5 Profiles of typical shallow-water communities on leeward (sheltered) and windward (exposed) coasts of the Tobago Cays

ATOLL RESEARCH BULLETIN NO. 178

A PRELIMINARY DESCRIPTION OF THE CORAL REEFS OF THE TOBAGO CAYS, GRENADINES, WEST INDIES

by John B. Lewia

Issued hy

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

January 15,1975

Contents

Introduction

List of corals found at Tobago Cays Description of Horseshoe Reef

Back reef Reef crest Reef front

Distri.bution of shallow water communities around the islands

Petit Rameau Petit Bateau Daradal

Jamesby Discussion References

Figures (following p .

9)

1 Map of Tobago Cays with inset showing Lesser Antilles and Grenadines.

2 Three dimensional sketch of a generalized transect across the Horseshoe Reef showing zonation. Sketch not to scale. Depth 15-20 meters; horizontal

distance approximately 100 meters.

3

Distribution of shallow water communities around Petit Rameau and Petit Bateau, Tobago Cays.

4

Distribution of shallow water communities around Baradal and Jamesby, Tobago Cays.

5

Profiles of typical shallow-water communities on leeward (sheltered) and windward (exposed) coasts of the Tobago Cays.

A PRELIMINARY DESCRIPTION OF THE CORAL REEFS OF THE TOBAGO CAYS, GRENADINES, WEST INDIES

1

/

by John B. Lewis-

INTRODUCTION

The Tobago Cays are composed of four small islands of the Grenadines lying between St. Vincent and Grenada, Vest 1ndi.e~ at 1 2 O 2 8 ' ~ , 61°22'~. They are exposed on a long, narrow submarine bank which stretches southward to Grenada.

All are low lying with narrow beaches and rocky coasts and are covered for the most part by scrub vegetation of the type described by Beard

(1949)

for the Grenadines. The largest

island, Petit Bateau, has a n elevation of about

45

meters while the smallest, Jamesby is only 20 meters in height. The islands are not populated. They are visited frequently by fishermen from the nearby islands and are politically administered from Grenada.

The Cays are protected on the east by a semicircular coral reef called the Horseshoe Reef. Heavy seas break over the reef during most of the year and strong and variable currents flow across the reef into the central area. A nap of the Cays and surrounding reef is shown in Fig. 1 .

The distribution of the fauna on Horseshoe Reef and around the Cays was investigated by free divers. Data was recorded on a n underwater slate and on photographs with a Nikonos I1 under- water camera. Three transects across the Horseshoe Reef were studied in detail. Because of the small size of the Cays it was possible to swim around the coast of each one and map the distribution of the shallow water communities. Representative samples of corals and other invertebrates were collected on each dive for subsequent identification.

The work was supported by a grant in aid of research from the National Research Council of Canada. I am grateful to Alan Emery for diving assistance.

-

L'Bellairs Research Institute of McGill University, St. James, Barbados, W.I., and The Redpath Museum, McGill University, Montreal, P . Q . , Canada.

(~anuscript received June, 1972--Ed. )

LIST OF CORALS FOUND AT TOBAGO CAYS Seriatoporidae:

Madracis decactis (~~rnan)

Madracis asperula Milne-Edwards and Haime

-

Acrouoridae: A

Acropora cervicornis (~amarck) - Acropora p a w (Lamarck)

-

Agaricidae:

Agaricia agaricites (Linnaeus) Agaricia fragilis (Dana)

-

Siderastreidae:

Siderastrea radians (pallas)

Siderastrea siderea ( ~ l l i s and solander) -

Poritidae:

Porites astreoides Lamarck Porites porites (pallas) Porites furcata Lamarck

-

Porites divaricata Leseuer Faviidae :

Favia fragvm ( ~ s ~ e r )

Diploria clivosa ( ~ l l i s and Solander) Diploria strigosa (Dana)

Diploria labyrinthiformis (Linnaeus) Colpophyllia natans (MUller)

Colpophyllia amaranthus ( ~ ~ l l e r ) Manicina areolat-aeus)

Solenastrea bournoni Milne-Edwards and Haime Montastrea annularis Ellis and Solander) Montas trea cave= [Linnaeus)

-

Trochosmiliidae:

Meandrina meandrites (Linnaeus)

- Dichocoenia stokesii Milne-Edwards and Haime Dendrogyra cylindrus Ehrenberg

Mussidae :

Mussa angulosa (pallas)

Isophyllastrea rigida ( ~ a n a )

Mycetophyllia lamarckana (~ilne-Edwards and ~ a i m e ) Isophyllia multiflora

erri ill)

Cariophylliidae:

Eusmilia fastigiata (Pallas)

DESCRIPTION OF HORSESHOE REEF

A three dimensional sketch of the zonation across the mid-region of Horseshoe Reef is shown in Fig. 2. Three

distinct regions were recognized, an inner zone or back reef, a reef crest and a reef slope or reef front.

1 . Back reef

This is an area of relatively flat bottom varying in depth between 1 and 2 meters and i n width between 50 and

75

meters. Between the back reef and the Cays the bottom is sandy with meadows of the sea grasses Thalassia testudinum KBnig and Syringodium filiforme Kiltzing, broken by the presence of clumps of corals, sponges, the sea fan - Rhipidogorgia f l a b e l l ~ (Linnaeus) and other alyconarians.

Sediments in the back reef region are composed of coarse calcareous sands and there are wide areas of flat reef rock pavement. Patches of reef are dominated by low clumps of Montastrea annularis which may be 3-4 meters in diameter at the outer edge of the zone. Large colonies of Siderastrea siderea are also common in this zone, together with Porites

-

astreoides, P. porites, Siderastrea radians, Diploria clivosa,

-

D. strigosa, D. labyrinthiformis, Favia fragum, Agaricia - - agaricites, Isophyllastrea rigida and Meandrina meandrites.

Towards the seaward limit of the zone scattered stunted growths of Acropora pairnata occur.

Alcyonarians are very conspicuous on the back reef,

especially the sea fan Rhipidogorgia. Other common alcyonarians include Briareum asbesty-, Pterogorgia acerosa

(pallas), Eunicia asperula (Milne-Edwards a n d x a u r e l i a dichotoma ( ~ s ~ e r ) , P. grisea ( ~ k z e ) , Plexaura flexuosa

T~amouroux) and Muricepsis flavida (~amarck).

Patches of Millepora sp. are common in the mid-region of the back reef and towards the reef crest. Both the flat-bladed form and the more fragile branched types ( ~ o s c h m a ,

1948)

are present.

Other conspicuous invertebrates in this zone include the sea urchins Diadema antillarum (philippi) on the coral patches and rock pavement, Tripneustes esculentus ( ~ e s k e ) on algae covered bottom, the large sedentary polychaete Sabellastarte magnifica

haw)

i n crevices between colonies of Montastrea

annularis, the smaller boring polychaete Spirobranchus giganteus T m a n d numerous species of sponges. Near the reef crest

zone extensive areas of flat reef rock pavement are densely covered with the yellow zooanthid Palythoa mammillosa (Ellis and Solander).

2. Reef crest

The reef crest zone is dominated by dense growths of the branching Acropora palmata. The water depth in mid-zone is

1-2 meters and the width varies between 10 and 2 5 meters across.

The bottom is covered with broken branches of Acropora or is composed of bare rock pavement encrusted with Millepora or

Palythoa and scattered colonies of Porites astreoides and Favia

- --

fragum. Narrow channels, a few meters in width, occur at -- frequent intervals along the reef and are bare of Acropora.

The reef crest zone is thus a band of prolific growth of Acropora and is subjected to heavy wave action and water --- turbulence.

3. Reef front

The reef front may conveniently be considered to begin within the area of turbulence where the water begins to deepen.

At the inner edge, clumps of Acropora palmata appear less dense and low mounds of Montastrea annularis are able to colonize the reef rock surface. There are large areas of uncolonized bare

rock surface, scattered colonies of Porites porites, P. astreoides and the encrusting zooanthid Palythoa.

The seaward slope drops steeply from the reef crest to depths of 15-20 meters. Its face is dominated by large massive mounds of Montastrea annularis from a depth of about 5 meters down. At the top, -- Montastrea forms tall pillar-like clumps but

then changes to shingle shaped colonies and broad sheets towards the bottom of the slope. There is much destruction of the clumps for a considerable amount of talus-like debris lies at the bottom of the slope or on the sandy bottom.

Mixed with the Montastrea are a number of other corals on the slope face. Acropora palmata is common near the top and there are numerous colonies of Porites --

para,

I?. astreoides, P. furcata, Agaricia fragilis, A. agaricites, DeGdrogyra

DISTRIBUTION OF SHALLOW WATER COMMUNITIES AROUND THE ISLANDS The pattern of distribution of shallow water communities around the islands was very similar in each of the four Cays.

Maps of the distribution of the major communities around the islands are shown i n Figs. 3 and 4 .

A prevailing current flows from east to west, across the Horseshoe Reef and past the four Cays. Longshore currents flow

along the east coasts of each of the Cays and are strongest at the northern and southern extremities of the islands. A strong current also flows between Rameau and Rateau Cays.

The direction of current flow are shown in Fig. 1 .

Each of the Cays is partially surrounded by a narrow reef.

Except for Jamesby Cay, reefs are absent on the leeward sides.

Between the reefs and the shore are mixed beds of Porites gorites, P. furcata and. Thalassia on patches of s a n d o r reef rock pavement. At the northern and southern extremities of

the islands, where the currents are strongest, there are luxuriant beds of Rhipidogorgia and other alcyonarians. The narrow reefs consist for the most part of low clumps or heads of coral on a sandy bottom which slopes gradually down into a channel. Typical sections of littoral shallow water fringing communi.ties for a leeward and windward coast are shown in Fig. 5.

1 . Petit Rameau

The southern coast of Rameau Cay is fringed by a narrow beach with a small patch of mangrove trees (Rhizophora sp.) near the eastern end. The eastern and western extremities are comprised of rocky outcrops.

Between the south coast reef and the beach the bottom is densely covered with a mixture of Porites p o r i t ~ , P. furcata, the turtlegrass m a l a s s i a and the algae of the genera Halimeda and Amphiroa.

Other corals commonly found in this zone include Manicina aereolata, Porites astreoides, Favia fragum and Stephanocoena - michelani. The anemones Condyla* sp., and ~ i p t a s i a sp., - are abundant, as are the sea urchins Xripneustes esculentus (Leske) and Echinometra lucunter (Linnaeus) and the brittle stars Ophiocoma riseii (Ltl-and 0. echinata (Lamarck).

Several species of sponges i n c l u d i n ~ ~ ~ h e ~ i o s ~ o n g i a vesparia (Lamarck) are abundant.

The Thalassia-Porites association develops upon the debris _P and erect branches of Porites p o r i t z and gorites furcata.

Sediment from two coralline algae of the genera H a l i m e e and Amphiroa is abundant throughout the community. Several other - species of algae are abundant including the genera Laurencia,

Dictyota, Dictyopterus and Zonaria.

-

On the slope below about 2-3 meters Thalassia is absent p--~~~

and beds of Porites porites, P. furcata are mixed with low

clumps of Montastrea annularis, Porites astreoides, Siderastrea radians, S. siderea,

Favia

fragurn and the hydroid gillepora.

Halimeda is still common and the bottom is thickly covered with

-

debris from the calvareous algae and rubble from the branching

P o r i t e s s p e c i e s . There a r e p r o f u s e growths of a number of

s p e c i e s of a l g a e of t h e g e n e r a - D i c t y o t a , P e n i c i l l u s and -- Udotea.

A t t h e bottom of t h e s l o p e and on t h e i n n e r edge of t h e c h a n n e l a t a b o u t 5 m e t e r s a more d i v e r s e c o r a l community i s p r e s e n t . M o n t a s t r e a a n n u l a r i s i s t h e most common s p e c i e s and o c c u r s i n z d e l y s e p a r a t e d clumps. M . c a v e r n o s a , S i d e r a s t r e a s i d e r e a , D i p l o r i a c l i v o s a , D. s t r i g o s a , C o l p o p h y l l i a n a t a n s ,

-

P o r i t e s f u r c a t a , D i c h o c o e n i a s t o k e s i i , A g a r i c i a a g a r i c i t e s and M i l l e p o r a a r e common. - R h i p i d o g o r g i a and o t h e r a l c y o n a r i a n s a r e a l s o p r e s e n t .

The middle of t h e c h a n n e l between t h e s o u t h c o a s t of P e t i t Rameau and t h e n o r t h c o a s t o f P e t i t Bateau i s composed of

c a l c a r e o u s sand and v a r i e s between 5 and 1 0 m e t e r s i n d e p t h . The west c o a s t of P e - t i t Rameau i s comprised of low rocky o u t c r o p s , broken by s m a l l s a n d y b e a c h e s . I n s h a l l o w w a t e r t h e bottom i s composed of c a r b o n a t e sand and l o o s e r u b b l e of b r a n c h i n g P o r i t e s and A c r o p o r a . There a r e s m a l l p a t c h e s of l i v i n g P o r i t e s p o r i - t e ~ a n d f u r c a t a . -- Mancina a e r e o l a t a i s common and Halimeda i s a b u n d a n t . I n g e n e r a l , however, t h e a r e a d o e s n o t s u u u o r t a d i v e r s e f a u n a . A A I n a l i t t l e d e e u e r A

w a t e r a few s c a t t e r e d c o r a l s , Favi.a f r a g u g , - S i d e r a s t r e a s i d e r e a , - P o r i t e s p o r i t e s ^{- 9} -- P o r i t e s a s t r e o i d e s -- and M i l l e p o r a o c c u r down t o sandy bottom a t a d e p t h of a b o u t

4

m e t e r s . A few i s o l a t e d p a t c h e s of Acropora p a l m a t a and M o n t a s t x a r e -- --

p r e s e n t i n d e p t h s of

4

o r 5 m e t e r s .

The n o r t h and e a s t c o a s t s and t h e f o u r c o r n e r s of t h e i s l a n d a r e c h a r a c t e r i z e d by low r o c k y c l i f f s , heavy wave a c t i o n and s t r o n g c u r r e n t s . P r o l i f i c growths of t h e s e a f a n R h i p i d o g o r g i a d e v e l o p i n t h e s e a r e a s , t o c e t h e r w i t h massi.ve b o u l d e r s of S i d e r a s t r e a s i d e r e a and D i p l o r i a - s p p . These a r c e n c r u s t e d on a r c e f r o c k pavement o r upon exposed c o u n t r y

r o c k . C l o s e t o s h o r e t h e r o c k s u b s t r a t e i s b a r e o r s e c o n d a r i l y e n c r u s t e d w i t h M i l l e p o r a and P a l y t h o a . R h i p i d o g o r g i a i s found c l o s e t o l o w w a i e r mark and t h e t i p s of t h e f a n s a r e somcti.mes exposed. Massive mounds of M o n t a s t r e a a n n u l a r i s a r e d e v e l o p e d i n d e e p e r w a t e r a t 3-4 m e t e r s .

A t t h e s o u t h west c o r n e r of t h e Cay, where t h e c u r r e n t i s l e s s s t r o n g and wave a c t i o n limi-Led, a more p r o l i f i c a s s o c i a t i o n of c o r a l s a r e f o u n d and d e v e l o p s c l o s e t o t h e s h o r e . Fewer a l c y o n a r i a n s a r e found h e r e b u t t h e c o r a l community i s much more d i v e r s e . -- M o n t a s t r e a annu1ari.s i s

dominant b u t a number of s p e c i e s of massive c o r a l s a r e p r e s e n t .

2 . P e t i t Bateau

The d i s t r i b u t i o n of b e n t h i c communities around B a t e a u Cay i s s i m i l a r t o t h a t of P e t i t Rameau. The n o r t h c o a s t l i e s

on t h e l e e s i d e and i s p r o t e c t e d from wave a c t i o n . There i s a wide b e a c h a l o n g most of t h e c o a s t . The s h a l l o w w a t e r a l o n g

t h e c o a s t i s c o v e r e d by e x t e n s i v e a r e a s of broken c o r a l r u b b l e w i t h a few p a t c h e s of T h a l a s s i a and small. c o l o n i e s of massive c o r a l s . T h i s bottom s i o p e s downward t o t h e c h a n n e l w i t h a sandy bottom a t a d e p t h of 4-5 m e t e r s . The n o r t h - e a s t promontory s u p p o r t s a d e n s e growth. of R h i p i d o g o r g i a , t h e b o u l d e r c o r a l s S i d e r a s t r e a s i d e r e a a n d - k p l o r i a -, s p e c i e s and Acropora p a l m a t a .

-

On t h e west s i d e of t h e i s l a n d t h e r e a r e s t e e p r o c k y c l i f f s w i t h p i l e s of r u b b l e a t t h e i r b a s e s ir: s h a l l o w w a t e r . Sea f a n s and o t h e r a l c y o n a r i a n s a r e abundant h e r e , e s p e c i a l l y on t h e p r o m o n t o r i e s where t h e c u r r e n t i s s t r o n g e s t . There a r e p a t c h e s of

--

Acropora p a l m a t a , A . c e r v i c o r n i s , d e n s e M i l l e p o r a and s m a l l c o l o n i e s of

--

~ o r i t e s - p o r i t e s -- and P. a s t r e o i d e s . --

F a v i a fragum and M a s t r e a r a d i a n s a r e common. O u t s i d e t h e

3 fathom l i n e t h e bottom i s c o m p r i s e d of sand and r u b b l e w i t h s c a t t e r e d c o r a l p a t c h e s .

Along t h e s o u t h e r n and e a s t e r n c o a s t s t h e r e a r e sandy beaches w i t h beds of P o r i t e s p o r i t e s and P o r i t e s f u r c a t a i n s h a l l o w w a t e r . T h a l a s s i a i s l e s s abundant h e r e t h a n on t h e s o u t h e r n c o a s t oT P e t i t Rameau. The T h a l a s s i a - P o r i t e s

a s s o c i a t i o n l i e s i n a narrow band a l o n g t h e c o a s t down t o d e p t h s of a b o u t 2 o r 3 m e t e r s . Beyond t h i s d e p t h t h e r e a r e d e n s e c o r a l communities s i m i l a r t o t h o s e of P e t i t Rarneau, dominated by M o n t a s t r e a a n n u l a r i s .

There i s a s a n d and r u b b l e b o t t o m i n s h a l l o w w a t e r a l o n g t h e s o u t h c o a s t of t h i s i s l a n d a n d t h e w a t e r i s v e r y t u r b u l e n t c l o s e t o s h o r e . The marine g r a s s e s T h a l a s s i a and Syrihgodium

--

a r e common b u t v e r y l i t t l e P o r i t e s o c c u r s h e r e . Manicina a e r e o l a t a i s common and t h e r e a r e numerous l o g g e r h e a d sponges S p h e c i o s p o n g i a and a r e d e n c r u s t i n g s p o n e e . E p n e u s t e s

- e s c u l e n t u s i s common i n t h e g r a s s b e d s . A l o n g s a n d s p i t i s

- p r e s e n t a t t h e s o u t h - e a s t end of t h e i s l a n d .

Along t h e e a s t e r n c o a s t t h e r e a r e r a t h e r narrow beds of P o r i t e s and T h a l a s s i a w i t h s c a t t e r e d c o r a l s i n d e e p e r w a t e r .

-

The T h a l a s s i a i s r e p l a c e d towards t h e n o r t h e r n end by s c a t t e r e d

patches of r e e f c o r a l s i n c l u d i n g Acropora pa=&, D i p l o r i a s p p . , S i d e r a s t r e a and

--

P o r i t e s . A l c y o n a r i a n s a r e abundant a t t h e n o r t h e r n and s o u t h e r n ends of t h e Cay. The bottom a l o n g t h e w e s t e r n c o a s t i s composed of s a n d and r u b b l e w i t h a heavy growth of g r e e n a l g a e of t h e g e n e r a Ulva and Enteromorpha.

4 . Jamesby

The s h a l l o w w a t e r a l o n g t h e w e s t e r n s i d e h a s f l o u r i s h i n g

communities of reef corals and alcyonarians similar to those on the east side of Petit Bateau. The west coast is rocky with much debris in shallow water. The water is turbid and strong currents prevail along this shore. A rather poorly developed Thalassia-Porites association with reef corals in deeper water occurs along the eastern coast.

DISCUSSION

The zonation of corals on the Horseshoe Reef is similar to that described for a number of other Caribbean reefs. The reef front or reef slope zone which is dominated by Montastrea annularis most closely resembles the reef front of Nicaraguan - reefs described by Milliman

(1969),

the Montastrea-Deep-Water

Zone at Abaco Island, Bahamas ( ~ t o r r ,

1964)

and the outer reef regions on Aruba noted by Roos (1

971

)

.

The reef crest with its dense growth of Acropora palmata is a characteristic feature of many Caribbean reefs and exists on the shallow frontal region in Florida ( ~ h i n n ,

1963),

in British Honduras (stoddart, 1962), Jamaica ( ~ o r e a u ,

1959),

Cayman Islands ( ~ o b e r t s , 1971), Curayao and Aruba ( ~ o o s ,

1964,

1971 ) and the Bahamas ( ~ e w e l l et al,

1959

and Storr,

1964).

The spur and buttress region described for Jamaican reefs by Goreau

(1959)

is not present on the Horseshoe Reef although the reef is bisected with channels.

The back reef region resembles the shallow water zones described by Stoddart (1 962), Roos (1 964,

1971

₎

,

^{Goreau (1}

⁹⁵⁹⁾

and Milliman (1969) as a patchwork distribution of corals and alcyonarians. The occurrence of Millepora and the colonial zooanthid Palythoa in shallow water is also characteristic of Caribbean reefs and has been reported by Lewis in Barbados

(1960),

Adams i n St. Vincent (1968), Milliman

(1969)

and Goreau (1

959).

The distribution of shallow water communities around each of the Cays appears to be related to the coastline configuration and to the current velocities. Currents are strongest at the eastern entrance to the channel between Bateau and Rameau, at the north-eastern tip of Petit Rameau, the northern and southern ends of Baradal and along the western side of Jamesby Cay.

There are flourishing patches of a number of reef corals in all these areas and dense stands of Rhipidogorgia and other alcyonarians. Thalassia-Porites associations are restricted to the southern coasts of Rameau and Bateau, along the

eastern sides of Baradal and Jamesby where the currents are less strong. In deeper water below a few meters the

composition of coral species is much the same for each Cay.

REFERENCES

Adams, R.D. 1968. The leeward reefs of St. Vincent, West Indies. Jour. Geol.,

76:

587-595.

Beard, J.S.

1949.

The natural vegetation of the Windward and Leeward islands. Oxford Forest. Mem., 21.

Boschma, H.

1948.

The species problem in - Millepora. Zool.

Verband Leiden I : 115pp.

Goreau, T.F.

1959.

The ecology of Jamaican coral reefs. I.

Species composition and zonation. Ecology,

40: 67-90.

Lewis, J.B. 1960. The coral reefs and coral communities of Barbados, W.I. Can. Jour. Zool., 38: 1 1 33-1

145.

Milliman, J.D. 1969. Four Southwestern Caribbean Atolls:

Courtown Cays, Albuquerque Cays, Roncador Bank and Serrana Bank. Atoll Res. Bull., 129: 26pp.

Newell, N.D., J. Imbrie, E.G. Purdy and D.L. Thurber.

1959.

Organism communities and bottom facies, Great Bahama Bank. Bull. Amer. Mus. Nat. Hist., 117: 177-228.

Roberts, H.H.

1971.

Environments and organic communities of North Sound, Grand Cayman Island, B.W.I. Caribb. Jour.

Sci., ll(No.1-2):

67-71.

Roos, P.J.

1964.

The distribution of reef corals in Curayao Stud. Fauna Curayao and other Caribbean Islands, 20:

1-51.

--- ^1971.

The shallow-water stony corals of the Netherlands Antilles. Stud. Fauna Curapao and other Caribbean Islands, 37 : 1 - 1 08.

Shinn, E.A.

1963.

Spur and groove formation on the Florida Reef Tract. Jour. Sed. Petro. 32: 291-303.

Stoddart, D.R. 1962. Three Caribbean atolls: Turneffe Islands, Lighthouse Reef and Glover's Reef, British Honduras.

Atoll Res. Bull.

87:

149pp.

Storr, J.F.

1964.

Ecology and oceanography of the coral-reef tract, Abaco Island, Bahamas. Geol. Soc. Amer. Special Paper 79: 98pp.

' I

1

:

8 INCHES TO DEPTHS I N FATHOMS

----

3 FATHOM CONTOUR -REEF FRONT

1 Map of Tobago Cays with inset showing Lesser Antilles and Grenadines.

MONTASTREA

ACROPORA I ~ ~ R U B B L E

fi] ^DIPLORIA I::'.::.:] ^SAND

[Z]PALYTHOA ]M]MILLEPORA

2 Three dimensional sketch of a generalized transect across the Horseshoe Reef showing zonation. Sketch not to scale. Depth 15-20 meters; horizontal distance approximately 100 meters.

/ t

l m l ALCYO N A R I A N S

. .

^/

I / /

I

3 Distribution of shallow water communities around Petit Rameau and Petit Bateau, Tobago Cays.

NAUTIC AL MILE

4 Distribution of shallow water communities around Baradal and Jamesby, Tobago Cays.

5 10 1'5 DISTANCE I N METERS

-.

.-

W T H A L A S S I A [ZPB1 P O R I T E S B ALCYONARIANS DIPLORIA a SIDERASTREA ACROPOR A

TP91 MONTASTREA RHIPIDOGORGIA

5 ^{Profiles of} typical shallow-water communities o n leeward (sheltered) and windward (exposed) coasts o f the T o b a g o Cays.