Gut, Boscobel, Tower Isle, Ocho Rios, Llandovery, and Runaway Bay to Duncans. On the south coast we examined the reefs betwecn East. Palisados, Maiden ...
CORAL REEF PROJECT-PAPERS
IN MEMORY OF DR. THOMAS
F.
GOREAU.
17.
THE ECOLOGY OF JAMAICAN CORAL REEFS. II. GEOMORPHOLOGY, ZONATION, AND SEDIMENTARY PHASESl THOMAS F. GOREAU AND NORA I. GOREAU2 Discovery Bay Marine Laboratory, Discovery Bay, Jamaica, W.I. ABSTRACT
The coral reef ecosystem is seen as a specialized chemical environment converting dissolved calcium carbonate ions into insoluble calcitic and aragonitic calcium carbonate. The movement of the calcareous material is a potent dynamic factor in the morphogenesis of the coral reefs. There is a precarious balance between accretion and ablation in the system. This paper is concerned with the sedimentary phases of the calcareous biota and the initial patterns of distribution and deposition of the calcareous material within the reefs, and not with the long-term depositional changes induced by erosion, diagenesis, and lithification. The calcareous material is deposited into two distinct phases: a rigid framework (built by primary hermatypes) and a clastic framework (contributed by secondary hermatypes). The reef builders, fillers, and cementers are eventually sediment producers. The unconsolidated skeletal remains of hermatypes make (mostly due to fragmentation) ramparts of imbricated shingles in the reef crest and landward side. In the deeper seaward slope, the corals produce talus cones (by steady biodegradation of corals or by gravitational slump). Silty and muddy sediments accumulate on the fore-reef slope; outcrops and pinnacles there support a rich diverse biota. The hermatypic calcareous algae are significant sediment producers. There is a relation of algal generic diversity to the available substrate. The lithophytes are present at greater depths than the psammophytes. In the fore reef, Halimeda constitutes about 80 per cent of the algal debris. Remains of Halimeda form the largest single part of the total carbonate produced in the whole reef. It is suggested that algal populations should be assessed by their turnover
rates, rather
than by species diversity
or biomass.
The main structural and biotic zones with their depth ranges and local variabilities are summarized. This manuscript in draft form was shelved in 1963 when Tom examined more closely the regions of the fore reef below 30 meters. N. I. Goreau brings it out for publication, supplemented by Tom's unpublished notes, well aware that on the basis of his new findings Tom would have changed radically the scope, form, and inferences of the subject as more quantitative observations were made. Still, the general description of the Jamaican reef zonation in Tom's words is the firsthand information as he learned about the coral-reef environment. Special thanks are for Lynton S. Land, University of Texas at Austin, who reassessed the data of the algal sediments (Table 2) of the fore reef. Also to Ivan M. Goodbody, Professor of Zoology, University of the West Indies, who dived with Tom and after Tom's death generously offered institutional space, academic courtesies, and encouragement to make possible this communication. Figures 19 and 21 were brought up to date from Tom's data up to 1970, and N. I. Goreau is obliged for the aid in this task of J. C. Lang and E. A. Graham. Deep appreciation is also extended to Tom's
1
friends who gave outright
criticism
and frank advice in the editing of this paper:
L. S. Land,
R. A.
Kinzie III, T. J. Goreau, J. C. Lang, R. K. Trench, P. Dust3!l1 P. D. Goreau, J. B. C. Jackson, E. A. Graham, I. M. Goodbody, E. Robinson, and Sir Maurice Yonge. Illustrations are by T. F. Goreau and Peter D. Goreau. "Present address: Department of Zoology, University of the West Indies, Mona, Kingston 7, Jamaica.
400
Bulletin of Marine Science
[23(2)
INTRODUCTION
Scope and Methods of the Current Work.-The central theme in tropical shallow-water coral reefs is the intensive biological secretion and accumulation of calcium carbonate on such a large scale that, under suitable conditions, it leads to the formation of complex and highly specialized ecosystems, which we call coral reefs. The problem is to correlate the physiological secretion of calcium carbonate with the ecological processes governing the growth and form of coral reefs. In this discussion, we regard the reef ecosystem as a specialized chemical environment, where occurs a large-scale conversion of calcium and carbonate ions from the dissolved state to insoluble calcitic and aragonitic calcium carbonates (Goreau, 1963). The growth of reefs, however, is not a matter of deposition alone. There is a precarious balance between accretion, the sum of all biological, skeletal and nonskeletal, processes of calcification, and ablation, which is the total of all physical, biological,
and chemical processes leading to loss of mineral
mattcr from
the system. This complex movement of the calcareous material through the community, under the impetus of biological, gravitational, and turbulent forces, is a potent dynamic factor in the morphogenesis of coral reef community organization. The investigations described in this paper were made in Jamaica from 1955 to 1962, on the fringing reef along the north coast off San San, Salt Gut, Boscobel, Tower Isle, Ocho Rios, Llandovery, and Runaway Bay to Duncans. On the south coast we examined the reefs betwecn East Palisados, Maiden Cay and South Cay. The localities are indicated on the map (Fig. 1). All zones of the reef (d., Table 1) were investigated, but more recently, our underwater studies have been centered on the bottom communities of the zone lying in the depth-range of 35 to 65 meters, the fore-reef slope. The surveys were performed by free divers equipped with self-contained, compressed air, demand breathing units and standard collecting gear. All these dives were led by the senior author and deep gratitude is due to those who took part in this work at different times and under various, sometimes hazardous, conditions: R. K. Trench, E. L. Bohm, D. L. Fraser, E. A. Graham, R. L. Walker, S. K. Amman, J. C. Lang, M. Dixon, H. G. Dixon, T. A. Smith, D. A. Catt, I. M. Goodbody, L. M. Passano, P. Droz, and D. M. Owen. We are also grateful for the assistance given by G. Hornby, K. Pilkington, and S. A. Downton of the Jamaican Branch of the British Sub-Aqua Club. Underwater photography was extensively used; panoramic views of benthic communities as well as extreme close-ups were taken in colour with flash-equipped cameras. Whenever possible, the work of the diving groups was supplemented by bathymetric surveys for the purpose of outlining the major morphological features of the reef and its associatcd
1973]
Goreau & Goreau:
401
Ecology of Jamaican Coral Reefs
01)
t::
.~
•.... -E~
::
~ ~ o ':'u ZGlGl o 't:I 0.. X ~
III
0\ •....•
~.;.; ::J
III
~c
l>::
:J 9
~
~
III
-
~
ctl
~
.2 ~
CI
.;:
a.
.~ c
0
Q. 0
0
::lE
0
0
II
~ CI CD
c
CI
a. 0 a. '0
(.)
~ ~ U ctl ~ .c ~ CI CI 0 u 0
~
."~
(.)
ctl
.;:
~ ~ c c
CI
CI
III
C
C
0
c
>
.c
~ CD CI u
0
~ ~ 0
CI
LLI
« 0 _ctl Z Cli
...J~ :::> ••..
-- -- - -.= CI CD
~
ctl
CI
~
CD
ctl
CI
CI
c
C
::lE
::lE
0
0
~
QI
ctl
CI
C CD
(.)~
0'" ~
Cli
'E~ CI u en u..O '0
1973]
Goreau & Goreau:
en
en
l.L.
l.L. l.L.
l.L. l.L.
CD l.L.
CD l.L.
en u..
W
«
C
..
« W
:IE c
il
In
~ .2 a; 1;;
.~ .~ c c CD 0
CD 0
C)
C)
c
.2
0
s:.
u..:IE
c
0
>.~
_'0
a E CD a
en
en
en
en
en
en
en
en
en
l.L. l.L.
l.L. l.L.
l.L. l.L.
l.L. l.L.
l.L. l.L.
l.L. l.L.
l.L. l.L.
l.L. l.L.
l.L.
l.L.
a c a
CD
E a
en
C)
u..
en l.L.
u..
u..
CD l.L.
In
Z '~ '0 0: c a 0 CD Z
I
en
435
Ecology of Jamaican Coral Reefs
C)
In
::I ~
'0 C
CI'
c
CD
c
~l C)
In
W
« 0
~ en en a ::> ~ >. :IE 0 ~ '0
~ ~
a
In 0
::I CI' C
a
~Ia
>.a ==
jl
E ::I ~:IE
'E
>.
C)
en
a
'iii
In
c
0
..a
CD
c
::I
In
C)
::I
,~
,~
E
>.
a C)
en
>.
s:.
Q.
0
In
W
« C a C a a c a
T
a
-I
a a
:I:a a..'0.
-
0: a
-I a .-'u >••
JI '~I .. ~ «.. .. .. .. .. a
CD ~
In
.2
>.
s:.
Q.
0
In
a E .2 a
>.
s:.
Q.
0 CD
'0 ,~
>.
s:.
a
>. s:.
~
>.
s:.
Q.
::
Q.
Q.
Q.
0 CD
0
0
0
CD
CD
CD
C)
C)
C)
C)
C)
:IE
:IE
:IE
:IE
:IE
>.
>.
>.
>.
>.
0·-
>- 1;;
U
a
>.==
==E Eln
a ::I l.L.W
Bulletin
436
•..>.
.:
....:•.. 0 ~ GI
CII
Qi
~ ~ ,...
C til
GI
.c >.
c:
•.. E •..
...J
C
+
.:
0
C)
:!:!
~
2!
•.. 0
c
0
U CII
0
•..0
0
.!:
U U C
"C
..
•..
•..
>--~
:I:~
en"': VI GI c"C
•..
uOlL.
>.
E
c
0':':
U
E
U
•.. 0
Cl. til
~
-.. -
c a
UIX) _10 =:10 .!:!IO .-
I
a:!
lL.
c:
.
:J
,...
.L:J
'E
•..Cl
C
C
C
o
:0
b
c
;.a § u
0
•..
ell
'C: .•... Q)
§
Gl
0
ILl
u
8
~
...CI .•...
'u Gl
In
>.
Gl
ell
l:Q
,....; N
E J::
0
.a
c
Ct
UJ
c
0
::I
00
UJ
::I
~
.s::. c >U
••
.!:! "0
c en
I
•
I en
[23(2)
Gl
u
c(
en ::I C Gl
C)
Q.
E >u en ::I C CD
C)
Q.
en
~
en
0 0
c
0
J:: a::
z
0 Ct C
c
:J
en ::I
en
en ::I
>
C CD
C)
0
C)
Gl
E Gl
C Gl
0
0
~
~I Gl
:!:! 0
c c ~ Gl
u
c
c c c
en
c
c
0
'Q.
c
E
C
0
~
en
u
::I
c c 'ii u
't:J Gl Q.
-il .JI .JI .JI .JI JI
1973]
Goreau & Goreau:
CI)
CI)
• CI)
CI)
CI)
CI)
CI)
CI)
...J
...J
...J
....I
...J
...J
...J
....I
0
- 'Il ... -... - - -... -= -- :§:J 0
...::J
0
0 )(
~
0
C)
en ::J C GI
C)
~
0
::J
tT II)
~ 'u GI
> .a ::J (/l
0
0
0 0>
...
c
0
:0 0
()
'0 C
>()
:>
c
GI
0
0
GI '0
0
cil c)l c)l c)l c)l
en
Q.
0
0
E c)l c)l
u..
u
u
u..
CI)
CI)
CI)
...J
...J
...J
...J
...J
...J
0
0
E
::J
0
GI C
E
0
.&:
0
GI 0> 0
en en >GI
0
.&:
c
0>
u..
0
0
0
u
(/l
'E
(/l
()
en ::J .a
443
Ecology of Jamaican Coral Reefs
c
;
a..
c)l
en ::J
C GI
C)
c 0
.&:
c 0 .&:
C
0 C)
...
Q.
E
en ::J
(/l
::J
CD
CD
II
0
•..
0 ".:; 0
CD
2!
CD 01
CD U C
CD
CD
III
II)
•.. 0•.. ~ 0 •.. E C
C\I
C CD
.5
III
~
{!. ~ ~ en
CD
.s::.
g ~E
0
u
(f)
[23(2)
of Marine Science
CD 0.
00 I-t!)
I-
~
iii
>-
u
CD
E
~
CD (f)
0
U
u
~a ai l: 0' .2 ~~ ca •.. a
l:
a
l: 0 N
.•.. CD CII
0
~.~ ._~ -0 a'" -0 CD
a: a:
- § 0
w
0.
III
0' 0'
a
••
CII
C c
0 N
'':; 0
.s::.
CD
0
Z
1973]
Goreau & Goreau: Ecology of Jamaican Coral Reefs
445
careous algae playa secondary, and relatively minor, role on the building up of the primary reef framework and the framework fill. Only in the breaker zone and reef flat do the massive encrusting Rhodophyceae (Lithothamnium, etc.) contribute significantly by their tendency to encrust and cement the underlying framework corals, but we have never observed these algae to participate in the deposition of the primary framework, as is commonly reported from the atoll reefs of the Indo-Pacific region (d., Tracey et al., 1948). The Jamaican calcareous algae are extremely significant sediment producers (c£., Fig. 21). Inspection of the fine, unconsolidated sediments associated with the reef, including samples taken from patches of sand in the crest among rich stands of corals, indicates that algal fragments constitute between 40 and 80 per cent of the total. The remainder is made up by foraminiferans, molluscs, echinoderms, etc. Particles of recognizable scleractinian origin are in the minority and sometimes difficult to find. The corals thus contribute far less to the fine sediments than might be expected from their dominant position as primary and secondary hermatypes. The importance of the calcareous algae as sediment builders here is due to the high turnover rate in addition to the small size and the comparatively fragile nature of their skeletal remains. The only algae that give rise to massive tough skeletons are the encrusting species in the family Corallinaceae; they are restricted mostly to the shallow, turbulent surf-zone, reef-flat, or inshore habitats (d., Fig. 21), and are not commonly found in sand. The rest of the calcareous algae produce more-or-less small, fragile skeletal structures that range from a maximum size of about 3 centimeters (Halimeda copiosa, H. disco idea, and H. tuna f. platydisca in deeper zones) to less than 0.2 millimeters (Jania, Coral/ina, Amphiroa, Penicillus, Udotea, etc.). Although the great majority of these algae inhabit the reef crest in large numbers, their calcareous remains are so small that they are quickly winnowed out by turbulence and transported into calmer environments, where they settle out. The characteristics of any given sediment will depend on the major contributing organisms and on the physical attributes of the depositional environment. We will cite examples of the most important, fine, unconsolidated algal sediments associated with various zones of the reef. The major correlations of sedimentary types, the organisms producing them, the depositional environment, and the zones of the reef are summarized in Table 3 and Figure 23. In the inshore region, which is as a rule shallow and exposed to turbulence, tidal fluctuations, and occasional contamination with fresh water, the sediments tend to be coarse and well sorted, ranging in size from 5 mm to less than 1 mm. The most important single contributor to this sand is Halimeda opuntia, but other species of Halimeda (incrassata, simulans), Peni-
Bulletin of Marine Science
446
[23(2)
.. ..
on
u
a.
