Acropora Hyacinthus Research Articles

UV-absorbing bacteria in coral mucus and their response to simulated temperature elevations

Reef-building corals encompass various strategies to defend against harmful ultraviolet (UV) radiation. Coral mucus contains UV-absorbing compounds and has rich prokaryotic diversity associated with it. In this study, we isolated and characterized the UV-absorbing bacteria from the mucus of the corals Porites lutea and Acropora hyacinthus during the pre-summer and summer seasons. A total of 17 UV-absorbing bacteria were isolated and sequenced. The UV-absorbing bacteria showed UV absorption at wavelengths ranging from λ max = 333 nm to λ min = 208 nm. Analysis of the DNA sequences revealed that the majority of the UV-absorbing bacteria belonged to the family Firmicutes and the remaining belonged to the family Proteobacteria (class Gammaproteobacteria). Comparison of the sequences with the curated database yielded four distinct bacterial groups belonging to the genus Bacillus, Staphylococcus, Salinicoccus and Vibrio. The absorption peaks for the UV-absorbing bacteria shifted to the UV-A range (320–400 nm) when they were incubated at higher temperatures. Deciphering the complex relationship between corals and their associated bacteria will help us to understand their adaptive strategies to various stresses.

Genetic variations within Symbiodinium clade C among zooxanthellate corals (Scleractinia) in the temperate zone of Japan

In a recent study most of the temperate-living corals were found to harbor stress-sensitive Symbiodinium clade C, which is common in the tropical zone. In this study, we investigated the genetic variations within Symbiodinium clade C among corals living in temperate waters of Japan (17 genera; 26 species) using rDNA internal transcribed spacers (ITSs) to clarify the genetic differences between climatic zones. We also focused on two widespread coral species, Acropora hyacinthus and Pocillopora damicornis, to compare the genetic differences of Symbiodinium clade C between subtropical and temperate regions. We found multiple haplotypes of Symbiodinium ITSs in clade C, which formed nine subclades. Our data indicate that five genera (Acropora, Cyphastrea, Stylocoeniella, Porites, Pocillopora) contained host-specific Symbiodinium, while members of the family Faviidae and others contained several Symbiodinium ITS haplotypes from two or three subclades. A comparative analysis using Acropora and Pocillopora also revealed that the temperate zone coral population formed a single subclade of Symbiodinium clade C that was genetically isolated from those of subtropical populations. In summary, the majority of corals living in temperate waters of Japan, such as faviid corals, have several ITS haplotypes which possibly are utilized as an opportunistic survival strategy under severe environmental conditions, whereas Acropora and Pocillopora at the very least harbor temperate zone-specific Symbiodinium.

Coverage, Diversity, and Functionality of a High-Latitude Coral Community (Tatsukushi, Shikoku Island, Japan)

BackgroundSeawater temperature is the main factor restricting shallow-water zooxanthellate coral reefs to low latitudes. As temperatures increase, coral species and perhaps reefs may move into higher-latitude waters, increasing the chances of coral reef ecosystems surviving despite global warming. However, there is a growing need to understand the structure of these high-latitude coral communities in order to analyze their future dynamics and to detect any potential changes.Methodology/Principal FindingsThe high-latitude (32.75°N) community surveyed was located at Tatsukushi, Shikoku Island, Japan. Coral cover was 60±2% and was composed of 73 scleractinian species partitioned into 7 functional groups. Although only 6% of species belonged to the ‘plate-like’ functional group, it was the major contributor to species coverage. This was explained by the dominance of plate-like species such as Acropora hyacinthus and A. solitaryensis. Comparison with historical data suggests a relatively recent colonization/development of A. hyacinthus in this region and a potential increase in coral diversity over the last century. Low coverage of macroalgae (2% of the benthic cover) contrasted with the low abundance of herbivorous fishes, but may be reasonably explained by the high density of sea urchins (12.9±3.3 individuals m−2).Conclusions/SignificanceThe structure and composition of this benthic community are relatively remarkable for a site where winter temperature can durably fall below the accepted limit for coral reef development. Despite limited functionalities and functional redundancy, the current benthic structure might provide a base upon which a reef could eventually develop, as characterized by opportunistic and pioneer frame-building species. In addition to increasing seawater temperatures, on-going management actions and sea urchin density might also explain the observed state of this community. A focus on such ‘marginal’ communities should be a priority, as they can provide important insights into how tropical corals might cope with environmental changes.

Calcification, Storm Damage and Population Resilience of Tabular Corals under Climate Change

Two facets of climate change–increased tropical storm intensity and ocean acidification–are expected to detrimentally affect reef-building organisms by increasing their mortality rates and decreasing their calcification rates. Our current understanding of these effects is largely based on individual organisms’ short-term responses to experimental manipulations. However, predicting the ecologically-relevant effects of climate change requires understanding the long-term demographic implications of these organism-level responses. In this study, we investigate how storm intensity and calcification rate interact to affect population dynamics of the table coral Acropora hyacinthus, a dominant and geographically widespread ecosystem engineer on wave-exposed Indo-Pacific reefs. We develop a mechanistic framework based on the responses of individual-level demographic rates to changes in the physical and chemical environment, using a size-structured population model that enables us to rigorously incorporate uncertainty. We find that table coral populations are vulnerable to future collapse, placing in jeopardy many other reef organisms that are dependent upon them for shelter and food. Resistance to collapse is largely insensitive to predicted changes in storm intensity, but is highly dependent on the extent to which calcification influences both the mechanical properties of reef substrate and the colony-level trade-off between growth rate and skeletal strength. This study provides the first rigorous quantitative accounting of the demographic implications of the effects of ocean acidification and changes in storm intensity, and provides a template for further studies of climate-induced shifts in ecosystems, including coral reefs.

Annual Variation in the Timing of Coral Spawning in a High-Latitude Environment: Influence of Temperature

This study was conducted at a high-latitude location (32°N; Kochi, Japan), where annual seawater temperatures show large fluctuations due to the meandering of the Kuroshio Current, providing a unique opportunity to examine the influence of temperature on coral reproduction. Annual spawning of individual colonies of four reef coral species-two Acropora species (Acropora hyacinthus and A. japonica) and two faviid species (Favites pentagona and Platygyra contorta)-was monitored in situ for 4 years in 2006-2009. The spawning of the four species always occurred around the last quarter moon in the local summer, July or August, irrespective of high annual variations in seawater temperatures (from 23.7 to 29.5 °C) and weather during the spawning period. However, the exact timing of spawning during the spawning period varied among the years and was correlated with the cumulative seawater temperature during the late period of gametogenesis (0-3 months before spawning). When seawater temperatures were higher, spawning occurred in the earlier spawning month (July) and vice versa, except in A. hyacinthus, which always spawned in July. In the case of the two Acropora species, higher (lower) temperatures led to spawning earlier (later) in the lunar cycle. Seawater temperature may have an influence on gametogenesis, causing the shift in spawning timing.

BIOPHYSICS, BIOENERGETICS AND MECHANISTIC APPROACHES TO ECOLOGY

Biophysics – the study of how the structure of individual plants and animals contributes to their function – has rarely been considered on the ecological scale. However, Mark Denny from Stanford University, USA, has a broader vision. Because the mechanisms that underpin individual performance

Holocene key coral species in the Northwest Pacific: indicators of reef formation and reef ecosystem responses to global climate change and anthropogenic stresses in the near future

The geological record of key coral species that contribute to reef formation and maintenance of reef ecosystems is important for understanding the ecosystem response to global-scale climate change and anthropogenic stresses in the near future. Future responses can be predicted from accumulated data on Holocene reef species identified in drillcore and from data on raised reef terraces. The present study analyzes a dataset based on 27 drillcores, raised reef terraces, and 134 radiocarbon and U–Th ages from reefs of the Northwest Pacific, with the aim of examining the role of key coral species in reef growth and maintenance for reef ecosystem during Holocene sea-level change. The results indicate a latitudinal change in key coral species: arborescent Acropora (Acropora intermedia and Acropora muricata) was the dominant reef builder at reef crests in the tropics, whereas Porites (Porites australiensis, Porites lutea, and Porites lobata) was the dominant contributor to reef growth in the subtropics between 10,000 and 7000 cal. years BP (when the rate of sea-level rise was 10 m/ka). Acropora digitifera, Acropora hyacinthus, Acropora robusta/A. abrotanoides, Isopora palifera, Favia stelligera, and Goniastrea retiformis from the corymbose and tabular Acropora facies were the main key coral species at reef crests between 7000 and 5000 cal. years BP (when the rate of sea-level rise was 5 m/ka) and during the following period of stable sea-level. Massive Porites (P. australiensis, P. lutea, and P. lobata) contributed to reef growth in shallow lagoons during the period of stable sea level. Key coral species from the corymbose and tabular Acropora facies have the potential to build reefs and maintain ecosystems in the near future under a global sea-level rise of 2–6 m/ka, as do key coral species from the arborescent Acropora facies and massive Porites facies, which show vigorous growth and are tolerant to relatively deep-water, low-energy environments. However, these species are likely to experience severe mortality in upcoming decades due to natural and anthropogenic stresses. Consequently, this damage will lead to a collapse in reef formation and the maintenance of reef ecosystems in the near future. This study emphasizes the need for research into the conservation of key coral species.

Protein evolution in two co-occurring types of Symbiodinium: an exploration into the genetic basis of thermal tolerance in Symbiodinium clade D

BackgroundThe symbiosis between reef-building corals and photosynthetic dinoflagellates (Symbiodinium) is an integral part of the coral reef ecosystem, as corals are dependent on Symbiodinium for the majority of their energy needs. However, this partnership is increasingly at risk due to changing climatic conditions. It is thought that functional diversity within Symbiodinium may allow some corals to rapidly adapt to different environments by changing the type of Symbiodinium with which they partner; however, very little is known about the molecular basis of the functional differences among symbiont groups. One group of Symbiodinium that is hypothesized to be important for the future of reefs is clade D, which, in general, seems to provide the coral holobiont (i.e., coral host and associated symbiont community) with elevated thermal tolerance. Using high-throughput sequencing data from field-collected corals we assembled, de novo, draft transcriptomes for Symbiodinium clades C and D. We then explore the functional basis of thermal tolerance in clade D by comparing rates of coding sequence evolution among the four clades of Symbiodinium most commonly found in reef-building corals (A-D).ResultsWe are able to highlight a number of genes and functional categories as candidates for involvement in the increased thermal tolerance of clade D. These include a fatty acid desaturase, molecular chaperones and proteins involved in photosynthesis and the thylakoid membrane. We also demonstrate that clades C and D co-occur within most of the sampled colonies of Acropora hyacinthus, suggesting widespread potential for this coral species to acclimatize to changing thermal conditions via ‘shuffling’ the proportions of these two clades from within their current symbiont communities.ConclusionsTranscriptome-wide analysis confirms that the four main Symbiodinium clades found within corals exhibit extensive evolutionary divergence (18.5-27.3% avg. pairwise nucleotide difference). Despite these evolutionary distinctions, many corals appear to host multiple clades simultaneously, which may allow for rapid acclimatization to changing environmental conditions. This study provides a first step toward understanding the molecular basis of functional differences between Symbiodinium clades by highlighting a number of genes with signatures consistent with positive selection along the thermally tolerant clade D lineage.

Coral-associated marine fungi form novel lineages and heterogeneous assemblages

Coral stress tolerance is intricately tied to the animal's association with microbial symbionts. The most well-known of these symbioses is that between corals and their dinoflagellate photobionts (Symbiodinium spp.), whose genotype indirectly affects whether a coral can survive cyclical and anthropogenic warming events. Fungi comprise a lesser-known coral symbiotic community whose taxonomy, stability and function is largely un-examined. To assess how fungal communities inside a coral host correlate with water temperature and the genotype of co-occurring Symbiodinium, we sampled Acropora hyacinthus coral colonies from adjacent natural pools with different water temperatures and Symbiodinium identities. Phylogenetic analysis of coral-associated fungal ribosomal DNA amplicons showed a high diversity of Basidiomycetes and Ascomycetes, including several clades separated from known fungal taxa by long and well-supported branches. Community similarity did not correlate with any measured variables, and total fungal community composition was highly variable among A. hyacinthus coral colonies. Colonies in the warmer pool contained more phylogenetically diverse fungal communities than the colder pool and contained statistically significant 'indicator' species. Four taxa were present in all coral colonies sampled, and may represent obligate associates. Messenger RNA sequenced from a subset of these same colonies contained an abundance of transcripts involved in metabolism of complex biological molecules. Coincidence between the taxonomic diversity found in the DNA and RNA analysis indicates a metabolically active and diverse resident marine fungal community.

Vertical distribution and settlement competencies in broadcast spawning coral larvae: Implications for dispersal models

Successful larval dispersal between coral reef populations is one of the key determinants of coral reef connectivity. Dispersal patterns are generally predicted using hydrodynamic models, but these are frequently constrained by a lack of information on larval biology. This study examines some of the life history traits that may affect coral larval transport and hence be useful for dispersal models, in particular their settlement competency periods and vertical distribution in the water column, which we hypothesized would occur synchronously. The settlement competencies of the larvae of two species of broadcast spawning scleractinian corals, Pectinia lactuca and Platygyra sinensis were followed for up to 16 d. Larvae of both species were able to settle within the first 2 d after the spawning event. Peak settlement of P. lactuca larvae was shortly after day three post-fertilization with 71.6 ± 4.8% of live larvae being able to settle, while peak settlement of P. sinensis larvae was delayed till the sixth day with 85.1 ± 4.0% of live larvae settling. Given their later peak settlement and extended settlement window, larvae of P. sinensis potentially have a larger dispersal potential than P. lactuca, which is consistent with the geographical ranges of the two species. Changes in the daytime depth distribution of larvae of three species of broadcast spawning scleractinian corals, P. lactuca, P. sinensis, and Acropora hyacinthus were followed using water-filled 2 m vertical tubes. A downward shift over time in the vertical distribution of all three species was observed, which could affect larval transport patterns due to the possible stratification of horizontal currents. Sinking rate, however, was not necessarily consistent with their peak settlement competency periods. Such inconsistencies between settlement and sinking suggest that larvae may not settle even when they are capable of doing so due to their vertical distribution in the water column. This has implications for dispersal models which traditionally rely on settlement competencies, as larval vertical position may alter the timing of settlement.

Recolonisation of Acropora hyacinthus following climate-induced coral bleaching on the Great Barrier Reef

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 438:97-104 (2011) - DOI: https://doi.org/10.3354/meps09272 Recolonisation of Acropora hyacinthus following climate-induced coral bleaching on the Great Barrier Reef C. Linares1,2,*, M. S. Pratchett2, D. J. Coker2 1Departament d’Ecologia, Facultat de Biologia, Universitat de Barcelona, Avda. Diagonal 645, 08028 Barcelona, Spain 2ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Queensland 4811, Australia *Email: cristinalinares@ub.edu ABSTRACT: Given projected increases in the frequency and/or severity of climatic disturbances, the persistence of corals may be more a function of their capacity for regeneration than resistance to such episodic disturbances. If so, climate change may favour those corals that regenerate fastest following acute disturbance. The tabular coral Acropora hyacinthus is fast-growing and typically dominates shallow wave-exposed habitats on the Great Barrier Reef, but it is extremely vulnerable to climate-induced coral bleaching and other disturbances (e.g. cyclones and outbreaks of crown-of-thorns starfish). The present study explores temporal changes in percentage cover and size structure of A. hyacinthus on reefs affected by the 2001−2002 bleaching event. Annual surveys conducted at 3 mid-shelf reefs from 2008 to 2010 revealed rapid, but very patchy, recovery of A. hyacinthus. Following extensive coral loss, local cover of A. hyacinthus increased due to growth of established colonies as well as addition and subsequent growth of new colonies. At one reef, recovery was mostly due to increased abundance of small colonies, assumed to have recruited since the bleaching, whereas recovery at the 2 other study reefs (<5 km away) was the sustained growth of established colonies. These results show that resilience of A. hyacinthus populations may be due to either recolonisation or ­persistence, but that, either way, these corals are well suited to rapid recovery following acute ­disturbance. KEY WORDS: Bleaching · Climate change · Coral reefs · Disturbance · Recovery · Resilience Full text in pdf format PreviousNextCite this article as: Linares C, Pratchett MS, Coker DJ (2011) Recolonisation of Acropora hyacinthus following climate-induced coral bleaching on the Great Barrier Reef. Mar Ecol Prog Ser 438:97-104. https://doi.org/10.3354/meps09272 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 438. Online publication date: October 05, 2011 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2011 Inter-Research.

How Quickly do Fragments of Coral “Self‐Attach” after Transplantation?

Transplantation of coral fragments is seen as a potential method to rapidly restore coral cover to areas of degraded reef; however, considerable research is still needed to assess the effectiveness of coral transplantation as a viable reef restoration tool. Initially, during restoration efforts, coral transplants are attached artificially. Self‐attachment (i.e., growth of coral tissue onto the substrate) provides a more secure and lasting bond, thus knowledge about self‐attachment times for corals is of importance to reef restoration. While it is known that coral fragments may generate new tissue and bond to substrata within a few weeks of transplantation, surprisingly little is known about the speed of self‐attachment for most species. Two independent experiments were carried out to examine the self‐attachment times of 12 scleractinian and one non‐scleractinian coral species to a natural calcium carbonate substrate. The first experiment examined times to self‐attachment in 11 species of differing morphologies from seven families over approximately 7 months, whereas the second experiment examined three fast‐attaching Acropora species over approximately 1 month. In the first experiment, the branching species Acropora muricata had a significantly faster self‐attachment time compared to all other species, while Echinopora lamellosa had the slowest self‐attachment time. For the second experiment, A. muricata was significantly slower to self‐attach than Acropora hyacinthus (tabular) and Acropora digitifera (corymbose‐digitate). The results suggest that a combination of factors including growth rates, growth form and life history may determine how quickly fragments of coral species self‐attach after fragmentation and transplantation.

Do fluctuating temperature environments elevate coral thermal tolerance?

In reef corals, much research has focused on the capacity of corals to acclimatize and/or adapt to different thermal environments, but the majority of work has focused on distinctions in mean temperature. Across small spatial scales, distinctions in daily temperature variation are common, but the role of such environmental variation in setting coral thermal tolerances has received little attention. Here, we take advantage of back-reef pools in American Samoa that differ in thermal variation to investigate the effects of thermally fluctuating environments on coral thermal tolerance. We experimentally heat-stressed Acropora hyacinthus from a thermally moderate lagoon pool (temp range 26.5–33.3°C) and from a more thermally variable pool that naturally experiences 2–3 h high temperature events during summer low tides (temp range 25.0–35°C). We compared mortality and photosystem II photochemical efficiency of colony fragments exposed to ambient temperatures (median: 28.0°C) or elevated temperatures (median: 31.5°C). In the heated treatment, moderate pool corals showed nearly 50% mortality whether they hosted heat-sensitive (49.2 ± 6.5% SE; C2) or heat-resistant (47.0 ± 11.2% SE; D) symbionts. However, variable pool corals, all of which hosted heat-resistant symbionts, survived well, showing low mortalities (16.6 ± 8.8% SE) statistically indistinguishable from controls held at ambient temperatures (5.1–8.3 ± 3.3–8.3% SE). Similarly, moderate pool corals hosting heat-sensitive algae showed rapid rates of decline in algal photosystem II photochemical efficiency in the elevated temperature treatment (slope = −0.04 day−1 ± 0.007 SE); moderate pool corals hosting heat-resistant algae showed intermediate levels of decline (slope = −0.039 day−1 ± 0.007 SE); and variable pool corals hosting heat-resistant algae showed the least decline (slope = −0.028 day−1 ± 0.004 SE). High gene flow among pools suggests that these differences probably reflect coral acclimatization not local genetic adaptation. Our results suggest that previous exposure to an environmentally variable microhabitat adds substantially to coral–algal thermal tolerance, beyond that provided by heat-resistant symbionts alone.

Survival Dynamics of Reef Coral Larvae With Special Consideration of Larval Size and the Genus Acropora

Temporal dynamics of larval survival were examined in vitro in four broadcast-spawning reef coral species, Acropora hyacinthus, A. japonica, A. solitaryensis, and Goniastrea pectinata. Larval size was treated as an important characteristic that may relate to larval lifespan. Two patterns were observed in larval survival dynamics between the three Acropora species (mean initial larval size; 0.05-0.08 mm(3)) and G. pectinata (0.02 mm(3)), based on the timing of a sharp drop in larval survival rates (ca. > 50% reduction over a 1-2 week period). Consequently, the majority of larvae of the three Acropora species had a lifespan of less than 2-3 weeks, whereas those of G. pectinata were extended a further 2-3 weeks despite the smaller larval size. No significant relationship was detected between the initial larval size and larval lifespan in any of the four reef coral species. These results suggest that (1) larval dispersal of spawning Acropora species may be on a more local scale than that of G. pectinata and most other reef coral species previously reported, and (2) larval size is not a good estimator of larval lifespan in reef coral species.

Inter-specific variation in susceptibility to grazing among common reef corals

Many species of reef fishes, such as butterflyfishes and wrasses, feed almost continuously and at very high rates upon reef-building corals. This study quantified grazing rates on 4 common reef corals (Acropora hyacinthus, A. millepora, Pocillopora damicornis, and massive Porites) to assess the variation in susceptibility to coral predation. We also assessed the variation in predation intensity within A. hyacinthus and A. millepora by standardising grazing rates by colony surface. Rates of grazing on individual colonies were lowest (0.95 ± 0.33 bites per 20 min; mean ± SE) for massive Porites and highest (16.75 ± 0.30 bites per 20 min) for A. hyacinthus. Within coral species, grazing rates showed a linear increase with increasing size of the colony; however, the intensity of predation showed a negative relationship with increasing colony size. Predation intensity was highest for small to medium sized colonies with a peak intensity of 1.13 ± 0.17 and 0.56 ± 0.09 bites per 100 cm2 per 20 min per colony for for A. hyacinthus and A. millepora colonies (200 to 600 cm2), respectively. In contrast, predation intensity was lowest for both very small and very large colonies, with very small colonies (<200 cm2) rarely being consumed by corallivorous fishes.

Exaptation in corals to high seawater temperatures: Low concentrations of apoptotic and necrotic cells in host coral tissue under bleaching conditions

Scleractinian corals are known to suffer bleaching or loss of their symbiotic zooxanthellae under conditions of elevated seawater temperatures often associated with climate change (i.e. global warming). This can occur on a massive scale and has caused the decimation of reefs on a global basis. During the bleaching process, the expelled zooxanthellae suffer cell damage from heat stress, characterized by irreversible ultrastructural and physiological changes which are symptomatic of cell degeneration and death (called apoptosis) or necrosis. A question that remains unanswered, however, is whether the coral hosts themselves are sensitive to seawater temperatures, and, if so, to what degree? In a controlled experiment, we exposed corals Acropora hyacinthus (Dana, 1846) and Porites solida (Forskål, 1775) with their symbiotic zooxanthellae ( Symbiodinium sp.) to temperatures of 28 °C (control), 30 °C, 32 °C, and 34 °C for 48 h and also to 36 °C for 12 h. We assessed coral and zooxanthellar cells in-situ for symptoms of apoptosis and necrosis using transmission electron microscopy (TEM), fluorescent microscopy (FM), and flow cytometry (FC). We found that the coral host cells in-situ exhibited, for the most part, little or no mortality from increased seawater temperatures. Damage to the coral hosts only occurred under conditions of prolonged exposure (≥ 12 h) at high temperatures (34 °C), or at exceptionally high temperatures (e.g. 36 °C). On the other hand, we found high levels of apoptosis and necrosis in the zooxanthellae in-situ under all treatment conditions of elevated seawater temperatures. We found that during bleaching, the host cells are not experiencing much mortality – but the zooxanthellae, even while still within the host, are. The host corals exhibit exaptation to accommodate temperatures as high as ≥ 34 °C. Temperature stress within these highly specific and coevolved symbiotic systems is derived not from host sensitivity to temperature, but from the symbiont's sensitivity and the loss of the coral's endosymbiotic partners.

Holocene coral reef development under windward and leeward locations at Ishigaki Island, Ryukyu Islands, Japan

Coral reef growth is largely controlled by the wave energy associated with ocean swells and local winds. This growth has responded to changes in wave conditions that evolved in concert with Holocene sea-level changes. We analyzed Holocene facies of the Ibaruma and Fukido reefs of Ishigaki Island, southern Ryukyu Islands, in the context of temporal and spatial changes in wave conditions by comparing present-day coral assemblages and internal (fossil) reef facies. Four major coral assemblages that developed under different wave-energy conditions were recognized. Six cores recorded a Holocene reef sequence consisting of four sedimentary facies that differed in the relative volumes of four coral taxa: Acropora digitifera and Acropora hyacinthus, and lesser amounts of Favia stelligera and Montastrea curta. Holocene windward reef growth began at 7820 cal. years BP after flooding of the Pleistocene reef limestone surface; the ensuing reef growth kept up with the rapid sea-level rise. A vertical growth rate of 7.5 m/1000 years during reef nucleation and early growth stages decreased to 3.5 m/1000 years during the main stage of reef framework development. The uppermost part of the windward reef consisted of a very robust framework, unlike the open framework of the leeward reef. Ages indicated that the uppermost leeward reef was ca. 3000 years younger than the uppermost windward reef. These variations in facies development and timing were caused by differences in local wind-driven wave conditions.

Trade-offs associated with dietary specialization in corallivorous butterflyfishes (Chaetodontidae: Chaetodon)

Increasing dietary specialization is an inherently risky strategy because it increases a species’ vulnerability to resource depletion. However, risks associated with dietary specialization may be offset by increased performance when feeding on preferred prey. Although rarely demonstrated, highly specialized species are expected to outperform generalists when feeding on their preferred prey, whereas generalists are predicted to have more similar performance across a range of different prey. To test this theory, we compared the growth rates of two obligate coral-feeding butterflyfishes (Chaetodon trifascialis and Chaetodon plebeius) maintained on exclusive diets of preferred vs nonpreferred prey. In the field, C. trifascialis was the most specialized species, feeding almost exclusively on just one coral species, Acropora hyacinthus. C. plebeius meanwhile, was much less specialized, but fed predominantly on Pocillopora damicornis. During growth experiments, C. trifascialis grew fastest when feeding on A. hyacinthus and did not grow at all when feeding on less preferred prey (P. damicornis and Porites cylindrica). C. plebeius performed equally well on both A. hyacinthus and P. damicornis (its preferred prey), but performed poorly when feeding on P. cylindrica. Both butterflyfishes select coral species that maximize juvenile growth, but contrary to expectations, the more specialized species (C. trifascialis) did not outperform the generalist species (C. plebeius) when both consumed their preferred prey. Increased dietary specialization, therefore, appears to be a questionable strategy, as there was no evidence of any increased benefits to offset increases in susceptibility to disturbance.

Decadal trends in a coral community and evidence of changed disturbance regime

A 23 year data set (1981–2003 inclusive) and the spatially explicit individual-based model “Compete©” were used to investigate the implications of changing disturbance frequency on cover and taxonomic composition of a shallow coral community at Lizard Island, Australia. Near-vertical in situ stereo-photography was used to estimate rates of coral growth, mortality, recruitment and outcomes of pair-wise competitive interactions for 17 physiognomic groups of hard and soft corals. These data were used to parameterise the model, and to quantify impacts of three acute disturbance events that caused significant coral mortality: 1982—a combination of coral bleaching and Crown-of-Thorns starfish; 1990—cyclone waves; and 1996—Crown-of-Thorns starfish. Predicted coral community trajectories were not sensitive to the outcomes of competitive interactions (probably because average coral cover was only 32% and there was strong vertical separation among established corals) or to major changes in recruitment rates. The model trajectory of coral cover matched the observed trajectory accurately until the 1996 disturbance, but only if all coral mortality was confined to the 3 years of acute disturbance. Beyond that date (1997–2003), when the observed community failed to recover, it was necessary to introduce annual chronic background mortality to obtain a good match between modelled and observed coral cover. This qualitative switch in the model may reflect actual loss of resilience in the real community. Simulated over a century, an 8 year disturbance frequency most closely reproduced the mean community composition observed in the field prior to major disturbance events. Shorter intervals between disturbances led to reduced presence of the dominant hard coral groups, and a gradual increase in the slow growing, more resilient soft corals, while longer intervals (up to 16 years) resulted in monopolization by the fastest growing table coral, Acropora hyacinthus.

Feeding Preferences of Acanthaster planci (Echinodermata: Asteroidea) under Controlled Conditions of Food Availability

Feeding preferences of the crown-of-thorns sea star, Acanthaster planci (L.), were studied in a series of laboratory-based feeding trials wherein sea stars were provided with equal availability of six different coral species. The order in which corals were consumed was then used to ascertain feeding preferences. Crown-of-thorns sea stars exhibited strong and consistent feeding preferences across replicate feeding trials. The most readily eaten coral species was Acropora hyacinthus, followed by A. gemmifera, A. nasuta, A. formosa, Stylophora pistillata, Montipora undata, and Pocillopora damicornis. Crown-of-thorns sea stars also consumed Goniopora lobata, Fungia fungites, Goniastrea retiformes, and Pavona cactus but only after all Acropora and Montipora (Family Acroporidae) as well as Pocillopora and Stylophora (Family Pocilloporidae) were eaten. The least preferred corals were Favites abidita, Porites lobata, Symphyllia recta, Echinopora horrida, and Porites cylindrica. Of these, P. cylindrica was never eaten in any of the feeding trials in which it was offered. Observed feeding preferences substantiate findings from previous studies, where corals from the families Acroporidae and Pocilloporidae were preferred over all other corals. Further research is required to assess the underlying basis of feeding preferences of A. planci, but this study confirms that these starfish readily distinguish between different corals and have innate preferences for certain species. Still, most corals were eventually consumed, showing that when food is limited (during population outbreaks) A. planci is likely to consume virtually all different coral species, causing extreme devastation to coral reef ecosystems.