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1.
Significant differences were found in the extent to which massive coral species at Enewetak are excavated by boring organisms: Goniastrea retiformis, 7.9%; Porites lutea, 2.5%; and Favia pallida, 1.2%. While polychaetes constituted the most abundant and diverse group of coral associates, clionid sponges accounted for approximately 70–80% of skeletal damage. Clionid boring rates are initially very high but burrowing ceases when a particular burrow size (˜0.6 cm) or distance from the surface (≦2 cm) is reached. Most coral skeletal excavation occurs within 2 cm of a dead surface. Therefore, bioerosional damage to corals depends primarily on the amount of skeletal surface not covered by live coral tissue. Damage to skeletons is inversely correlated with colony size but is not correlated with coral growth rates or water depth. Massive corals have a potential escape in size from catastrophic bioerosion. Models relating 1) coral growth forms to skeletal density and stability in currents, 2) resistance of coral skeletons to breakage by water movement and suspended rubble, and 3) dead surface area on coral heads to bioerosional damage and consequent probability of detachment from the substrate, are proposed. 相似文献
2.
Anthropogenic increases in atmospheric carbon dioxide concentration have caused global average sea surface temperature (SST) to increase by approximately 0.11°C per decade between 1971 and 2010 – a trend that is projected to continue through the 21st century. A multitude of research studies have demonstrated that increased SSTs compromise the coral holobiont (cnidarian host and its symbiotic algae) by reducing both host calcification and symbiont density, among other variables. However, we still do not fully understand the role of heterotrophy in the response of the coral holobiont to elevated temperature, particularly for temperate corals. Here, we conducted a pair of independent experiments to investigate the influence of heterotrophy on the response of the temperate scleractinian coral Oculina arbuscula to thermal stress. Colonies of O. arbuscula from Radio Island, North Carolina, were exposed to four feeding treatments (zero, low, moderate, and high concentrations of newly hatched Artemia sp. nauplii) across two independent temperature experiments (average annual SST (20°C) and average summer temperature (28°C) for the interval 2005–2012) to quantify the effects of heterotrophy on coral skeletal growth and symbiont density. Results suggest that heterotrophy mitigated both reduced skeletal growth and decreased symbiont density observed for unfed corals reared at 28°C. This study highlights the importance of heterotrophy in maintaining coral holobiont fitness under thermal stress and has important implications for the interpretation of coral response to climate change. 相似文献
3.
Stable between‐group differences in collective behavior have been documented in a variety of social taxa. Here we evaluate the effects of such variation, often termed collective or colony‐level personality, on coral recovery in a tropical marine farmerfish system. Groups of the farmerfish Stegastes nigricans cultivate and defend gardens of palatable algae on coral reefs in the Indo‐Pacific. These gardens can promote the recruitment, growth, and survival of corals by providing a refuge from coral predation. Here we experimentally evaluate whether the collective response of farmerfish colonies is correlated across intruder feeding guilds – herbivores, corallivores and egg‐eating predators. Further, we evaluate if overall colony responsiveness or situation‐specific responsiveness (i.e. towards herbivores, corallivores, or egg‐eaters in particular) best predicts the growth of outplanted corals. Finally, we experimentally manipulated communities within S. nigricans gardens, adding either macroalgae or large colonies of coral, to assess if farmerfish behavior changes in response to the communities they occupy. Between‐group differences in collective responsiveness were repeatable across intruder guilds. Despite this consistency, responsiveness towards corallivores (porcupinefish and ornate butterflyfish) was a better predictor of outplanted coral growth than responsiveness towards herbivores or egg‐eaters. Adding large corals to farmerfish gardens increased farmerfish attacks towards intruders, pointing to possible positive feedback loops between their aggression towards intruders and the presence of corals whose growth they facilitate. These data provide evidence that among‐group behavioral variation could strongly influence the ecological properties of whole communities. 相似文献
4.
Temporal and spatial variation in the growth parameters skeletal density, linear extension and calcification rate in massive Porites from two nearshore regions of the northern Great Barrier Reef (GBR) were examined over a 16‐year study period. Calcification rates in massive Porites have declined by approximately 21% in two regions on the GBR ~450 km apart. This is a function primarily of a decrease in linear extension (~16%) with a smaller decline in skeletal density (~6%) and contrasts with previous studies on the environmental controls on growth of massive Porites on the GBR. Changes in the growth parameters were linear over time. Averaged across colonies, skeletal density declined over time from 1.32 g cm ?3 (SE = 0.017) in 1988 to 1.25 g cm ?3 (0.013) in 2003, equivalent to 0.36% yr ?1 (0.13). Annual extension declined from 1.52 cm yr ?1 (0.035) to 1.28 cm yr ?1 (0.026), equivalent to 1.02% yr ?1 (0.39). Calcification rates (the product of skeletal density and annual extension) declined from 1.96 g cm ?2 yr ?1 (0.049) to 1.59 g cm ?2 yr ?1 (0.041), equivalent to 1.29% yr ?1 (0.30). Mean annual seawater temperatures had no effect on skeletal density, but a modal effect on annual extension and calcification with maxima at ~26.7 °C. There were minor differences in the growth parameters between regions. A decline in coral calcification of this magnitude with increasing seawater temperatures is unprecedented in recent centuries based on analysis of growth records from long cores of massive Porites. We discuss the decline in calcification within the context of known environmental controls on coral growth. Although our findings are consistent with studies of the synergistic effect of elevated seawater temperatures and pCO 2 on coral calcification, we conclude that further data on seawater chemistry of the GBR are required to better understand the links between environmental change and effects on coral growth. 相似文献
6.
X-radiography and carbon and oxygen stable isotope analysis have been used to examine the effects of prolonged bleaching on the growth rate and chemical composition of the skeleton of the massive reef coral, Montastrea annularis. The post-bleaching linear growth of one colony that remained bleached for 10 to 12 months following the 1987 Caribbean-wide bleaching event was only 37% of mean annual growth from pre-bleaching years, and was manifest as a loss of the following year's low density band. Two colonies that did not bleach (normal) and two that bleached and regained their coloration (recovered) had linear growth rates over the same period that were 81 to 98% of mean pre-bleaching annual growth. Linear growth by a third recovered coral was 66% of pre-bleaching growth. No sub-annual stress bands were associated with the bleaching. The skeleton of the bleached colony had carbon and oxygen isotopic compositions that were reduced in range and enriched (increased) in both 13C and 18O in the post-bleaching year. The skeletons of two of the nine colonies, one bleached and one recovered, had depleted (reduced) 18O values (-5.3 and -4.8%., respectively) during the bleaching episode that agree with the suggestion that positive temperature anomalies occurred during, and may have caused, the bleaching event. The range and values for all other normal and recovered corals, however, were not different between the post-bleaching year and previous years. Our data suggest that stress bands and isotopic analysis of coral skeletons may not always be reliable tools for examining the occurrence, cause or effects of certain discrete stress events that may interrupt skeletal growth. 相似文献
7.
When large, predatory fishes and invertebrates were excluded from areas of a coral reef in the Florida Keys, USA, densities
of the normally rare gastropod Cyphoma gibbosum, a principal predator of gorgonian corals, increased 19-fold. Gorgonians in predator exclosures were grazed more frequently
and extensively by C. gibbosum than were gorgonians in uncaged areas. In exclosures, 14% of all gorgonians showed recent predation by C. gibbosum, with 62% of the entire colony surface being removed from these attacked individuals. In areas where predators of C. gibbosum were not excluded, only 5% of gorgonians exhibited recent damage, with only 26% of the colony surface being removed from
these few damaged individuals. Thus, the increases in both frequency and extent of attack combined to produce an 8× increase
in gorgonian damage following removal of large predators. These patterns suggest that predators typically suppress C. gibbosum populations, that overfishing of these predators could release C. gibbosum from top-down control, and that this release will allow increased damage to gorgonian corals. 相似文献
8.
A suite of processes drive variation in coral populations in space and time, yet our understanding of how variation in coral density affects coral performance is limited. Theory predicts that reductions in density can send coral populations into a predator pit, where concentrated corallivory maintains corals at low densities. In reality, how variation in coral density alters corallivory rates is poorly resolved. Here, we experimentally quantified the effects of corallivory and coral density on growth and survival of small colonies of the staghorn coral Acropora pulchra. Our findings suggest that coral density and corallivory have strong but independent effects on coral performance. In the presence of corallivores, corals suffered high but density-independent mortality. When corallivores were excluded, however, vertical extension rates of colonies increased with increasing densities. While we found no evidence for a predator pit, our results suggest that spatio-temporal variation in corallivore and coral densities can fundamentally alter population dynamics via strong effects on juvenile corals. 相似文献
9.
Ecological theory suggests that the behaviour, growth and abundance of predators will be strongly influenced by the abundance
of prey. Predators may in turn play an important role in structuring prey populations and communities. Responses of predators
to variation in prey abundance have most commonly been demonstrated in low-diversity communities where food webs are relatively
simple. How predators respond in highly diverse assemblages such as in coral reef habitats is largely unknown. This study
describes an experiment that examined how the movement, diet and growth of the coral reef piscivore, Cephalopholis boenak (Serranidae) responded to variation in the abundance of its prey. Predator densities were standardised on small patch reefs
made from the lagoonal reef-building coral, Porites cylindrica. These patch reefs exhibited natural variation in the abundance and community structure of multiple species of prey. However,
our experiment generated a relatively simple predator–prey relationship, with C. boenak primarily responding to the most abundant species of prey. Three responses of predators were observed: aggregative, functional
and developmental. Thirty-one per cent of individuals moved between patch reefs during the experiment, all from areas of relatively
low to high prey density. Feeding rates were higher on patch reefs of high prey density, while growth rates of fish that remained
on low prey density reefs throughout the experiment were lower. Growth rates of C. boenak on the experimental reefs were also much higher than for those living on natural patch reefs over the same time period, corresponding
with overall differences in prey abundance. These results suggest that local abundance, feeding rate and growth of C. boenak were closely linked to the abundance of their main prey. This combination of predatory responses is a potential mechanism
behind recent observations of density-dependent mortality and population regulation of prey in coral reef fish communities. 相似文献
10.
X-radiographs were made of vertical slices through the centers of 47 hermatypic coral colonies collected at Eniwetok Atoll, Marshall Islands. The image thus obtained are useful for the study of colony geometry, development, and response to damage.Comparison of radioactive inclusions of known age with previously reported cyclic skeletal density variations normal to the axis of growth confirms the annual nature of the density banding. Growth rates based on density bands and radioactivity inclusions are calculated for all 47 specimens, and measurements of the individual ‘growth bands’ are presented for 25 of them.Bulk densities measured by X-ray transmission ranged from 1.0 to 2.2 g/cm 3, with an average range of 1.3–1.6 g/cm 3. Intra-specimen skeletal densities typically vary by 10–30%; the period of high density skeletal deposition appears to coincide with the season of higher rainfall and warmer surface water at Eniwetok. Pigment residues left by boring algae are more commonly found in low density portions of the skeletons, but this distribution is believed to result from rather than cause the variations in the density of the deposited aragonite.Linear growth rates for the same specimen vary by factors of two or more from year to year, but the 25 specimens studied did not show a common pattern in the linear growth rate. Other than showing some general trends in growth as a function of species and depth, linear growth rates do not appear to be a particularly informative parameter.The density and growth rate variations are important factors in the measurement of coral growth and metabolism, and to the study of environmental controls of coral growth. 相似文献
12.
Summary The reefs near Safaga, Egypt, are built mainly by coral species of Porites and Acropora. These genera are in general important for the formation of coral communities and reef structures. While Montipora or Pavona are also species rich, their mean colony size is too small for a substantial role in the build-up of carbonate mass. Yet
as a host coral, Montipora is more important than Porites; both may accommodate the pectinid Pedum and certain species of mytilid Lithophaga. Such associations appear to be typical for specific reef areas and to be correlated to the food supply of the bivalves.
These findings can be used for an actuopaleontological interpretation of the fossil situation. In addition to the frequency
of occurrence, factors such as the growth form, growth rate, skeletal density and lifespan of corals are essential in determining
their share in reef construction. 相似文献
13.
Measurements of the skeletal extension rate of branches of the reef coral Pocillopora damicornis showed that the linear extension rate is independent of colony size for colonies from 1.9 to 19 cm in diameter. Analysis of existing data from Western Australia, Samoa, the Great Barrier Reef and Hawaii supports the finding that linear extension is not related to colony size in this species. 相似文献
14.
Partial mortality or tissue necrosis was quantified in the massive scleractinian coral Porites at three sites in The Philippines (Bolinao, NW Luzon; Puerto Galera, Mindoro; and El Nido, N Palawan). Overall, 15 ± 1 (mean ± 1 standard error, 642 replicates) percent of colony area was dead, mean colony area was 1135 plusmn; 127 cm 2, and lesion density was 1.7 ± 0.1 dm —2. Total live coral cover varied between 20 and 63% in belt transects, and Porites and Acropora cover were inversely correlated. ANOVA models incorporating effects of site, colony size, sedimentation rates, wave exposure and depth were highly significant but explained only a small proportion of the variation observed in lesion density and percent dead area (respectively 8 and 2%). Lesion density was found to vary significantly with site (contributed 29% to this explained variance), decrease with increasing colony area (33%), and increase with increasing sedimentation (23%) and wave exposure (14%). Colony size was significantly explained by the factor site (contributing 61% to the total 29% explained variance) and depth (34%), with the smallest colonies being observed in Bolinao and the largest in El Nido. Densities of lesions were highest in Bolinao, intermediate in Puerto Galera, and lowest in El Nido. This pattern is parallel to intensity of human reef exploitation and opposite to that in colony size, live coral cover and Acropora cover. Since only a small part of the observed variance in partial mortality estimators was explained by the ANOVAs, other factors not quantified here must have been more important (e.g. disease incidence, predation, human exploitation). 相似文献
15.
With coral cover in decline on many Caribbean reefs, any process of coral mortality is of potential concern. While sparisomid
parrotfishes are major grazers of Caribbean reefs and help control algal blooms, the fact that they also undertake corallivory
has prompted some to question the rationale for their conservation. Here the weight of evidence for beneficial effects of
parrotfishes, in terms of reducing algal cover and facilitating demographic processes in corals, and the deleterious effects
of parrotfishes in terms of causing coral mortality and chronic stress, are reviewed. While elevated parrotfish density will
likely increase the predation rate upon juvenile corals, the net effect appears to be positive in enhancing coral recruitment
through removal of macroalgal competitors. Parrotfish corallivory can cause modest partial colony mortality in the most intensively
grazed species of Montastraea but the generation and healing of bite scars appear to be in near equilibrium, even when coral cover is low. Whole colony
mortality in adult corals can lead to complete exclusion of some delicate, lagoonal species of Porites from forereef environments but is only reported for one reef species ( Porites astreoides), for one habitat (backreef), and with uncertain incidence (though likely <<10%). No deleterious effects of predation on
coral growth or fecundity have been reported, though recovery of zooxanthellae after bleaching events may be retarded. The
balance of evidence to date finds strong support for the herbivory role of parrotfishes in facilitating coral recruitment,
growth, and fecundity. In contrast, no net deleterious effects of corallivory have been reported for reef corals. Corallivory
is unlikely to constrain overall coral cover but contraints upon dwindling populations of the Montastraea annularis species complex are feasible and the role of parrotfishes as a vector of coral disease requires evaluation. However, any
assertion that conservation practices should guard against protecting corallivorous parrotfishes appears to be unwarranted
at this stage. 相似文献
16.
Skeletons of massive coral colonies contain annual density bands that are revealed by X-radiography of slices cut along growth axes. These bands allow measurement of skeletal growth parameters such as annual extension rate and annual calcification rate. Such measurements have been important in understanding coral growth, in assessing environmental impacts and in recovering proxy environmental information. Measurements of coral calcification rate from annual density banding require measurements of skeletal density along tracks across skeletal slices and, until now, such density measurements have depended upon specialized and expensive equipment. Here, we describe a straightforward, inexpensive and accurate technique for measuring skeletal density from digitized images of X-radiographs of coral skeletal slices. An aragonitic step-wedge was included in each X-radiograph of a coral slice together with two aluminium bars positioned along the anode-cathode axis. Optical density was measured along tracks across the X-ray images of these different objects. The aragonite step-wedge provided a standard for converting optical density to skeletal density. The aluminium bars were used to correct for the heel effect—a variation in the intensity of the X-ray beam along the anode-cathode axis that would, otherwise, introduce large errors into measurements of skeletal density. Exposure was found to vary from X-radiographs to X-radiograph, necessitating the inclusion of the calibration standards in each X-radiograph of a coral slice. Results obtained using this technique compared well with results obtained by direct gamma densitometry of skeletal slices. 相似文献
17.
To know if the variation in the number of settling fish larvae can be dampened by density-dependent postsettlement mortality,
we investigated the relationship between settler density and predator-induced mortality of a coral reef damselfish, Chromis viridis. Totals of 2, 3, 5, 8, 10, 12, 14, 16, 18, and 20 fish of 10 or 20 mm total length were released in experimental cages enclosing
a coral head of Porites rus (to provide settlement habitat) and five predators. The results showed that the mortality rate of both 10- and 20-mm fish
was density independent. 相似文献
18.
The effects of multiple predators on their prey are frequently non‐additive because of interactions among predators. When prey shift habitats through ontogeny, many of their predators cannot interact directly. However, predators that occur in different habitats or feed on different prey stages may still interact through indirect effects mediated by prey traits and density. We conducted an experiment to evaluate the combined effects of arboreal egg‐stage and aquatic larval‐stage predators of the African treefrog, Hyperolius spinigularis. Egg and larval predator effects were non‐additive – more Hyperolius survived both predators than predicted from their independent effects. Egg‐stage predator effects on aquatic larval density and size and age at hatching reduced the effectiveness of larval‐stage predators by 70%. Our results indicate that density‐ and trait‐mediated indirect interactions can act across life‐stages and habitats, resulting in non‐additive multi‐predator effects. 相似文献
19.
Recent micro-analytical studies of coral skeletons have led to the discovery that the effects of biology on the skeletal chemical
and isotopic composition are not uniform over the skeleton. The aim of the present work was to provide histological observations
of the coral tissue at the interface with the skeleton, using Stylophora pistillata as a model, and to discuss these observations in the context of skeletal ultra-structural organization and composition. Several
important observations are reported: (1) At all scales of observation, there was a precise morphological correspondence between
the tissues and the skeleton. The morphological features of the calicoblastic ectoderm correspond exactly to the shape of
individual crystal fiber bundles in the underlying skeleton, indicating that the calicoblastic cell layer is in direct physical
contact with the skeletal surface. This is consistent with the previously observed chemical and isotopic composition of the
ultra-structural components in the skeleton. (2) The distribution and density of desmocyte cells, which anchor the calicoblastic
ectoderm to the skeletal surface, vary spatially and temporally during skeletal growth. (3) The tissue above the coenosteal
spines lack endoderm and consists only of ectodermal cell-layers separated by mesoglea. These findings have important implications
for models of vital effects in coral skeletal chemistry and isotope composition. 相似文献
20.
Mutualistic symbioses are ubiquitous in nature and facilitate high biodiversity and productivity of ecosystems by enhancing the efficiency of energy and nutrient use within ecological communities. For example, small groups of fish that inhabit coral colonies in reef ecosystems potentially enhance coral growth through defense from coral predators, aeration of coral tissue and nutrient provisioning. This study examines whether the prevalence and consequences of fish-coral interactions vary among sites with different environmental conditions in a coral reef lagoon, using the humbug damselfish Dascyllus aruanus and its preferred coral host Pocillopora damicornis as a study system. Using a field experiment, we tested the site-specific effects of D. aruanus on coral growth, and show that the cost-benefit ratio for corals hosting fish varies with local environmental variation. Results of this study also demonstrate that fish prefer to inhabit coral colonies with particular branch-spacing characteristics, and that the local abundance of D. aruanus influences the proportion of coral colonies within a site that are occupied by fish rather than increasing the number of fish per colony. We also show that corals consistently benefit from hosting D. aruanus via defense from predation by corallivorous butterflyfish, regardless of local environmental conditions. These findings highlight the need to consider the potential for multiple scale- and state-dependent interaction effects when examining the ecology of fish-coral associations. We suggest that fluctuating cost-benefit ratios for species interactions may contribute to the maintenance of different colony phenotypes within coral populations. 相似文献
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