ATOLL RESEARCH BULLETIN NO* 271 CAY SAL BANK

ATOLL RESEARCH BULLETIN NO* 271 CAY SAL BANK

A T O L L RESEARCH B U L L E T I N
NO* 271
CAY S A L BANK, BAHAMAS: A B I O L O G I C A L L Y I M P O V E R I S H E D , P H Y S I C A L L Y
T R O L L E D ENVIRONMENT
SEPTEMBER 198 3
CAY S A L BANK, BAHAMAS: A B I O L O G I C A L L Y IMPOVERISHED
P H Y S I C A L L Y CONTROLLED ENVIRONMENT
1
by Walter M. Goldberg
ABSTRACT
Cay Sal Bank is a shallow water, oceanic platform whose
lagoonal surface is 9-16m below sea level. Benthic
communities on the bank are divided into four major zones
based upon biotic composition and substrate. These are (1)
rubble- Lobophora 12) Sargassm-gorgonian-sponge (3) Halodule
and associates aKd ( ) a patchy Thalassia zone. Sediment
is largely restricted to the western portion of the lagoon,
especially in zone 3. Although occasional patch reefs are
noted, the bank lagoon is virtually devoid of coral reefs
and coral communities, The submerged, leeward bases of
islands and cays represent the principal substrate for the
development of scleractinian corals, but these do not appear
to form a reef framework, Scleractinian development on the
windward sides of the islands is negligible, Patch reefs and
spur and groove systems are usually poorly developed on the
outer bank slope to depths approaching 30m, The best
developed coral communities occur below this depth with the
exception of the southwestern sector where reefs are smothered
in sediment,
The biological structure of the bank lagoon is interpreted
as being controlled largely by wind and periodic storm forces
that result in frequent resuspension and eventual offbank
transport of sediment, especially to the southwest, Gay SaX
is not a drowned bank; it is a submerged platform on which
biological impoverishment appears to be maintained through
disturbance phenomena engendered by an open and poorly
developed rim. These stresses prevent establishment of more
complex coral reefs or coral communities, and promote
domination by fleshy algae and other more tolerant organisms.
l ~ e ~ a r t m e nof
t Biological Sciences, Florida International
University, Miami, Florida 33199, U.S.A.
(Manuscript received March 1983 - Eds.)
INTRODUCTION
Cay S a l Bank i s a s h a l l o w , d e t a c h e d c a r b o n a t e bank
l y i n g r o u g h l y 1 0 0 km s o u t h o f t h e F l o r i d a Keys, 54 km n o r t h
o f Cuba a n d 50 km w e s t o f t h e G r e a t Bahama Bank ( F i g . 1 ) .
I t i s 1 0 5 km by 6 6 km i n i t s g r e a t e s t d i m e n s i n s , and
c o n s t i t u t e s a n o v e r a l l a r e a o f n e a r l y 4000 km
The r i m
i s l i n e d w i t h a s c a t t e r i n g o f i s l a n d s and r o c k s e s p e c i a l l y
a l o n g t h e n o r t h e r n and e a s t e r n margins.
Over 9 9 p e r c e n t o f
t h e bank i n c l u d i n g t h e s o u t h e r n f l a n k a n d t h e e n t i r e c e n t e r
a r e c o m p l e t e l y submerged, p r i m a r i l y i n d e p t h s r a n g i n g from
9-16m.
9.
Few s t u d i e s h a v e b e e n made o f t h i s r e g i o n i n s p i t e of
i t s s i z e and p r o x i m i t y t o U,S, c o a s t a l w a t e r s .
Agassiz
( 1 8 9 4 ) v i s i t e d t h e b a n k , b r i e f l y d e s c r i b i n g some o f i t s
geomorphic f e a t u r e s ; a d e s c r i p t i o n o f t h e bathymetry o f t h e
bank s l o p e ( M a l l o y ti H u r l e y , 1 9 7 0 ) a n d s t r a t i g r a p h i c
s t u d i e s from a w e l l d r i l l e d t o 5766111 by S t a n d a r d O i l Company
(Myerhoff & H a t t e n , 1 9 7 4 ) h a v e made more r e c e n t c o n t r i b u t i o n s
t o o u r knowledge o f t h e a r e a ,
However, d e s c r i p t i o n s o f
t h e m a r i n e c o m m u n i t i e s of Cay S a l Bank h a v e a p p a r e n t l y n o t
been p u b l i s h e d ,
T h i s paper d e s c r i b e s t h e n a t u r e and d i s t r i b u t i o n of t h e
s h a l l o w - w a t e r c o m m u n i t i e s o f Cay SaP Bank by a e r i a l a n d
s a t e l l i t e photographk., c o u p l e d w i t h s h i p - b a s e d b o t t o m
Physical
t r u t h i n g by SCUBA o b s e r v a t i o n a n d d r e d g e s a m p l i n g .
f a c t o r s i n c l u d i n g s t o r m t r a c k s and f r e q u e n c y , wind a n d wave
d a t a and s e d i m e n t d e p t h s on t h e bank l a g o o n a r e a n a l y z e d a n d
r e l a t e d t o community s t r u c t u r e .
M a t e r i a l s a n d Methods
A t o t a l o f 1 8 d a y s w e r e s p e n t on Gay S a l Ban
Biologics
d u r i n g t h e sumxer months o f 1980-1982,
t i o n s w e r e made a t 9 7 s t a t i o n s s c a t t e r e d a c r o s s t h e s h a l l o w
These
Lagoon a n d o u t e r m a r g i n t o a d e p t h of 6 0 m ( F i g , 2 ) .
c o n s i s t e d of simple v i s u a l surveys t o confirm composition o f
the b e n t h o s ,
c o l l e c t i o n s assisted
minute Gapeto
redge tows,
Samples o
m a t e r i a l s hav
e n d e p o s i t e d i n the FIU
e x c e p t a s n o t e d ere i d e n t i f i e d by t h e a u t h o r .
S e d i m e n t d e p t h s were r e c o r d e d a t 27 s t a t i o n s (1982 o n l y )
using a steel probe,
Where s e d i m e n t s e x c e e d e d a d e p t h o f
o n e m e t e r , a 2 1/2 HP w a t e r pump was employed t o f o r c e s e a Sediment
w a t e r t h r o u g h a 5 meter l e n g t h o f PVC p i p e .
f l u i d i z e d i n t h i s manner e n a b l e d t h e p i p e t o q u i c k l y p e n e t r a t e
t o bedrock.
The names o f emergent i s l a n d s u s e d i n t h i s p a p e r
correspond t o t h o s e given i n B r i t i s h Admiralty Chart
No. 1217 ( F i g . 2 ) . C o o r d i n a t e l o c a t i o n s have been
m o d i f i e d a c c o r d i n g t o more r e c e n t d a t a (see a p p e n d i x ) .
RESULTS
a.
The Lagoonal Environment
The l a g o o n a l s u r f a c e o f t h e bank c a n b e d i v i d e d i n t o
f o u r major b i o t i c zones ( F i g . 3 ) . The n o r t h w e s t e r n s e c t o r
w i t h i t s i n c l u d e d s a n d r i d g e s i s c h a r a c t e r i z e d by a s p a r s e
b u t c o n s i s t e n t c o v e r o f s e a g r a s s e s and a l g a e i n c l u d i n g
H a l o d u l e w r i g h t i i , C a u l e r p a s p p . , Syringodiurn f i l i f o r m e
and v a r i o u s s p e c i e s o f c a l c a r e o u s c h l o r o p h y t e s ( F i g . 4 A ) .
Members o f t h i s community ( h e r e a f t e r r e f e r r e d t o a s t h e
Halodule community) a r e summarized i n T a b l e 1. A d e n s e r
H a l o d u l e community a p p e a r s t o be r e s p o n s i b l e f o r s e v e r a l o f
t h e l a r g e d a r k p a t c h e s n o t e d i n s a t e l l i t e imagery of t h i s
zone,
The s e d i m e n t c o v e r o f t h i s q u a d r a n t r a n g e s from 2 c m
t o 1 m.
The d e e p e r s a n d a c c u m u l a t i o n s o c c u r b e h i n d and
s o u t h o f Double Headed S h o t Cays, ( h e r e a f t e r r e f e r r e d t o a s
DHS Cays) p a r t i c u l a r l y i n a s s o c i a t i o n w i t h t h e i n t e r s e c t i n g
s e t s o f bedforrns prominent i n t h e w e s t e r n p a r t o f t h e z o n e ,
and t h o s e t r e n d i n g NE t o SW 20 km t o t h e e a s t , The
H a l o d u l e zone g r a d e s i n t o a s e d i m e n t - b a r e , r u b b l e bottom
e a s t o f Muertos Cays. T h i s n o r t h e a s t e r n s e c t o r i s c o v e r e d
by a mixed Sargassum-gorgonian-sponge community.
The r u b b l e c h a r a c t e r i s t i c o f t h e n o r t h e a s t bank l a g o o n
continues throughout t h e southeast s e c t o r b u t without a s
much v e g e t a t i o n , The bottom i s c o v e r e d p r i m a r i l y by a
s c a t t e r i n g o f t h e brown a l g a Lobophora v a r i e g a t a , w i t h an
o c c a s i o n a l c l u s t e r of sponges and g o r g o n i a n s as above,
Along t h e s o u t h e r n and e a s t e r n b o r d e r s o f t h i s zone t h e
r u b b l e i s i n t e r s p e r s e d w i t h a g g r e g a t i o n s of c o r a l s , e s p e c i a l l y
D i p l o r i a s p p , , A g a r i c i a a g a r i c i t e s and M o n t a s t r e a a n n u l a r i s ,
t o g e t h e r w i t h s p o n g e s and g o r g o n i a a s ( F i g ,
For t h e
most p a r t t h e s e do n o t form p a t c h r e e f s f i .
no a p p r e c i
r e l i e f above b o t t o m ) , However, two r e e f a r e a s a r e e n c o u n t e r e d
a l o n g t h e w e s t e r n edge o f t h i s zone a s n o t e d i n f i g u r e 3.
One o f t h e s e n e a r 23'34' and 7 9 ° 4 8 ~ o n s i s t so f numerous
b u t s m a l l (1-2mZ) D i p l o r i a , P o r i t e s and M o n t a s t r e a p a t c h e s
r i s i n g l m above t h e bottom ( d e p t h = 7-8m).
The most
s i g n i f i c a n t p a t c h r e e f a r e a , s e v e r a l km2 i n e x t e n t , i s
l o c a t e d 10 krn s o u t h w e s t o f Damas Cays. T h i s subzone was
c h a r a c t e r i z e d by t h i c k e t s o f Acro o r a c e r v i c o r n i s r i s i n g t o
a d e p t h o f 6m from a 10m b 0 t t . h 4 C ) .
Scattered
c o l o n i e s o f M o n t a s t r e a a n n u l a r i s- , ~ g a r i c i aa g a r i c i t e s and
I t may b e
C o l p o p h y l l i a n a t a n s c o n t r i b u t e t o t h e framework,
s i g n i f i c a n t t h a t much o f t h e r u b b l e s u b s t r a t e i n t h i s zone
consists of what appears to be recent Acropora cervicornis.
There is little evidence of recolonization.
The last zone consists of a sigmoidally shaped area
extending across the bank from Cay Sal to the Damas Cays.
This area is characterized by patches of Thalassia
testudinum which become somewhat more extensive toward the
southwestern (leeward) side. Turtle grass becomes
particularly well developed in the lee of larger islands on
the bank, especially the Double-Headed Shot Cays and the
Anguilla Cays (Fig. 4E). Farther behind the latter group,
Thalassia grades into a Halodule-calcareous green algae
subzone (Fig. 3).
At the edges of this area Thalassia intermingles with
other communities. This is particularly notable west of
Damas Cays where zonation overlap is extensive (Fig. 3)The Damas Cays area is also notable for the existence of
several "blue holes" (Capt, Bob Mbein, pers, corn,). One
of these located at 23O49@8% and 70°47'28, 2.
the islands, was briefly investigated. It measures
approximately lOOm across and lO0m deep, beginning on the
bank at a depth of 10-b3m (surface to bottom = 110-ll3m).
The surrounding area is a Thalassia-gorgonian-sponge
bottom, grading into colonies of Montastrea cavernosa and
Agaricia agaricites at the edge of the blue hole, The
variegata to a
vertical walls are covered wit
depth of l8m, below which Halimeda goreauii dominates,
Submersible observations at the bottom reveal numerous
Strornbus qigas shells apparently the result of the animal
becoming entrapped while migrating through the surrounding
turtle grass ( E , Shinn, pers, comm.). A wider and slightly
deeper blue hole is located a few km farther west (Fig* 4F),
The sediment cover of the Thalassia zone is highly
variable, Through most of this region the range is 2-5cm,
increasing to 20-60cm under Thalassia itself, Just north
of Gay Sad Island in an area covered by a mixed community
of scattered angiosperms and cabcareous green algae, a
sand body 4-4-5 meters deep was encountered (Pig, 4@), The
area covered by this accumulation was not
several sediment stations taken around the periphery of
Cay Sal indicates that it is highly localized,
b.
The Bank Rim and Slope
The only areas characterized by substantial coral
development are the bank slope below 30m and the submerged
portions of the islands. Most of the larger cays have
been examined and appear to be uniform with regard to their
flora and fauna from the littoral zone to the base of the
island (Table 1). The sublittoral portions are
characterized by an intertidal bench cemented with an
unidentified encrusting coralline alga. Immediately below
this surge zone, dropping vertically to a depth of 7-8 m, is
a coral community consisting of yellow and purple sea fans
(Gorgonia ventalina and G. flabellurn) plus a variety of
other gorgonians, corals-and hydrocorals, especially Millepora
complanata (Fig. 5A). In general the amount of scleractinian
development is greater along the northern border of islands,
but only along the lagoonal side where Montastrea annularis,
Diploria spp. Siderastrea siderea, Agaricia agaricites and
Porites porites become especially numerous (Table 1,
Fig. 5B). However, the coral communities appear to be
insufficiently developed under the best of circumstances to
prevent erosion of the underlying substrate. Large blocks
of island material are usually found adjacent to the cays and
these serve as substratum for additional albeit superficial
coral development (Fig. 5C ,D),
Shallow water coral development along the oceanic side
of the islands is not appreciable, Acropora palmata, for
example, is found only in isolated pockets (e.g. between
Water Cays and some of the Damas Cays, There is no "palrnata
zon@ (cf, Geister, 1977) characteristic of any of the
islands. Along the eastern bank there is little difference
between exposed and sheltered sides of the islands with
regard to coral development. The same species of coral as
noted above form spurs <lm in height in 10m depth directly
in front of many islands along the Santaren Channel.
However, even this limited amount of coral growth does not
occur on the ocean side of the DHS Cays where the bottom at
lorn is composed of rock colonized by Sargassum spp.,
Dictyosphaeria cavernosa and Microdictyon sp., along with
occasional gorgonia and sponges (Fig. 5 E ) . Coral communities
are not developed on either the exposed nor the sheltered
sides of south
guilla Cay or Cay Sal due to accumulation
of sand,
In depths of 15 to 2 5 m along the eastern bank, spurs
3m high are covered by
cervicornis, iderastrea
siderea, Hontastrea ann
onq with Jarq quantities
gorgonians, ~ a l i r n e d a s ~ _
of south Anauilla Cav (in the ~icholasCZ
groove deveiopment is somewhat greater (Fig. 6 ~ but
)
simil
in composition and in coral density to those at Dog Rocks.
There appear to be no comparable coral communities in thes
depths along the DHS Cays or near Cay Sal.
4
.
Outer reef slopes have been investigated briefly on
several sides of the bank in depths ranging from 25-60m. At
25m the angle of slope begins to increase, allowing a
relatively dense algae-sponge-gorgonian community. Some
scleractinian coral development is also in evidence but is
not strongly represented (Fig. 6B). The outer reef
escarpment ("dropoff") begins at 44-46m on the eastern side
of the bank and at 38-40m on the western and northwestern
sides. There is a substantial difference in the structure
of the deep reefs developed on these slopes. Off south
Anguilla, for example, the dominant organisms are Lobophora
variegata and Halimeda spp. interspersed by sponges, some
coral (primarily Montastrea spp.), whip-like gorgonians
(Ellisella and Eunicea spp.) and antipatharians
(Cirrhipathes luetkeni). The diversity of deep reef
organisms here is relatively low; the face of the escarpment
is smooth, without appreciable development of ledges, caves
and overhangs. The same description applies to the deep
reefs off southern Dog Rocks, however diversity of organisms
and relief in the slope is somewhat greater off the northern
Dog Rocks group,
Scleractinian coral development at depths below 25m is
greatest off the northwestern and western border of the bank,
along the edge of the Straits of Florida, Off Elbow Cay,
for example, an appreciable development of Montastrea spp.
Porites astreoides and Wgaricia agaricites begins at 25m
(Fig. QC), The latter species forms an extensive cover
that continues over the escarpment to depths of at least
50m, The central portion of the western bank margin drops
precipitously into the Straits of Florida. The outer reef
slope here is as well developed as I have seen it in this
area. The escarpment beginning at 38m is characterized by
spurs extending seaward nore than lorn from the wall. From
the amount of coral cover these appear to be the result of
recent growth although no cores have been taken. Flat,
platey forms of Montastrea spp. and Agaricia lamarcki,
along with large colonies'of Colpophyllia natans dominate
these structures along with numerous sponges, gorgonians
and antipatharians (Fig. QE), In direct contrast, the
outer slope around Cay Sal island has no reef development
at all; off the northern end in particular, the outer
reef slope is totally inundated with sediment (Figs, 6D,7).
DISCUSSION
Unlike the larger Bahamian banks, Cay Sal has a
largely submerged, poorly developed rim. Agassiz (1894) and
Davis (1928) refer to the bank as a drowned atoll emphasizing
the apparent inability of coral growth to keep pace with
subsidence or rise in sea level. The process of drowning may
be initiated by a variety of factors (reviewed by Schlager,
1981) which commonly result in bank or platform surfaces
50m or more below present sea level (Davis, 1928). In such
cases the use of the term "drowning" may be justified because
processes operating in the past have placed reefassociated organisms out of their effective depth range
for photosynthesis. Cay Sal Bank lagoon, on the other
hand is only 9-16 m deep, submerged, but well within the
range of appreciable carbonate production (Schlager, 1981)
and reef growth (Macintyre, 1967; Porter, 1973; Goreau &
Land, 1974; ~iitzler& Macintyre, 1982). As noted above,
reef growth is occurring on at least some of Cay Salts
deeper margins. Therefore the notion of reef drowning as
means of accounting for this bank's present biotic
composition is untenable.
The antithesis of platform drowning is physical control
by shallow water processes. Shallow water is subject to
a wide variety of environmental alterations inimical to
reef development. These may include exposure and thermal
et al,, 1982) chemical
disturbances (Glynn, 1968; Roberts et al., 1959; Voss c Voss, 1960;
alterations (Newell Milliman, 1 9 7 3 ) and floods of fresh or turbid water
(Goodbody, 1961; Lighty et aE., l 7 8 ) , Although none
these processes is likely operati e on Cay Sax Bank to
such stresses may have served to reduce early olocene reef
growth enough to account for its poorly developed rim, The
hack of a protective rim, in turn, may have promoted
conditions which account for the sparsely colonized, bow
diversity, ahermatypic environment typical of the bank
shallows.
Although the mechanisms and trends of the sequential
replacement of communities through time are controversial
(Connell & Slayter, 1977; Sousa, 1980; Greene & Schoener,
l982), the process of succession is generally understood
to culminate in one or more communities called chimaxes,
Such communities are widzspread in a given ciimatic regime
and are typically characterized y an equilibrium between
production and respiration, a re a t i v e k y high diversity of
species, a well-developed spacial structure and a complex
food web lodurn, 1969) , In the coral reef enviro
normal successional process redicts eventual st
of soft bottom communities by Thalassia ( G i n s b u r g &
Lowenstam, 1 58; Patriq~in,1975) or coral communities
(Jones, 1977)- However, it is generally recognized that
local conditions may often prevent the succession to climax,
In these cases, terms such as edaphic climax, cyclic climax,
disclimax or subclimax have been applied ( O d m , 1971)
Species diversity as one of the more readily measurable
ecological parameters, is often employed as a standard by
which the degree of community complexity can be gauged,
High diversity is maintained by some measure of disturbance
or non-equilibrium conditions that prevents monopolization
of resources by superior competitors (Connell, 1978;
Pearson, 1981; Sheppard, 1982). However, frequent and/or
s e v e r e d i s t u r b a n c e c a n r e t u r n t h e community t o an immature
( e a r l y successional) s t a g e o r perhaps i n h i b i t succession
entirely.
F o r example D o l l a r (1982) found t h a t wave and
s t o r m stress c a u s e d f r e q u e n t mass m o r t a l i t i e s on a n
Hawaiian r e e f , r e s u l t i n g i n a low d i v e r s i t y , r e l a t i v e l y
s i m p l e c o r a l r e e f community. F r e q u e n t l y a f t e r d i s t u r b a n c e
by s t o r m s o r o t h e r s t r e s s e s , damaged r e e f s w i l l be c o l o n i z e d
by f l e s h y a l g a e ; t h e i r c o n t i n u e d dominance i s l i m i t e d by
t h e t i m e r e q u i r e d f o r r e c o v e r y o f t h e c o r a l community
( P e a r s o n , 1 9 8 1 and c o n t a i n e d r e f e r e n c e s ) . Thus a l g a l dominated r e e f s may b e viewed a s an i n d i c a t i o n o f d i s t u r b a n c e
t o a d e g r e e t h a t does n o t a l l o w t h e normal p r o c e s s o f
s u c c e s s i o n o r r e c o v e r y t o o c c u r . L i g h t y (1981) h a s d e s c r i b e d
s u c h an environment i n t h e n o r t h e r n Bahamas (which h e
u n f o r t u n a t e l y r e f e r s t o a s a " c l i m a x community") and
c o r r e l a t e s t h i s c o n d i t i o n w i t h h i g h e n e r g y stress. A someet a l , (1977)
what s i m i l a r s i t u a t i o n i s d e s c r i b e d by Adey i n t h e Lesser A n t i l l e s . The f o l l o w i n g e v i d e n c e s u g g e s t s
t h a t Cay S a l B a n k ' s low c o r a l d i v e r s i t y ( T a b l e 1) and
dominance by f l e s h y a l g a e a s w e l l a s o t h e r f l o r a , i s a l s o
a f u n c t i o n of e n v i r o n m e n t a l stress.
The l a g o o n o f Gay S a l i s dominated by t h e s e a g r a s s
Malodule w r i g h t i i and a s s o c i a t e s , H a l o d u l e i s an o p p o r t u n i s t
species t h a t colonizes areas e i t h e r unsuitable for Thalassia
o r a r e a s where T h a l a s s i a h a s become d i s t u r b e d bv
* storms o r
o t h e r f a c t o r s (den H a r t o g , 1 9 7 7 ) . A s a p i o n e e r , H a l o d u l e
i s a poor c o m p e t i t o r and u n d e r normal c o n d i t i o n s i s r e p l a c e d
by s p e c i e s wikh more e x t e n s i v e , s t a b i l i z i n g b l a d e and rhizome s y s t e m s ( S c o f f i n , 1970; B u r r e l l and S c h u b e l , 1 9 7 7 ) .
T h i s s u c c e s s i o n i s n o t e v i d e n t a t Cay S a l where T h a l a s s i a i s
s t r o n g l y developed only i n t h e l e e of l a r g e r i s l a n d s .
The d i s t r i b u t i o n of s e d i m e n t on t h e bank (Fig. 3 )
s roughly with t h e g e n e r a l d e s c r i p t i o n g i
One o f t h e more s t r i k i n g a s p e c t s o f t
d i s t r i b u t i o n i s t h e m o u n t s f ank s u r f a c e
s e d i m e n t . More t h a n h a l f of t h e lagoon i s
e s p e c i a l l y t h e e a s t e r n s i d e , The s e d i m e n t
is concentrated largely i n
i n c r e a s e s toward t
o f s a n d waves b e h i n d D H S Cays, and i n a r e l a t i v e l y
) s a n d body r e s t r i c t e d t o t h e n o r t h s i d e of Cay S a l
I s l a n d . The v i r t u a l a b s e n c e o f s e d i m e n t on t h e e a s t e r n
margin and i t s a c c u m u l a t i o n toward t h e s o u t h w e s t s u g g e s t s
a c t i v e t r a n s p o r t , Moreover, t h e s m o t h e r i n g o f t h e o u t e r
r e e f s l o p e c o r a l communities around Cay S a l I s l a n d p r o v i d e s
e v i d e n c e t h a t t h i s t r a n s p o r t is o f f b a n k , a s c o n f i r m e d
r e c e n t l y by seismic p r o f i l e s ( H i n e , p e r s o n a l communication).
Wind and s t o r m g e n e r a t e d f l o w s a r e l i k e l y a g e n t s o f
et a l . , 1981; Hubbard et al,,
o f f b a n k s e d i m e n t t r a n s p o r t (Hine 1 9 8 1 ) . Two c a t e g o r i e s o f s t o r m s t o c o n s i d e r a r e a c u t e ,
p e r i o d i c t r o p i c a l s t o r m s o c c u r r i n g i n summer and t h e more
regular, chronic disturbances associated with t h e passage
of w i n t e r f r o n t a l systems.
A c h a r t d e p i c t i n g t h e approximate
p a t h o f t r o p i c a l s t o r m and h u r r i c a n e s y s t e m s p a s s i n g w i t h i n
L O O km o f Cay S a l Bank i s p r e s e n t e d i n F i g u r e 8 , Although
n o d a t a a r e g i v e n on s t o r m i n t e n s i t i e s , 32 c y c l o n i c s t o r m s
have been n o t e d s i n c e 1871, p l u s an a d d i t i o n a l 4 t r o p i c a l
depressions.
Nine s t o r m s o r h u r r i c a n e s h a v e c r o s s e d t h e
s o u t h e a s t e r n bank i n t h e v i c i n i t y o f t h e A n g u i l l a Cays,
9 more h a v e c r o s s e d ( o r p a s s e d p a r a l l e l ) i n an e a s t - w e s t
d i r e c t i o n , w h i l e a n o t h e r 7 c r o s s e d t h e bank n e a r Cay S a l e
Given t h e o p e n n e s s o f t h e b a n k , s e v e r e s t o r m s and h u r r i c a n e s
a r e c e r t a i n t o e f f e c t damage, e v e n on d e e p e r r e e f s ( c f .
Woodley, 1 9 8 0 ) . However, t h e o v e r a l l i m p o r t a n c e o f t r o p i c a l
With a n a v e r a g e
s t o r m s on Cay S a l i s d i f f i c u l t t o a s s e s s .
o f 3 s t o r m s p e r d e c a d e , Cay S a l i s l e s s f r e q u e n t l y a f f e c t e d
by s u c h s y s t e m s t h a n t h e F l o r i d a Keys o r L i t t l e Bahama
Bank where an a v e r a g e o f 7-8 s t o r m s p e r d e c a d e o c c u r s
et a l . , 1977; Wine, 1 9 7 7 ) . D u r i n g t h e l a s t d e c a d e
(Neumann o n l y one h u r r i c a n e h a s p a s s e d n e a r t h i s a r e a ( 1 9 8 1 ) ; moreo v e r , t h e p a t t e r n of storm c r o s s i n g s does n o t correspond
w i t h e i t h e r t h e d e g r e e o f community development o r t h e
p a t t e r n of o b s e r v e d s e d i m e n t a c c u m u l a t i o n ,
The s m a l l amount o f hydrographic/meteorological i n f o r m a t i o n a v a i l a b l e f o r t h e a r e a i s summarized i n F i g u r e 9. Winds
a r e p r i n c i p a l l y from t h e e a s t d u r i n g most o f t h e y e a r b u t
d i s p l a y a p r o m i n e n t s h i f t t o t h e n o r t h and n o r t h e a s t d u r i n g
t h e winter.
T h i s change c o r r e s p o n d s w i t h t h e i n c r e a s e i n
The p a s s a g e o f
p e r c e n t o f s e a and s w e l l n e a r t h e bank,
f r o n t a l s y s t e m s from t h e n o r t h and n o r t h e a s t i s a r e l i a b l e
and p e r s i s t e n t w i n t e r phenomenon i n t h i s r e g i o n (U.S. Naval
Weather S e r v i c e Cornand, 1 9 7 5 ) and may a c c o u n t f o r t h e
following observations,
1) Wcropora c e r v i c o r n i s r u b b l e i s common i n t h e s o u t h e a s t e r n s e c t o r o f t h e bank w h i l e l i v i n g c o l o n i e s a r e r e l a t i v e l y uncommon,
S t o m f o r c e s may p r o v i d e r u b b l e s u b s t r a t u m
t h r o u g h r e c u r r e n t c y c l e s o f Acropora g r o w t h and r e c o v e r y
H a l l , 1 9 7 6 ; T u n n i c l i f f e , 1 9 8 1 ) f o l l o w e d by s t o r m
destruction.
The dominance o f a n u n s t a b l e r u b b l e s u b s t r a t e
i n t u r n r e d u c e s t h e chance of c o r a l s u r v i v a l and r e c o l o n i z a t i o n ( G o r e a u , 1 9 5 9 ; S t o d d a r t , 1974; P e a r s o n , 1 9 8 1 ) .
2 ) The b e s t d e v e l o p e d s h a l l o w c o r a l communities a r e
on t h e p r o t e c t e d l a g o o n s i d e o f t h e n o r t h e r n c a y s ; t h e
The
p o o r e s t development i s on t h e u n p r o t e c t e d o c e a n s i d e .
r e a s o n f o r t h i s c o n t r a s t may b e t h e a b r u p t t r a n s i t i o n between
s h a l l o w and d e e p w a t e r t h a t a l l o w s l a r g e waves t o pound t h e
o u t s i d e of t h e s e cays.
For e x a m p l e , a 50 km h r - 1 wind from
t h e n o r t h o r n o r t h e a s t w i l l p r o d u c e waves a t l e a s t 3.2 m
h i g h (U.S. Army CERC, 1 9 7 3 ) . Such wind/wave c o n d i t i o n s a r e
p r o b a b l y common n e a r Cay S a l (see b e l o w ) .
3 ) A T h a l a s s i a zone f i r s t n o t e d i n 8m d e p t h b e h i n d
n o r t h e r n Dog Rocks d u r i n g J u l y , 1 9 8 1 , was r e p l a c e d by r u b b l e
t w e l v e months l a t e r . A e r i a l p h o t o g r a p h s t a k e n d u r i n g May,
1982 r e v e a l e d c r e s c e n t i c "blowout'' s t r u c t u r e s i n T h a l a s s i a
b e d s b e h i n d Water Cays i n 8-9m d e p t h ( F i g s . 6 D , E ) , a n d n o r t h
o f Cay S a l i n s i m i l a r d e p t h s ( F i g . 4C). T h e s e a r e known t o
r e s u l t from s t o r m damage a n d i n d i c a t e t h e d i r e c t i o n o f e n e r g y
p r o p a g a t i o n ( P a t r i q u i n , 1 9 7 5 ) . The b l o w o u t s on Cay S a l Bank
are concave from t h e n o r t h .
Storm-induced b o t t o m c u r r e n t s and wave a c t i v i t y , a r e
c a p a b l e o f c o n s i d e r a b l e s e d i m e n t r e s u s p e n s i o n and t r a n s p o r t
e t a l . , 1981; Murray et a l . , 1 9 7 7 ) known t o b e
(Mine -d e t r i m e n t a l t o c o r a l d e v e l o p m e n t (Dodge et a l . , 1 9 7 4 ; Loya,
l 9 7 6 ) , The amount o f t r a n s p o r t c a n b e e s t i m a t e d u s i n g
e s t a b l i s h e d r e l a t i o n s h i p s ( F i g s . 3-15, 3 - 2 9 , 4-20 and 4-21
i n U,S. Army CERC, 1 9 7 7 ) b e t w e e n wind stress and maximum
i n d u c e d m o t i o n on t h e s e a f l o o r (Urnax(-dl,
N o r t h e a s t and e a s t e r l y w i n d s n e a r Cay S a l r e a c h s p e e d s
0-25% of t h e t i m e d u r i n g October-April.
o f 50 krn h s - 1 ,
Winds d u r i n g t h s t h e r months a p p r o a c h t h i s s p e e d o n l y 6-12%
o f t h e t i m e ( U , S . Naval Weather S e r v i c e Command, l 9 7 5 ) ,
Winds o f 50 krn h r - I from t h e e a s t i n % I m w a t e r d e p t h
( a v e r a g e l a g o o n d e p t h ) w i l l g e n e r a t e waves 1,4m h i g h , w i t h
p e r i o d s o f 4.7 s e c and w i l l p r o d u c e Urnax(-d) o f 25 c m sec-l
on t h e l a g o o n f l o o r . T h i s i s w i t h i n t h e g e n e r a l l y a c c e p t e d
r a n g e o f 1 5 - 30 c m sec-l r e q u i r e d f o r f i n e t o m o d e r a t e
s i z e d s a n d g r a i n m o t i o n ( U . S . A m y CERC, 1 9 7 7 ; see a l s o
d i s e u s s i o n i n Mine et a l . , 1 9 8 1 ) . The p r i n e i p a l l i m i t a t i o n
t o b o t t o m c u r r e n t g e n e r a t i o n w i t h e a s t e r l y w i n d s on Cay S a l
i s t h e l i m i t e d f e t c h ( 6 5 km), However, w i t h w i n d s from t h e
Thus a 50 km h r - I
northeast, fetch increases 2 l/2 fold.
wind w i l l p r o d u c e waves 1 - 5 m h i g h , w i t h p e r i o d s o f 5 , 2 sec
and w i l l p r o d u c e urnax(-df o f
7 cm sec-a,
This f i g u r e is
o v e c r i t i c a l v e l o c i t y and may a c c o u n t for a c c u m u l a t i o n
of sediment toward t h e southwest, a s w e l l a s d i s t u r b a n c e t o
the l a g o o n and SW bank s l o p e c o m u n i t i e s ,
Thus t h e p h y s i c a l e n v i r o n m e n t of Cay S a l Bank a p p e a r s
t o b e s u f f i c i e n t l y v i g o r o u s t o p r o d u c e d i r e c t wave stress as
w e l l a s current-induced sediment stress, These c o n d i t i o n s ,
w h i l e by n o means u n i q u e , combine w i t h t h e h i s t o r i c a l l y
d e r i v e d l a c k o f a p r o t e c t i v e r i m t o produce high energy
c h a n n e l s i n t o t h e bank i n t e r i o r .
The r e s u l t i s t h e m a i n t e nance of a v i r t u a l l y r e e f l e s s environment.
Table 1.
Marine plants and invertebrates characteristic of
Cay Sal Bank Lagoon. Zones: 1 = Halodule,
2 = Thalassia, 3 = Rubble-Lobophora, 4 = Sargassumgorgonian-sponge, 5 = Island-littoral
Angiosperms
Zone
Halodule wrightii Ascherson
Thalassia testudinum Koenig
Syringodium filiforme Kutzing
Algae
Avrainvillea nigricans Becaisne
Caulerpa prolifera Lamoroux
Caulerpa cupressoides Agardh
Cladophora sp.
Dasycladus vermicularis Krasser
Dictyopteris justii Lamoroux
Dictyosphaeria cavernosa Boergesen
Dictyota dentata Lamoroux
Galaxaura squakida Kjellrnan
HaLirneda incrassata Lamoroux
Malimeda lacrirnosa Mowe
Malirneda opuntia (Lamoroux)
Laurencia papillosa (Forsskal)
Lobophora variegata Womersley
Microdictyon sp.
Padina sanctae-crucis Boergesen
Penicillus capitatus Lamarck
Penicillus dumetosus (Lamoroux)
Penicillus pyriformis Gepp
.Rhipocephalus phoenix Kutzing
Sargassum cymosum Agardh
Sargassum hystrix Agardb
Sargasswrn polyceratium Taylor
Sargassum vulgare Agasdh
Stypopodium zonale Papenfuss
Turbinaria turbinata Muntae
Udotea spinulosa Bowe
Sponges
Anthosigmella varians var. incrustans (D&M)
Spheciospongia vesparium (Lamarck)
Goraonians
Eunicea spp.
Gorgonia flabellurn Linn.
Gorgonia ventalina Linn.
Muricea muricata (Pallas)
Muriceopsis f3avida (Lamarck)
5
lP2,3t4
Plexaura flexuosa Lamoroux
Plexaura homomalla (Esper)
Plexaurella spp.
Pseudopterogorgia americana (Gmelin)
Pterogorgia anceps (Pallas)
Scleractinians
Acropora cervicornis (Lamarck)
Agaricia agaricites (Linn.)
Diploria labyrinthiformis (Linn.)
Diploria strigosa (Dana)
Montastrea annularis (E&S)
Porites astreoides Lamarck
Porites porites Lamarck
Siderastrea siderea (E&S)
'
Molluscs
Wcanthopleura granulata Gmelin
Acmea antillarum Sowerby
Antigonia listeri Gray
Chione paphia Linn,
Chiton squamosus Linn,
Echininus nodulosus Pfeiffer
Glycymeris undata Gmelin
Laevicardium kaevigatum (%inn,)
Littorina zic-zac Gmelin
Livona pica Gray
Nerita peloronta Linn,
Nerita versicolor Gmelin
Purpura patula Linn.
Strombus costatus Gmelin
Stsonbus gigas Linn,
Tais rustica Lmarck
Teetarius murieatus &inn,
Arthropods
G r a p s u s grapsus IEinn,)
Metapenaeopsis cf. goodei (Smith)
Portunus bahamensis Rathbun
Portunus ordwayi (Stimpson)
Portunus spinimanus Latreille
Tetraclita sp.
Echinoderms
Astichopus multifidus (Sluiter)
Astropecten duplicatus Gray
Oreaster reticulatus (Linn.)
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J o u r n . Sed. P e t r o l . ~ i i t z l e r ,K,, M a c i n t y r e , I , G , 1 9 8 2 , T h e h a b i t a t d i s t r i b u t i o n
a n d community s t r u c t u r e o f t h e b a r r i e r r e e f complex
In: RGtzler, M e ,
a t C a r r i e Bow C a y , B e l i z e .
M a c i n t y r e , I . G . , ( e d s ) The A t l a n t i c b a r r i e r r e e f
I. S t r u c t u r e and
e c o s y s t e m a t C a r r i e Bow C a y , B e l i z e .
c o m m u n i t i e s , S m i t h s o n i a n C o n t r . Mar. S c i . 1 2 . p p . 9-45.
.
S c h l a g e r , W. 1 9 8 1 .
The p a r a d o x o f drowned r e e f s a n d
carbonate platforms.
Geol. Soc. America. B u l l ,
92
:L97-211,
S c o f f i n , T , P , 1 9 7 0 , The t r a p p i n g a n d b i n d i n g o f s u b t i d a l
c a r b o n a t e s e d i m e n t s by m a r i n e v e g e t a t i o n i n B i m i n i
L a g o o n , Bahamas.
J o u r , Sed, P e t r o b , -
Sheppard, C.R,C, 1982, C o r a l p o p u l a t i o n s on r e e f s l o p e s
a n d t h e i r major c o n t r o l s ,
Mar, E c o l , P r o g , S e r e
7 : 83-115.
S o u s a , W.P. 1 9 8 0 . The r e s p o n s e s o f a community t o
d i s t u r b a n c e : The i m p o r t a n c e o f s u c c e s s i o n a l a g e a n d
45~72-81,
speciess l i f e histories.
Oecologia S t o d d a r t , D.R. 1 9 7 4 . P o s t - h u r r i c a n e c h a n g e s o n t h e B r i t i s h
Honduras r e e f s : r e - s u r v e y o f 1972.
I n : C a m e r o n , A.M.
e
t
a
l
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(
e
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S
e
c
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n
d
I
n
t
l
.
Symp.
Coral Reefs.
-Great B a r r i e r Reef Comrn, B r i s b a n e 2:473-483.
T u n n i c l i f f e , V. 1981. Breakage and p r o p a g a t i o n o f t h e
s t o n y c o r a l Acropora c e r v i c o r n i s .
Proc. N a t l . Acad.
S c i . 78:2427-2431.
U.S.
Army C o a s t a l E n g i n e e r i n g Research C e n t e r . 1977. S h o r e
p r o t e c t i o n manual V . 1 . U.S. Govt. P r i n t i n g O f f i c e ,
Washington, D.C. pp. 1-180.
U n i t e d S t a t e s Naval Weather S e r v i c e Command. 1975. Summary
o f s y n o p t i c m e t e r o l o g i c a l o b s e r v a t i o n s , North American
C o a s t a l m a r i n e a r e a s , Vol. 4 . N a t i o n a l C l i m a t i c C e n t e r ,
A s h e v i l l e , N C . , USA. gp. 80-146.
Voss, G . L . , Voss, N . A . 1960. An e c o l o g i c a l s u r v e y o f t h e
marine i n v e r t e b r a t e s of B i m i n i , Bahamas, w i t h a
c o n s i d e r a t i o n of t h e i r z o o g e o g r a p h i c a l r e l a t i o n s h i p s .
10~96-116.
B u l l , Mar. S c i . Gulf and C a r i b . W i l s o n , P , 1909. R e p o r t on t h e b o t a n i c a l e x p l o r a t i o n of
J o u r . NY. B o t ,
t h e i s l a n d s of S a l t Key Bank, dahamas.
Garden, 10 :173-176.
Woodley, J . D . 1980. H u r r i c a n e A l l e n d e s t r o y s Jamaican c o r a l
287~387.
reefs.
Nature. West I n d i e s P i l o t , 1957, Hydrographic Dept. B r i t i s h
A d m i r a l t y , London, 5 t h e d . v. 3.
S t r a t i f i c a t i o n and c i r c u l a t i o n i n t h e
Wust, G. 1 9 6 4 .
Antillean-Caribbean basins.
Columbia U n i v e r s i t y P r e s s ,
New York, pp. 1-201.
ACKNOWLEDGMENTS
T h i s s t u d y was made p o s s i b l e t h r o u g h s h i p t i m e g r a n t s
T am
s u p p o r t e d by t h e F l o r i d a I n s t i t u t e f o r Oceanography,
g r a t e f u l t o C a p t a i n R. M i l l e n d e r , J r . , t h e crew of R/V
Bellows and t h e s t a f f of FIO f o r t h e i r c o o p e r a t i o n and
1 thank
a s s i s t a n c e i n making a s u c c e s s o f t h e s e c r u i s e s ,
t h e Government of t h e Bahamas, M i n i s t r y of F i s h e r i e s f o r
t h e i r c o o p e r a t i o n and c o u r t e s y i n g r a n t i n g p e r m i s s i o n t o
c o n d u c t r e s e a r c h i n Bahamian w a t e r s ,
Funding f o r a e r i a l
photography was p r o v i d e d by a g r a n t t o t h e a u t h o r from
I t h a n k K e i t h Wylde f o r
Florida International University,
h i s e x p e r t p i l o t i n g ; M. McLean and M. U p r i g h t t o o k t h e
a e r i a l photographs.
P. McLaughlin and R. L e m a i t r e i d e n t i f i e d
t h e c r u s t a c e a n s and A. Labonte p r o v i d e d t h e equipment u s e d
I t h a n k my c o l l e a g u e
i n sediment depth d e t e r m i n a t i o n s .
J . C . Makemson f o r d r a f t i n g t h e pen and i n k d r a w i n g s and
l a b e l s accompanying t h e f i g u r e s i n t h i s p a p e r , and
C a p t . Bob K l e i n f o r p r o v i d i n g t h e a e r i a l photograph o f t h e
Damas Cay b l u e h o l e ( F i g . 4 F ) . F i n a l l y I t h a n k A . E . Hine f o r
comments t h a t c o n s i d e r a b l y improved t h e m a n u s c r i p t .
FIGURE LEGENDS
Figure 1.
Geographic position of Cay Sal Bank from ERTS/
LANDSAT imagery. Scale bar = 10 km.
Figure 2.
British Admiraly Map No. 1217 (Rev. 1977).
Station positions on Cay Sal Bank.
Figure 3 .
ERTS/LANDSAT composite depicting the biological
zones and subzones of Cay Sal Bank, Encircled
numbers indicate thickness of sediment in cm.
Sand waves in northwest lagoon are covered with
Halodule as are NE-SW oriented sand waves to the
east. Dark region between these structures is
result of denser accumulations of Halodule and
calcareous green algae. Note sand accumulation
near Cay Sal on the southwest corner. Double
Headed Shot Cays, Dog Rocks, Damas Cays and
Anguilla Cays are also visible along the bank
margin.
Figure 4,
Communities of Cay Sal Bank Lagoon:
(A) Halod-ule-Caulerpa-calcareous green algae
community typical of the central lagoon. Note
numerous volcano-like burrows, possibly of
callianassid shrimp; Sea star Oreaster reticulatus
lies next to scale bar, = QOcm; depth = 13m at
23O50'N and 80°20W 13 km SE of ~ l b o wCay.
(B) Rubble dominated bottom along southeast bank
is occasionally colonized by coral clusters
composed of gorgonians, especially ~seudopterogorgia
spp., and scleractinians Montastrea annularis,
Agaricia agaricites and Porites porites (vertical
view, Depth: 13m),
(C) Acropora patch reef southwest of Bamas Cays
in 7-8m depth at 23O34'N and 79O48'W(D) Aerial view of Thalassia development, eastern
Water Cay; scale bar = Sm, Note crescentic
blowouts indicating bankward storm direction from
the north,
(E) Und-erwater detail of above; crescent is l o r n
in diameter; depth = 8-9m.
(F) Blue hole 5-6km west of Damas Cays; note coral
patches developed on edge under boat; scale bar =
loom,
( G ) Sand body 4.0-4.5m deep in 8m of water, 2km
north of Cay Sal. Divers are measuring sand depth
by inserting 5m length of PVC pipe. Note oriented
megaripples indicating sand motion, and sparse
colonization of sediment by Halodule and calcareous
green algae.
Inset:
Figure 5.
Communities of the Bank Rim:
(A) Intertidal' bench with typical wave resistant
Gorgonia spp. from lagoon side of Bellows Cay
(see appendix map).
(B) coral development below the surge zone with
extensive cover of Agaricia agaricites and large
(-lm3) colony of Montastrea annularis : lagoon
side Crenula Cay, 0-6m (see appendix map). Scale
bar = 60cm.
(C) Eolianite blocks broken from lagoon side of
northernmost Dog Rocks; scale bar = 2m.
(D) Colonization of above by Millepora
-- complanata
and small colonies of Diploria strigosa and
Montastrea annularis: scale bar = 60 cm.
(E) Ocean side Elbow Cay showing lack of coral
development on island base. ~ o t espur and groovelike system and scour holes; scale bar = 60 cm,
depth = 3-10m.
Figure 6 ,
Communities of the Outer Reef Slope:
(A) Deep spur systems in Nicholas Channel south
of Anguilla Cays, 23'22'N and 79O34'WS Note
profusion of gorgonians and sponges, Scleractinian
development is occasionally moderate but generally
poor. Spur height = 3-4m; Depth = 20-25m.
(B) Edge of escarpment at above location. TJote
gorgonians and sponges but poor scleractinian
development; Depth = 35m.
(C) Development of Agaricia agaricites and porites
astreoides on the edge of the escarpment off Elbow
Cay; flabellate gorgonian is Iciligoria schrammi,
Depth = 30m,
(D) Escarpment off north Cay Salblanketed in fine
sediment of undetermined thickness. Coral at
center is mud-dwelling sclearactinian, Meandrina
danae
l2.cm Long, Note conch trails (~trombus
gigas) above; Depth = 30m.
( E ) Deep spurs on the escarpment north of Rompidas
Ledge composed largely of platey growths of
Montastrea annularis,
-
Figure '7,
Comparison of fathometer profiles from Gay SaL
Island northward at 15 to 30m depth. Arrow
indicates increased inflection of outer reef
slope at 20m. Distances north of Cay Sal:
1 = 3km, 2 = 4km, 3 = 5.5km, 4 = 6,5km, 5 = 8km.
Note smooth surfaces indicative of sediment
drowning near Cay Sal and increased reef development
toward Rompidas.
Figure 8.
Tropical storm and hurricane track passing within
100 km of Cay Sal Bank, i871 through 1981. Year
of each track indicates direction of continued
motion. Data from Neumann et
-al. (1978) with
additions from NOAA Mariner's Weather Log
(1977-1982).
Figure 9.
Climatic and hydrographic conditions near Cay Sal
Bank. Data compiled from West Indies Pilot
(1957), WBst (l964), NOAA (1973) and U.S. Naval
Weather Service Command (1975)
.
Figure 1
Sea and Swell Conditions
>2m
month
sea s m observations
O/O
May
18
8
4,448
August
15
6
6,4 17
November
25
15
5,338
February
20
12
4,667
APPENDIX
The l a c k o f b a s i c i n f o r m a t i o n on Cay S a l Bank i s
p e r h a p s n o b e t t e r r e f l e c t e d t h a n b y c o n s i d e r a b l e errors i n
i t s c h a r t e d p o s i t i o n ( B r i t i s h Admiraly 1217; Defense
Mapping Agency 1 1 4 5 1 ; NOAA 1 1 0 1 3 ) . The p u r p o s e o f t h i s n o t e
i s t o c o r r e c t mapping e r r o r s by e m p l o y i n g a e r i a l a n d
s a t e l l i t e photography coupled w i t h ship-based n a v i g a t i o n a l
t e c h n i q u e s and bottom s o u n d i n g s .
Additional information is
p r e s e n t e d o n t h e b i o t i c c o m p o s i t i o n a n d morphology o f m a j o r
islands.
D a t a on t h e bank were o b t a i n e d d u r i n g t h r e e c r u i s e s
o f t h e R/V B e l l o w s i n t h e summers o f 1 9 8 0 t h r o u g h 1 9 8 2 .
P o s i t i o n f i x i n g a b o a r d t h e v e s s e l employed b y s i m u l t a n e o u s
u s e o f a 7100 M i c r o m a r i n e LORAN C N a v i g a t o r c o m p u t e r , p l u s
An I T T
a M i c r o l o g i c ML-320 LORAN-C N a v i g a t o r a s a b a c k u p .
Decca M a r i n e 8 0 1 s a t e l l i t e n a v i g a t i o n c o m p u t e r a n d a Decca
RM 5314 r a d a r u n i t ( 7 7 km r a n g e ) w e r e u s e d t o c o n f i r m LO
data.
B a t h y m e t r y i n f o r m a t i o n was o b t a i n e d u s i n g a
R a y t h e o n E x p l o r e r I11 r e c o r d i n g f a t h o m e t e r ( t o 7 5 f a t h o m s )
a n d a R a y t h e o n DE-731 r e c o r d i n g f a t h o m e t e r t o ( 4 1 0 f a t h o m s )
811 i s l a n d s and r o c k s w e r e s u r v e y e d b y o b l i q u e a e r i a l
p h o t o g r a p h y f r o m a n a l t i t u d e o f 600 meters.
These w e r e
s u p p l e m e n t e d by a e r i a l p h o t o g r a p h s o f t h e A n g u i l l a C a y s
made a v a i l a b l e by t h e U.S. D e f e n s e I n t e l l i g e n c e Agency,
The low a l t i t u d e p h o t o g r a p h s w e r e employed i n c o n j u n c t i o n
w i t h ERTS/LANDSAT i m a g e r y a n d s h i p b o a r d p o s i t i o n f i x i n g i n
t h e c o n s t r u c t i o n o f a map o f t h e b a n k , a c c u r a t e t o w i t h i n
+- 300 meters.
R e s u l t s o f t h e mapping o f Cay S a l Bank a r e d e p i c t e d i n
F i g u r e 1. Comparison w i t h t h e 1890 B r i t i s h AZamirality
C h a r t ( F i g * 2 ) shows an e r r o r b e t w e e n 1 a n d 5 km i n t h e
p o s i t i o n o f t h e i s l a n d s , t h e magnitude o f which i s g r e a t e s t
i n t h e s o u t h e a s t e r n p o r t i o n of t h e bank,
The s h a p e o f
l a r g e r i s l a n d s h a s b e e n more a c c u r a t e l y d e p i c t e d and s o m e
h a v e b e e n named ( @ r e n u l a C a y , N o r t h a n d S o u t h D a n g e r o u s
Rocks a n d B e l l o w s C a y ) , The b a t h y m e t r y of t h e bank a s
o r i g i n a l l y presented appears t o be e s s e n t i a l l y c o r r e c t f o r
t h e r e l a t i v e p o s i t i o n o f t h e 5 fathom c u r v e .
Only m i n o r
c o r r e c t i o n s have been i n s e r t e d ,
The p o s i t i o n o f t h e
25 f a t h o m ( = l o 0 F ) c u r v e h a s b e e n f i t t e d u s i n g s a t e l l i t e
imagery ( t e x t f i g . 3)
.
Some o f t h e s h o a l w a t e r a r e a s d e p i c t e d on t h e B r i t i s h
c h a r t ( a n d c o p i e d on a l l o t h e r c h a r t s ) c o u l d n o t b e l o c a t e d
d e s p i t e numerous a t t e m p t s .
Most n o t a b l y , a r e a s s u c h a s
L a v a n d e r a s R o c k s , e a s t o f Cay S a l a n d " D a n g e r o u s S h o a l "
d e p i c t e d on t h e c e n t r a l e a s t e r n b o r d e r ( F i g . 2 ) a r e n o
.
s h a l l o w e r t h a n 3.5 t o 4 fathoms.
This i s a l s o t r u e f o r t h e
s h o a l a r e a s n e a r t h e c e n t e r o f t h e bank.
Repeated
c r o s s i n g s have i n d i c a t e d t h a t t h e lagoon i s g e n e r a l l y no
s h a l l o w e r t h a n 3.5 fathoms (6.4m) a t MSL. The exception to
t h i s r u l e i s a s m a l l ( s l k r n 2 ) a r e a on t h e w e s t e r n bank
r e f e r r e d t o a s Rompidas Ledge, where t h e b o t t o m s h o a l s t o
less t h a n two f a t h o m s , and l a r g e s c a t t e r e d h e a d s o f
Montastrea a n n u l a r i s p r o j e c t c l o s e t o t h e surface.
N a v i g a t i o n a l maps p l a c e Rompidas o v e r 5km from i t s a c t u a l
position.
However, t h e s i t e i s now marked by a c a r g o s h i p ,
M/V Cork t h a t r a n aground on Rompidas i n 1983.
The
l o c a t i o n o f t h i s submerged s h o a l c a n now b e s e e n c l e a r l y
from a d i s t a n c e o f o v e r 15km.
APPENDIX
F I G U R E LEGENDS
F i g u r e 1.
C h a r t o f Cay S a l Bank w i t h r e v i s e d c o o r d i n a t e s
a c c o r d i n g t o LORAN a n d r a d a r p o s i t i o n i n g ; t w e n t y f i v e f a t h o m (=100F) c u r v e f i t t e d f r o m s a t e l l i t e
imagery.
F i g u r e 2.
Comparison o f new c h a r t ( s o l i d l i n e s ) w i t h
B r i t i s h A d m i r a l i t y C h a r t No. 1 2 1 7 ( d a s h e d l i n e s )
showing 25 fathom c u r v e and p o s i t i o n o f m a j o r
i s l a n d s , When t h e 24' a n d 80' c o o r d i n a t e s o f
t h e two maps are o v e r l a p p e d e r r o r s o f u p t o 5km
are shown a l o n g t h e s o u t h e a s t e r n s e c t o r o f t h e
U . S . D e f e n s e Mapping Agency No. 1 1 4 6 1 i s
bank,
v i r t u a l l y i d e n t i c a l w i t h t h e B r i t i s h map.
F i g u r e 3.
I s l a n d s o f Cay S a l Bank,
( A ) U,S, A i r F o r c e p h o t o g r a p h o f s o u t h A n g u i l l a
Cay; s c a l e b a r = 500m. N o t e embayed m a r g i n s
and s a n d s h o a l s .
S a l i n i t y of s a l i n e l a k e i n
Lake
J u n e , 1 9 8 2 was 37. Gy,, by c o n d u c t i v i t y .
marqins a r e covered with e y a n o b a c t e r i a l mats
( ~ s c i l l a t o r i as p , ) a l o n g w i t h t h o s e of a n
A
u n i d e n t i f i e d red photosynthetic bacterium,
s i m i l a r l a k e on n b r t h g l n g u i l i a Cay r e t a i n e d a
s a l i n i t y o f 45C/,0.
( B ) S u r f a c e o f s o u t h A n g u i 1 l a Cay from e a s t w a r d
Development o f
f a c i n g dune c r e s t b o o k i n g n o r t h :
p a l m s ( C o c c o t h r i n a x a r g e n t a t a Brown) and s c r u b
vegetation.
E a s t e r n dune f a c e i s s t e e p l y s l o p i n g
and e r o d e d .
P o o r l y cemented e o l i a n s a n d g r a i n s
a r e t y p i c a l o f t h e windward s i d e .
( C ) Lagoon ( w e s t e r n ) s i d e o f s o u t h A n g u i l l a Cay:
bedded s t r u c t u r e o f w e l l - c e m e n t e d e o l i a n i t e c l i f f s .
(D) Cay S a l from 600m l o o k i n g t o w a r d s o u t h e r n
F l o r i d a S t r a i t s , Unpaved a i r s t r i p a t n o r t h e r n
t i p of i s l a n d ends a t edge of h y p e r s a l i n e lagoon,
H i g h e s t p o r t i o n of i s h a n d i s 10m r i d g e a t t h e
e a s t e r n t i p ( l o w e r l e f t ) , Note s a n d y s h o a l s
a r o u n d i s l a n d and w e a k l y d e v e l o p e d b l o w o u t
s t r u c t u r e s a t l o w e r right corner, S c a l e b a r =
l50m.
( E ) Elbow Cay i s t y p i c a l o f m o s t i s l a n d s o n Cay
S a l Bank, c o n s i s t i n g o f k a r s t i f i e d e o h i a n i t e a n d
c o r a l r u b b l e c o l o n i z e d by m a r i t i m e v e g e t a t i o n ,
p r i m a r i l y Sesuvium p o r t u l a c a s t r u m L i n n . a n d
T o u r n e f o r t i a g n a p h a l o d e s Brown.
See Wilson (1909)
a n d G i l l i s ( 1 9 7 6 ) f o r a d d i t i o n a l n o t e s on Cay
S a l Bank t e r r e s t r i a l f l o r a .
T h i s and o t h e r rocky
i s l a n d s o f t h e bank s e r v e a s n e s t i n g s i t e s f o r
enormous numbers o f s o o t y and brown noddy t e r n s
d u r i n g t h e summer m o n t h s .
S e e Buden and S c h w a r t z
(1968) f o r a review o f h e r p e t o - and a v i f a u n a o f
Cay S a l .
A p p e n d i x Fig. 1
Appendix F i g , 2