Coasta l Living Resources of Singapore: Proceedings of a Symposium on the Assessme nt of Living Resources in the Coas tal Areas of Singapore .

A QUANTITATIVE STUDY OF THE REEF COMMUNITY AT PULAU SATUMU

(RAFFLES LIGHTHOUSE)

Leng C.B., Lee K.S. and Esther G.L. Koh Department of Zoology

National University of Singapore Lower Kent Ridge Road

Singapore 0511

ABSTRACT

Data collected from four 1 OOm line transects perfo1111ed at Pulau Satumu (Raffles Lighthouse) at the 3m and 1 Om depth of two sites on opposite sides of the island were analysed to show the percentage cover of the various coral reef components. Differences in the coral cover between sites as well as between depths existed. The highest and lowest coral cover occurred at the western side of the island, with the highest (45.2%) at the 3m depth and lowest (1.0%) at the 10m depth. Corals with foliose and encrusting growth fo1111s dominated both sites. The substratum was particularly rocky. Twenty-five scleractinian genera and one octocorallian genus (Heliopora) were recorded.

INTRODUCTION

Raffles Lighthouse is situated on the southern-most island (Pulau Satumu) from the Singapore mainland, (1 ° l0'N and 103° 45'E). Reclamation in 1976 to increase the island's size affected most of the reef flat of the surrounding fringing reef. The reef is also popular with sport divers. Water visibility is usually between 2-3 metres. Water current was observed to be stronger on the western side of the island, with the eastern side being more sheltered.

No previous study of this nature has been made on the coral reef community here. The present study see}(s to characterise the reef slope communities at two sites on opposite sides of the island and is undertaken as part of the on-going ''Living Resources in Coastal Areas'' Project (Asean-Australia Cooperative Programme on Marine Science) to collect baseline data on coral reefs south of Singapore.

MATERIALS AND METHODS

The 100m line transect technique employed in this study has been fully described in Dartnall and Jones (1986). The method essentially involves the laying of a graduated

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100m transect tape at a fixed depth along the contours of the reef slope. Data gathered from the transects were analysed to obtain the percentage cover of the various reef components at each site and depth. Scleractinian coral samples were brought back to the laboratory for identification, using coral taxonomic guides of Veron (1986) and Wood (1983).

Transects were carried out on the eastern (Rl) and western (R2) flanks of the reef (Fig. 1), along the slope at two depths, 3m and 10m from the reef crest. The surveys were conducted between September 1987 and June 1988, using SCUBA equipment .

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Fig. 1. Map of Pulau Satumu showing survey sites.

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Rl

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LEGEND

0 Reef

~Land

15

-

I I Line transect

RESULTS

The distribution of the various reef components found from the transects at the two sites are summarised in Table 1 and Fig. 2. The highest live coral cover was found at R2 at the 3m depth (45.2% ), which also had the highest dead coral cover (33.62% ). The 10m depth of R2 also had a high percentage (31.15 % ) of dead coral cover and the lowest coverage of live coral (1.0% ). Lowest dead coral cover was found at Rl at the 10m depth (10.17% ).

Table 1. Distribution of biotic and abiotic components along transects at Pulau Satumu

---------------~-------------~----------~------------------~--~ Reef Site

Depth (m)

Live coral

Percentage cover

Dead coral

Algae Other .Pauna

Abiotic

-----------------------------------------------------------------------R1

R2

3m 10m

3m 10m

28.65 5.37

45.20 1.00

23.50 10.17

33.62 31 .15

o.oo o.oo 0.22 o.oo

4.20 32.03

3.78 13.15

43.65 52.43

17. 18 54.70

---------------------------------------------------------------------

,-.. N .._,

$-4 OJ > 0 C)

OJ >

"M .u C'O ~ OJ ~

100

90

70

60

50

40

30

20

10

0

Rl (3m) Rl ( 10m) R2(3m) R2 ( 10m)

Survey site (depth)

Fig. 2 Stacked bar chart showing relative proportion of various reef component s at Pulau Satumu.

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-

The proportion of non-coral benthic fauna was greater at the 1 Om depth than the 3m depth, with the 10m depth at Rl having the highest value (32.03%). These consisted mainly of soft corals and sponges, found in abundance here, together with sea urchins, sea anemones and gorgonians.

Abiotic components covered more than half the transects at the 10m depth with a large proportion of this consisting of rock. Along the transect carried out at the 1 Om depth at Rl, rocks covered 46.53% of the transect while at the same depth at R2, they covered

•

17 .87%. The data indicates the particularly rocky nature of the substratum. At the 3m depth, coral rubble accounted for most of the abiotic cover. No macroalgae was recorded along any of the transects.

The distribution of coral growth for1ns along the four transects is shown in Figs. 3 to 6. The transect at the 3m clepth at R 1 had a higher proportion off oliose and encrusting forms (16.25o/o & 5.7o/o respectively). These two growth for1ns were also prominent at the 3m depth of R2 (foliose, 21.59%; encrusting, 12.30% ), together with massive colonies

( 10.09o/o ).

At the 1 Om depth, mostly branching, encrusting and submassive corals were found at R 1, while at R2, mainly ,,encrusting forms were present. No dominance by any growth forrn was evident. Branching and tabulate forrns of Acropora were found only at the 3m depth, and in small quantities (0.3o/o at R2 and 1.15% at Rl).

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ACB a branchina Acropora ACT I tabulate Acropora AC! a encru1tin1 Acropora ACS• 1ub-u11ive Acropora am I au1hroo• coral

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CB a branchina coral 0( I aa11iva coral C! t encru1tin1 coral CS 1 1ub-ma111v• coral er I folio•• coral

ACB ACT ACE . ACS CB CM CE CS CF CMR

Coral growth. form

Fig. 3. Percentage distribution of various coral growth forms at 3m depth of transect R 1.

112

40

30

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M Q)

> 0 (J

20 Q) bO ro .u c:: Q) (J M Q)

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CB CM CE cs

Coral growth form

Cl I branchln1 coral QC I aa11iv• coral Cl a encruatina coral CS I 1ub•aa1alv• coral er I folio•• coral

CF CMR

Fig. 4 Percentage distribution of various coral growth forms at 1 Om depth of transect R 1.

M Q)

> 0 u Q)

bO ro .u c:: Q) (J M Q)

P--4

40

30

20

10

0

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Coral growth form

CB • branching coral • CM I ma111ve coral C! s encrusting coral CS I 1ub-maa1ive coral · CF I folio•• coral

l

)

cs CF CMR

Fig. 5. Percentage distribution of various coral growth forms at 3m depth of transect R2.

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...

~

~ ~

$-1 (l)

> 0 CJ

(l) bO co +J ~ (l) CJ $-1 CJ ~

40,------------------------

30

20

10

0 ACB ACT ACE ACS

ACB I branching Acropora ACT I tabulate Acropora ACE I encrusting Acropora ACS I sub-massive Acropora CMR I mushroom coral

CB I branching coral CM: massive coral CE: encrusting coral CS: sub-massive coral CF I foliose coral

CB CM CE CS CF CMR CME CHL

Fig. 6. Percentage distribution of various coral growth forms at 1 Om depth of transect R2.

Seventeen coral genera were recorded at R 1 and 21 genera at R2, with 11 genera common between the two sites. In all, a total of 26 genera was recorded from the reefs at Pulau Satumu (Table 2).

DISCUSSION

The coral cover of the two sites surveyed was not high compared to the upper reef slopes of four other reefs covered in an earlier study by Chou and Koh (1986), in which live coral cover ranged from 15.11 % to 62.00%.

Coral life was richer at site 2 than at site 1. Live coral cover decreased markedly with increasing depth at both sites surveyed. This attenuation of coral cover is also recorded at the fringing reef off Pulau Hantu (Chou, 1988), where the coral reef communities at three sites have been surveyed. Studies of the coral reef development in the turbid waters of Fanning Lagoon (Roy & Smith, 1971) showed that the coral cover in turbid water areas of the lagoon were lower than the clear water areas. Since light plays an important part in the formation of the calcareous skeletons of hermatypic corals (Gareau, 1963), the poor coral cover at l Om depth can be explained by the reduced growth rate due to the lowered penetration of light in the deeper sediment-filled waters.

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Table 2. Generic distribution of the hard coral community on the upper and lower reef slopes of Pulau Satumu. (+=present,-= absent)

---------------------------------------------------------------------------~--FAMILY & Genera

Site Depth

R1 3m

R2 10m 3m 10m

----------------------------------------------------------------------------------ACROPORIDAE Acropora Astreopora Montipora

AGARICIIDAE Leptoseris Pachyseris Pavona

FUNGIIDAE Fungia

PORITIDAE Goniopora Porites

FAVIIDAE Cyphastrea ·oiploastrea Echinopora Favia Favites Goniastrea Hydnophora Leptoria Montastrea Platygyra

MERULINIDAE Merulina

MUSSIDAE Lobophyllia Symphyllia

PECTINIIDAE Echinophyllia Mycedium Oxypora Pectinia

CARYOPHYLLIIDAE Euphyllia Physogyra Plerogyra

DENDROPHYLLIIDAE Tubastraea Turbinaria Dendrophyllia

HELIOPORIDAE Heliopora

SIDERASTREIDAE Psammocora

Total no. of genera

+ -. +

-+ +

-+ +

-----+ + ---+

---+ -+

+ -+

--+

+

+

16

-----------------------

l ------+ -+ I

-+

3

+ -+

-+ +

+ ·

-+

+ + + + -----+

+

+ -+ --+

+ -+

+ + --+

21

-----~----------------+

-------+ ----2

------------------------------------... -------------------------------------

115

With reference to the generic diversity, the total of 26 genera recorded at Pulau Satumu is lower than the total number of genera recorded at the patch reef west of Pulau Hantu, and reefs atP. Hantu, Cyrene and P. Semakau, with 28, 29, 31 and 32 genera respectively (Chou & Koh, 1986).

The dominance of foliose and encrust~ng growth forrns at both sites suggests that these morphological f or1ns are more efficient than the other f orrns for growth and the deposition of skeletal material in low light conditions (Davies, 1980). Branching corals, apart from Acropora, were scarce at site 2 perhaps due to the exposed nature of the site, causing breakage of the more delicatr branching for1ns. This site is also exposed to the strong wash of tankers that sail by just off the southern shore of the island.

REFERENCES

Chou, L.M., 1988. The impact of human influence on the fringing reef of Pulau Hantu, Singapore. Proceedings of the Sixth International Coral Reef Symposium, Australia, 1988. 2:201-205.

Chou, L.M. and G. E. L. Koh, 1986. Initial characterisation of upper reef slope communities in Singapore waters. Journal of the Singapore National Academy of Science" 15 :5-8.

Dartnall, A.J. and M. Jones (eds.), 1986. A Manual of Survey Methods for Living Resources in Coastal Areas. Australian Institute of Marine Science, Townsville.

Davies, P.S., 1980. Respir~tion in some Atlantic reef corals in relation to vertical distribution and growth form. Biological Bulletin 158: 187-194.

Goreau, T.F., 1963. Calcium carbonate deposition by coralline algae and corals in relation to their roles as reef-builders. •Annals of the New York Academy of Science 109:127-167. 1 •

Roy K.J. and S.V. Smith, 1971. Sedimentation and coral reef development in turbid water: Fanning Lagoon. Pacific Science 25:234-248.

Veron, J.E.N., 1986. Corals of Australia and the Indo-Pacific. Angus & Robertson Publishers. 644pp.

Wood, E., 1983. Corals of the World, Biology and Field Guide. T.F.H. Publications, Hong Kong. 256pp.

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