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1.
Extension rates of corals at two sites in subtropical eastern Australia (Solitary Islands and Lord Howe Island) were measured
to determine whether growth was low relative to tropical locations. Growth was measured using alizarin staining of skeletons
and X-radiographic analysis, and was compared between colonies, species, and sites. Linear extension of individual Pocillopora damicornis colonies averaged 12.4 to 16.1 mm per year at Solitary Islands and Lord Howe Island respectively, which is 50% to 80% of
published values for this species at tropical sites. Similarly, average extension of most massive faviid species examined
at these sites was between 2.6 mm and 4.6 mm per year, considerably lower than most values reported from lower latitudes (generally
6 mm to 10 mm per year). However, growth rates of Acropora yongei, Turbinaria frondens, and Porites heronensis were close to those of closely-related taxa from the tropics. Causal links between latitude, growth rates of coral colonies,
and the potential for reef accretion remain unclear.
Accepted: 22 April 1999 相似文献
2.
The distribution and abundance of soft coral genera on reefs of the central Great Barrier Reef was investigated in relation
to reef position, recent history of disturbance, wave exposure, substratum slope and depth. Eighty-five 25 m long transects
were surveyed at 10 m depth on windward sides of 14 mid- and outer-shelf reefs. A further 75 transects in different zones
on one mid-shelf reef (Davies Reef) between 5 and 30 m depth were investigated. The crown-of-thorns starfish Acanthaster planci had caused large-scale mortality of scleractinians on eight of these reefs five to ten years prior to the study, and as a
result, scleractinian cover was only 35–55% of that on the six unimpacted reefs. On the impacted reefs, stony corals with
massive and encrusting growths form had smaller average colony diameters but similar or slightly lower numerical abundance.
In contrast, mean colony size, cover and abundance of branching stony corals showed no difference between impacted and unimpacted
reefs. Twenty-four genera of soft corals (in eight families) were recorded, and none showed different abundance or cover in
areas of former A. planci impact, compared to unaffected sites. Similarly, no difference was detected among locations in the numbers or area cover
of sponges, tunicates, zoanthids, Halimeda or other macro-algae. Mean soft coral cover was 2 to 5% at 10 m on sheltered mid-shelf reefs, and 12 to 17% on more current-exposed
reefs. Highest cover and abundances generally occurred on platforms of outer-shelf reefs exposed to relatively strong currents
but low wave energy. On Davies Reef, cover and colony numbers of the families Nephtheidae and Xeniidae were low within the
zone of wave impact, in flow-protected bays and lagoons, on shaded steep slopes, and at depths above 10 and below 25 m. In
contrast, distributions of genera of the family Alcyoniidae were not related to these physical parameters. The physical conditions
of a large proportion of habitats appear “sub-optimal” for the fastest growing taxa, possibly preventing an invasion of the
cleared space. Thus, in the absence of additional stress these shallow-water fore-reef zones appear sufficiently resilient
to return to their pre-outbreak state of scleractinian dominance.
Accepted: 20 August 1996 相似文献
3.
A spectacular mound-like reef formation (126 m in circumference, 10 m high) dominated by highly arched and record-size colonies
of the unattached mushroom coral Halomitra pileus, along with 17 other species of the family Fungiidae, occurs in 31 m of water on the sedimentary lagoon floor of the Great
Astrolabe Reef, Fiji. Core samples show radiocarbon dates which indicate that the formation hypothetically began building
∼4500 y ago, with a calculated mean accretion rate of 2.2 mm ⋅ y -1. The majority of fossil and living material is contributed by H. pileus colonies between 40–70 cm mean diameter, with some individuals up to 1.5 m in diameter. The size, fungiid diversity, and
geological history of the bioherm is unprecedented and represents the first example of a coral reef constructed almost entirely
by Fungiidae.
Accepted: 29 July 1996 相似文献
4.
Efforts to map coral reef ecosystems in the Hawaiian Archipelago using optical imagery have revealed the presence of numerous
scleractinian, zoothanthellate coral reefs at depths of 30–130+ m, most of which were previously undiscovered. Such coral
reefs and their associated communities have been recently defined as mesophotic coral ecosystems (MCEs). Several types of
MCEs are found in Hawai‘i, each of which dominates a different depth range and is characterized by a unique pattern of coral
community structure and colony morphology. Although MCEs are documented near both ends of the archipelago and on many of the
islands in between, the maximum depth and prevalence of MCEs in Hawai‘i were found to decline with increasing latitude. The
Main Hawaiian Islands (MHI) had significantly deeper and greater percentages of scleractinian coral, and peaks in cover of
both scleractinian corals and macroalgae occurred within depth bins 20 m deeper than in the Northwestern Hawaiian Islands
(NWHI). Across the archipelago, as depth increased the combined percentage of living cover of mega benthic taxa declined sharply
with increasing depth below 70 m, despite the widespread availability of hard substrate. 相似文献
5.
In a time of unprecedented ecological change, understanding natural biophysical relationships between reef resilience and physical drivers is of increasing importance. This study evaluates how wave forcing structures coral reef benthic community composition and recovery trajectories after the major 2015/2016 bleaching event in the remote Chagos Archipelago, Indian Ocean. Benthic cover and substrate rugosity were quantified from digital imagery at 23 fore reef sites around a small coral atoll (Salomon) in 2020 and compared to data from a similar survey in 2006 and opportunistic surveys in intermediate years. Cluster analysis and principal component analysis show strong separation of community composition between exposed (modelled wave exposure > 1000 J m−3) and sheltered sites (< 1000 J m−3) in 2020. This difference is driven by relatively high cover of Porites sp., other massive corals, encrusting corals, soft corals, rubble and dead table corals at sheltered sites versus high cover of pavement and sponges at exposed sites. Total coral cover and rugosity were also higher at sheltered sites. Adding data from previous years shows benthic community shifts from distinct exposure-driven assemblages and high live coral cover in 2006 towards bare pavement, dead Acropora tables and rubble after the 2015/2016 bleaching event. The subsequent recovery trajectories at sheltered and exposed sites are surprisingly parallel and lead communities towards their respective pre-bleaching communities. These results demonstrate that in the absence of human stressors, community patterns on fore reefs are strongly controlled by wave exposure, even during and after widespread coral loss from bleaching events. 相似文献
6.
Coastal reef degradation and widespread bleaching of corals, i.e. loss of pigments and/or symbiotic zooxanthellae, is increasing
globally. Remote sensing from boats, aircraft or satellites has great potential for assessing the extent of reef change, but
will require ground-verified spectral algorithims characteristic of healthy and degraded reef populations. We collected seven
species of Caribbean reef corals and also representative macroalgae from reefs near Lee Stocking Island, Bahamas and quantified
their pigments using high performance liquid chromatography. We also measured the fluorescence and reflectance spectra of
corals and macroalgae using an in situ benthic spectrofluorometer. In visibly pigmented (unbleached) coral from 4 to 5 m depth,
the mean (±SD) surface density of pigments (3.0±1.3 μg chlorophyll-a cm -2 and 2.1±0.7 μg peridinin cm -2) was similar between colonies of the same species, but differed among species. The mean quantity of pigment per zooxanthella
(1.8±0.9 pg chl-a cell -1 and 1.4±0.7 pg peridinin cell -1) also differed among species and sometimes between colonies of the same species. Chl-a and peridinin densities per surface
area of coral were positively correlated. When excited with blue light (480 nm), macroalgae and corals had typical chlorophyll
fluorescence with a peak at 680 nm and a smaller shoulder peak at 730 to 740 nm. Most corals, unlike macroalgae, also had
distinct fluorescence peaks between 500 and 530 nm. In visibly bleached corals 680 nm fluorescence was greatly reduced in
amplitude. Pigmented coral, under natural lighting conditions, had a reflected light peak at about 570 nm. Reflectance increased
over all wavelengths in bleached corals, with the greatest increase at the wavelengths where chlorophyll and accessory pigments
absorb light, i.e. 670 and 450 to 550 nm. Both fluorescence and reflectance spectra appear promising to remotely differentiate
between pigmented and bleached coral and between coral and macroalgae.
Accepted: 15 March 1999 相似文献
7.
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 相似文献
8.
Large storm-relocated Porites coral blocks are widespread on the reef flats of Nansha area, southern South China Sea. Detailed investigations of coral reef ecology, geomorphology and sedimentation on Yongshu Reef indicate that such storm-relocated blocks originated from large Porites lutea corals growing on the spurs within the reef-front living coral zone. Because the coral reef has experienced sustained subsidence and reef development during the Holocene, dead corals were continuously covered by newly growing coral colonies. For this reason, the coral blocks must have been relocated by storms from the living sites and therefore the ages of these storm-relocated corals should approximate the times when the storms occurred. Rapid emplacement of these blocks is also evidenced by the lack of coral overgrowth, encrustation or subtidal alteration.U-series dating of the storm-relocated blocks as well as of in situ reef flat corals suggests that, during the last 1000 years, at least six strong storms occurred in 1064±30, 1210±5-1201±4, 1336±9, 1443±9, 1685±8-1680±6, 1872±15 AD, respectively, with an average 160-year cycle (110-240 years). The last storm, which occurred in 1872±15 AD, also led to mortality of the reef flat corals dated at ∼130 years ago. Thus, the storm had significant impacts on coral reef ecology and morphology. 相似文献
9.
Summary The Upper Rhaetian coral limestone of Adnet, southeast of Salzburg Austria has been repeatedly referred to as one of the most
spectacular examples of an ancient ‘autochthonous’ coral reef structure. The ‘Tropfbruch’ quarry is probably the best outcrop
for interpreting the distributional patterns of biotic successions and communities of a late Triassic patch reef. Our study
is based on the interpretation of a) outcrop photographs, b) reef maps resulting from quadrat transects, and c) the analysis
of quantitative data describing the distribution and frequency of reef organisms and sediment. A new methodological approach
(combination of reef mapping and photo-transects) is used to obtain quantitative field data which can be compared in greater
detail with data from modern coral reefs investigated by corresponding quantitative surveys.
Three unconformities and three well-defined ‘reef growth stages’ reflecting the vertical and lateral development of the reef
structure were differrentiated using transects:
Stage 1, representing the reef growth optimum, is characterized by laterally differentiated coral reef knobs with corals in
growth position. Criteria supporting this interpretation are the extraordinary size of the corals, their preservation in situ
and the great thickness of this interval. The massive coral Pamiroseris grew under higher energy conditions at the rim of the reef knob, whereas branching Retiophyllia colonies preferred less agitated water in the center. Vertical changes are reflected by an increase in frequency of the dasycladacean
alga Diplopora adnetensis and by the decreasing size of Retiophyllia. These sedimentological and biological criteria together with the unconformity above indicate a fall in the sea level as
a major control mechanism.
Stage 2, separated from stage 1 by an unconformity caused by partial subaerial exposure and karstification, is characterized
by vertically stacked coral successions with diverse reef debris. Facies heterogeneity is reflected by differences in the
diversity, taphonomy and packing density of reef-building organisms as well as by differences in sediment input from the platform.
Water depths and accommodation space were lower, therefore minor sea level fluctuations had a stronger effect on the biotic
composition. The high percentage of coral debris and corals reworked by storms and the increase in the input of platform sediment
led to a reduction of reef growth.
Stage 3, again separated at the base by an unconformity associated with karstification, is characterized by bioclastic sediments
with isolated reefbuilders forming a level-bottom community. The distribution of different coral morphotypes suggests that
sea level fluctuations were not the only controlling factor. Variations in the substrate were caused by differences in the
input of platform sediment.
The three-step development seen in Adnet documents the response of low-diverse coral associations to variations caused by
small-scale sea level changes, storm activity and sedimentation. The vertical changes in reef community structures correspond
to a sequence of ‘allogenic replacements’.
The Adnet reef structure should not be regarded as a general model of Alpine Upper Rhaetian reefs, because of the particular
setting of the patch reef. Only the ‘capping beds’ of the Upper Rhaetian Reef Limestone of the Steinplatte exhibit criteria
similar to Adnet.
Potential modern analogues of features seen in the coral communities of Adnet are the internal structure of the Retiophyllia thickets, the key role of branching corals within the communities, the scattered distribution and low and even diversity
of corals subsequent to breaks in settlement, segration patterns of corals indicating ‘contact avoidance’, toppling of large
coral colonies by intensive boring, and decreasing coral coverage from deeper and sheltered settings to more shallower water
depths. 相似文献
10.
Tropical Pacific sea surface temperature is projected to rise an additional 2–3 °C by the end of this century, driving an increase in the frequency and intensity of coral bleaching. With significant global coral reef cover already lost due to bleaching-induced mortality, efforts are underway to identify thermally tolerant coral communities that might survive projected warming. Massive, long-lived corals accrete skeletal bands of anomalously high density in response to episodes of thermal stress. These “stress bands” are potentially valuable proxies for thermal tolerance, but to date their application to questions of community bleaching history has been limited. Ecological surveys recorded bleaching of coral communities across the Palau archipelago during the 1998 and 2010 warm events. Between 2011 and 2015, we extracted skeletal cores from living Porites colonies at 10 sites spanning barrier reef and lagoon environments and quantified the proportion of stress bands present in each population during bleaching years. Across Palau, the prevalence of stress bands tracked the severity of thermal stress, with more stress bands occurring in 1998 (degree heating weeks = 13.57 °C-week) than during the less severe 2010 event (degree heating weeks = 4.86 °C-week). Stress band prevalence also varied by reef type, as more corals on the exposed barrier reef formed stress bands than did corals from sheltered lagoon environments. Comparison of Porites stress band prevalence with bleaching survey data revealed a strong correlation between percent community bleaching and the proportion of colonies with stress bands in each year. Conversely, annual calcification rates did not decline consistently during bleaching years nor did annually resolved calcification histories always track interannual variability in temperature. Our data suggest that stress bands in massive corals contain valuable information about spatial and temporal trends in coral reef bleaching and can aid in conservation efforts to identify temperature-tolerant coral reef communities. 相似文献
11.
The disastrous effects of the intense 198283 El Niño-SouthernOscillation (ENSO) bring new insight into the long-term developmentof eastern Pacific coral reefs. The 198883 ENSO sea surfacewarming event caused extensive reef coral bleaching (loss ofsymbiotic zooxanthellae), resulting in up to 7095% coralmortality on reefs in Costa Rica, Panama, Colombia and Ecuador.In the Galapagos Islands (Ecuador), most coral reefs experienced>95% coral mortality. Also, several coral species experiencedextreme reductions in population size, and local and regionalextinctions. The El Niño event spawned secondary disturbances,such as increased predation and bioerosion, that continue toimpact reef-building corals. The death of Pocillopora colonieswith their crustacean guards eliminated coral barriers now allowingthe corallivore Acanthaster planci access to formerly protectedcoral prey. Sea urchins and other organisms eroded disturbedcorals at rates that exceed carbonate production, potentiallyresulting in the elimination of existing reef buildups. In otherreefbuilding regions following extensive, catastrophic coralmortality, rapid recovery often occurs through the growth ofsurviving corals, recruitment of new corals from nearby sourcepopulations, and survival of consolidated reef surfaces. Inthe eastern Pacific, however, the return of upwelling conditionsand the survival of coral predators and bioeroders hamper coralreef recovery by reducing recruitment success and eroding coralreef substrates. Thus, coral reef growth that occurs betweendisturbance events is not conserved. Repeated El Niñodisturbances, which have occurred throughout the recent geologichistory of the eastern Pacific, prevent coral communities fromincreasing in diversity and limit the development and persistenceof significant reef features. The poor development of easternPacific coral reefs throughout Holocene and perhaps much ofPleistocene time may result from recurrent thermal disturbancesof the intensity of the 198283 El Niño event. 相似文献
12.
To determine what happens to scleractinian corals that have been killed by black band disease (BBD), massive corals with
BBD were monitored for 11 years on a shallow reef (<10 m depth) in St. John, US Virgin Islands. Small quadrats (0.039 m 2) were used to compare the rates of scleractinian recruitment to the skeletons of corals killed by either BBD or physical
disturbance (Hurricane Hugo 1989). Coral recruitment was also quantified on the adjacent fringing reef using larger quadrats
(0.25 m 2) to detect possible biases associated with using small, permanent quadrats to assess recruitment to BBD-killed corals. Of
28 tagged colonies with BBD in 1988, 43% were lost to Hurricane Hugo in 1989, 7% were lost to unknown causes between 1991
and 1992, and 14 were monitored annually for 11 years; of these, 71% were dead and still in their original growth position
in 1998. Between 1988 and 1997, corals recruited to the BBD-killed surfaces at a rate of 1.1 ± 0.3 recruits · 0.039 m −2 · decade −1 (mean ± SE, n = 14), although mortality reduced the density to 0.3 ± 0.2 recruits · 0.039 m −2 by 1997. The rate of recruitment and the taxonomic composition of the coral recruits to BBD-killed corals were indistinguishable
statistically from those to corals killed by Hurricane Hugo. This demonstrates that BBD creates space that is functionally
the same as other dead coral surfaces in providing a substratum for coral recruitment. However, because coral recruits are
dispersed widely, clumped in distribution and temporally variable in density on the fringing reef as a whole, it is unlikely
that they will be found on monitored coral colonies that have been killed by BBD. While this hypothesis is consistent with
the higher density of recruits on the fringing reef compared with BBD-killed corals, further studies are required to investigate
alternative explanations such as the role of substratum age in favoring recruitment to surfaces other than those killed recently
by BBD.
Accepted: 26 August 1999 相似文献
13.
Feeding aggregations of three corallivorous gastropods, Drupella cornus, D. fragum and D. rugosa, have caused considerable coral damage on reefs across the Indo-West Pacific. Distribution and abundance of these three species
were explored at Lizard Island, Great Barrier Reef, to determine within-reef variations in density, and spatial relationships
between Drupella and their prey corals. The scales of greatest variation were between reef habitats (combinations of exposure and depth) and
individual coral colonies. Density varied 12-fold among four habitats: exposed crests (2.55/m 2), exposed slopes (0.22/m 2), sheltered crests (0.34/m 2) and sheltered slopes (2.07/m 2). Species composition also varied markedly between habitats. Individuals were highly aggregated, usually forming small clusters
(<10 individuals) on live coral colonies and other substrata, and occasional large aggregations of=200 to>2000. Five basic
tenets for sampling Drupella are established, based on patterns of variation in density and species composition, and small-scale habitat use.
Accepted: 8 February 1999 相似文献
14.
Colony age and size can be poorly related in scleractinian corals if colonies undergo fission to form smaller independent
patches of living tissue (i.e., ramets), but the implications of this life-history characteristic are unclear. This study
explored the ecological consequences of the potential discrepancy between size and age for a massive scleractinian, first
by testing the effect of colony origin on the growth of small colonies, and second by quantifying the contribution of ramets
to population structure. Using Siderastrea siderea in St. John (US Virgin Islands) as an experimental system, the analyses demonstrated that the growth of small colonies derived
from sexual reproduction was 2.5-fold greater than that of small ramets which were estimated to be ≈100 years older based
on the age of the parent colonies from which they split. Although fission can generate discrete colonies, which in the case
of the study reef accounted for 42% of all colonies, it may depress colony success and reef accretion through lowered colony
growth rates. 相似文献
15.
In this paper, the relationship between reef building (accretion) and depth in an optimal inter-island channel environment in Hawaii is analyzed. For accretion, the growth rate of Porites lobata is used as a proxy for the reef community, because it is the most abundant and dominant species of reef building coral in Hawaii. Optimal growth of P. lobata occurs at a depth of 6 m, below which both growth rate and abundance decrease with increasing depth. A lower depth limit for this species is found at about 80–100 m, yet reef accretion ceases at ~50 m depth. Below 50 m, rates of bio-erosion of colony holdfasts equal or exceed the growth of basal attachments, causing colonies to detach from the bottom. Continued bio-erosion further erodes and dislodges colonies leading to their breakdown and ultimately to the formation of coralline rubble and sand. Thus, within this channel environment in Hawaii, a threshold for reef building exists at ~ 50 m depth, where coral accretion is interrupted by bio-erosion. Conceptually viewed, this depth horizon is analogous to a vertical Darwin Point, although quite narrow in space and time. More importantly, it explains the history of reef morphology in the Au’au Channel where a chronological hiatus exists at a depth near 50 m. This hiatus separates shallower modern growth (about 100 years or less) from the deeper reef which is all due to accretion during the early Holocene or Pleistocene epochs. 相似文献
16.
A small-scale, “no-use zone policy” has been implemented since 1992 at Eilat’s Coral Nature Reserve (Northern Red Sea). Six
years later, the status of this closed-to-the-public reef area was compared to two nearby open-to-the-public sites, by evaluating
populations of the scleractinian coral Stylophora pistillata in the strolling zone (0.5–1.5 m depth). Results from the open sites show that: (1) Live coral cover was three times lower
than at the closed site; (2) numbers of small colonies (recruits) were significantly higher than in the closed site, while
numbers of medium and large size colonies (geometric mean radius, rˉ>4.1 cm) per m 2 were significantly lower; (3) maximum rˉ was almost half than that in the closed site (9.6 cm versus 16.7 cm); (4) average number of broken colonies was three times
higher than in the closed site; (5) significantly fewer colonies were partially dead. The latter result may reflect senescence
processes in the large colonies of the closed site. Although colony breakage is reduced, it appears that the “no-use zone”
policy is not sufficient for protecting small reef areas. The intense exploitation of Eilat’s coral reef by the tourist industry
requires’ in addition to the conventional protective measures, the initiation of novel management solutions such as reef restoration
by sexual and asexual recruits.
Accepted: 11 August 1999 相似文献
17.
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 CO 2, 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 CO 2. 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. 相似文献
18.
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 相似文献
20.
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 相似文献
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