BULLETIN OF MARINE SCIENCE, 58(1): 301-313,
1996
CORAL REEF PAPER
WAVE-LIKE OUTWARD GROWTH OF SOME TABLE- AND
PLATE-FORMING CORALS, AND A HYPOTHETICAL MECHANISM
J. Stimson
ABSTRACT
Wave-like outward growth of the surfaces of concentrically growing plate- and tableforming species of coral have been reported from various sites in the Pacific, This paper
reports the same phenomenon in Acropora, Montipora and Merulina at sites on the north
west coast of Western Australia and in the plate form of Montipora verrucosa (Lamarck) in
Hawaii. Inter-crest distances of the waves are on the order of 10 to 12 cm in table Acropora,
and 2 to 5 em in the other genera, and are hypothesized to represent 1 year's radial growth,
This hypothesis is examined indirectly in the Australian species using published linear growth
rates from a third location on the western Australian coast and an inverse relationship between
growth rate and latitude, It is examined directly in the plate form of M, verrucosa in Hawaii.
It is concluded that one cycle of the wave represents 1 year of growth. The wave-like growth
form is proposed to be the result of the annual variation in irradiance; more specifically, the
decrease in slope of the wave as growth approaches a crest and the negative slope following
the crest, are the result of inhibition of upward growth by increasing and high levels of
irradiance in the spring and summertime, possibly the UV-B component.
Inside the skeletons of many corals there is a record of their annual linear
growth and therefore a record of the conditions in the environment during the
span of the life of the coral (Knutson et aI., 1972; Buddemeier et aI., 1974; Dodge
and Thomson, 1974; Isdale, 1977). This record is contained in alternating bands
of high and low density skeleton as revealed by X rays of thin slabs cut radially
through colonies.
External features of the coralla of some species may also record annual growth
increments. Some table-, vase- and plate-forming corals, and even the vertical
blades of MilLepora complanata (Lewis, 1991) develop externally visible ridges
resulting from wave like patterns of linear growth (Fig. 1). Abe (1940), Ma
(1958), Smith and Harrison (1977), and Veron (1986) have reported these waves
and have proposed that they represent annual radial growth increments, but no
evidence has been offered that they record annual growth increments nor have
mechanisms for their production been presented.
This study reports the same phenomenon in three genera of corals (Acropora,
Montipora and Merulina) at sites in Western Australia, and in Montipora verrucosa at a site in Hawaii. The periods of the waves are quantitatively described,
the correspondence between features of the waves and the season of their production are reported, and a mechanism for the production of the waves is proposed,
METHODS
Measurements were made of the distance between concentric crests on the upper surfaces of table
Acropora (Acropora spicifera (Dana, 1846)), plate forming Montipora spp. and multi-tiered vasiform
Merulina spp. at three locations in Western Australia. Seven sites were sampled in the sheltered central
area of the Easter Group of the Houtman Abrolhos (HA) Islands (28°30'S, 114°E) (Fig. 2). All sites
were less than 3 m in depth and represented the upper slopes of lagoonal patch reefs. The results from
all sites were combined for analysis. Measurements of the corals were made in late April 1990. Seven
sites were also sampled along the south central section of the Ningaloo reef, a narrow barrier/fringing
reef system (Veron and Marsh, 1988) along the north west shore of Western Australia (22-23°S, 114°E)
between the Tropic of Capricorn and the town of Exmouth. The sites were all at depths of less than
301
302
Figure I.
BULLETIN OF MARINE SCIENCE. VOL. 58. NO. I. 1996
Colony of Acropora spicifera showing concentric growth waves. Slate is 30 cm in length.
3 m and were on the slopes of small patch reefs which dot the lagoonal waters close to the barrier
reef. Measurements were made in late May 1990. A third location, Bundegi reef (21°50'N), 10 km
NNE of Exmouth and sheltered on the west by the Cape Range Peninsula, was characterized by the
presence of brown silt and sand. The corals examined here in late May 1990 were in water of less
than 3 m depth and were part of an extensive shallow reef formation several hundred meters offshore.
Since there are no measurements of the annual linear growth of the coral species used in this study
at the particular Western Australian sites which were sampled, the test of the idea that waves represent
annual increments at these sites, was done indirectly by comparing the inter-crest measurements with
published annual growth increments for a similar table Acropora at a more northerly latitude on the
Western Australian coast. Linear growth is evidently negatively related to latitude in at least one genus
(Porites, Krasnov, 1981; Grigg, 1982). This relationship was examined further by collecting published
reports of linear growth rates for massive Porites and for Pocillopora damicornis and plotting these
rates against latitude. The existence of an inverse relationships between growth rate and latitude in
these two genera was then used to interpret the latitudinal pattern of wave lengths for the corals at
the Australian study sites.
Measurements of growth rate and observations on wave formation were also made in Hawaii on
the slope of the windward fringing reef of Moku 0 Loe (Coconut Island) in Kaneohe Bay, Oahu from
1991 to 1992. Plate forming Montipora verrucosa occur at depths of 3 to 7 m on the reef slope, or
in shallow shaded locations. The deepest colonies examined were at about 6 m. Plates grow outward
at an angle of about 10° above horizontal.
In all genera, measurements of the distance between crests of concentric waves were made along
imaginary radial lines running from the center, or point of attachment of a colony, to the margin.
Measurements were made along only one radial line on each colony: up to five consecutive crest to
crest measurements could be made along the line. Measurements were also made of the distance from
the outermost crest to the edge of the colony (Fig. 3). Measurements were to the nearest cm; grcater
precision was not warranted because the shallowness of the crests and the rough surfacc texture of
the corallum made it difficult to locate the highest point on the crest. The corals on which measurements were made were not chosen at random; only corals which showed distinct crcsts were used.
The Acropora colonies used were >40 cm in diameter and grew outwards almost horizontally. Montipora and Merulina colonies were generally less than 50 cm in diameter; Montipora plates grew
almost horizontally while the foliose plates of Merulina grew at an angle of about 45° from horizontal.
303
STIMSON: WAVE-LIKE GROWTH FORM IN CORALS
B
A
Pt. Murat
WESTERN
AUSTRALIA
HOUTMAN
ABROLHOS
ISLANDS
I
I'
1\
o
NORTH
WEST
CAPE
c
~ Pt. Cloates
HOUTMAN
ABROLHOS
GROUP
~
WALlABI
GROUP
"
.p;'"'1
I,
EASTER
GROUP ; (~
o t ) ••
\~.,.
o
10 KM
(:\. (PElSAERT
GROUP
\1,
Figure 2_ Map of the West Coa~t of Australia (A), Ningaloo Reef (B) and the Houtman Abrolhos
Islands (C).
In Hawaii, measurements of the distance between crests of consecutive waves, and between the
outermost crest and colony-edge, were made approximately monthly on colonies of M. verrucosa
growing at depths of 4-7 m on the reef slope. Up to 15 colonies were measured during each sampling,
the colonies were distributed along 400 m of reef slope habitat. These measurements make it possible
to determine what part of the wave was produced by the growing edge of the colony in each season
of the year and provide an estimate of annual radial growth. Not all colonies at 4-7 m show wavelike growth.
The rate of radial growth of M. verrucosa was also measured over monthly intervals on tagged
colonies which occurred at a somewhat shallower depth (3-5 m) and so were more accessible by
snorkeling. These colonies grew as horizontal plates, but did not usually show the wave-like growth
found in colonies at depths of 4-7 m. Also, some differed from the deeper colonies in producing
vertical branches from the older, more central parts of the plate. Plastic or glass posts were inserted
in holes drilled vertically through the plates ~5 cm from the edge; these provided reference points
for the measurement of radial growth. Because of tag loss, tissue death and corallum breakage, few
colonies were followed for an entire year.
Measurements were made from the summer of 1991 to summer of 1993.
RESULTS
For Acropora spicifera the crest-to-crest distances at Ningaloo are significantly
greater (t test, P < 0.001, df = 57) than those at the HA (Table 1). The most
304
BULLETIN
OF MARINE
SCIENCE,
VOL.
58, NO.
I, 1996
Measurment
Crest
Crest
to Crest
to Edge
Figure 3, Drawing of a colony of table Acropora showing the wave-like form in cross section and
the features used in making measurements,
northerly location sampled, Bundegi, is not included in this comparison because
the environment was very different. Dark brown sand and silt discolored and
obscured the white of the carbonate sands at this location, suggesting that the
conditions for coral growth may be sub-optimal. The distance from the outer-most
crest to the perimeter of the coral (crest-to-edge) was about 0.65 of the crest-tocrest distance at all three study locations (Table 1).
Table I. Inter-site comparison of the average crest-to-crest distance on the surface of Acropora spiClfera colonies. Crest-to-crest distances are for the three or four outermost intervals, numbering from
the inside. The decreasing sample size for more proximal crests reflects the fact that the outer-most
crests were more discernable. Average crest-to-crest distance is the average of each colony's average
crest-to-crest distance. Figures in the ratio column are based on the ratio of the crest-to-edge distance
for each colony divided by the average crest-to-crest distance for the same colony.
Crest-la-crest
distance
(em)
by interval
4
Avg.
crest-la-crest
distance
(em)
Crest-lo-edge
distance
(em)
Avg.
ratio
Houtman Abro]hos Sites (28°S)
]0.25
Mean
9.50
SD
0.50
0.80
No. corals
2
6
10.40
2.45
]0
10.39
1.75
15
10.42
1.65
15
6.73
2.82
\5
0.67
0.31
]5
Ningaloo Sites (23°S)
Mean
\\.00
SD
No. corals
II
]2.02
1.53
26
12.59
1.88
44
12.36
1.41
44
7.65
1.51
44
0.62
0.12
44
10.44
1.63
34
10.35
1.18
36
10.52
1.17
36
7.14
1.98
36
0.68
0.]6
36
Bundegi Site (22°S)
Mean
10.78
0.97
SD
No. corals
\8
12.23
1.1\
305
STIMSON: WAVE-LIKE GROWTH FORM IN CORALS
1
2.0
12
1
10
~
••>-.
<Il
1.5
OJ
t:
:>
:0
5. •
2.
2
II)
91
••
0:
=
0
6!
2.
!a
5:!
3
1.0
.S
;:
.1
7
Q.
11.
11.
•
4!
0.5
7
af fa
a,
a.
Cl
0.0
0
5
10
15
20
25
30
Latitude
Figure 4.
Re]ationship between estimated annual growth rate (increase in radius, cm·y ') and latitude
for massive Indo-Pacific
Porites species. Data was restricted to corals growing in the field in waler
less than ~ 10 m in depth. Standard errors of the mean are shown when available. The number of
corals examined is given in parentheses,
in order of increasing latitude if there is more than one site
per reference. Studies cited: I) Knutson et a!., 1972 (]); 2) Buddemeier,
] 974 (3, ]); 3) Buddemeier
et a!., ]974 (5); 4) Isdale ]977 (28); 5) Polyakov and Krasnov, 1976 (3, I); 6) Highsmith,
]979 (]2);
7) Krasnov, 1981 (17,30);
8) Grigg, ]982 (4, ]2,7, ]0, 10, ]4); 9) Hudson, ]985 (4); 10) Jokiel and
Tylel~ 1993 (], ]); II) Charuchinda
and Chansang,
1985 (6); 12) Scoffin et a!., 1992 (II).
The three outer crest-to-crest distances in A. spicifera colonies (Table 1) were
compared using a randomized blocks ANOV A (Sokal and Rohlf, 1981). The three
consecutive crest to crest intervals were the classes to be compared and each coral
at a location constituted a block (a set of related measurements) in the analysis,
For each of the locations, no significant differences were detected among intervals.
No data are available on the linear growth rates of Acropora spicifera at the
locations used in this study, so to test whether the wave lengths represent annual
growth increments it is necessary to compare the wave lengths to the annual radial
growth of table Acropora measured at a nearby location. The annual growth in
radius of tagged Acropora hyacinth us colonies has been estimated at a site on the
northwest coast of Western Australia, at Dampier Archipelago (20.5°S) (Simpson,
1988), and is approximately 12.9 cm (no SD given, based on records from five
colonies from a depth of 4 m). This value is slightly greater than the crest-tocrest distance (12.34 em) of the waves of the colonies sampled at Ningaloo (22°S),
and greater than the crest-to-crest distances (10.49 cm) measured at Houtman
Abrolhos (28°S) (Table 1). The wave lengths measured at the three locations used
in this study are comparable to but less than the annual radial growth of another
table Acropora at a more northerly site on the same coast.
On the basis of studies in other coral genera it can be established that linear
growth rates of corals are inversely related to latitude. This latitudinal effect may
account for the difference between wave lengths for A. spicifera at HA and Ningaloo. The inverse relationship has been demonstrated by Krasnov (1981) for
massive Porites (P. lobata and P. lutea) in the South Pacific (Fig. 4, points labeled
306
BULLETIN OF MARINE SCIENCE. VOL. 58. NO. I, 1996
6
12 .) 12
.1
5
~
',.,"
• 6
CD
;;;
4
13.'14
Co
.15
E
2
.::!'"
3
9 ••
7.r4
"t:l
'"
a:
-=~
0
!2
13
2
.8
."9
.~"
Cl
11.
o'---_ .....•.
o
5
...a....__
10
---'
-'15
20
L.- __
25
• 3
.3
-'- __
30
----J
35
Latitude
Figurc 5. Rclationship between cstimated annual growth rate (increase in radius, cm·y-I) and latitudc
for Pocillopora damicornis. Some of these estimates of annual growth were made from data spanning
less than a I-year period. Standard errors of the mean are shown when available. Studies cited: I)
Glynn and Stewart, 1973; 2) Stephenson and Stephenson, 1933; 3) Crossland, 1981; 4) Mayor, 1924;
5) Simpson, 1988; 6) Polacheck, 1978; 7) Neudecker, 1977; 8) Ward, 1991; 9) Alcala et aI., 1981;
10) Edmondson, 1929; 11) Price (pers. comm, Univ. Hawaii); 12) Wellington, 1982a; 13) Glynn,
1977; 14) Richmond, 1985; 15) Wellington, 1982b.
9 and 11), and by Grigg (1982) for Porites lobata over the latitudinal range of
this species in the Hawaiian archipelago (Fig. 4, points labeled 12). A compilation
of these and other published records based on annual linear growth increments
or density banding in massive Porites in the Pacific also indicates a significant
inverse relationship using a non-parametric test of association (Kendall's Tau, t
= -0.354, N = 22 studies, P < .05, Fig. 4). A non-parametric test of association
was used because the underlying relationship is not known and the data are not
bivariate normal. Records of linear growth of P. damicornis also show a significant inverse relationship between growth rate and latitude (Kendall's Tau, t =
-0.453, N = 19 studies, P < .01, Fig. 5). The wave lengths measured of A.
spicifera at 22°5 and 28°5 also show an inverse relationship with latitude, suggesting the same phenomenon exists in this species.
These results, the correspondence between the annual growth of table Acropora
at one site and the crest to crest distances at two other sites, and the inverse
relationship between latitude and growth rate, support the hypothesis that the
waves in the coralla of the Australian corals examined in this study represent
annual growth increments.
Numerous consecutive waves are visible on the smoother surfaces of plateforming Montipora spp. and foliaceous Merulina spp. The crest-to-crest distances
are much smaller in these species (Table 2) than they are for Acropora spicifera.
No attempt was made in the field to distinguish between Montipora species, so
some of the variance in the crest-to-crest measurements for this genus is presumably due to interspecific differences. The ratio of crest-to-crest versus crest-to-
307
STIMSON: WAVE·LIKE GROWTH FORM IN CORALS
Table 2. Crest-to-crest measurements on Montipora spp. and Merulina sp. at Western Australian study
sites. The mean intercrest distance tabulated is based on the mean intercrest value for each colony
sampled. Values in the ratio column are based on the crest-to-edge distance of a colony in April or
May divided by the average crest-to-crest distance for the same colony; the figures for all colonies
were then averaged.
Site
Inter-crest
Houtman
Ningaloo
Inter-crest
Houtman
Ningaloo
Lalitude
measurements-Montipora
Abrolhos
Rf.
measurements-Merulina
Abrolhos
Rf.
Corals
(no.)
4.03
5.18
1.33
1.47
12
24
1.72
2.93
0.41
0.42
5
3
Avg.
mtio
0.72
0.64
sp.
28°5
23°5
Islds.
SD
sp.
28°5
22°5
Islds.
Mean
(em)
edge distances for Montipora spp. at the two sites are 0.72 and 0.64, approximately the same as the ratio in A. spicifera.
Both the time between production of consecutive crests and the month of crest
production was determined for M. verrucosa in Hawaii. The crest-to-edge (CE)
measurement on each colony divided by the average inter-crest distance (CC) for
that colony was used to calculate the percentage of wave completed on a given
date. This percentage figure corrected for differences in absolute growth rate
among corals. The time of year when the value of the percentage CE/CC is 0.0
or 1.0 is estimated to be the time of production of the crest, and as shown in
Figure 6, this occurs in February or March. The value of the proportion increases
almost linearly from spring to winter. The average crest to crest distance, calculated as the average of all 12 sample averages (the 12 samples in Fig. 6) was 4.4
1.1
1.0
0.9
t(l1)
t
;(5)
(10)
(14)
0.8
(10),
0.7
~
!
0.6
(3)
0
~
w
0.5
0
(5)
0.4
(15)
0.3
0.2
+
1
i
(10)
(10)
+
f
,,,t
+
(14) •
0.1
0.0
Jan
Feb Mar
Apr
May
Jun JuI
Month
Aug
Sep
Oct
Nov
Dec
Figure 6. Percent completion of waves in the coralla of M. verrucosa in Hawaii throughout the year.
Percent completion is expressed as the ratio of average crest to edge distance (CE) divided by the
average crest to crest distance (CC) for the colonies measured on each date. Numbers are the number
of colonies sampled on each date.
308
BULLETIN OF MARINE SCIENCE, VOL. 58, NO. I, 1996
cm (N = 12, SD = 0.5). Linear growth rates were measured On a set of shallower
colonies (3-5 m depths); the annual growth of six tagged colonies in this set
which were followed for a year, averaged 4.2 cm'y-I (SD = 1.3).
DISCUSSION
Externally visible features presumably representing annual growth increments
have been described by Abe (1940), Ma (1958), Smith and Harrison (]977), Jakie]
(1986), Veron (1986) and Lewis (1991), but these authors did not report how the
annual nature of the waves was determined or offer mechanisms for their production. It seems reasonable to conclude that the wave-like surface features of
colonies reported in this and other studies are also annual increments, because:
1) the Hawaiian coral M. verrucosa shows an annual periodicity of wave production, 2) the wave length of the Australian Acropora approximates the annual
growth increment of other nearby table Acropora, and 3) annual changes in another skeletal feature, skeletal density of massive corals, have been reported (Buddemeier, 1974; Buddemeier et aI., ]974; Highsmith, ]979).
The season of production of the features of these waves can be established for
both the Australian and Hawaiian corals investigated and provide clues about the
mechanism of the waves production. At both the HA and the Ningaloo reefs the
last increment of growth (crest-to-edge) in the Acropora and Montipora was about
65% of the average crest-to-crest distance (Tables 1, 2). If radial growth were
constant through the year, this figure would mean that 65% of the growth occurring in one crest-to-crest cycle had been completed at the time of the late April
(HA) and late May (Ningaloo) sampling. There is however, good evidence from
the data of Simpson (1988) and Crossland (198]) to show that linear growth of
corals on the west coast of Australia at the latitudes included in this study is very
seasonal with maximum linear growth rates in the summer months. Approximately
60% of the annual growth occurs in the 6-month October to March period at
Dampier and ~75% of growth occurs in the same period at HA (Crossland, ]981;
Simpson, 1988). Other studies (Shinn, 1966; Glynn, 1977; Yap and Gomez, et
aI., 1984) also show seasonality of growth, even within 8° of the equator.
To estimate the month or season of production of the wave crests of the table
Acropora it was necessary to calculate the percentage of the annual growth which
occurs each month. This was done using the data of Simpson (1988) for A. hyacinthus at Dampier Archipelago, Western Australia. The values of percent growth
per month were then summed backward through the year, starting from the month
in which the data in this study were collected, until approximately 65% of the
annual growth had been accumulated. This process results in the estimate that the
date of production of the crest is early November at Ningaloo. The production of
the crests is before the time of maximum irradiance and maximum water temperature at both HA (Crossland, 1981) and Dampier (Simpson, 1988). The production of crests occurs prior to the months of greatest linear growth of the
colonies in mid summer (Crossland, 198]; Simpson, 1988).
The study of growth and wave formation in the Hawaiian species M. verrucosa
provides direct evidence of the timing of crest production. The estimated time of
production of crests is in the late winter or spring, that is when the CE/CC ratio
is 0 or 1.0 (Fig. 5). This is prior to the time of maximum irradiance, and at about
the time of minimum water temperature in Hawaii (Smith et aI., 1981). In both
the Hawaiian and Australian corals the crests of the waves are evidently formed
at the time of increasing irradiance levels, and in Australia occurs at the time
when radial growth in the table A. hyacinthus is increasing (Simpson, ]988).
309
STIMSON: WAVE-LIKE GROWTH FORM IN CORALS
Jan Feb Mar Apr May Jun
Winter
Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
Summer
Winter
Summer
Figure 7. Schematic side-views of table- or plate -forming corals. illustrating the hypothesized
relationship between season and orientation of growth. The year is divided into "summer"
and "winter"
halves. Arrows indicate 3 possible orientations
of branchlets or polyps at the growing tip; lengths of
arrows indicate the relative extension rates in a particular season. See text for further explanation.
The wave like growth form reported here may be the result of the annual cycles
in irradiance and temperature reported in tropical waters (Glynn, 1977; Crossland,
1981; Charuchinda and Hylleberg, 1984; Yap and Gomez, 1984; Simpson, 1988).
Temperature and light level are often invoked to explain inter-site and inter-season
differences in coral growth rates (Buddemeier and Kinzie, 1976; Glynn, 1977;
Highsmith, 1979; Crossland, 1981; Wellington and Glynn, 1983). The directionality of radiant energy seems to lead more readily to the generation of testable
hypotheses for explaining the wave-like features.
Since wave crests were produced in spring or early summer, inhibition of upward growth by high or increasing levels of irradiance in these seasons seems a
reasonable hypothesis to account for the crests. The argument is as follows: Dur-
ing summer, irradiance levels are high, favoring rapid calcification (Kawaguti and
Sakamoto, 1948; Goreau, 1959; Goreau and Goreau, 1959; Vandermeulen and
Muscatine, 1974; Chalker and Taylor, 1975) and outward growth of the colony,
however, the high or increasing levels of irradiance, particularly UV-B, may also
inhibit the growth of polyps or tissues on the upper surface of the colony's growing edge, i.e., the tissues most directly exposed to the radiation (Siebeck, 1988;
Shick et aI., 1991). The more successful growth of downward-oriented polyps
may result in downward orientation in the growth of the corallum, as is represented by the direction and relative lengths of the arrows in Figure 7. In fall and
winter the radiation could be less inhibitory or non-inhibitory to tissues of the
upper surface, which could then be the faster growing due to their exposure to
more optimal light levels; as a result growth of the tips or edge of the colony
could be oriented upward, but the rate of branch tip elongation would not be as
high as in summer because of the lower levels of photosynthetically active radiation. In winter, biologically damaging radiation (DUV) is estimated to be 15 to
67% of summertime values at latitudes of 20° to 30° (Stordal et aI., 1982).
Some support for this hypothesis comes from the following studies. Jokiel and
York (1982) found that Pocillopora damicornis housed in shallow tanks (30 em
deep) and protected from UV-B radiation by acrylic plastic, grew more than controls which were exposed to uv. Growth was measured during a 40-day period
310
BULLETIN OF MARINE SCIENCE. VOL. 58. NO. I, 1996
Table 3. Annual growth of Montipora species at various field sites for comparison with the intercrest measurements in Table 2. Time period is the length of the interval over which growth measurements were made.
Annual increment
(ern)
Site
Latitude
Magnetic Island
(Australia)
Bolinao
(Phil.)
Dumaguerte
(Phil.)
Dumaguerte
(Phil.)
Batangas
(Phil.)
Hawaii
19°5
M. digitata
l6°N
M. sp.
2.4 cm (9 mo)
2.8 cm (13 mo)
(I yr)
3.6
9°N
M. foliosa
3.25
(3 yr)
Gomez et aI., 1985
9°N
M. undata
2.60
(1 yr)
Gomez et aI., 1985
l3°N
M. sp.
3.20
(1.2-2
21°N
M. verrucosa
3.25
(I yr)
Species
yr)
Reference
Heyward and
Collins, 1985
Gomez et aI., 1985
Gomez et aI., 1985
This study
in August and September, Secondly, Baker and Weber (1975), Bak (1976), Huston
(1985) and Jokiel (1986) have found that in situ colonies of some coral species
(Agaricia agaricites, Montastrea annularis, Montastrea cavernosa, Porites compressa and perhaps Porites astreoides) grew more rapidly at intermediate depths
than at shallow depths; this could be interpreted to mean that these species may
have less protection from high intensity radiation than other species, Third, Gleason and Wellington (1993) have demonstrated that there is enough damaging UV
radiation at 12m depth to cause loss of zooxanthellae from corals transferred to
this depth from 18 or 24 m. Fourth, Barnes and Taylor (1973) found a marked
inhibition of calcification at saturating light intensities. Finally, protection from
damaging radiation is in part provided by UV absorbing compounds (mycosporine-like amino acids) whose concentration is known to decrease with depth over
the vertical range of a coral species (Maragos, 1972; Jackson, 1983; Dunlap ct
aI., 1986; Gleason and Wellington, 1993); the decrease suggests these compounds
are produced in response to the quantity of radiation encountered at a particular
depth. Experimental increases in UV radiation are known to result in increases in
the concentration of these compounds, but it evidently takes three weeks or more
to reach control concentrations (Gleason and Wellington, 1993; Shick et aI., 1991).
The evidence just cited suggests that UV can be inhibitory to corals, and that
they do respond biochemically to the presence of UV; it may also be possible
they respond to changes in UV levels by making morphological changes.
The presence of concentric waves on table Acropora at Enewetak at depths of
from 15-25 m (Smith and Harrison, 1977) argues that inhibition by UV radiation
may not be the explanation, because so little UV radiation would be expected at
this depth in tropical waters (Calkins, 1982). However, even corals at a depth of
20 m have been found to contain the same UV absorbing compounds contained
by shallow water congeners (Dunlap et aI., 1986) suggesting some UV-B does
penetrate to these depths. Estimates of the extinction coefficients of UV and UVB are available for clear tropical waters, They are in the range k = O. I5 to O. I8
(Smith and Baker, 1979; Calkins, 1982), greater than the value of O. 11 estimated
for clear oceanic water (lerlov, 1976; Oliver et aI., 1983) and would result in
from 0.067 to 0.105 of surface UV penetrating to 15m and from 0.0 I I to 0.0235
penetrating to 25 m.
The crest-to-crest distances in Australian Montipora spp. and Merulina are
much smaller than those of Acropora spicifera (Table 2). The Montipora distances
STIMSON: WAVE-LIKE GROWTH FORM IN CORALS
311
are similar in magnitude but greater than published annual growth rates for this
genus (Table 3); no comparative values are available for Merulina, but Ma (1958),
using the same wave-like morphological features, estimated the annual growth in
this genus from 1.7 to 4.8 em. The ratio of length of the final increment to the
crest-to-crest measurements in the Australian Montipora are similar to those observed in Acropora spicifera, 0.72 and 0.64, suggesting a common environmental
influence on the production of the wave like growth of these different genera.
The phenomenon of wave-like growth form is widespread geographically and
taxonomically. On the basis of the measurements presented here, one wave length
seems to represent an annual increment of outward growth. Its possible that the
wave-like growth form is a response to seasonal variation in damaging UV radiation. The directionality of the irradiance in the environment of corals makes
the annual changes in UV energy a more reasonable explanation than temperature
change. The broad taxonomic distribution of the phenomenon and the regularity
of distances between crests argues against the waves being a response to fluctuation in coralivory by reef fishes or some other biotic factor.
ACKNOWLEDGMENTS
I wish to thank Dr. M. Johnson and the Zoology Department of The University of Western Australia
for use of their equipment and facilities, Dr. R. Black for his hospitality and for assisting in making
the field work in Western Australia possible, Dr. B. Hatcher for making it possible to work at the
Houtman Abrolhos Islands, Dr. P. Helfrich for access to the facilities of H.I.M.B., and Dr. S. V. Smith,
Dr. T. Hazzard and Ms. S. Romano for commenting on an earlier draft of this paper.
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DATE ACCEPTED:
ADDRESS:
October
3, 1994.
Zoology Department, University of Hawaii, Honolulu, Hawaii 96822,
USA.