Holocene uplifted coral reefs in Lanyu and Lutao Islands to the southeast of Taiwan

Lanyu and Lutao Islands to the southeast of Taiwan are located in the northern extension of the Luzon Arc. Crustal deformation of these islands provides a key to understand the collision of the Luzon Arc against Taiwan. To clarify the style and the rate of vertical movement during the Holocene, uplifted coral reefs fringing these two islands were investigated. Living corals were also investigated for comparison with fossil corals. It was found that Isopora palifera lives dominantly in the upper slope of the present-day fringing coral reefs in Lanyu Island at an average depth of 101 ± 46 cm (one standard deviation) below mean sea level. Using I. palifera as an accurate indicator of paleo-sea levels, Holocene relative sea-level changes were reconstructed. Lanyu Island has been uplifted continuously at a rate of 2.0 mm yr⁻¹, at least during the late Holocene from 2,269 cal. yr BP to the present. Lutao Island has been uplifted at an average rate of 1.2 mm yr⁻¹, since at least 5,749 cal. yr BP, although it is unclear whether the uplift was continuous. The present observations, combined with the GPS displacement field and deep crustal structure, suggest that the continuous uplift is related to aseismic slip on the Longitudinal Valley Fault.     

Estimation of photosynthesis and calcification rates at a fringing reef by accounting for diurnal variations and the zonation of coral reef communities on reef flat and slope: a case study for the Shiraho reef, Ishigaki Island, southwest Japan

Seven coral reef communities were defined on Shiraho fringing reef, Ishigaki Island, Japan. Net photosynthesis and calcification rates were measured by in situ incubations at 10 sites that included six of the defined communities, and which occupied most of the area on the reef flat and slope. Net photosynthesis on the reef flat was positive overall, but the reef flat acts as a source for atmospheric CO₂, because the measured calcification/photosynthesis ratio of 2.5 is greater than the critical ratio of 1.67. Net photosynthesis on the reef slope was negative. Almost all excess organic production from the reef flat is expected to be effused to the outer reef and consumed by the communities there. Therefore, the total net organic production of the whole reef system is probably almost zero and the whole reef system also acts as a source for atmospheric CO₂. Net calcification rates of the reef slope corals were much lower than those of the branching corals. The accumulation rate of the former was approximately 0.5 m kyr⁻¹ and of the latter was ~0.7–5 m kyr⁻¹. Consequently, reef slope corals could not grow fast enough to keep up with or catch up to rising sea levels during the Holocene. On the other hand, the branching corals grow fast enough to keep up with this rising sea level. Therefore, a transition between early Holocene and present-day reef communities is expected. Branching coral communities would have dominated while reef growth kept pace with sea level rise, and the reef was constructed with a branching coral framework. Then, the outside of this framework was covered and built up by reef slope corals and present-day reefs were constructed.     

Last interglacial reef limestones, northeastern St. Croix, US Virgin Islands—evidence of tectonic tilting and subsidence since MIS 5.5

Most last interglacial (MIS 5.5) coral reef deposits in the Caribbean are emergent. However, in St. Croix, these are found mainly at depth, underneath Holocene material and confirmed by TIMS U–Th dated corals from eight cores through Holocene reefs. The only emergent MIS 5.5 marine deposit peaks at +1.5 m MSL at the northwestern end of the island. The Late Pleistocene surface decreases at least 9.25 m (based on reef crest elevations) in elevation over 15 km along a 0.62 m/km eastward (alongshore) slope. Neither differential erosion nor a naturally sloping deposit is likely, thus the directional elevation decrease requires the influence of tectonic processes. Platform tilting or differential subsidence increasing in rate to the east probably operated both during and since the last interglacial and created progressively greater accommodation space for increasingly thicker overlying Holocene reefs in an eastward direction. Rates of subsidence since MIS 5.5 increase from west to east, from 0.02 mm/year to 0.1 mm/year, assuming a MIS 5.5 +6-m sea level and +4 m initial reef elevation. St. Croix’s association with extensional shelf faulting from the northern part of the Virgin Islands Basin, the Anegada Fault to the east and the Puerto Rico Trench to the north may be significant in terms of identifying mechanisms for, or past events resulting in, directional tilting. Identification of differential elevations of MIS 5.5 reefs adds substantially to the information on Late Quaternary tectonism of the area.     

Demise of reef-flat carbonate accumulation with late Holocene sea-level fall: evidence from Molokai,Hawaii

Twelve cores from the protected reef-flat of Molokai revealed that carbonate sediment accumulation, ranging from 3 mm year⁻¹ to less than 1 mm year⁻¹, ended on average 2,500 years ago. Modern sediment is present as a mobile surface veneer but is not trapped within the reef framework. This finding is consistent with the arrest of deposition at the end of the mid-Holocene highstand, known locally as the “Kapapa Stand of the Sea,” ~2 m above the present datum ca. 3,500 years ago in the main Hawaiian Islands. Subsequent erosion, non-deposition, and/or a lack of rigid binding were probable factors leading to the lack of reef-flat accumulation during the late Holocene sea-level fall. Given anticipated climate changes, increased sedimentation of reef-flat environments is to be expected as a consequence of higher sea level.     

The Role of Surface and Subsurface Processes in Keeping Pace with Sea Level Rise in Intertidal Wetlands of Moreton Bay,Queensland, Australia

Increases in the elevation of the soil surfaces of mangroves and salt marshes are key to the maintenance of these habitats with accelerating sea level rise. Understanding the processes that give rise to increases in soil surface elevation provides science for management of landscapes for sustainable coastal wetlands. Here, we tested whether the soil surface elevation of mangroves and salt marshes in Moreton Bay is keeping up with local rates of sea level rise (2.358 mm y⁻¹) and whether accretion on the soil surface was the most important process for keeping up with sea level rise. We found variability in surface elevation gains, with sandy areas in the eastern bay having the highest surface elevation gains in both mangrove and salt marsh (5.9 and 1.9 mm y⁻¹) whereas in the muddier western bay rates of surface elevation gain were lower (1.4 and −0.3 mm y⁻¹ in mangrove and salt marsh, respectively). Both sides of the bay had similar rates of surface accretion (~7–9 mm y⁻¹ in the mangrove and 1–3 mm y⁻¹ in the salt marsh), but mangrove soils in the western bay were subsiding at a rate of approximately 8 mm y⁻¹, possibly due to compaction of organic sediments. Over the study surface elevation increments were sensitive to position in the intertidal zone (higher when lower in the intertidal) and also to variation in mean sea level (higher at high sea level). Although surface accretion was the most important process for keeping up with sea level rise in the eastern bay, subsidence largely negated gains made through surface accretion in the western bay indicating a high vulnerability to sea level rise in these forests.     

Holocene sea level changes and reef development in the southwestern Indian Ocean

 The sedimentological and chronological study of Holocene reef sequences recovered in drill cores through modern reefs of Mauritius, Réunion Island and Mayotte allows the reconstruction of sea level changes and reef growth patterns during the Holocene. The branching-coral facies systematically predominates over coral head facies throughout the Holocene reef sequences, and Acropora is the main frame builder among the branching forms. The reconstructed sea level curves, based both on identification of coral assemblages and on radiometric U/Th ages, are characterized by a rapid rise between 10 and 7.5 ky BP, followed by a clear inflection between 7.5 and 7 ky BP. The stabilization of sea level at its present level occurred between 2000 and 3000 years ago, probably without a higher sea level stand. Rates of vertical reef accretion range between 0.9 and 7 mm. y^-1. In Mauritius, and also probably in Réunion Island, the reef first tracked, then caught-up to sea level to reach an equilibrium position (“catch-up” growth), while the barrier reef margin off Mayotte has been able to keep pace with rising sea level (“keep-up” growth). Accepted: 1 March 1997     

Reef demise and back-stepping during the last interglacial, northeast Yucatan

The elevation of reefs and coastal deposits during the last Interglaciation (MIS-5e) indicates that sea level reached a highstand of as much as 6 m above the present, but it is uncertain how rapidly this level was attained and how it impacted reef development. To investigate this problem, I made a detailed sedimentological analysis of a well-dated reef from the northeast coast of the stable Yucatan Peninsula. Two linear reef tracts were delineated which are offset and at different elevations. The lower reef tract crops out along northern shore for 575 m and extends from below present mean sea level to +3 m. The reef crest facies consists of large Acropora palmata colonies dispersed within a coral boulder-gravel and is flanked by an A. cervicornis-dominated reef-front and a large area of lagoonal framework formed by coalesced patches of A. cervicornis and Montastraea spp. Constituents in the upper centimetre of the lower tract are heavily encrusted by a cap of crustose corallines and, in places, are levelled by a discontinuous marine-erosion surface. The upper reef tract crops out ~150 m inland up to an elevation of +5.8 m and parallels the southern section of shore for ~400 m. It also consist of an A. palmata-dominated crest facies flanked by reef-front, back-reef and lagoonal frameworks. In this case, however, lagoonal frameworks are dominated by a sediment-tolerant assemblage of branching coralline algae. Also different is the lack of encrustation by corallines, and the infiltration of upper tract facies by beach-derived shell-gravels from regressive shoreface deposits above. These results indicate that the lower reef tract and lagoonal patch-reefs formed at a sea level of +3 m. Final capping by crustose corallines and discontinuous marine erosion indicates that the lower tract was terminated by the complete demise of corals on the crest but only patchy demise in the lagoon. Areas of continuous framework accretion between the lagoonal patch reefs and the upper reef-tract, however, require that the demise of this reef was ecologically synchronous with initiation of the upper reef-tract, which had back-stepped 100 m into the lagoon. In this new position, the upper tract developed a reef crest that corresponded to a final sea-level position of +6 m. Reef flat development at +5 m and large in-place colonies of A. palmata at the base of the crest unit indicate, however, that sea level must have risen rapidly from +3 to more than +5 m to accommodate back-stepping. This sea-level jump created a higher energy wave field that mobilized back-reef and lagoonal sediments, and the resulting high sediment flux eroded lagoonal framework and prevented the recovery of the submerged lower reef crest. So this single jump in sea level was responsible not only for reef demise and back-stepping but also for marine erosion and suppression of subsequent reef development—features that elsewhere have been used to support multiple sea-level excursions during the last interglacial.     

Extraordinarily high coral cover on a nearshore,high-latitude reef in south-west Australia

Photographic line transects were used to quantify the benthic community at Hall Bank, a small, nearshore, high-latitude reef in south-west Australia. On one of the seven transects, the coral cover was 72.5% (mean = 52.6 ± 0.45%), which is the highest ever recorded coral cover at or beyond 32°S. There were no macro-algae, possibly due to the high density of herbivorous sea-urchins (mean = 5.0 ± 0.8 m⁻²). Fourteen species of scleractinian corals dominated the benthos, seven of which were from the family Faviidae. Given that Hall Bank is at the limit of environmental tolerance for reef formation, it represents a valuable research opportunity for understanding the factors that build and maintain coral reef biodiversity and resilience.     

Effect of macrophyte diet and initial size on the survival and somatic growth of sub-adult <Emphasis Type="Italic">Strongylocentrotus purpuratus</Emphasis>: a laboratory experimental approach

Recently recruited urchins from the same brood, but with different initial sizes, may respond differently to similar environmental factors. The aim of this study was to assess and compare the effects of starvation and diet on the survival, growth rates in size and weight, and gonad index among small and large sub-adult purple sea urchins, Strongylocentrotus purpuratus. Small urchins ranged from 7.3 to 7.8 mm and large urchins from 11.8 to 14.1 mm (test diameters). Two independent experiments were performed. In the first experiment, sea urchins were fed during 22 weeks on Egregia menziesii (ad libitum) and for only 1 day month⁻¹ (starved condition). Feeding regime significantly affected survival, somatic growth rate in size and weight, and gonad index, with higher means in the ad libitum treatments than in starving conditions. A recurrent cannibalism event by conspecifics occurred in small sea urchins under starving conditions. In the second experiment, sea urchins were fed during 13 weeks ad libitum with four diets: kelp (E. menziesii), coralline algae (Bossiella orbigniana), eelgrass (Phyllospadix scouleri) and a mixed diet of the three species. Survival was not affected by diet or urchin size, but diet significantly affected somatic growth rate in size and weight and gonad index. Kelp promoted the highest growth rate (2.23 ± 0.21 mm month⁻¹), the mixed diet produced an intermediate growth (1.26 ± 0.21 mm month⁻¹), while the lowest values corresponded to coralline algae and the eelgrass (0.30 ± 0.12 and 0.10 ± 0.03 mm month⁻¹, respectively, means ± SE). The mean growth rate of small urchins (averaging all diets) was higher than in large specimens (1.17 ± 0.37 and 0.77 ± 0.28 mm month⁻¹, respectively).     

Model of fringing reef development in response to progressive sea level fall over the last 7000 years – (Kikai-jima, Ryukyu Islands, Japan)

 Kikai-jima in the central Ryukyu Islands of Japan is fringed by exposed terraces of Holocene reefs, which formed as a result of periodic local tectonic uplift associated with subduction/collision. The terraces form four topographically distinct features (TI-IV) around the island and represent reefs that grew to sea level at 9000–6065 y BP, 6065–3390 y BP, 3790–2630 y BP, and 2870 to 1550 y BP. The modern reef terrace has been growing since approximately 1550 y BP. The reef terraces were uplifted sequentially around 6050 y BP (4 m), 3390–3790 y BP (2.5 m), 2630–2870 y BP (1 m) and 1550 y BP (2.5 m). Five sites were studied to define reef development in response to periodic relative sea level fall and different stillstand recovery periods. Thirty coral genera and 70 species were recorded from four distinct shallow reef flat to upper reef slope and one deeper reef slope coral assemblage. Significant lateral variations in total coral abundance, genera number, diversity, and the coverage density of Acropora spp. and Faviids occur both within and between the terraces. Stratigraphically, drill core and outcrop data recorded shallowing upward sequences characterised by tabulate Acropora spp. overlying massive Porites sp. and Faviids. The biological variations may represent growth strategies responding to initial colonisation, episodic perturbation (relative sea level fall) and differing recovery times during stillstands, and indicate a reef ecosystem stable and strong enough to recover after substantial perturbations. However, this study suggests that relatively small geological changes have had substantial biological effects, and modelling indicates that such changes would have been more profound had a third factor, such as substrate angle, varied more dramatically. In such a case, the drowning growth strategy exhibited in the drill core transect may have been more prevalent, and reefs would be struggling to grow around Kikai-jima today. Accepted: 27 May 1998     

Trends in surface elevations of American Samoa mangroves

Rates of change in elevation of mangrove surfaces, determined from observations of changes in the height above the mangrove surface of stakes, generally inserted through the organic peat layer to reach consolidated substrate, were measured in one fringe and one basin mangrove wetland on Tutuila Island, American Samoa. Knowledge of trends in elevation change of coastal wetlands contributes to assessing vulnerability to projected relative sea level rise. The fringe and basin mangroves had rates of change in elevation of −0.6 mm yr⁻¹ (±2.0) and −2.2 mm yr^-1 (±5.6), where a negative result means lowering in elevation. These trends were not statistically significant (P > 0.05) and the error intervals around the point estimates of trends in change in elevation overlap zero for both study sites, meaning that it is not clear if the mangrove surfaces have been lowering, rising or not changing. Despite the large error intervals, likely due to short-term variability and cyclical patterns in sedimentation, results indicate that the fringe mangrove has been experiencing a rise in sea level relative to the mangrove surface as the relative sea level rise rate (+1.65 to +2.29 mm yr⁻¹) has been exceeding the rate of change in elevation of the mangrove surface (−2.6 to +1.4 mm yr⁻¹). It is unclear if the basin mangrove has been experiencing a rise in sea level relative to the mangrove surface. If upper projections for accelerated relative sea level rise in American Samoa occur over coming decades, American Samoa mangroves will migrate landward, where unobstructed, as a natural response to relative sea level rise.

Patch-reef morphology as a proxy for Holocene sea-level variability,Northern Florida Keys,USA

A portion of the northern Florida Keys reef tract was mapped with the NASA Experimental Advanced Airborne Research Lidar (EAARL) and the morphology of patch reefs was related to variations in Holocene sea level. Following creation of a lidar digital elevation model (DEM), geospatial analyses delineated morphologic attributes of 1,034 patch reefs (reef depth, basal area, height, volume, and topographic complexity). Morphometric analysis revealed two morphologically different populations of patch reefs associated with two distinct depth intervals above and below a water depth of 7.7 m. Compared to shallow reefs, the deep reefs were smaller in area and volume and showed no trend in topographic complexity relative to water depth. Shallow reefs were more variable in area and volume and became flatter and less topographically complex with decreasing water depth. The knoll-like morphology of deep reefs was interpreted as consistent with steady and relatively rapidly rising early Holocene sea level that restricted the lateral growth of reefs. The morphology of shallow “pancake-shaped” reefs at the highest platform elevations was interpreted as consistent with fluctuating sea level during the late Holocene. Although the ultimate cause for the morphometric depth trends remains open to interpretation, these interpretations are compatible with a recent eustatic sea-level curve that hindcasts fluctuating late Holocene sea level. Thus it is suggested that the morphologic differences represent two stages of reef accretion that occurred during different sea-level conditions.     

Contributions of dust to phosphorus cycling in tropical forests of the Luquillo Mountains,Puerto Rico

The input of phosphorus (P) through mineral aerosol dust deposition may be an important component of nutrient dynamics in tropical forest ecosystems. A new dust deposition calculation is used to construct a broad analysis of the importance of dust-derived P to the P budget of a montane wet tropical forest in the Luquillo Mountains of Puerto Rico. The dust deposition calculation used here takes advantage of an internal geochemical signal (Sr isotope mass balance) to provide a spatially integrated longer-term average dust deposition flux. Dust inputs of P (0.23 ± 0.08 kg ha⁻¹ year⁻¹) are compared with watershed-average inputs of P to the soil through the conversion of underlying saprolite into soil (between 0.07 and 0.19 kg ha⁻¹ year⁻¹), and with watershed-average losses of soil P through leaching (between 0.02 and 0.14 kg ha⁻¹ year⁻¹) and erosion (between 0.04 and 1.38 kg ha⁻¹ year⁻¹). The similar magnitude of dust-derived P inputs to that of other fluxes indicates that dust is an important component of the soil and biomass P budget in this ecosystem. Dust-derived inputs of P alone are capable of completely replacing the total soil and biomass P pool on a timescale of between 2.8 ka and 7.0 ka, less than both the average soil residence time (~15 ka) and the average landslide recurrence interval (~10 ka).     

Stratigraphie et chronologie du site de Gaolingpo dans le bassin de Bose,sud de la Chine

The Bose Paleolithic industry in the Bose Basin, Guangxi, South China is well known in the international scientific community for its bearing handaxes dated back to 803 ka. Seven terraces were developed in the basin and terrace 4 is the most important because handaxes and tektites were recovered from this terrace. Since the first site was discovered in 1973, additional sites of the Bose Paleolithic industry have been investigated and excavated, most of which are located on terrace 4. The previous studies concluded that there is only one phase within this industry and its age is 803 ka. However, before 2013, no attempt had been made to dig down to the basal gravels from the top of terrace 4 in archaeological excavations. Therefore, the stratigraphy and the layers from which the stone artifacts derive of terrace 4 are not clear. In 2013–2014, we conducted an excavation of 200 m² at the Gaolingpo site, which is one of the most important Paleolithic sites in the Bose Basin. We excavated to the basal gravel deposits from the top of this terrace, and a section of more than 7 meters thick deposit was exposed and clearly shows the stratigraphic layers of Pleistocene and Holocene deposits. Furthermore, features and about 800 stone artifacts including choppers, picks, scrapers, etc. were excavated from several stratigraphic layers, which are different in age and other aspects. Based on stratigraphy and the stone artifacts, three stages of Paleolithic cultural remains from the Gaolingpo site can be established. The first stage is in the age of at leat 803 ka. The second stage can be dated to 15 ka and the third stage to about 10 ka.     

Growth of Mediterranean reef of<Emphasis Type="Italic"> Cladocora caespitosa</Emphasis> (L.) in the Late Quaternary and climate inferences

A sclerochronological analysis was performed on Cladocora caespitosa corals from Late Pleistocene terraces near Taranto (Apulia, Italy) to reconstruct the main palaeoenvironmental conditions at the time of their growth. The fossil corallites were sampled in the Santa Teresiola uplifted bank or ‘open frame reef’ attributed to the Last Interglacial Period. The typical, annual growth pattern of the temperate coral with two alternate high- and low-density bands allowed the reconstruction of two multidecadal growth curves of 61 and 95 years. Trend analysis showed oscillations in annual growth rates similar to those observed in recent, living colonies sampled along a north–south latitudinal transect around the Italian and Croatian coasts as far as Tunisia. The mean growth rate of the fossil reef (4.2 ± 2 mm year⁻¹) is comparable to those measured on colonies living in the coldest part of the Mediterranean Sea. The comparison with data from living Croatian banks shows how fossil C. caespitosa lived in a semi-enclosed environment characterized by seasonal inputs of fresh, cold water. The greatest variations in decadal growth rates of the fossil colonies support the hypothesis of larger amplitude of the seasonal cycles in the past. The death of the fossil bank was probably due to a sudden alluvial input that suffocated the reef with a great amount of mud. Another possible cause of the death of the bank was a prolonged increase in summer temperatures that caused colony mortality and enhanced algal colonization.     

Pleistocene morphology and Holocene emergence of Christmas (Kiritimati) Island, Pacific Ocean

 Christmas (Kiritimati) Island is an unusually large coral atoll, of which a large proportion of the surface is presently subaerial. Extensive outcrops of in situ branching Acropora corals, together with Porites microatolls, Tridacna, and other shallow marine biota, indicate that the present low-lying area of interconnecting lakes in the island interior formed as a reticulate lagoon. Radiocarbon dating indicates that these lagoonal reefs flourished between 4500 and 1500 radiocarbon years BP, and surveying confirms that sea level was 0.5–1.0 m above present at that time, with subaerial exposure resulting from Late Holocene emergence. Boreholes undertaken for a water resources survey of the island penetrated near-surface Pleistocene limestones on the northern, southern, and eastern sides of the island. These are highly weathered and fractured, and although aragonitic clasts are preserved, U-series dating indicates a Middle Pleistocene or older age. At one location flanking the Bay of Wrecks, an outcrop of limestone, with an erosional notch, 1–2 m above present sea level, yielded a U-series age of 130 ka, and is interpreted as Last Interglacial in age. In contrast to previous interpretations which have suggested that Christmas Island comprised an atoll superstructure that is entirely Holocene, or the layer-cake interpretation appropriate for many mid-ocean atolls, Christmas Island appears to have had a form similar to its present in the Middle Pleistocene or earlier. It has undergone karstification during lowstands. Interglacials, particularly the Last Interglacial and the Holocene, appear to have resulted in only a minor veneer of coral over older limestone surfaces. Christmas Island is considered characteristic of an atoll that has not experienced significant subsidence through the Late Quaternary. Accepted: 15 May 1998     

Increased sea level promotes coral cover on shallow reef flats in the Andaman Sea, eastern Indian Ocean

Sea level in the Indian Ocean is subject to considerable temporal and spatial variabilities. During the period 1960–2009 at Phuket, Thailand, in the NE Indian Ocean, mean sea level increased by 2.7 mm y⁻¹. Regular monitoring of coral cover on fringing reef flats at Phuket since 1979 revealed a sensitive response of this habitat to both transient sea-level depressions and sea-level elevation. Since 1987 when more frequent sampling began, coral cover was positively correlated with the mean sea level experienced over the preceding months. Changing mean sea level explained a high proportion of the observed variation in cover, with overall increasing sea levels and a lack of negative sea-level anomalies promoting cover on the outer reef flats. Concomitantly, there have been no changes in reef community structure or any apparent shifts in zonation patterns across the reef. While future benefits of continued increases in mean sea level on reef flats in the region will be constrained by the frequency and intensity of sea-level depressions associated with the Indian Ocean Dipole, and bleaching events, the overall picture for these shallow reefs is a positive one as they respond to increasing sea level and show rapid recovery from environmental disturbances.     

Holocene coral reef accretion in Hawaii: a function of wave exposure and sea level history

 In the high Hawaiian Islands, significant accretion due to coral reef growth is limited by wave exposure and sea level. Holocene coral growth and reef accretion was measured at four stations off Oahu, Hawaii, chosen along a gradient in wave energy from minimum to maximum exposures. The results show that coral growth of living colonies (linear extension) at optimal depths is comparable at all stations (7.7–10.1 mm/y), but significant reef accretion occurs only at wave sheltered stations. At wave sheltered stations in Hanauma Bay and Kaneohe Bay, rates of long term reef accretion are about 2.0 mm/y. At wave exposed stations, off Mamala Bay and Sunset Beach, reef accretion rates are virtually zero in both shallow (1 m) and deeper (optimal) depths (12 m). At wave sheltered stations, such as Kaneohe Bay and Hanauma Bay, Holocene reef accretion is on the order of 10–15 m thick. At wave exposed stations, Holocene accretion is represented by only a thin veneer of living corals resting on antecedent Pleistocene limestone foundations. Modern coral communities in wave exposed environments undergo constant turnover associated with mortality and recruitment or re-growth of fragmented colonies and are rarely thicker than a single living colony. Breakage, scour, and abrasion of living corals during high wave events appears to be the major source of mortality and ultimately limits accretion to wave sheltered environments. Depth is particularly important as a modulator of wave energy. The lack of coral reef accretion along shallow open ocean coastlines may explain the absence of mature barrier reefs in the high Hawaiian Islands. Accepted: 14 May 1998     

Habitat association and depth distribution of two sympatric groupers of the genus Cephalopholis (Serranidae: Epinephelinae)

 Habitat association and depth distribution of two sympatric coral reef groupers of the genus Cephalopholis were examined at Rota, Mariana Islands. The two species are similar in body size, morphology, and social organization. In this study, they differed in their association with habitat and microhabitat and in depth distribution. Cephalopholis spiloparaea occurred on the reef slope between the reef terrace and deep sand flats at depths between 15 and 26 m. This species was associated mainly with Porites rus corals. Cephalopholis urodeta occurred largely on the upper reef terrace at 1–12 m. This species was associated mainly with coral pavement. The observed pattern of segregation might be the result of competitive or noncompetitive interactions or of phylogenetic constraints, but the exact mechanism or combination thereof remains unknown. Received: May 30, 2000 / Revised: September 5, 2001 / Accepted: October 25, 2001