortality varying from 5 % in the Indo-West
Pacific (Wilkinson et al. 1999), to 95 % in the Atlantic
Ocean (Wilkinson & Hodgson 1999).
Overall, given that the combination of natural and/or
human stressors is a developing scenario for the XXI cen-
tury (Chin et al. 2011), we hypothesized that the interac-
tion of COTS outbreak in 2010-2014 (observed by Tiitii,
2015 at Samoa) and unusually high temperature in 2015
(observed in the world) could act as a killer combina-
tion, destroying all alive corals in Western Samoa (Fig.
2). Other stressors could, nevertheless, also explain a part
of this coral decline such as overfishing of herbivorous
fish or a pesticide pollution. Thus, some future surveys
at Samoa and elsewhere in the South Pacific Islands
are necessary to validate our observations locally and
regionally. The present study provided the first monitor-
ing data on coral cover of Western Samoa and will help
scientists, conservationists and reef managers to have
access to robust and long-term datasets which today are
uncommon for most regions of the world (Bruno & Selig
2007, Wilkinson & Souter 2008, Chin et al. 2011). Such
long-term monitoring on several South Pacific Islands
will allow to better ensure the persistence of coral reefs
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Received on March 18, 2016
Accepted on May 5, 2016
Associate editor: A Chenuil