Goh Ah Hong and A. Sasekumar

ATOLL RESEARCH BULLETIN NO.

244

THE COMMUNITY STRUCTURE OF THE FRINGING CORAL REEF, CAPE RACHADO, MALAYA

by

Goh Ah Hong and A. Sasekumar

Issued

by

THE SMITHSONIAN INSTITUTION Washington, D. C., U.S.A.

July

1981

THE COMMUNITY STRUCTURE OF THE FRINGING CORAL REEF, CAPE RACHADO, MALAYA

by

Goh Ah Hong and A. Sasekumarl

ABSTRACT

L i v e c o r a l c o v e r w a s l o w ( 3 2 . 9 % ) on a b e l t t r a n s e c t 87 meters long and one metre wide, on t h e c o r a l r e e f a t Cape Rachado, P o r t Dickson.

Considered s e p a r a t e l y t h e reef edge had a l i v e c o r a l cover of 59.6% and t h e reef f l a t 26.5%. The abundance of s o f t c o r a l s (alcyonaceans) on t h e r e e f f l a t a s compared t o o t h e r r e e f s i s probably due t o t h e i r a b i l i t y t o t o l e r a t e t u r b i d i t y and extreme low t i d e s . High s p e c i e s r i c h n e s s , d i v e r s i t y , abundance and l a r g e s i z e index a t t h e r e e f edge i n d i c a t e t h a t t h e environment t h e r e i s more favourable t o t h e hard c o r a l s ( s c l e r a c t i n i a n s ) than t h e r e e f f l a t . Macroalgae a r e abundant.

INTRODUCTION

S t u d i e s on c o r a l r e e f s i n Malaysian waters have been mainly d e s c r i p t i v e . These include t h e study of Purchon (1956) which was

l i m i t e d t o a r e f e r e n c e c o l l e c t i o n of c o r a l s occurring around Singapore.

Chuang (1961) a l s o made a c o l l e c t i o n around Singapore and extended it with somecollections i n Malaysian s e a s (Chuang, 1973). Work by Scheer

(1970) on t h e second Xarifa Expedition i n 1958 b r i e f l y surveyed t h e a r e a from Penang t o t h e Sembilan I s l a n d s , approximately 80 n a u t i c a l miles t o t h e south i n t h e S t r a i t s of Malacca. A d e s c r i p t i o n of t h e s p e c i e s found, t o g e t h e r with e c o l o g i c a l n o t e s of t h e c o l l e c t i o n s i t e s , i s given by P i l l a i and Scheer (1974). This paper p r e s e n t s a d e s c r i p t i o n of t h e community s t r u c t u r e i n terms of s p e c i e s composition, zonation and

d i v e r s i t y p a t t e r n s of t h e f r i n g i n g reef community a t Cape Rachado.

l ~ e ~ a r t m e n t of Zoology, University of Malaya, Kuala Lumpur 22-11, Malaysia. Manuscript received August 1979 --Eds.

METHODS

A t Cape Rachado (Fig. 1 ) t h e f r i ~ g i n g r e e f extends a s a r e e f f l a t almost a l l t h e way round t h e cape. The r e e f f l a t where t h i s study was c a r r i e d o u t extends from t h e rocky shore i n a westerly d i r e c t i o n f o r a d i s t a n c e of over 85 metres t o t h e r e e f edge (Fig. 1 ) .

The r e e f was f i r s t surveyed f o r a r e f e r e n c e c o l l e c t i o n of c o r a l s . Hard c o r a l s were i d e n t i f i e d following S e a r l e (19561, while s o f t c o r a l s were i d e n t i f i e d by D r . J. Verseveldt (The Netherlands). The method employed f o r q u a n t i t a t i v e sampling of t h e c o r a l d i s t r i b u t i o n i s t h e contiguous t r a n s e c t technique (Maragos 1974). A t r a n s e c t was marked by l a r g e n a i l s hammered i n t o c o r a l heads a t v a r i o u s i n t e r v a l s . A one metre q u a d r a t , subdivided i n t o a g r i d of 100 squares of equal s i z e was used i n sampling a l l along one s i d e of a t r a n s e c t l i n e (beginning with quadrat 1 l o c a t e d near t h e rocks and ending w i t h q u a d r a t 87 a t t h e r e e f edge). A sketch of t h e c o r a l c o l o n i e s i n each q u a d r a t was drawn t o s c a l e on a d a t a s h e e t . Any colony growing independently of i t s neighbour was considered an i n d i v i d u a l colony, i . e . whenever an empty space was recorded between two a d j a c e n t c o l o n i e s (Loya 1972). Growth forms were noted. For growth forms more i n c l i n e d t o f l a t h o r i z o n t a l growth such a s t h e laminated Astraeopora myriophthalma, t h e percentage cover was d e r i v e d d i r e c t l y from t h e number of squares occupied w i t h i n t h e quadrat. For growth forms such a s those of t h e massive Goniastrea retifonnis where e n c r u s t i n g c o r a l l i t e s a r e found on t h e v e r t i c a l f a c e of t h e boulders, t h e depth was measured and recorded on t h e s k e t c h and used t o c a l c u l a t e t h e s u r f a c e a r e a . This i s a b e t t e r assessment of c o r a l cover than a two dimensional accounting t h a t was a p p l i e d t o t h e f l a t form. The cover of v a r i o u s s p e c i e s of macroalgae w i t h i n t h e q u a d r a t was a l s o recorded. The study was c a r r i e d o u t from A p r i l t o September 1976.

RESULTS Environmental parameters

T i d a l exposure of t h e r e e f f l a t ( c a l c u l a t e d f o r August and

September 1976 based on t i d a l d a t a obtained from t h e Tide Tables) show t h a t t h e r e e f f l a t was exposed 6% of t h e time f o r t h e above p e r i o d . A t extreme low s p r i n g t i d e s t h e r e e f f l a t may be exposed t o t h e a i r f o r more than 3 hours. The r e e f f l a t extends from t h e rocky shore f o r about 50 metres where it s l o p e s g e n t l y again f o r a d i s t a n c e of 10 metres before reaching t h e r e e f edge where numerous surge channels a r e p r e s e n t

(Fig. 2 ) . These channels a r e t r e n c h e s which a r e i n c o n t i n u i t y with t h e open s e a . The r e e f edge extends f o r about 17 metres and then f a l l s

o f f g e n t l y t o a f l a t muddy bottom. Corals grow on t h e r e e f s l o p e up t o a depth of 8 metres.

T u r b i d i t y readings determined a t t h e r e e f edge were v a r i a b l e ranging from Secchi d i s c readings of 2 m on an o v e r c a s t day with rough s e a when water had a high sediment load t o readings of 7 m on a c l e a r day with calm s e a and a lower sediment load.

Coral fauna

The l i s t of t h e c o r a l s found i n Cape Rachado with t h e i r r e l a t i v e abundance and morphological forms a r e presented i n Table 1. A t l e a s t 41 s p e c i e s were p r e s e n t which includes 35 s c l e r a c t i n i a n hermatypes, one m i l l i p o r i n i d and 5 alcyonaceans. Only one genus of s o l i t a r y c o r a l , Fungia

,

was found.

The abundance, frequency and s i z e index of c o r a l s p e c i e s found on t h e t r a n s e c t a r e included i n Table 1. Abundance r e f e r s t o t h e

percentage cover of t h e s p e c i e s with r e s p e c t t o t h e t o t a l a r e a of t h e t r a n s e c t . The frequency of a s p e c i e s i s t h e number of q u a d r a t s i n which t h e s p e c i e s i s p r e s e n t . Of t h e 87 quadrats i n t h e t r a n s e c t , only t h r e e d i d not contain any c o r a l . These q u a d r a t s had sandy s u b s t r a t e s . Size index was c a l c u l a t e d f o r i n d i v i d u a l s p e c i e s and quadrats. The d a t a from t h e former allows comparison of colony s i z e between s p e c i e s , while t h e l a t t e r , between quadrats. S i z e index f o r s p e c i e s i s derived from t h e d i v i s i o n of t o t a l cover of t h e s p e c i e s ( f o r t h e whole t r a n s e c t ) by t h e number of i t s c o l o n i e s . This i s a measure of t h e average s i z e of t h e c o r a l s p e c i e s (Table 1 ) . S i z e index f o r q u a d r a t s i s derived from t h e d i v i s i o n of percentage cover i n one quadrat by t h e number of c o l o n i e s found i n it (Fig. 3 ) .

Species r i c h n e s s i . e . t h e number of s p e c i e s p e r u n i t a r e a was a l s o c a l c u l a t e d . This was computed f o r quadrat s i z e s of 1 m Z , 2 m Z , 5 mZ and 10 mZ (Fig. 4 ) . Species r i c h n e s s i s a measure of d i v e r s i t y which t a k e s i n t o account t h e number of s p e c i e s without considering t h e

r e l a t i v e proportion of each s p e c i e s . To i n c l u d e t h e l a t t e r parameter i n t h e c a l c u l a t i o n , t h e Shannon-Weaver (1949) index was computed using

where Pi i s t h e proportion (percent cover) of t h e ' i t h ' s p e c i e s i n a sample and In r e f e r s t o t h e n a t u r a l logarithm. This index was computed f o r contiguous quadrats of f i v e and i s presented t o g e t h e r with c o r a l abundance i n Fig. 5. Abundance here r e f e r s t o t h e percentage cover of c o r a l s i n t h e quadrats i r r e s p e c t i v e of t h e s p e c i e s composition i n t h e quadrats.

To measure dominance of one o r few s p e c i e s i n a q u a d r a t , t h e Evenness Index (Pielou, 1966) was used. This i s t h e r a t i o of t h e observed Shannon-Weaver d i v e r s i t y index, H c ' , t o t h e maximum d i v e r s i t y index H I m a x . The d i v e r s i t y index i s maximal when t h e proportion of a l l s p e c i e s i n a sample i s equal. When one o r few s p e c i e s i s much more abundant than t h e r e s t , t h e Evenness index i s low (Fig. 6 ) . Numerical abundance of c o r a l s measures d i s t r i b u t i o n of c o r a l c o l o n i e s without regard t o number of s p e c i e s and proportion of each s p e c i e s (Fig. 7 ) . For a zonation model of t h e r e e f , t h e c o r a l cover of 15 contiguous quadrats a r e pooled t o g e t h e r (Fig. 8 ) . The zones a r e named a f t e r t h e dominant s p e c i e s .

T a b l e 1. Abundance i n t e r m s o f % c o v e r , r e l a t i v e abundance, f r e q u e n c y and s i z e i n d e x of c o r a l s found i n Cape Rachado.

R e l a t i v e abundance ( p e r c e n t a g e c o v e r ) o f s p e c i e s on t h e t r a n s e c t a r e b a s e d on t h e f o l l o w i n g s c a l e o f q u a n t i f i c a t i o n : Abundant (A) = 2 % , Common ( C ) = 1 - 2 % , O c c a s i o n a l ( 0 ) = 0 . 3

-

1 % and Rare ( R ) = 0.3%.

C o r a l s n o t found on t h e t r a n s e c t a r e l i s t e d l a s t ( a s t e r i s k s ) . Key f o r growth forms: B = b r a n c h i n g ; F ⁼ f o l i a c e o u s ; G = g l o b u l a r ; L = l a m i n a t e ; M= massive.

S p e c i e s Growth forms

A l l c o r a l s

Lobophyt um c r a s s u m Von M a r e n z e l l e r Loboph y t um

c r a s s o s p i c u l a t um Moser

Lobophytum p a u c i f l o r u m (Ehrenberg)

S a r c o p h y t o n e h r e n b e r g i Von M a r e n z e l l e r A s t r a e o p o r a

m y r i o p h t h a l m a (Lamarck)

Montipora i n f o r m i s Bernard

Pavona f r o n d i f e r a Lamarck

Pavona c r a s s a (Dana) P a c h y s e r i s s p e c i o s a

(Dana)

Fungia f u n g i t e s (Linnaeus ) Gonipora l o b a t a

Milne-Edwards Haime

P o r i tes c o n v e x a V e r r i l l

P o r i t e s n i g r e s c e n s Dana

Porites l u t e d Milne- Edwards & Haime

Abundance

(% c o v e r ) 3 2 - 9 4

0.83 1.49

1 - 0 6 2.28 2.00

0.87 1.33 0.14 0 . 1 1 0.02 0.03

2.15 0.17 7.39

R e l a t i v e Frequency abundance (No. o f

q u a d r a t s )

S i z e I n d e x

-

1.95 1 . 7 1

3.85 9.45 5.24

5.03 2.89 12.00 10.00 2.00 0.75

6.68 14.50 13.40

Species Growth Abundance R e l a t i v e Frequency S i z e

forms ( % cover) abundance (No. of Index

q u a d r a t s )

Porites e r i d a n a B

Umbgrove

F a v i a s p e c i o s a (Dana) G

F a v i t e s a b d i t a M ( E l l i s & S o l a n d e r ) G o n i a s t r e a p e c t i n a t a ^M

(Ehrenberg)

G o n i a s t r e a retiformis M (Lamarck)

G o n i a s t r e a benhami M Vaughan

P l a t y g y r a l a m e l l i n a ^M (Ehrenberg)

M e r u l i n a a m p l i a t a L ( E l l i s & Solander)

Gal axed f a s c i c u l a t i s G (Linnaeus 1

L o b o p h y l l i a h e m p r i chii M (Ehrenberg)

* M i l l e p o r a p l a t y p h y l l a Hemprich & Ehrenberg

* S i n u l a r i a 1 e p t o c l a d o s (Ehrenberg)

*

P s m o c o r a t o g i a n e n s i s Umbgrove

*

P o c i l 1 o p o r a v e r r u c o s a ( E l l i s & Solander)

*Monti Dora sol a n d e r i Bernard

* M o n t i p r a l a e v i s Quelch

* A c r o p r a conci nna (Brook)

6

Species

*Acropora t u b i c i n a r i a (Dana)

"Podabacia c r u s t a c e a (Pallas)

*Goniopora m a l a c c e n s i s Brueggemann

* A l v e o p o r a e x c e l s a Verill

*

Hydnophora r i g i d a (Dana)

* C y p h a s t r e a c h a l ci d i cum

(Forskaal)

*Mycedium t u b i f e x (Dana)

" P e c t i n i a l a c t u c a (Pallas)

* ~ u r b i n a r i a p e l t a t a (Esper)

Growth Abundance Relative Frequency Size forms ( % cover) abundance (No. of Index

quadrats )

Macroalgae associated with corals

Both living and dead coral skeleton provide a habitat and

substrate for algae and a variety of sessile and burrowing organisms.

A conspicuous feature of the Cape Rachado coral reef is the abundance of macroalgae. The brown algae predominate represented by Sargassum sp., P a d i n a commersonij. and T u r b i n a r i a sp. Another abundant species is the red coralline algae, C o r a l l i n a sp. The above four species were quantitatively surveyed along 70 metres of the transect (Table 2).

Padina forms small individual bunches of pale brown, fan shape fronds

with concentric rings, but cover only little space. T u r b i n a r i a occurs in clumps near the reef edge. C o r a l l i n a , with biramous branching resulting in thick bushy growth occupies little space, thus its distribution, is patchy and occupied only a few squares (Table 2).

Table 2: D i s t r i b u t i o n and abundance of macroalgae on t h e t r a n s e c t . Numbers r e p r e s e n t t h e number o f 10 cm s q u a r e s occupied by t h e a l g a e i n each one metre q u a d r a t .

SPECIES SPECIES SPECIES

' rl ' rl 0 r:

:: I

8

([I r:

-

^rl

'tl

2

2

([I r:

'1 '-i '-i

8 2

2

([I r:

'1 '-i '-i

8 2f

DISCUSSION AND CONCLUSIONS

F i f t y s i x p e r c e n t of c o r a l s p e c i e s found i n Cape Rachado were

p r e s e n t on t h e 1 x 87 metre b e l t t r a n s e c t s t u d i e d . Live c o r a l cover on t h e r e e f was low ( 3 2 . 9 % ) . However, i f c o n s i d e r e d s e p a r a t e l y t h e r e e f edge comprising 17 metres of t h e t r a n s e c t h a s a c o r a l cover of 59.6%

and t h e r e e f f l a t of 70 metres o n l y 26.5%. The high c o r a l cover a t t h e r e e f edge compares f a v o u r a b l y w i t h t h e r e e f s l o p e a t Fanning I s l a n d , Line I s l a n d s , where Maragos (1974) o b t a i n e d a v a l u e of 60%.

S i z e i n d i c e s along t h e t r a n s e c t (beginning from q u a d r a t 1 a t rocky s h o r e t o q u a d r a t 87 a t r e e f edge) show extreme v a r i a b i l i t y ( F i g . 3 ) , ranging from 1% t o 95%. However, t h e two r e g i o n s from q u a d r a t 25 t o 35 and 46 t o 64, show s i g n i f i c a n t l y lower s i z e index t h a n t h e a d j a c e n t r e g i o n s . The former corresponds t o a r e a s dominated by G o n i a s t r e a r e t i f o r m i s and Lobophytum spp. The l a t t e r an a r e a dominated by A s t r a e o p o r a m y r i o p h t h a l m a , Pavona f r o n d i f e r a and Porites e r i d a n i . These two r e g i o n s a l s o show low abundance ( F i g . 5 ) b u t t h e number of c o l o n i e s between them d i f f e r g r e a t l y ( F i g . 7 ) .

The o p p o s i t e ends o f t h e t r a n s e c t between q u a d r a t s 5-15 ( P . l u t e a zone) and q u a d r a t s 70-87 (mixed zone) show s i g n i f i c a n t l y h i g h e r abundance

( F i g . 5 ) . The f i r s t a r e a (on t h e r e e f f l a t ) , e x c l u s i v e l y c o l o n i z e d by P . l u t e a a l s o showed low d i v e r s i t y , s p e c i e s r i c h n e s s , evenness index and

frequency b u t l a r g e s i z e index. I n d i v i d u a l c o l o n i e s of t h e s p e c i e s a r e s p r e a d over l a r g e a r e a s , t h e r e b y e x c l u d i n g o t h e r s p e c i e s . T h i s reduces t h e d i v e r s i t y , speci-es r i c h n e s s and frequency. On t h e o t h e r hand, t h e second a r e a i s a zone e q u a l l y dominated by a number of s p e c i e s such a s S a r c o p h y t o n e h r e n b e r g i , P o r i t e s c o n v e x a , M e r u l i n a a m p l i a t a and G o n i a s t r e a spp. ( F i g . 8 ) . Here t h e zone i s c h a r a c t e r i s e d by high d i v e r s i t y ,

s p e c i e s r i c h n e s s , evenness index and frequency and a l s o a l a r g e s i z e index.

G e n e r a l l y t h e f i r s t and second a r e a s r e f l e c t t h e c h a r a c t e r i s t i c c o r a l s p e c i e s of t h e r e e f f l a t and r e e f edge r e s p e c t i v e l y . T h i s d i f f e r e n c e i n c o r a l s p e c i e s c h a r a c t e r s i s a r e s u l t of c o n t r a s t i n g environmental c o n d i t i o n s . The r e e f f l a t i s s u b j e c t t o s t r e s s of high temperature and v a r i a b l e s a l i n i t y . Exposure t o t h e sun d u r i n g p e r i o d s o f low s p r i n g t i d e s i n c r e a s e s t h e temperature c o n s i d e r a b l y and s u b j e c t t h e c o r a l s t o s e v e r e d e s i c c a t i o n . Loya (1976) r e p o r t e d mass m o r t a l i t y of c o r a l s i n t h e Gulf of E i l a t d u r i n g a p e r i o d of extreme low t i d e s i n 1970. I n t h e e v e n t of r a i n d u r i n g p e r i o d s of t i d a l exposure, t h e s a l i n i t y may be reduced. Regular o c c u r r e n c e of such f l u c t u a t i o n s c a u s e s m o r t a l i t y of l e s s hardy and c o m p e t i t i v e s p e c i e s ; t h e r e b y

reducing t h e d i v e r s i t y . S p e c i e s which can t o l e r a t e such environmental c o n d i t i o n s dominate t h e s u b s t r a t e .

Another p o s s i b l e f a c t o r f o r t h e d i f f e r e n c e between t h e r e e f f l a t and r e e f edge i s t h e p r e s e n c e of s u r g e channels i n t h e l a t t e r . These s u r g e channels probably b r i n g i n a good supply o f oxygen and food.

F u r t h e r , t h e e x t r a v e r t i c a l dimension of t h e r e e f edge i n c r e a s e s t h e a r e a of s u b s t r a t e f o r t h e s e t t l i n g of p l a n u l a e .

- ~ E i s

phenomenon

of h i g h abundance and d i v e r s i t y on t h e r e e f edge i s e q u i v a l e n t t o t h e 'edge e f f e c t ' r e p o r t e d by P o r t e r ( 1 9 7 2 ) .

A s t r a e o p o r a m y r i o p h t h a l m a and P o r i t e s e r i d a n i a r e t h e dominant c o r a l s of t h e r e g i o n between q u a d r a t s 50 t o 60, a zone t h a t i s i n t h e t r o u g h of t h e r e e f f l a t . I t i s a l s o a zone t h a t shows low s p e c i e s r i c h n e s s , abundance, frequency and d i v e r s i t y i n d i c e s . I n d i v i d u a l c o l o n i e s of A s t r a e o p o r a m y r i o p h t h a l m a a r e spread over l a r g e a r e a s i n t h i s zone a s shown by i t s r e l a t i v e l y h i g h s i z e index and hence it has reduced t h e d i v e r s i t y by p h y s i c a l e x c l u s i o n of o t h e r c o r a l s . The environment h e r e i s l e s s s e v e r e a s it i s n o t s u b j e c t t o t i d a l exposure.

The seaward end of t h e r e e f f l a t (between q u a d r a t s 60 and 70) i s covered mostly by Porites c o n v e x a and S a r c o p h y t o n e h r e n b e r g i . Porites c o n v e x a i s only found seaward from t h i s r e g i o n onwards which i n view of i t s p r o x i m i t y w i t h t h e r e e f edge, b e n e f i t from t h e food and oxygen brought i n by t h e surge channels. Maragos (1974) d e s c r i b e d t h e S a r c o p h y t o n sp. a s a s o f t c o r a l c h a r a c t e r i s e d by a continuous spongy

"corallum" t h a t seemingly smothers o t h e r c o r a l s by growing over them.

T h i s alcyonacean may be capable of r a p i d growth and t h i s may h e l p i n a c h i e v i n g l o c a l dominance.

A n a l y s i s of t h e s i z e index of q u a d r a t s ( F i g . 3 ) i n d i c a t e s t h a t t h e s m a l l e s t c o l o n i e s e x i s t e d i n t h e middle r e g i o n of t h e r e e f f l a t

( q u a d r a t s 15 t o 65) and t h e l a r g e s t c o l o n i e s o c c u r r e d a t b o t h t h e seaward and landward ends of t h e r e e f f l a t . These d a t a s u p p o r t t h e h y p o t h e s i s t h a t l a r g e c o l o n i e s of Porites l u t e a and S a r c o p h y t o n e h r e n b e r g i may p h y s i c a l l y exclude o t h e r c o r a l s .

T u r b i d i t y which i s c o r r e l a t e d t o sediment l o a d i s very h i g h i n Cape Rachado. V i s i b i l i t y was l i m i t e d . Compared t o v i s i b i l i t y of Fanning I s l a n d which i s 50 m i n terms of S e c c h i d i s c r e a d i n g s (Maragos

1 9 7 4 ) , t h e water h e r e i s indeed v e r y t u r b i d . Sediments which s e t t l e on t h e r e e f f l a t smother t h e c o r a l s . T h i s l e a d s t o a s i g n i f i c a n t l y lower l i v i n g coverage and d i v e r s i t y , a c o n c l u s i o n t h a t i s a l s o s h a r e d by Loya (1972) concerning t h e E i l a t c o r a l r e e f f l a t .

S o f t c o r a l s (alcyonaceans) which do n o t c o n t r i b u t e t o t h e r e e f s k e l e t a l framework a r e abundant i n Cape Rachado c o n t r i b u t i n g 17% of t o t a l c o r a l cover on t h e t r a n s e c t . T h i s i s i n c o n t r a s t t o t h e s i t u a t i o n i n most r e e f s , e.g. t h e Great B a r r i e r Reef where t h e s o f t c o r a l s a r e n e g l i g i b l e . S o f t c o r a l abundance i n t h e Red Sea i s due t o t h e i r a b i l i t y t o t o l e r a t e t u r b i d i t y and o c c a s i o n a l extreme low t i d e s b e t t e r t h a n s t o n y c o r a l s which a r e more adapted t o s t r o n g c u r r e n t s and

s w e l l s (Schuhmacher 1975)

.

I t i s a p p a r e n t t h a t t h e abundance of s o f t c o r a l s i n Cape Rachado i s a l s o a consequence of t h e same a b i o t i c f a c t o r s . The a b i l i t y of s o f t c o r a l s t o s u r v i v e i n t u r b i d c o n d i t i o n s may be due t o t h e i r s t r u c t u r a l f l e x i b i l i t y which a l l o w s them t o d i s l o d g e any sediments s e t t l i n g on them. During extreme low t i d e s , t h e s o f t c o r a l s droop over t h e s u b s t r a t e , r e d u c i n g t h e exposure of p o l y p s t o d i r e c t s u n l i g h t .

They are also able to retain water in their structures which acts as a coolant to the heat from solar radiation. All these coupled with mucus secretions enable the soft corals to overcome desiccation.

Loya (1972) suggested that the best strategy for scleractinian corals trying to grow in areasof high sedimentation is to develop some kind of cleaning mechanism or evolve a special growth form which avoids sediment accumulation. Three out of the four most abundant species in the high sedimentation rate areas, on the coral reef in Eilat were branching corals. Roy and Smith (1971) working on Fanning Lagoon, Line Islands, also showed that ramose (branching) forms dominate the turbid water rather than the massive forms. In contrast, the most abundant species in Cape Rachado are corals with massive forms such as Porites l u t e a and the faviid species such as F a v i a s p e c i o s a , F a v i t e s a b d i t a , G o n i a s t r e a r e t i f o r m i s , G . p e c t i n a t a , G . benhami and P l a t y g y r a

l a m e l l i n a . These corals probably have a cleaning mechanism to remove

sediments through mucus secretions or ciliary action. Large specimens of the massive faviid corals often have a dead top indicating that polyps exposed directly to sedimentation are unable to cope with the problem. It is the polyps encrusted on the vertical plane of the boulders which are able to survive as sediments do not settle there.

Porites l u t e a shows essentially the same trend but large specimens have

been found with short stunted projections which have less horizontal surfaces where sediments can settle. This development by Porites l u t e a towards branching or ramose forms is an adaptation to the stress of high sedimentation.

ACKNOWLEDGEMENTS

The critical reading of the manuscript by Professor Nelson Marshall (University of Rhode Island) is much appreciated. The Department of Zoology, University of Malaya, provided the facilities for the study. Thanks are due to Mr. Kuldip Singh for field assistance, Mr. Amir Salleh for drawing the figures and Ms. S. Dawood for typing the manuscript.

The first author Goh Ah Hong died in a road accident on 21 May 1978 while this manuscript was in preparation.

REFERENCES

Chuang, S.H. 1961. O n Malayan S h o r e s . Muwu Shosa, Singapore.

255 pp.

Chuang, S.H. 1973. Life of the Seashore, In: T h e l a n d o f S i n g a p o r e and i t s L i f e (Ed. by S.H. Chuang), pp. 150-174. Singapore University Press, Singapore.

Loya, Y. 1972. Community structure and species diversity of hermatypic corals at Eilat, Red Sea. Mar. B i o l . 13: 100-123.

Loya, Y. 1976. R e c o l o n i z a t i o n of Red Sea c o r a l s a f f e c t e d by n a t u r a l c a t a s t r o p h e s and man-made p e r t u r b a t i o n s . Ecology, 57: 278-289.

Maragos, J . E . 1974. C o r a l Communities on a seaward Reef Slope, Fanning I s l a n d . Pac. Sci. 28: 257-273.

p i e l o u , E . C . 1966. S p e c i e s d i v e r s i t y and p a t t e r n d i v e r s i t y i n t h e s t u d y of e c o l o g i c a l s u c c e s s i o n . J. theoret. Biol. 19: 37-383.

P i l l a i , C.S.G., and S c h e e r , G. 1974. On a C o l l e c t i o n o f S c l e r a c t i n i a from t h e S t r a i t of Malacca. Proc. Second International Coral Reef Symposium, Brisbane, 1: 445-464.

P o r t e r , J . W . 1972. Ecology and S p e c i e s d i v e r s i t y o f c o r a l r e e f s on o p p o s i t e s i d e s of t h e Isthmus o f Panama. Bull. Biol. Soc.

Wash. 2: 89-115.

Purchon, R.D. 1956. A l i s t o f c o r a l s c o l l e c t e d i n t h e v i c i n i t y of Singapore. Proc. Linn. Soc. N.S.W., 81: 157-158.

Roy, K.S., and Smith, S . V . 1971. Sedimentation and c o r a l r e e f development i n t u r b i d w a t e r , Fanning Lagoon. Pac. Sci. 25:

234-248.

S c h e e r , G. 1970. Coral Reefs and Coral Genera i n t h e Red Sea and I n d i a n Ocean. Symp. Zool. Soc. Lond. 28: 329-367.

Schuhmacher, H . 1975. The r o l e o f s o f t c o r a l s (Alcyonacea, O c t o c o r a l l i a ) i n t h e r e e f biocoenoses o f t h e Red Sea and t h e A u s t r a l i a n G r e a t B a r r i e r Reef. Verh. Dtsch. Zool. Ges. 1974, 380-384.

S e a r l e , A.G. 1956. An i l l u s t r a t e d key t o Malayan hard c o r a l s . Malay. Nat. J. 7: 1-26.

Shannon, C . , and Weaver, W. 1949. The mathematical theory of communication. U n i v e r s i t y o f I l l i n o i s P r e s s , Urbana. 117 pp.

P:O -

CORAL REEF

...

s::;

...

SANDY BEACH

MANGROVE SWAMP

E

Fig. 1 Cape Rachado and surrounding c o r a l r e e f s . Study t r a n s e c t i n d i c a t e d by arrow

Reef - ^Flat _Edge

>

CHART DATUM

u,

3.0-

b)

2-5

9 ^2.0-

-S 1.5

Distance in Metres

--- MHWS

-

---I

MHWN

-

Fig. 2 Bathymetry of r e e f t r a n s e c t i n r e l a t i o n t o t h e v a r i o u s t i d a l l e v e l s

QUADRAT NUMBER

F i g . 3 S i z e i n d e x f o r q u a d r a t s ( a n e s t i m a t e o f a v e r a g e c o l o n y a r e a ) p l o t t e d a s a f u n c t i o n o f t r a n s e c t l o c a t i o n

SINGLE QUADRAT

--a

-

GROUPS OF 5 QUADRATS GROUPS OF 10 OUADRATS

I

10 20 30 40 50 60 70 80

I I I I I I I

QUADRAT NUMBER

F i g . 4 S p e c i e s r i c h n e s s p l o t t e d a s f u n c t i o n o f t r a n s e c t l o c a t i o n f o r s i n g l e q u a d r a t s , f o r g r o u p s o f 2 , 5 and 10 q u a d r a t s

QUADRAT NUMBER

F i g . 5 C o r a l abundance and t h e Shannon-Weaver d i v e r s i t y index p l o t t e d a s a f u n c t i o n of t r a n s e c t l o c a t i o n w i t h v a l u e s based on p o o l i n g of

contiguous groups of f i v e q u a d r a t s

Fig. 6 Evenness Index ( H C ' / H max) p l o t t e d a s a f u n c t i o n of t r a n s e c t l o c a t i o n f o r groups of f i v e q u a d r a t s

0 10 20 30 40 50 60 70 80 90 QUADRAT NUMBER

Fig. 7 Number of q u a d r a t s a t 5 meter i n t e r v a l s a l o n g t r a n s e c t

Distance in Meters

-

a

Paites ~ u t e a

@

Lobophyturn crassospiculaturn

@

Merulina ampliota Goniastma sp. @ Pavona frondifera

0

Sarcophy ton ehrenbergi Favia speciosa

0

Astmeopaa m y r i o p h t h ~ l r n ~

v

Pwites eridani Favites abdita Porites convexa

Fig. 8 Zonation model o f c o r a l r e e f t r a n s e c t a t Cape Rachado