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First report of a dramatic rapid loss of living coral on the north coast of Western Samoa

Authors:
Cecile Berthe at CRIOBE
Cecile Berthe
  • CRIOBE
Yannick Chancerelle at École Pratique des Hautes Études
Yannick Chancerelle
David Lecchini at École Pratique des Hautes Études
David Lecchini
Laetitia Hédouin at French National Centre for Scientific Research
Laetitia Hédouin
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Abstract and Figures

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 communities 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.
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INTRODUCTION
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-
bances.
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: lecchini@univ-perp.fr
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.
CORAL COVER
ACANTHASTER PLANCI
BLEACHING
BIOMONITORING
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
two years.
RESULTS
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).
DISCUSSION
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
through time.
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Received on March 18, 2016
Accepted on May 5, 2016
Associate editor: A Chenuil
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Article
Full-text available
  • Aug 2020
  • CORAL REEFS
In 2016, many tropical corals worldwide were exposed to anomalously high temperatures due to one of the strongest El Niño events ever recorded. Bleaching impacts were reported on 23 islands within three archipelagos of French Polynesia (Tuamotu, Society and Marquesas archipelagos). A detailed study on the effects of elevated temperatures on corals was performed on five islands (Mo’orea, Makemo, Hikueru, Marutea and Katiu) and revealed contrasting patterns of coral bleaching responses between Mo’orea (Society Archipelago) and the four islands of the Tuamotu Archipelago. While some reefs from the Tuamotu lost more than half of their coral cover, in Mo’orea, less than 1% mortality was recorded 6 months after bleaching. During the 2016 bleaching event, certain reefs at 12 m depth in the outer reef habitats were not exposed to sufficiently long high-temperature periods (heat stress not exceeding 1.1 °C weeks in Mo’orea) to cause large-scale bleaching-related coral mortality. In contrast, other reefs in the Tuamotu Archipelago had DHW reaching up to 9.2 °C weeks and experienced severe mortality (up to 71%). Our study showed how differential heat stress exposure across reefs of French Polynesia led to different impacts on corals. Until now, Mo’orea reefs have been spared abnormally high temperatures leading to mortality and should be considered an important source of larvae to help maintain reefs on the surrounding islands.
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The crown-of-thorns seastar species complex: knowledge on the biology and ecology of five corallivorous Acanthaster species
Article
Full-text available
  • Dec 2023
  • MAR BIOL
Coral-eating crown-of-thorns seastars (CoTS, Acanthaster spp.) are major contributors to the coral reef crises across the Indo-Pacific region. Until recently, CoTS throughout the Indo-Pacific were regarded to be a single species, Acanthaster planci. However, genetic and morphological analyses demonstrated that there are at least four distinct species: Acanthaster benziei in the Red Sea, Acanthaster mauritiensis and A. planci in the Indian Ocean, and Acanthaster cf. solaris in the western Pacific. Acanthaster cf. ellisii in the eastern Pacific needs more taxonomic attention. Here, we review the biological knowledge for each species adapting a pragmatic geographical species definition and using a systematic literature review complemented with more focused searches for individual species. The vast majority of CoTS research (88%) was conducted on A. cf. solaris, with much of this research undertaken on the Great Barrier Reef or in Japan. Many studies of A. cf. solaris are focused on monitoring or documenting incidences of outbreaks, though there is a solid base of knowledge on larval, juvenile and adult ecology derived from field and laboratory experiments. By contrast, most of the published studies on the four remaining species simply document cases of population outbreaks. The major taxonomic bias in CoTS research constitutes a significant limitation for understanding and managing these species for two reasons. First, even for A. cf. solaris, which is the most studied species, limited fundamental knowledge of their biology and ecology constrains understanding of the drivers of outbreaks and hinders corresponding management actions for prevention and control of these events. Second, understanding and management of other species are predicated on the assumption that all CoTS species have similar biology and behaviour, an unsatisfying assumption for ecosystem management.
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Coral reefs and the 1997-1998 mass bleaching and mortality
Article
Full-text available
  • Apr 1999
From mid-1997 to late 1998, hard and soft corals in widely separate parts of the world were affected by significant bleaching. Much of this bleaching coincided with a large El Nino event, immediately switching over to a strong La Nina. Scientists and other observers responding to calls for reports from the Global Coral Reef Monitoring Network, and survey teams participating in Reef Check, reported unprecedented bleaching in places as widespread as (from west to east) the Middle East, East Africa, the Indian Ocean, South, Southeast and East Asia, far west and far east Pacific, the Caribbean, and the Atlantic Ocean. A wide spectrum of situations has been reported, ranging from catastrophic bleaching with massive mortality (often near 95% of shallow corals) through to insignificant or no bleaching over large areas of the world's corals. The consensus is that this was probably the most severe bleaching event ever observed. More problematic is whether the observed bleaching will result in death or recovery of the corals, and whether there is potential for the damaged reefs to bounce back and recover from this event. But the most important question is whether this is just a severe, one-off event, as it now appears, or whether events like this will occur more frequently as the world's atmosphere and waters warm up.
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Long term monitoring of coral and fish assemblages (1983-2014) in Tiahura reefs, Moorea, French Polynesia
Article
Full-text available
  • Nov 2015
  • CYBIUM
Les récifs coralliens sont des systèmes dynamiques et diversifiés régulièrement soumis à des perturbationsnaturelles et anthropiques, sources d’hétérogénéité spatiale et temporelle dans la structure et la dynamique deces communautés d’organismes que sont, entre autres, les poissons et les coraux. Récemment, il a été démontréque les activités humaines pouvaient modifier les régimes naturels de perturbations des récifs coralliens en transformantles événements ponctuels en perturbations persistantes ou en stress chronique, soit en introduisant denouveaux types de perturbations, soit en ajoutant ou altérant certaines perturbations naturelles nécessaires au bonmaintien de la dynamique inhérente aux récifs. Dans cette étude, nous présentons la base de données qui nouspermettra d’analyser les tendances à long-terme des assemblages de poissons et de coraux de l’île de Moorea(Polynésie française) entre 1983 et 2014 sur une période de 32 ans, comprenant deux proliférations d’Acanthasterplanci (1987 et 2006) et plusieurs cyclones (1982, 1983, 1991 et 2010), sur trois sites de suivi permanents(quadrats de 50 × 2 m2) sur les récifs barrière et frangeant ainsi que sur la pente externe. La couverture corallienneprésente de fortes oscillations, en particulier sur la pente externe où elle a répondu fortement à la proliférationd’A. planci et des cyclones. Les abondances des poissons totaux et des poissons commercialisés montrent destendances contrastées sur les trois habitats, avec, plus particulièrement, une augmentation sur le récif barrière etune diminution sur la pente externe après 2000. Ces tendances se retrouvent chez les poissons herbivores dansces deux habitats. La richesse spécifique des poissons totaux, commerciaux et herbivores, augmente de façoncontinue au cours de la période d’étude dans les trois habitats. Des groupes particuliers d’espèces répondentdifféremment aux perturbations de la pente externe au cours du suivi : alors que certaines espèces ont tendanceà disparaître pendant quelques années avant de réapparaître, d’autres présentent un pic en terme d’abondanceen milieu de suivi ; d’autres espèces ont des abondances qui augmentent ou diminuent de façon continue, etd’autres encore montrent des abondances stables. Ceci indique que les récifs coralliens sont des systèmes trèsdynamiques dans lesquels les perturbations naturelles peuvent affecter les espèces de façon différente. Alors quele régime de perturbations naturelles semble être important pour la dynamique de la couverture corallienne danscertains habitats, cela se retrouve beaucoup moins pour les poissons. Cette atténuation des fluctuations spatialeset temporelles peut être due aux aptitudes de dispersion de nombreuses espèces de poissons, capables de chercherun autre habitat favorable en cas de perturbation de l’habitat corallien d’origine.
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Ecological and socioeconomic impacts of 1998 coral mortality in the Indian Ocean: An ENSO impact and a warning of future change?
Article
Full-text available
  • Mar 1999
The year 1998, was the warmest year since the start of temperature recordings some 150 years ago. Similarly, the 1990s have been the warmest decade recorded. In addition, 1998 saw the strongest El Nino ever recorded. As a consequence of this, very high water temperatures were observed in many parts of the oceans, particularly in the tropical Indian Ocean, often with temperatures of 3°to 5°C above normal. Many corals in this region bleached and subsequently died, probably due to the high water temperatures in combination with meteorological and climatic factors. Massive mortality occurred on the reefs of Sri Lanka, Maldives, India, Kenya, Tanzania, and Seychelles with mortalities of up to 90% in many shallow areas. Reefs in other parts of the Indian Ocean, or in waters below 20 m, coral mortality was typically 50%. Hence, coral death during 1998 was unprecedented in severity. The secondary socioeconomic effects of coral bleaching for coastal communities of the Indian Ocean are likely to be long lasting and severe. In addition to potential decreases in fish stocks and negative effects on tourism, erosion may become an acute problem, particularly in the Maldives and Seychelles. If the observed global trends in temperature rises continue, there will be an increased probability of a recurrence of the phenomenon observed in 1998 on the coral reefs of the Indian Ocean, as well as in other parts of the tropical oceans in coming years. Coral reefs of the Indian Ocean may prove to be an important signal of the potential effects of global climate change, and we should heed that warning.
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Fish larvae prefer coral above algal water cues: Implications of coral reef degradation
Article
Full-text available
  • Feb 2013
Many marine reef fishes have pelagic larval stages that develop in offshore waters. These larvae face the great challenge of relocating to patchily distributed reef environments in a vast oceanic matrix. We explored how chemical cues emitted from coral versus algal reefs attract fish larvae at Rangiroa Atoll (French Polynesia). Experiments with 2-channel choice chambers showed that during the recruitment stage, 7 of the 10 fish species studied preferred water from reefs dominated by coral compared to reefs dominated by algae (e.g. Aulostomus chinensis, Chromis viridis, Ptereleotris microlepis, and Sargocentron spiniferum). Only Zebrasoma veliferum preferred water from reefs dominated by algae. Overall, olfactory cues could play an important role in directing pelagic larval stage fishes to a suitable reef on which they can settle.
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Effects of alternate reef states on coral reef fish habitat associations
Article
Full-text available
  • Jun 2012
The present study describes ontogenetic shifts in habitat use for 15 species of coral reef fish at Rangiroa Atoll, French Polynesia. The distribution of fish in different habitats at three ontogenetic stages (new settler, juvenile, and adult) was investigated in coral-dominated and algal-dominated sites at two reefs (fringing reef and inner reef of motu). Three main ontogenetic patterns in habitat use were identified: (1) species that did not change habitats between new settler and juvenile life stages (60% of species) or between juvenile and adult stages (55% of species no ontogenetic shift); (2) species that changed habitats at different ontogenetic stages (for the transition "new settler to juvenile stage": 15% of species; for the transition "juvenile to adult stage": 20% of species); and (3) species that increased the number of habitats they used over ontogeny (for the transition "new settler to juvenile stage": 25% of species; for the transition "juvenile to adult stage": 25% of species). Moreover, the majority of studied species (53%) showed a spatial variability in their ontogenetic pattern of habitat use according to alternate reef states (coral reef vs algal reef), suggesting that reef state can influence the dynamics of habitat associations in coral reef fish.
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Feeding preferences of Acanthaster planci (Echinodermata: Asteroidea) under controlled conditions of food availability
Article
  • Jan 2007
Feeding preferences of the crown-of-thorns sea star, Acanthaster planci (L.), were studied in a series of laboratory-based feeding trials wherein sea stars were provided with equal availability of six different coral species. The order in which corals were consumed was then used to ascertain feeding preferences. Crown-of-thorns sea stars exhibited strong and consistent feeding preferences across replicate feeding trials. The most readily eaten coral species was Acropora hyacinthus, followed by A. gemmifera, A. nasuta, A. formosa, Stylophora pistillata, Montipora undata, and Pocillopora damicornis. Crown-of-thorns sea stars also consumed Goniopora lobata, Fungia fungites, Goniastrea retiformes, and Pavona cactus but only after all Acropora and Montipora (Family Acroporidae) as well as Pocillopora and Stylophora (Family Pocilloporidae) were eaten. The least-preferred corals were Favites abidita, Porites lobata, Symphyllia recta, Echinopora horrida, and Porites cylindrica. Of these, P. cylindrica was never eaten in any of the feeding trials in which it was offered. Observed feeding preferences substantiate findings from previous studies, where corals from the families Acroporidae and Pocilloporidae were preferred over all other corals. Further research is required to assess the underlying basis of feeding preferences of A. planci, but this study confirms that these starfish readily distinguish between different corals and have innate preferences for certain species. Still, most corals were eventually consumed, showing that when food is limited (during population outbreaks) A. planci is likely to consume virtually all different coral species, causing extreme devastation to coral reef ecosystems.
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Coral loss and fish guild stability on a Caribbean coral reef: 1974–2000
Article
  • Apr 2014
Data on reef substrate composition and fish guild structure was extracted from filmed underwater surveys conducted in 1974 and 2000 at a coral reef in the Florida Keys. During the course of this 26-year interval the reef underwent a dramatic (>75 %) loss of stony coral cover, particularly acroporids, accompanied by significant increases in turf algae, crustose-coralline algae, octocorals, and macroalgae. At the same time, marked changes occurred in the structure of a guild of large herbivorous reef fishes. Total abundance declined, and the relative abundance of constituent species and functional groups changed as well. In contrast, we recorded no change in any measure of structural stability in either of two carnivorous fish guilds (lutjanids, haemulids) that feed by night in off-reef habitats. These results are generally consistent with the hypothesis that coral loss differentially impacts functionally dissimilar groups of fishes, according to dependency on reef substrates for food and/or shelter. The persistence of sizeable herbivore populations along with the relatively low (
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