by D. R. Stoddart and T. P. Scoffin

ATOLL RESEARCH BULLETIN NO. 224

MICROATOLLS: REVIEW OF FORM, ORIGIN AND TERMINOLOGY

by D. R. Stoddart and T. P. Scoffin

Issued by

THE SMITHSONIAN INSTITUTION

Washington, D.

C., U.S.A.

September

1979

Not t o scale

Figure 1. Dimensions of i n c l i n e d m i c r o a t o l l s of

Goniastrea aspera

(cm)

,

a f t e r Abe

(1937).

MICROATOLl.3: REVIEW OF F O M , ORIGIN AND TEMINOLOGY

by D. R. s t o d d a r t ' and T. P. s c o f f i n 2

P e r u s a l of much r e c e n t l i t e r a t u r e r e v e a l s wide d i f f e r e n c e s i n usage o f terms r e f e r r i n g t o m i c r o a t o l l s ( i n t h e s e n s e o f i n d i v i d u a l c o r a l c o l o n i e s ) and s m a l l a t o l l - s h a p e d r e e f s . Though many w r i t e r s mention d i f f e r e n c e s i n i n t e r p r e t a t i o n of such f e a t u r e s , t h e r e i s no comprehensive r e c e n t summary o f work on t h e s u b j e c t , o t h e r than R. W. F a i r b r i d g e ' s a r , t i c l e on m i c r o a t o l l s i n h i s E n c y c l o p a e d i a o f G e o m r p h o l o g y ( 1 9 6 8 ) . Work by t h e a u t h o r s on m i c r o a t o l l s d u r i n g t h e Royal S o c i e t y and U n i v e r s i t i e s of Queensland Expedition t o t h e n o r t h e r n G r e a t B a r r i e r Reef i n 1973 ( S c o f f i n and S t o d d a r t , i n l i t t 3 emphasised t n e need f o r such a summary, which i s provided i n t h e p r e s e n t p a p e r .

GENERAL DEFINITION

E a r l y d e s c r i p t i o n s o f m i c r o a t o l l s were given by Darwin(1842, 6 ) , Dana (1872; 1875, 72, 9 4 ) , Semper (1880; 1889, 224-226)

,

and Guppy

( 1 8 8 6 ) , u s i n g g e n e r a l names such a s c o r a l head o r c o r a l block. Thus Dana (1849, 39) d e s c r i b e d s i t u a t i o n s where " c o r a l s , when growing beneath t h e w a t e r , form s o l i d hemispheres, o r rounded h i l l o c k s ; b u t on r e a c h i n g t h e s u r f a c e , t h e t o p d i e s , and enlargement t a k e s p l a c e o n l y on t h e s i d e s . I n t h i s manner t h e hemisphere i s f i n a l l y changed t o a broad c y l i n d e r w i t h a f l a t top". P o s s i b l y t h e e a r l i e s t d e s c r i p t i o n o f t h i s phenomenon was t h a t o f Chamisso (1821, 1 4 3 ) , who n o t e d t h a t " s p e c i e s , which

o t h e r w i s e assume a s p h e r i c a l form, s p r e a d o u t i n p l a c e s where sand i s c a r r i e d , i n t o f l a t s u r f a c e s , with a r a i s e d edge, because t h e sand k i l l s t h e upper p a r t , and t h e y can o n l y l i v e and grow on t h e circumference".

'

Department o f Geography, Cambridge U n i v e r s i t y , Cambridge, England.

G r a n t I n s t i t u t e of Geology, U n i v e r s i t y of Edinburgh, din burgh, S c o t l a n d .

(Manuscript r e c e i v e d January 1974

--

^Eds.)

Guppy (1886) spoke of " m i n i a t u r e a t o l l s " , A g a s s i z (1895) o f " d i m i n u t i v e a t o l l s " , and Krempf (1927) of "dwarf a t o l l s " ( " a t o l l s n a i n s " )

.

^The

t e r m micro-atoll was f i r s t u s e d by Krempf (1927, 1 3 )

,

b u t w i t h o u t c o n c i s e d e f i n i t i o n . I t w a s widely adopted and v a r i o u s l y d e f i n e d . Kuenen (1933, 64) used i t f o r " a colony o f c o r a l s " w i t h "a r a i s e d r i m , more o r l e s s completely s u r r o u n d i n g a l o w e r , dead s u r f a c e " . MacNeil

(1954, 394) u s e d i t f o r "massive c o l o n i a l c o r a l s growing p e r i p h e r a l l y i n s h a l l o w a r e a s and whose dead upper s u r f a c e (sometimes made concave by s o l u t i o n ) i s exposed a t low t i d e . M i c r o a t o l l s o f t e n form a

pavement o f c l o s e l y spaced s t e p p i n g s t o n e s " . Such pavements have r e c e n t l y been termed " r e e f t a b l e s " by F i s h e l s o n (1973, 1 9 3 ) . Most d e f i n i t i o n s of m i c r o a t o l l s i n c l u d e e l e m e n t s o f morphology, l o c a t i o n , o r i g i n , and, r a r e l y , i n t e r n a l s t r u c t u r e .

CHARACTERISTICS

Most a u t h o r s use m i c r o a t o l l " t o d e s i g n a t e a s p e c i a l t y p e o f growth o f c o r a l c o l o n i e s " (Kuenen 1933, 9 0 ) , n o t f o r ring-shaped assemblages o f a v a r i e t y o f c o r a l s f o r which t h e word faro i s more a p p r o p r i a t e

(Gardiner 1931, 19; MacNeil 1954, 399; G u i l c h e r 1971, 77; Scheer 1972, 1 0 2 ) . T y p i c a l m i c r o a t o l l s comprise s i n g l e c o l o n i e s of massive c o r a l s ("monospecific m i c r o a t o l l s " o f Mergner and S c h e e r , 1974, l l ) , e s p e c i a l l y o f Porites, u s u a l l y round (though complexity of form i s s t r e s s e d by Kuenen 1933, 6 4 ) , and w i t h a f l a t o r concave upper s u r f a c e devoid o f l i v i n g p o l y p s . S e v e r a l a u t h o r s have s t r e s s e d t h e importance o f a w e l l - d e f i n e d p e r i p h e r a l r i d g e of l i v i n g c o r a l s e v e r a l c e n t i m e t r e s h i g h and wide, s u r r o u n d i n g t h e dead i n n e r a r e a (Krempf, 1927, 1 5 ) ; Semper (1899, 226) found t h i s f e a t u r e p r e s e n t o n l y i n l a r g e r c o l o n i e s , and Pichon (1964, 135) found i t g e n e r a l l y a b s e n t i n s o u t h w e s t

Madagascar m i c r o a t o l l s .

Most m i c r o a t o l l s a r e found i n p o o l s on r e e f s u r f a c e s o r on r e e f f l a t s . Kuenen (1933, 65) s t a t e d t h a t w i t h r e s p e c t t o s e a - l e v e l t h e s u r f a c e s of m i c r o a t o l l s were h i g h e r on t h e windward t h a n t h e leeward s i d e s o f r e e f s , and t h a t e x c e p t i o n a l l y h i g h m i c r o a t o l l s c o u l d b e found i n ponded s i t u a t i o n s on r e e f - f l a t s . Most m i c r o a t o l l s d e s c r i b e d a r e up t o 6 m i n d i a m e t e r . The g e n e r a l c h a r a c t e r i s t i c s o f m i c r o a t o l l s may b e d e r i v e d from t h e f o l l o w i n g r e g i o n a l d e s c r i p t i o n s :

Cocos-Keeling Atoll. "One l a r g e c i r c u l a r mass o f Madrepora ( w i t h s h o r t b r a n c h e s ) , which measured 1 8 f e e t a c r o s s and 2 f e e t i n

h e i g h t , p o s s e s s e d a dead c e n t r e t h a t w a s d e p r e s s e d 9 o r 10 i n c h e s below t h e l e v e l o f i t s l i v i n g margin.

...

^An a d j a c e n t f l a t - t o p p e d mass o f Porites, measuring 1 3 f e e t a c r o s s , a t t h e same c o n d i t i o n o f t h e t i d e p r e s e n t e d an example o f a n o t h e r m i n i a t u r e a t o l l . I t s c e n t r a l p o r t i o n was dead and hollowed o u t i n t o a b a s i n , which w a s o c c u p i e d by a s m a l l p o o l o f w a t e r " (Guppy 1886, 8 9 3 ) .

B i k i n i A t o l l . A t B i k i n i , i n t h e o u t e r H e l i o p o r a zone of windward r e e f s , Emery e t a l . (1954, 28) d e s c r i b e m i c r o a t o l l s i n "1 t o 4 f e e t of water a t low t i d e

...

l a r g e s u b c i r c u l a r masses, 3 t o 25 f e e t o r even more i n d i a m e t e r , c o n s i s t i n g l a r g e l y of t h e b l u e

a l c y o n a r i a n , H e l i o p o r a , [and which] r i s e c l o s e t o low-tide l e v e l . I n t h e o u t e r p a r t of t h i s zone t h e m i c r o a t o l l s a r e formed mainly by t h e s c l e r a c t i n i a n c o r a l , Acropora p a l i f e r a . T h i s zone i s a p a r t of t h e b e l t of m i c r o a t o l l s . I n t h e s e s t r u c t u r e s , a s i n t r u e a t o l l s , t h e r e i s a c o n c e n t r a t i o n of l i v i n g forms around t h e

p e r i p h e r y , a l t h o u g h l i v e c o l o n i e s , p a r t i c u l a r l y Heliopora and a l g a e , may be growing s p o r a d i c a l l y a l l o v e r t h e s t r u c t u r e . The Acropora, which a p p a r e n t l y i s n o t q u i t e s o hardy a form a s t h e H e l i o p o r a , i s c o n c e n t r a t e d around t h e edge o f t h e m i c r o a t o l l , and most o f t h e c o l o n i e s a r e a t a somewhat lower l e v e l t h a n t h e

Helioporas; a t low t i d e t h e t i p s of many H e l i o p o r a c o l o n i e s break water. The upward growth o f t h e m i c r o a t o l l s i s d e f i n i t e l y

l i m i t e d by low-tide l e v e l , b u t t h e growth around t h e r i m o f each s t r u c t u r e i s r i c h , and t h e masses appear t o be expanding l a t e r a l l y i n a l l d i r e c t i o n s . A s t h e y c o a l e s c e , t h e y form a new r e e f

s u r f a c e - n o t s o f i r m a s u r f a c e a s t h e pavement from which t h e y grow b u t one t h a t may become s o e v e n t u a l l y by continued o r g a n i c growth and s i l t i n g . Many of t h e dead Helioporas i n t h e c e n t e r s of t h e m i c r o a t o l l s a r e covered by a f i l m of s a n d v e r y r i c h i n Foraminif e r a "

.

G r e a t B a r r i e r R e e f . "Typical o f t h e r e e f f l a t i s t h e m i c r o a t o l l which i s formed by one of s e v e r a l s p e c i e s of c o r a l t h a t grow r a d i a l l y i n t h e h o r i z o n t a l p l a n e and produce a f l a t - t o p p e d mass t h a t i s c i r c u l a r i n o u t l i n e o r c o n s i s t s o f s e v e r a l merging c i r c l e s . The t o p of t h e m i c r o a t o l l i s e n c r u s t e d by c a l c a r e o u s a l g a e and t h e l i v i n g c o r a l s u r v i v e s mainly around t h e margins and o u t e r f a c e . The c o r a l Porites forms t h e compact, p u r p l e and brown m i c r o a t o l l s which a r e p o s s i b l y t h e most common. The b l u e - H e l i o p o r a and g r e y

Goniopora a r e a l s o r e s p o n s i b l e f o r compact m i c r o a t o l l s , w h i l e more open s t r u c t u r e s , g e n e r a l l y yellow and p a l e g r e e n i n , c o l o u r , a r e produced by c e r t a i n branching s p e c i e s , " e.g. a t Heron I s l a n d

(Maxwell 1968, 1 1 5 ) . E a r l i e r , f i e l d s o f m i c r o a t o l l s had been d e s c r i b e d forming " c o r a l p l a t f o r m s " a t Low I s l e s by Stephenson

e t a l . (1931, 46-47): "Montipora ramosa, ~ c r o p o r a hebes and massive Porites

...

e x h i b i t a c u r i o u s development connected w i t h t h e

shallowness of t h e water. They grow i n a normal f a s h i o n u n t i l t h e i r t o p s p r o j e c t above t h e l e v e l of low w a t e r ; t h e y may then s u r v i v e w i t h p r o j e c t i n g t i p s f o r a l o n g e r o r s h o r t e r p e r i o d ; b u t sooner o r l a t e r t h e p r o j e c t i n g p a r t s a r e k i l l e d , become i n f e s t e d by microphytic a l g a e and sediment, and e n c r u s t e d by n u l l i p o r e s

(Melobesiae) ; s o t h a t u l t i m a t e l y t h e c o r a l c o l o n i e s a r e converted i n t o f l a t - t o p p e d p l a t f o r m s , dead a c r o s s t h e t o p and a l i v e around t h e edges. T h i s p r o c e s s may a f f e c t i n d i v i d u a l c o l o n i e s o r , i f t h e growth has been dense s o t h a t f i e l d s of branching c o r a l s have been formed, it may c o n v e r t a whole f i e l d i n t o a p l a t f o r m . The g e n e r a l r e s u l t o f t h i s i s t o c r e a t e a b e w i l d e r i n g maze of l e v e l p l a t f o r m s w i t h p o o l s between.

...

The e x t e n t and composition o f t h e p l a t f o r m s v a r i e s i n d i f f e r e n t p a r t s of t h e moat [ a t Low ~ s l e s ] ; massive

P o r i t e s becomes converted i n t o platforms a s r e a d i l y as t h e branched s p e c i e s , though t h e d e t a i l s a r e a l i t t l e d i f f e r e n t . Astraeid c o r a l s , e s p e c i a l l y s p e c i e s of Favia, a r e common among t h e platform-building forms

...

and these a l s o o f t e n develop dead f l a t t e n e d tops".

I t i s c l e a r from t h e s e d e s c r i p t i o n s t h a t both massive ( P o r i t e s ) and branching ( A c r o p r a ) s c l e r a c t i n i a n c o r a l s and a l s o alcyonarians

( H e l i o p r a ) commonly form m i c r o a t o l l s . Wells (1957) l i s t s s i x genera of massive s c l e r a c t i n i a n s (Favia, Favi t e s , Platygyra, Cyphastrea, Goniastrea, P o r i t e s ) forming m i c r o a t o l l s i n t h e Marshall I s l a n d s , together with two s p e c i e s of branching c o r a l s (Acropora p a l i f e r a , A. brueggemanni), and a l s o Heliopora. Kre~npf (1927, 15) mentions Pori t e s , Acropora and Heliopora

,

and a l s o t h e hydrozoan M i l l e p r a

.

I n Madagascar, Pichon (1964, 135) found P o r i t e s somaliensis Gravier t o be the main former of m i c r o a t o l l s up t o 3 m i n diameter, with smaller m i c r o a t o l l s lacking a c e n t r a l depression b u i l t by s p e c i e s of Acropora andPavona,andalso Turbinaria sp. c f . stephensoni Crossland. A t Alacran Reef, Gulf of Mexico, examination of 41 specimens of " a t o l l - shaped heads" and "atoll-shaped c o r a l colonies" ( t h e authors using t h e term m i c r o a t o l l f o r l a r g e r patch r e e f s ) showed t h a t n e a r l y a l l s p e c i e s of massive c o r a l s found on t h e r e e f were r e p r e s e n t e d , forming colonies 2-53 inches i n diameter (Kornicker and Boyd 1962, 667). Microatolls a r e a l s o described i n t h e s p i c u l a r s k e l e t a l m a t e r i a l deposited i n t h e t i s s u e s of t h e alcyonarian Sclerophytum i n American Samoa (Cary 1931, 6 1 ) .

I n a d d i t i o n t o " c o r a l s " sensu l a t o ( S c l e r a c t i n i a , Hydrozoa,

Alcyonaria), some authors consider t h a t c o n s t r u c t i o n a l f e a t u r e s formed by o t h e r animals morphologically resemble m i c r o a t o l l s t o t h e e x t e n t of using t h e same term f o r them. Rock r i m s coated by t h e pelecypod Brachyodontes erosus a t P o i n t Peron, Western A u s t r a l i a , a r e termed m i c r o a t o l l s by F a i r b r i d g e (1950, 5 2 ) . S i m i l a r rock r i m s coated with tubes of s e r p u l i d worms a t Bermuda have f r e q u e n t l y been r e f e r r e d t o a s m i c r o a t o l l s (Agassiz 1895; Krempf 1927; F a i r b r i d g e 1950).

Constructions by vermetid gastropods a r e a l s o s o r e f e r r e d t o by Krempf (1927) and by S a f r i e l (1974). C o r a l l i n e a l g a l rims on r e e f f l a t s and limestone t e r r a c e s a r e termed m i c r o a t o l l s a t Cozumel, Yacatan, by Boyd, Kornicker and Rezak (1963), though where c h a r a c t e r i s t i c a l l y developed, e.g. i n t h e western P a c i f i c ( L i s t e r 1891; Stoddart 1969), they a r e n o t annular.

M i c r o a t o l l s have been described i n t h e f o s s i l s c l e r a c t i n i a n H e l i a s t r a e a reussana Milne Edwards and Haime by Vasicek (19481, b u t reference t o h i s f i g u r e shows t h a t t h e t y p i c a l m i c r o a t o l l form i s n o t p r e s e n t i n t h i s lobate c o r a l .

ORIGINS OF MICROATOLLS

A v a r i e t y of modes of o r i g i n has been proposed f o r t y p i c a l microatolls. Often these modes overlap i n s e v e r a l p a r t i c u l a r s , but broadly t h r e e main explanations can be recognised.

(1) Low-water l e v e l control

Many authors have suggested t h a t low-water l e v e l forms an upper growth l i m i t f o r c o r a l colonies; t h a t when t h i s i s reached upward growth ceases and i s replaced by l a t e r a l growth, leaving a dead, f l a t c e n t r a l area. Semper (1899, 224-226) described how up-growing small massive hemispherical colonies would be transformed t o microatolls as t h e i r upper s u r f a c e s reached low-water l e v e l , and very s i m i l a r

explanations were given by Kuenen (1933, 64-65) and by Pichon (1964, 135-136). One of t h e e a r l i e s t d e t a i l e d accounts r e l a t i n g form of the corallum t o measured water heights was t h a t of Manton (1935, 300) a t Low I s l e s , Great B a r r i e r Reef. She s t a t e s t h a t : "The upper l i m i t of c o r a l growth i s determined i n the f i r s t place by the range of water l e v e l .

In the Moat the height of the branched and'massive c o r a l platforms appears t o be c o n t r o l l e d by t h e permanent l e v e l of low water, and l i e s a t 0.3 and 0.15 f e e t r e s p e c t i v e l y above the l a t t e r . Outside the Boulder Tract and rampart c o r a l growth s t a r t s a t a lower l e v e l , j u s t above datum [ i . e . l e v e l of lowest low water springs]

...,

so t h a t c o r a l s a r e only exposed t o the a i r i n t e r m i t t e n t l y a t exceptionally low t i d e s . No platforms a r e here formed with f l a t dead o r l i v i n g tops a t a constant

l e v e l s i n c e t h e water i s continually changing, but over the l e v e l

inshore p a r t of Traverse I1 c o r a l growth, except f o r Acropora hebes, i s checked above 1.6 f e e t above datum. Massive c o r a l s with f l a t dead tops have been noted i n o t h e r regions

...

The d i s t r i b u t i o n of such dead- topped c o r a l s on the t r a v e r s e s and on Low I s l e s generally, where they a r e found abundantly i n Moats b u t r a r e l y o u t s i d e t h e Boulder T r a c t , even i n regions where sediment i s a l i m i t i n g f a c t o r , and the d i r e c t

c o r r e l a t i o n of t h e height of such colonies with low-water l e v e l , i n d i c a t e s t h a t here water l e v e l and not sediment i s the main f a c t o r responsible f o r such growth forms on Low I s l e s " . This r e l a t i o n s h i p i s so close t h a t the presence of microatolls i n Pleistocene r e e f s has been used a s an i n d i c a t o r of low-water spring t i d e s (Braithwaite e t a l . 1973, 321).

More r e c e n t l y , Roy (1970, 12-13) has described m i c r o a t o l l s , mainly of s i n g l e colonies of Porites compressa, i n Kaneohe Bay, Oahu, up t o 20 f t i n diameter, a l l r i s i n g t o within a few inches of lower low water.

He f i n d s t h a t the morphology of the microatolls i s r e l a t e d t o depth of surrounding water, though he does not d i s c u s s t h i s r e l a t i o n s h i p i n h i s t e x t (Table 1).

A t i d a l - l e v e l c o n t r o l could explain a f l a t , bevelled upper surface of the kind found by Pichon i n Madagascar, but l e s s e a s i l y the existence of a r a i s e d r i m of l i v i n g c o r a l round the dead c e n t r a l area. Semper

(1899) and Agassiz (1895, 258) both proposed t h a t a f t e r growth ceased

the c e n t r a l area was hollowed out by b i o l o g i c a l , chemical and mechanical erosion t o form both t h e f l a t o r concave centre and g u l l i e s and channels i n it. Krempf (1927, 19) could f i n d no evidence of such erosion: i n Annam he found t h e c e n t r a l area sound, and often with small growing

c o r a l s on it. Various conditions could form the s p e c i f i c cause of death a t o r near the s e a - a i r i n t e r f a c e . Fishelson (1973, 193) has suggested t h a t exceptionally low t i d e s , which may be aperiodic, could k i l l the upper surfaces of c o r a l s through emersion a t E i l a t i n t h e Red Sea. I n Bermuda Iams (1969, 70) has described s e v e r a l possibly

pathological conditions leading t o the disappearance of l i v i n g polyps from otherwise healthy c o r a l heads, and G a r r e t t and Ducklow (1975) have described apparent evidence of disease from the same a t o l l . Once

skeleton i s exposed i t i s open t o many processes of bioerosion, of which the a c t i v i t i e s of t r i d a c n i d clams a r e conspicuous on western P a c i f i c microatolls (Figure 2 and 3 ) .

Table 1. Relation of microatolls morphology t o water depth, Kaneohe Bay, Oahu (source : Roy, 1970, t a b l e 3)

.

Depth of water on surrounding bottom

( f e e t )

Microatoll morphology

No l i v e c o r a l on the r i m : top dead, centre eroded nearly t o the l e v e l of the surrounding bottom.

P a r t of t h e r i m i s l i v e c o r a l : top dead, centre p a r t l y eroded.

A l l of the r i m i s l i v e coral: top dead, f l a t , not eroded.

A l l of the r i m i s l i v e coral: some l i v e c o r a l on top, top tends t o be domal r a t h e r than f l a t , not eroded.

,Sedimentation leading t o d i f f e r e n t i a l growth

Wood Jones (1912, 107-109, 247-251) observed t h a t c o r a l colonies with dead upper surfaces were frequently found a t Cocos-Keeling A t o l l well below low-tide l e v e l . He proposed t h a t the steady r a i n of sediment through t h e water led t o accumulation on t h e f l a t upper

surfaces of c o r a l colonies, e s p e c i a l l y of massive hemispherical Porites colonies, t h e consequent death of l i v i n g polyps, and t h e ultimate

formation of an " a t o l l reef i n miniature". Krempf (1927, 131 s i m i l a r l y observed deep microatolls i n Annam. He argued t h a t sedimentation on

h o r i z o n t a l s u r f a c e s was a i d e d by ectodermal mucus s e c r e t i o n t r a p p i n g f i n e p a r t i c l e s , though i t i s now u s u a l l y h e l d t h a t mucus h e l p s remove sediment from c o r a l s . T h i s c o n t r o l was a b s e n t on v e r t i c a l s u r f a c e s , which consequently grew f a s t e r , l e a v i n g a f l a t dead a r e a w i t h i n . An e a r l y s t a g e i n t h i s p r o c e s s produced " u m b i l i c a l " c o l o n i e s , round w i t h a c e n t r a l d e p r e s s i o n . Vasicek (1948) has p o i n t e d o u t t h a t t h i s p r o c e s s o f c o n t r o l by s e d i m e n t a t i o n a p p e a r s more a p p l i c a b l e t o massive t h a n t o branching and p l a t y c o r a l s . He h a s a l s o noted t h a t t h e r e s u l t i n g

d i f f e r e n t i a l growth o f d i f f e r e n t p a r t s o f t h e s k e l e t o n should be c l e a r l y observed i n s k e l e t a l s t r u c t u r e s .

Marshall and O r r (1931, 131) noted a t Low I s l e s , G r e a t B a r r i e r Reef, t h a t m i c r o a t o l l s were formed n e a r low t i d e l e v e l by b o t h l a r g e - polyped F a v i a s p e c i e s and small-polyped Porites s p e c i e s , t h e former e f f i c i e n t sediment-removers and t h e l a t t e r n o t , and they concluded t h a t m i c r o a t o l l s were probably n o t t h e r e f o r e p r i m a r i l y caused by

s e d i m e n t a t i o n . Other f a c t o r s , such a s growth form, c o u l d , however, a f f e c t t h e e f f i c i e n c y of sediment removal.

I n t e r e s t i n g v a r i a t i o n s on normal m i c r o a t o l l form have a l s o been d e s c r i b e d i n shallow-water s i t u a t i o n s . I n Iwayama Bay, P a l a u , Abe

(1937, 253-256) d e s c r i b e d m i c r o a t o l l s of G o n i a s t r e a a s p e r a V e r r i l l w i t h i n c l i n e d upper s u r f a c e s ; such i n c l i n a t i o n was n o t found i n Porites s o m a l i e n s i s . F i g u r e 1 g i v e s mean dimensions f o r 1 7 measured G o n i a s t r e a m i c r o a t o l l s w i t h i n c l i n e d s u r f a c e s ; Abe a l s o gave d a t a on 23 more

c o l o n i e s where t h e r i m was incomplete because o f t h e i n t e r r u p t i o n of i t s narrower lower p a r t . The mean o r i e n t a t i o n o f t h e long a x e s of t h e complete m i c r o a t o l l s was 117O, and t h e mean a n g l e o f i n c l i n a t i o n o f t h e upper s u r f a c e about 17O. These o r i e n t a t i o n s a r e " t o t h e d i r e c t i o n o f t h e upper stream a t r i s i n g t i d e " (1937, 2 5 3 ) ; Abe b e l i e v e d t h a t sediment i n t h e c u r r e n t was probably an i m p o r t a n t c o n t r o l . Elsewhere, e s p e c i a l l y . on shallow r e e f f l a t s , sediment may accumulate t o form c o n s p i c u o u s t a i l s i n t h e l e e o f m i c r o a t o l l s , a s n e a r Gan, Addu A t o l l , Maldive I s l a n d s

( S t o d d a r t e t a l . , 1966, 1 9 ) ; b o t h h e r e , on P o r i t e s , and i n t h e Gulf of E i l a t on P l a t y g y r a , t h e dead upper s u r f a c e s o f t h e m i c r o a t o l l s a r e conspicuously c o l o n i s e d by t h e a l g a T u r b i n a r i a ( F i s h e l s o n , 1973, f i g . 3 b ) .

( 3 ) Food s u p p l y , c u r r e n t s , and d i f f e r e n t i a l growth

Some a u t h o r s have s u g g e s t e d t h a t a s a c o r a l grows, it w i l l i n f l u e n c e h y d r o l o g i c c o n d i t i o n s n e a r i t , and t h a t i n g e n e r a l c u r r e n t s and food s u p p l i e s w i l l be g r e a t e r round t h e p e r i p h e r y t h a n i n t h e c e n t r e . Hence t h e margins w i l l grow more r a p i d l y t h a n t h e c e n t r e and a m i c r o a t o l l form w i l l r e s u l t . T h i s h a s been proposed f o r a l c y o n a r i a n m i c r o a t o l l s i n Samoa ( C a r y 1931, 61) and f o r f o s s i l c o r a l s by Vasicek (1948).

( 4 ) Overgrowth on older c o r a l colonies

Kornicker and Boyd (1962, 667-668, f i g . 33) produced a novel

explanation of microatoll development a t Alacran Reef. Gulf of Mexico.

Here microatolls "have developed p r i n c i p a l l y (about 90 per cent) by peripheral growth around the r i m s of overturned c o r a l heads; a few have formed a f t e r the c e n t r a l p a r t of the dome was encrusted with

calcareous algae t h a t e f f e c t i v e l y stopped c o r a l growth i n t h a t area but permitted continued growth around the edge. Atoll-shaped c o r a l

colonies formed on overturned heads have convex-downward bases.

Specimens were collected t h a t had evidently been turned over several times so t h a t both top and bottom were atoll-shaped". Overgrowth on dead c o r a l blocks, not necessarily overturned, t o form microatolls was noted with P o r i t e s i n Madagascar by Pichon (1964, 1361, who a l s o found it t o be the s o l e mode of microatoll development i n Turbinaria.

SUSCEPTIBILITY TO MICROATOLL FORMATION

Abe (1937) contributed important data on microatolls (termed by him "coral t a b l e s " ) a t Iwayama Bay, Palau. He measured the depth from mean water l e v e l of the upper surfaces of microatolls and of round-

topped colonies of three common species ( P o r i t e s s o m l i e n s i s , Favia speciosa, Goniastrea planulata) a t three s i t e s i n the Bay (Stations 1 and 2 a r e reef margin s i t e s , Station 3 a reef f l a t and pool s i t e ) . H i s data a r e summarised i n Table 2. The lowest t i d e recorded i n 1935 was

100 cm below mean water l e v e l , though i n such a topographic s i t u a t i o n l o c a l v a r i a b i l i t y must be considerable.

Table 2. Depth below mean water l e v e l of microatolls and hemispherical c o r a l colonies a t Iwayama Bay, Palau (from data i n Abe 1937, 306-307)

Microatolls Hemispherical colonies

Mean Minimum Maximum n Mean Minimum Maximum n

depth depth depth depth depth depth

- - -

~ o r i t e s soma1 i ensi s

S t a t i o n 1 101.9 86 1 2 4 25 122.8 106 1 4 4 1 2

Station 2 123.8 116 130 1 2 139.2 134 148 5

S t a t i o n 3 115.3 108 1 2 4 2 1

- - - -

Favia speciosa

Station 1 96.5 78 1 1 4 4 126

- -

1

S t a t i o n 2 104

- -

^{1 -}

^{- - -}

Goniastrea planulata

S t a t i o n 1 108 106 1 1 2 6 1 2 4

- -

1

Depths i n cm; depth of lowest low t i d e i n 1935 100 cm.

A t S t a t i o n 1, f o r which d a t a are f u l l e s t , Abe found (1937, 305- 309) c o n s i d e r a b l e d i f f e r e n c e s between s p e c i e s i n t h e l e v e l s a t which m i c r o a t o l l s form. ~ a v i a s p e c i o s a formed m i c r o a t o l l s a t t h e h i g h e s t l e v e l (mean d e p t h 96.5 cm)

,

t h e n P o r i t e s s o m a l i e n s i s (mean 1 0 1 . 9 ) and d e e p e s t Goniastrea p l a n u l a t a (mean 1 0 8 ) . These d i f f e r e n c e s must r e f l e c t v a r i a t i o n s i n t o l e r a n c e between d i f f e r e n t s p e c i e s o f t h e c o n t r o l l i n g f a c t o r s . Abe a l s o found t h a t t h e same s p e c i e s formed m i c r o a t o l l s a t d i f f e r e n t d e p t h s a t t h e t h r e e d i f f e r e n t s t a t i o n s . Thus P o r i t e s s o m a l i e n s i s m i c r o a t o l l s a r e found a t a mean d e p t h o f 102 cm a t S t a t i o n 1 (round c o l o n i e s a t 123 a); a t 124 c m a t S t a t i o n 2 (round c o l o n i e s a t 140 c m ) ; and 115 cm a t S t a t i o n 3 (no round c o l o n i e s ) . Abe f e l t t h a t t h e s e d i f f e r e n c e s c o u l d n o t b e e x p l a i n e d by t i d a l c o n t r o l a l o n e . He n o t e d t h e p r e v a l e n c e o f muddy s e d i m e n t s a t S t a t i o n 2 , and a r g u e d (1937, 313-314) t h a t m i c r o a t o l l s formed a t lower l e v e l s a t t h i s s t a t i o n b e c a u s e o f t h e amount o f suspended mud i n t h e w a t e r .

MICROATOLLS AT ABNORMALLY H I G H LEVELS

Mention h a s a l r e a d y been made o f Kuenen's (1933, 65) o b s e r v a t i o n o f m i c r o a t o l l s i n ponded s i t u a t i o n on r e e f f l a t s i n t h e E a s t I n d i e s , and s u c h a s i t u a t i o n is i m p l i c i t i n t h e r e c o r d s o f m i c r o a t o l l growth and e l e v a t i o n on t h e s u r f a c e s o f low wooded i s l a n d - r e e f s o f t h e G r e a t Barrier Reef by Manton (1935, 3 0 0 ) . I n d e s c r i b i n g r e e f - t o p p o o l s a t Low I s l e s , F a i r b r i d g e and T e i c h e r t (1947, 4) s t a t e t h a t " t h e r e i s o f t e n a c t i v e c o r a l growth r e a c h i n g s e v e r a l f e e t above t h e normal upper l i m i t o f s u c h growth, a s i g n i f i c a n t p o i n t f o r t h o s e who would u s e c o r a l which h a s grown i n s i t u as a datum f o r former s e a - l e v e l s " . The h e i g h t d a t a u s e d by F a i r b r i d g e and T e i c h e r t are t h e same as t h o s e u s e d by Manton, d e r i v e d from t h e c a r e f u l s u r v e y s by Spender ( 1 9 3 0 ) . C l e a r l y , i f s u c h r e e f - t o p p o o l s a r e d r a i n e d t h e n s u c h abnormally h i g h m i c r o a t o l l s might b e k i l l e d ; s u c h changes c o u l d r e s u l t from h u r r i c a n e m o d i f i c a t i o n o f r e e f topography (Moorehouse 1 9 3 6 ) .

High-standing dead m i c r o a t o l l s which m i g h t b e r e f e r r e d e i t h e r t o growth i n f o r m e r l y e x i s t i n g p o o l s o r t o growth when s e a - l e v e l i t s e l f w a s h i g h e r t h a n a t p r e s e n t were f i r s t d e s c r i b e d i n d e t a i l a t F u n a f u t i A t o l l , E l l i c e I s l a n d s . H e r e S o l l a s (1904, 20-22) n o t e d a n a r e a o f P o r i t e s m i c r o a t o l l s a n d H e l i o p o r a c o l o n i e s w i t h i n a mangrove swamp, a t a l e v e l submerged by s e v e r a l f e e t a t h i g h w a t e r b u t emerged d u r i n g much o f t h e day. The c o r a l s t h e m s e l v e s w e r e p a r t l y c o v e r e d by a cemented s h i n g l e r a m p a r t . The f l a t t o p s o f t h e c o r a l s were a s c r i b e d t o "an a r r e s t o f upward growth

...

by t h e l e v e l o f low water". S o l l a s p r o c e e d e d t o d i s c u s s t h e i n t e r p r e t a t i o n o f t h e s e m i c r o a t o l l s :

" I f it b e a d m i t t e d t h a t t h e s u r f a c e of t h e P o r i t e s clumps marks a n a n c i e n t l e v e l o f low water, t h e n it o b v i o u s l y becomes a problem o f e x t r e m e i n t e r e s t t o compare t h i s l e v e l w i t h t h a t o f t h e e x i s t i n g sea.

...

^{t h e} summits o f t h e P o r i t e s clumps now s t a n d 1 f o o t 4 i n c h e s above mean t i d a l l e v e l , i - e . , 4 f e e t 6 i n c h e s above low water a t s p r i n g t i d e s o r 3 f e e t 9 i n c h e s above low water a t neap t i d e s . I t h e r e f o r e concluded t h a t a

change i n s e a - l e v e l i n a negative d i r e c t i o n t o t h e e x t e n t of about 4 f e e t had occurred over t h e s i t e of t h e Mangrove Swamp s i n c e t h e growth of i t s a n c i e n t r e e f " (1904, 2 2 ) .

David and Sweet (1904, 67) placed t h e downward movement of t h e s h o r e l i n e so i n d i c a t e d a t "from 44 t o 6$ f e e t " . Elsewhere on F u n a f u t i , however, Finckh (1904, 138-139) found l i v i n g Heliopora c o l o n i e s a t unusually high

l e v e l s i n moated s i t u a t i o n s s i m i l a r t o those l a t e r found a t Low I s l e s . Both H e l i o p r a and P o r i t e s were found a t t h e n o r t h end of Arnatuku I s l a n d , F u n a f u t i , growing i n a pool a t a h e i g h t of 2 f e e t above low- water s p r i n g t i d e : " g r e a t c a r e was e x e r c i s e d t o determine t h e e x a c t height of t h i s c o r a l growth, s i n c e it would seem t o o f f e r an explanation f o r t h e occurrence i n s i t u of dead Heliopora considerably above low- water mark i n t h e Mangrove Swamp and i n o t h e r l o c a l i t i e s on t h e main

i s l a n d of Funafuti". David and Sweet (1904, 6 7 ) , however, while accepting t h i s o b s e r v a t i o n , d i d n o t f e e l t h a t modern growth i n pools could account f o r t h e main a r e a s of dead m i c r o a t o l l s . I t "may e x p l a i n small heads above low water l e v e l , b u t n o t t h e H e l i o p r a s l i g h t l y above high water l e v e l

...

^{nor i n s i t u} h e a d s o f P o r i t e s " i n many cases over a f o o t , some

...

4 f e e t above high water. These immense heads could n o t have grown i n land-locked r e e f p o o l s , b u t must have f l o u r i s h e d under t h e most favourable c o n d i t i o n s , such a s f r e e access t o food-bringing

c u r r e n t s , e t c . , would provide".

The Funafuti s i t u a t i o n i s d i r e c t l y analogous t o t h a t found on t h e northern Great B a r r i e r Reef i n 1973, and t h e r e i s some suggestion i n t h e l i t e r a t u r e t h a t abnormally high dead m i c r o a t o l l s (though perhaps n o t . c h a r a c t e r i s e d a s such) a r e f a i r l y widespread i n t h e western P a c i f i c e.g. i n t h e Marshall I s l a n d s (Emery e t d l . 1954, Buddemeier et d l . 1975, Tracey and Ladd 1974) and t h e G i l b e r t I s l a n d s (Cloud 1952).

PROBLEMS OF TERMINOLOGY

Microatoll mis-used f o r patch r e e f s

A s described above t h e usage of t h e term " m i c r o a t o l l " a s introduced by Krempf i s r e l a t i v e l y unambiguous. Unfortunately s e v e r a l r e c e n t a u t h o r s have used t h e term f o r q u i t e d i f f e r e n t kinds of f e a t u r e s and hence produced confusion.

I n t h e Bahamas, Newel1 and Rigby (1957, 36) used t h e term f o r

" c e r t a i n ring-shaped patch r e e f s

. . .

i n many a r e a s n e a r l y c i r c u l a r

. . .

measuring 10 t o 200 metres across. A s viewed from a b o a t ox from t h e a i r , t h e f a r o s [ s i c ] s t a n d o u t a s dark r i n g s o r f r i n g e s of gorgonians upon a r i m of stony c o r a l s . The c e n t r a l a r e a i s more o r l e s s dead, s l i g h t l y depressed, and covered with c o r a l fragments". Newel1 (1954, 12) considers t h e use of t h e term m i c r o a t o l l f o r s i n g l e c o r a l c o l o n i e s

"not very appropriate" and suggests it be reserved f o r such ring-shaped patch r e e f s ( c f . Newel1 et d l . 1951, 23; I l l i n g , 1954); he does n o t e x p l a i n why m i c r o a t o l l i n t h i s r e d e f i n e d sense and f a r 0 a r e used synonymously.

Similarly, a t Raroia Atoll, Tuamotu Archipelago, Doty and Morrison (1954, 52) speak of l a r g e r reef patches "progressively l i k e microatolls i n t h a t the centre i s more apt t o be a pool a few f e e t deep and the edge a r i m a few f e e t wide more or l e s s complete and higher, j u s t below low t i d e level". Kinsey and Domm (1974, 51) described " a very large number of patch r e e f s " a t One Tree Island, Great Barrier Reef, "many taking the form of microatolls. These vary from about 3 m t o 200 m i n diameter and a r e characterised by being f u l l y .or nearly f u l l y enclosed by l i v i n g reef. The walls a r e usually v e r t i c a l on the sides and 2-5 m thick.

Within these enclosures the water depth, during the 5-6 hr low-tide

slack water period, i s ' ty p i c a l l y 0.5-2 m and the bottom has sparse c o r a l cover being predominantly sandy with some rubble". Similar features of comparable s i z e had e a r l i e r been termed "miniature a t o l l s " a t Pearl and Hermes Reef, Leeward Hawaiian Islands, by Galtsoff (1933, 1 4 ) .

A t Alacran Reef, Hoskin (1963, 2 7 ) used microatoll i n an inclusive sense f o r "growths of massive corals which resemble a doughnut i n shape.

They range i n s i z e from single heads

...

t o very large and complex

s t r u c t u r e s .

...

The l a r g e s t microatolls a r e c a l l e d patch r e e f s

...

^[and]

may be up t o 20 f e e t i n diameter". These Alacran r e e f s are also

described by Kornicker and Boyd (1962, 658-659): "The upper surfaces of two microatolls about 2 miles north of I s l a Perez were examined i n d e t a i l . They r i s e within a few f e e t of the surface from a depth of about 40 f e e t , and t h e i r upper surfaces form c i r c u l a r areas 325 and 200 f e e t i n diameter respectively. The water depths a t the margins of these surfaces a r e t y p i c a l l y about 5 f e e t t o the base of the corals and 2+ f e e t t o t h e tops of the corals. Between the outer edge and the c e n t r a l lagoon, depths are as shallow as 13 f e e t t o t h e coral tops and 3 f e e t t o the base of t h e corals. The deeper p a r t s of the lagoons a r e about 4$ f e e t beneath the surface. Beyond the outer edge of t h e l a r g e r microatoll, *he slope i s steep and was estimated a t 30°.

...

^{each of}

these microatolls could be mapped as a c i r c u l a r b e l t of massive corals enclosing a sand-bottom area and surrounded by sand bottom." These f e a t u r e s are c l e a r l y q u i t e d i f f e r e n t from classically-defined microatolls, and there seems no good reason f o r misusing t h i s term t o describe them.

Similar d i f f i c u l t i e s a r i s e i n new terminology proposed f o r lagoon patch r e e f s a t Bermuda by Garrett et al. (1971, 650). These authors use llmicroatoll reef" f o r patch r e e f s which "resemble small a t o l l s i n possessing a growing perimeter and a sediment-filled i n t e r i o r " . One example described measured 150 x 700 m , with an upper sandy surface 4 m deep; t h i s they a l s o term a "rough-topped mesa". ^A mesa reef i s defined as a broad reef i n the Bermuda lagoon bounded by steep slopes;

f u r t h e r , " i f the top i s bowl-shaped and sandy, depth 4 m , the reef

becomes a microatoll r e e f " (Garrett et al. 1971, 651). They a l s o s t a t e t h a t "continued l a t e r a l growth a s well a s coalescence of adjacent r e e f s r e s u l t s i n poorer c i r c u l a t i o n f o r the c e n t r a l areas [of lagoon r e e f s ] , which d i e o f f ; t h e reef i s then a microatoll" ( G a r r e t t et al. _1971, 644). This misuses terms already well-defined and established i n t h e l i t e r a t u r e , and i t adds no precision t o the features being described.

The need f o r a s e r i e s of terms t o d i f f e r e n t i a t e members of a

h i e r a r c h y of forms from m i c r o a t o l l s e n s u strict0 t o a t o l l was r e c o g n i s e d by Scheer (1969, 1972). He proposed f o u r terms: m i c r o a t o l l

( c l a s s i c a l l y d e f i n e d a s r e f e r r i n g t o i n d i v i d u a l c o l o n i e s ) ; m i n i - a t o l l ; f a r o ; and a t o l l . M i n i - a t o l l i s used f o r p a t c h r e e f s i n a t o l l lagoons w i t h c e n t r a l d e p r e s s i o n s 2.5-3.5 m deep, comparable t o t h e p a t c h r e e f s d e s c r i b e d by Newel1 and by Doty and Morrison b u t termed by them

m i c r o a t o l l s . Scheer was q u i t e c l e a r t h a t t h e term m i c r o a t o l l "should be r e s e r v e d t o t h e loaf-shaped, round c o r a l l a of t h e o u t e r r e e f f l a t , whose upper p a r t s a r e dead" (1972, 99-100). Faro r e f e r s t o l a r g e r r e e f s of ring-shaped form, u s u a l l y found round t h e margins of c e r t a i n a t o l l s i n t h e Maldives i n s t e a d o f l i n e a r r e e f s (Gardiner 1903, 155;

1931, 1 9 ) . The term i s o f t e n r e s t r i c t e d t o p e r i p h e r a l r e e f s of a t o l l s o r o u t e r r e e f s of b a r r i e r s (Kuenen 1950, 426; MacNeil 1954, 3931, i n which s e n s e it i s c l o s e t o t h e term " a t o l l o n " used by Guppy (1889, 472)

and d e f i n e d by Stamp (1961, 3 6 ) , b u t it i s a l s o p r o p e r l y a p p l i e d t o ring-shaped p a t c h r e e f s w i t h i n a t o l l lagoons (MacNeil 1954, 399;

G u i l c h e r 1971, 77; Scheer 1972). "Bason-formed r e e f " o f Darwin (1842, 106) and "lagoon a t o l l " of Davis (1928, 1 5 ) a r e o b s o l e t e v e r s i o n s of f a r o

.

Cognate terms

C e r t a i n cognate terms have been i n t r o d u c e d f o r f e a t u r e s a s s o c i a t e d e i t h e r with t r u e m i c r o a t o l l s s e n s u Krempf o r f o r f e a t u r e s improperly termed m i c r o a t o l l s by some r e c e n t a u t h o r s .

The dead c e n t r a l a r e a o r e n c l o s e d p o o l of t r u e m i c r o a t o l l s i s termed a microlagoon by Vasicek (1948, 56) and by Boyd e t a l . (1963).

Micro-lagoon i s used f o r t h e l a r g e r p a t c h r e e f s a t R a r o i a , f o r "pool a r e a s i n t h e r e e f p a t c h t o p s

...

a s a r u l e sand o r sediment f l o o r e d and a f o o t t o a metre deep" (Doty and Morrison 1954, 5 2 ) . Morrison (1954, 5 ) c u r i o u s l y u s e s micro-lagoon i n a t o t a l l y d i f f e r e n t s e n s e , a l s o a t R a r o i a , f o r " b r a c k i s h water lagoons

...

[ i n ] incomplete channels between i s l a n d s [ i . e . hoa] o r s m a l l embayments c l o s e t o t h e lagoon of t h e a t o l l , and more o r l e s s completely c u t o f f from t h e s a l t water of t h e lagoon by sand b a r r i e r s " ; o t h e r t e r m s , n o t a b l y b a r a c h o i s , a r e a v a i l a b l e f o r t h i s phenomenon (Bourne 1888, 4 4 2 ) , and M o r r i s o n ' s usage i s t h u s redundant a s w e l l a s confusing. M i c r o a t o l l l a g o o n i s used by G a r r e t t e t a l . (1971, 651) f o r t h e water up t o 4 m deep o v e r t h e wide sandy p l a i n of t h e i r misnamed m i c r o a t o l l r e e f s .

I n s p i t e of t h e p o p u l a r i t y of t h e term m i c r o a t o l l , t h e r e a r e few r e f e r e n c e s t o m i c r o b a r r i e r s

.

F a i r b r i d g e (1950, 345, f i g

.

4) a p p l i e d t h i s term t o a submerged l i n e a r r e e f 1500-2000 f t seaward from t h e main r e e f r i m on t h e s o u t h s i d e of P i c k e r s g i l l Reef, G r e a t B a r r i e r Reef;

" p a t c h e s o f growing c o r a l connect it w i t h t h e main r e e f , b u t deep, rounded p o o l s a r e l e f t between".

REFERENCES

Agassiz, A. 1895. A v i s i t t o t h e Bermudas i n March, 1894. B u l l . Mus. cwmp. 2001. Harvard C o l l . 26: 209-281.

Bourne, G. C. 1888. The a t o l l of Diego Garcia and t h e c o r a l formations of t h e Indian Ocean. P r o c . Roy. S o c . Lond. 43:

440-461.

Boyd, D. W . , IGornicker, L. S. and Rezak, R. 1963. C o r a l l i n e a l g a l m i c r o a t o l l s near Cozumel I s l a n d , Mexico. Univ. Wyoming D e p t . G e o l . C o n t r . G e o l . 2 ( 2 ) : 105-108; a b s t r a c t i n G e o l . S o c . Am.

S p e c . Paper 73: 120-121.

Braithwaite, C. J. R . , Taylor, J. D . , and Kennedy, W . J. 1973. The evolution of an a t o l l : t h e d e p o s i t i o n a l and e r o s i o n a l h i s t o r y of Aldabra. P h i l . T r a n s . R. S o c . Lond. B 266: 307-340.

Buddemeier, R. W . , Smith, S. V . , and Kinzie, R . A. 1975. Holocene windward r e e f - f l a t h i s t o r y , Enewetak A t o l l . B u l l . g e o l . S o c . Am.

86: 1581-1584.

Cary, L. R. 1931. S t u d i e s on t h e c o r a l r e e f s of T u t u i l a , American Samoa, with e s p e c i a l r e f e r e n c e t o t h e Alcyonaria. Papers T o r t u g a s

Lab. 27: 53-98.

Chamisso, A. von. 1821. Remarks and opinions of t h e n a t u r a l i s t of t h e expedition. I n 0. von Kotzebue: A v o y a g e o f d i s c w v e r y i n t o the S o u t h Sea and B e e r i n g ' s S t r a i t s , f o r the p u r y o s e o f e x p l o r i n g a n o r t h - e a s t p a s s a g e , u n d e r t a k e n i n the y e a r s 1 8 1 5-1 81 8 (London:

Longman, Hurst, Rees, Orme and Brown, 3 v o l s . ) , 11, 349-433; 111, 1-318.

Cloud, P. E . , Jr. 1952. Preliminary r e p o r t on geology and marine environments of Onotoa A t o l l , G i l b e r t I s l a n d s . A t o l l R e s . B u l l . 1 2 : 1-73.

Dana, J. D. 1849. G e o l o g y ( U n i t e d S t a t e s E x p l o r i n g E x p e d i t i o n . During the y e a r s 1 8 3 8 , 1 8 3 9 , 1 8 4 0 , 1 8 4 1 , 1 8 4 2 . Under the command o f C h a r l e s Wilkes, U.S.N. V o l . X ) . P h i l a d e l p h i a : C. Sherman. v i i i , 756 pp.

Dana, J. D. 1872. C o r a l s and c w r a l i s l a n d s . New York. English e d i t i o n , London: Sampson Low, Marston, Low and, S e a r l e (1875), 348 pp.

Darwin, C. R. 1842. T h e s t r u c t u r e and d i s t r i b u t i o n o f c o r a l r e e f s . London: Smith, Elder and Co. 214 pp.

David, T. W. Edgeworth and Sweet, G. 1904. The geology of Funafuti.

In The a t o l l o f F u n a f u t i (London: The Royal S o c i e t y ) , 61-124.

Davis, W. M. 1928. The c o r a l r e e f problem. Am. G e o g . S o c . S p e c . P u b . 9: 1-596.

Doty, M. S. and Morrison, J. P. E. 1954. I n t e r r e l a t i o n s h i p s o f t h e organisms o n R a r o i a a s i d e from man. A t o l l R e s . B u l l . 35: 1-61.

m e r y , K. O . , T r a c e y , J. I., J r . , and Ladd, H. S. 1954. Geology o f B i k i n i and nearby a t o l l s . U . S . G e o l . S u r v . P r o f . P a p e r 260-A:

1-265.

F a i r b r i d g e , R. W. 1950a. The geology and geomorphology of P o i n t Peron, Western A u s t r a l i a . J. R o y . S o c . W . A u s t r . 34: 35-72.

F a i r b r i d g e , R. W. 1950b. Recent and P l e i s t o c e n e c o r a l r e e f s o f A u s t r a l i a . J. G e o l . 58: 330-401.

F a i r b r i d g e , R. W. 1968. M i c r o a t o l l . I n R. W. F a i r b r i d g e : T h e E n c y c l o p e d i a o f G e o n w r p h o l o g y (New York: Reinhold Book C o r p . ) ,

701- 705.

F a i r b r i d g e , R. W. and T e i c h e r t , C. 1947. The r a m p a r t system a t Low Isles, 1928-45. R e p t . G t . B a r r . R e e f . Comm. 6: 1-16.

Finckh, A. E. 1904. Biology of t h e reef-forming organisms a t F u n a f u t i A t o l l . I n T h e a t o l l o f F u n a f u t i (London: The Royal S o c i e t y ) ,

125-150.

F i s h e l s o n , L. 1973. E c o l o g i c a l and b i o l o g i c a l phenomena i n f l u e n c i n g c o r a l - s p e c i e s c o m p o s i t i o n on ithe r e e f t a b l e s a t E i l a t (Gulf o f Aqaba, Red Sea)

.

^{Mar. B i o l}

. ^,

B e r l i n , 19: 183-196.

G a l t s o f f , P. H. 1933. P e a r l and Hermes R e e f , Hawaii, h y d r o g r a p h i c a l and b i o l o g i c a l o b s e r v a t i o n s . B u l l . B e r n i c e P . B i s h o p Mus. 107:

1-49.

G a r d i n e r , J. S. 1903. The Maldive and Laccadive Groups, w i t h n o t e s on o t h e r c o r a l f o r m a t i o n s i n t h e t l n d i a n Ocean. I n J. S. G a r d i n e r , ed. : T h e F a u n a a n d G e o g r a p h y o f the M a l d i v e a n d L a c c a d i v e

A r c h i p e l a g o e s (Cambridge: U n i v e r s i t y P r e s s ) , 1: 12-50, 146-183, 313-346, 376-423.

G a r d i n e r , J. S. 1931. C o r a l r e e f s a n d a t o l l s ' . London: Macmillan.

1 8 1 pp.

G a r r e t t , P. and Ducklow, H. 1975. C o r a l d i s e a s e s i n Bermuda. N a t u r e , L o n d . 253: 349-350.

G a r r e t t , P., Smith, D. L., Wilson, A. 0. and P a t r i q u i n , D. 1971.

Physiography, e c o l o g y , and s e d i m e n t s o f two Bermuda p a t c h r e e f s . J. G e o l . 79: 647-668.

Gui . l c h e r , A. 1971. Mayotte b a r r i e r r e e f and lagoon, Comoro I s l a n d s , as compared w i t h o t h e r b a r r i e r r e e f s , a t o l l s and lagoons i n t h e world. Symp. Zool. S o c . Lond. 28: 65-86.

Guppy, H. B. 1886. Notes on t h e c h a r a c t e r and mode of f o r m a t i o n of t h e c o r a l r e e f s of t h e Solomon I s l a n d s , b e i n g t h e r e s u l t s o f

o b s e r v a t i o n s made i n 1882-84, by H. B. Guppy, M.B., F.G.S., d u r i n g t h e s u r v e y i n g c r u i s e of H.M.S. Lark. P r o c . R o y . S o c . E d i n b . 13:

857-904.

Guppy, H. B. 1889. The Cocos-Keeling I s l a n d s . S c o t t . Geog. Mag. 5:

281-297, 457-474, 569-588.

Hoskin, C. M. 1963. Recent c a r b o n a t e s e d i m e n t a t i o n of Alacran Reef, Yucatan, Mexico. N a t . Acad. S c i . - N a t . R e s . Coun. Pub. 1089:

1- 160.

Iams, W. J . 1969. New methods of s t u d y i n g t h e growth r a t e s o f r e e f - b u i l d i n g organisms. S p e c . P u b l . Bermuda B i o l . Stn. R e s . 2:

65-76.

I l l i n g , L. V. 1954. Bahamian c a l c a r e o u s s a n d s . B u l l . Am. A s s . P e t r o l . G e o l . 38: 1-94.

Kinsey, D. W. and Dornrn, A. 1974. E f f e c t s o f f e r t i l i z a t i o n on a c o r a l r e e f environment

-

primary p r o d u c t i o n s t u d i e s . P r o c . 2nd I n t . C o r a l R e e f Symp. 1: 49-66.

Kornicker, L. S. and Boyd, D. W. 1962. Shallow-water geology and environments o f Alacran Reef complex, Campeche Bank, Mexico.

B u l l . Am. A s s . P e t r o l . G e o l . 46: 640-673.

Krempf, A . 1927. L a forme d e s r 6 c i f s c o r a l l i e n s e t l e r6gime d e s v e n t s a l t e r n a n t s . M&. T r a v . S e r v . OcBanogr. P e c h e I n d o c h i n e , 2:

1-33.

Kuenen, P. H. 1933. Geology of c o r a l r e e f s . S c i . R e p t s . S n e l l i u s Exped. Ned. E a s t I n d i e s , 5 ( 2 ) : 1-126.

L i s t e r , J. J. 1891. The geology of t h e Tonga I s l a n d s . Q u a r t . J. G e o l . S o c . Lond. 47: 590-617.

McNeil, F. S. 1954. Organic r e e f s and banks and a s s o c i a t e d d e t r i t a l sediments. Am. J. S c i . 252: 385-401.

Manton, S. M. 1935. ^. E c o l o g i c a l s u r v e y s of c o r a l r e e f s . S c i . R e p t . G t . B a r r . R e e f Exped. 1928-29, 3: 273-312.

M a r s h a l l , S. M. and O r r , A. P. 1931. S e d i m e n t a t i o n on Low I s l e s r e e f and i t s r e l a t i o n t o c o r a l growth. S c i . R e p t . G t . B a r r . R e e f

Exped. 1928-29, 1: 93-133.

Maxwell, W. G. H. 1968. A t l a s o f the G r e a t B a r r i e r R e e f . Amsterdam: E l s e v i e r . 258 pp.

Mergner, H. and S c h e e r , G. 1974. The p h y s i o g r a p h i c z o n a t i o n and t h e e c o l o g i c a l c o n d i t i o n s o f some s o u t h I n d i a n and Ceylon c o r a l r e e f s . P r o c . 2nd I n t . C o r a l R e e f Symp. 2: 3-30.

Moorhouse, F. W. 1936. The cyclone o f 1934 and i t s e f f e c t on Low Isles, w i t h s p e c i a l o b s e r v a t i o n s on P o r i t e s . R e p t . G t . B a r r . R e e f Comm. 4: 37-44.

Morrison, J. P. E . 1954. Animal ecology o f R a r o i a A t o l l , Tuamotus. I . E c o l o g i c a l n o t e s o n t h e mollusks and o t h e r animals o f R a r o i a . 11.

Notes o n t h e b i r d s o f R a r o i a . A t o l l R e s . B u l l . 34: 1-26.

Newell, N . D. 1954. E x p e d i t i o n t o R a r o i a , Tuamotus. A t o l l R e s . B u l l . 31: 1-23.

Newell, N. D. and Rigby, J. K. 1957. G e o l o g i c a l s t u d i e s o n t h e G r e a t Bahama Bank. S p e c . P u b l s

.

S o c . Econ

.

P a l a e o n t o l

.

^Miner.

^,

T u l s a , 5 : 15-72.

Newell, N. D . , Rigby, ^{J .} K . , Whiteman, A. J . , and B r a d l e y , ^{J .} S. 1951.

Shoal-water geology and environments, e a s t e r n Andros I s l a n d s , Bahamas. B u l l . Am. Mus. n a t . H i s t . 97: 1-30.

Pichon, M . 1964. C o n t r i b u t i o n

a

1 ' 6 t u d e d e l a & p a r t i t i o n d e s

~ a d r e p o r a i r e s s u r l e r e c i f d e T u l g a r . R e c . T r a v . S t a t . mar.

E n d o u m e - M a r s e i l l e , f a s c . h o r s - s g r i e , 2: 79-203.

Roy, K. J. 1970. Change i n b a t h y m e t r i c c o n f i g u r a t i o n , Kaneohe Bay, Oahu, 1882-1969. Hawaii I n s t i t u t e o f G e o p h y s i c s , R e p t . HIG-70-15, 26 PP-

S a f r i e l , U. N. 1974. Vermetid g a s t r o p o d s and i n t e r t i d a l r e e f s i n I s r a e l and Bermuda. S c i e n c e , N.Y. 186: 1113-1115.

S c h e e r , G. 1969. I n v e s t i g a t i o n s o f c o r a l r e e f s i n t h e Maldive I s l a n d s w i t h n o t e s on l a g o o n p a t c h r e e f s and t h e method of c o r a l s o c i o l o g y . A b s t r . Symp. C o r a l s and C o r a l R e e f s , Mandapam Camp.

S c h e e r , G. 1972. I n v e s t i g a t i o n s o f c o r a l r e e f s i n t h e Maldive I s l a n d s w i t h n o t e s on l a g o o n p a t c h r e e f s and t h e method of c o r a l s o c i o l o g y . P r o c . Symp. C o r a l s and C o r a l R e e f s 1 9 6 9 (Marine B i o l o g i c a l Assoc.

I n d i a ) : 87-120.

S c o f f i n , T. P. and S t o d d a r t , D. R . i n litt. N a t u r e and s i g n i f i c a n c e of m i c r o - a t o l l s . P h i l . T r a n s . R. S o c . Lond.

Semper, C. 1880. D i e n a t i l r l i c h e n E x i s t e n z b e d i n g u n g e n d e r T h i e r e . L e i p z i g . 2 v o l s .

Semper, C. 1899. T h e n a t u r a l c o n d i t i o n s o f existence a s t h e y a f f e c t a n i m a l l i f e . London: Kegan Paul, Trench, TrUbner and Co. 5 t h e d i t i o n . 472 pp. ( F i r s t English e d i t i o n 1881).

S o l l a s , W. J. 1904. Narrative of t h e expedition i n 1896. I n T h e

a t o l l o f F u n a f u t i (London: The Royal S o c i e t y )

,

1-28.

Spender, M. A. 1930. I s l a n d - r e e f s of t h e Queensland c o a s t . G e o g r l J.

76: 194-214, 273-297.

Stamp, L. D . , ed. 1961. A g l o s s a r y o f g e o g r a p h i c a l terms. London:

Longmans. 539 pp.

Stephenson, T. A . , Stephenson, A . , Tandy, G . , and Spender, M. A. 1931.

The s t r u c t u r e and ecology of Low I s l e s and o t h e r r e e f s . S c i . R e p t . G t . B a r r . R e e f Exped. 1928-29, 3: 17-112.

S t o d d a r t , D. R. 1969. Geomorphology of t h e Solomon I s l a n d s c o r a l r e e f s . P h i l . T r a n s . R o y . S o c . Lond. B 255: 355-382.

S t o d d a r t , D. R . , Davies, P. S., and Keith, A. C. 1966. Geomorphology of Addu A t o l l . A t o l l R e s . B u l l . 116: 13-41.

Tracey, J. I . , Jr., and Ladd, H. S. 1974. Quaternary h i s t o r y of Eniwetok and B i k i n i A t o l l s , Marshall I s l a n d s . P r o c . 2nd I n t .

C o r a l R e e f Symp. 2: 537-550.

Vasicek, M. 1948. Theorie o vzniku mikroatolu (Theories of t h e o r i g i n of m i c r o a t o l l s ) . S b o r n i k C e s k o s l o v e n s k e S p o l m o c t i 2001. 55:

50-58.

Wells, J. W. 1957. Coral r e e f s . Mem. G e o l . S o c . Am. 6 7 ( 1 ) : 609-631.

Wood-Jones, F. 1912. C o r a l and a t o l l s : a h i s t o r y and d e s c r i p t i o n o f the K e e l i n g - C o c o s I s l a n d s , w i t h a n a c c o u n t o f their fauna and f l o r a , and a d i s c u s s i o n o f the method o f d e v e l o p m e n t and t r a n s f o r m a t i o n o f

coral s t r u c t u r e s i n g e n e r a l . London: L. Reeve and Co. 392 pp.

Zaneveld, J. S. 1957. Micro-atobls i n t h e Netherlands A n t i l l e s . Rep.

Inter-Isl. Mar. B i o l . C o n f . (Univ. Pto Rico I n s t . M a r . B i o l . ) : 18-19.