Massive Coral Porites Research Articles

Finding the winners in competition for substratum between coral polyps and epilithic algae on damaged colonies of the coral Porites lutea

The study was conducted at the fringing reef of Sesoko Island (Okinawa, Japan), in the north-western Pacific. Artificial injuries were inflicted to the upper portions of colonies of the massive coral Porites lutea . The colonies were fixed to cement blocks and placed at two reef locations of different light intensity: one with moderate light (20–30% of incident photosynthetic active radiation, PAR0) and one with low light (2–5% PAR0). After six months of the treatment, all injuries were photographed. Analysis of photographs made under light and electron microscopes showed that the coral was able to recover from the injuries at both light variants. Under moderate light, some of the injuries completely healed and some injuries recovered partially. Under low light all injuries recovered partially. These partially recovered injuries were occupied by algae at dead portions of the injuries. In moderate light, coral polyps overgrew all algal settlers and were the winners in the competition for substratum. In low light, Peyssonnelia conchicola , Corallophila apiculata , Centroceras clavulatum , Anortichium tenue , and Lobophora variegata that colonized the injured areas overgrew coral polyps and were the winners in the competitive struggle for the substratum. It was shown that overgrowing is the main mechanism of coral–algal competition for substratum in light ranging from 2 to 30% PAR0. This mechanism of overgrowth of corals by algae, and the reverse, are discussed in detail.

American Samoa’s island of giants: massive Porites colonies at Ta’u island

[Extract] One of the largest and oldest single hermatypic coral colonies known is a massive Porites coral located on the southwest corner of Ta'u island (14°15S, 169°30W) in the Manu'a group of American Samoa. The coral is believed to be Porites lutea based on colony and corallite morphology; however, Porites taxonomy is notoriously difficult and recent genetic work has revealed surprising levels of cryptic diversity (Forsman et al.2009). Small (1 cm) cores were collected for genetic and microscopic work, and to determine skeletal density. DNA sequence for mitochondrial (COI, COIII) and nuclear (ITS region) markers were deposited in GenBank (accession numbers ITS-FJ416523-6, mt COI-FJ423967, and mt control FJ427369), and skeletal voucher specimens have been deposited at the Bishop Museum (SC4164).

Mayotte coral reveals hydrological changes in the western Indian Ocean between 1881 and 1994

We reconstruct the hydrologic history of the tropical western Indian Ocean by calculating the δ18Oseawater from coupled coral Sr/Ca and δ18O measurements in a massive Porites coral from Mayotte (Comoros) between 1881 and 1994. We found that the precipitation‐evaporation balance varies naturally on time scales of 5–6 years and 18–25 years. High (low) SSTs are associated with positive (negative) δ18Oseawater implying that atmospheric variability is linked with remote climate modes in the Indian Ocean and the tropical/extratropical Pacific Ocean. Warm El Niño‐Southern Oscillation events are associated with a negative freshwater balance at Mayotte. This case study demonstrates that a much denser network of δ18Oseawater reconstructions is crucial for understanding the spatial patterns of hydrological conditions.

The decline of winter monsoon velocity in the South China Sea through the 20th century: Evidence from the Sr/Ca records in corals

A modern massive Porites coral was collected from the Longwan Bay (19°20′N, 110°39′E) on the east coast of the Hainan Island, China. The coral was sectioned vertical to the growth axis into discs of double density-bands representing annual growth. The samples were analyzed for the Sr/Ca ratio by inductively coupled plasma atomic emission spectrometry. The history of winter sea-surface temperature (SST) is reconstructed using the Sr/Ca ratio in winter bands of corals. The winter SST at Xisha in the middle of the South China Sea (SCS) is weakly correlated with the instrument-measured winter monsoon velocity (WMV) with a correlation coefficient of 0.19. The winter SST data from corals at Longwan Bay, Hainan, in the northern SCS are moderately correlated with the WMV ( r = 0.40). Interestingly we found that the difference of winter SSTs between the two sites (Xisha and Longwan Bay, Hainan) (the X– H index) is significantly negatively correlated with the WMV ( r = − 0.73). This negative correlation may be related to the intrusion of the warm Kuroshio Current into the SCS through the Luzon Strait promoted by the strong northeastern monsoon winds in the winter. Using the relationship between our coralline data and observed WMV, the calculated winter monsoon velocity (WMVc) was obtained for 87 years. This data set in combination with the instrument-measured data between 1993 and 1998 generate a record of WMVc for a period of 93 years from 1906 to 1998. The WMVc in the 20th century shows significant interannual and decadal variability with a trend of persistent decline in the whole 20th century at the rate of decrease of − 0.02 (m/s)/a. The lowest wind velocity occurred during the last two decades of the 20th century. The WMVc has decreased significantly by about 30% from the early to the late of 20th century. The 20th century decline of winter monsoon velocity evidenced from the SCS coral records is consistent with the atmosphere–ocean general circulation models (AOGCMs) simulations for monsoon response to increasing temperatures. In addition, an obvious decline shift of WMV around 1976 can be seen in both instrumental and proxy records and it coincides with many other Pacific records. This shift is likely to correspond to a Pacific-wide change in the Pacific Decadal Oscillation occurring at the same time.

High resolution stable isotope records of sclreractinian corals near Ishigaki Island: Their implication as a potential paleoclimatic recorder in middle latitude regions

We propose skeletal δ18O of Platygyra, a hermatypic reef building massive coral, as a potential paleo-SST proxy in midlatitude regions, where the commonly used massive Porites corals are rare. Skeletal δ18O ratio (δ18Oc) of a Platygyra and Porites corals collected from Ishigaki Island, Japan, shows a clear seasonality corresponding to SST variation. The temperature dependence of the Platygyra coral was estimated, for the first time with appropriate sampling resolution, at −0.219‰/°C (T = −4.57δ18Oc + 2.65, r2=0.96). Massive Platygyra colonies show a wide distribution from the tropics to mid-latitudes further northwards than Porites. Platygyra’s adaptation to colder water temperatures and strong temperature dependence of δ18Oc suggest its application as a potential paleo-SST proxy for mid-latitude regions, where high resolution SST proxies are not available, as well as in tropical to subtropical regions.

Identification of 1771 Meiwa Tsunami deposits using a combination of radiocarbon dating and oxygen isotope microprofiling of emerged massive Porites boulders

The Meiwa Tsunami, one of the largest tsunamis recorded in historical documents in Japan struck Ishigaki Island and neighboring islands of the Ryukyu Arc in April 1771 AD, killing more than 12 000 people. An enormous number of massive Porites coral boulders are scattered on the shore and in the reef moat of eastern Ishigaki Island. Although these boulders likely were cast ashore by the Meiwa Tsunami, a detailed examination has not yet been conducted. When the marine reservoir effect is taken into account, one of mode values of calibrated radiocarbon dates possibly corresponds to the time of the 1771 event. However, the range of calibrated radiocarbon ages indicates that the transport of the boulders cannot be ascribed solely to the tsunami. Oxygen isotope microprofiling, which indicates sea-surface temperature variation, was therefore conducted to further investigate the mechanism of transport. The results suggest that the skeletal growth of most coral colonies was interrupted in summer or autumn; hence, tropical storms and typhoons are also very likely to be agents of transport. Thus, by combining radiocarbon dating with oxygen isotope microprofiling to investigate Porites coral boulders, it is possible to separate paleotsunami boulders from those transported by storm events as far as tsunamis occurred during the non-storm season.

Dissolution of Dead Corals by Euendolithic Microorganisms Across the Northern Great Barrier Reef (Australia)

Spatial and temporal variabilities in species composition, abundance, distribution, and bioeroding activity of euendolithic microorganisms were investigated in experimental blocks of the massive coral Porites along an inshore-offshore transect across the northern Great Barrier Reef (Australia) over a 3-year period. Inshore reefs showed turbid and eutrophic waters, whereas the offshore reefs were characterized by oligotrophic waters. The euendolithic microorganisms and their ecological characteristics were studied using techniques of microscopy, petrographic sections, and image analysis. Results showed that euendolithic communities found in blocks of coral were mature. These communities were dominated by the chlorophyte Ostreobium quekettii, the cyanobacterium Plectonema terebrans, and fungi. O. quekettii was found to be the principal agent of microbioerosion, responsible for 70-90% of carbonate removal. In the offshore reefs, this oligophotic chlorophyte showed extensive systems of filaments that penetrated deep inside coral skeletons (up to 4.1 mm) eroding as much as 1 kg CaCO3 eroded m(-2) year(-1). The percentage of colonization by euendolithic filaments at the surface of blocks did not vary significantly among sites, while their depths of penetration, especially that of O. quekettii (0.6-4.1 mm), increased significantly and gradually with the distance from the shore. Rates of microbioerosion (0.1-1.4 kg m(-2) after 1 year and 0.2-1.3 kg m(-2) after 3 years of exposure) showed a pattern similar to the one found for the depth of penetration of O. quekettii filaments. Accordingly, oligotrophic reefs had the highest rates ofmicrobioerosion ofup to 1.3 kg m(-2) year(-1), whereas the development of euendolithic communities in inshore reefs appeared to be limited by turbidity, high sedimentation rates, and low grazing pressure (rates < 0.5 kg m(-2) after 3 years). Those results suggest that boring microorganisms, including O. quekettii, have a significant impact on the overall calcium carbonate budget of coral reef ecosystems, which varies according to environmental conditions.

Coral‐based climate variability in the Western Pacific Warm Pool since 1867

We have generated monthly resolved, stable isotope (δ18O and δ13C) and Sr/Ca time series from a massive Porites coral from Rabaul (4°S, 152°E): a site located in the warmest sector of the Western Pacific Warm Pool (WPWP). The coral δ18O and Sr/Ca time series are well correlated to each other and positive excursions in both records coincide with times of ENSO warm phase events. These time series contain abundant interannual variability that exhibits the well‐recognized pattern of low amplitude ENSO variation between ∼1920–1960 and high amplitude ENSO variation between 1880–1920 and 1960–1997. The ENSO‐filtered coral δ18O and Sr/Ca time series are well matched to each other (r = 0.73) and to similarly filtered coral δ18O records from Papua New Guinea (r &gt; 0.56). There is no long‐term trend in the coral δ18O record, but there is a long‐term trend of increasing coral Sr/Ca from 1867 to 1997. This trend in coral Sr/Ca suggests a cooling of ∼0.7°C, which is rather unlikely and implies that factors other than SST may be influencing the coral Sr/Ca record. The trend in coral Sr/Ca is not an analytical artifact, nor a product of time varying riverine input, nor a product of skeletal diagenesis, nor the results of kinetic effects, but may reflect surface‐water variability in Sr/Ca. Despite the presence of a nonclimatic trend in coral Sr/Ca, the Rabaul coral records contain abundant interannual‐ to multidecadal‐scale variability, much of which is coherent with other proxy records from the WPWP and with instrumental records of ENSO variability.

Effects of elevated pCO2 on epilithic and endolithic metabolism of reef carbonates

AbstractWe investigated effects of elevated partial pressure of CO2 (pCO2) on the metabolism of epilithic and endolithic phototrophic communities that colonized experimental coral blocks. Blocks of the massive coral Porites lobata were exposed to colonization by epilithic and endolithic organisms at an oceanic site in Kaneohe Bay (Hawaii) for 6 months, and then were transported to laboratory tanks. A bubbling system was used to maintain two treatments for 3 months, one at ambient pCO2 (400 ppm) and the second at elevated pCO2 (750 ppm). Net photosynthetic rates of epilithic communities in the high pCO2 treatment, dominated by encrusting coralline algae, decreased by 35% while respiration rates remained constant. In contrast, metabolism of endolithic phototrophs, comprised of cyanobacteria and algae, was not significantly affected by the elevated pCO2 even though endoliths contributed about 63% to block production.

Coral barium/calcium record of mid-Holocene upwelling activity in New Caledonia, South-West Pacific

A variety of inimical factors, i.e. sea surface temperature, nutrient input, nature of substrates, were invoked previously to explain the retardation in reef settlement in New Caledonia during the Holocene. In order to clarify the respective role played by temperature and nutrient level in the growth of fringing reefs along the southwest coast of the island, trace element ratios, i.e. Sr/Ca and Ba/Ca, were used, respectively, as a paleothermometer and as a tracer of nutrient load from modern and mid-Holocene (about 6000 calendar years old) massive Porites coral colonies. The results obtained from the modern coral record indicate that, near the outer barrier reef, upwelling activity is controlled by southeast winds blowing in summer. By contrast, along the southwest coastline, the fringing reefs are subjected to barium input mainly derived from weathering of barite-rich rocks cropping out in the adjacent mainland. Comparison between the fossil and modern coral Sr/Ca and Ba/Ca records shed light on three different aspects of the mid-Holocene climate and coral reef evolution in New Caledonia: (1) the variability of paleo-sea surface temperature (SST) seems to have been similar to the modern one, although the island probably experienced SST about 1 °C higher than at present; (2) upwelling activity appears to have been greater than at present. Barium being supplied from the open sea to coastal zones by strong-wind generated upwelling currents, in relation to cooling events; (3) the onset of reef development in the southwest areas of New Caledonia was delayed due to the stronger upwelling of nutrient-enriched waters during the early–middle Holocene. The flowing of upwelled waters over the southwest coastal areas began at 8200 calendar years BP, and ceased at the time when the outer barrier reef crest reached present-day sea level, about 5500 to 5000 calendar years ago.

Coral skeletal δ 15N reveals isotopic traces of an agricultural revolution

This study introduces a new method of tracing the history of nutrient loading in coastal oceans via δ 15N analysis of organic nitrogen preserved in the skeleton of the massive Porites coral. Four coral cores were collected in Bali, Indonesia, from reefs exposed to high levels of fertilizers in agricultural run-off, from lagoonal corals impacted by sewage, and from a reef located 30 km offshore. Skeletal δ 15N in the agriculturally exposed coral declined from 10.7 ± 0.4‰ in 1970–1971, when synthetic fertilizers (−0.8‰ ± 0.2‰) were introduced to Bali, to a depleted “anthropogenic” baseline of 3.5‰ ± 0.4% in the mid-1990s. δ 15N values were negatively correlated with rainfall, suggesting that marine δ 15N lowers during flood-bourn influxes of waste fertilizers. Reef cores exposed to untreated sewage in terrestrial discharge were enriched (7.8 and 7.3 ± 0.4‰), while the offshore core reflected background oceanic signals (6.2 ± 0.4‰). δ 15N, N concentration, and C:N systematics indicate that the N isotopic composition of skeletal organic matter was generally well preserved over 30 years. We suggest that skeletal organic δ 15N can serve as a recorder of past nitrogen sources. In Bali, this tracer suggests that the intensification of Western style agricultural practices since 1970 are contributing to the degradation of coastal coral reefs.

Cross-shelf differences in the pattern and pace of bioerosion of experimental carbonate substrates exposed for 3 years on the northern Great Barrier Reef, Australia

Patterns of bioerosion of dead corals and rubbles on the northern Great Barrier Reef were studied by using blocks of the massive coral Porites experimentally exposed at six sites, located on an inshore–offshore profile, for 1 year and 3 years. Rates of microbioerosion by microborers, grazing by fish, and macrobioerosion by filter-feeding organisms were simultaneously evaluated using image analysis. Microbioerosion, grazing, and total bioerosion were lower at reefs near the Queensland coast than at the edge of the continental shelf (1.81 kg m−2 and 6.07 kg m−2 after 3 years of exposure respectively, for total bioerosion). The opposite pattern was observed for macrobioerosion. Bioaccretion was negligible. These patterns were evident after 1 year of exposure, and became enhanced after 3 years. Microborers were established and were the main agent of bioerosion after 1 year of exposure, and as the principal support for grazing, continued to be the main cause of carbonate loss after 3 years. Full grazing activity and establishment of a mature community of macroborers required more than 1 year of exposure. After 1 year, macroborers and grazers were the second most important agents of bioerosion on both inshore and offshore reefs. However, after 3 years, grazers became the main agents at all sites except at the inshore sites, where macroborers were the principal agents. Because the contribution of microborers, grazers, and macroborers to bioerosion varies in space and time, we suggest that the estimation of reef carbonate budgets need to take in account the activities of all bioerosion agents.

Measurement of luminescence in coral skeletons

Luminescent lines in skeletons of the massive coral Porites record periods when seawater was significantly diluted by land runoff. Records developed from such lines would be useful in a wide range of areas, including climatology, oceanography, civil engineering, agriculture, water resources and reef management. To realise this enormous potential, we built an instrument for routine, reliable recovery of luminescence information from coral skeletons. Skeletal slices were laid on a table that moved in 0.25 mm steps. The coral skeleton was illuminated with ultra-violet light (UV) at 390 nm and luminescent emissions at 490 nm were recorded. Light at 490 nm was then shone on the same 2 mm diameter point on the skeleton and the reflection of 490 nm light was recorded. Luminescent emissions from a point were then standardised by the reflectivity of that same point. Slices cut from three corals that grew at an inshore reef had many strong luminescent lines. Measurements of luminescence in these colonies were nearly identical, both for multiple tracks across one slice and for tracks across slices from the different corals. There was a clear link with discharge from a nearby river. Slices cut from two corals that grew at a reef 56 km offshore had occasional, weak luminescent lines that were also linked with river discharge. Tracks across these slices were similar but the weak luminescence due to river discharge was partially obscured by weak luminescence associated with the annual density banding pattern that characterises massive coral skeletons. The technique recovered excellent information about skeletal luminescence. However, there is a need to gain better understanding of the link between seawater dilution and luminescence and to develop procedures for data processing before the technique can be used to construct useful proxy environmental records.

Evidence for stronger El Niño‐Southern Oscillation (ENSO) Events in a Mid‐Holocene massive coral

We present a 47‐year‐long record of sea surface temperature (SST) derived from Sr/Ca and U/Ca analysis of a massive Porites coral which grew at ∼ 4150 calendar years before present (B.P.) in Vanuatu (southwest tropical Pacific Ocean). Mean SST is similar in both the modern instrumental record and paleorecord, and both exhibit El Niño‐Southern Oscillation (ENSO) frequency SST oscillations. However, several strong decadal‐frequency cooling events and a marked modulation of the seasonal SST cycle, with power at both ENSO and decadal frequencies, are observed in the paleorecord, which are unprecedented in the modern record.

Investigation of luminescent banding in solid coral: the contribution of phosphorescence

This study investigates the nature and components of annual luminescent banding in massive Porites coral skeletons, with a view to refining the technique for using this banding to reconstruct past environmental conditions. Three-dimensional excitation-emission-matrix spectroscopy and optical fibre beam delivery have been used to investigate the luminescence properties of the bright and dull bands of solid coral. Six characteristic excitation/emission peaks have been identified: 280/450–600, 340/450, 370/470, 390/485, 420/505 and 450/530 nm. The first peak corresponds to protein-type fluorescence. The others are characteristic of humic acid luminescence. The difference in luminescence intensity between bright and dull bands has been quantified and characterised spectroscopically. The luminescence of the bright bands is up to 25% more intense than their neighbouring dull bands with the greatest increase in relative intensity in the long wavelength emission region, between 500 and 600 nm. The contribution of long-lived phosphorescence to the total luminescence intensity has been determined by time-resolved measurements on the 100 ms timescale. Both bright and dull bands show long-lived phosphorescence with decay times up to 1.5 s. This phosphorescence accounts for about 10% of the total luminescence intensity of bright bands. The difference in phosphorescence intensity between bright and dull bands is substantially greater than the difference in total luminescence intensity: the phosphorescence of bright bands is up to twice as intense as that of dull bands. This suggests that phosphorescence plays an important role in defining luminescent banding in coral. Furthermore, the large observable difference in phosphorescence between bright and dull bands indicates that measurement of phosphorescence profiles across growth bands in corals may prove to be a more sensitive indicator of past environmental conditions than measurements of total luminescence.

Endolithic fungi in reef-building corals (Order : Scleractinia) are common, cosmopolitan, and potentially pathogenic

Reef-building corals appear to exist in dynamic equilibria with four principal partners: interconnected polyps of a colonial coelenterate, endosymbiotic dinoflagellate zooxanthellae residing in the host’s endoderm, endolithic algae that penetrate coral skeletons, and endolithic fungi that attack both endolithic algae and the polyps. Although reports of fungal and algal-like endoliths in corals date back almost 150 years (1) and evidence of a fossil history extends as far back as the Upper Devonian (;370 ma) (2), most attention has been paid to the structure (3), function (4, 5), and diversity (6) of the coral-zooxanthellae interactions, ignoring the endolithic members of the consortium. Recently, Le Campion-Alsumard et al. (1995) (7, 8) described an interrelationship between endolithic algae and fungi within the massive coral Porites lobata Dana 1846 (Poritidae), on Moorea island near Tahiti, French Polynesia. Fungi were also found to penetrate the most recently deposited skeletal material and to be associated with pearllike skeletal deposits formed by polyps of P. lobata in response to attack by their heterotrophic, endolithic symbionts. Here we extend these observations to the pocilloporid coral Pocillopora eydouxi and to the acroporid corals Acropora cytherea, Acropora humulis, and Montipora cf. studeri, collected at Johnston Atoll, central Pacific Ocean. Our observations suggest that direct coral-fungal interaction is widespread, not only geographically, but taxonomically as well. Thus, fungal endoliths, acting as opportunistic pathogens, may play a greater role in the ecology of coral reef systems than previously recognized. The oligophotic, siphonal green alga Ostreobium quekettii is ubiquitous in skeletons of live corals (9, 10). It is also common in other carbonate substrates, including dead shells and limestone, down to a depth of 300 m in clear waters of the Bahamas (11). Two other phototrophic organisms were reported from skeletons of live corals, the filamentous cyanobacterium Plectonema terebrans and conchocelis stages of bangiacean rhodophytes (12). Endolithic fungi in coral skeletons are equally common. They penetrate the corallum (euendolithic) and are often intermingled with endolithic algae, frequently parasitizing the latter (7). Fungi attack algal filaments by specialized hyphal branches, or haustoria, and often continue to grow inside algal filaments. Dense populations of algal and fungal endoliths have been associated with black-stained bands in specimens of P. lobata (13). Although skeletons of dead corals are bored by a variety of endolithic microorganisms, there has been no evidence that endoliths can penetrate the layer of tissue that covers living coral surfaces, leading to the conclusion that infestation by a limited number of specialized endoliths occurs early in the life of a coral, and that endolithic algae and fungi continue to grow in parallel with the accretion of the corallum (8). Most filaments of O. quekettii and endolithic fungi extend in the direction of the axes of skeletal growth. In P. lobata, borings were detected in newly deposited skeletal spines (pali), demonstrating that the endoliths are able to keep up with the rates of skeletal accretion (7, fig. 2). The pearl-like skeletal deposits are always associated with fungal attacks during the residence of polyps in actively growing calicies. The polyps encapsulate the advancing hypha into dense repair aragonite, forming a distinct skeletal structure referred to as a “cone” (7). The present study has two main objectives: to determine whether the relationship exhibited between P. lobata and endolithic fungi as described from the island of Moorea, in Received 7 July 1999; accepted 29 November 1999. *To whom correspondence should be addressed. E-mail: cbentis @bu.edu Reference: Biol. Bull. 198: 254–260. (April 2000)

Environmental controls on growth of the massive coral Porites.

Annual density banding provided growth characteristics for 245 similar-sized, massive colonies of Porites from similar locations on 29 reefs from across the length and breadth of the Great Barrier Reef (GBR), Australia. Values obtained were density, extension rate, and calcification rate. Tissue thickness, the depth to which skeletons were occupied by tissue at the time of collection, was also measured. Extension rate, calcification rate, and tissue thickness were significantly greater at the top of colonies than at the sides. Extension rate and calcification rate decreased from north to south along the GBR (latitudinal range of approximately 9 degrees ) and were significantly and directly related to annual average sea surface temperature (SST; range approximately 25-27 degrees C). For each 1 degrees C rise in SST, average annual calcification increased by 0.39 g cm(-2) year(-1) and average annual extension increased by 3.1 mm year(-1) (c.f. average values of 1.63 g cm(-2) year(-1) and 12.9 mm year(-1), respectively). Density was inversely correlated with extension rate and increased with distance offshore. Data for massive Porites colonies from the GBR were extended though 20 degrees of latitude and an average annual SST range of 23-29 degrees C using published data for the Hawaiian Archipelago (Grigg, R.W., 1981. Coral reef development at high latitudes in Hawaii. Proc. 4th Int. Coral Reef Symp., Manila, Vol. 1, pp. 687-693; Grigg, R.W., 1997. Paleoceanography of coral reefs in the Hawaiian-Emperor Chain - revisited. Coral Reefs 16, S33-S38) and Phuket, Thailand (Scoffin. T.P., Tudhope. A.W., Brown. B.E., Chansang. H., Cheeney. R.F., 1992. Patterns and possible environmental controls of skeletogenesis of Porites lutea, South Thailand. Coral Reefs 11, 1-11). The response of calcification rate to temperature remained linear. Variation in annual average SST accounted for 84% of the variance. For each 1 degrees C rise in SST, average annual calcification increased by 0.33 g cm(-2) year(-1) and average annual extension increased by 3.1 mm year(-1) (c.f. average values of 1.50 g cm(-2) year(-1) and 11.6 mm year(-1), respectively). The sensitivity of calcification rate in Porites to SST, combined with observed 20th Century increases in SSTs, suggests that calcification rates may have already significantly increased along the GBR in response to global climate change.

Assessing between-colony oxygen isotope variability in the coral Porites lobata at Clipperton Atoll

The eastern Pacific warm tongue is a region of stable and elevated sea surface temperature (SST) located just north of the equator in the eastern Pacific. This warm water mass is thought to influence the position of the Intertropical Convergence Zone (ITCZ) in the eastern Pacific and to directly influence climate in Central America. To assess the use of corals in the development of paleoclimatic reconstructions in this region, we have developed oxygen isotope (δ18O) time-series from multiple specimens of the massive coral Porites lobata collected at Clipperton Atoll (10°18′N, 109°13′ W). Six near-monthly δ18O records from different sized (age) colonies where produced for the interval 1986–1994, and three of these were extended back to 1969. All corals sampled were found to contain numerous fish-grazing skeletal scars (∼0.5 mm deep scallop shaped hiatuses). Samples collected at 1 mm intervals showed anomalous 18O/16O in the area of a bite scar, with 2 to 2.5 mm sampling intervals (10–12/year) minimizing these effects. Our results show that the average δ18O disequilibrium offset (vital effect) from equilibrium seawater composition for individual corals can vary by up to 0.4‰. However all δ18O results suggest that the vital effect offset is constant over time. Similar “offsets” are observed in the tops of old (age=∼100 y) and young (age=∼10 y) colonies, further suggesting that the biologically mediated vital effect offset does not change as a Porites colony ages. A 6-coral average composite δ18O record was constructed from 1985–1994 and a 3-coral average δ18Oanomaly record was constructed from 1969–1994. Regression analysis between monthly SST and the 6 coral average δ18O records yields an r2 correlation of 0.54 (individual r2-values ranged from 0.27–0.55). The 3 coral δ18Oanomaly average record has an even lower correlation to SST, with an r2 of 0.40. Potential causes of the only moderate correlation to SST are explored and we find that inferred salinity effects, fish grazing scars, and slight chronology imperfections have all contributed to a reduced correlation to SST. Nevertheless, all El Nino events in this time period appear to be recorded by coral skeletal δ18O.

Preliminary observations on change of sex by the coral-inhabiting snails Coralliophila violacea (Lamarck) (Gastropoda: Coralliophilidae)

The coral-inhabiting snails, Coralliophila violacea (Lamarck), are widely distributed in the Indo–Pacific region. It has been inferred from field data that sex changes have occurred and might be influenced by neighbors. In this study, we designed a field experiment with 2 treatments, i.e. `single males' and `male–female pairings' to test the hypothesis of sex changes as well as the role of neighbors on sex changes. Snails were collected by SCUBA diving from the surface of massive coral Porites lobata in shallow waters (<6 m) in southern Taiwan. A total of 73 males and 32 females were marked and returned to the surface of a colony of the massive coral, P. lobata. After 4–5 months, a total of 25 marked males and eight marked females were recaptured. In the treatment of `single males', eight of 17 males had changed their sex. None of eight recaptured males in the treatment of `male–female pairings' had changed their sex. The occurrence of sex changes is dependent on the presence or absence of a female neighbor ( P<0.05, Fisher's exact test). In this study, we have provided direct evidence of socially controlled sex changes in Coralliophila violacea.

Monsoon Climate and Arabian Sea Coastal Upwelling Recorded in Massive Corals from Southern Oman

Corals living in the coastal waters of southern Oman experience the influence of the seasonally reversing Asian monsoon system. The objective of the research reported here is to assess the potential for using the skeletal chemistry of these corals to investigate past variability in the monsoon climate. To this end, 20-year long, monthly resolution geochemical records are presented for cores from two massive Porites corals, located 20 km apart near Marbat on the Arabian Sea coast of southern Oman. We consider four aspects of skeletal chemistry: oxygen and carbon isotopic composition, barium content and the nature and occurrence of annual fluorescent bands within the coral skeletons. Coral skeletal 180 documents variations in sea surface temperature which have regional and basin-wide significance. In particular, the 80 of coral skeleton precipitated during the period of the NE monsoon is strongly correlated with annual rainfall anomalies in India, whilst that precipitated during the period of the SW monsoon appears to provide information on variability in the strength of coastal upwelling. The stable carbon isotope composition and barium content of these particular corals display strong annual cycles,