The corals Acropora palifera and Acropora cuneata are genetically and ecologically distinct

Two of the most abundant corals of the Great Barrier Reef Acropora cuneata and Acropora palifera, can be distinguished reliably by conventional taxonomic methods only if large specimens of both species are collected from the same uniform biotope. In this study gross and microscopic examination of the corallite structures of large coralla, collected from a reef crest biotope, were used to confirm the assignment of these specific names to two electrophoretically distinct groups of corals. Identifications based on genetic and morphological data gathered from small fragments of coralla collected from five different sites were in agreement for two sites within which skeletal data were adequate for taxonomic purposes (i.e. one reef crest and one outer lagoon site). However, specimens collected from the other three sites could be identified reliably only by using the electrophoretic data. These results confirm that small fragments from diverse habitats may not be adequate for morphologically based identification. The application of electrophoretic identifications to the results of an earlier electrophoretic survey of 76 sites on 11 reefs revealed that, although A. palifera and A. cuneata frequently co-occur, they have significantly different habitat distributions. Acropora cuneata is more commonly associated with high energy environments such as the reef crest, whereas A. palifera occurs most commonly in the sheltered reef lagoons and on the deeper reef slopes.     

Gametogenesis and fecundity of <Emphasis Type="Italic">Acropora tenella</Emphasis> (Brook 1892) in a mesophotic coral ecosystem in Okinawa,Japan

Mesophotic coral ecosystems (below 30–40 m depth) host a large diversity of zooxanthellate coral communities and may play an important role in the ecology and conservation of coral reefs. Investigating the reproductive biology of mesophotic corals is important to understand their life history traits. Despite an increase in research on mesophotic corals in the last decade, their reproductive biology is still poorly understood. Here, gametogenesis and fecundity of the Indo-Pacific mesophotic coral, Acropora tenella, were examined in an upper mesophotic reef (40 m depth) in Okinawa, Japan for the first time. Acropora tenella is a hermaphrodite with a single annual gametogenic cycle, and both oogenesis and spermatogenesis occurring for 11–12 and 5–6 months, respectively. Timing of spawning of this species was similar to other shallow Acropora spp. in the region. However, colonies had longer gametogenic cycles and less synchronous gamete maturation compared to shallow acroporids with spawning extended over consecutive months. Both the polyp fecundity (number of eggs per polyp) and gonad index (defined as the number of eggs per square centimeter) of A. tenella were lower than most acroporids. Our findings contribute to understanding of the life history of corals on mesophotic reefs and suggest that the reproductive biology of upper mesophotic corals is similar to that of shallow-water corals.     

Biannual Spawning and Temporal Reproductive Isolation in Acropora Corals

Coral spawning on the oceanic reef systems of north-western Australia was recently discovered during autumn and spring, but the degree to which species and particularly colonies participated in one or both of these spawnings was unknown. At the largest of the oceanic reef systems, the participation by colonies in the two discrete spawning events was investigated over three years in 13 species of Acropora corals (n = 1,855 colonies). Seven species spawned during both seasons; five only in autumn and one only in spring. The majority of tagged colonies (n = 218) spawned once a year in the same season, but five colonies from three species spawned during spring and autumn during a single year. Reproductive seasonality was not influenced by spatial variation in habitat conditions, or by Symbiodinium partners in the biannual spawner Acropora tenuis. Colonies of A. tenuis spawning during different seasons separated into two distinct yet cryptic groups, in a bayesian clustering analysis based on multiple microsatellite markers. These groups were associated with a major genetic divergence (G”_ST = 0.469), despite evidence of mixed ancestry in a small proportion of individuals. Our results confirm that temporal reproductive isolation is a common feature of Acropora populations at Scott Reef and indicate that spawning season is a genetically determined trait in at least A. tenuis. This reproductive isolation may be punctuated occasionally by interbreeding between genetic groups following favourable environmental conditions, when autumn spawners undergo a second annual gametogenic cycle and spawn during spring.     

Temporal consistency in background mortality of four dominant coral taxa along Australia’s Great Barrier Reef

Studies on the population and community dynamics of scleractinian corals typically focus on catastrophic mortality associated with acute disturbances (e.g., coral bleaching and outbreaks of crown-of-thorns starfish), though corals are subject to high levels of background mortality and injuries caused by routine and chronic processes. This study quantified prevalence (proportion of colonies with injuries) and severity (areal extent of injuries on individual colonies) of background mortality and injuries for four common coral taxa (massive Porites, encrusting Montipora, Acropora hyacinthus and branching Pocillopora) on the Great Barrier Reef, Australia. Sampling was conducted over three consecutive years during which there were no major acute disturbances. A total of 2276 adult colonies were surveyed across 27 sites, within nine reefs and three distinct latitudinal sectors. The prevalence of injuries was very high (>83%) across all four taxa, but highest for Porites (91%) and Montipora (85%). For these taxa (Montipora and Pocillopora), there was also significant temporal and spatial variation in prevalence of partial mortality. The severity of injuries ranged from 3% to more than 80% and varied among coral taxa, but was fairly constant spatially and temporally. This shows that some injuries have considerable longevity and that corals may invest relatively little in regenerating tissue over sites of previous injuries. Inter-colony variation in the severity of injury also had no apparent effect on the realized growth of individual colonies, suggesting that energy diverted to regeneration has a limited bearing on overall energetic allocation, or impacts on other life-history processes (e.g., reproduction) rather than growth. Establishing background levels of injury and regeneration is important for understanding energy investment and life-history consequences for reef-building corals as well as for predicting susceptibility to, and capacity to recover from, acute disturbances.     

Genetic Susceptibility,Colony Size,and Water Temperature Drive White-Pox Disease on the Coral Acropora palmata

Outbreaks of coral diseases are one of the greatest threats to reef corals in the Caribbean, yet the mechanisms that lead to coral diseases are still largely unknown. Here we examined the spatial-temporal dynamics of white-pox disease on Acropora palmata coral colonies of known genotypes. We took a Bayesian approach, using Integrated Nested Laplace Approximation algorithms, to examine which covariates influenced the presence of white-pox disease over seven years. We showed that colony size, genetic susceptibility of the coral host, and high-water temperatures were the primary tested variables that were positively associated with the presence of white-pox disease on A. palmata colonies. Our study also showed that neither distance from previously diseased individuals, nor colony location, influenced the dynamics of white-pox disease. These results suggest that white-pox disease was most likely a consequence of anomalously high water temperatures that selectively compromised the oldest colonies and the most susceptible coral genotypes.     

The dynamics of microbial partnerships in the coral Isopora palifera

Both bacteria and algal symbionts (genus Symbiodinium), the two major microbial partners in the coral holobiont, respond to fluctuations in the environment, according to current reports; however, little evidence yet indicates that both populations have any direct interaction with each other in seasonal fluctuation. In this study, we present field observations of a compositional change in bacteria and Symbiodinium in the coral Isopora palifera in three separate coral colonies following monthly sampling from February to November in 2008. Using massively parallel pyrosequencing, over 200 000 bacterial V6 sequences were classified to build the bacterial community profile; in addition, the relative composition and quantity of Symbiodinium clades C and D were determined by real-time PCR. The results showed that coral-associated bacterial and Symbiodinium communities were highly dynamic and dissimilar among the tagged coral colonies, suggesting that the effect of host specificity was insignificant. The coral-associated bacterial community was more diverse (Shannon index up to 6.71) than previous estimates in other corals and showed rapid seasonal changes. The population ratios between clade C and D groups of Symbiodinium varied in the tagged coral colonies through the different seasons; clade D dominated in most of the samples. Although significant association between bacteria and symbiont was not detected, this study presents a more detailed picture of changes in these two major microbial associates of the coral at the same time, using the latest molecular approaches.     

Effects of coral bleaching on the feeding response of two species of coral-feeding fish

Coral bleaching is an increasingly prominent threat to coral reef ecosystems, not only to corals, but also to the many organisms that rely on coral for food and shelter. Coral-feeding fishes are negatively affected by coral loss caused by extensive bleaching, but it is unknown how feeding behaviour of most corallivorous fishes changes in response to coral bleaching. In this study, coral bleaching was experimentally induced in situ to examine the feeding response of two obligate corallivorous fish, Labrichthys unilineatus (Labridae) and Chaetodon baronessa (Chaetodontidae). Feeding rates were monitored before, during, and immediately after experimental bleaching of prey corals. L. unilineatus significantly increased its feeding on impacted corals during bleaching, but showed a steady decline in feeding once corals were fully bleached. Feeding response of L. unilineatus appears to parallel the expected stress-induced mucous production by bleaching colonies. In contrast, C. baronessa preferentially fed from healthy colonies over bleached colonies, although bleached colonies were consumed for five days following manipulation. Feeding by corallivorous fishes can play an important role in determining coral condition and mortality of corals following stress induced bleaching.     

Natural Disease Resistance in Threatened Staghorn Corals

Disease epidemics have caused extensive damage to tropical coral reefs and to the reef-building corals themselves, yet nothing is known about the abilities of the coral host to resist disease infection. Understanding the potential for natural disease resistance in corals is critically important, especially in the Caribbean where the two ecologically dominant shallow-water corals, Acropora cervicornis and A. palmata, have suffered an unprecedented mass die-off due to White Band Disease (WBD), and are now listed as threatened under the US Threatened Species Act and as critically endangered under the IUCN Red List criteria. Here we examine the potential for natural resistance to WBD in the staghorn coral Acropora cervicornis by combining microsatellite genotype information with in situ transmission assays and field monitoring of WBD on tagged genotypes. We show that six percent of staghorn coral genotypes (3 out of 49) are resistant to WBD. This natural resistance to WBD in staghorn corals represents the first evidence of host disease resistance in scleractinian corals and demonstrates that staghorn corals have an innate ability to resist WBD infection. These resistant staghorn coral genotypes may explain why pockets of Acropora have been able to survive the WBD epidemic. Understanding disease resistance in these corals may be the critical link to restoring populations of these once dominant corals throughout their range.     

Seasonal and depth variation in fecundity of Acropora palifera at two reefs in Papua New Guinea

Fecundity and abundance of Acropora palifera and the abundance of other scleractinians were compared at two reefs in the Huon Gulf, Papua New Guinea. While temperature and salinity were similar at both reefs, turbidity and sedimentation were higher on one of the reefs. A negative correlation was found between fecundity of A. palifera and three factors: depth, turbidity and sedimentation rate. There was also a negative correlation between coral cover and water transparency and sedimentation. The results suggest that high rates of sedimentation and low transparency depress fecundity of A. palifera, and limit the depth distribution and reduce the abundance of this species and other scleractinians. Lower fecundity in February and March was correlated with higher water temperatures. It is suggested that coral reproduction can be used as a biological indicator of stress on coral reefs.     

More than one genotype: how common is intracolonial genetic variability in scleractinian corals?

In recent years, a few colonial marine invertebrates have shown intracolonial genetic variability, a previously unreported phenomenon. Intracolonial genetic variability describes the occurrence of more than a single genotype within an individual colony. This variability can be traced back to two underlying processes: chimerism and mosaicism. Chimerism is the fusion of two or more individuals, whereas mosaicism mostly derives from somatic cell mutations. Until now, it remained unclear to what degree the ecologically important group of hermatypic (reef building) corals might be affected. We investigate the occurrence of intracolonial genetic variability in five scleractinian corals: Acropora florida, Acropora hyacinthus, Acropora sarmentosa, Pocillopora species complex and Porites australiensis. The main focus was to test different genera for the phenomenon via microsatellite markers and to distinguish which underlying process caused the genetic heterogeneity. Our results show that intracolonial genetic variability was common (between 46.6% for A. sarmentosa and 23.8% for P. species complex) in all tested corals. The main process was mosaicism (69 cases of 222 tested colonies), but at least one chimera existed in every species. This suggests that intracolonial genetic variability is widespread in scleractinian corals and could challenge the view of a coral colony as an individual and therefore a unit of selection. However, it might also hold potential for colony survival under rapidly changing environmental conditions.     

Real-time PCR reveals a high incidence of <Emphasis Type="Italic">Symbiodinium </Emphasis>clade D at low levels in four scleractinian corals across the Great Barrier Reef: implications for symbiont shuffling

Reef corals form associations with an array of genetically and physiologically distinct endosymbionts from the genus Symbiodinium. Some corals harbor different clades of symbionts simultaneously, and over time the relative abundances of these clades may change through a process called symbiont shuffling. It is hypothesized that this process provides a mechanism for corals to respond to environmental threats such as global warming. However, only a minority of coral species have been found to harbor more than one symbiont clade simultaneously and the current view is that the potential for symbiont shuffling is limited. Using a newly developed real-time PCR assay, this paper demonstrates that previous studies have underestimated the presence of background symbionts because of the low sensitivity of the techniques used. The assay used here targets the multi-copy rDNA ITS1 region and is able to detect Symbiodinium clades C and D with >100-fold higher sensitivity compared to conventional techniques. Technical considerations relating to intragenomic variation, estimating copy number and non-symbiotic contamination are discussed. Eighty-two colonies from four common scleractinian species (Acropora millepora, Acropora tenuis, Stylophora pistillata and Turbinaria reniformis) and 11 locations on the Great Barrier Reef were tested for background Symbiodinium clades. Although these colonies had been previously identified as harboring only a single clade based on SSCP analyses, background clades were detected in 78% of the samples, indicating that the potential for symbiont shuffling may be much larger than currently thought.     

Expression of putative immune response genes during early ontogeny in the coral Acropora millepora

Background

Corals, like many other marine invertebrates, lack a mature allorecognition system in early life history stages. Indeed, in early ontogeny, when corals acquire and establish associations with various surface microbiota and dinoflagellate endosymbionts, they do not efficiently distinguish between closely and distantly related individuals from the same population. However, very little is known about the molecular components that underpin allorecognition and immunity responses or how they change through early ontogeny in corals.

Methodology/Principal Findings

Patterns in the expression of four putative immune response genes (apextrin, complement C3, and two CELIII type lectin genes) were examined in juvenile colonies of Acropora millepora throughout a six-month post-settlement period using quantitative real-time PCR (qPCR). Expression of a CELIII type lectin gene peaked in the fourth month for most of the coral juveniles sampled and was significantly higher at this time than at any other sampling time during the six months following settlement. The timing of this increase in expression levels of putative immune response genes may be linked to allorecognition maturation which occurs around this time in A.millepora. Alternatively, the increase may represent a response to immune challenges, such as would be involved in the recognition of symbionts (such as Symbiodinium spp. or bacteria) during winnowing processes as symbioses are fine-tuned.

Conclusions/Significance

Our data, although preliminary, are consistent with the hypothesis that lectins may play an important role in the maturation of allorecognition responses in corals. The co-expression of lectins with apextrin during development of coral juveniles also raises the possibility that these proteins, which are components of innate immunity in other invertebrates, may influence the innate immune systems of corals through a common pathway or system. However, further studies investigating the expression of these genes in alloimmune-challenged corals are needed to further clarify emerging evidence of a complex innate immunity system in corals.     

Acquisition of symbiotic dinoflagellates (Symbiodinium) by juveniles of the coral Acropora longicyathus

Scleractinian corals may acquire Symbiodinium from their parents (vertically) or from the environment (horizontally). In the present study, adult colonies of the coral Acropora longicyathus from One Tree Island (OTI) on the southern Great Barrier Reef (Australia) acquired two distinct varieties of symbiotic dinoflagellates (Symbiodinium) from the environment. Adult colonies had either Symbiodinium from clade C (86.7%) or clade A (5.3%), or a mixture of both clades A and C (8.0% of all colonies). In contrast, all 10-day-old juveniles were associated with Symbiodinium from clade A, while 83-day-old colonies contained clades A, C and D even though they were growing at the same location. Symbiodinium from clade A were dominant in both 10- and 83-day-old juveniles (99 and 97% of all recruits, respectively), while clade D was also found in 31% of 83-day-old juveniles. Experimental manipulation also revealed that parental association (with clade A or C), or the location within the OTI reef, did not influence which clade of symbiont was acquired by juvenile corals. The differences between the genetic identity of populations of Symbiodinium resident in juveniles and adult A. longicyathus suggest that ontogenetic changes in the symbiosis may occur during the development of scleractinian corals. Whether or not these changes are due to host selective processes or differences in the physical environment associated with juvenile versus adult colonies remains to be determined.     

Chimerism in Wild Adult Populations of the Broadcast Spawning Coral Acropora millepora on the Great Barrier Reef

Background

Chimeras are organisms containing tissues or cells of two or more genetically distinct individuals, and are known to exist in at least nine phyla of protists, plants, and animals. Although widespread and common in marine invertebrates, the extent of chimerism in wild populations of reef corals is unknown.

Methodology/Principal Findings

The extent of chimerism was explored within two populations of a common coral, Acropora millepora, on the Great Barrier Reef, Australia, by using up to 12 polymorphic DNA microsatellite loci. At least 2% and 5% of Magnetic Island and Pelorus Island populations of A. millepora, respectively, were found to be chimeras (3% overall), based on conservative estimates. A slightly less conservative estimate indicated that 5% of colonies in each population were chimeras. These values are likely to be vast underestimates of the true extent of chimerism, as our sampling protocol was restricted to a maximum of eight branches per colony, while most colonies consist of hundreds of branches. Genotypes within chimeric corals showed high relatedness, indicating that genetic similarity is a prerequisite for long-term acceptance of non-self genotypes within coral colonies.

Conclusions/Significance

While some brooding corals have been shown to form genetic chimeras in their early life history stages under experimental conditions, this study provides the first genetic evidence of the occurrence of coral chimeras in the wild and of chimerism in a broadcast spawning species. We hypothesize that chimerism is more widespread in corals than previously thought, and suggest that this has important implications for their resilience, potentially enhancing their capacity to compete for space and respond to stressors such as pathogen infection.     

The influence of repetitive thermal stresses on the dominance of reef-building Acropora spp. (Scleractinia) on coral reefs of the Maldive Islands

The distribution and size-age structure of Acropora corals were studied in two Maldivian atolls that differ in their geographic position and sea surface temperature regimes. The frequency and strength of thermal anomalies for the last 2 decades had a significant influence on the abundance, mortality rates, and age structures of acroporid communities. The long-term temperature amplitude was higher and the maxima were more pronounced in the northernmost Ihavandippolu Atoll than those in the equatorial South Huvadhoo Atoll. These differences resulted in a 10.4% mean cover of Acropora at Ihavandippolu Atoll, whereas the Acropora cover in the South Huvadhoo Atoll reached 59.5%. In the northern atoll, the coral mortality rate after the 2010 thermal anomaly was 3 times higher than that in the southern atoll. Younger acroporid colonies (up to 2 years old) dominated the northern atoll reefs, while the southern atoll showed a high proportion of older mature colonies. In both atolls, healthy table colonies of Acropora cytherea with a disk diameter greater than 2 m were observed that apparently survived three thermal anomalies since 1998. The mechanisms of acclimatization of Acropora and the prospects for its dominance in the Maldives under changing environmental conditions are discussed.     

Changes in Bleaching Susceptibility among Corals Subject to Ocean Warming and Recurrent Bleaching in Moorea,French Polynesia

Background

Climate-induced coral bleaching poses a major threat to coral reef ecosystems, mostly because of the sensitivities of key habitat-forming corals to increasing temperature. However, susceptibility to bleaching varies greatly among coral genera and there are likely to be major changes in the relative abundance of different corals, even if the wholesale loss of corals does not occur for several decades. Here we document variation in bleaching susceptibility among key genera of reef-building corals in Moorea, French Polynesia, and compare bleaching incidence during mass-bleaching events documented in 1991, 1994, 2002 and 2007.

Methodology/Principal Findings

This study compared the proportion of colonies that bleached for four major genera of reef-building corals (Acropora, Montipora, Pocillopora and Porites), during each of four well-documented bleaching events from 1991 to 2007. Acropora and Montipora consistently bleached in far greater proportions (up to 98%) than Pocillopora and Porites. However, there was an apparent and sustained decline in the proportion of colonies that bleached during successive bleaching events, especially for Acropora and Montipora. In 2007, only 77% of Acropora colonies bleached compared with 98% in 1991. Temporal variation in the proportion of coral colonies bleached may be attributable to differences in environmental conditions among years. Alternately, the sustained declines in bleaching incidence among highly susceptible corals may be indicative of acclimation or adaptation.

Conclusions/Significance

Coral genera that are highly susceptible to coral bleaching, and especially Acropora and Montipora, exhibit temporal declines in their susceptibility to thermal anomalies at Moorea, French Polynesia. One possible explanation for these findings is that gradual removal of highly susceptible genotypes (through selective mortality of individuals, populations, and/or species) is producing a coral assemblage that is more resistant to sustained and ongoing ocean warming.     

Growth Dynamics of the Threatened Caribbean Staghorn Coral Acropora cervicornis: Influence of Host Genotype,Symbiont Identity,Colony Size,and Environmental Setting

Background

The drastic decline in the abundance of Caribbean acroporid corals (Acropora cervicornis, A. palmata) has prompted the listing of this genus as threatened as well as the development of a regional propagation and restoration program. Using in situ underwater nurseries, we documented the influence of coral genotype and symbiont identity, colony size, and propagation method on the growth and branching patterns of staghorn corals in Florida and the Dominican Republic.

Methodology/Principal Findings

Individual tracking of> 1700 nursery-grown staghorn fragments and colonies from 37 distinct genotypes (identified using microsatellites) in Florida and the Dominican Republic revealed a significant positive relationship between size and growth, but a decreasing rate of productivity with increasing size. Pruning vigor (enhanced growth after fragmentation) was documented even in colonies that lost 95% of their coral tissue/skeleton, indicating that high productivity can be maintained within nurseries by sequentially fragmenting corals. A significant effect of coral genotype was documented for corals grown in a common-garden setting, with fast-growing genotypes growing up to an order of magnitude faster than slow-growing genotypes. Algal-symbiont identity established using qPCR techniques showed that clade A (likely Symbiodinium A3) was the dominant symbiont type for all coral genotypes, except for one coral genotype in the DR and two in Florida that were dominated by clade C, with A- and C-dominated genotypes having similar growth rates.

Conclusion/Significance

The threatened Caribbean staghorn coral is capable of extremely fast growth, with annual productivity rates exceeding 5 cm of new coral produced for every cm of existing coral. This species benefits from high fragment survivorship coupled by the pruning vigor experienced by the parent colonies after fragmentation. These life-history characteristics make A. cervicornis a successful candidate nursery species and provide optimism for the potential role that active propagation can play in the recovery of this keystone species.     

Host Coenzyme Q Redox State Is an Early Biomarker of Thermal Stress in the Coral Acropora millepora

Bleaching episodes caused by increasing seawater temperatures may induce mass coral mortality and are regarded as one of the biggest threats to coral reef ecosystems worldwide. The current consensus is that this phenomenon results from enhanced production of harmful reactive oxygen species (ROS) that disrupt the symbiosis between corals and their endosymbiotic dinoflagellates, Symbiodinium. Here, the responses of two important antioxidant defence components, the host coenzyme Q (CoQ) and symbiont plastoquinone (PQ) pools, are investigated for the first time in colonies of the scleractinian coral, Acropora millepora, during experimentally-induced bleaching under ecologically relevant conditions. Liquid chromatography-mass spectrometry (LC-MS) was used to quantify the states of these two pools, together with physiological parameters assessing the general state of the symbiosis (including photosystem II photochemical efficiency, chlorophyll concentration and Symbiodinium cell densities). The results show that the responses of the two antioxidant systems occur on different timescales: (i) the redox state of the Symbiodinium PQ pool remained stable until twelve days into the experiment, after which there was an abrupt oxidative shift; (ii) by contrast, an oxidative shift of approximately 10% had occurred in the host CoQ pool after 6 days of thermal stress, prior to significant changes in any other physiological parameter measured. Host CoQ pool oxidation is thus an early biomarker of thermal stress in corals, and this antioxidant pool is likely to play a key role in quenching thermally-induced ROS in the coral-algal symbiosis. This study adds to a growing body of work that indicates host cellular responses may precede the bleaching process and symbiont dysfunction.     

Coral transplantation as an aid to reef rehabilitation: evaluation of a case study in the Maldive Islands

As part of a study of reef rehabilitation, whole coral colonies (primarily Acropora, Pocillopora, Porites, Eavia and Favites) were transplanted and cemented in place onto three approximately 20 m² areas of Armorflex concrete mats on a 0.8–1.5 m deep reef-flat in the Maldives which had been severely degraded by coral mining. Growth, in situ mortality, and losses from mats due to wave action of a total of 530 transplants were monitored over 28 months. Natural recruitment of corals to both the transplanted Armorflex areas and concrete mats without transplants was also studied. Overall survivorship of corals 28 moths after transplantation was 51%. Most losses of transplants due to wave action occurred during the first 7 months when 25% were lost, with only a further 5% of colonies being lost subsequently. Within 16 months most colonies had accreted naturally to the concretemats. Thirty-two percent of transplants which remained attached died with Acropora hyacinthus and Pocillopora perrucosa having the highest mortality rates (approx. 50% nortality over two years) and Porites lobata and P. lutea the lowest (2.8 and 8.1% mortality respectively over two years). Growth rates were very variable with a quarter to a third of transplants showing negative growth during each inter-survey period. Acropora hyacinthus, A. cytherea and A. divaricata transplants had the highest growth rates (colony mean linear radial extension 4.15–5.81 cm y^-1), followed by Pocillopora verrucosa (mean 2.51 cm y^-1). Faviids and poritids had lowest growth rates. Favia and Favites showed the poorest response to transplantation whilst Acropora divaricata, which combined a high growth rate with relatively low mortality, appeared particularly amenable to transplantation. Natural recruitment did not differ significantly between concrete mats with and without transplanted corals. Visible recruits wer first recorded 10 months after emplacement of the mats and were predominantly Acropora and Pocillopora. On near vertical surfaces their density was almost 18 m^-2. Recruits grew fast producing many 20–30 cm diameter colonies on the mats within 3.5 years. Growth and survival of transplants are compared with results of transplantation studies in other locations. We conclude: (1) species transplanted should be selected with care as certain species are significantly more amenable than others to transplantation, (2) the choice of whether fragments or whole colonies are transplanted may profoundly influence survival, (3) considerable loss of transplants is likely from higher energy sites whatever method of attachment, (4) transplantation should, in general, be undertaken only if recovery following natural recruitment is unlikely.     

Effects of corallivory and coral colony density on coral growth and survival

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.