Seriatopora Hystrix Research Articles

Symbiodinium Genotypic and Environmental Controls on Lipids in Reef Building Corals

BackgroundLipids in reef building corals can be divided into two classes; non-polar storage lipids, e.g. wax esters and triglycerides, and polar structural lipids, e.g. phospholipids and cholesterol. Differences among algal endosymbiont types are known to have important influences on processes including growth and the photobiology of scleractinian corals yet very little is known about the role of symbiont types on lipid energy reserves.Methodology/Principal FindingsThe ratio of storage lipid and structural lipid fractions of Scott Reef corals were determined by thin layer chromatography. The lipid fraction ratio varied with depth and depended on symbiont type harboured by two corals (Seriatopora hystrix and Pachyseris speciosa). S. hystrix colonies associated with Symbiodinium C1 or C1/C# at deep depths (>23 m) had lower lipid fraction ratios (i.e. approximately equal parts of storage and structural lipids) than those with Symbiodinium D1 in shallow depths (<23 m), which had higher lipid fraction ratios (i.e. approximately double amounts of storage relative to structural lipid). Further, there was a non-linear relationship between the lipid fraction ratio and depth for S. hystrix with a modal peak at ∼23 m coinciding with the same depth as the shift from clade D to C types. In contrast, the proportional relationship between the lipid fraction ratio and depth for P. speciosa, which exhibited high specificity for Symbiodinium C3 like across the depth gradient, was indicative of greater amounts of storage lipids contained in the deep colonies.Conclusions/SignificanceThis study has demonstrated that Symbiodinium exert significant controls over the quality of coral energy reserves over a large-scale depth gradient. We conclude that the competitive advantages and metabolic costs that arise from flexible associations with divergent symbiont types are offset by energetic trade-offs for the coral host.

The role of deep reefs in shallow reef recovery: an assessment of vertical connectivity in a brooding coral from west and east Australia

Approximately one quarter of zooxanthellate coral species have a depth distribution from shallow waters (<30 m) down to mesophotic depths of 30-60 m. The deeper populations of such species are less likely to be affected by certain environmental perturbations, including high temperature/high irradiance causing coral bleaching. This has led to the hypothesis that deep populations may serve as refuges and a source of recruits for shallow reef habitats. The extent of vertical connectivity of reef coral species, however, is largely unquantified. Using 10 coral host microsatellite loci and sequences of the host mtDNA putative control region, as well as ribosomal DNA (rDNA) ITS2 sequences of the coral's algal endosymbionts (Symbiodinium), we examine population structure, connectivity and symbiont specificity in the brooding coral Seriatopora hystrix across a depth profile in both northwest (Scott Reef) and northeast Australia (Yonge Reef). Strong genetic structuring over depth was observed in both regions based on the microsatellite loci; however, Yonge Reef exhibited an additional partitioning of mtDNA lineages (associated with specific symbiont ITS2 types), whereas Scott Reef was dominated by a single mtDNA lineage (with no apparent host-symbiont specificity). Evidence for recruitment of larvae of deep water origin into shallow habitats was found at Scott Reef, suggesting that recovery of shallow water habitats may be aided by migration from deep water refuges. Conversely, no migration from the genetically divergent deep slope populations into the shallow habitats was evident at Yonge Reef, making recovery of shallow habitats from deeper waters at this location highly unlikely.

Distribution and Diversity of Corals on Artificial Reefs at Pasir Akar and Teluk Kalong, Redang Island, Malaysia

Present study was conducted to determine the propagation and biodiversity of corals on artificial reefs at Teluk Kalong and Pasir Akar, Malaysia to check the feasibility of artificial reef to rehabilitate natural reef ecosystems and to provide artificial habitat for marine organisms. Two types of artificial reef deployed in these areas were Dome Reef and EnviroReef which were developed by the Dorken Company. Based on the results obtained, coral distribution was higher at Pasir Akar compared to Teluk Kalong. The Shannon diversity index (H’) and evenness index (EH’) of coral at Teluk Kalong were 0.6425 and 0.1766, respectively while the Shannon diversity index (H’) and Pielou evenness index (EH’) of coral at Pasir Akar were 1.7410 and 0.3247, respectively. Overall, 2 species were found and identified at Teluk Kalong and 10 species were at Pasir Akar with Seriatopora hystrix as the dominant species at both the stations. Coral distribution was higher on Dome Reef compared to EnviroReef. The diversity index (H’) and Pielou evenness index (EH’) of EnviroReef were 0.5359 and 0.1284 respectively while it was 2.2192 and 0.4274, respectively in Dome Reef. A total of 3 and 9 species were found and identified from the EnviroReef and Dome Reef, respectively with Seriatopora hystrix being the dominant in both the reef structures. We conclude that both artificial reefs structures were suitable as habitat for coral propagation.

Adaptive divergence in a scleractinian coral: physiological adaptation of Seriatopora hystrix to shallow and deep reef habitats.

BackgroundDivergent natural selection across environmental gradients has been acknowledged as a major driver of population and species divergence, however its role in the diversification of scleractinian corals remains poorly understood. Recently, it was demonstrated that the brooding coral Seriatopora hystrix and its algal endosymbionts (Symbiodinium) are genetically partitioned across reef environments (0-30 m) on the far northern Great Barrier Reef. Here, we explore the potential mechanisms underlying this differentiation and assess the stability of host-symbiont associations through a reciprocal transplantation experiment across habitats ('Back Reef', 'Upper Slope' and 'Deep Slope'), in combination with molecular (mtDNA and ITS2-DGGE) and photo-physiological analyses (respirometry and HPLC).ResultsThe highest survival rates were observed for native transplants (measured 14 months after transplantation), indicating differential selective pressures between habitats. Host-symbiont assemblages remained stable during the experimental duration, demonstrating that the ability to "shuffle" or "switch" symbionts is restricted in S. hystrix. Photo-physiological differences were observed between transplants originating from the shallow and deep habitats, with indirect evidence of an increased heterotrophic capacity in native deep-water transplants (from the 'Deep Slope' habitat). Similar photo-acclimatisation potential was observed between transplants originating from the two shallow habitats ('Back Reef' and 'Upper Slope'), highlighting that their genetic segregation over depth may be due to other, non-photo-physiological traits under selection.ConclusionsThis study confirms that the observed habitat partitioning of S. hystrix (and associated Symbiodinium) is reflective of adaptive divergence along a depth gradient. Gene flow appears to be reduced due to divergent selection, highlighting the potential role of ecological mechanisms, in addition to physical dispersal barriers, in the diversification of scleractinian corals and their associated Symbiodinium.

Niche specialization of reef-building corals in the mesophotic zone: metabolic trade-offs between divergent Symbiodinium types.

The photobiology of two reef corals and the distribution of associated symbiont types were investigated over a depth gradient of 0–60 m at Scott Reef, Western Australia. Pachyseris speciosa hosted mainly the same Symbiodinium C type similar to C3 irrespective of sampling depth. By contrast, Seriatopora hystrix hosted predominantly Symbiodinium type D1a or D1a-like at shallow depths while those in deeper water were dominated by a Symbiodinium C type closely related to C1. The photosynthesis/respiration (P/R) ratio increased consistently with depth at the two sampling times (November 2008 and April 2009) for P. speciosa and in November 2008 only for S. hystrix, suggesting a reduction in metabolic energy expended for every unit of energy obtained from photosynthesis. However, in April 2009, shallow colonies of S. hystrix exhibited decreased P/R ratios down to depths of approximately 23 m, below which the ratio increased towards the maximum depth sampled. This pattern was mirrored by changes in tissue biomass determined as total protein content. The depth of change in the direction of the P/R ratio correlated with a shift from Symbiodinium D to C-dominated colonies. We conclude that while photobiological flexibility is vital for persistence in contrasting light regimes, a shift in Symbiodinium type may also confer a functional advantage albeit at a metabolic cost with increased depth.

Evaluating the temporal stability of stress-activated protein kinase and cytoskeleton gene expression in the Pacific reef corals Pocillopora damicornis and Seriatopora hystrix

The gastrodermal tissues of anthozoans that harbor endosymbiotic Symbiodinium experience light-dependent fluxes in dinoflagellate derived photosynthetic compounds that have the potential to impact the osmotic homeostasis of the animal. To explore this unusual osmoregulatory scenario, genes encoding proteins that play highly conserved roles in osmoregulation (mitogen-activated protein kinases, [MAPKs]) and the maintenance of the cytoskeleton ( ß-actin, tropomyosin, and α-tubulin) were quantified over diel cycles using quantitative real-time polymerase chain reaction. The expression of MAPK genes in Pocillopora damicornis increased at night, while the expression of cytoskeleton genes in Seriatopora hystrix decreased. The increase in P. damicornis MAPK expression may reflect host osmolyte production in response to reduced osmotic pressure at night. The concomitant decrease in expression of genes encoding cytoskeleton proteins at night is consistent with this interpretation, indicating reduced production of spatially demanding proteins under periods of intracellular crowding. However, the latter interpretation is confounded by the fact that molecularly-inferred Symbiodinium densities were found to be significantly greater at night in both corals, so changes in cytoskeletal gene expression may also reflect crowding to accommodate the greater density of these endosymbionts. In addition to providing insight into an unusual physiological attribute of photosynthetic endosymbioses, this study represents the first to measure gene behavior in field and cultured corals with a method that considers the dual-compartment nature of the associations.

Determining the community structure of the coral Seriatopora hystrix from hydrodynamic and genetic networks

The exchange of genetic information between coral reefs through the transport of larvae can be described in terms of networks that capture the linkages between distant populations. A key question arising from these networks is the determination of the highly connected modules (communities). Communities can be defined using genetic similarity or distance statistics between multiple samples but due to limited specimen sampling capacity the boundaries of the communities for the known coral reefs in the seascape remain unresolved. In this study we use the microsatellite composition of individual corals to compare sample populations using a genetic dissimilarity measure ( F ST) which is then used to create a complex network. This network involved sampling 1025 colonies from 22 collection sites and examining 10 microsatellites loci. The links between each sampling site were given a strength that was created from the pair wise F ST values. The result is an undirected weighted network describing the genetic dissimilarity between each sampled population. From this network we then determined the community structure using a leading eigenvector algorithm within graph theory. However, given the relatively limited sampling conducted, the representation of the regional genetic structure was incomplete. To assist with defining the boundaries of the genetically based communities we also integrated the communities derived from a hydrodynamic and distance based networks. The hydrodynamic network, though more comprehensive, was of smaller spatial extent than our genetic sampling. A Bayesian Belief network was developed to integrate the overlapping communities. The results indicate the genetic population structure of the Great Barrier Reef and provide guidance on where future genetic sampling should take place to complete the genetic diversity mapping.

Variation in the structure of epifaunal invertebrate assemblages among coral hosts

The high biodiversity of coral reefs is attributable to the many invertebrate groups which live in symbiotic relationships with other reef organisms, particularly those which associate with the living coral habitat. However, few studies have examined the diversity and community structure of coral-dwelling invertebrates and how they vary among coral species. This study quantified the species richness and composition of animals associated with four common species of branching corals (Acropora nasuta, A. millepora, Pocillopora damicornis, and Seriatopora hystrix) at Lizard Island in the northern Great Barrier Reef. One hundred and seventy-eight nominal species from 12 different phyla were extracted across 50 replicate colonies of each coral host. A single coral colony, approximately 20 cm in diameter, harbored as many as 73 individuals and 24 species. There were substantial differences in invertebrate species composition among coral hosts of different families as well as genera. Twenty-seven species (15% of all taxa collected) were found on only one of the four different coral species, which may potentially indicate some level of specialization among coral hosts. The distinct assemblages on different coral species, and the presence of potential specialists, suggests invertebrate communities will be sensitive to the differential loss of branching coral species resulting from coral reef degradation.

Genetic divergence across habitats in the widespread coral Seriatopora hystrix and its associated Symbiodinium.

BackgroundCoral reefs are hotspots of biodiversity, yet processes of diversification in these ecosystems are poorly understood. The environmental heterogeneity of coral reef environments could be an important contributor to diversification, however, evidence supporting ecological speciation in corals is sparse. Here, we present data from a widespread coral species that reveals a strong association of host and symbiont lineages with specific habitats, consistent with distinct, sympatric gene pools that are maintained through ecologically-based selection.Methodology/Principal FindingsPopulations of a common brooding coral, Seriatopora hystrix, were sampled from three adjacent reef habitats (spanning a ∼30 m depth range) at three locations on the Great Barrier Reef (n = 336). The populations were assessed for genetic structure using a combination of mitochondrial (putative control region) and nuclear (three microsatellites) markers for the coral host, and the ITS2 region of the ribosomal DNA for the algal symbionts (Symbiodinium). Our results show concordant genetic partitioning of both the coral host and its symbionts across the different habitats, independent of sampling location.Conclusions/SignificanceThis study demonstrates that coral populations and their associated symbionts can be highly structured across habitats on a single reef. Coral populations from adjacent habitats were found to be genetically isolated from each other, whereas genetic similarity was maintained across similar habitat types at different locations. The most parsimonious explanation for the observed genetic partitioning across habitats is that adaptation to the local environment has caused ecological divergence of distinct genetic groups within S. hystrix.

The recovery of coral genetic diversity in the Sunda Strait following the 1883 eruption of Krakatau

Surveys of microsatellite variation show that genetic diversity has largely recovered in two reef-building corals, Pocillopora damicornis and Seriatopora hystrix (Scleractinia: Pocilloporidae), on reefs which were decimated by the eruption of the volcano Krakatau in 1883. Assignment methods and gene flow estimates indicate that the recolonization of Krakatau occurred mainly from the closest upstream reef system, Pulau Seribu, but that larval input from other regions has also occurred. This pattern is clearer in S. hystrix, which is traditionally the more dispersal-limited species. Despite these observed patterns of larval dispersal, self-recruitment appears to now be the most important factor in supplying larvae to coral populations in Krakatau. This suggests that the colonization of devastated reefs can occur quickly through larval dispersal; however, their survival requires local sources of larvae for self-recruitment. This research supports the observation that the recovery of genetic diversity in coral reef animals can occur on the order of decades and centuries rather than millennia. Conservation measures aimed at sustaining coral reef populations in Krakatau and elsewhere should include both the protection of upstream source populations for larval replenishment should disaster occur as well as the protection of large adult colonies to serve as local larval sources.

Fine-scale analysis of genetic structure in the brooding coral Seriatopora hystrix from the Red Sea

The dispersal of gametes and larvae plays a key role in the population dynamics of sessile marine invertebrates. Species with internal fertilisation are often associated with very localised larval dispersal, which may cause small-scale patterns of neutral genetic variation. This study on the brooding coral Seriatopora hystrix from the Red Sea focused on the smallest possible scale: Two S. hystrix stands (~100 colonies each) near Dahab were completely sampled, mapped and analysed at five microsatellite markers. The sexual mode of reproduction, the likely occurrence of selfing and the level of immigration were in agreement with previous studies on this species. Contrary to previous findings, both stands were in Hardy–Weinberg proportions. Also, no evidence for spatially restricted larval dispersal within the sampled areas was found. Differences between this and previous studies on S. hystrix could reflect variation in life history or varying environmental conditions, which opens intriguing questions for future research.

Ecologically relevant dispersal of corals on isolated reefs: implications for managing resilience

Coral reefs are in decline worldwide, and marine reserve networks have been advocated as a powerful management tool for maximizing the resilience of coral communities to an increasing variety, number, and severity of disturbances. However, the effective design of reserves must account for the spatial scales of larval dispersal that affect the demography of communities over ecological time frames. Ecologically relevant distances of dispersal were inferred from DNA microsatellite data in a broadcast-spawning (Acropora tenuis) and a brooding (Seriatopora hystrix) coral at isolated reef systems off northwest Australia. Congruent with expectations based on life histories, levels of genetic subdivision among populations were markedly higher in the brooder than in the broadcast spawner. Additionally, significant subdivision for both species between systems (>100 km), and between (>10 km) or within reefs (<10 km) within systems, indicated that many reefs or reef patches are demographically independent. There was also a clear distinction in the scale of genetic structure between the different systems; at the more geographically complex of the systems, a much finer scale structure was detected in both species. This suggested that the hydrodynamics associated with these complex reefs restrict distances regularly traveled by larvae. The primary implication is that short-term recovery of these coral communities after severe disturbance requires the input of larvae from viable communities kilometers to a few tens of kilometers away. Therefore, to be self-sustaining, we suggest that coral reef protected areas need to be large enough to encompass these routine dispersal distances. Further, to facilitate recovery from severe disturbances, protected areas need to be replicated over these spatial scales. However, specific designs also need to account for size, complexity, and isolation of reefs, which will either restrict or enhance dispersal within this range.

Genetic Traces of Recent Long-Distance Dispersal in a Predominantly Self-Recruiting Coral

BackgroundUnderstanding of the magnitude and direction of the exchange of individuals among geographically separated subpopulations that comprise a metapopulation (connectivity) can lead to an improved ability to forecast how fast coral reef organisms are likely to recover from disturbance events that cause extensive mortality. Reef corals that brood their larvae internally and release mature larvae are believed to show little exchange of larvae over ecological times scales and are therefore expected to recover extremely slowly from large-scale perturbations.Methodology/Principal FindingsUsing analysis of ten DNA microsatellite loci, we show that although Great Barrier Reef (GBR) populations of the brooding coral, Seriatopora hystrix, are mostly self-seeded and some populations are highly isolated, a considerable amount of sexual larvae (up to ∼4%) has been exchanged among several reefs 10 s to 100 s km apart over the past few generations. Our results further indicate that S. hystrix is capable of producing asexual propagules with similar long-distance dispersal abilities (∼1.4% of the sampled colonies had a multilocus genotype that also occurred at another sampling location), which may aid in recovery from environmental disturbances.Conclusions/SignificancePatterns of connectivity in this and probably other GBR corals are complex and need to be resolved in greater detail through genetic characterisation of different cohorts and linkage of genetic data with fine-scale hydrodynamic models.

A comparative study of the components of the hard coral Seriatopora hystrix and the soft coral Xenia umbellata along the Jeddah coast, Saudi Arabia

En este estudio se compararon la estructura de los polipos y los tipos celulares del coral duro Seriatopora hystrix y del coral blando Xenia umbellata, ademas de la composicion de los acidos grasos en sus tejidos. S. hystrix mostro una aparente carencia de celulas alimenticias especializadas, particularmente, un pequeno numero de celulas glandulares mucosas y un bajo porcentaje de nematocistos conteniendo veneno. Los P-mastigoforos estuvieron presentes en el 1,52-5,7% de los nematocistos y los B-mastigoforos en el 1,28%. Por el contrario, hubo un alto porcentaje de nematocistos holotricos (24,86 - 55,5%) en los tentaculos y filamentos mesentericos, respectivamente. Las zooxantelas fueron abundantes en la gastrodermis. Estas caracteristicas sugieren que S. hystrix depende esencialmente de una nutricion autotrofa. Los polipos de X. umbellata no presentaron cnidae, y las glandulas mucosas fueron abundantes, especialmente en la parte mas basal del polipo. La presencia de materia particulada en el celenteron y el bajo numero de zooxantelas indican que X. umbellata es un suspensivoro, que utiliza mucus para atrapar las particulas en los tentaculos pinados. Un estudio comparativo de su composicion quimica tambien revelo diferencias entre ambas especies. X. umbellata presento un alto contenido proteico y lipidico mientras que S. hystrix se caracterizo por un alto contenido de carbonato de calcio. En S. hystrix, los acidos grasos fueron predominantemente saturados (87,3%), siendo 16:0 y 18:0 los mas abundantes. X. umbellata mostro predominancia de acidos grasos insaturados (77,7%), siendo 16:1 y 18:1 los mas abundantes. Las diferencias morfologicas y en composicion bioquimica sugieren que S. hystrix tiene mayor dependencia de una alimentacion autotrofa mientras que X. umbellata es mas bien un suspensivoro heterotrofo

Mating system variation in the hermaphroditic brooding coral, Seriatopora hystrix

Self-compatible, hermaphroditic marine invertebrates have the potential to self-fertilize in the absence of mates or under sperm-limited conditions, and outcross when sperm is available from a variety of males. Hence, many hermaphroditic marine invertebrates may have evolved mixed-mating systems that involve facultative self-fertilization. Such mixed-mating strategies are well documented for plants but have rarely been investigated in animals. Here, I use allozyme markers to make estimates of selfing from population surveys of reef slope and reef flat sites, and contrast this with direct estimates of selfing from progeny-array analysis, for the brooding coral Seriatopora hystrix. Consistent heterozygote deficits previously reported for S. hystrix suggests that inbreeding (including the extreme of selfing) may be common in this species. I detected significant levels of inbreeding within populations (F(IS)=0.48) and small but significant differentiation among all sites (F(ST)=0.04). I detected no significant differentiation among habitats (F(HT)=0.009) though among site differentiation did occur within the reef slope habitat (F(SH)=0.06), but not within the reef flat habitat (F(SH)=0.015). My direct estimates of outcrossing for six colonies and their progeny from a single reef flat site revealed an intermediate value (t(m) (+/-s.d.)=0.53+/-0.20). Inbreeding coefficients calculated from progeny arrays (F(e)=0.31) were similar to indirect estimates based on adult genotype frequencies for that site (F(IS)=0.38). This study confirms that the mating system of this brooding coral is potentially variable, with both outcrossing and selfing.

The morphology and ultrastructure of the peripheral olfactory organ in newly metamorphosed coral-dwelling gobies, Paragobiodon xanthosomus Bleeker (Gobiidae, Teleostei)

We examined the peripheral olfactory organ in newly metamorphosed coral-dwelling gobies, Paragobiodon xanthosomus (SL = 5.8 mm ± 0.8 mm, N = 15), by the aid of electron microscopy (scanning and transmission) and light microscopy. Two bilateral olfactory placodes were present in each fish. They were oval-shaped and located medio-ventrally, one in each of the olfactory chambers. Each placode had a continuous cover of cilia. The placode epithelium contained three different types of olfactory receptor neurons: ciliated, microvillous and crypt cells. The latter type was rare. Following a pelagic larval phase, P. xanthosomus settle to the reef and form an obligate association with one species of coral, Seriatopora hystrix. Their well-developed olfactory organs likely enable larvae of P. xanthosomus to detect chemical cues that assist in navigating towards and selecting appropriate coral habitat at settlement. Our findings support past studies showing that the peripheral olfactory organ develops early in coral reef fishes.

Niche partitioning of closely related symbiotic dinoflagellates

Reef-building corals are fundamental to the most diverse marine ecosystems, yet a detailed understanding of the processes involved in the establishment, persistence and ecology of the coral-dinoflagellate association remains largely unknown. This study explores symbiont diversity in relation to habitat by employing a broad-scale sampling regime using ITS2 and denaturing gradient gel electrophoresis. Samples from Pocillopora damicornis, Stylophora pistillata and Seriatopora hystrix all harboured host-specific clade C symbiont types at Heron Island (Great Barrier Reef, Australia). While Ser. hystrix associated with a single symbiont profile along its entire depth distribution, both P. damicornis and Sty. pistillata associated with multiple symbiont profiles that showed a strong zonation with depth. It is shown that, with an increased sampling effort, previously identified 'rare' symbiont types within this group of host species are in fact environmental specialists. A multivariate approach was used to expand on the common distinction of symbionts by a single genetic identity. It shows merit in its capacity not only to include all the variability present within the marker region but also to reliably represent ecological diversification of symbionts. Furthermore, the cohesive species concept is explored to explain how niche partitioning may drive diversification of closely related symbiont lineages. This study provides thus evidence that closely related symbionts are ecologically distinct and fulfil their own niche within the ecosystem provided by the host and external environment.

New monoecious seagrass of Halophila sulawesii (Hydrocharitaceae) from Indonesia

A new seagrass species, Halophila sulawesii, is described in the section Halophila. This species has a similar vegetative appearance as Halophila ovalis (R. Br.) J. D. Hook with the ovate laminae, and has been reported as “deep water H. ovalis” in the literature. However, H. ovalis is a dioecious plant while H. sulawesii is a monoecious one, a feature resembling H. capricorni Larkum, that is the presence of a single male or female flower in separate floral axils of the same rhizome. Both H. sulawesii and H. capricorni have finely serrulated laminal margins however, the laminal surface of the former species is glabrous, while the latter one possesses a few stiff abaxial hairs. H. sulawesii is found on coral sand between 10 to 30 metres and grows adjacent to corals Seriatopora hystrix Dana and Acropora sp. and other seagrasses such as Halophila decipiens Ostenfeld and Halodule uninervis (Forsakål) Ascherson in several reef islands of the Spermonde Archipelago in south-western Sulawesi, Indonesia.

Coral degradation and the structure of tropical reef fish communities

Coral reefs can be degraded by a variety of perturbations, including bleaching and predation by crown-of-thorns starfish. The combination of these disturbances has contributed to a global decline of live coral cover on reefs. While the effects of bleaching and starfish predation on corals are relatively well known, their consequences for fish communities are less understood. We compared fish assemblages associated with 2 coral species, Pocillopora damicornis and Seriatopora hystrix, among 3 coral health categories: (1) live, (2) degraded and (3) dead colonies with recent algal growth. Categories 2 and 3 occur sequentially during the first few weeks following bleaching or crown-of-thorns starfish predation. The abundance of species with an obligate association with live coral differed among coral health categories. Average total abundance of all fish species was lowest in algal-covered colonies of both coral species and these assemblages were dominated by species that are not closely associated with live coral. Lower fish abundance on algal-covered colonies was largely due to the low number of small size classes (new recruits and juveniles). This study suggests that habitat health may play an important role in structuring coral-associated fish assemblages.

Multiple scales of genetic connectivity in a brooding coral on isolated reefs following catastrophic bleaching

Understanding the pattern of connectivity among populations is crucial for the development of realistic and spatially explicit population models in marine systems. Here we analysed variation at eight microsatellite loci to assess the genetic structure and to infer patterns of larval dispersal for a brooding coral, Seriatopora hystrix, at an isolated system of reefs in northern Western Australia. Spatial autocorrelation analyses show that populations are locally subdivided, and that the majority of larvae recruit to within 100 m of their natal colony. Further, a combination of F- and R- statistics showed significant differentiation at larger spatial scales (2-60 km) between sites, and this pattern was clearly not associated with distance. However, Bayesian analysis demonstrated that recruitment has been supplemented by less frequent but recent input of larvae from outside the local area; 2-6% of colonies were excluded from the site at which they were sampled. Individual assignments of these migrants to the most likely populations suggest that the majority of migrants were produced at the only site that was not decimated by a recent and catastrophic coral bleaching event. Furthermore, the only site that recovered to prebleaching levels received most of these immigrants. We conclude that the genetic structure of this brooding coral reflects its highly opportunistic life history, in which prolific, philopatric recruitment is occasionally supplemented by exogenously produced larvae.