Skeletal Density Banding Research Articles

Correction Factors for δ18O-Derived Global Sea Surface Temperature Reconstructions From Diagenetically Altered Intervals of Coral Skeletal Density Banding

Reconstruction of sea surface temperature (SST) from the δ18O and Sr/Ca composition of coral skeletal density banding (CSDB), identified with x-ray diffraction and micro computed tomography, provides invaluable centuries-long records of ocean circulation and climate change. Comparison with age-equivalent instrument measurements of SST over the last 125 years has proven these δ18O-derived SST reconstructions to be generally reliable. However, notable exceptions occur within discrete CSDB stratigraphic intervals that yield δ18O-derived SST underestimates of as much as 9°C with respect to instrument measured SST. Here we combine high-resolution optical and electron microscopy with geochemical modeling to establish correction factors for the impact of marine seafloor physical, chemical, and biological alteration (diagenesis) within these altered intervals of CSDB stratigraphy. Four cores were collected from Porites coral heads across a 4-24 m water depth bathymetric transect at Myrmidon Reef, Great Barrier Reef, Australia. Precise mapping of diagenetic aragonite cementation was completed within CSDB patterns digitally overlaid on 35 petrographic thin sections fully covering 2.1 m of core. The vast majority of core skeletal material exhibited little to no diagenetic aragonite cementation. However, extensive diagenetic alteration was observed within discrete CSDB intervals near the base of the two deeper water Porites heads. This diagenesis serves to modify skeletal density and CSDB stratigraphy in these intervals, as well as structurally reinforce the coral skeleton. Reliable δ18O-based SST correction factors for these diagenetically altered CSDB intervals are established here by applying the percent mixing of diagenetic aragonite cement to a binary mixing model. This approach, with quantitative extents of mixing established with both microscopy and existing globally distributed coral δ18O and Sr/Ca data sets, accurately restores modern and fossil coral δ18O-derived SST records. Results indicate that as little as 5% mixing of diagenetic aragonite cement with original coral skeleton will cause δ18O-based SST anomalies of 0.9°C.

Dissepiments, density bands and signatures of thermal stress in Porites skeletons

The skeletons of many reef-building corals are accreted with rhythmic structural patterns that serve as valuable sclerochronometers. Annual high- and low-density band couplets, visible in X-radiographs or computed tomography scans, are used to construct age models for paleoclimate reconstructions and to track variability in coral growth over time. In some corals, discrete, anomalously high-density bands, called “stress bands,” preserve information about coral bleaching. However, the mechanisms underlying the formation of coral skeletal density banding remain unclear. Dissepiments—thin, horizontal sheets of calcium carbonate accreted by the coral to support the living polyp—play a key role in the upward growth of the colony. Here, we first conducted a vital staining experiment to test whether dissepiments were accreted with lunar periodicity in Porites coral skeleton, as previously hypothesized. Over 6, 15, and 21 months, dissepiments consistently formed in a 1:1 ratio to the number of full moons elapsed over each study period. We measured dissepiment spacing to reconstruct multiple years of monthly skeletal extension rates in two Porites colonies from Palmyra Atoll and in another from Palau that bleached in 1998 under anomalously high sea temperatures. Spacing between successive dissepiments exhibited strong seasonality in corals containing annual density bands, with narrow (wide) spacing associated with high (low) density, respectively. A high-density “stress band” accreted during the 1998 bleaching event was associated with anomalously low dissepiment spacing and missed dissepiments, implying that thermal stress disrupts skeletal extension. Further, uranium/calcium ratios increased within stress bands, indicating a reduction in the carbonate ion concentration of the coral’s calcifying fluid under stress. Our study verifies the lunar periodicity of dissepiments, provides a mechanistic basis for the formation of annual density bands in Porites, and reveals the underlying cause of high-density stress bands.

Luminescence and density banding patterns in massive Porites corals around the Thai-Malay Peninsula, Southeast Asia

We characterized the annual luminescent and skeletal density banding patterns in 51 massive Porites corals from 15 reefs from six locations around the Thai-Malay Peninsula in Southeast Asia, and explored the seasonal environmental cues/drivers of band formation. Location-specific recurrent annual luminescent banding patterns were found at all study locations with a brighter band occurring toward the end of the year (∼October/November/December) (at five locations) and in ∼June (one location). Annual density banding patterns could only be discerned at four locations, and were categorized into those that formed a dense band commencing ∼November/December, and those starting ∼May/June. Overall, compared to luminescence, variations in skeletal density provided a less clear signal for demarcation of annual growth increments. Seasonal variations in luminescence showed clearest relationships with salinity, as a proxy for freshwater/river runoff. No convincing relationship between intra-annual luminescence intensity and density variations was found, which supports the notion that luminescent banding is due to inclusions of fluorophores into the coral skeleton rather than variations in skeletal architecture. The relationships between seasonal density variations and significant wave height and rainfall suggest density banding in this region is likely related to wave energy, or some other correlated environmental parameter/s. The large variability in skeletal banding patterns not only highlights the current relatively poor understanding of their nature and causes, but also the need for replication in their interpretation, especially in settings with complex seasonal hydrodynamic/hydrological patterns such as those found around the Thai-Malay Peninsula.

Density banding pattern of the south western Atlantic coral Mussismilia braziliensis

The South Atlantic Ocean is a region that lacks data regarding the long-term monitoring of oceanographic parameters. In addition, proxy indicators in this region are not yet well established. We evaluate the density-banding pattern of the coral Mussismilia braziliensis to calibrate it for use as a proxy of paleoceanographic parameters, such as temperature and light availability. Colonies of the coral were stained with alizarin red in the field and in an aquarium system to determine the periodicity and cyclicity of the skeletal density banding and to determine whether this coral species presents banding pattern characteristics useful as an environmental proxy. The results show that M. braziliensis forms annual density bands in nature that comprise a pair of high- and low-density bands (light and dark bands, respectively, in negative X-radiography). Furthermore, M. braziliensis forms high-density bands starting from October to November, when the average monthly temperature is between 25°C and 25.5°C, and low-density bands starting from May, when temperature is around 26.5°C and 26°C. In a time series (1997 to 2005) of M. braziliensis growth observed in core slabs and collected in Abrolhos, no significant difference in the widths of the low and high density bands was observed, although clear asymmetry was observed in the temperature seasonality. Thus, the resultant linear extension rate is lower during the warming period comparing with the cooling period. However, colonies of this species that were maintained for one year in a closed aquarium system at a constant temperature of 26°C±0.2°C and 12h of illumination also formed a new and complete density cycle despite the absence of seasonality in temperature and photoperiod during the experiment. This result implies that the primary cue for density banding is endogenous, possibly the reproductive cycle, and that temperature plays a secondary role in fine-tuning the banding cycle. Thus, we conclude that this species can be used as an archive for environmental parameters. On the other hand, it can be used to evaluate environmental impacts induced by human action and/or by global climatic changes on the growth of corals in recent decades and centuries along the coast and the continental shelf of the tropical western Atlantic Ocean.

Gender-related differences in the apparent timing of skeletal density bands in the reef-building coral Siderastrea siderea

Density banding in skeletons of reef-building corals is a valuable source of proxy environmental data. However, skeletal growth strategy has a significant impact on the apparent timing of density-band formation. Some corals employ a strategy where the tissue occupies previously formed skeleton during as the new band forms, which leads to differences between the actual and apparent band timing. To investigate this effect, we collected cores from female and male colonies of Siderastrea siderea and report tissue thicknesses and density-related growth parameters over a 17-yr interval. Correlating these results with monthly sea surface temperature (SST) shows that maximum skeletal density in the female coincides with low winter SSTs, whereas in the male, it coincides with high summer SSTs. Furthermore, maximum skeletal densities in the female coincide with peak Sr/Ca values, whereas in the male, they coincide with low Sr/Ca values. Both results indicate a 6-month difference in the apparent timing of density-band formation between genders. Examination of skeletal extension rates also show that the male has thicker tissue and extends faster, whereas the female has thinner tissue and a denser skeleton—but both calcify at the same rate. The correlation between extension and calcification, combined with the fact that density banding arises from thickening of the skeleton throughout the depth reached by the tissue layer, implies that S. siderea has the same growth strategy as massive Porites, investing its calcification resources into linear extension. In addition, differences in tissue thicknesses suggest that females offset the greater energy requirements of gamete production by generating less tissue, resulting in differences in the apparent timing of density-band formation. Such gender-related offsets may be common in other corals and require that environmental reconstructions be made from sexed colonies and that, in fossil corals where sex cannot be determined, reconstructions must be duplicated in different colonies.

Skeletal extension rate of the reef building coral <i>Porites</i> species from Aqaba and their environmental variables

Annual skeletal extension rates of the sclera-actinian corals Porites species were investigated in 32 colonies from the northern Gulf of Aqaba fringing reef at various depths (1 - 42 m). All corals reveal clear and regular skeletal density banding patterns. Results showed that the high-density annual growth bands were formed during winter and the low-density annual growth bands during summer. The mean annual extension rates of the studied corals reveal a large inter-colony variability with values ranged between 2.36 to 20.0 mm/year. While a general trend of decreasing coral extension rate with depth was observed and best explained by a simple exponential model, the rates clustered into two groups: 10.86 ± 2.54 mm/year in water depths less than 10 m, and 5.23 ± 1.99 mm/year below 12 m. Light intensity seems to be the primary environmental factor responsible for decreasing coral extension rate with depth since the effect of other environmental parameters could be neglected from the Gulf of Aqaba. Time series record of the mean annual coral extension rate showed a slight increasing linear trend which could be linked to increase seawater temperature over the period of time represented.

On the nature and causes of luminescent lines and bands in coral skeletons: II. Contribution of skeletal crystals

Slices cut from skeletons of massive Porites display two types of luminescence when illuminated by ultra-violet (UV) light: (1) faint luminescent banding associated with the annual skeletal density banding pattern and (2) narrow lines of strong luminescence associated with monsoonal runoff of fresh water from nearby land. Barnes and Taylor [Barnes, D.J. Taylor, R.B. 2001a. On the nature and causes of luminescent lines and bands in coral skeletons. Coral Reefs 19, 221–230] showed how larger skeletal holes could give rise to increased luminescence—thus accounting for the link between skeletal density banding and faint luminescent banding. Work described here tests the notion that strongly luminescent lines are also regions of lower skeletal density. Experiments involving real and artificial coral skeletons indicated that likely changes in hole size in real skeletons cannot account for the amount of luminescence associated with luminescent lines. Larger particles (< 50 μm) of powdered skeleton from cut from luminescent lines were more luminescent than similar particles cut from adjacent less luminescent skeleton. However, very small particles (< 3 μm) from the two regions of skeleton showed no difference in luminescence. Since skeletal crystals would have been largely destroyed by powdering skeleton to very small particle sizes, most of the luminescence of strongly luminescent lines is probably associated with changed crystal size and packing, with changed crystal chemistry, or with a combination of these possibilities.

Implication of water depth on stable isotope composition and skeletal density banding patterns in a Porites lutea colony: results from a long-term translocation experiment

This study investigates the effect of water depth on stable isotope composition and density-band forma- tion in the skeletal material of the zooxanthellate coral Porites lutea. In February 1991, several colonies were stained with Alizarin red-S and then transferred from 6 to 40 m. Ten years later, in February 2001, one colony was retrieved and analyzed. This provided us with the unique opportunity to maintain the coral's genetic integrity and hence to isolate environmental factors affecting skeletal isotopic composition and density pat- terns. Despite extreme environmental changes experi- enced by the corals, the downward transplants showed no mortality after 10 years. Acclimatization of the coral to the deep-water environment involved changes in mean annual extension rates and colony morphology. The growth rate at 6 m was 5.66±0.47 mm/year, almost twice the growth rate following transplantation to 40 m, which was 3.00±0.37 mm/year. A significant difference in mean annual d 18 O between the shallow and deep shallow-water colonies. The timing of density-band formation was found to be depth independent. At both depths, low-density skeleton is produced during sum- mer, and high-density skeleton is produced during win- ter, implying that it is intrinsically controlled rather than environmentally governed. The implications of these results on paleoclimate and sea level reconstruction are discussed.

Mg/Ca and Sr/Ca ratios of Porites coral skeleton: Evaluation of the effect of skeletal growth rate

We examined whether the Mg/Ca and Sr/Ca ratios of Porites coral skeletons are influenced by skeletal growth rate. A colony of Porites australiensis was collected from the Ryukyu Islands, Japan, and analyzed for the elemental ratios along two synchronous growth axes with different extension/calcification rates. The results showed little difference in the Mg/Ca and Sr/Ca profiles between the two growth axes. The Mg/Ca and Sr/Ca profiles have synchronous annual cycles with a broad peak in summer and a narrow trough in winter. This shape suggests that skeletal extension is faster in summer than in winter. A detailed description of the skeletal growth is given in combination with (1) X-ray image of skeletal density banding, (2) skeletal density measurements, and (3) the depth of skeleton occupied by organic tissue layer (i.e., polyp layer). We concluded that both the Mg/Ca and Sr/Ca ratios are independent of skeletal growth rate at least in the approximate range of 11–20 mm/year (skeletal extension rate) when bulk density of the skeleton is 1.1–1.2 mg/mm3, or 13–23 mg mm–2 year–1 (calcification rate). It is also concluded that the Mg/Ca ratio may be susceptible to biological/metabolic effect.

Coral microatolls and 20th century sea level in the eastern Indian Ocean

Coral microatolls are discoid intertidal corals that are limited in their upward growth by subaerial exposure during low tides. Microatoll upper surface morphology preserves a filtered record of changes in the height of living coral (HLC), the upper limit to which corals can grow, and by proxy a historical record of former constraining water levels. Chronologies for these variations in HLC were established in this study using annual skeletal density bands revealed when skeletal slices were X-radiographed, supplemented by annual fluorescent bands visible when samples were illuminated with ultra-violet light. The upper surface morphologies of two large microatolls from separate reef-flat sites on the Cocos (Keeling) Islands are well correlated and indicate that the upper limit to coral growth has fluctuated by more than 5 cm since the early 1900s. The upper surfaces of these microatolls also indicate that there has been little net rise in sea level in the eastern Indian Ocean during the 20th century. Microatoll surface morphology suggests that average rates of sea-level rise in the eastern Indian Ocean over this period were less than 0.35 mm yr−1, a rate considerably lower than the rate of average global sea-level change determined from aggregated tide-gauge data. The broad surface undulations do not appear to correlate directly with either El Niño-Southern Oscillation events or occurrence of the Indian Ocean dipole mode of ocean-atmosphere circulation. Microatolls provide a simple and effective method for extrapolating broad variations in sea level beyond the tide-gauge record in remote mid-oceanic settings.

Microborings and growth in Late Ordovician halysitids and other corals

Microborings in the Late Ordovician tabulate corals Catenipora rubra (a halysitid) and Manipora amicarum (a cateniform nonhalysitid) and in an epizoic solitary rugose coral differ from nearly all of those previously reported in Paleozoic corals. These microborings were formed within the coralla by endolithic algae and fungi located beneath living polyps. Comparable structures in the Late Ordovician tabulate Quepora ?agglomeratiformis (a halysitid) represent algal microborings, not spicules, and halysitids are corals, not sponges as suggested by Kaźmierczak (1989).Endolithic algae in cateniform tabulates relied primarily on light entering through the outer walls of the ranks rather than through the polyps; lacunae within coralla permitted appropriate levels of light to reach many corallites. The direction of boring was determined by corallum microstructure and possibly also by the distribution of organic matter within the skeleton. There is an apparent inverse correlation between boring activity and coral growth rate.The location and relative abundance of pyritized microborings within calcareous coralla can be established quantitatively and objectively from electron microprobe determinations of weight percent sulfur along appropriate traverses of the coral skeleton. The distribution of such microborings in Catenipora rubra and Manipora amicarum is comparable to algal banding in modern corals; this is the first report of such banding in the interiors of Paleozoic corals. Change in the intensity of boring within each corallum was evidently a response to variation in the linear growth rate of the coral, or to fluctuation in an environmental factor (perhaps light intensity) that could control both algal activity and growth rate in these corals. Change in the algal boring intensity and linear growth rate of the coral was generally but not always seasonal and usually but not invariably associated with change in the density of coral skeletal deposition.Cyclic bands of boring abundance maxima within fossil colonial corals provide a measure of annual linear growth comparable to the widely accepted method based on skeletal density bands. Algal bands are more sporadically developed than density bands within and among coralla, thus increasing the difficulty of interpretation. Fluctuations in the abundance of algal microborings apparently provide a detailed record of changes in the linear growth rate of colonies and of individuals within colonies. Combined analyses of microboring abundance and skeletal density will contribute significantly to our understanding of the biological and environmental factors involved in endolithic activity and coral growth.

The nature of skeletal density banding in scleractinian corals: fine banding and seasonal patterns

X-radiographs were made of slices cut from the growth axes of two 0.4–0.5 m diameter colonies of Parites lobata, and of a slice cut from a 720 mm long core drilled from the growth axis of a large colony of P. solida. X-radiographs of the core-slice of P. solida were made with the slice tilted lengthways at several different angles. The annual density banding patterns for the two colonies of P. lobata revealed that one grew exceptionally quickly (≈ 19 mm · yr −1) while the other grew more slowly than is usual ( ≈ 8 mm · yr −1). The fast-growing colony maintained a smooth outer surface while the slower-growing colony displayed the more usual bumpy outer surface throughout most of its growth. X-radiographs of the smooth-surfaced fast-growing colony of P. lobata showed a series of alternating dense bands ≈ 1 mm wide and less dense bands up to 3 mm wide. Similar fine bands have been previously reported as lunar banding within the familiar annual density banding pattern in massive corals of one dense band and one less dense band. An annual pattern appeared to be present as groupings of the fine dense bands. The fine bands were clearly displayed because the colony grew unusually quickly, and because it maintained a relatively smooth outer surface. As a result, the fine bands were aligned, through the thickness of the skeletal slice, with the X-ray beam that displayed them. Fine bands were not so apparent in X-radiographs of the bumpy-surfaced colony because they were seldom aligned with the X-ray beam. The annual banding pattern in Porites, and in many, if not all, massive corals, appears to be composed of such fine bands. The fine bands may not necessarily represent lunar periodicity. The thickness of slices removed from colonies for X-radiography, together with the alignment and curvature of fine bands within the slices, tends to merge or overlap the X-ray image of individual fine bands and, as a result, emphasizes seasonal patterns in their width, frequency and, perhaps, density. The fundamental nature of the fine banding pattern was demonstrated by X-radiographs of the core-slice of P. solida taken at different angles. At certain angles, the fine bands were displayed in regions where, at other angles, only the familiar annual density pattern had been seen. Fine bands appear to be generated at the outer growth surface of colonies and may represent a direct and immediate response to environmental factors.

Fluorescent and skeletal density banding in Porites lutea from Papua New Guinea and Indonesia

Shallow water Porites lutea corals were collected along two transects normal to mainland shorelines, parallel to gradients in water quality: one, 7 km long, near Motupore Island in South Papua New Guinea, the other, 70 km long, from Jakarta Bay along the Pulau Seribu chain in the Java Sea. The corals were slabbed and studies were made of skeletal density bands as revealed by X-ray photography and fluorescent bands as revealed by ultraviolet light. Water quality measurements and rain-fall data were assembled for the two areas and related to skeletal banding patterns. For both areas, with increasing distance form mainland there is a decrease in overall brightness of fluorescence in corals and an increase in the contrast between bright and dull fluorescent bands. Fluorescence is bright, but seasonal banding is obscure in corals within about 2 km of stream mouths at Motopure and about 5 km of the coast in Jakarta Bay; this suggests that, despite low freshwater run-off during dry seasons, there are sufficient organic compounds which cause fluorescence in coral skeletons, to swamp seasonal effects. During the wet seasons, deluges of freshwater consequent on mainland rainfall of greater than about 150 mm/ month extend at least 7 km offshore in the Motupore area and perhaps tens of kilometres into Java Sea, giving distinctive bright and dull fluorescent banding in off-shore corals. The fluorescent banding pattern within corals on the Motupore reefs is similar in most corals along the transect and it correlates well with the Port Moresby monthly rainfall data. This relationship suggests that the same body (or bodies) of freshwater affect all reefs of the area during the wet season. The fluorescent banding in Java Sea corals does not show a precise correlation with either mainland or island monthly rainfall data; indeed the pattern of fluorescent banding on Pulau Seribu can only be matched in corals from reefs less than about 25 km apart. This suggests that in this area discrete water bodies carrying the relevant organic acids for coral fluorescence affect the fringing reefs on the chain of islands. Comparisons of fluorescent and density banding have revealed that for these areas, in general, periods of high freshwater run-off are times of deposition of less dense skeleton in Porites lutea corals.

Variations in skeletal architecture associated with density banding in the hard coral Porites

Slices of skeleton were obtained from along the growth axis of a colony of Porites lutea and a colony of P. australiensis. These skeletal slices were x-radiographed to display the density banding pattern which is characteristic of massive coral colonies. The density banding patterns displayed were consistent with the common pattern which is one dense band and one less dense band deposited each year. Skeletal densities were measured in the bands and in samples removed from certain bands. Techniques for measurement of skeletal density which preserved and included skeletal meso-architecture in the measurements (weight per unit volume and the attenuation of gamma radiation) showed statistically significant differences between densities measured for dense bands and those measured for less dense bands. Meso-architecture largely describes the arrangement of the various macroscopic skeletal elements to form the familiar, compartmented structure of a colonial skeleton. Those techniques which destroyed the meso-architecture, or which were not influenced by it (density of powdered skeleton and weight in air : weight in water), did not show significant differences between measurements for dense bands and less dense bands. Both sets of techniques preserved and were influenced by the skeletal micro-architecture. Micro-architecture describes, essentially, the arrangement and packing of acicular crystals of aragonitic calcium carbonate within the skeletal elements. It is concluded that skeletal density banding patterns in Porites almost entirely result from systematic variations in skeletal meso-architecture.

Rhodoliths and coralliths of Muri Lagoon, Rarotonga, Cook Islands

Free-living massive and branching spheroidal growths (about 5 cm diameter) of calcareous red algae (rhodoliths) and corals (coralliths) occur in abundance on the sea bed of shallow Muri Lagoon on Rarotonga's reef flat. The rhodoliths are composed of one or more species of Neogoniolithon, Lithophyllum, Tenarea, and Porolithon; the coralliths are Pavona varians (Verrill) and Porites lutea (Milne-Edwards and Haime). Muri Lagoon is the only area on Rarotonga's reef flat that is sheltered by reef islands from ocean waves. The tidal currents, which are predominantly unidirectional in Muri Lagoon, are concentrated by the reef islands into channels through which sand and gravel sediment is regularly transported. However, these prevailing currents do not normally roll the rhodoliths and coralliths. The results of field experiments on the pick-up velocity of the various types of spheroidal structure, combined with observations on growth histories of massive coralliths as revealed by the non-concentric nature of skeletal density banding, indicate that the rhodoliths and coralliths may remain static for periods up to several months yet maintain a complete envelope of living tissue. This downward survival may depend on the strong currents. Not only is the water flushing through the upper millimetre or so of the sediment substrate, but it is also capable of moving the sand and gravel grains which laterally support the rhodoliths and coralliths so that no one point of a spheroidal structure is in direct contact with the substrate for a fatal length of time. Massive rhodoliths have a high preservation potential as discrete spheroidal structures; in contrast, branching rhodoliths and coralliths are prone to fragmentation, and massive coralliths grow into stable microatolls. We conclude that a similar assemblage of rhodoliths, coralliths and microatolls in the fossil record may be indicative of the former existence of contemporary reef flat islands.

Carbonate production of the coral Diploria labyrinthiformis in south Florida patch reefs

Average annual production of CaCO 3 (aragonite) by the hermatypic coral Diploria labyrinthiformis in the Florida reef tract is 11.8 ± 0.3 kg/m 2 of reef space occupied by the coral. Annual production was estimated from a population of 271 Diploria colonies measured in situ. The mass produced annually is the volume of annual growth times the skeletal density. Cores of thirty-one Diploria colonies were slabbed and X-rayed to reveal annual growth bands. The mean vertical growth rate is 0.35 ± 0.06 cm/yr for skeletal density bands representing up to 34 years of growth. The annual volume of growth is approximated by a simple geometric shell whose thickness is determined by the horizontal and vertical growth rates of the colony. Horizontal growth rates are estimated from the ratio of the two lateral axes to the vertical axis. Bulk density determined by dry weight/volume of 9 cyclindrical cores is 1.64 ± 0.13 g/cm 3. Productivity of 11.8 kg/m 2/yr for area occupied by the coral does not vary appreciably among a nearshore patch reef and two outer-shelf patch reefs. For comparison, production rates for 244 Porites astreoides near Key West, Florida, is 14 ± 3.3 kg/m 2/yr for area occupied by the coral. The 271 colonies of D. labyrinthiformis potentially produce sediment which, if spread evenly, would accumulate at a rate of 0.026 m/10 3 yr for 9008 m 2 of reef surveyed. Potential vertical accretion by all corals for the patch reef surveyed is estimated at 2.2 to 6.6 m/10 3 yr.