ATOLL RESEARCH BULLETIN

ATOLL RESEARCH BULLETIN

136. Coral

Islands of

the

Western Indian

Oeean

Ed&& by D.

R.

S&dalars

ATOLL RESEAlPCH BU1,LETIN No. 136

CORAL ISLANDS OF THE WESTERN INDIAN OCEAN

E d i t e d by D . R . S t o d d a r t

I s s u e d by

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

August 2 8 , 1970

ACKNOWLEDGEMENT

The A t o l l Research B u l l e t i n i s i s s u e d by t h e Smithsonian I n s t i t u t i o n a s a p a r t o f i t s T r o p i c a l Biology Program. I t i s

co-sponsored by t h e Museum o f N a t u r a l H i s t o r y , t h e O f f i c e of Environ- mental S c i e n c e s , and t h e Smithsonian P r e s s . The P r e s s s u p p o r t s and handles p r o d u c t i o n and d i s t r i b u t i o n . The e d i t i n g i s done by t h e T r o p i c a l Biology s t a f f i n t h e Museum of N a t u r a l H i s t o r y .

The B u l l e t i n was founded and t h e f i r s t 117 numbers i s s u e d by t h e P a c i f i c Science Board, N a t i o n a l Academy o f S c i e n c e s , w i t h f i n a n c i a l s u p p o r t from t h e O f f i c e of Naval Research. I t s pages were l a r g e l y devoted t o r e p o r t s r e s u l t i n g from t h e P a c i f i c S c i e n c e Board's Coral A t o l l Program.

The s o l e r e s p o n s i b i l i t y f o r a l l s t a t e m e n t s made by a u t h o r s o f p a p e r s i n t h e A t o l l Research B u l l e t i n r e s t s w i t h them, and s t a t e m e n t s made i n t h e B u l l e t i n do n o t n e c e s s a r i l y r e p r e s e n t t h e views of t h e Smithsonian n o r t h o s e o f t h e e d i t o r s o f t h e B u l l e t i n .

Editors

F. R . Fosberg M . - H . S a c h e t

Smithsonian I n s t i t u t i o n Washington, D. C . 20560

D . R. S t o d d a r t

Department of Geography U n i v e r s i t y o f Cambridge Downing P l a c e

Cambridge, England

C. J . Bayne

Museum o f Zoology, U n i v e r s i t y o f Michigan, Ann Arbor, Michigan, U.S.A.

C. W. Benson

Department o f Zoology, U n i v e r s i t y o f Cambridge, Cambridge, England B. H. Cogan

Department o f Entomology, B r i t i s h Museum ( N a t u r a l H i s t o r y ) , London, S.W.7.

A. W . Diamond

C u l t e r t y F i e l d S t a t i o n , Newburgh, Aberdeenshire, S c o t l a n d F. R. Fosberg

Smithsonian I n s t i t u t i o n , Washington, D . C . , U.S.A.

J. F r a z i e r

Department o f Zoology, U n i v e r s i t y o f Oxford, Oxford, England P. Grubb

Department of Zoology, U n i v e r s i t y o f Ghana, Legon, Ghana A. Hutson

Department o f Entomology, B r i t i s h Museum ( N a t u r a l H i s t o r y ) , London, S.W.7.

J. F. G. Lionnet

Department of A g r i c u l t u r e , P o r t V i c t o r i a , M a h e ' , S e y c h e l l e s I . S. C . P a r k e r

Box 21199, N a i r o b i , Kenya

J.

F. Peake

Department o f Zoology, B r i t i s h Museum ( N a t u r a l H i s t o r y ) , London, S.W.7.

M . E . D . Poore

The Nature Conservancy, 19 Belgrave Square, London, England S. A. Renvoize

The Herbarium, Royal B o t a n i c Gardens, Kew, Richmond, S u r r e y , England

F. Staub

Royal Road, Curepipe, M a u r i t i u s D. R . S t o d d a r t

Department of Geography, U n i v e r s i t y of Cambridge, Cambridge, England

J . D . Taylor

Department o f Zoology, B r i t i s h Museum (Natural H i s t o r y ) , London, S.W.7.

Contents

I n t r o d u c t i o n

D. R . S t o d d a r t

Geography and ecology o f Farquhar A t o l l D. R . S t o d d a r t and M . E . D . Poore P l a n t s o f Farquhar A t o l l

F. R . Fosberg and S . A. Renvoize

An o l d r e c o r d o f a Blue Pigeon A l e c t r o e n a s s p e c i e s and s e a - b i r d s on Farquhar and Providence

D . R . S t o d d a r t and C . W . Benson Geography and ecology o f Cosmoledo A t o l l

C . J . Bayne, B . H . Cogan, A . W . Diamond, J . F r a z i e r , P . Grubb, A. Hutson, M. E . D.

Poore, D . R . S t o d d a r t , and J . D . T a y l o r P l a n t s of Cosmoledo A t o l l

F. R . Fosberg and S . A . Renvoize Land ( i n c l u d i n g s h o r e ) b i r d s o f Cosmoledo

C . W . Benson

Geography and ecology o f Astove

C . J . Bayne, B . H . Cogan, A. W . Diamond, J . F r a z i e r , P . Grubb, A . Hutson, M . E . D . Poore, D . R . S t o d d a r t and J . D . T a y l o r P l a n t s of Astove

F . R . Fosberg and S . A. Renvoize Note on t h e L e p i d o p t e r a o f Astove A t o l l

J . F. G . Lionnet

Land ( i n c l u d i n g s h o r e ) b i r d s o f Astove C . W . Benson

E c o l o g i c a l change and e f f e c t s o f phosphate mining on Assumption I s l a n d

D . R . S t o d d a r t , C . W . Benson, and J . F. Peake P l a n t s o f Assumption I s l a n d

F. R . Fosberg and S . A. Renvoize Geography and ecology o f Desroches

D . R . S t o d d a r t and M . E . D . Poore

Page

1 5 . P l a n t s of Desroches

F. R . Fosberg and S . A . Renvoize 16. Geography and ecology o f Remire

D . R . S t o d d a r t and M . E. D . Poore 1 7 . P l a n t s o f Remire (Eagle) I s l a n d , Amirantes

F. R . Fosberg and S. A. Renvoize 18. Geography and ecology o f A f r i c a n Banks

D . R . S t o d d a r t and M. E . D . Poore 19. P l a n t s of A f r i c a n Banks ( I l e s A f r i c a i n e s )

F. R . Fosberg and S . A. Renvoize

20. An i n t r o d u c t i o n of S t r e p t o p e l i a p i c t u r a t a i n t o t h e Amirantes

C . W . Benson

21. Geography and ecology o f Tromelin I s l a n d F. Staub

22. Some o r n i t h o l o g i c a l o b s e r v a t i o n s from t h e western I n d i a n Ocean

I . S . C . P a r k e r

Page 167

Appendix: Names o f I s l a n d s J . F. G . Lionnet

TABLES

Page 1

.

S c i e n t i f i c s t u d i e s a t Farquhar A t o l l

. . .

¹⁰

2

.

Marine f a u n a recorded from Farquhar A t o l l

. . .

18 3

.

I n s e c t s r e c o r d e d from Farquhar A t o l l by t h e

. . .

Percy Sladen Expedition

4

.

S c i e n t i f i c s t u d i e s a t Cosmoledo A t o l l

. . .

38 5

.

Mollusca c o l l e c t e d on Cosmoledo A t o l l . 1968

. . .

46 6

.

C r u s t a c e a (Decapoda) c o l l e c t e d on Cosmoledo

. . .

A t o l l . 1968 46

7

.

I n s e c t s r e c o r d e d from Cosmoledo A t o l l by t h e

Percy Sladen Expedition

. . .

47

. . .

8

.

S c i e n t i f i c s t u d i e s a t Astove 85

9

.

Mollusca c o l l e c t e d on Astove. 1968

. . .

91 10

.

C r u s t a c e a (Decapoda) c o l l e c t e d on Astove. 1968

. . .

92 11

.

I n s e c t s r e c o r d e d from Astove by t h e Percy

Sladen Expedition

. . .

⁹²

12

.

S c i e n t i f i c s t u d i e s a t Assumption I s l a n d

. . .

123 13

.

Monthly r a i n f a l l a t Assumption

. . .

126 14

.

I n s e c t s r e c o r d e d from Assumption by t h e Percy

Sladen E x p e d i t i o n

. . .

133 15

.

S c i e n t i f i c s t u d i e s a t Desroches

. . .

¹⁵⁷

16

.

I n s e c t s r e c o r d e d from Desroches by t h e Percy

S l a d e n E x p e d i t i o n

. . .

¹⁶⁰

17

.

S c i e n t i f i c s t u d i e s a t Remire

. . .

173 18

.

I n s e c t s r e c o r d e d from Remire by t h e Percy

. . .

Sladen Expedition 175

19

.

S c i e n t i f i c s t u d i e s a t A f r i c a n Banks

. . .

¹⁸⁸

20

.

M e t e o r o l o g i c a l d a t a . mean monthly figu.res 1955.1968.

Tromelin

. . .

²⁰⁰

v i

Page

21

.

F r e g a t a m i n o r c o l o n i e s o n T r o m e l i n

. . .

²⁰⁷

22

.

Breeding b i r d s and o c c a s i o n a l v i s i t o r s . Tromelin

. . .

208

FIGURES 1

.

The Southwest Indian Ocean

. . .

F r o n t i s p i e c e Page 2

.

F a r q u h a r A t o l l

. . .

8

3

.

Cosmoledo A t o l l

. . .

³⁹

4

.

The Aldabra Group

. . .

⁴⁰

5

.

^Astove

. . .

84

6

.

Assumption

. . .

122

7

.

^Desroches

. . .

¹⁵⁶

8

.

^Remire

. . .

¹⁷²

9

.

Ombrothermic diagram f o r Tromelin

. . .

198

10

.

Tromelin. showing d i s t r i b u t i o n o f b r e e d i n g b i r d c o l o n i e s

. . .

198

PLATES

Farquhar A t o l l ( f o l l o w i n g p . 26)

1. Scaevola community on h i g h dunes, n o r t h end of South I s l a n d 2 . Unvegetated b a r a c h o i s , lagoon s h o r e , n o r t h end of South I s l a n d 3 . Cay sandstone o u t c r o p on e r o d i n g lagoon s h o r e , North I s l a n d 4 . Scaevola and Casuarina on e r o d i n g seaward s h o r e , North I s l a n d 5 . Prograding lagoon shore w i t h Scaevola and C a s u a r i n a , North I s l a n d 6 . Conglomerate p l a t f o r m o u t c r o p p i n g on t h e s i d e s o f t h e channel

between t h e n o r t h e r n Manaha I s l a n d and North I s l a n d ; view towards t h e lagoon

7 . Open Casuarina woodland on o l d dunes, North I s l a n d

8 . Woodland of Cocos and C a s u a r i n a on o l d dunes, North I s l a n d ; n o t e t h e h u r r i c a n e damage t o coconuts

9 . Replanting of coconuts i n hurricane-damaged a r e a o f North I s l a n d Open woodland o f

-

Cocos w i t h F i m b r i s t y l i s on f l a t g r a v e l

North I s l a n d

s p r e a d ,

11. Coconut woodland with grove of wild C a r i c a papaya, n o r t h end of North I s l a n d

12-16. Sooty Terns and Noddies on G o e l e t t e I s l a n d . Note t h e low herb-mat v e g e t a t i o n , and t h e s c a r c i t y o f dwarf s h r u b s

17. Copra sheds a t S e t t l e m e n t , North I s l a n d

Assumption I s l a n d ( f o l l o w i n g p . 145)

18. Low champignon c l i f f s and perched beach, e a s t c o a s t , view towards t h e s o u t h

1 9 . Pocket beach i n t h e champignon c l i f f s , continuous with t h e h i g h e r perched beach; n o r t h o f t h e high dunes, e a s t c o a s t

20. Eroded i n n e r edge o f t h e r e e f f l a t where i t p a s s e s b e n e a t h t h e beach a t t h e f o o t o f t h e h i g h dunes, e a s t c o a s t

v i i i

21. T r a n s v e r s e e r o s i o n a l grooves i n t h e r e e f f l a t , backed by a rocky e r o s i o n ramp, beach, and h i g h dunes; e a s t c o a s t

Outer edge o f t h e r e e f f l a t n e a r t h e h i g h dunes, e a s t c o a s t Small dunes on t h e perched beach, which i s densely covered w i t h g r a s s e s ; e a s t c o a s t , l o o k i n g n o r t h

Clumps o f S u r i a n a maritima and s c a t t e r e d F i m b r i s t y l i s on t h e e r o d i n g seaward f a c e o f t h e h i g h e s t dune

Scaevola and F i m b r i s t y l i s on t h e h i g h dunes

View from t h e summit o f t h e h i g h e s t dune. with -- T o u r n e f o r t i a s c r u b , a c r o s s t h e low mixed s c r u b o f t h e c e n t r e o f Assumption. The

l i n e o f Casuarina t r e e s on t h e west s h o r e marks t h e S e t t l e m e n t The l e e s l o p e o f t h e h i g h e s t dune, w i t h T o u r n e f o r t i a and Scaevola T o u r n e f o r t i a and S u r i a n a forming t h e l i t t o r a l hedge on t h e

p r o g r a d i n g west c o a s t , view n o r t h from S e t t l e m e n t

S u r i a n a and Pemphis forming t h e l i t t o r a l hedge n e a r t h e n o r t h e r n end o f t h e west c o a s t

L e a f l e s s P i s o n i a i n t h e low mixed s c r u b i n t h e c e n t r e o f t h e i s land

F l a t p l a t i n almost devoid o f s o i l and v e g e t a t i o n , n o r t h e r n end o f t h e i s l a n d ; Ficus i n t h e foreground

-

Nephrolepis b i s e r r a t a i n a s o l u t i o n h o l e , n o r t h end

Agave, massive T e r m i n a l i a , and Cocos a t t h e s i t e o f t h e o l d s e t t l e m e n t ; n o t e t h e w a t e r t a n k b e h i n d t h e coconut

Labourers' h u t s a t S e t t l e m e n t ; compare w i t h t h e i l l u s t r a t i o n given o f s i m i l a r q u a r t e r s i n F r y e r (1910)

Guano r a i l w a y and sheds a t S e t t l e m e n t

Desroches ( f o l l o w i n g p.165)

3 6 . Scaevola and Casuarina on t h e s o u t h c o a s t n e a r P o i n t e Helene 37. S u r i a n a on t h e s o u t h c o a s t n e a r M u r a i l l e Bon Dieu

38. Massive beachrock n e a r t h e c e n t r e of t h e s o u t h c o a s t 39. Massive beachrock a t t h e southwest p o i n t

40. Scaevola and Cocos on t h e lagoon s h o r e a t S e t t l e m e n t

-

41. Mixed Cocos and Casuarina woodland n e a r La G'uigui

-

42. Labourers' q u a r t e r s a t S e t t l e m e n t , t h e p a t h f l a n k e d by

-

Cocos and Hymenocallis

43. L a b o u r e r ' s q u a r t e r s a t S e t t l e m e n t Tromelin ( f o l l o w i n g p . 209)

44.

--

S u l a s u l a r u b r i p e s : c h i c k w i t h "brown and white" p a r e n t s

45.

--

S u l a s u l a r u b r i p e s : c h i c k n e a r l y f l e d g e d t o "bro~m" j u v e n i l e form 46.

--

S u l a s u l a r u b r i p e s : "brown" j u v e n i l e

47.

--

S u l a s u l a r u b r i p e s : a d u l t "brown and white" form w i t h few w h i t e s c a p u l a r markings.

S u l a s u l a r u b r i p e s : a d u l t "brown and white" form w i t h back n e a r l y

--

white

49.

--

S u l a s u l a r u b r i p e s : a d u l t "white" form

50. S u l a d a c t y l a t r a melanops: p a r e n t s w i t h c h i c k 51. Tromelin Meteorological S t a t i o n

52. Male and f o u r females o f F r e g a t a minor w i t h Red-footed Booby i n f l i g h t

53. Nesting colony of F r e g a t a minor and S u l a s u l a r u b r i p e s n e a r

--

a i r s t r i p , with T o u r n e f o r t i a t h i c k e t s and herb-mat v e g e t a t i o n

F i g . 1. The Southwest I n d i a n Ocean

CORAL ISLANDS OF TIIE WESTERN INDIAN OCEAN

1 . INTRODUCTION D. R . S t o d d a r t

A s p a r t of t h e programme of r e s e a r c h on Aldabra A t o l l i n t h e southwest Indian Ocean, which began i n August 1967 (Stoddart 1967, 1969a), it h a s been p o s s i b l e f o r p a r t i e s from t h e Royal S o c i e t y Expedition t o Aldabra t o v i s i t o t h e r western Indian Ocean c o r a l i s l a n d s from time t o time. These v i s i t s , though b r i e f , have been important f o r two r e a s o n s . F i r s t , t h e arguments f o r t h e c o n s e r v a t i o n of Aldabra i t s e l f f o r s c i e n t i f i c r e s e a r c h r e s t e d , a t l e a s t i n p a r t , on a comparative a n a l y s i s of t h e e c o l o g i c a l s t a t u s of neighbouring i s l a n d s . Second, much of t h e a v a i l a b l e information on t h e s e i s l a n d s i s many decades o l d , and some have never been d e s c r i b e d . This

s e r i e s of r e p o r t s aims f i r s t , t h e r e f o r e , t o r e c o r d t h e new information obtained d u r i n g v i s i t s i n 1967 and 1968 t o seven such i s l a n d s , and second, t o p r o v i d e s u c c i n c t summaries and guides t o t h e l a r g e b u t s c a t t e r e d l i t e r a t u r e , much of i t taxonomic i n n a t u r e , b u t which c o n t a i n s o c c a s i o n a l r e f e r e n c e s t o them. I n t h i s way i t i s hoped t o provide convenient accounts of t h e s e i s l a n d s f o r t h e use of f u t u r e workers, and a l s o t o i n d i c a t e t o v i s i t i n g s c i e n t i s t s a t t h e Aldabra Research S t a t i o n t h e p o s s i b i l i t i e s f o r i n v e s t i g a t i o n o f p a r t i c u l a r problems o r p a r t i c u l a r groups elsewhere i n t h e western Indian Ocean.

A c e r t a i n amount of r e p e t i t i o n i n b i b l i o g r a p h i c a l l i s t s , acknowledge- ments e t c . , has been unavoidable t o maintain t h e independence of t h e c h a p t e r s on t h e d i f f e r e n t i s l a n d s .

The c o r a l i s l a n d s of t h e western I n d i a n Ocean (Figure 1) may be t a k e n t o comprise t h e following groups:

(a) t h e i s l a n d s of t h e Mozambique Channel, i n c l u d i n g Europa;

(b) t h e Aldabra group, i n c l u d i n g Aldabra, Assumption, Cosmoledo and Astove;

A t o l l Research B u l l e t i n No. 136: pp. 1-5, 1970.

(c) t h e Farquhar group, comprising Farquhar, S t P i e r r e and Providence;

(d) t h e Amirantes, i n c l u d i n g (from n o r t h t o s o u t h ) A f r i c a n Banks, Remire, D'Arros, S t Joseph, Desroches, Poivre, E t o i l e ,

Boudeuse, Marie-Louise, and Desnoeufs;

( e ) Bird and Dennis I s l a n d s , n o r t h e r n S e y c h e l l e s Bank;

( f ) Cargados C a r a j o s ;

(g) i s o l a t e d i s l a n d s , i n c l u d i n g G l o r i o s a , Agalega, Tromelin, Coetivy and Alphonse.

Most e a r l y n a v i g a t o r s completely n e g l e c t e d t h e c o r a l i s l a n d s i n t h e accounts o f t h e i r t r a v e l s . Thus Owen, who surveyed Farquhar and o t h e r i s l a n d s i n t h e 1820s, r e f e r r e d t o t h e i s l a n d s of t h e Amirantes simply a s "low, sandy, s t e r i l e , and a l t o g e t h e r i n s i g n i f i c a n t " (Owen, 1833, 11, 159), and n e i t h e r h e , n o r F a i r f a x Moresby, a f t e r whose s h i p s t h e Menai and Wizard i s l a n d s on Cosmoledo A t o l l a r e named, n o r

-

Wharton, who c a r r i e d out t h e f i r s t thorough hydrographic survey i n t h e 18705, pay much a t t e n t i o n t o i s l a n d form, v e g e t a t i o n o r animal l i f e . The f i r s t u s e f u l accounts a r e g e n e r a l l y t h o s e d a t e d from t h e p e r i o d 1890-1910, by Abbott, Dupont and o t h e r s . Two major e x p e d i t i o n s ,

i n H.M.S. A l e r t i n 1882, t o t h e Amirantes and G l o r i o s a , and by H.M.S.

S e a l a r k in=, t o most o f t h e western I n d i a n Ocean i s l a n d s , r e s u l t e d i n l a r g e c o l l e c t i o n s and many r e c o r d s s c a t t e r e d through a l a r g e

l i t e r a t u r e . While t h e c o l l e c t i o n s i n t o t a l were l a r g e , however, i n d i v i d u a l i s l a n d s were o f t e n r e p r e s e n t e d by s m a l l and i n a d e q u a t e c o l l e c t i o n s . Gardiner (1936, Gardiner and Cooper 1907) c o n t r i b u t e d b r i e f accounts of many i s l a n d s t o t h e Reports of t h e Percy Sladen T r u s t Expedition, and J . C . F. F r y e r (1910) wrote u s e f u l accounts of B i r d and Dennis I s l a n d s i n a d d i t i o n t o h i s work on t h e Aldabra group.

Apart from Vesey-FitzGerald's work i n t h e 19305, t h e most important subsequent i n v e s t i g a t i o n s have been t h o s e of Baker (1963) and P i g g o t t (1961, 1968), who v i s i t e d a l l of t h e B r i t i s h - a d m i n i s t e r e d i s l a n d s d u r i n g a g e o l o g i c a l and s o i l survey i n 1960, and of Gwynne, Wood and P a r k e r , who c o l l e c t e d p l a n t s and b i r d s d u r i n g a c r u i s e i n 1967 (Gwynne and Wood 1969). Summaries o f t h e e a r l i e r work on Assumption, Astove, G l o r i o s a , Cosmoledo, Farquhar, S t P i e r r e and Providence were p u b l i s h e d by S t o d d a r t (1967b).

The p r e s e n t s e r i e s of s t u d i e s i s based on v i s i t s by Royal S o c i e t y Expedition personnel t o Farquhar, Cosmoledo, Astove, Assumption,

Desroches, Remire, and A f r i c a n Banks. I n a d d i t i o n , t h e r e have been e x c e l l e n t r e c e n t r e p o r t s on Europa I s l a n d (Legendre 1966) and on Cargados Carajos Shoals (Staub and ~ u i h o 1968). Gibson-Hill (1952) summarised d a t a from Agalega, and Brygoo (1955) p u b l i s h e d o b s e r v a t i o n s on Tromelin. These western I n d i a n Ocean s t u d i e s a r e l i n k e d w i t h o t h e r s

i n t h e c e n t r a l I n d i a n Ocean, i n t h e s o u t h e r n Maldives ( S t o d d a r t 1966) and i n t h e Chagos Archipelago ( S t o d d a r t and T a y l o r , i n p r e p a r a t i o n ) . These p e r m i t some p r e l i m i n a r y g e n e r a l i s a t i o n s on r e g i o n a l v a r i a t i o n i n I n d i a n Ocean r e e f s and i s l a n d s ( S t o d d a r t 1969b).

Important gaps remain, however, even a t t h e l e v e l of t h e summary r e p o r t s p r e s e n t e d i n t h i s B u l l e t i n . Though l a r g e c o l l e c t i o n s of marine and t e r r e s t r i a l fauna were made a t Coetivy i n 1905, t h e r e i s no account o f t h i s i s l a n d a v a i l a b l e . There h a s been no s t u d y i n t h i s c e n t u r y of G l o r i o s a (though G u i l c h e r and o t h e r s (1965) g i v e a e r i a l p h o t o g r a p h s ) , i n s p i t e of i t s p r o b a b l e importance i n t h e c o l o n i s a t i o n of t h e Aldabra group from Malagasy. Apart from t h e t h r e e i s l a n d s d i s c u s s e d h e r e , t h e r e i s no account of t h e fauna and f l o r a of t h e Amirantes, and our knowledge o f Agalega i s v e r y p a t c h y . Tromelin has been among t h e l e a s t w e l l known o f a l l t h e s e i s l a n d s ; t h e

account i n c l u d e d h e r e (Staub 1970) f o l l o w s a v i s i t t o t h e i s l a n d i n 1968 by M . France Staub o f Curepipe, M a u r i t i u s .

I t i s , o f c o u r s e , u n f o r t u n a t e t h a t more comprehensive accounts were n o t compiled s e v e n t y y e a r s ago, f o r Coppinger, Abbott, Gardiner and o t h e r s were a b l e t o g i v e t a n t a l i s i n g r e f e r e n c e s t o i s l a n d f e a t u r e s t h e n l a r g e l y u n a l t e r e d by man. S i n c e t h a t t i m e t h e sandy i s l a n d s have been almost e n t i r e l y p l a n t e d w i t h coconuts, and t h e rocky i s l a n d s

g e n e r a l l y d e v a s t a t e d by s u r f a c e guano mining. The e f f e c t of t h e l a t t e r on i s l a n d ecology i s w e l l i l l u s t r a t e d by Assumption, though t h e c a s e of Remire s u g g e s t s t h a t a t l e a s t p a r t i a l r e c o v e r y i s p o s s i b l e o v e r a

p e r i o d of a few decades, b u t endemic s p e c i e s once e x t i n c t cannot be brought back. I t i s p o s s i b l e t h a t more i n f o r m a t i o n on t h e former

s t a t e of t h e s e i s l a n d s s t i l l e x i s t s i n m a n u s c r i p t form o r i n Government a r c h i v e s : we have, f o r example, been f o r t u n a t e t o have had t h e l o a n o f d i a r i e s and p a p e r s b e l o n g i n g t o M r H . A ' C . Bergne and S i r John Fryer, d a t i n g from 1900-1910, which c o n t a i n i m p o r t a n t i n f o r m a t i o n on t h e i s l a n d s t h e y v i s i t e d . There i s no doubt t h a t modern work can now i n many c a s e s o n l y r e c o r d t h e s t a t e o f i s l a n d e c o l o g i e s i n t e n s e l y d i s t u r b e d and modified by man, and w i t h t h e e x c e p t i o n o f marine l i f e it i s now d i f f i c u l t t o a t t e m p t t o r e c o n s t r u c t t h e s t a t e o f i s l a n d ecosystems b e f o r e human e x p l o i t a t i o n began.

The i s l a n d s t r e a t e d i n t h i s r e p o r t f a l l i n t o two main groups:

(a) e l e v a t e d r e e f - l i m e s t o n e i s l a n d s , i n c l u d i n g Cosmoledo, Astove and Assumption, which s h a r e many o f t h e c h a r a c t e r i s t i c s o f Aldabra; and

(b) sand cays on s e a - l e v e l r e e f s , i n c l u d i n g Farquhar, Desroches,

Remire and A f r i c a n Banks. They a l s o e x p e r i e n c e c o n s i d e r a b l e v a r i a t i o n i n r a i n f a l l , though r e c o r d s have n o t been k e p t on any o f them e x c e p t Assumption and Tromelin. I n t e r p o l a t i o n from known i s l a n d r e c o r d s

( S t o d d a r t 1969b) s u g g e s t s t h a t Cosmoledo, Astove and Assumption have 1000 mm o r l e s s p e r annum, Farquhar about 1200 mm, and Desroches, Remire and A f r i c a n Banks, i n t h e n o r t h e r n Amirantes, about 1500 mm.

Acknowledgements

S p e c i f i c acknowledgements and t h a n k s a r e given i n many i n d i v i d u a l papers i n t h i s B u l l e t i n , b u t I wish t o thank h e r e t h e f o l l o w i n g :

Captain C . R. K. Roe, D.S.C., R . N . , and t h e o f f i c e r s and crew of H.M.S. Vidal, f o r making t h e 1967 v i s i t t o Assumption p o s s i b l e ; and C a p t a i n M . i l l i a m s and Captain T. Phipps f o r t h e i r a i d w i t h M.F.R.V.

Manihine d u r i n g v i s i t s t o t h e o t h e r i s l a n d s i n 1968. The c o o p e r a t i o n o f M r B a s i l B e l l , D i r e c t o r of t h e East A f r i c a n Marine F i s h e r i e s Research Organization, Zanzibar, helped t o make t h e s e v i s i t s i n Manihine a

s u c c e s s .

The Lessees and Managers o f t h e i s l a n d s v i s i t e d , f o r t h e i r h o s p i t a l i t y and a s s i s t a n c e d u r i n g o u r s h o r t v i s i t s .

The Royal S o c i e t y of London, which i s sponsoring t h e Aldabra i n v e s t i g a t i o n s , and whose support t h u s made t h e s e v i s i t s p o s s i b l e .

The Frank M. Chapman Memorial Fund, whose g r a n t t o C . W . Benson enabled t h e March 1968 v i s i t t o Astove and Cosmoledo t o t a k e p l a c e .

M r J. A ' C . Bergne and Lady Joan F r y e r f o r t h e loan of manuscript r e c o r d s made by t h e l a t e M H. A ' C . r Bergne and t h e l a t e S i r John Fryer, r e s p e c t i v e l y ; and t h e L i b r a r i a n o f t h e Old I n d i a O f f i c e Library, f o r a c c e s s t o F a i r f a x Moresby's manuscripts.

References

Baker, B. H. 1963. Geology and m i n e r a l r e s o u r c e s o f t h e S e y c h e l l e s Archipelago. Mem. Geol. Surv. Kenya, 3: 1-140.

Brygoo, E . 1955. Observations s u r l e s o i s e a u x de Tromelin. N a t u r a l i s t e Malgache, 7: 209-214.

Fryer, J . C. F. 1910. Bird and Dennis I s l a n d s , S e y c h e l l e s . Trans.

Linn. Soc. London, s e r . 2, Zool., 14: 15-20.

Gardiner, J . S. 1936. The r e e f s o f t h e western Indian Ocean. I . Chagos Archipelago. 11. The Mascarene Region. Trans. Linn. Soc.

London, s e r . 2 , Zool., 19: 393-436.

Gardiner, J . S . , and Cooper, C . F. 1907. D e s c r i p t i o n of t h e Expedition, 11. Mauritius t o S e y c h e l l e s . T r a n s . Linn. Soc.

London, s e r . 2 , Zool., 12: 111-175.

Gibson-Hill, C . A. 1952. Notes on t h e b i r d s r e p o r t e d from t h e Agalega I s l a n d s , western I n d i a n Ocean. B u l l . R a f f l e s Mus. 24: 257-269.

G u i l c h e r , A . , B e r t h o i s , L . , Le Calvez, Y . , B a t t i s t i n i , R . , and C r o s n i e r , A. 1965. Les r 6 c i f s c o r a l l i e n s e t l e lagon de l ' t l e Mayotte

(Archipel des Comores, 0c6an I n d i e n )

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P a r i s : O f f i c e de l a Recherche S c i e n t i f i q u e e t Technique Outre-Mer, 1-210.

Gwynne, M. D . , and Wood, D. 1969. P l a n t s c o l l e c t e d on i s l a n d s i n t h e w e s t e r n I n d i a n Ocean d u r i n g a c m i s e of t h e M.F.R.V. "Manihine", S e p t . - O c t . 1967. A t o l l . Res. B u l l . 134: 1-15.

Legendre, R . 1966. Mission s c i e n t i f i q u e

i

l f i ' l e Europa. M&. Mus.

Nat. H i s t . Natur., N.S.,

s6r.

A, Zool., 41: 1-220.

Owen, W . F. W. 1833. N a r r a t i v e o f voyages t o e x p l o r e t h e s h o r e s of A f r i c a , Arabia and Madagascar; performed i n H.M. Ships Leven and B a r r a c o u t a . London, 2 v o l s .

P i g g o t t , C . J. 1961. A r e p o r t on a v i s i t t o t h e Outer I s l a n d s between October and November 1960. D i r e c t o r a t e o f Overseas Surveys, Land Resources D i v i s i o n , t y p e s c r i p t , 1-71.

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1968. A s o i l s u r v e y o f S e y c h e l l e s . D i r e c t b r a t e o f Overseas Surveys, Land Resources D i v i s i o n , Tech. B u l l . 2 : 1-89 Staub, F. 1970. Geography and ecology of Tromelin I s l a n d . A t o l l Res

B u l l . ( t h i s i s s u e ) .

S t a u b , F., and ~ u g h o , J . 1968. The Cargados C a r a j o s S h o a l s o r S t Brandon: r e s o u r c e s , a v i f a u n a and v e g e t a t i o n . P r o c . Roy. Soc.

A r t s S c i . M a u r i t i u s , 3 ( 1 ) : 7-46.

S t o d d a r t , D . R . . 1966. Reef s t u d i e s a t Addu A t o l l , Maldive I s l a n d s : p r e l i m i n a r y r e s u l t s o f an e x p e d i t i o n t o Addu A t o l l i n 1964. A t o l l Res. B u l l . 116: 1-122.

---

1967a. Ecology of Aldabra A t o l l , I n d i a n Ocean. A t o l l Res.

B u l l . 118: 1-141.

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1967b. Summary o f t h e ecology of c o r a l i s l a n d s n o r t h o f Madagascar ( e x c l u d i n g A l d a b r a ) . A t o l l Res. B u l l . 118: 53-61.

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1969a. R e t r o s p e c t and p r o s p e c t o f Aldabra r e s e a r c h . Nature, 221: 1004-1006.

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1969b. Regional v a r i a t i o n i n I n d i a n Ocean c o r a l r e e f s . Marine B i o l o g i c a l A s s o c i a t i o n o f I n d i a , Symposium on C o r a l s and C o r a l Reefs, i n p r e s s .

S t o d d a r t , D. R . , and T a y l o r , J . D . , e d i t o r s . I n p r e p a r a t i o n .

Geography and ecology o f Diego G a r c i a A t o l l , Chagos A r c h i p e l a g o . A t o l l Res. B u l l .

2. GEOGRAPHY AND ECOLOGY OF FARQIJHAR ATOLL D . R. S t o d d a r t and M. E . D . Poore

I n t r o d u c t i o n

Farquhar A t o l l ( l O O 1 l ' S , 51°07'E) l i e s 285 km n o r t h e a s t o f Madagascar and 1150 km from t h e c o a s t l i n e o f A f r i c a . I t i s roughly t r i a n g u l a r i n shape, with an a r e a o f 170 s q km. Apart from s m a l l sand cays on t h e n o r t h e r n r i m ( I l e s des ~ g p o s e ' s , du Milieu, Lapin) dry land i s confined t o t h e e a s t e r n o r windward s i d e . T o t a l l a n d a r e a , by p l a n i m e t r y from Figure 2, i s 7.5 s q km o r 4.4 p e r c e n t of t h e a r e a of t h e a t o l l .

The f i r s t c h a r t of Farquhar was made by Margaro i n 1776 and p u b l i s h e d , w i t h a d d i t i o n s by W . F. W. Owen i n 1824, a s Admiralty Chart 718 i n 1878. This c h a r t is v e r y rudimentary. The a t o l l was

surveyed by Cdr W . J . L . Miharton i n 1878, w i t h a l a r g e - s c a l e survey o f t h e lagoon e n t r a n c e by L t . J . T. A. White, and t h e s e s u r v e y s formed t h e b a s i s o f a r e v i s i o n o f Chart 718 i n 1879. Wharton's survey, w i t h some r e c e n t a d d i t i o n s , i s t h e b a s i s of p r e s e n t c h a r t s ; it i s d e t a i l e d only f o r t h e n o r t h e r n r i m and t h e e a s t e r n i s l a n d s . Figure 2 i s based on a i r photograph cover o f t h e a t o l l flown i n 1960, with t o p o g r a p h i c c o n t r o l and bathymetry from t h e Admiralty c h a r t : while r e e f f e a t u r e s a r e shown i n d e t a i l , t h i s map should n o t be used f o r n a v i g a t i o n a l purposes.

The f i r s t b i o l o g i c a l o b s e r v a t i o n s on r e c o r d a r e t h o s e o f F a i r f a x Moresby i n 1822, b u t t h e s e remained u n p u b l i s h e d . The Percy Sladen Expedition s p e n t t h r e e days on Farquhar i n 1905, when S t a n l e y Gardiner worked over North I s l a n d , e s p e c i a l l y t h e seaward r e e f , and t h e

entomologist Bainbrigge F l e t c h e r , o v e r South I s l a n d . The c o l l e c t i o n s made were small and heterogeneous; d e t e r m i n a t i o n s p u b l i s h e d f o r

v a r i o u s groups i n t h e Percy Sladen Expedition Reports a r e l i s t e d , with c i t a t i o n s , i n Table 1. Most a t t e n t i o n was given d u r i n g t h i s v i s i t t o t h e i n s e c t s , and Table 2 l i s t s t h e d e t e r m i n a t i o n s on i n s e c t s , by o r d e r s and f a m i l i e s , i n t h e E x p e d i t i o n R e p o r t s . C o l l e c t i o n s made i n some groups, such a s t h e c o r a l s , remain u n p u b l i s h e d ; o t h e r groups were n e g l e c t e d . Thus it i s d i f f i c u l t t o g a i n an impression o f t h e ecology o f Farquhar from t h e work o f t h e Percy Sladen team.

Apart from a v i s i t i n 1937 by Vesey-FitzGerald, who r e p o r t e d on t h e b i r d s (1940, 1941), l i t t l e f u r t h e r work was done on Farquhar u n t i l

A t o l l Research B u l l e t i n No. 136: pp. 7-26, 1970

Fig. 2 . Farquhar A t o l l . Data reproduced from BA Chart No. 718 w i t h t h e s a n c t i o n o f t h e C o n t r o l l e r , HM S t a t i o n e r y O f f i c e and o f t h e Hydrographer o f t h e Navy.

t h e 1960s. The a t o l l was v i s i t e d i n 1960 by t h e g e o l o g i s t B. H.

Baker and t h e agronomist C . J . P i g g o t t , and though no c o l l e c t i o n s were made s e v e r a l u s e f u l a c c o u n t s were p u b l i s h e d (Baker 1963, 80-85;

P i g g o t t 1968, 56-57; P i g g o t t , unpublished, 48-53). I n 1967 M . F . R . V . Manihine c a l l e d a t Farquhar w i t h a p a r t y c o l l e c t i n g f o r t h e N a t i o n a l Museum, N a i r o b i , and i n c l u d i n g I . S. C . P a r k e r , D . Wood and M . D.

Gwynne; b i r d s and p l a n t s were c o l l e c t e d (Gwynne and Wood 1969, P a r k e r 1970). On 19 September 1968 Manihine r e v i s i t e d Farquhar w i t h a Royal S o c i e t y p a r t y comprising T . S. W e s t o l l , M . E . D . Poore and D . R . S t o d d a r t . S t o d d a r t and Poore t r a v e r s e d North I s l a n d , I l e s Manahas, and t h e n o r t h e r n h a l f o f South I s l a n d , and v i s i t e d G o e l e t t e ; p l a n t s were c o l l e c t e d and o b s e r v a t i o n s made on b i r d s . I n s p i t e o f t h e b r e v i t y o f t h e s e v i s i t s , and of t h e o t h e r s l i s t e d i n Table 1, it i s p o s s i b l e t o g i v e some account of t h e ecology o f t h e a t o l l , and t o

i n d i c a t e a r e a s i n which more d e t a i l e d work i s r e q u i r e d .

Table 1. S c i e n t i f i c S t u d i e s a t Farquhar A t o l l

Date

- -

^Study

1504 Discovered by 3020 de Nova; named

a f t e r him.

1776 Charted by M. Margaro

1821 May L i e u t . Hay, schooner

-

E l i z a 1822 March 12 L i e u t . Hay, Wizard and

-

Menai 1822 J u l y 26 V i s i t by F a i r f a x Moresby, b i r d

n o t e s

Chart a d d i t i o n s by W . F. W . Owen;

renamed a f t e r S i r R . Farquhar, Governor of M a u r i t i u s

F u r t h e r c h a r t i n g by L t Hay French c h a r t by M . L i e u t a r d Hydrographic c h a r t by W. J . L . l a a r t o n

1905 S e p t . 28-

Oct. 2 Percy Sladen E x p e d i t i o n : J. S . Gardiner, C . F. Cooper, T. B.

F l e t c h e r

1937 L. D. E . F . Vesey-FitzGerald,

b i r d s t u d i e s , economic i n s e c t s 1956 W . T r a v i s , underwater and g e n e r a l

o b s e r v a t i o n s

1957 Dec. 7 W . D . Hartman, l a n d b i r d s 1960 S e p t . 26-

29 B. H. Baker (geology) and C . 3 . P i g g o t t ( s o i l s )

1961 S e p t . 28-

Oct. 3 P . 0 . Wiehe, p l a n t s

1967 Oct. 3 M . D . Gwynne, D. Wood, I . S. C . P a r k e r , c o l l e c t i o n s o f p l a n t s and b i r d s

1968 S e p t . 19 D. R . S t o d d a r t , M. E . D. Poore, T. S. Westoll, c o l l e c t i o n o f p l a n t s , o b s e r v a t i o n s of geomorphology and b i r d s

Reference

Moresby (1842) S t o d d a r t and Benson (1969)

Gardiner and Cooper (1907), Gardiner (1936)

T r a v i s (1959) Hartman (1958)

Baker (1963) P i g g o t t (1961, 1968)

Fosberg and Renvoize, t h i s i s s u e

P a r k e r (1970) ; Gwynne and Wood

(1969)

T h i s r e p o r t

Geomorphology Lagoon and r e e f s

Knowledge of t h e r e e f s and submarine topography comes e n t i r e l y from hydrographic surveys and a e r i a l photographs (Figure 2 ) , b u t i t i s c l e a r t h a t Farquhar lagoon i s one o f t h e most complex i n topography and presumably i n geomorphic h i s t o r y i n t h e world. Three main

d i v i s i o n s may be noted: (1) t h e main lagoon b a s i n , 17 km long and with a g r e a t e s t width of 7.5 km; ^{( 2 )} a t r i a n g u l a r a r e a on t h e s o u t h s i d e , extending 4.5 km southwards from t h e r i m of t h e main lagoon b a s i n ; and ( 3 ) a submerged spur a t t h e northwest corner, extending

f o r 7 km northwestwards with d e p t h s of 11-30 m .

The main lagoon b a s i n i s c r o s s e d by a s e r i e s of narrow continuous r i d g e s , up t o 5 km long, t r e n d i n g approximately NE-SW. A i r photographs suggest t h a t t h e s e a r e not a c t i v e r e e f s a t t h e p r e s e n t time. These r i d g e s d i v i d e t h e basin i n t o t h r e e p a r t s : a western p a r t w i t h a p p a r e n t l y smooth f l o o r a t depths of 10-15 m , with h a r d l y any r e e f k n o l l s ; a

c e n t r a l p a r t with very numerous k n o l l s and p a t c h e s , and depths

probably about 8-10

m;

and an e a s t e r n p a r t with r i d g e s and few k n o l l s , and depths of 4-11 m . The s o u t h e r n t r i a n g u l a r extension i s crowded with k n o l l s and patches, with deep h o l e s of up t o 16.5 m. The

s o u t h e r n r e e f f l a t h e r e i s wide, with much c o r a l growth around broad shallow e n t r a n c e s . Nothing i s known of t h e northwest e x t e n s i o n a p a r t from t h e bathymetry shown i n Figure 2 .

The asymmetry of t h e shallow f e a t u r e s of t h e a t o l l i s t h u s marked;

it i s emphasised f u r t h e r by t h e c h a r a c t e r o f t h e p e r i p h e r a l r e e f . The e a s t e r n r e e f f l a t i s rocky, s t r a i g h t , and t i d a l l y emergent; i t i s l a r g e l y covered with d e t r i t a l i s l a n d s . The r e e f on t h e south s i d e i s a p p a r e n t l y a c t i v e l y growing, and i t s f l a t i s low enough f o r c o r a l growth. The r e e f f l a t on t h e west and n o r t h s i d e s i s p o o r l y d e f i n e d , with only small patches r i s i n g t o i n t e r t i d a l l e v e l s . A i r photographs show t h a t t h e p e r i p h e r a l r e e f f l a t s , b o t h o f t h e main b a s i n and of t h e southern t r i a n g l e , t r u n c a t e s t r u c t u r e s w i t h i n t h e lagoon. Thus lagoonal r i d g e s n e a r Goelette and South I s l a n d p a s s i n t o r e e f f l a t d e p o s i t s , and i n t h e southern t r i a n g l e d e b r i s s h e e t s from t h e r e e f f r o n t a r e burying r e e f k n o l l s i n t h e back r e e f a r e a .

There i s only one e n t r a n c e t o t h e lagoon, a narrow channel 6-10 m deep n e a r t h e n o r t h p o i n t , though much water must e n t e r t h e lagoon over t h e windward r e e f f l a t s o u t h of G o e l e t t e and l e a v e over t h e leeward r e e f s .

Bottom topography seaward of t h e p e r i p h e r a l r e e f s i s a l s o unusual.

Gn t h e e a s t e r n s i d e depths of l e s s than 30 m a r e found between 1 and 2 . 5 km from t h e r e e f edge, though t h e f l o o r then f a l l s more s t e e p l y t o depths of hundreds of metres. Along t h e n o r t h c o a s t t h e zone l e s s than 30 m deep i s 1 km o r l e s s wide, though broadening a t t h e northwest p o i n t .

These f e a t u r e s a r e i m p o s s i b l e t o i n t e r p r e t w i t h o u t f i e l d i n v e s t i - g a t i o n , b u t t h e y probably r e s u l t from a complex h i s t o r y , p o s s i b l y i n v o l v i n g d i f f e r e n t i a l movement o r t i l t i n g o f t h e a t o l l i t s e l f . The c e n t r a l o v a l lagoon i s probably an o l d f e a t u r e , though i t s l i n e a r r i d g e s a r e uncommon i n a t o l l lagoons e l s e w h e r e . The s t r a i g h t windward r e e f appears t o be r e t r e a t i n g lagoonward, t r u n c a t i n g lagoon f e a t u r e s and l e a v i n g a s h e l f a t 20-30 m t o seaward. I t i s p o s s i b l e t h a t t h e s o u t h e r n t r i a n g u l a r r e e f a r e a i s a r e c e n t a d d i t i o n t o t h e a t o l l , perhaps formed by r e e f growth on a former submarine s p u r s i m i l a r t o t h a t now extending t o t h e n o r t h w e s t . The s h a r p d i s t i n c t i o n i n t h e main lagoon between r i d g e s , a p p a r e n t l y l a r g e l y r e e f l e s s , and t h e a d j a c e n t deeper f l o o r may r e s u l t from k a r s t e r o s i o n o f o l d r e e f r i d g e s d u r i n g P l e i s t o c e n e low s e a l e v e l s t a n d s .

There i s no i n f o r m a t i o n on t h e modern r e e f s . Gardiner (1936, 432-433) noted t h e absence of a b o u l d e r zone and f i s s u r e d ( a l g a l ) zone on t h e e a s t e r n r e e f f l a t , which h e c o r r e c t l y s t a t e d was a rock f l a t w i t h few c o r a l s . He d e s c r i b e d H e l i o p o r a and P o r i t e s i n t h e lagoon, t o g e t h e r w i t h much Cymodocea. Living r e e f s a r e c e r t a i n l y damaged by f r e q u e n t t r o p i c a l cyclones, and some e f f e c t s a r e d e s c r i b e d by T r a v i s (1959, 69-73).

I s l a n d s

The e a s t e r n r e e f f l a t has a width o f 1 - 1 . 5 km, and t h e i s l a n d s s t a n d i n g on it a r e of s i m p l e form and s t r u c t u r e . South I s l a n d , t h e

l a r g e s t , i s 5 . 7 km l o n g , 0.6-0.9 km wide, and h a s an a r e a o f 3.9 s q km.

The c r e s c e n t i c North I s l a n d measures 8 . 5 km i n l e n g t h a l o n g i t s a x i s , i s 0 . 2 - 1 km wide, and h a s an a r e a o f 3.2 s q km. Most of South I s l a n d i s formed o f dunes, both a c t i v e c o a s t a l dunes up t o

20 m h i g h ( P l a t e I ) , and o l d e r i n l a n d dunes forming a hummocky s u r f a c e . The lagoon s h o r e of South I s l a n d i s formed by a wide sand r i d g e , i n p l a c e s e n c l o s i n g i n f r e q u e n t l y - f l o o d e d u n v e g e t a t e d a r e a s ( P l a t e 2 ) ,

f l o o r e d with p o o r l y - s o r t e d sands and g r a v e l s , which resemble t h e b a r a c h o i s of t h e Chagos a t o l l s . On North I s l a n d t h e dunes a r e lower,

and a r e found i n t h e c e n t r e and on t h e lagoon s i d e o f t h e i s l a n d a s w e l l a s on t h e seaward s i d e . Beaches a r e g e n e r a l l y sandy, w i t h l o c a l beachrock on t h e lagoon s i d e up t o 1 m above low w a t e r l e v e l ( P l a t e 3 ) . Seaward beaches on North I s l a n d a r e e r o d i n g ( P l a t e 4 ) , w i t h r e s u l t i n g t r u n c a t i o n o f v e g e t a t i o n zones: dune f a c e s a r e a l s o e r o d i n g both on North I s l a n d and a t t h e n o r t h end of South I s l a n d . Lagoon beaches by c o n t r a s t a r e p r o g r a d i n g ( P l a t e 5 ) . The only c o b b l e beach seen was on t h e n o r t h s i d e o f South I s l a n d , f a c i n g t h e channel between it and t h e Manahas. Gravel i s found i n p l a c e s on t h e i s l a n d s u r f a c e s and on t h e f l o o r s of t h e South I s l a n d b a r a c h o i s , b u t i s n o t common.

The t h r e e s m a l l Manahas i s l a n d s a r e o f c o n s i d e r a b l e p h y s i o g r a p h i c i n t e r e s t . Each i s a cay of sand and g r a v e l , r e s t i n g on a p l a t f o r m o f cemented cay d e p o s i t s which e x t e n d s up t o 200 m seaward o f t h e i s l e t ( P l a t e 6 ) . The p l a t f o r m o u t c r o p s along t h e s i d e s o f channels between t h e i s l e t s , where it has a width of o n l y a few metres, and

resembles o u t c r o p s o f c l a s t i c r o c k s on t h e s i d e s o f s i m i l a r channels (hoa)

-

i n t h e Tuamotu a t o l l s . Such a conglomerate p l a t f o r m , which ^{i s} q u i t e d i s t i n c t from t h e i n t e r t i d a l r e e f p l a t f o r m , was n o t seen on t h e main i s l a n d s , except p a t c h i l y on t h e lagoon s h o r e o f North I s l a n d , but may be forming beneath them a s a cay s a n d s t o n e . The s u r f a c e of t h e Manahas conglomerate s t a n d s about 0.5 m above high w a t e r l e v e l , and i s f r e t t e d by s u b a e r i a l e r o s i o n .

G o e l e t t e i s a small f l a t f e a t u r e l e s s i s l a n d with seaward beaches of i m b r i c a t e cobbles; it c o n s i s t s of sand and g r a v e l s , p a r t l y

phosphatised (Baker 1963, 8 5 ) . I t has no beachrock. There a r e s e v e r a l small i s l e t s on t h e n o r t h e r n r e e f , b u t t h e y have n o t been v i s i t e d .

Gardiner (1936, 432) claimed t o f i n d "evidence i n i s o l a t e d masses o f rock on t h e o u t e r s i d e s o f t h e e n c i r c l i n g r e e f , and e s p e c i a l l y on t h e i s l e t s , o f an almost continuous o r q u i t e continuous r e e f t h a t stood up f o r 10 f e e t o r more above t h e w a t e r l e v e l , and formerly surrounded t h e whole bank, a p p a r e n t l y about covering t h e e x i s t i n g r e e f " . I f t h e s e f e a t u r e s e x i s t t h e y may be storm-cast r e e f - b l o c k s : no t r a c e o f them was seen i n 1968, though e l e v a t e d r e e f - r o c k . would be expected i f t h e h i s t o r y o f t h e a t o l l has been a s complex a s t h e lagoon bathymetry s u g g e s t s .

P i g g o t t (1968) d i s t i n g u i s h e s f o u r s o i l s e r i e s on t h e Farquhar i s l a n d s : (1) t h e Farquhar S e r i e s , developed on f i n e dune sands; (2) Shioya S e r i e s , on non-dune c a l c a r e o u s sands; (3) s m a l l a r e a s o f p h o s p h a t i c hardpan s o i l d e s c r i b e d a s Jemo S e r i e s , though d i f f e r i n g i n some r e s p e c t s from t h e type Jemo S e r i e s d e s c r i b e d by Fosberg (1954);

and (4) a s m a l l a r e a of S a l i n e Marsh on South I s l a n d . The p a r e n t m a t e r i a l s o f t h e Farquhar S e r i e s a r e r e l a t i v e l y homogeneous, f i n e r and more a n g u l a r than t h o s e of Shioya S e r i e s , and Farquhar S e r i e s s o i l s a r e g e n e r a l l y developed on r o l l i n g topography with a deep w a t e r t a b l e . Parent m a t e r i a l s o f Shioya S e r i e s range from sands t o g r a v e l s . Baker (1963) h a s given a n a l y s e s of guano and p h o s p h a t i c rock from P i g g o t t ' s Jemo S e r i e s .

T r o p i c a l cyclones a r e common on Farquhar, and major storms occurred i n 1893, 1926, 1950 and 1954. Apart from t h e i r e f f e c t s on r e e f s , t h e s e storms have l e d t o beach e r o s i o n , c u t t i n g back of dunes, and t h e m a n t l i n g of i s l a n d s u r f a c e s w i t h c o a r s e d e p o s i t s .

Vegetation

Though p l a n t s were c o l l e c t e d on Farquhar by F l e t c h e r d u r i n g t h e Percy Sladen E x p e d i t i o n i n 1905, no l i s t was e v e r p u b l i s h e d . The following paper by Fosberg and Renvoize d e s c r i b e s c o l l e c t i o n s made by Gwynne and Wood i n October 1967 and by S t o d d a r t and Poore i n

September 1968. The l a t t e r c o l l e c t i o n t o t a l l e d 62 s p e c i e s of f l o w e r i n g p l a n t s , one moss and one l i c h e n , t o which can be added t e n s p e c i e s o f flowering p l a n t s recorded a s s i g h t r e c o r d s o n l y . Gwynne and Wood

(1969) r e c o r d 47 s p e c i e s , i n c l u d i n g 16 s i g h t r e c o r d s .

Both f l o r a and v e g e t a t i o n d i f f e r markedly from t h o s e o f e l e v a t e d limestone i s l a n d s i n t h e Aldabra group, and resemble more t h o s e of t h e sand cays of t h e Amirantes and t h e c e n t r a l Indian Ocean. No r a i n f a l l r e c o r d s have been k e p t , b u t with probably 1200 mm/yr Farquhar i s c o n s i d e r a b l y w e t t e r than Aldabra and Asswnption. Both t h e r a i s e d limestone community and t h e mangrove community a r e absent on Farquhar.

The i s l a n d s a r e simple sand cays w i t h dunes, b u t t h e v e g e t a t i o n , though c h a r a c t e r i s t i c of such h a b i t a t s , i s complicated by a long h i s t o r y of human i n t e r f e r e n c e , w i t h t h e r e s u l t t h a t t h e r e i s a s t r o n g g r a d i e n t i n number of introduced s p e c i e s southwards from t h e s e t t l e m e n t on t h e North I s l a n d . The channel between North and South I s l a n d s forms a major break i n t h i s g r a d i e n t , and though both of t h e main i s l a n d s a r e l a r g e l y covered with coconuts, North I s l a n d has many more introduced s p e c i e s of herbs and g r a s s e s i n t h e ground l a y e r than h a s South.

Nesting s e a b i r d s a l s o i n f l u e n c e t h e v e g e t a t i o n , p a r t i c u l a r y on t h e s m a l l e r i s l a n d s . Farquhar i s a f f e c t e d by a major cyclone about once i n 25 y e a r s , when t h e l i t t o r a l v e g e t a t i o n and a l s o t h e t r e e s , e s p e c i a l l y t h e coconuts, a r e s u b j e c t t o major damage.

Nine v e g e t a t i o n t y p e s can be d i s t i n g u i s h e d on Farquhar on t h e b a s i s of our b r i e f reconnaissance i n 1968:

(1) Seaward beach without dunes: where t h e beach i s s t a b l e t h e r e i s a hedge of Scaevola, T o u r n e f o r t i a , Pemphis and S u r i a n a ; where t h e beach i s r e t r e a t i n g , i n l a n d s p e c i e s such a s Casuarina a r e found a t t h e beach c r e s t .

(2) Seaward c o a s t a l dunes: t h e s e a r e covered with a mosaic o f S u r i a n a , Scaevola and T o u r n e f o r t i a , with F i m b r i s t y l i s and P o r t u l a c a .

(3) Inland s t a b l e dunes : mainly under coconuts and Casuarina, with a ground cover of g r a s s e s ( P l a t e s 7 , 8 and 9 ) .

(4) Inland sand o r f i n e g r a v e l a r e a s , under coconuts o r Casuarina, w i t h c o n s i d e r a b l e d i v e r s i t y i n ground cover ( P l a t e 1 0 ) .

(5) Lagoon beach, mainly edged by Scaevola, S u r i a n a and Pemphis.

(6) Barachois, edged by Pemphis and S u r i a n a , with a s p a r s e i r r e g u l a r cover of g r a s s e s and sedges.

(7) Inland depressions with s t a n d i n g water o r wet ground. These a r e uncommon; one on North I s l a n d has a s o l i t a r y Rhizophora.

(8) Herb mat community dominated by Boerhavia and Achyranthes, found i n t h e t e r n - n e s t i n g a r e a on G o e l e t t e I s l a n d .

(9) Vegetation i n t h e main s e t t l e m e n t and a l s o a d j a c e n t t o

i n d i v i d u a l houses elsewhere, dominated by i n t r o d u c e d d e c o r a t i v e and c u l t i v a t e d p l a n t s .

North I s l a n d

The v e g e t a t i o n of North I s l a n d has been much a f f e c t e d by r e c e n t cyclones: t h e seaward beach has eroded, and many coconuts and Casuarina t r e e s have been broken i n l a n d . The main v e g e t a t i o n t y p e i s coconut woodland i n t h e f l a t t e r i n l a n d a r e a s . Apart from Casuarina and,

e s p e c i a l l y i n t h e n o r t h , wild C a r i c a papaya ( P l a t e l l ) , few o t h e r t r e e s

a r e p r e s e n t , and t h o s e which a r e found a r e c o n c e n t r a t e d n e a r t h e lagoon shork beach hedge. They i n c l u d e Cordia subcordata, a Ficus, and Hernandia sonora, none of them common; Guettarda s p e c i o s a and Thespesia populnea were n o t s e e n . According t o P i g g o t t (1968, 36) w i l d Carica i s an i n d i c a t o r of phosphatic s o i l s , and groves of t h i s s p e c i e s were erowing wild on ~ o E t h I s l a n d a s e a r l v as-1905 (Gardiner

&d Cooper 1967, 1 4 i ) .

The sward beneath t h e coconuts i s extremely v a r i a b l e , more e s p e c i a l l y i n t h e n o r t h where it i s c l e a r l y f r e a u e n t l v c u t . In a d h i t i o n t o g r a s s e s (Cenchrus e c h i n a t u s ,

itar aria

h o r i z o n t a l i s , Stenotaphrum dimidiatum, Dactyloctenium aegyptium, C h l o r i s b a r b a t a ) and sedges ( F i m b r i s t y l i s cymosa, Cyperus dubius, Cyperus l i g u l a r i s ) , and t h e v i n e Cassytha, t h e r e a r e more than twenty s p e c i e s o f flowering p l a n t s p r e s e n t . Those c o l l e c t e d i n c l u d e :

Ipomoea t u b a Kalanchoe p i n n a t a Laportea a e s t u a n s Launaea i n t y b a c e a Lippia n o d i f l o r a

Parthenium hysterophorus P a s s i f l o r a suberosa Phy l l a n t h u s amarus

Phyllanthus maderaspatensis P o r t u l a c a o l e r a c e a

S i d a c f . p a r v i f o l i a

-

S t a c h y t a r p h e t a jamaicensis S t r i g a a s i a t i c a

T r i b u l u s c i s t o i d e s Turnera u l m i f o l i a Vernonia c i n e r e a

Turnera i s p a r t i c u l a r l y conspicuous i n many p l a c e s , b u t o f t e n t h e r e i s a v e r y d i v e r s e assemblage w i t h no s i n g l e dominant. The f e r n

Nephrolepis b i s e r r a t a i s p r e s e n t and l o c a l l y abundant on t h e ground.

The coconuts a r e g e n e r a l l y 10-12 m t a l l . I n t h e middle of t h e i s l a n d many a r e snapped o f f and crownless ( P l a t e 8 ) . Newly p l a n t e d coconuts towards t h e s o u t h e r n end a r e 2-3 m t a l l . Mature Casuarina t r e e s throughout t h e i s l a n d r e a c h 20 m i n h e i g h t .

The seaward beach on North I s l a n d i s sandy and r e t r e a t i n g ( P l a t e 4 ) . Broken, sometimes dead, j u v e n i l e Casuarina l i n e much of t h e beach c r e s t , with a zone of s p i n d l y Scaevola t a c c a d a t o landward. Pemphis i s a l s o found on t h e seaward beach. The ground under t h e shrubs i s o f t e n b a r e , but T r i u m f e t t a procumbens was c o l l e c t e d on t h e beach i t s e l f . The lagoon shore i s prograding, with a dense hedge of Scaevola taccada and S u r i a n a maritima, and o c c a s i o n a l t r e e s of

--

Casuarina and Cordia.

Dunes c a r r y a d i s t i n c t i v e v e g e t a t i o n . On a c t i v e dunes, a s a t t h e southern t i p of t h e i s l a n d , t h e r e i s a shrub l a y e r o f bushy

Scaevola taccada 1 . 5 m high, w i t h a l a r g e l y b a r e ground s u r f a c e d o t t e d w i t h r o s e t t e s of F i m b r i s t y l i s cymosa and E r a g r o s t i s : t h e ground h e r e

i s being eroded by wind and t h e sedges and g r a s s e s s t a n d on small

p i n n a c l e s . Non-active dunes a r e common o v e r t h e i s l a n d and c a r r y mature Casuarina woodland with a mixed ground v e g e t a t i o n .

One small marshy a r e a i n t h e c e n t r e o f t h e i s l a n d c o n t a i n s a s o l i t a r y t a l l Rhizophora, t h e only mangrove seen on Farquhar, with a dense ground cover o f Stenotaphrum.

The main s e t t l e m e n t a t t h e n o r t h end o f North I s l a n d c o n t a i n s s e v e r a l t r e e s n o t seen elsewhere, i n a d d i t i o n t o t a l l Casuarina and Hernandia s o n o r a . These i n c l u d e O c h r o s i a o p p o s i t i f o l i a , Moringa o l e i f e r a , T e r m i n a l i a c a t a p p a , Calophyllum inophyllum, and Tabebuia p a l l i d a , t h e l a s t a New World d e c o r a t i v e . C u l t i v a t e d p l a n t s

L f economic v a l u e i n c l u d e Gossypium h i r s u t u m , Agave, G s a , Ricinus communis, v a r i o u s c u c u r b i t s , and maize; d e c o r a t i v e s i n c l u d e a r e d - f l o w e r e d - Opuntia, c a t h a r a n t h u s r o s e u s , Bidens s u l p h u r e a , i-ieliotropium indicum, Solanum c f , melongena, Malvastrum coromandelianum, G a i l l a r d i a l a n c e o l a t a and Zinnia e l e g a n s . The whole a r e a o f t h e s e t t l e m e n t h a s t h e appearance o f long-continued human o c c u p a t i o n and a l t e r a t i o n . Manaha I s l a n d s

These t h r e e s m a l l i s l e t s between North and South I s l a n d s a r e covered w i t h a t a l l woodland of

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Cocos and Casuarina. Each h a s a l i t t o r a l hedge of T o u r n e f o r t i a a r g e n t e a , Scaevola t a c c a d a and S u r i a n a maritima. The eround v e e e t a t i o n b e n e a t h t h e coconuts c o n s i s t s of _{" "}

abundant v i n e s o f Ipomoea t u b a , clumps o f F i m b r i s t y l i s cymosa, and l i t t l e e l s e . The c o n t r a s t w i t h t h e d i v e r s i t y of similar ground v e g e t a t i o n on North I s l a n d i s very s t r i k i n g .

South I s l a n d

Like North I s l a n d , South I s l a n d h a s a small s e t t l e m e n t , n o t permanently occupied, a t i t s n o r t h e r n end; a l a r g e p a r t of t h e

i s l a n d i s covered with dunes; and most of t h e r e s t by coconut o r Casuarina woodland. I n t h e coconut woodland few o t h e r t r e e s a r e p r e s e n t ( r a r e Hernandia sonora and Cordia s u b c o r d a t a ) and t h e r e a r e few s h r u b s . The ground cover i s s i m i l a r t o t h a t under coconuts on North I s l a n d , b u t fewer s p e c i e s a r e p r e s e n t . Grasses i n c l u d e

E r a g r o s t i s s p . , Cenchrus e c h i n a t u s , and Dactyloctenium aegyptium; t h e sedges F i m b r i s t y l i s cymosa and CE l i g u l a r i s . Other f l o w e r i n g p l a n t s n o t e d i n t h e ground l a y e r i n c l u d e :

Achyranthcs as= P h y l l a n t h u s anlarus Boerhavia d i F f u s a

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^{. .}

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P o r t u l a c a c f . a u s t r a la f i l i f o r m i s - S i d a s p .

A s i n g l e bryophyte, c o l l e c t e d on t h e s u r f a c e of o l d dunes i n heavy shade, can o n l y be determined as

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Brywn s p . o r P o h l i a s p . by C . C . Townsend.

The seaward dunes a r e covered w i t h a dense growth o f S c a e v o l a t a c c a d a , w i t h S u r i a n a maritima and some T o u r n e f o r t i a a r g e n t e a . The

lagoon beach i s l i n e d mainly w i t h Scaevola and S u r i a n a , and t h e long i n l e t s o r b a r a c h o i s by S u r i a n a and Pemphis a c i d u l a . The l i c h e n Usnea was c o l l e c t e d from S u r i a n a on t h e margins of one o f t h e b a r a c h o i s .

The s m a l l s e t t l e m e n t h a s i n t r o d u c e d t r e e s , p a r t i c u l a r l y Moringa o l e i f e r a b u t a l s o i n c l u d i n g a s i n g l e young B a r r i n g t o n i a a s i a t i c a . Musa s p . , R i c i n u s communis and Amaranthus dubius a r e c u l t i v a t e d , and

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t h e d e c o r a t i v e s i n c l u d e M i r a b i l i s j a l a p a and G a i l l a r d i a l a n c e o l a t a .

G o e l e t t e I s l a n d

The t e r n - b r e e d i n g i s l a n d o f G o e l e t t e i s almost devoid of t r e e s (one Cocos and one Casuarina, b o t h s m a l l and s i c k l y ) and s h r u b s

( s o m e l o w ~ u r i a n a maritima and T o u r n e f o r t i a a r g e n t e a on t h e n o r t h w e s t s h o r e ) . Almost t h e whole i s l a n d i s covered with a low mat o f Ipomoea p e s - c a p r a e v i n e s , t h e sedges F i m b r i s t y l i s cymosa and Cyperus l i g u l a r i s ,

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and e s p e c i a l l y Boerhavia d i f f u s a and Achyranthes a s p e r a , t h e l a t t e r forming t h e t a l l e s t v e g e t a t i o n a p a r t from t h e r a r e t r e e s and s h r u b s . No s p e c i e s n o t p r e s e n t elsewhere on t h e a t o l l were found on G o e l e t t e , b u t t h e absence o f S t a c h y t a r p h e t a j a m a i c e n s i s , dominant i n s i m i l a r b i r d c o l o n i e s on Desnoeufs, Amirantes (Ridley and Percy 1 9 5 5 ) , and p r e s e n t on North I s l a n d , may be n o t e d .

Fauna o t h e r t h a n B i r d s

Both t h e l a n d and marine f a u n a o f Farquhar a r e v e r y i n a d e q u a t e l y known, f o r a p a r t from G a r d i n e r ' s p a r t y i n 1905 no a t t e n t i o n h a s been p a i d t o any group except t h e b i r d s . G a r d i n e r ' s own c o l l e c t i o n s were

small by comparison with t h o s e h e made on o t h e r i s l a n d s d u r i n g t h e Percy Sladen E x p e d i t i o n . A s i n g l e marine a l g a i s recorded (Gepp and Gepp 1909), b u t t h e c o l l e c t i o n s o f marine fauna, o t h e r t h a n p e l a g i c forms, a r e v e r y s m a l l (Table 2 ) . G a r d i n e r and Cooper (1907, 144-145) d e s c r i b e d t h e Green T u r t l e n e s t i n g on Farquhar, and i t s t i l l does s o . According t o Rothschild (1915) t h e Giant Land T o r t o i s e Geochelone g i g a n t e a f o r m e r l y e x i s t e d on Farquhar b u t h a s become e x t i n c t . No

evidence f o r t h i s s t a t e m e n t i s k n o w n , , e i t h e r h i s t o r i c a l l y o r i n t h e f o s s i l r e c o r d . However, two Giant T o r t o i s e s from Aldabra a r e p r e s e n t on North I s l a n d : one of t h e s e was s e e n i n 1968, i n t h e coconut

woodland n e a r t h e s o u t h end o f t h e i s l a n d , and i s c o n s i d e r a b l y l a r g e r t h a n any t o r t o i s e now l i v i n g on Aldabra, presumably i n response t o t h e w e t t e r c l i m a t e , r i c h e r v e g e t a t i o n , and absence o f c o m p e t i t i o n .

Boulenger (1909) recorded two r e p t i l e s , a Hemidactylus and a Phelsuma, b u t n e i t h e r was seen i n 1968. Two c r a b s (Cardisoma, Coenobita) a r e

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Table 2. Marine Fauna r e c o r d e d from Farquhar A t o l l

Group Number o f s p e c i e s Reference

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C o e l e n t e r a t a Hydroids Siphonophorae Medusae

A l c y o n a r i a Annelida P o l y c h a e t a Echinodermat a

C r u s t a c e a Decapoda Anomura Brachyura Stomatopoda

Mollusca Gastropoda

Pteropoda Heteropoda

J a r v i s (1922) Browne (1926) Browne (1916) Thomson and Mackinnon (1910)

P o t t s (1910) B e l l (1909) L a u r i e (1926), B o r r a d a i l e (1907) B o r r a d a i l e (1907), Rathbun (1911) T a t t e r s a l l (1912) M e l v i l l (1909) Tesch (1910) Tesch (1910)

r e c o r d e d by B o r r a d a i l e (1907), and n i n e s p e c i e s o f Arachnida (Neumann 1907, Hirst 1 9 1 1 ) . There a r e no n a t i v e mammals. Bainbrigge F l e t c h e r c o l l e c t e d i n s e c t s i n 1905, and t h i s accounts f o r t h e 66 s p e c i e s o f i n s e c t s r e c o r d e d i n t h e Percy Sladen Reports: c i t a t i o n s o f Farquhar m a t e r i a l i n t h e s e Reports a r e keyed i n Table 3 .

Table 3 . I n s e c t s r e c o r d e d from Farquhar A t o l l by t h e Percy Sladen Expedition

Group Apterygota O r t h o p t e r a Dermaptera Hemiptera Neuroptera Lepidoptera C o l e o p t e r a

Hymenoptera

D i p t e r a

Number of Speci-es Reference

C a r p e n t e r (1916) B o l i v a r (1912, 1924) Burr (1910)

D i s t a n t (1909, 1913), Green (1907)

Needham (1913)

F l e t c h e r (1910), F r y e r (1912), Meyrick (1911) Arrow (1922), Champion

(1914), F l e u t