ATOLL RESEARCH BULLETIN NO. 309 THE DECAPOD REPTANTIA AND STOMATOPOD CRUSTACEANS OF A TYPICAL HIGH ISLAND CORAL REEF COMPLEX IN FRENCH POLYNESIA (TIAHURA, MOOREA ISLAND): ZONATION, COMMUNITY COMPOSITION AND TROPHIC STRUCTURE BY MARIO MONTEFORTE ISSUED BY NATIONAL MUSEUM OF NATURAL HISTORY SMITHSONIAN INSTITUTION WASHINGTON, DL., U.S.A. October 1987 THE DECAPOD REPTANTIA AND STOMATOPOD CRUSTACEANS OF A TYPICAL HIGH ISLAND CORAL REEF COMPLEX IN FRENCH POLYNESIA (TIAHURA, MOOREA ISLAND): ZONATION, COMMUNITY COMPOSITION AND TROPHIC STRUCTURE. BY MARIO MONTEFORTE flksttdact : In a typica l High Island coral reef comple;: of French Polynesia ( t r ansec t of Tiahura, tloorea Island, Society Archipelago?, 73 species of decapod Reptant i a and stomatopod crustaceans were col lec ted . Dver 9 ; ta t ions local i sed along the t r a n s x t , 3 d i f f e r en t un i t s of hard coral subs t r a t e of si tnilar volume (about 17 l i t r e s each) , were sampled a t each s t a t i on . The r e s u l t s a r e discussed from two aspects : the f i r s t shows tha t a t l e a s t 50 carcinologic species occur within t he cavi tary biatopes ; lb species (na in ly Xanthid c r abs ) , represent more than 901 af a l l col lec- ted individuals. Host of the dominant species a r e widely d i s t r i bu ted a!ong the t ransect (Chihro~ dieiin brxata, Ptiod jt~s eugi!, hha~~iiidgs inntegerrinis, Ghhhea g d e a t a ) , and 1 ocal 1 y, some others ar E numerical 1 y i wpor t an t ( C t h r o d i h i l s h g y i s s i g a , Nhboeiigqnus globhqus, Dajrp epridta, h y p i j g s uquiau~s, e t c . ) . The second aspfc t concerns the r epa r t i t i on of species i n t he d i f f e r en t biotopes i n r e l a t i on t o t h e i r feeding habi ts . Eased on the functional morphclogy of chelipeds, mouth-parts and g a s t r i c p i l l , and on gut rontent analysi;, the species were placed i n t o 5 HORPHD- LOGIC 6R3UFS : i i ! ter-suspensian feeders , asnivo;es/herSi v o m , or~nivoreslcarnivores, generalised otinivores and predators. The feeding h a b i t s and the d i s t r i buticn pat tern of abundant species suggest t ha t t rophic and hab i t a t p a r t i t i m i n g nay e x i s t . The pr~dominant species show e i the r d i f f e r en t nu t r i t i ona l modes, or inhabi t d i f f e r en t areas and/or biotopes. Dis t r ibut ian pa t t e rns cf the morphologic groups i ? t he d i f f e r en t substrate; a r e proposed, and schew; of in terspeci f i c re la t ion; a r e anal ysed. INTRODUCTION. In French Polynesia, studies concerning the carci no- logic fauna have essentially dealt with systematics and biogeography of the decapod Reptantia (Jacquinot & Lucas, 1853 ; Milne-Edwards, 1861-1904 ; Forest & Guinot, 1961, 1962 ; SerPne, 1972 ; Yaldwin, 1972 ; Griffin & Yaldwin, 1977). The few biological and ecological studies on these crustaceans are 1 imi ted to commercial and edible species (Guinot, 1967 George, 1972, 1974), as we1 1 as to species associated to madreporian corals (Kropp & Birkeland, 1981; Odinetz, 1983). Ecole Pratique des Hautes Etudes. Laboratoire de Biologie Marine et Malacologie. 55, Rue Buffon. 75005, Paris. France. Present adress : Centro de Investigaciones Biologicas. POB. 128. La Pat, B.C.S. Mexico. The t r a n s e c t o f T i a h u r a (Moorea I s l a n d ) , i s a t y p i c a l H i g h I s l a n d c o r a l r e e f complex ( S a l v a t , e t a l . , 1972) . As such, many s t u d i e s have been c a r r i e d o u t t h e r e (Anony- mous, 1977) . However, t h e on1 y e c o l o g i c a l r e s e a r c h on decapod c rus taceans d e a l s w i t h s p e c i e s o f t h e c r y p t o f auna (Peyrot-Clausade, 1977b ; M o n t e f o r t e , 1984a, b ) , t h e "pe- t i t e faune" a s s o c i a t e d t o a l g a e (Naim, 1980a), and t h e c r u s t a c e a n s a s s o c i a t e d w i t h p o c i 1 l o p o r i d c o r a l s (Od ine tz , 1983) . I n T iahura , a l t h o u g h c r u s t a c e a n s do n o t account f o r a s l a r g e a number o f s p e c i e s as m o l l u s c s and f i s h e s , t h e i r r e l a t i v e abundance must n o t be underes t ima ted : Odum & Odum ( l ? S S ) , and H i a t t & S t r a s b u r g (1960) , p o i n t e d o u t t h a t c r u s t a c e a n s r e p r e s e n t a v e r y i m p o r t a n t l i n k i n t h e energy t r a n s f e r f rom p roducers and l o w - l e v e l consu- mers t o h i g h e r consumers i n c o r a l r e e f s , and t h e l a r v a l i n p u t o f t h e s e s p e c i e s t o t h e water i s a l s o known t o be v e r y r i c h . The impor tance o f c a v i t a r y c r u s t a c e a n s i n c o r a l r e e f s has been s t u d i e d b y Gar th (1974) and Peyrot-Clausade (1977a, b ) , b u t t h e i r t r o p h i c r o l e w i t h i n b e n t h i c communi- t i e s i s n o t w e l l known. Feeding h a b i t s o f c r u s t a c e a n s have been s t u d i e d f r o m morpho log ic and/or e m p i r i c a l ob- s e r v a t i o n s (Or ton , 1927 ; N i c o l , 1932 ; Scha fe r , 1954 ; E b l i n g , e t a l . , 1964 ; Muntz, e t a l . , 1975 ; Warner, 1977 Z i p s e r & Vermei j, 1978 ; Kunze & Anderson, 1979 ; Kropp, 1981 ; R h e i n a l l t & Hughes, 1985 ; R h e i n a l l t , 1986 ; S k i l l e t e r & Anderson, 1986) . Works on t r o p h i c r e l a t i o n s i n n a t u r e a r e few and i s o l a t e d ; most o f them s t u d i e d t h e c rus taceans a s s o c i a t e d w i t h s a b e l l a r i i d r e e f s (R ivosec- c h i , 1967 i n I t a l y ; F a u s t o - F i l h o & Fu r tado , 1970 i n B r a s i l ; Gruet , 1970, 1971 i n t h e N o r t h o f France ; Gore, e t a l . , 1978 i n F l o r i d a ) . For French P o l y n e s i a , our work i s t h e f i r s t approach t o t h i s s u b j e c t . We have s t u d i e d t h e d i s t r i b u t i o n o f c rus tacean s p e c i e s i n t h e r e e f o f T i a h u r a (Moorea I s l a n d ) i n r e l a t i o n t o t h e i r d i f f e r e n t f e e d i n g h a b i t s . Spec ies i n c l u d e t h o s e s t r i c t l y i n h a b i t i n g t h e h a r d s u b s t r a t e s ( l i v i n g and dead c o r a l s ) , and o t h e r s p e c i e s e i t h e r f a c u l t a t i v e l y i n h a b i t i n g t h e s e s u b s t r a t e s o r endogenous t o sand s u b s t r a t e s . T H E STUDY AREA. The t r a n s e c t o f T i a h u r a i s l o c a t e d a t t h e Nor thwest c o a s t o f Moorea I s l a n d ( F i g . 1 4 ) . T h i s area, " a t y p i c a l H i g h - I s l a n d c o r a l r e e f complex" ( S a l v a t , e t d l . , 1972), i s d i v i d e d i n t o t h r e e s e c t i o n s ( F i g . 1B). From t h e beach towards t h e r e e f f r o n t (800 m l o n g ) , t h e s e a r e : BARRIER-REEF Fig . 1.- L o c a l i z a t i o n of t h e s t udy area.- 1 A : P o s i t i o n of t h e t r a n s e c t of T iahura i n Moorea I s l a n d and g e n e r a l a s p e c t of t h e area. 1B : D i s t r i b u t i o n of t h e sampling s t a t i o n s a long t h e t r a n s e c t of T iahura . - t h e f r i n g i n g r e e f (250 m l o n g and 0.20 m t o 0 .50 m average depth , and 2 m on t h e channel m a r g i n ) . - t h e channel ( 5 0 m l ong , 10 t o 13 m d e p t h ) . - t h e b a r r i e r - r e e f (500 m l o n g , 1.5 t o 2.50 m d e p t h near t h e channe l , and 0.50 m d e p t h around t h e r e e f f r o n t ) . A ) The F r i n g i n g Reef. S o f t s u b s t r a t e s (sand sed imen ts ) and d e b r i s a r e domi- n a n t i n t h e f r i n g i n g r e e f . Towards t h e channe l , l i v i n g c o r a l c o l o n i e s become abundant (f's'mmocora, Synarea ) , and t h e y f o r m huge c o r a l heads a t t h e marg ins o f t h e channe l ( F i g . 2 ) . Hard s u b s t r a t e s a r e m a i n l y r e p r e s e n t e d b y f'samnocora, r a y o n s c a c t u s and Synarea, and dead c o r a l c o l o n i e s , wh ich h e r e cover a l a r g e r a r e a t h a n 1 i v i n g c o r a l s . Dead c o r a l p r o v i d e s an optimum env i ronment f o r a l g a l c o l o n i z a t i o n : a l g a e cover a l a r g e p r o p o r t i o n o f t h e f r i n g i n g r e e f i n T i a h u r a ( F i g . 2 ) . B) The Channel. The b o t t o m o f t h i s channel i s c o n s t i t u t e d a lmos t t o t a l l y o f sand sed imen ts ( F i g . 2 ) . T h i s zone i s under t h e c o n s t a n t i n f l u e n c e o f a s t r o n g c u r r e n t f l o w i n g p a r a l - l e l t o t h e c o a s t ( F i g . 1A) . The o n l y b e n t h i c s p e c i e s i n h a b i t i n g i t a r e endogenous (Conus see., p o l y c h a e t e s , Thal 1 a s s i n i dae) . C ) The B a r r i e r - r e e f . S c a t t e r e d c o r a l heads a r e s i t u a t e d on t h e o u t e r mar- g i n s o f t h e channe l . Towards t h e r e e f f r o n t , t h e r e i s a g r a d u a l i n c r e a s e o f c o r a l c o l o n i e s . L i v i n g c o r a l c o l o n i e s a r e more abundant t h a n i n t h e f r i n g i n g r e e f , t h e r e f o r e a l g a l c o l o n i s a t i o n i s l e s s h e r e t h a n i n t h e fo rmer r e e f s e c t i o n ( F i g . 2 ) . Pavona c a c t u s , Egnmipgoa, h r i t g s and A c r o p r a a r e we1 1 r e p r e s e n t e d . The r e e f f r o n t i s c o n s t i t u t e d by a r i d g e o f c a l c a - r e o u s a l g a e which, t o g e t h e r w i t h e n c r u s t i n g c o r a l s , p r o - v i d e s a we1 1 deve loped c a v i t a r y b i o t o p e tho rough1 y c o l o - n i z e d by t h e c r y p t o f a u n a . MATERIALS AND METHODS. N i n e s t a t i o n s were e s t a b l i s h e d a l o n g t h e t r a n s e c t o f T i a h u r a ( F i g . 1 8 ) . A t o t a l o f 5 0 l i t e r s o f h a r d s u b s t r a t e was sampled b y SCUBA d i v i n g a t each s t a t i o n , 1 / 3 o f wh ich was composed b y dead c o r a l s and t h e o t h e r 2 / 3 o f l i v i n g i I FRINGING REEF !CHANNEL BARRIER- REEF SEDIMENTS 1 LIVING CORALS / DEAD CORALS (DEAD SUBSTRATUM) Fig . 2.- D i s t r i b u t i o n and r e l a t i v e c o v e r i n g a r e a o f t h e p r i n c i p a l t y p e s o f b i o t o p e s i n t h e t r a n s e c t of T iahura . c o r a l s. The c o r a l c o l o n y (dead o r a l i v e ) t o be sampled was s e l e c t e d by i t s s i z e ( a l l u n i t s sampled were s i m i l a r i n vo lume) , i t s a r c h i t e c t u r e ( r e l a t i v e l y r e g u l a r geomet r i c shapes and presence o f a complex c a v i t a r y n e t w o r k ) , and i t s r e p r e s e n t a t i v e n e s s i n t h e sampl ing s t a t i o n . On t h e f r i n g i n g r e e f , dead s u b s t r a t e and l i v i n g c o r a l c o l o n i e s o f Pavona c a c t u s and f"anfincgra were sampled a t each s t a t i o n . On t h e b a r r i e r - r e e f , dead s u b s t r a t e and l i v i n g c o r a l c o l o n i e s o f Payopa cac tus , P lgn t ipora and P o r i t e s - - - - - - - were taken. The s e l e c t e d c o l o n y was covered i n s i t u w i t h a p l a s - t i c bag (25x35 cm) i n o r d e r t o a v o i d t h e escape o f t h e c a v i t a r y fauna. The c o l o n y was t h e n detached f rom t h e s u b s t r a t e and t h e bag was c l o s e d immed ia te l y . The a r e a around was surveyed, and some l a r g e and/or n o n - s t r i c t l y c a v i t a r y s p e c i e s were c a p t u r e d b y hand and a l s o counted. However, t h e abundance o f t h e s e s p e c i e s may have been underes t imated, e i t h e r because o f d i f f i c u l t y i n l o c a l i- z i n g t h e i n d i v i d u a l s (endogenous s p e c i e s ) , t h e i r f a c i 1 i t y t o escape (swimming c r a b s ) , o r t h e i r h a b i t o f f o r m i n g aggrega tes ( p a g u r i d c r a b s : B a l l , 1950 ; B a l l & Haig, 1974 ; H a z l e t t , 1974) . La rge -s i zed n o c t u r n a l s p e c i e s ( v e r y r a r e ) , t h o s e c a p t u r e d a t t h e o u t e r s lope , and l a r g e semi t e r r e s t r i a l s p e c i e s (Cgengb j ta e e r l a t u s and Cardisoma --------- c a r n i f e x --------~ b o t h v e r y abundant ) , were n o t i n c l u d e d i n t h e counts . D e t e r m i n a t i o n o f t h e f e e d i n g h a b i t s o f t h e c rus tacean fauna i n t h i s s t u d y was based upon o b s e r v a t i o n o f t h e f u n c t i o n a l morphology o f c h e l i p e d s , mouth-par ts and gas- t r i c m i 11. Gut c o n t e n t a n a l y s e s were a l s o accompl i shed , b u t t h e y were mere ly q u a l i t a t i v e because o f t h e s m a l l s i z e o f most o f t h e i n d i v i d u a l s ( < 20 mm w i d t h ) , and t h e d e f i c i e n t s t a t e of c o n s e r v a t i o n o f t h e c o l l e c t i o n a f t e r 3 months o f s t o r a g e and t r a n s p o r t ( P o l y n e s i a - P a r i s ) . Never- t h e l e s s , t h e i n f o r m a t i o n t h u s o b t a i n e d was v e r y u s e f u l f o r d e f i n i n g 5 MORPHOLOGIC GROUPS o f spec ies , r e l a t e d t o t h e i r a l i m e n t a r y p r e f e r e n c e s . RESULTS. A t o t a l of 73 s p e c i e s o f decapod R e p t a n t i a and stoma- topod c r u s t a c e a n s was i d e n t i f i e d a t t h e t r a n s e c t o f T i a - hu ra , x a n t h i d c r a b s b e i n g l a r g e l y dominant (Tab. 1 ) . Compared w i t h a t o t a l o f 140 s p e c i e s c o l l e c t e d d u r i n g o u r whole m i s s i o n i n French P o l y n e s i a (Moorea, T a h i t i , Taka- p o t o , Makatea and M a t a i v a ) , t h e observed s p e c i f i c r i c h - ness o f T i a h u r a was q u i t e h i g h : 52% o f t o t a l c o l l e c t e d spec ies , 18% o f which were "endemic". T h i s compar ison seems t o c o n f i r m t h e r e p r e s e n t a t i v e n e s s o f t h e t r a n s e c t o f T i a h u r a as a t y p i c a l H i g h I s l a n d c o r a l r e e f complex ( S a l v a t , e t a l . , 1972 ; M o n t e f o r t e , 1984a,b). Twenty-e igh t s p e c i e s were c o l l e c t e d on t h e f r i n g i n g r e e f , 10 on t h e b a r r i e r - r e e f , 19 on t h e r e e f f r o n t (some o f them appeared a l s o on t h e o u t e r s l o p e ) , and 16 s p e c i e s were founded b o t h on t h e f r i n g i n g r e e f and t h e b a r r i e r - r e e f . Severa l o f t h e s e 1 a s t were numer i ca l 1 y dominant a l o n g t h e t r a n s e c t . A t o t a l o f 2500 i n d i v i d u a l s was c a p t u r e d i n t h e t r a n s e c t o f T iahura , hand c a p t u r e s i n c l u d e d (Tab. 1 ) . Four s p e c i e s accounted f o r more t h a n 75% o f t h e t o t a l : Ch lo rodLe l l a bacbata, P l l o d l u s e u s l l , Galathea acu lea ta and L j o c a r p i 1 odes j n t e q e r r i mu?. These, w i t h 12 a d d i t i o n a l spec ies , accounted f o r about 95% o f t h e t o t a l c o l l e c t e d i n d i v i d u a l s . The 16 s p e c i e s c h a r a c t e r i z e t h e c a r c i n o l o g i c fauna o f T i a h u r a (Peyrot-Clausade, 1977b ; Montef o r t e , 1984a, b ) . The most numer i ca l 1 y i m p o r t a n t o f t h e s e s p e c i e s a r e Chi o r o d i g L l a i a e v i 2s jma ( b a r r i e r - r e e f ) , L i omera b e l l s ( w i d e d i s t r i b u t i o n ) , Phymodius gnggiutgs ( f r i n g i n g r e e f ) , Actaea c a y l e e s ( w i d e d i s t r i b u t i o n ) , C h l o r o d i e l l a gythtrga (w ide d i s t r i b u t i o n ) ( F i g . 3 ) . The 4 dominant s p e c i e s over t h e t r a n s e c t a r e wide1 y d i s t r i b u t e d , excep t on t h e r e e f f r o n t ( F i g . 3 ) . I n f a c t , t h e 12 s p e c i e s f o l l o w i n g i n abundance a r e t h o s e t h a t p r i m a r i l y d e f i n e t h e d i f f e r e n c e s between t h e c r u s t a c e a n communi t ies o f t h e f r i n g i n g r e e f , t h e b a r r i e r - r e e f , and t h e r e e f f r o n t . T h i s l a s t a r e a p r e s e n t s a c h a r a c t e r i s t i c arrangement o f spec ies , some o f them appear ing n o t v e r y f a r back towards t h e lagoon a r e a o f t h e t r a n s e c t , b u t o f t e n l y t o 6 m depth on t h e o u t e r s l o p e . Decapod c r u s t a c e a n s a r e p r i m a r y and secondary consu- mers : f i l t e r - s u s p e n s i on f e e d e r s , omnivores and preda- t o r s . The l i m i t s o f t h e s e d i v i s i o n s a r e n o t we1 1 d e f i n e d because o f t h e v a r i o u s f e e d i n g h a b i t s (Gordon, 1964 ; Warner, 1977) . However, t h e f u n c t i o n a l morphology o f a l i m e n t a r y body s t r u c t u r e s has a c l o s e r e l a t i o n s h i p w i t h t h e k i n d o f f o o d u t i l i z e d by t h e s p e c i e s and f e e d i n g behav iou r (Dah l , 1952 ; Scha fe r , 1954 ; Bovb je rg , 1960 ; Bakus, 1975 ; Caine, 1975 ; Warner, 1977) . O b s e r v a t i o n o f Tab. 1.- L i s t o f decapod R e p t a n t i a and stomatopod s p e c i es: Nurner i c a l abundance o f i n d i v i d u a l s c o l l e c t e d i n each s t a t i o n a t t h e t r a n s e c t o f T i ahu ra (Moored) . OSL : Outer Slope. TOT : T o t a l t r a n s e c t . SPECIES STOHATOPDDA Sonodactylus espinos~s Sonodacty!us viridi; PA61'SIC:bE Gniculis anicslus Ca!cinus qaizardi Calcinu; Iaevinanus Cai~inus lai~ns Calcinus sp. 1 Oalcinus sp.? Calcinus sp.3 Dardanus gemmatus Dardanus lagopodes Pajurixus sp, Trizopagurus strigatu; GALATHEIDAE Galathea aculeata PORCELLANIDAE Petrolisthes 5 ~ . 1 Petrolisthes sp.? Petrolisthes sp.3 Petrolishtes sp.4 Petrolisthes sp.5 Petrolisthes sp.6 Petrolisthes sp.7 Pachycheles sp, HIPPIDAE Hippa sp, CALAPPIDAE Calappa hepatica PORTUNIDAE Carupa tenuipes Portunus granulatus Thalamita admete Thalami ta rrenata Thalami ta pi lumnoides XANTHIDAE Actaea cavipes Actaea sp. bctaeodes hirsutissina Atergatis floridus Tab. 1 ( c o n t . ) . STATIDMS SPECIES 1 2 3 4 5 6 7 8 9OSLTDT ..................................................................... Ater ja tops is c f . qernaini 1 1 Chlorodiel l a barbata 4 232 196 54 20 28 30 1 5b4 Chlorodiella cytherea 5 B 13 8 34 Chlorodiella 1 aevissima 61 14 12 5 92 Chlorodiella n igra 13 7 20 Daira pe r l a t a 11) b 5 18 Etisus anaglyptus ! 1 2 Etisus dentatus 3 1 4 Euxanthus exsculptus 1 1 Globopiluenus jlobosus 2 28 5 35 Lathnopodus b identa tus 1 3 4 Lachnopodus subacutus 1 2 Y Leptodius sanguineus ? 5 7 Liocarpi lodes integerrimus 9 5 3 8 1 3 5 1 2 3 15 21 34t Liomera be1 l a 24 20 7 2 2 55 Lionera rubra 1 1 Liomera rugata 1 1 1 3 Lioxanthodes alcocki 5 10 23 Lophozozywus edwardsii 1 1 2 Lophozozywus dodone 2 2 Lophozozymus gl aber 3 3 Lybia t e s s e l a t a 1 1 ledaeus noel ens i s 3 3 2 8 Paractaea re tusa ! O 10 Paraxanthias nota tus 15 b 21 Phyrodius monticulosus 10 9 27 Phymodius n i t i d u s 12 1 13 Phymodius ungulatus 20 28 1 49 Pi lodius p u j i l 2 9 6 1 6 2 41 22 67 32 422 Pi lodius scabr iculus 9 3 2 2 5 2 23 Pi 1 umnus sp. 1 2 2 Psaumis cavipes 2 3 1 4 4 2 2 6 8 1 3 1 Pseudo1 iomera variolosa 2 2 Xanthias lamarcki 9 2 1 6 1 1 20 Xanthias l a t i f r o n s IJ L b GRAPSIDAE Pachyqrapsus minutus 3 5 8 Pachygrapsus pl i ca tus 2 2 -------------------------------------------------------------------------- -- ............................. Pilodiur scabriculus e Glo~op~lumnur globosus ..................... ............. - ........................................ Lioxonthoder olcocki ......................... 0 Poractoeo retuso ........................ - ..... . . Tholomito pilumnoides 0 <.... <-7.. . Liomero bell0 Phymodius monticulosus 0 Colcinus lotens 0- - G., Chlorodiello niqro Actaeodea hirsutissimus Phymodius .......... .<-> Psaumis cavipes -- 0 Poroxonthios nototus ..................... 0 Liocarpilodes integerrimus Chlorodiello ...... Chlorodiello borboto Fig. 3.- Zonation and relative abundance of the principal Decapod Reptantia collected in the transect of Tiahura (only species collected in hard substrates). t h e s e s t r u c t u r e s was a c r i t e r i o n f o r p lacement o f a p a r t i c u l a r s p e c i e i n t o one o r a n o t h e r o f t h e 5 MORPHOLO- G I C GROUPS d e f i n e d i n our s tudy . Other c r i t e r i a were : i n s i t u o b s e r v a t i o n s , g u t c o n t e n t a n a l y s i s , and o t h e r s t u - d i e s on m o r p h o l o g i c a l l y s i m i l a r spec ies . The g roups a re : f i l t e r - s u s p e n s i o n o r d i r e c t b o t t o m - d e p o s i t f e e d e r s , omni- v o r e s / h e r b i v o r e s , o m n i v o r e s / c a r n i v o r e s , g e n e r a l i z e d omni- v o r e s and p r e d a t o r s . C. 1 ) F i l t e r - s u s p e n s i o n o r D i r e c t Bot tom-deposi t Feeders. Spec ies o f t h i s g roup b e l o n g e s s e n t i a l l y t o t h e f a m i - 1 i e s Gal a t h e i d a e (Gal a t h e a a c u l -------- e a t a ) and P o r c e l l a n i d a e ( P e t r o l i s thes see. ) , wh ich ag rees w i t h o t h e r p r i n c i p a l works ( N i c o l , 1932 ; Knudsen, 1964 ; Caine, 1975 ; Gore, e t a l . , 1978 ; Kropp, 1981) . These s p e c i e s show f l a t and s l e n d e r c h e l i peds . The f i n g e r s a r e l o n g and a c u t e w i t h t h e i r i n t e r n a l marg ins o f t e n f i n e l y d e n t a t e . On t h e v e n t r a l s u r f a c e o f t h e f i x e d f i n g e r s t h e r e i s a row o f f i n e s h a r p - p o i n t e d s p i n e s wh ich sometimes s e r v e a c t i v e 1 y when t h e an imal o b t a i n s f o o d b y r a s p i n g t h e s u b s t r a t e ( N i c o l , 1932 ; Caine, 1975) . The 3 rd . p a i r o f m a x i l l i p e d s i s v e r y i m p o r t a n t . These a r e ext reme1 y m o b i l e s t r u c t u r e s b e a r i n g l o n g and r e l a t i - v e l y s t i f f s e t a e a t t h e i r d i s t a l marg in wh ich f u n c t i o n as a n e t t o t r a p suspended p a r t i c l e s o r t o sweep t h e b o t t o m d i r e c t l y ( F i g . 4 ) . These s e t a e a r e c leaned by t h e 2nd. and 1 s t . p a i r o f m a x i l l i p e d s wh ich t h e n b r i n g t h e f o o d t o t h e mouth ( N i c o l , 1932 ; Kropp, 1981) . A t t h e i n t e r i o r o f t h e endostome t h e r e i s a p a i r o f we1 1 - c a l c i f i ed mandi b l es. I n EaLathea a c u l e a t a and P e t r o - l i s t h e s ~ e p . c o l l e c t e d a t T i a h u r a , t e e t h w i t h f i n e l y - - - - - - - t u b e r c u l a t e d s u r f aces were observed on t h e s e mand ib les . The s t r u c t u r e o f t h e g a s t r i c m i l l , a l t h o u g h d i f f i c u l t t o a p p r e c i a t e , seems t o show f i n e l y d e n t a t e m a s t i c a t o r y o s s i c l e s w i t h s o f t s e t a e a t t h e i r marg ins . These f e a t u r e s a r e commonly found i n s p e c i e s f e e d i n g upon s m a l l and r a t h e r s o f t p a r t i c l e s (Ca ine , 1975) . I n a d d i t i o n , t h e s e i n d i v i d u a l s a r e v e r y s m a l l (EaLChLhea a c u l e a t a : 5 t o 7 mm t o t a l l e n g t h , and f ' e t ro l i s thes see. < 5 mm w i d t h ) , wh ich s u g g e s t s t h a t t h e i r f o o d c o n s i s t s o f such f i n e m a t e r i a l as p l a n k t o n , phy toben thos , l a r v a l f o r m s and d e t r i t u s . U n f o r t u n a t e 1 y, i d e n t i f i c a t i o n o f g u t c o n t e n t s was n o t p o s s i b l e , s o t h e degree o f a l i m e n t a r y s e l e c t i v i t y f o r t h e s e s p e c i e s i s unknown t o us. E i g h t s p e c i e s o f t h i s morpho log i c g roup were found a t T i a h u r a , a c c o u n t i n g f o r 17% o f t o t a l i n d i v i d u a l s i n t h e Fig. 4.- Group of filter-suspension or direct bottom- deposit feeders : 3rd. pair of maxillipeds of Petrolisthes 3. (ventral view). t r a n s e c t (Tab. 2 ) . One s p e c i e s was l a r g e l y dominant , Ga la thea a c u l e a t a , wh ich r e p r e s e n t s about 15% ; t h e o t h e r 2% was sha red among 7 s p e c i e s o f Petyo1 i s t h e s . On t h e f r i n g i n g r e e f , f i l t e r - s u s p e n s i o n f e e d e r s r e - p r e s e n t e d 13% o f t o t a l i n d i v i d u a l s . On t h e b a r r i e r - r e e f , t h i s g roup was c o m p a r a t i v e l y more i m p o r t a n t : 25% o f t o t a l i n d i v i d u a l s (Tab. 2 ) . C.2) Omnivorous Species. These s p e c i e s a r e a b l e t o e x p l o i t a l a r g e b i o t o p e , t h e i r a l i m e n t a r y r e s o u r c e s b e i n g v e r y d i v e r s i f i e d : a l - gae, s m a l l c a v i t a r y s p e c i e s a s p o l y c h a e t e s , sponges, echinoderms, m o l l u s c s , o t h e r c rus taceans , a s we1 1 as d i s i n t e g r a t e d o r g a n i c m a t e r i a l and c a r r i o n . The morphology o f c h e l i p e d s i s one o f t h e p r i n c i p a l bases u t i l i z e d t o c l a s s i f y t h e omnivorous s p e c i e s , a l - though t h e morphology o f t h e g a s t r i c m i l l , s i z e o f spe- c i e s and g u t c o n t e n t s a r e a l s o r e g i s t e r e d . Some main f e a t u r e s o f t h e c h e l i p e d s a r e r e l e v a n t : 1 ) C h e l i p e d s a r e more o r l e s s vo luminous, s t r a i g h t o r somewhat concave. 2 ) I n t e r n a l m a r g i n s o f f i n g e r s : - w i t h c u t t i n g edges. - w i t h t u b e r c u l a t e s u r f aces ( d e n t i f o r m p r o c e s s e s ) . 3 ) The c laws, once c l o s e d : - l e a v e a w ide space between f i n g e r s ( n o n - j o i n e d c l a w s ) . - c l o s e a lmost p e r f e c t l y ( j o i n e d c l a w s ) . 4 ) The f i n g e r t i p s a r e : - p o i n t e d o r s l i g h t l y b l u n t . - excavated as a w e l l - d e f i n e d h o o f . These c h a r a c t e r i s t i c s a r e n o t p r e s e n t s e p a r a t e l y i n a p a r t i c u l a r spec ies , b u t o f t e n l y occu r i n comb ina t i on . There a r e s p e c i e s h a v i n g s i m i l a r c h e l i p e d s i n s i z e and f o r m (homoche l i a ) , o r s p e c i e s w i t h d i f f e r e n t c h e l i p e d s ( h e t e r o c h e l i a ) . The morphology o f d e n t a r y s u r f aces may a l s o b e s i m i l a r i n b o t h c h e l i p e d s (homodon t ia ) , o r d i f f e - r e n t ( h e t e r o d o n t i a ) (Scha fe r , 1954) . From t h e d i s t r i b u t i o n o f t h e s e morpho log i c c h a r a c t e - r i s t i c s i n a p a r t i c u l a r spec ies , i t was p o s s i b l e t o deduce h a b i t u a l f o o d t y p e v e r y c l o s e l y , and t h e methods u t i l i z e d t o o b t a i n i t . Upon t h e bases o f t h e s e observa- t i o n s , 3 MORPHOLOGIC GROUPS o f omnivorous s p e c i e s were c o n s t i t u t e d : omni v o r e s / h e r b i vores , omni v o r e s / c a r n i vores , and g e n e r a l i z e d omnivores. We must r e c a l l t h a t t h e s e d i v i s i o n s a r e n o t s t r i c t : a s i n g l e s p e c i e s showing w ide d i s t r i b u t i o n i n t h e t r a n s e c t cou ld present more g e n e r a l i - sed o r more r e s t r i c t e d feed ing h a b i t s depending on t h e resources a v a i l a b l e , t h e b i o l o g i c a l c y c l e (o f t h e spec ies i t s e l f o r o f t h e organisms composing i t s food resou rce ) , o r on t h e presence o f a compet i to r (Gore, e t a l . , 1978). C.2.1) Omni vo res /herb i vores. Species rep resen t i ng t h i s group a r e C h l o r o d i e l l a barba ta ------- I Lniqyr, L c y t h e r e a , C. 1 aev i s s i m a , Phymodi us unsulatus, P,monticulosus, P i l o d i g s eug , i l , P,scabrLculus and Lioxanthodes a l c o c k i . The che l i peds o f these spec ies a r e r a t h e r s t r a i g h t and n o t very massive. F inge rs a r e s lender and e v e n t u a l l y show 2 o r 3 wel l -developed mo la r i f o rm t e e t h a t t h e i r i nne r margins, b u t t h e r e s t o f t h e den ta ry su r faces a r e smooth. The c laws a re non- jo ined. The f i n g e r t i p s a r e excavated fo rming a hoof -1 i ke s t r u c t u r e , general 1 y we1 1 de f i ned (F ig . 5). Th is l a s t c h a r a c t e r i s t i c i s commonly found i n crabs hav ing p r e f e r e n t i a l l y herb ivo rous feed ing h a b i t s (Crane, 1947; Knudsen, 1960, 1964; G r i f f i n , 1971 ; Warner, 1977). I t i s i n f a c t a s t r u c t u r e very w e l l adap- t e d t o c u t out laminar p ieces f rom a lgae (Fores t , pers. comm., 1984 pers . obs. ) , or t o spoon e n c r u s t i n g mater i a1 f rom t h e s u b s t r a t e ( S k i l l e t e r & Anderson, 1986). Homochelia i s common i n some spec ies ( C h l o r o d i e l l a zpp., Phymodius see.), bu t sometimes a s l i g h t heteroche- 1 i a i s present ( P i 1 od i us see-, !.Agxa.A&hodes a lcgckL) . Homodontia i s a l s o common i n t h i s group. The p a r t i c u l a r s t r u c t u r e o f t h e g a s t r i c m i l l ( f i n e l y t u b e r c u l a t e mas t i ca to ry s u r f aces, b l u n t o s s i c l e s w i t h abundant se tae ) , suggests t h a t these spec ies u t i l i z e food p a r t i c l e s no t r e q u i r i n g ex tens i ve g r i n d i n g . Moreover, i n t h e gu t con ten ts t h e r e were appa ren t l y no fragments o f mol lusc she1 l s , b u t a l g a l m a t e r i a l seemed t o predominate. The s i z e o f these spec ies i s sma l l , r a r e l y over 10 mm wid th . A t o t a l of 17 spec ies o f t h e t r a n s e c t o f T iahura were i nc luded i n t h i s assemblage, o r 24% of t o t a l spec ies r i chness . The r e l a t i v e abundance of t h i s group was about 59% of t o t a l i n d i v i d u a l s i n t h e t r a n s e c t ; i t was t h e dominant group, where C h l o r d j e l l a barba ta and P i l o d i u s p u q i l accounted f o r more than 35%. I n t h e f r i n g i n g r e e f , 11 spec ies represented 74% of t o t a l i n d i v i d u a l s i n t h i s sec to r . &:barbat a and P . p u s i l were t h e dominant species, b u t t h e r e was a l s o an abundant Group o f spec ies such as C h l o r o d i e l l a n i q r a , Phymgnjus For t h e r e e f f l a t o f t h e b a r r i e r - r e e f , C.barbata and Plpuqil were s t i 11 abundant, be ing gradual 1 y rep1 aced towards t h e r e e f f r o n t by C h l o r o d i e l l a i aey j ss ima which then became one o f t h e dominant species. I n t o t a l f o r t h e b a r r i e r - r e e f , 17 spec ies o f t h i s group accounted f o r 38% o f t o t a l i n d i v i d u a l s . The che l i peds o f spec ies i nc luded i n t h i s group a re g e n e r a l l y massive and s t r a i g h t , a1 though they may be s l i g h t l y concave i n some smal l -s i zed spec ies (L-omera q e - , Psaumis cav ipes, -------- Xanth ias -------- lamarck i ) . The f i n g e r s a r e s h o r t and q u i t e s t rong , bea r i ng t u b e r c u l a t e , c u t t i n g , o r t u b e r c u l a t e - c u t t i n g den ta ry s u r f aces, general l y we1 1 - developed. The f i n g e r t i p s a r e p o i n t e d o r 1 i g h t l y rounded. The c laws a r e j o i n e d (F ig . 6 ) . Homochelia and homodontia flc taeodes a r e common (Xanthias lama!xki, l j o m e r a see:, --------- h j r s u t i s s i ma, Psaumi s ~ayipee, Da i ra per 1 a t a ) . I 1 1 -marked he te roche l i a a l s o e x i s t s (Lep tod iug sanquineus) , b u t when d i f f e r e n c e s e x i s t , these a r e very ev iden t (Pi lumnus see:, Paraxanthias notatus, Globoeilumnus globosus, l i o s a r e i l o z des integerrirnns) . Th i s combinat ion o f s t r u c t u r e s , and ma in l y t h e presence o f p ro tube ran t t e e t h over t h e i n t e r - n a l margins of f i n g e r s , c h a r a c t e r i z e t h e c rabs hav ing a p r e f e r e n t i a l l y ca rn i vo rous a1 imentary regime (Schaf e r , 1954 ; Knudsen, 1964 ; Vermei j, 1977a ; Warner, 1977 ; Zipser & Vermei j , 1978). Pol ychaetes and smal l mo l l uscs s u r e l y c o n s t i t u t e a very impor tan t p a r t o f t h e i r d i e t , as shown by t h e gu t con ten t a n a l y s i s i n which f ragments o f she1 l s , opercu les and mandibules o f po lychae tes were o f t e n found. The s t r u - c t u r e o f che l i peds and f i n g e r s i s e f f i c i e n t f o r t h e man ipu la t i on o f ha rd and voluminous o b j e c t s and f o r tea- r i n g o f f s o f t t i s s u e s f rom s h e l l s (Warner, 1977 ; S k i l l e - t e r 81 Anderson, 1986). The g a s t r i c m i l l i s much more massive than i n t h a t o f he rb i vo rous species, hav ing t h e mas t i ca to ry o s s i c l e s edged w i t h f i n e b u t sharp spines, we1 1-developed g r i n d i n g s u r f aces, and few setae. There were 28 spec ies o f t h i s group i n Tiahura, o r 39% o f t o t a l spec ies r i chness . The i r r e l a t i v e abundance was est imated i n 18% o f t o t a l i n d i v i d u a l s . I n t h e f r i n g i n g r e e f , 13 spec ies composed 7% o f t o t a l i n d i v i dua l s, where IAompya b p d l g and Actappdps h i r s u t i s- sima accounted f o r 5%) . ---- Fig. 6. - Group of carnivore/herbivore species : Right cheliped of Globopilumnus globosus (Xanthidae ) , a facultative malacophage crab. For t h e b a r r i e r - r e e f , 21 s p e c i e s were p r o p o r t i o n a l l y more i m p o r t a n t : 33% o f t o t a l i n d i v i d u a l s i n t h i s s e c t o r . L i o c a r p i l o d e s i n t e q e r r i m u s were n u m e r i c a l l y dominant w i t h i n t h i s group (25% o f t o t a l i n d i v i d u a l f o r t h e b a r - r i e r - r e e f . However, t h i s s p e c i e s was g radua l l y r e p 1 aced by a group o f abundant o m n i v o r e / c a r n i v o r e s p e c i e s towards t h e r e e f f r o n t (G lobop i lumngs q lhbosus, P a r a x a n t h i a s eotatus, D a i r a e e r l a t a ) . C.2.3) G e n e r a l i z e d Omnivores. Severa l a u t h o r s c o n s i d e r as g e n e r a l i z e d omnivores t h e c r a b s o f t h e f a m i l y Graps idae (Bacon, 1971 ; G r i f f i n , 1971 ; Gore, e t a1 . , 1978), and t h o s e o f t h e s u p e r f ami 1 y Pagur idea (Orton,1927 ; Samuelson, 1970 ; H a z l e t t , 1974 ; Caine, 1975) . However, some s p e c i e s may behave as preda- t o r s (Vermei j, l 9 7 8 ) , o r even as c o r a l l i v o r e s (Glynn & S t e w a r t , 1972 ; Glynn, 1973) . I n t h e Graps id s p e c i e s c o l l e c t e d a t T i a h u r a ( P a ~ h y ~ Qrapsus minutus , P . p l i c a t u s , b o t h b e i n g s m a l l - s i z e d o f some 5 mm w i d t h ) , t h e c h e l i p e d s a r e s m a l l and s t r a i g h t . The i n t e r n a l marg ins o f f i n g e r s show c u t t i n g o r f i n e l y s e r r a t e d s u r f a c e s w i t h o u t p rominen t m o l a r i f o r m t u b e r c u - l e s . The f i n g e r t i p s a r e p o i n t e d . H e t e r o c h e l i a and h e t e r o - d o n t i a a r e weakly pronounced, t h e c h e l i p e d s b e i n g r e l a t i - v e l y s i m i l a r . The c laws a r e j o i n e d (space between f i n g e r s i s n a r r o w ) . Concern ing t h e p a g u r i d c rabs , t h e i r c h e l i p e d s have two f u n c t i o n s : t h e y a r e a u x i l i a r y i n t h e a l i m e n t a r y a c t i v i t i e s , and p l a y t h e r o l e o f an o p e r c l e f o r s p e c i e s i n h a b i t i n g gas t ropod s h e l l s . H e t e r o c h e l i a and heterodon- t i a a r e t h e r e f o r e s t r o n g l y pronounced. However, a l t h o u g h t h e s t r u c t u r e o f f i n g e r s i s adapted t o t h i s l i v i n g s t y l e , t h e i r i n t e r n a l marg ins do n o t bear p r o t u b e r a n t t u b e r c l e s , t h e s e s u r f a c e s b e i n g f o r c u t t i n g o r f i n e l y s e r r a t e d . The f 0 0 r e s o u r c e s o f genera l i zed omni v o r e s p e c i e s a r e v e r y d i v e r s i f i e d . They can a c t u a l l y use a1 1 k i n d s o f d e t r i t u s and o r g a n i c d e b r i s , c a r r i o n , u rban r e s i d u e s , e t c . , and a l t h o u g h t h i s morpho log ic group was r e p r e s e n t e d a t T i a h u r a by 11 s p e c i e s (15% o f t o t a l s p e c i e s r i c h n e s s ) , n u m e r i c a l l y , t h e y were v e r y few (2% o f t o t a l i n d i v i d u a l s i n t h e t r a n s e c t ) . On t h e f r i n g i n g r e e f t h i s group compr i - ses 3% o f i n d i v i dua ls . Pachyqyt-psgg rnigntgs (Graps i dae) and C a l c i n u s l a t e n s (Pagur idae) were p r a c t i c a l l y t h e o n l y n u m e r i c a l l y i m p o r t a n t spec ies . I n t h e b a r r i e r - r e e f t h i s g roup was absent . C. 3 ) P r e d a c i o u s / c a r n i vores . Some o m n i v o r e / c a r n i v o r e s p e c i e s may be a b l e t o behave as p redac ious , p r o v i d e d t h a t t h e y have a l a r g e a d u l t s i z e ( o v e r 30 mm w i d t h ) , massive subequal c l a w s w i t h sharp- p o i n t e d f i n g e r s , we1 1 developed m o l a r i f orm t e e t h on t h e i n t e r n a l marg in o f f i n g e r s , and t h e presence o f a p a r t i - c u l a r y p rominen t t o o t h s i t u a t e d i n p r o x i m a l p o s i t i o n over t h e d a c t y l u s , g e n e r a l l y on t h e major c h e l i p e d . These c a r a c t e r i s t i c s d i s t i n g u i s h t h e p r e d a c i o u s malacophage c r a b s (Scha fe r , 1954 ; Crane, 1947 ; Reyno lds & Rey- n o l d s , 1977 ; Verme i j , 1977 ; Warner, 1977). Other we1 1-known p r e d a c i o u s s p e c i e s a r e t h e P o r t u n i - dae (Scha fe r , 1954 ; Muntz, e t a l . , 1965 ; Ropes, 1968 ; Hami l ton , 1976 ; Warner, 1977 ; R e h i n a l l t , 1985, 1986) , t h e Ca lapp idae (Shoup, 1968 ; Warner, 1977 ; Vermei j, l 9 7 8 ) , and t h e stomatopods (Burrows, 1969 ; C a l d w e l l & D i n g l e , 1975) . These s p e c i e s a r e m a i n l y s p e c i a l i z e d mala- cophages (Ca l appi dae) and sometimes p i s c i vo res ( p o r t u n i ds and stomatopods) ( F i g s . 7, 8 ) . Seven predac i ous s p e c i e s were c o n s i d e r e d i n T i hau ra (10% o f t o t a l s p e c i e s ) . The o m n i v o r e s / c a r n i v o r e s showing f a c u l t a t i v e p r e d a c i o u s h a b i t s were n o t counted f o r t h i s group. Almost a l l o f t h e s e s p e c i e s a r e w i d e l y d i s t r i b u t e d i n t h e t r a n s e c t , excep t Cal apes h e a t i c a (endogenous spe- c i e s , f r i n g i n g r e e f ) , and k r g e a t e n u i p e z ( c a v i t a r y Por- t u n i d a e o f t h e r e e f f r o n t ) . The t o t a l r e l a t i v e abundance o f t h i s group was e s t i - mated as 4%. For t h e f r i n g i n g r e e f , 3% o f t o t a l i n d i v i - d u a l s found i n t h i s s e c t o r b e l o n g t o t h e p r e s e n t group ; f o r t h e b a r r i e r - r e e f t h e y accounted f o r 5% o f t h e i n d i v i - d u a l s o f t h i s s e c t o r . The most abundant s p e c i e s on b o t h a reas were GonodactyLgs y i r i d i s and G.espjnosus, two c a v i t a r y stomatopods observed on1 y i n Pavona cactus (H igh I s l a n d s ) (Montef o r t e , 1984a). A1 though t h e abundance o f f r e e - 1 i v i n g s p e c i e s (Tha la - mLna admete, T. c r e n a t a , Po r tunus g r a n u l a t u s ) , and t h a t o f endogenous s p e c i e s (cgbaeea hepatic.), may have been u n d e r e s t i mated because o f t h e v a r i o u s c a p t u r e problems, i t seems t h a t p r e d a c i o u s c r a b s p l a y o n l y an i n f e r i o r r o l e i n t h e t r o p h i c ne twork o f a H igh I s l a n d r e e f complex. I n t h i s t y p e o f system, t h e h i g h e r t r o p h i c l e v e l s seem t o be occup ied m a i n l y b y c a r n i v o r o u s f i s h e s which a r e much more e f f i c i e n t t h a n c r a b s (PerPs & P i c a r d , 1969 ; V i v i e n & Peyrot-Clausade, 1974 ; Galz i n, 1977b ; Harmel i n-Vi v i en, 1981) . Fig. 8.- Group of predacious/carnivore species : Right (major) cheliped of Calappa hepatica :Calappidae). A typical crushing chela of a specialized malacophage crab. Other a1 imenta ry h a b i t s impor tan t t o mention a r e those represen ted by decapod crustaceans o b l i g a t o r i l y assoc ia ted w i t h p o c i l l o p o r i d c o r a l s (Lcapegia see.) which a r e morpholog ica l l y adapted t o feed upon c o r a l l i a n mucus (Odinetz, 1983), by c o r a l l i v o r o u s pagu r i d c rabs (An i cg igs an i cu lus , Trizopaguwus strigatas), and by p i n n o t h e r i d -------- crabs and t h e p o r t u n i d L i s s o c a r c i n u s ------------- ----------- o r b i c u l a r i s , respec- t i v e l y commensal w i t h b i v a l v e s and h o l o t u r i ans. L i v i n g s u b s t r a t e s seem t o c o n t a i n t h e m a j o r i t y (52%) o f a1 1 c o l 1 ec ted i n d i v i dua l s. However, each c o r a l speci es i s co lon i zed d i f f e r e n t l y . Paygna cac tus and Psa-qgcora a r e p r e f e r e n t i a l l y occupied (21% and 19% r e s p e c t i v e l y , o f t o t a l i n d i v i d u a l s ) , then Montipot-5 (B%), and f i n a l l y P o r i t e s ------- (3%) . Dead s u b s t r a t e i s a l s o h i g h l y co lon i zed by c a v i t a r y crustaceans (44% o f t o t a l i n d i v i dual s ) . The remain ing 4% correspond t o i n d i v i d u a l s captured by hand (Tab. 2, F ig . 9 ) . I n p o c i l l o p o r i d c o r a l s , Odinetz (1983) found abundant popul a t i ons o f non-associ a ted brachyuran and anomuran crustaceans. Comparing these da ta o f abundance of non- assoc ia ted crabs/volume o f t h e c o r a l co lony w i t h those o f our study, P o c i l l o p o r a and Psammocoya seem t o be s i m i l a r - l y co lon ized by c a v i t a r y crustaceans. Nevertheless, Pavo- " cactus i s t h e l i v i n g c o r a l co lony t h a t ga the rs t h e most abundant c a v i t a r y popu la t i ons , which i s a d i r e c t consequence o f i t s a r c h i t e c t u r a l complex i ty . D . l ) The F r i n g i n g Reef. The omni vo re /he rb i vo re spec ies a r e dominant i n a1 1 s u b s t r a t e s (Tab. 2, F ig . 10) . W i th in t h i s group, Chloro- d i e l l a barba ta ( t h e dominant spec ie ) , shows a f f i n i t i e s f o r dead subs t ra tes . On t h e con t ra ry , P i l o d i u s e y g i i (nex t i n abundance), i s more abundant i n Psammocoya. F i l t e r / s u s p e n s i o n feeders (ga la thea a c y l e a t a i s t h e o n l y n u m e r i c a l l y impor tan t one), show a l i g h t a f f i n i t y f o r dead s u b s t r a t e (39% o f t o t a l i n d i v i d u a l s o f t h i s group f o r t h e f r i n g i n g r e e f ) (Tab. 2, F ig . 10 ) . The few exemples o f P e t r o l i s t h e s r;pe. were a l l c o l l e c t e d i n t h i s subs t ra te . Concerning t h e l i v i n g co lon ies , Galathea acu- 1 ea ta showed n o t i ceabl e p re fe rences f o r Ps;_ammoccr_a (34%) , ----- be ing l e s s abundant i n Pavona c_ac_&us (26%) (F ig . l o ) . I t i s p o s s i b l e t h a t t h e swimming a b i l i t y o f t h i s spec ie enables i t t o f r equen t t h e e x t r a c a v i t a r y b io topes so as t o reduce t h e compe t i t i on w i t h c o r a l s and o the r b e n t h i c f i l t e r - f e e d e r s . PSAMMOCORA SP. - SUBSTRATUM F i g . 9.- R e l a t i v e abundance o f i n d i v f d u a l s c o l l e c t e d i n d i f f e r e n t s u b s t r a t e s sampled i n each s e c t o r of t h e reef i n T i a h u r a . F'R : F r i n g i n g r e e f . BR : B a r r i e r - r e e f . Tab. 2 . - R e l a t i v e abundance o f morphologic groups i n d i f f e r e n t s u b s t r a t e s sampled i n each r e e f s e c t o r o f t h e t r a n s e c t o f T i a h u r a ( s e e F i g . 10 f o r r e f e r e n c e ) . FR : F r i n g i n g r e e f . BR : B a r r i e r - r e e f . TT : T o t a l t r a n s e c t . CAPTURES RELATIVE ABUNDANCE RELATIVE ABUNDANCE NUMERIC ABUNDANCE OF INDIVIDUALS OF MORPH. GROUPS HORPHOLOGIC GROUPS SUBSTRATES FR BR TT FR BR TT FR BR TT Dead subs t . 71 132 203 4.9 12.5 8.1 39.2 50.6 45.9 Psammocora 62 62 4.3 2.5 34.3 14.0 FILTER-SUSPENSION P.cactus 48 42 90 3.3 4.0 3.6 26.5 16.1 20.4 H o n t i p o r a 65 65 6.2 2.6 24.9 14.7 P o r i t e s 22 22 2.1 0.9 8.4 5 , 0 TOTAL 181 261 442 12.5 24.8 17.6 40.9 59.0 100,- .......................................................................................... Dead s u b s t . 388 212 600 26.7 20.1 23.9 36.0 53.7 40.7 Psammocora 38t 386 26.6 15.4 35.8 26.2 OHNIVORESIHERBIV. P.cactus 303 57 360 20.9 5.4 14.3 28.1 14.4 24.4 l o n t i pora 105 105 10.0 4.2 26.6 7 , l P o r i t e s 21 21 2.0 0.8 5.3 1.4 TOTAL 1077 395 1472 74.2 37.5 58.8 73.2 26.8 100,- .......................................................................................... Dead subs t . 31 224 255 2.1 21.3 10.2 29.0 64,7 56.3 P s a m ~ o c o r a 40 40 2.8 1.6 37.4 8.8 OHNIVORESICARNIV. P.cactus 36 51 87 2.5 4.8 3.5 33.6 14,7 19.2 l o n t i p o r a 40 40 3.8 1.6 11,5 8.8 P o r i t es 31 31 2.9 1.2 9.0 6.8 TOTAL 107 346 453 7.4 32.8 18.1 23,6 76.4 100.- .......................................................................................... Dead s u b s t , 50 50 3.4 2.0 100.- 100, - P s a ~ ~ n o c o r a GENER, OHNIVORES P.cactus H o n t i p o r a P o r i t e s TOTAL 50 50 3.4 2,O 100,- 100,- .......................................................................................... PREDACIDUSICARNIV, D i r . cap t . 37 51 88 2.8 4.8 3.5 TOTAL 37 51 88 2.8 4.8 3 , s 42.0 58,8 100,- .......................................................................................... Dead subst . 540 568 1108 37.2 53.9 44.2 P s a m ~ o c o r a 488 488 33.6 19.5 TOTAL FAUNA P.cactus 387 150 537 26.6 14.2 21.4 (see Fig, 9) t i o n t i p o r a 210 210 19.9 8.4 P o r i t e s 74 74 7.0 2 ,9 O i r . capt . 37 51 88 2.5 4.8 3.5 SUH. TOT. 1452 1053 2505 58.0 42.0 100.- .......................................................................................... The omni vo re / ca rn i vo re spec ies a r e weak1 y represented i n t h e f r i n g i n g r e e f . They seem t o chose p r e f e r e n t i a l l y t h e l i v i n g s u b s t r a t e s (37% o f t o t a l i n d i v i d u a l s o f t h i s group i n t h e f r i n g i n g r e e f f o r Psammocora, 33% f o r Pavona cactus, and 29% f o r dead s u b s t r a t e ) , bu t t hey account f o r a low p r o p o r t i o n i n comparison w i t h t h e t o t a l i n d i v i d u a l s c o l l e c t e d on each s u b s t r a t e (Tab. 2, F i g . 10) . The general i zed omnivore spec ies were e x c l u s i v e l y c o l l e c t e d i n dead s u b s t r a t e a t beach margins. They were weakly represented (Tab. 2, F i g . 10) . Among t h e p redac ious / ca rn i vo re species, ~ o n o d a c ~ y l u s v i r i d i s and G.esejnosus were o n l y c o l l e c t e d i n Paygna ------- cactus. Ihatmamjta admete, 1,yrenata and h l a e e g heeat ica were c o l l e c t e d by hand. T h i s group was weakly represented i n t h e f r i n g i n g r e e f . D.2) The B a r r i e r - r e e f . The omnivore/herb ivore spec ies a r e n u m e r i c a l l y domi- nant on a l l t h e s u b s t r a t e s o f t h i s sec to r , except i n dead subs t ra te , a1 though i t i s p r e f e r e n t i a l l y co lon i zed by them (54% o f t o t a l i n d i v i d u a l s o f t h i s group i n t h e b a r r i e r - r e e f ) . For l i v i n g c o r a l co lon ies , Montieqt-a i s p r e f ered (27%), i n s t e a d o f Paygma ~ a c t g s ( 14%) and P g r i z t e s (5%). --- The abundant spec ies a re a l s o p a r t i c u l a r l y d i s t r i bu- t e d i n t h e d i f f e r e n t s u b s t r a t e s : i n t h i s case, @ l g r q = d i e 1 1 a barba ta and C. l aev i zs ima a r e abundant on dead s u b s t r a t e and Mont ipora, w h i l e P i l g d i g s e g q i i c o l o n i z e p r e f e r e n t i a l l y Pavona cactus. Plqntipot-a i s an enc rus t i ng c o r a l . The c o l o n i e s o f f e r f r e e su r faces f o r a l g a l c o l o n i s a t i o n ( s p e c i a l l y i n t h e o u t e r b a r r i e r - r e e f ; P a y r i , 1982), t o which t h e omnivore/ h e r b i v o r e spec ies a r e then a t t r a c t e d , bu t appa ren t l y no t f o r t h e c o r a l spec ies i t s e l f . The re1 a t i ve abundance o f omni vo res / ca rn i vores i s more impor tan t i n t h i s sec to r than i n t h e f r i n g i n g r e e f . These spec ies become s l i g h t l y dominant i n t h e dead sub- s t r a t e s t o which they show s t r o n g p re fe rences (65% o f t o t a l i n d i v i d u a l s o f t h i s group f o r t h e b a r r i e r - r e e f ) . Among l i v i n g c o r a l co lon ies , Paygna ya~xgs was b e t t e r co lon i zed (15%), then Mont ipora (12%), and f i n a l l y P o r i z t e s (9%). L A c a y p i l o d e s jn tgqer r i rngs i s t h e dominant --- spec ie w i t h i n t h i s group i n t h e i n n e r b a r r i e r - r e e f , be ing g r a d u a l l y rep laced towards t h e r e e f f r o n t by o the r omni- vo res / ca rn i vores ( G l obopi 1 umnus q l obosus, Paraxanth no ta tus , Dai r a e e r l a t a , e t c . 1 . Th i s scheme cou ld suggest PSAMMOCORA DEAD SUBSTRATUM FRINGING R E E F BARRIER- R E E F FILTER-SUSPENSION FEEDERS OMNIVORE /HERBIVORE SPECIES ............... ............... ............... ............... ............... OMNIVORE / CARNIVORE SPECIES 1 GENERALISED OVMNIVORE SPECIES F i g . 10.- R e l a t i v e abundance o f Morphologic Groups i n d i f f e r e n t s u b s t r a t e s sampled i n e a c h r e e f s e c t o r o f t h e t r a n s e c t of T i a h u r a ( s e e Tab. 2 f o r r e f e r e n c e ) . h a b i t a t p a r t i t i o n i n g among t hese spec ies which show s i m i - l a r i t i e s i n t h e i r f e e d i n g behav iou r . I n f i 1 t e r / s u s p e n s i on f eede rs , Eaiadhea a c u l e a t a shows a l s o a s t r o n g tendency t o c o l o n i z e dead s u b s t r a t e s (51% o f t o t a l i n d i v i d u a l s o f t h i s group f o r t h e b a r r i e r - r e e f 1 . Among 1 i v i n g c o r a l c o l o n i e s , G. a c u l e a t a c o l o n i z e s ma in l y M o n t i p r g (257.1, t hen Pavona cac tu? ( 16%) , and f i n a l l l y P o r i t e s (8%). ------- The p r e d a c i o u s / c a r n i v o r e s spec ies a r e weakly r e p r e - sented i n t h i s s e c t o r , and most o f them a r e n o t c a v i t a r y . We no ted once aga in Gonodactyils ~ L r L g g s and L e s e i n o s u s on1 y i n Payoma cac tus . DISCUSSION. The t r a n s e c t o f T i ahu ra i s a r e e f complex where t h e most common b i o t o p e s o f Po l ynes ian H igh I s l a n d s a r e p re - sen t ( S a l v a t , e t a l . , 1972). Be ing a h i g h l y d i v e r s i f i e d env i ronment , t h e number and t h e t y p e o f s p e c i e s i n h a b i - t i n g i t i s l a r g e and v a r i e d . The coex i s t ence o f a g r e a t number o f s p e c i e s w i t h i n a g i v e n a rea produces i n t e r s p e - c i f i c r e l a t i o n s o f t e n v e r y complex and s p e c i a l i z e d . Each o f t h e b i o t o p e s s t u d i e d i n t h i s work shows an assemblage o f f l o r i s t i c and f a u n i s t i c spec ies , g e n e r a l l y w e l l - d e f i - ned, whose compos i t i on depends on t h e i n t e r a c t i o n o f s e v e r a l f a c t o r s : presence and d i s t r i b u t i o n o f s u b s t r a t e s a v a i l a b l e t o c o l o n i s a t i o n (Conne l l , 1972 ; Gore, e t a l . , l 9 7 8 ) , i n t e r s p e c i f i c r e l a t i o n s (Pa ine, 19741, c o m p l e x i t y o f b i o t o p e s (Kohn & Nybakken, 1975) , b i o t i c and a b i o t i c env i ronmenta l c o n d i t i o n s (Abele, 1972 ; Conne l l , . 1975) , and b i oeco log i c c h a r a c t e r i s t i c s o f t h e s p e c i e s concerned. The 73 s p e c i e s c o l l e c t e d a t T i ahu ra a r e a d j u s t e d t o t h i s schema, and a l t hough t h e dominant s p e c i e s t end t o a w ide d i s t r i b u t i o n i n t h e t r a n s e c t , t h e q u a l i t a t i v e compo- s i t o n (and m a i n l y t h e q u a n t i t a i v e composi t i o n ) o f popu la- t i o n s i s r a t h e r d i f f e r e n t f r om one a rea t o another . These d i f f e r e n c e s a r e de f i ned , f i r s t , by t h e s p a t i a l d i s t r i b u - t i o n o f t h e 10-12 spec ies f o l l o w i n g i n abundance t h e 4 dominant spec ies , and second, by t h e p a r t i c u l a r r e p a r t i - t i o n o f each spec ies i n t h e s u b s t r a t e s . I n agreement w i t h Abele ( l 9 7 2 ) , Gore e t a1 . ( l 9 7 8 ) , and o t h e r s , t h e n u m e r i c a l l y dominant s p e c i e s w i t h i n a b i o t o p e a r e g e n e r a l l y t hose t h a t possess t h e b e s t adapta- t i o n s (morpho log ica l o r o t h e r s ) f o r f a v o r a b l e e x p l o i t a - t i o n o f t h e i r resources. One o f t hese a d a p t a t i o n s which seems t o have a s t r o n g i n f l u e n c e over t h e community composi t i o n i n t h e d i f f e r e n t b i o t o p e s i s t h e a1 imen ta r y reg ime of spec ies (Odum & Odum, 1955 ; Paine, 1966). The t y p e o f f o o d o f c r u s t a c e a n s i s c l o s e 1 y r e l a t e d w i t h t h e morphology and t h e s i z e o f t h e spec ies , b o t h t h e consumer and t h e p r e y ( a f t e r d i f f e r e n t a u t h o r s ) . On t h a t b a s i s , we have proposed 5 MORPHOLOGIC GROUPS. I n each a r e i n c l u d e d s p e c i e s h a v i n g morpho log ic s i m i l a r i t i e s which may i n d i c a t e t h e u t i l i s a t i o n o f t h e same k i n d o f food. These d i v i s i o n s a r e n o t s t r i c t : c r a b s a r e w e l l - known t o show tendences t o omnivor ism, and t h e h i g h d i v e r s i t y of a , h i g h i s l a n d c o r a l r e e f system may f a v o r a non--speci a1 i zed f eed i ng behav i o u r , t h e c h o i c e o f r e s o u r - ces b e i n g q u i t e l a r g e . N e v e r t h e l e s s , some morphol o g i c f e a t u r e s observed i n t h e c r u s t a c e a n s i n o u r work suggest t h a t t h e r e a c t u a l l y e x i s t s a c e r t a i n degree o f f e e d i n g s e l e c t i v i t y . Bes ides , t h e s i m i l a r s i z e s o f s p e c i e s (most o f them do n o t measure more than 20 mm w i d t h i n t h e i r a d u l t s t a g e ) , suggest t h e u t i l i z a t i o n o f s i m i l a r a l i m e n t a r y r e s o u r c e s , and i n con- sequence, t h e r e would be a c o m p e t i t i o n f o r these, f o r t h e y a r e c e r t a i n 1 y n o t u n l i m i t e d . T h i s c o n d i t i o n c o n f i r m s t h e e x i s t e n c e o f a1 i m e n t a r y s p e c i a l i s a t i o n , main1 y i n abundant spec ies , as ment ioned b y Gore, e t a l . (1978) . The e f f e c t o f t h i s s p e c i a l i s a t i o n i s r e f l e c t e d i n t h e r e p a r t i t i o n o f s p e c i e s i n t h e t r a n s e c t and i n t h e d i f f e - r e n t s u b s t r a t e s . Two f a c t o r s i n h e r e n t t o t h e s u b s t r a t e s s t u d i e d c o u l d de te rm ine t h e s e d i f f e r e n c e s : t h e degree o f n e c r o b i o s i s o f t h e c o r a l c o l o n y wh ich p e r m i t s a more o r l e s s e x t e n s i v e c o l o n i s a t i o n b y a l g a e and t h e i r a s s o c i a t e d fauna, and t h e c o m p l e x i t y o f t h e c a v i t a r y ne twork which o f f e r s adequate s h e l t e r t o t h e c r y p t o f auna. I n t h e s e te rms, t h e dead s u b s t r a t e would be t h e b e s t , i t shows a h i g h a l g a l c o l o n i s a t i o n , an abundant a s s o c i a t e d fauna, and i n most cases, a we1 1-developed c a v i t a r y ne twork . For l i v i n g c o r a l s , Fbygna cactus and Psammocora p r e s e n t more f a v o r a b l e f a c t o r s f o r t h e c o l o n i s a t i o n by t h e c a r c i n o l o - g i c c r y p t o f a u n a , which i s n o t t h e case f o r P o r i t e g ( t h e c o l o n y i s compact w i t h few o r no a n f r a c t u o s i t i e s ) . Moreover, i t i s necessary t o t a k e i n - t o account t h e e f f e c t o f t h e e c o l o g i c c o n d i t i o n s p r o p e r t o each r e e f s e c t o r . Thus, t h e t r a n s e c t o f T i a h u r a i s s p a t i a l l y shared b y t h e o m n i v o r e / h e r b i v o r e s p e c i e s t h a t p r e f e r t h e f r i n - g i n g r e e f where dead s u b s t r a t e (and t h e r e f o r e a l g a e ) , i s more abundant, and by t h e omni v o r e / c a r n i v o r e s p e c i e s t h a t t e n d t o aggrega te i n t h e b a r r i e r - r e e f , m a i n l y i n t h e o u t e r r e e f f l a t and t h e r e e f f r o n t a reas , where po lychae- t e s and mo l luscs , t h e i r p r i n c i p a l f o o d respurce , a r e more abundant (Peyrot-Clausade, 1976 ; Naim, 1980b ; R ichard , 1982) . The f i l t e r / s u s p e n s i o n f e e d e r s sea rch f o r low- s e d i m e n t a t i o n a reas w i t h modera te l y s t r o n g c u r r e n t s ( i n - n e r b a r r i e r - r e e f ) , f a v o r a b l e t o t h e i r f i l t e r i n g a c t i v i - t i e s , w h i l e t h e g e n e r a l i z e d omnivores p r e f e r t h e a reas o f o rgan i c d e p o s i t i o n ( s h a l l ow beach ma rg i ns ) . P redac ious / c a r n i v o r e s spec ies a r e n o t abundant i n lagoon a reas o f t h e t r a n s e c t , a1 though some f a c u l t a t i v e malacophages a r e l o c a l i z e d i n t h e r e e f f r o n t . W i t h i n each o f t h e morpho log ic groups, t h e r e a r e one o r two n u m e r i c a l l y dominant spec ies whose r e p a r t i t i o n over t h e t r a n s e c t o f T iahura , and i n t h e d i f f e r e n t sub- s t r a t e s suggests t h e i n f l u e n c e o f a t r o p h i c p a r t i t i o n i n g phenomenpn@choener, 1974 ; Gore, e t a l . , 1978). The f o u r most abundant spec ies i n t h e t r a n s e c t ( C h l o r o d i e l l a b a r - ba ta , P i l o d i u ? e u ~ i i , L i o c a r p i l o d e s h t e q e r r i m u ? and Gala thea a c u l e a t a ) , u t i 1 i z e a p p a r e n t l y d i f f e r e n t t y p e s o f -------- -------- food, a r e d i s t r i b u t e d i n a p a r t i c u l a r p a t t e r n i n t h e s u b s t r a t e s , and occupy more o r l e s s t h e same areas. The f i v e o r s i x f o l l o w i n g spec ies a l s o seem t o show t hese t h r e e t y p e s o f r e l a t i o n s h i p s . There would e x i s t t h e r e f o- r e , two main s t r a t e g i e s t o a v o i d o r t o reduce c o m p e t i t i o n among t hese spec ies : a t r o p h i c p a r t i t i o n i n g by r e s t r i c - t i o n o f t h e i r a l i m e n t a r y reg ime when two o r more abundant spec ies l i v e i n t h e same a rea ( i n t h i s case each spec ies w i l l show d i f f e r e n t a l i m e n t a r y needs) , and a h a b i t a t p a r t i t i o n i n g when two spec ies l i v i n g i n t h e same a rea search f o r s i m i l a r a l i m e n t a r y r esou rces (here , one o f t h e spec ies would be l e s s r e s t r i c t i v e t han t h e o t h e r i n i t s a l i m e n t a r y regime, t h u s a b l e t o e x p l o i t a more e x t e n s i v e b i o t ope , i .e. i n h a b i t o t h e r t y p e s o f s u b s t r a t e ) , o r , i f c o m p e t i t i o n i s i n a v o i d a b l e , a s p a t i a l e x c l u s i o n t a k e s p l ace . I n t e r s p e c i f i c r e l a t i o n s a r e q u i t e c l e a r , i n t h e p re - sen t work, among t h e dominant spec ies and among some o f t h e abundant spec ies , b o t h i n te rms o f s p a t i a l d i s t r i b u - t i o n and r e p a r t i t i o n on t h e s u b s t r a t e s . However, t h e p i c t u r e becomes more complex when more spec ies i n t e r a c t . I n t h i s case, i t i s p o s s i b l e t h a t i n t e r s p e c i f i c r e l a t i o n s would occur w i t h assemblages o f spec ies . We may ment ion L i o c a r p i l o d e s h t e g e r r i m u s (omni v o r e / c a r n i v o r e : dominant s p e c i e s ) , w i t h t h e group o f l e s s abundant omn i vo re / ca rn i - v o r e spec ies i n t h e b a r r i e r - r e e f and t h e r e e f f r o n t (Eioboellumnus q i ~ k o s u s , Paraxanthias notatus, D a i r a e e r l a t a , e t c . ) ; Ch lo rodLe lLa b a r b a t a and P i l o d i g s p g q i l ( omn i vo res /he rb i vo res : dominant s p e c i e s ) , w i t h t h e group o f omn i vo re /he rb i vo re spec ies i n t h e f r i n g i n g r e e f (F'hy: modius m q u l a t u s , Plnit idus, P i l o d i u s s c a b r i c u l g s , e t c . ) ------ Abele (1974) and Gore, e t a l . (19781, s t a t e d t h a t mar ine decapod c rus taceans u t i l i z e t h e s u b s t r a t e i n t h r e e main ways : 1) as a permanent she1 t e r , 2 ) as a f e e d i n g s i t e , 3 ) as a d i r e c t f ood resource . The d a t a o b t a i n e d i n t h i s s t u d y agree w i t h t h e s e f i n d i n g s , more t h a n 90% o f t h e s p e c i e s c o l l e c t e d u t i l i z e t h e c a v i t a r y s u b s t r a t e a s she1 t e r (excep t endogenous and " f r e e l i v i n g " s p e c i e s ) . Then, t h e o b s e r v a t i o n s o f g u t c o n t e n t s suggest t h a t s p e c i e s u t i l i z e t h e s u b s t r a t e a l s o as a f e e d i n g s i t e . But concern ing t h e u t i l i s a t i o n o f s u b s t r a t e a s a d i r e c t a l i m e n t a r y resource , t h i s c o u l d on1 y happen i n 1 i v i n g c o r a l s , and i t i s n o t a lways e v i - den t . Except f o r some o f t h e we1 l -known c o r a l i v o r e s pagu- r i d c rabs , we cannot demonst ra te t h e e x i s t e n c e o f o t h e r c o r a l i v o r e s p e c i e s ( e i t h e r s t r i c t o r f a c u l t a t i v e ) , a l - though t h i s p o s s s i b i l i t y i s l i k e l y t o occur , c h e l i p e d s w i t h sha rp -po in ted f i n g e r t i p s would be m o r p h o l o g i c a l l y adapted t o c r u s h t h e o u t e r s u r f a c e o r t h e c o r a l i t e s and t h e n e x t r a c t t h e s o f t t i s s u e s f r o m t h e i n t e r i o r . Gore, e t a1 . ( l 9 7 8 ) , observed a s i m i 1 a r behav i our i n Men_ippe n d i I f r o n s i n h a b i t i n g t h e s a b e l l a r i i d r e e f s . ----- P r e d a t i o n a c t i v i t i e s among c r u s t a c e a n s p e c i e s appear l i m i t e d . C e r t a i n more o r l e s s l a r g e - s i z e d s p e c i e s such a s tXgbop i 1 umnus q l obosus, Xanth i a? i a m a r c k i and D a i r a p e r - h t _ a _ , may p r o b a b l y a t t a c k s m a l l e r s p e c i e s i n h a b i t i n g t h e same a r e a (L ioxan thodes a l c o c k i P a r a x a n t h i a s n o t a t u s ------------ - - - - - - - I ------------ - - - - - - - 9 L_ iocayp i l odes i n t e q e r r i m u s , C h l o r o d i e l l a ------------ ----------~ l a e v i s s i m a e t c . ) . J u v e n i l e s , and i n d i v i d u a l s undergo ing m o l t i n g s t a g e s c o u l d a1 so become p rey . Besides, ma1 acophage c r a b s would consume numbers o f p a g u r i d c r a b s i nhab i t i ng g a s t r o - pod s h e l l s (Rossi & P a r i s i , 1973). F i n a l l y , we may d e f i n e t h e t r a n s e c t o f T i a h u r a a s a t o p o g r a p h i c a l 1 y complex and i r r e g u l a r h a b i t a t , h a v i n g a r e l a t i v e 1 y c o n s t a n t a b i o t i c env i ronment , which f a v o r s a h i g h s p e c i f i c d i v e r s i t y and numer ic abundance. However, i t i s n o t f a v o r a b l e t o an e c o l o g i c s p e c i a l i s a t i o n o f s p e c i e s and t o t h e presence o f l a r g e p r e d a c i o u s c rabs . The s ta temen t b y Kohn (1968, 1971a) f o r Conus popu la- t i o n s , and b y Abe le (1974) : "more s t r u c t u r a l l y complex h a b i t a t s c o u l d s u p p o r t a h i g h e r number o f s p e c i e s t h a n s t r u c t u r a l 1 y s i m p l e r h a b i t a t s " , would have been conf i rmed i f we had compared t h e c rus tacean communi t ies o f H i g h I s l a n d s and a t o l l s , a s t u d y t h a t s h o u l d be done i n t h e f u t u r e . ACKNOWLEDGEMENTS. My s p e c i a l t h a n k s t s M. Bernard S a l v a t , D i r e c t o r o f t h e L a b o r a t o i r e de B i o l o g i e M a r i n e e t M a l a c o l o g i e o f t h e E c o l e P r a t i q u e des Hautes Etudes, P a r i s , and t o M. Georges R ichard , C h i e f o f Research i n t h e L a b o r a t o r y , and t o a1 1 t h e s t a f f who made p o s s i b l e t h e developpement o f t h i s work, b o t h i n F rench P o l y n e s i a and P a r i s . "You a r e always p resen t i n my t hough t s " . I am a l s o g r a t e f u l t o Dr. A u s t i n W i l l i a m s o f t h e Smi thson ian I n s t i t u t i o n f o r h i s c o n s t r u c t i v e a d v i c e and c o r r e c t i o n s t o t h e manuscr ip t . BIBLIOGRAPHY. .Abele, L.G., 1972. Comparat ive h a b i t a t d i v e r s i t y and f auna l r e l a t i o n s h i p s between t h e P a c i f i c and Car ibbean Panamian decapod Crus tacea : a p r e l i m i n a r y r e p o r t w i t h some remarks on t h e c rus tacean fauna of Panama. B u l l . B i o l . Soc. Wash.,' 2 : 125-138. .Abele, L.G., 1974. Spec ies d i v e r s i t y o f decapod c r u s t a - ceans i n mar ine h a b i t a t s . Ecology, 55(1) : 156-161. .Anonymous, 1977. Cora l r e e f and l agon resea rch i n French P o l y n e s i a : 123 p u b l i c a t i o n s w i t h a b s t r a c t s . Rev. Algo- 1 09. Fasc. Hors Ser . , 1 : 43 pp . .Bacon, M.R., 1971. Zona t ion and h a b i t s o f t h e g r a p s i d c rabs f'i'gusia capens i s and k e $ ~ g r ~ p s u s v a r i e g a t g s . Tane, 17 : 123-127. .Bakus, G. J. , 1975. Mar ine z o n a t i o n and eco logy o f Cocos I s l a n d , o f f C e n t r a l America. A t o l l Res. B u l l . , 179:l-9. . B a l l , G.H., 1950. Examinat ion o f Hawaian mar ine c r u s t a - ceans f o r g rega r i ness . Pac. Sc i . , 4 : 283. . B a l l , E.E. & J. Haig, 1974. Hermi t c rabs f rom t h e T r o p i - c a l Eas te rn P a c i f i c . I. - D i s t r i b u t i o n , c o l o r and n a t u r a l h i s t o r y o f some common s h a l l ow-water spec ies . B u l l . South. C a l i f . Acad. Sc i . , 73(2) : 27-49. .Bovb jerg , R.V. , 1960. Behav iou ra l eco logy o f t h e c r a b Pac iygrapsus cyass iegs . Ecology, 41 (4) : 668-672. .Burrows, M., 1969. The mechanics and n e u r a l c o n t r o l o f t h e p r e y c a p t u r e s t r i k e i n t h e man t id shr imps SguLlia and Hem isqu i l i a . 2 . Verg l , Phys i o l , , 62 : 361-381. .Caine, E.A., 1975. Feeding and m a s t i c a t o r y s t r u c t u r e s o f s e l e c t e d Qnomura (Crustacea, Decapoda) . Jour . Exp. Mar. B i 01. Eco l . , 18 : 227-301. .Ca ldwe l l , R.L. & D i n g l e , 1975. Ecology and a g o n i s t i c behav i our i n stomatopods. Naturwissenschaf ten , 62 : 214- 222. .Conne l l , J.H., 1972. On t h e r o l e o f n a t u r a l enemies i n p r e v e n t i n g c o m p e t i t i v e e x c l u s i o n i n some mar ine an ima ls and i n r a i n f o r e s t t r e e s . Proc. Adv. Stud. I n s t . Dyna- m i cs Numbers Pop., (Oosterbeek) : 298-312. .Conne l l , J.H., 1975. Community i n t e r a c t i o n s i n mar ine r o c k y i n t e r t i d a l shores. Ann. Rev. Eco l . Sys t . , 3 : 169- 172. .Crane, J., 1947. Eas te rn P a c i f i c E x p e d i t i o n of t h e New York Z o o l o g i c a l S o c i e t y . X X X V I I I. - I n t e r t i d a l brachygna- t hous c r a b s f rom t h e west coas t o f t r o p i c a l America w i t h s p e c i a l r e f e r e n c e t o eco logy. Zoo log ica , 32 : 69-95. .Dah l , E., 1952. Some aspec ts o f t h e eco logy and z o n a t i o n of t h e fauna on sandy beaches. O i kos, 4 : 1-27. . E b l i n g , F .J . , et d,, 1964. The eco logy o f Lough L i ne . X I I1 . - Exper imen ta l o b s e r v a t i o n s o f t h e d e s t r u c t i o n o f M y & i l y s edgdiz and N u c e l l a h p i d y s by crabs. Jour . Anim. Eco l . , 35 : 559-566. . Faus to -F i l ho & E. Fu r tado , 1970. Nota p r e l i m i n a r sobre a faune das c o l o n i e s de S a b e l l a r i i d a e do l i t t o r a l do Esta- do do Ceara (Annelids, S e d e n t a r i a ) . Rev. B r a 6 i 1 B i o l . , 30 : 285-289. . Fo res t , J. & D. Gu ino t , 1961. Crus taces Decapodes Bra- chyoures de T a h i t i e t des Tuamotu. E x e d i t i o n F r a n c a i s e s u r l e s r e c i f s c o r a l l i e n s de l a N o u v e l l e Ca ledon ie . Ed. Singer -Po l ignac , Vo l . p r e l . : 195 pp. . Fo res t , J. & D. Gui n o t , 1962. Remarques b iogeograph i ques s u r l e s c rabes des A r c h i p e l s de l a S o c i g t e e t des Tuamo- t u . Cah. P a c i f . , 4 : 41-57. .Ga lz in , R., 1977b. R ichesse e t p r o d u c t i v i t e des ecosys- temes l a g u n a r i e s e t r e c i f aux. Appl i c a t i o n A 1 'P tude dynamique d 'une p o p u l a t i o n de P o m a c e ~ t r u s n ig r i cans du Lagon de Moorea. These Doct. 39me Cyc le . M o n t p e l l i e r : 109 pp. .Garth, J.S., 1974. Decapod c rus taceans i n h a b i t i n g r e e f - b u i l d i n g c o r a l s o f Ceylon and M a l d i v e I s l a n d s . Jour . B i o l A s s . I n d i a , 15 : 195-212. .George, R. W., 1972. I l e s du P a c i f i que Sud : Ressources en Langoustes. FCIO, Rome, F I : RAS/69/102/9, (426/73) : 73 P P - .George, R.W., 1974. C o r a l r e e f and r o c k l o b s t e r e c o l o g y i n t h e Indo-West P a c i f i s r e g i o n . Proc. 2nd. I n t . C o r a l Reef Symp. , 1 : 321 -325. .Glynn, P.W., 1973. Aspects o f t h e e c o l o g y o f c o r a l r e e f s i n Western A t l a n t i c r e g i o n . I n : B i o l o g y aand Geology o f C o r a l Reefs, Vo l . 1 : 273-324. 0.4. Jones and R. Endean (Eds.) . New York Acad. Press. .Glynn, P.W. & R.H. S t e w a r t , 1972. P a c i f i c c o r a l r e e f s o f Panama : s t r u c t u r e , d i s t r i b u t i o n and p r e d a t o r s . Geol. Rundechan, 61 : 481-519. .Gordon, I. , 1964. Crus tacea -General c o n s i d e r a t i ons. In:, C.S.4. S p e c i a l i s t Mee t ing on Crustaceans. OAU/STRC (Zan- z i b a r ) , Pub. 96 : 27-86. .Gore, R. H. , d,, 1978. S t u d i e s on t h e decapod Crus ta - cea f r o m t h e I n d i a n R i v e r , F l o r i d a . 1V.- Community com- p o s i t i o n , s t a b i 1 i t y and t r o p h i c p a r t i t i o n i n g i n decapod c r u s t a c e a n s i n h a b i t i n g some s u b t r o p i c a l s a b e l l a r i i d worm r e e f s . B u l l . Mar. S c i . , 2 8 ( 2 ) : 221-248. G r i f f i n , D. J.G., 1971. The e c o l o g i c a l d i s t r i b u t i o n o f g r a p s i d and ocypodi d sho re c r a b s (Crus tacea, B rachyura ) i n Tasmani a. Jour . Ani m. Eco l . , 40 : 597-622. G r i f f i n , D.J.G & J.C. Yaldwin, 1977. B rachyura (Crus ta - cea, Decapoda) . Mem. N a t i o n . Mus. V i c t o r i a , A u s t r a l i d , 32 : 43-63. .Gruet , Y., 1970. Faune assoc ige des " r g c i f s " P d i f i P s p a r 1 ' Anne1 i de S a b e l l a r i a a1 veo l a t a ( L i ring) en B a i e de Mont Sa in t -M iche l : Banc des Hermel les . Mem. Soc.Sci. Cher- bourg, 54 : 1-21. . Gruet , Y., 1971. Morpho log ie , c r o i ssance e t f dune asso- c i e e des r g c i f s de S a b e l l a r i a a l y e o l a t g ( L i n n P ) de l a Berner ie-en-Retz ( L o i r e A t l a n t i q u e ) . Te thys , 3 : 321- 380. .Gu ino t , D., 1967. Les c rabes c o m e s t i b l e s de 1 ' I n d o - P a c i f i que. Ed. F o n d a t i o n S inger -Po l i gnac , 145 pp. .Hamil t on , P.V., 1976. P r e d a t i o n on L i t t o r i n a i r r o r a t a (Mol l u s c a , Gastropoda) b y Gal 1 i n e c t e s s a p i d u s (Crus ta - cea, P o r t u n i a d e ) . B u l l . Mar. S c i . , 26 : 403-409. .Harmel i n - V i v i e n , M. L., 1981. T roph i c r e l a t i o n s h i p s o f r e e e f f i shes i n Tu l ear (Madagascar ) . Ocean01 . Acta. , 4 ( 3 ) : 365-374. . H a z l e t t , B.A., 1974. F i e l d obse rva t i ons on t h e in te rspe- . c i f i c a g o n i s t i c behaviour i n he rm i t crabs. Crustaceans, 26 : 33-138. . H i a t t , R.W. & D.W. St rasburg, 1960. Eco log i ca l r e l a t i o n - s h i p s o f t h e f i s h fauna o f c o r a l r e e f s of t h e Marshal l I s l ands . Ecol . Monogr., 30 (1 ) : 65-127. .Jacquinot , H. & H. Lucas, 1853. A t l a s Crustacgs. i n : Hombron e t Jaquinot (Eds. ) : Voyage au P81e Sud e t dans 1 'Oceanie execute pendant 1837-1840. Zoologie, P a r i s : 107 pp. .Knudsen, J.W., 1960. Aspects o f t h e ecology o f t h e C a l i f o r n i a x a n t h i d crabs. Eco l . Monogr., 30 (2 ) : 165- 185. . Knudsen, J. W. , 1964. Observat ions o f t h e r e p r o d u c t i v e c y c l e s and eco logy o f t h e common Brachyura and c r a b - l i k e Anomura o f Puget Sound, Washington. Pac. Sc i . , 17 : 3- 33. .Kohn, A. J . , 1968. Microhabi t a t s , abundance and food o f Cgngs on a t o l l r e e f s i n t h e Mald ive and Chagos Is lands . Ecology, 49 (6 ) : 1046-1062. .Kohn, A.J., 1971a. D i v e r s i t y , u t i l i s a t i o n of resources and a d a p t a t i v e r a d i a t i o n i n sha l low-water mar ine i n v e r - t e b r a t e s of t r o p i c a l oceanic i s 1 ands. L i mnol . Oceanogr., 16 : 332-348. .Kohn, A.J. & J.W. Nybakken, 1975. Ecology o f Gongs on Eastern I n d i a n Ocean f r i n g i n g r e e f : D i v e r s i t y of spe- c i e s and resource u t i l i s a t i o n . Mar. B i o l . , 29 : 211-234. .Kropp, R.K. & B i r ke land , 1981. Comparison o f crustacean assoc ia tes o f Pocillgpm-5 ver rgcosa f rom h i g h i s l a n d and a t o l l . Proc. 4th. I n t . Coral Reef Symp., Mani la, Vol. 2: 627-632. . Kunze, J. & D. T. Anderson, 1979. Func t i ona l morphology of t h e mouth-parts and g a s t r i c m i l l i n t h e he rm i t c rabs CLLbanarigs teen iagys, Clibanaa-igs yiynscees, Paquyisges squamosus and Dardanus s e t i f g y . Aust r . Jour. Freshwat. R e s . , 30 : 683-772. . M i lne-Edwards, H. , 1861-1904. Reccuei 1 de t ravaux sur l e s CrustacPs Decapodes de l ' l ndo -Pac i f i que . Arch ives du Museum Na t i ona l d ' H i s t o i r e Nature1 l e , Par is . . Montef o r t e , M., 1984a. C o n t r i b u t i o n d 1 a connai ssance de l a faune c a r c i n o l o g i que de Po l ynes ie Franca ise. Thase Doct. Eco le P r a t i q u e des Hautes Etudes, P a r i s : 198 pp. . Montef o r t e , M. , 1984b. Etudes des peupl ements des Crus- t acgs Dgcapodes e t Stomatopodes de Pol yngs i e Franca i se. These Doct. 3Bme Cycle. Univ. P a r i s V I . .Muntz, L.F., d:, 1975. The eco logy o f Lough L ine . X I V . - Preda to ry a c t i v i t y o f l a r g e crabs. Jour. Anim. Eco l . , 35 : 315-329. .Naim, O., 1980a. Etude q u a l i t a t i v e e t q u a n t i t a t i v e de l a f aune mobi l e assoc iee aux a lgues du Lagon de Tiahura. Th&e Doct. 3eme Cycle. Univ. P a r i s V I : 105 pp. . Nai m, O., 1980b. Etude de l a f aune ma1 aco l o g i que asso- c i e e aux a lgues du Lagon de T iahura (Moored). H a l i o t i s , l O ( 2 ) : 178. . N i c o l , E. A. T. , 1932. The f eed ing h a b i t s o f t h e Gal a t h e i - dae. Jour. Mar. B i o l . Assoc. U.K., 18 : 87-106. .Odinetz, O., 1983. Eco log ie e t s t r u c t u r e des peuplements de Crustaces Decapodes assoc ies aux coraux du genre Poc i ------- 11 opora --- en Pol ynhs i e F ranca i se e t en M i c rones i e (Guam). These Doct. 3eme Cycle. Univ. P a r i s V I : 221 pp. .Odum, H.T. & E.P. Odum, 1955. Troph ic s t r u c t u r e and p r o d u c t i v i t y o f a windward c o r a l r e e f community (Eni we- e t o k ) . Eco l . Monogr., 25 : 291-320. .Orton, J.H., 1927. On t h e methods o f f eed ing o f t h e h e r m i t c rab Egeaqgugs kernhardus and some o the r Decapo- da. Jour. Mar. B i o l . Assoc. U.K., 14 : 909-921. .Paine, R. T., 1966. Food web comp lex i t y and spec ies d i - v e r s i t y . Amer. Natur . , 100 : 65-75. . Paine, R. T. , 1974. I n t e r t i d a l community s t r u c t u r e . Expe- r i m e n t a l s t u d i e s i n t h e r e l a t i o n s h i p between a dominant compet i to r and i t s p r i n c i p a l p reda to r . Oecologia, 15 : 93-120. . P a y r i , C., 1982. Les macrophytes du Lagon de T iahura ( I l e de Moorea, Po l yngs ie F ranca i se ) . These Doct. 3eme Cycle. U.S.T.L., M o n t p e l l i e r : 260 pp. . P e r k , J.M. & J. P i ca rd , 1969. Ref l e x i o n s sur l a s t r u c - t u r e t r o p h i q u e des e d i f i c e s r g c i f a u x . Mar. B i o l . , 3 ( 3 ) : 227-232. .Peyrot-Clausade, M., 1977a. Faune c a v i t a r i e m o b i l e des p l a t i e r s c o r a l 1 i e n s de l a r P g i o n de Tu lea r (Madagascar). These Sc i . Nat . , Un iv . A i x - M a r s e i l l e I 1 : 184 pp. . Peyro t -C l ausade, M. , 1977b. Decapodes Brachyoures e t Anomoures ( A 1 ' e x c l u s i o n des Pagur idae) de 1 a c r y p t o f au- ne du r P c i f de T iahura , Moorea. Cah. P a c i f . , 20 : 211- 221. .Reynolds, W.W. & L .J . Reynolds, 1977. Zoogeography and t h e p r e d a t o r - p r e y "arm-race" : a compar ison o f E r i p h i a and N e r i t a ------ s p e c i e s f rom t h r e e f auna l r e g i o n s . Hydrob io- l o g i a , 56 : 63-68. . R h e i n a l l t , T., 1986. S i z e s e l e c t i o n by t h e c r a b Liocai~ c i n u s puber f e e d i n g on mussels M y t i l g s e d u l i s and on ----- shore c rabs Ca rc i ngs maenas : t h e impor tance o f mechani- c a l f a c t o r s . Mar. Eco l . P rogr . Ser., 29 ( 1 ) : 45-53. .Rhe ina l l t , T. & R. W. Hughes, 1985. Hand1 i n g methods used by t h e v e l v e t swimming c rab l .Agcarcinus puber when f e - ed i ng on m o l l uscs and shore c rabs. Mar. Eco l . Progr . Ser . , 2 5 ( 1) : 63-70. .R ichard , G., 1982. Mol lusques l a g o n a i r e s e t r e c i f aux de Po l ynPs ie F r a n c a i s e : I n v e n t a i r e f a u n i s t i q u e , b ionomie, b i l a n q u a n t i t a t i f , c r o i s sance , p r o d u c t i o n . ThrSse Sc i . Nat . , P a r i s : 313 pp. .R ivosecch i , E.T., 1961. Observaz ion i s u l l e b i ocenos i d e l banco a S a b e l l a r i a d i L a v i n i o . E s t r . Rend. Occad. Naz io- n a l e XL, Ser. 4, 12 : 1-11. .Ropes, J.W., 1968. The f e e d i n g h a b i t s o f t h e green c rab Carc inus maenas. F i sh . B u l l . , 67 : 183-203. .Ross i , A.C. & V. P a r i s i , 1973. Exper imen ta l s t u d i e s o f p r e d a t i o n by t h e c rab E rLgh ia ve r rucosa on b o t h s n a i l s and h e r m i t c r a b s o f conspec i f i c gas t ropod s h e l l s . B u l l . Zool. , 40 : 117-135. . S a l v a t , B. e& d-, 1972. Moorea-Tiahura : Etude des peuplements du l agon e t du r e c i f . Museum/EPHE, Ontenne de T a h i t i . Rapport i n t e r n e : 104 pp. .Samuelson, T., 1970. The b i o l o g y of s i x spec ies of Anomura (Crus tacea, Decapoda), f r om Rannef jo rden, Wes- t e r n Norway. Sa rs i a , 45 : 25-52. .Ischafer, W., 1954. Form und f u n k t i o n der Brachyuren- Schere. Obh. Senckenb.Naturf . Gee., F r a n k f u r t , 489: 1-65. .Schoener, T.W., 1974. Resource p a r t i t i o n i n g i n e c o l o g i - c a l communi t ies. Science, 185 : 27-39. .Ser@ne, R., 1972. On t h e Brachyuran f aune o f t h e Indo- West P a c i f i c c o r a l r e e f s. Proc. Symp. C o r a l s and C o r a l Reefs. Jou r . Mar. B i o l . A s s . I n d i a : 419-424. .Shoup, J.B., 1968. She1 1 open ing by c r a b s o f t h e genus &slappa. Sc ience, 160 : 887-888. . S k i l l e t e r , G.A. & D.T. Anderson, 1986. F u n c t i o n a l mor- pho logy o f t h e c h e l i p e d s , mouth-par ts and g a s t r i c m i l l o f g g j g g k r u n c a t u g ( M i 1 ne-Edwards) ( X a n t h i dae) , and hptgqraesgs yarl-gaags ( F a b r i c i u s ) (Graps i dae) (Bra- c h y u r a ) . Aust . Jou r . Mar. Freshwat . Res., 3 7 ( 1 ) : 67- .Ve rme i j , G.J., 1977a. P a t t e r n s i n c r a b c law s i z e : t h e geography o f c r u s h i n g . Sys t . Zool . , 26 : 138-151. . Vermei j, G. J . , 1978. Biogeography and a d a p t a t i o n . P a t - t e r n s o f mar ine l i f e . Harva rd Un iv . Press . : 332 pp. . V i v i e n , M. L. & M. Peyrot -Clausade, 1974. A compara t i ve s t u d y o f t h e f e e d i n g behav iou r o f t h r e e c o r a l r e e f f i s h e s ( H o l o c e n t r i d a e ) , w i t h s p e c i a l r e f e r e n c e t o t h e p o l y c h a e t e s o f r e e f c r y p t o f a u n a as p rey . Proc. 2nd. I n t . C o r a l Reef Symp. , 1 : 179-1 92. .Warner, G. F., 1977. The B i 01 ogy o f c rabs . Van Nos t rand R e i n h o l d Co. (Ed.) : 202 pp. .Ya ldwin , J.C., 1972. Decapod Crus tacea f r o m South P a c i - f i c r e e f s and I s l a n d s . Oceanography o f t h e South Pac i - - f i c , 1972. Comp. R. F r a s e r , New Zealand. Nat . Comm. UNESCO. W e l l i n g t o n , 1973 : 503-511. . Z i p s e r , E. & G.J. Ve rme i j , 1978. Crush ing behav iou r o f t r o p i c a l and tempera te c rabs . Jour . Exp. Mar. B i o l . Eco l . , 31 : 155-172.