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Journal of Coastal Development ISSN : 1410-5217
Volume 12, Number 2 : February 2009: 90 - 99
90
DIVERSITY, DISTRIBUTION AND BIOLOGICAL ACTIVITY OF
SOFT CORALS (OCTOCORALLIA, ALCYONACEA)
IN SINGAPORE
Beverly Pi Lee Goh*, Grace Enhui Tan, and Lik Tong Tan*
Natural Sciences and Science Education, National Institute of Education, Nanyang Technological
University, 1 Nanyang Walk, Singapore 637616
Received : October, 10, 2008 ; Accepted : December, 20, 2008
ABSTRACT
The Southern Islands of Singapore are known to contain coral reefs which are high in biodiversity.
However, the diversity of soft corals had received little attention to date. This study was conducted to
determine the soft coral diversity in Singapore reefs as well as to conduct preliminary bioactivity tests
on the organic extracts from these soft corals. A 100-meter line transect was used to survey soft corals
at a 3m depth at ten different sample sites. Sclerites from samples were used to identify the soft corals
to the generic level. This study uncovered the following genera of soft corals: Carijoa spp., Cladiella
spp., Sinularia spp., Lobophytum spp., Sarcophyton spp., Stereonephthya spp., and Nephthea spp. In
addition, an unidentified genus of soft coral was observed at Kusu Island. Cladiella spp. yielded the
highest number of colonies, and Sarcophyton spp. had the highest coverage in terms of total colony
diameter. The brine shrimp (Artemia salina) toxicity assay was carried out to screen for toxicity of the
soft coral extracts at concentrations of 10, 100, and 1000 ppm. Results showed high levels of toxicity in
extracts of Sarcophyton spp. and Cladiella spp., indicating that these soft corals are potentially good
sources of bioactive compounds for drug discovery.
Key words: Octocorallia diversity, Singapore, toxicity of octocorals, brine shrimp lethality assay
Correspondance : Phone: +65 6790 3820; Fax: +65 6896 9432; E-mails: beverly.goh@nie.edu.sg,
liktong.tan@nie.edu.sg
INTRODUCTION
Soft coral communities (Octocorallia,
Alyconacea), excluding the gorgonians
(Suborder Holaxonia, Calcaxonia and
Scleraxonia) have been documented in coral
reef studies from Southern Taiwan
(Benayahu et al., 2004), Indonesia
(Manuputty, 1992), Thailand (Satapoomin
and Sudara, 1991) and the Red Sea, Israel
(Benayahu et al., 2002). In all, a total of 21
genera have been reported from Indo-Pacific
reefs (Satapoomin and Sudara, 1991;
Manuputty, 1992). There have been no
comprehensive studies of soft corals
undertaken in the reefs around the Southern
Islands of Singapore and very little is known
about their diversity and distribution.
Although much information has been
gathered on coral reefs in Singapore, these
studies have not given much attention to soft
corals, but rather have focused on other reef
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Volume 12, Number 2 : February 2009: 90 - 99
91
organisms, particularly hard corals (Chou
and Teo, 1983; Chong, 1985; Chong, 1986;
Chou, 1988; Goh et al., 1990; Chua, 1990;
Goh and Chou, 1991; Low and Chou, 1991;
Low and Chou, 1992; Leng and Lim, 1992;
Goh and Chou, 1993; Chou et al., 1994a).
A total of 197 hard corals species from 55
genera have been recorded here, accounting
for almost 25% of the global total (Chou et
al., 1994a; Chou and Goh, 1998; Tan et al.,
2007). In addition, studies on gorgonians in
Singapore have also been documented (Goh
and Chou, 1998; Goh et al., 1999; Koh et
al., 2000). Information on soft coral
communities reported in previous studies
however, did not give any account of their
diversity (Goh and Chou, 1991; Goh and
Chou, 1994).
The coral reefs located around the
Southern Islands of Singapore are known to
be rich in biodiversity (Loo et al., 1991;
Chou and Tun, 2004). However, these coral
reefs have seen a steady decline over the
past few years (Chua and Chou, 1992; Chou
et al., 1994b; Chou, 2002). It has been
estimated that 60% of the reefs have been
lost through foreshore reclamation since the
late 1960’s (Chou and Goh, 1998).
Extensive reclamation has had negative
impacts on the reefs and it is almost
impossible to reverse the declining status
(Chou et al., 1994b). It has been estimated
that the coral reef cover today has been
reduced to only about 30 km2 (Chou and
Tun, 2004). This has led to growing
concerns about coral reef conservation in
Singapore. With increasing focus on
conservation of reefs in Singapore, an
assessment of the biodiversity of soft corals
obtained from this survey will provide a
good reference for further comparative
studies.
Much has been documented about the
significant role of reefs, particularly their
potential use in biomedical science. The
dense concentration of marine species
makes them potential source for drug
discovery (Newman and Cragg, 2004). Soft
corals in particular have been a prolific
source of bioactive compounds belonging
mainly to the terpenoid structural class. One
example is a cembranoid compound,
sarcophytol A, isolated from the soft coral
Sarcophyton glaucum having potent
antitumor as well as cancer
chemopreventive activity (Yokomatsu et al.,
1994). Extracts with bioactive properties
have also been screened from gorgonians in
Singapore (Goh et al., 1995). However, no
research has so far focused on other
Alyconacea in Singapore, in particular the
soft corals. This study aims to document the
diversity and distribution of soft corals in
Singapore reefs as well as to carry out
preliminary screening for bioactive
compounds based on the brine shrimp
toxicity assay from these soft corals.
MATERIALS AND METHODS
Sample sites.
The study was conducted at selected sites at
the Southern Islands of Singapore (Fig. 1).
A total of 10 sites were surveyed from
January 2008 to April 2008. These were
fringing reefs surrounding the islands of
Raffles Lighthouse, (1o10’N, 103o45’E),
Pulau (P.) Semakau (1o 12’N, 103o45.5’E),
Sister’s island (1o 13’N, 103o50’E), Kusu
Island (1o13’N, 103o51’E), two patch reefs
west of P. Hantu (1o 13’N, 103o45’E) and a
jetty located in the south of P. Hantu.
Sampling method.
The depth-specific 100m line transect as
described in English et al. (1994) was used
to sample reef communities at a depth of
3meters from the reef crest for all sites
except the jetty at P. Hantu. At P. Hantu
jetty, pillars supporting the jetty were
surveyed by observation at a depth of 3
meters. Since this was not a coral reef on
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92
which a transect could be laid, only total
colony counts of soft corals were recorded
from the four pillars. All surveys were
carried out using SCUBA. Soft corals
encountered along the transects were
measured (colony diameter, m) and sections
of the colonies were collected in separate
bags.
Fig 1. Map of the Southern Islands of Singapore showing the location of sample sites. Inset:
Enlarged maps of individual sample sites indicating transects. (H1: P. Hantu 1, H2: P.
Hantu 2, K1: Kusu Island 1, R1: Raffles Light House 1, R2: Raffles Light House 2,
S1: P. Semakau 1, S2: P. Semakau 2, SS1: The Sister’s Island 1, SS2: The Sister’s
island 2. HJ: P. Hantu Jetty)
Samples of soft corals were frozen
immediately. In the laboratory, about
0.5cm2 of soft coral tissues were removed
and dissolved in 10% sodium hypochlorite
to obtain sclerites for identification.
Identification was carried out to the genus
level with the use of keys from the
Australian Institute of Marine Science
(Fabricius and Alderslade, 2001). There are
no published resources for identifying soft
corals to the species level. Soft corals
obtained in this study were therefore
identified only to the genus level.
Brine shrimp (Artemia salina) toxicity
assay.
The brine shrimp toxicity assay based on
Meyer et al. (1982) was used to test for
biological activity from samples of the soft
corals. Extracts were obtained by soaking
samples in MeOH for 24h and followed by
filtration using the buchner funnel.
Removal of organic solvent was achieved
using the roto-evaporator. Three different
concentrations of extracts were used to test
for toxicity by re-suspending dried extracts
in artificial sea water in 20 ml glass vials to
give resulting concentrations of 100 ppm,
100 ppm, and 10 ppm. A total of five
replicates were tested for each
concentration, together with controls
containing no extracts. Brine shrimps
(Artemia salina) larvae were hatched from
cysts 48h prior to the commencement of the
assay. For each test concentration and
controls, 20 brine shrimp larvae were
introduced into each vial using long
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93
stemmed pipettes. The percentage mortality
of the brine shrimp was observed after 24h.
RESULTS AND DISCUSSION
Results
A total of seven genera of soft corals were
identified at the ten sites surveyed,
representing the families Clavulariidea,
Alcyoniidae and Neptheidae (Table 1). In
addition, four colonies of an unidentified
soft coral genus were found at Kusu Island.
The largest coverage of soft corals, in terms
of colony diameter, was found at Kusu
Island (total of 4.76m) while the lowest
coverage was found at Sister’s Island 1
(total of 0.31m). In terms of abundance
(number of colonies), P. Semakau yielded
the highest number of soft corals with
Cladiella spp. having the highest occurrence
at all sample sites (Table 1). Furthermore,
Sarcophyton spp. was observed to have the
highest cover at all sites.
Table 1. Total soft coral cover (colony diameter in m) for each genus along a 100m transect at
sample sites in the Southern Islands of Singapore. The abundance (number of
colonies) of each genus is stated in parentheses. (H1: P. Hantu 1, H2: P. Hantu 2, K:
Kusu Island 1, R1: Raffles Light House 1, R2: Raffles Light House 2, S1: P.
Semakau 1, S2: P. Semakau 2, SS1: The Sister’s Island 1, SS2: The Sister’s island 2.
*HJ: P. Hantu Jetty (only number of colonies indicated), Car: Carijoa spp.; Cla:
Cladiella spp.; Sin: Sinularia spp.; Lob: Lobophytum spp.; Nep: Nephthea spp.; Sar:
Sarcophyton spp.; Ste: Stereonephthya spp.; UG: Unknown).
Clav
ularii
dae
Alcyoniidae
Neptheidae
Sample
sites
Car
Cla
Lob
Sar
Sin
Nep
Ste
UG
Total
H1
0.32 (7)
0.10 (1)
0.42 (8)
H2
0.11 (2)
0.23 (1)
0.12 (3)
0.46 (6)
K
1.63 (3)
0.72 (3)
0.92 (5)
0.12 (1)
1.37 (4)
4.76 (16)
R1
0.80 (6)
0.53 (3)
0.17 (1)
0.20 (2)
1.70 (12)
R2
0.11 (1)
1.48 (7)
0.64 (2)
0.11 (1)
2.34 (11)
S1
0.11 (1)
0.40(4)
0.21 (3)
0.72 (8)
S2
0.56 (1)
2.23(15)
0.17 (2)
0.57 (3)
0.28 (4)
3.80 (25)
SS1
0.10 (1)
0.21 (3)
0.31(4)
SS2
1.06 (6)
0.28 (1)
0.23 (5)
0.46 (2)
2.03(14)
*HJ
(5)
Total
(5)
4.03(25)
2.57(11)
4.15(23)
0.7 (10)
2.12(13)
1.61(18)
1.37 (4)
Extracts of six soft coral species
(Sarcophyton spp., Sinularia spp., Cladellia
spp., Nephthea spp., Carijoa spp, and the
unidentified soft coral from P. Hantu)
showed significant biological activity with
mortality greater than 80% at 1000 ppm
(Fig. 2). Both extracts of Sacrophyton spp.
and Cladellia spp. indicated high toxicity (>
80% mortality) when tested at a lower
concentration of 100 ppm. No significant
toxicity responses were observed at the
lowest concentration of 10 ppm for all
Journal of Coastal Development ISSN : 1410-5217
Volume 12, Number 2 : February 2009: 90 - 99
94
0
0
20
40
60
80
100
Lobophytum spp.
Sarcophyton spp.
Stereonephthya spp.
Sinularia spp.
Cladiella spp.
Nephthea spp.
Carijoa spp.
Unknown
Soft Coral Species
Mean Percentage Mortality
10 ppm
100 ppm
1000 ppm
extracts. All controls indicated no mortality
of brine shrimp larvae.
Fig 2. Graph showing mean percentage mortality of brine shrimp larvae (pooling of five
replicates) at three test concentrations of soft coral extracts.
Discussion
This study documents for the first time
seven named genera of soft corals in the
reefs of Singapore, and Alcyoniidae as the
most abundant family observed. Past
records of soft corals from Singapore
obtained from preserved specimens at the
Raffles Museum of Biodiversity Research
(NUS) and reports (Wee and Ng, 1994) have
listed the genera: Sinularia spp., Cladiella
spp., Lobophytum spp., Sarcophyton spp.
and Dendronephthya spp. Only
Dendropnephthya spp. was not sampled in
this study.
The soft coral diversity observed in
this study was low compared to records of
hard corals from the Southern Islands of
Singapore over the past few years. Past
records have reported over 150 species of
hard corals from 55 genera (Chou et al.,
1994a; Chou and Goh, 1998). The results
here also indicate fewer soft corals in terms
of abundance and diversity compared to
other countries in the region. A survey
conducted in Indonesia, Seribu Island,
reported 17 genera from six different
families (Manuputty, 1992). Records from
the gulf of Thailand showed ten different
genera from five families (Satapoomin and
Sudara, 1992), and reefs in Taiwan were
observed to have 22 genera from seven
families (Benayahu et al., 2004). Our study
surveyed a relatively small area compared to
the other studies, and a more comprehensive
survey covering a wider area of reefs in
Singapore may reveal more species of soft
corals.
In this study, Cladiellia spp. was the
most abundant with 25 collected throughout
the survey, and hence it may be the
dominant soft coral genus in Singapore. The
survey concentrated on areas of the coral
reef close to the reef flat, which is a region
which experiences high wave action.
Cladiella spp. is a thick encrusting
octocoral, and has been reported to be able
to tolerate some wave action (Fabricius and
Alderslade, 2001). This may explain its high
abundance in this study. Cladiella spp. was
Journal of Coastal Development ISSN : 1410-5217
Volume 12, Number 2 : February 2009: 90 - 99
95
also found to be one of the dominant genera
in the gulf of Thailand (Satapoomin and
Sudara, 1991).
Members of the Alcyoniidae, such as
Sarcophyton spp., Sinularia spp. and
Lobophytum spp. have been reported to be
fast growing and able to grow well in
moderately turbid, well lit coastal areas
(Fabricius and Alderslade, 2001). These
soft corals were frequently sampled at all the
survey locations in this study, and it may be
an indication of the higher tolerance of these
particular genera for sedimented waters, like
those occurring in Singapore .
The low soft coral abundance
observed in the study could be attributed to
the high sedimentation rate in Singapore
waters. Average sedimentation rates of 5-
20mg cm-2 day -1 have been reported with
maximum rates of up to 44.64 cm-2 day -1
recorded (Low and Chou, 1994). Rogers
(1990) postulated that “normal”
sedimentation rates in coral reefs are in the
order of approximately 10mg cm-2 day -1.
Heavy sediment loading from land
reclamation, dredging and dumping have
contributed to a high sedimentation rate in
Singapore waters, causing anthropogenic
stress to reefs (Chou et al., 1994a). In
addition, sedimentation also results in a
reduction in light penetration and thus also
affects coral reef organisms that
photosynthesize (Goh and Chou, 1991).
Chua and Chou (1992) have further reported
that the deeper zones of the coral reef have
become denuded as a result of a reduction in
light penetration. Thus may also explain
why the soft corals sampled in this study
were located in the shallow reef crest.
Chou (2002) documented a steady
decrease in live coral cover at most reef sites
since 1986. Even Raffles Lighthouse, the
island furthest from Singapore mainland was
also reported to suffer a decrease in live
coral cover, from 76.35% in 1987 to 48% in
1997. Sinularia spp., the only soft coral
monitored in a 1998 study showed complete
mortality during a mass bleaching event in
1998. The overall reduction in total live
coral cover through bleaching was most
evident at the reef crest and this was
attributed to an increase in sea surface
temperature causing thermal stress to reefs
organisms (Chou, 2002). Hence the two
factors: sedimentation and temperature
increase could have lead to the decline of the
reef community in terms of abundance and
species richness (Chou et al., 1994a), and
may also explain the low abundance of soft
corals observed in this study.
Other factors also play a role in reef
diversity. In particular, substrate type
determines how reef organisms may be
established. Satapoomin and Sudara (1991)
stated that a stable substrate was important
for attachment by soft corals. Loo et al.
(1991) documented the sea floor of the
southern islands of Singapore to be covered
with unconsolidated sand and mud. Hence
the low diversity and abundance of soft
corals at the patch reefs of P. Hantu in this
study may be due to the fact that the bottom
substrate is mainly composed of dead coral
covered with sediment (personal
observation).
A study of coral establishment on
submerged concrete pillars at P. Hantu
conducted by Chong (1985) focussed on
hard corals, and no soft corals were
documented. In the present study, Carijoa
spp. was the only genus found at the pillars
of the P. Hantu jetty, and it was not sampled
at the other nine study sites. Carijoa spp. is
a common fouling organism on jetties and
wrecks (Fabricius and Alderslade, 2001),
and this may explain its occurrence at the P.
Hantu jetty.
Although the soft coral fauna of
Singapore’s reefs represent a small
proportion of the total reef community, it is
believed to play a significant role in the reef
ecosystem through many interspecific
interactions (Goh and Chou, 1991).
Results of the brine shrimp toxicity
assay indicated the presence of bioactive
compounds in the soft corals collected in
Journal of Coastal Development ISSN : 1410-5217
Volume 12, Number 2 : February 2009: 90 - 99
96
this study. Extracts from Stereonephythya
spp. yielded the lowest mortality rates at
every test concentration, and hence had the
lowest toxicity effect. Sarcophyton spp. and
Cladiella spp. were shown to be active even
at 100 ppm, and thus their extracts may be
considered to be more toxic than those from
the other genera. Therefore, this preliminary
test of bioactivity in soft corals from
Singapore showed promising results,
particularly for the genera Sarcophyton spp.
and Cladiella spp., and may be investigated
further as source of bioactive compounds for
drug discovery.
The use of the brine shrimp toxicity
assay in this study has proven to be a quick
and cost effective method to establish
preliminary toxicity activity in these soft
corals. A search of the literature has shown
that a number of pharmaceutically important
marine-derived compounds, such as curacin
A (Gerwick et al., 1994), have been
identified through the use of this assay.
Furthermore, studies have shown good
correlations between brine shrimp toxicity
data and cell-based cytotoxicity data
(Carballo et al., 2002). In spite of the small
sample size of just eight soft coral species
used in this study, high incidence of toxicity
data was indicated in six of them. This
further demonstrates that in general marine
organisms from local waters are significant
source of bioactive compounds for drug
discovery and highlights the importance of
conserving local marine flora and fauna.
CONCLUSION
In conclusion, this preliminary study
revealed seven known genera and one
unknown soft coral genus from the Southern
Islands of Singapore. The brine shrimp
toxicity assays indicated the presence of
bioactive compounds from the soft coral
extracts, particularly from Sarcophyton spp.
and Cladiella spp. This suggests a good
potential for drug discovery in these two
genera and further analysis of the active
compounds from the soft coral extracts
should be conducted to uncover the specific
compound(s) responsible for the toxicity. It
is evident that further research should be
conducted to identify the soft corals in
Singapore to the species level, as well as
identify and classify the unknown soft coral
genus into an appropriate taxonomic group
for future reference. In addition, more sites
in the Southern Islands of Singapore could
be surveyed for a more comprehensive study
of soft coral diversity and ecology.
ACKNOWLEDGEMENTS
The authors wish to thank Marco Perrig and
Natalie Low for assistance during field
collections. Invaluable assistance in the
field trips and laboratory work were also
provided by Natalie Low, Annabelle Tay,
NSSE laboratory technicians and various
volunteers. Thanks are also due to the
Raffles Museum of Biodiversity Research
that provided free access to their records and
specimen collections. Financial support for
this study was generously provided from
research grants (RP 5/02 GPL and RI 8/05
TLT) from the National Institute of
Education, Nanyang Technological
University.
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