Acropora Nasuta Research Articles

Coral calcification mechanisms in a warming ocean and the interactive effects of temperature and light

Ocean warming is transforming the world’s coral reefs, which are governed by the growth of marine calcifiers, most notably branching corals. Critical to skeletal growth is the corals’ regulation of their internal chemistry to promote calcification. Here we investigate the effects of temperature and light on the calcifying fluid chemistry (using boron isotope systematics), calcification rates, metabolic rates and photo-physiology of Acropora nasuta during two mesocosm experiments simulating seasonal and static temperature and light regimes. Under the seasonal regime, coral calcification rates, calcifying fluid carbonate chemistry, photo-physiology and metabolic productivity responded to both changes in temperature and light. However, under static conditions the artificially prolonged exposure to summer temperatures resulted in heat stress and a heightened sensitivity to light. Our results indicate that temperature and light effects on coral physiology and calcification mechanisms are interactive and context-specific, making it essential to conduct realistic multi-variate dynamic experiments in order to predict how coral calcification will respond to ocean warming.

The impact of acute benzo(a)pyrene on antioxidant enzyme and stress-related genes in tropical stony corals (Acropora spp.)

Coral reefs have extremely high ecological value in tropical and subtropical waters worldwide. However, they have been subjected to the most extensive and prolonged damage in recent decades. Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous hazardous pollutants and are highly resistant to degradation in marine environments. Among these compounds, benzo(a)pyrene (BaP) has exerted pressure on corals due to water discharges, oil spills and coastal tourism. In the present study, the physiological response, oxidative stress and stress-related genetic expressions of two Acropora spp. (Acropora formosa and Acropora nasuta) were analysed. These two coral species were exposed to 10 and 40 μg·L−1 BaP for 24 hand 72 h, respectively. The results show that (1) BaP affects the health of the zooxanthellae in coral symbiosis after BaP exposure for 72 h due to a significant decline in chlorophyll a concentrations in Acropora spp. during this period. (2) An exposure of 10 μg·L−1 BaP for 24 h induced serious oxidative damage to Acropora spp., with a significant decline and increase in superoxide dismutase (SOD) activities in A. formosa and A. nasuta. (3) The P-gp gene is more sensitive in A. formosa, while the Hsp70 gene is more sensitive in A. nasuta. (4) A. formosa showed a lower ability to resist organic pollutants in coral reefs. Overall, further ecotoxicological studies are needed to investigate the impact of chemical pollutants on corals and to compare their different response mechanisms.

Sulfur-Containing Carotenoids from A Marine Coral Symbiont Erythrobacter flavus Strain KJ5.

Erythrobacter flavus strain KJ5 (formerly called Erythrobacter sp. strain KJ5) is a yellowish marine bacterium that was isolated from a hard coral Acropora nasuta in the Karimunjawa Islands, Indonesia. The complete genome sequence of the bacterium has been reported recently. In this study, we examined the carotenoid composition of this bacterium using high-performance liquid chromatography coupled with ESI-MS/MS. We found that the bacterium produced sulfur-containing carotenoids, i.e., caloxanthin sulfate and nostoxanthin sulfate, as the most abundant carotenoids. A new carotenoid zeaxanthin sulfate was detected based on its ESI-MS/MS spectrum. The unique presence of sulfated carotenoids found among the currently known species of the Erythrobacter genus were discussed.

Spatial and Temporal Variation in Fecundity of Acropora spp. in the Northern Great Barrier Reef

The amount of energy invested in sexual reproduction by scleractinian corals depends on their life history strategies (i.e., allocation of energy between growth, reproduction, and maintenance). However, energy allocated to reproduction will also be affected by the amount of energy acquired and prevailing environmental conditions. Coral fecundity is therefore likely to vary spatially, especially along marked gradients in environmental conditions. One of the foremost gradients in reef structure and environmental conditions occurs with distance from the coast, whereby inner-shelf or near shore reefs are generally subject to higher levels of nutrients, sediments and pollutants, which often adversely affect reef-building corals. This study quantified fecundity (oocytes per polyp) for three species, Acropora nasuta, A. spathulata, and A. hyacinthus, at six locations in the northern Great Barrier Reef (GBR), encompassing inner-, mid- and outer-shelf reefs. Replicate colonies were sampled at each location prior to the predicted date of spawning in 2013 and 2014. Both shelf position and year were important factors explaining variation in fecundity for each of the three coral species. Most notably, there were clear and consistent declines in the number of oocytes between 2013 and 2014, coinciding with the incidence of category 4 Cylone Ita in early 2014. Contrary to expectations, polyp-level fecundity was no lower (and in some cases substantially higher) on inner-shelf reefs, compared to conspecifics growing on mid-shelf or outer-shelf reefs. The observed patterns are much more complicated than anticipated, necessitating further research to understand differential population dynamics of corals on inner-shelf versus mid- and outer-shelf reefs.

Plasticity in Three-Dimensional Geometry of Branching Corals Along a Cross-Shelf Gradient

Scleractinian corals often exhibit high levels of morphological plasticity, which is potentially important in enabling individual species to occupy benthic spaces across a wide range of environmental gradients. This study tested for differences in the three-dimensional (3D) geometry of three branching corals, Acropora nasuta, Pocillopora spp. and Stylophora pistillata among inner-, mid- and outer-shelf reefs in the central Great Barrier Reef, Australia. Important attributes of coral morphology (e.g., surface area to volume ratio) were expected to vary linearly across the shelf in accordance with marked gradients in environmental conditions, but instead, we detected non-linear trends in the colony structure of A. nasuta and Pocillopora spp. The surface area to volume ratio of both A. nasuta and Pocillopora spp. was highest at mid-shelf locations, (reflecting higher colony complexity) and was significantly lower at both inner-shelf and outer-shelf reefs. The branching structure of these corals was also far more tightly packed at inner-shelf and outer-shelf reefs, compared to mid-shelf reefs. Apparent declines in complexity and inter-branch spacing at inner and outer-shelf reefs (compared to conspecifics from mid-shelf reefs) may reflect changes driven by gradients of sedimentation and hydrodynamics. The generality and explanations of observed patterns warrant further investigation, which is very feasible using the 3D-photogrammetry techniques used in this study.

Limited Cross-Shelf Variation in the Growth of Three Branching Corals on Australia’s Great Barrier Reef

Pronounced differences exist in the biodiversity and structure of coral reef assemblages with increasing distance from shore, which may be expected given marked cross-shelf gradients in environmental conditions. Cross-shelf variation in the abundance of coral reef organisms is likely to be caused, at least in part, by differences in demography (e.g., growth and survival), though this has rarely been tested. This study quantified growth of three distinct branching coral taxa (Acropora nasuta, Pocillopora spp. and Stylophora pistillata) at six locations on Australia’s Great Barrier Reef (GBR), encompassing inshore, mid-shelf and outer-shelf reefs. Replicate colonies (0–15 colonies per species, per reef) were stained using Alizarin Red in December 2015 and retrieved one year later to quantify linear extension on replicate branches for each colony. Annual linear extension varied within and among coral taxa, with pronounced differences among reefs. For A. nasuta. and S. pistillata, growth rates were highest at one of the inshore reefs, Orpheus Island. However, inter-reef differences in linear extension were not explained by shelf position. Based on differences in skeletal density, which did vary according to shelf position, branching corals at the inshore sites may actually have higher rates of calcification compared to conspecifics on mid-and outer-shelf reefs. This study shows that growth of branching corals is not lower at inshore sites (and perhaps even higher) compared to sites at mid-shelf and outer reefs, despite generally higher levels of sedimentation and turbidity.

Phenotypic variations in the preferred host coral impact the occupancy of an obligate coral-dwelling fish.

Habitat specialists form tight relationships with their host habitat and are able to make microscale decisions when selecting final habitat locations. The obligate coral-dwelling fish, Gobiodon histrio, is thought to make habitat choices based on the coloration and structural characteristics of Acropora nasuta, their preferred coral host. Yet, most studies on the habitat preference of G. histrio have been conducted on Australia's Great Barrier Reef with no understanding if geographic differences in preferences exist. Here, we tested the habitat preference of G. histrio towards A. nasuta on the reefs of Kadavu and Tavewa Islands, Fiji. First, to assess the natural distribution, belt transect surveys of all acroporid corals were conducted. Transects indicated that, while G. histrio is most frequently found in A. nasuta over other acroporid corals, the coral's structural characteristics rather than the coral's color variation was the preferred characteristic. In contrast, the Australian G. histrio have been found to be more frequent in blue A. nasuta opposed to the brown color variation, suggesting a geographic difference in habitat preferences among the species. In addition, we conducted two in-situ behavioral field experiments to determine whether G. histrio would 1) move from dead A. nasuta to a live brown or blue A. nasuta and, 2) preferentially select between the brown or blue colored A. nasuta when placed on a dead A. nasuta. The results of the in-situ experiments support the finding that Fijian G. histrio does not discriminate between A. nasuta using color but uses only structural morphologies to guide its habitat selection process. Habitat selection is a complex process, and microscale habitat preferences within a species can vary between geographic locations. This study sheds light on the need to expand research findings to incorporate large geographic regions when attempting to understand the preferences of coral reef symbionts.

The complete mitochondrial genome of the Acropora pruinosa

In this study, the complete mitogenome sequence of stony coral, Acropora pruinosa (Scleractinia), has been decoded for the first time by next generation sequencing and genome assembly. The assembled mitogenome, consisting of 18,480 bp, has unique 13 protein-coding genes (PCGs), three transfer RNAs, and two ribosomal RNAs genes. The complete mitogenome of Acropora pruinosa showing 99% identities to Acropora nasuta. The complete mitogenome provides essential and important DNA molecular data for further phylogenetic and evolutionary analyses for coral phylogeny.

Benthic composition influences habitat use and toxicity of coral-dwelling fishes

The distribution and abundance of habitat specialists is often associated with the availability of preferred habitat; however, other environmental features can also influence habitat selection. Coral-dwelling gobies are habitat specialist fishes that depend on the availability of a few key species of coral for their survival and rely on skin toxins to reduce predation risk. This study investigated the influence of benthic substratum around coral colonies on patterns of habitat use and toxicity of two species of coral-dwelling gobies (Gobiodon erythrospilus and Gobiodon histrio) that compete for access to the coral, Acropora nasuta. Field surveys demonstrated that the benthic substratum around A. nasuta coral colonies differed between colonies occupied by G. histrio and G. erythrospilus. Juvenile, single adult and breeding pairs of G. erythrospilus mostly inhabited A. nasuta colonies surrounded by branching corals. In contrast, juvenile and single adult G. histrio associated with A. nasuta coral colonies that had adjacent epilithic algal matrix and G. histrio breeding pairs inhabited colonies surrounded by sand/rubble. Habitat choice experiments demonstrated that both goby species prefer A. nasuta coral colonies with benthic substratum mainly composed by epilithic algal matrix and sand; suggesting that competition for coral colonies in preferred locations could influence patterns of habitat use observed in the field. The substratum around preferred coral colonies also influenced the toxicity levels of associated fishes. Gobies inhabiting A. nasuta coral colonies surrounded by epilithic algal matrix and sand showed higher levels of toxicity than gobies collected from colonies surrounded by branching corals. Given the potential for toxicity level to reduce the risk of predation, this could explain why gobies would compete for access to colonies of the preferred coral species surrounded by epilithic algal matrix and sand. These results show that the habitat use of coral habitat specialist fishes can be affected by the benthic composition around preferred coral colonies and demonstrate how competition for important secondary resources can influence patterns of habitat use.

Monitoring of the in situ growth of three Acropora corals by individual identification over 5 years at the northern outer reef of Sekisei Lagoon (24°N), Okinawa

We monitored juvenile Acropora corals (n = 719, <12 mm in the first survey) on the northern outer reef of the Sekisei Lagoon, 1 year after spawning in May 2008 and May 2009 and for the 4 subsequent years. The first-year colonies were an encrusting (EC) form. In the second year, approximately half of the colonies were of the EC form and the others grew one branch (OB) or several branches (SB). In the third year, two thirds of the colonies were of the EC–SB form, while the remainder grew wider branches (WB). After the third year, the WB colonies showed a typical species-specific growth form and spread laterally. Growth until the third year in the SB colonies was slow, while growth in the WB colonies was fast. Although we assumed that Acropora corals <12 mm in size were in their first year after a spawning event, 23 and 10 % of the second-year colonies (spawned in 2008 and 2009, respectively) were <12 mm. By the fifth year, three dominant corals were identified as different species, i.e., Acropora hyacinthus, Acropora digitifera, and Acropora nasuta, and their maximum sizes were 226, 202, and 144 mm, respectively.

Coral colony size and structure as determinants of habitat use and fitness of coral-dwelling fishes

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 553:163-172 (2016) - DOI: https://doi.org/10.3354/meps11745 Coral colony size and structure as determinants of habitat use and fitness of coral-dwelling fishes Pedro Henrique Cipresso Pereira*, Philip L. Munday College of Marine and Environmental Sciences and ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, QLD 4811, Australia *Corresponding author: pedro.pereira@my.jcu.edu.au ABSTRACT: Competition for space affects patterns of habitat use and individual performance of coral-dwelling fishes; however, the physical attributes of corals that influence habitat preferences are uncertain. In this study, we investigated the influence of coral colony size and branching structure of 2 coral species, Acropora nasuta and Acropora spathulata, on habitat use and growth rate of 2 coral gobies, Gobiodon histrio and G. erythrospilus. First, we examined 2 key aspects of coral colony structure (interbranch depth and interbranch width) that may influence habitat preferences. We then used laboratory and field-based experiments to test the effects of coral species, coral colony size and branching structure on habitat preference and growth rates of G. histrio and G. erythrospilus. The preferred coral species, A. nasuta, had smaller interbranch width than A. spathulata. A binary-choice laboratory experiment demonstrated that both goby species preferred coral colonies with smaller interbranch width, except when they had the opportunity to occupy A. nasuta over A. spathulata. A field transplant experiment showed that both goby species grew faster on larger coral colonies and in colonies with smaller interbranch width. G. erythrospilus grew faster than G. histrio on A. spathulata, indicating that it suffers less fitness loss when occupying this alternative habitat. Our results show that coral physical attributes are important factors driving habitat preference of coral-dwelling gobies; however, there must also be additional factors that influence their habitat use. Declining average coral size and reduced habitat complexity on coral reefs could have significant impacts on the performance of fishes, affecting ecological processes such as competition. KEY WORDS: Habitat complexity · Competition · Growth rate · Goby · Gobiodon spp. · Acropora spp. Full text in pdf format PreviousNextCite this article as: Pereira PHC, Munday PL (2016) Coral colony size and structure as determinants of habitat use and fitness of coral-dwelling fishes. Mar Ecol Prog Ser 553:163-172. https://doi.org/10.3354/meps11745 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 553. Online publication date: July 14, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Competitive mechanisms change with ontogeny in coral-dwelling gobies.

Recent theory suggests that a mix of lottery and niche processes can facilitate coexistence between competing species, but this has not yet been empirically tested. Previous research has suggested that a competitive lottery for space promotes coexistence between two ecologically similar species, Gobiodon histrio and Gobiodon erythrospilus. However, not all the assumptions of lottery competition have been tested, and patterns of habitat use by adults suggest niche partitioning. Here, we investigated the hypothesis that the mechanism of competition changes with ontogeny, with a lottery for space operating at settlement and niche partitioning occurring in adults. Patterns of resource use in the field were compared for juveniles and adults of the two species. Pelagic larval duration (PLD) and size-at-settlement was also estimated to determine if size differences at settlement could affect the outcome of competitive interactions among juveniles. Habitat preference and size-based competitive ability were then tested for juveniles and adults in laboratory experiments. Finally, a transplant experiment was performed to test the fitness-associated consequences of niche partitioning among adults and its implications for coexistence of the two species. G. histrio had a similar PLD (20.7 ± 2.0 days) to G. erythrospilus (18.5 ± 1.9 days), and there was no difference in size-at-settlement between the species. Juveniles of the two species had similar patterns of habitat use and similar competitive abilities, supporting the lottery mechanism at settlement. However, adults differ in their habitat use, supporting the prediction that resource partitioning increases with ontogeny. In laboratory experiments, adults of each species preferred colonies of Acropora nasuta. However, G. histrio was a superior competitor and prevented G. erythrospilus from using A. nasuta in > 70% of the trials. In the field transplant experiment, G. erythrospilus (inferior competitor) suffered less of a fitness loss when occupying the non-preferred coral (A. spathulata) compared with G. histrio, which could explain its ability to persist when displaced by the superior competitor. These results suggest that the competitive mechanism operating between the two Gobiodon species shifts from a lottery for space to niche partitioning through ontogeny, and that these two mechanisms of competitive coexistence are not mutually exclusive.

Positive and negative responses of coral calcification to elevated pCO2: case studies of two coral species and the implications of their responses

Fragments of 2 coral species (Acropora nasuta and Pocillopora damicornis), collected from the South China Sea, were incubated for 94 d under controlled conditions of pCO(2) = 389, 700, and 1214 mu atm. Our incubation experiments showed that the net calcification rate of A. nasuta responded negatively to elevated pCO(2) in both short and mid-term incubations. In contrast, the net calcification rate of P. damicornis increased under elevated pCO(2) during the first 17 d, but then returned to background rates. Based on previous models, our modified models showed that the different responses of these 2 coral species depended on the dissolved inorganic carbon (DIC) and pH levels in coral calcifying fluid. In the studied models, the positive responses of coral calcification to higher pCO(2) could be explained by either low DIC due to a higher photosynthesis rate or a stronger H+ pump. If DIC in calcifying fluid is greatly reduced by photosynthesis, the de creased DIC in calcifying fluid may be benefited by enhanced external seawater CO2, which will partially offset the dissolution due to ocean acidification. Therefore, in addition to our experimental results, our model provides a theoretical basis showing how coral may respond negatively and positively to ocean acidification.

A first endeavour in restoring denuded, post-bleached reefs in Tanzania

The worldwide decline in coral reefs has prompted a search for effective restoration protocols. We transplanted 6912 and 7110 corals (Acropora muricata, Acropora nasuta, Acropora hemprichi, Pocillopora verrucosa, Porites cylindrica, Millepora sp.) in Changuu, Zanzibar and Kitutia, Mafia, Tanzanian reefs that suffered in 1998 from a massive coral bleaching incident, causing a wide spread coral death. No sign for natural recovery has been recorded thereafter. In each site, we randomly set up 12 plots (36 m2 each), of which three were transplanted with a mix of three Acropora spp. (Treatment 1, T1), three with a mix of all six scleractinian species (T2), and six served as controls. Within one month of transplantation, an outbreak of Acanthaster planci in Changuu caused mortality at 50%. One year survival of transplants in T1 and T2 at Kitutia reached 66.4% and 62.5% respectively, significantly higher than at Changuu; an outcome recorded through species-by-species comparisons on four species only (P. verrucosa, P. cylindrica, A. muricata, A. nasuta). After one year no significant difference was documented in ecological volumes (EV) between T1 and T2 in stark contrast to the among species comparisons in T1, at each site. A within treatment one-way ANOSIM comparison for fish assemblage structures performed between the first and last three months of the transplantation year (Kitutia reef) revealed strong separation (T1, Global R = 0.743, P < 0.001; T2, R = 0.445, P < 0.001 and T3, R = 0.694, P < 0.001) while the same treatment revealed weak separation at Changuu site T1 (R = 0.035, P > 0.262) and T2 plots (R = 0.119, P < 0.043). Similarly, one-way ANOSIM done on the initial and last 3-month periods on invertebrates' community composition (at all sites, except T1 of Changuu reef), showed no significant difference between community composition at both ends of the sampling period. Altogether, transplantation cost (US$0.19/colony) suggested that large scale transplantation is economically viable. Cumulatively, field results and economic evaluations showed that transplantation of nursery-grown colonies might uphold critical ecosystem functions while used in reversing phase shift states in coral reefs.

Validation of internal reference genes for gene expression analysis in Montipora digitata, Pocillopora damicornis and Acropora nasuta by quantitative real-time PCR

Abstract The highest concentrations of Indo-Pacificreef coral species occur in the Coral Triangle (CT). A large part of the CT is bordering the edge of the Sunda Shelf, with the highest species richness to the north and east of the Sunda Shelf, including parts of Malaysia, Indonesia, the Philippines, Papua New Guinea, Timor Leste, and the Solomons. Within eastern Indonesia also differences in coral reef fauna can be observed, e.g. between Sulawesi and West Papua. There is no relation with Wallace’s Line or with Wallacea, the area in between the Sunda and Sahul shelves, which both relate to terrestrial biogeography. The west-east variation in marine species diversity can be explained hypothetically in four ways. The CT has more species because of (1) plate tectonics; (2) a higher species survival during the Last Glacial Maximum (LGM); (3) higher habitat variability, especially from near-shore (shallow, sheltered, murky water) to offshore (deep, ex-posed clear water); (4) inter-oceanic currents running in north-south direction between the Pacificand the Indian Ocean, such as the Indonesian Through Flow (ITF), pre-venting connections between west and east. Future re-search should give more insight in the relative im portance of these four factors and whether there are clear-cut lines of division or zones of transition with ever-changing species compositions.

The Coral-Seaweed Battleground

Goby fish may not seem like great underwater warriors, but when it comes to protecting corals from poisonous and invasive seaweeds, the pretty little reef dwellers are an essential line of defense. Earlier this month, a paper in Science reported that 3-cm-long goby fish called Gobiodon histrio respond to a chemical distress signal given out by the coral Acropora nasuta when it comes into contact with poisonous seaweed called Chlorodesmis fastigiata. The goby fish save the day by eating this toxic seaweed—which most reef fish deliberately avoid—so that it cannot hurt its coral host (DOI: 10.1126/science.1225748). This is more than just a straightforward case of goby homeland security. The goby is defending Acropora coral, a genus that is among the first coral to die when a reef is under duress from environmental stressors such as ocean acidification. This kind of coral is also important for reef architecture, providing “the structural ...

Corals chemically cue mutualistic fishes to remove competing seaweeds.

Corals in the genus Acropora generate much of the structural complexity upon which coral reefs depend, but they are susceptible to damage from toxic seaweeds. Acropora nasuta minimizes this damage by chemically cuing symbiotic goby fishes (Gobiodon histrio or Paragobiodon echinocephalus) to remove the toxic seaweed Chlorodesmis fastigiata. Within minutes of seaweed contact, or contact from only seaweed chemical extract, the coral releases an odor that recruits gobies to trim the seaweed and dramatically reduce coral damage that would otherwise occur. In turn, chemically defended gobies become more toxic after consumption of this noxious alga. Mutualistic gobies and corals appear to represent a marine parallel to terrestrial ant-plants, in that the host provides shelter and food in return for protection from natural enemies.

Effects of water turbidity on the symbiotic zooxanthella of hermatypic corals

Five species of reef-building coral (Acropora millepora, Acropora nasuta, Pocillopora damicornis, Galaxea fascicularis and Porites lutea) were used to study the effects of water turbidity stress on the symbiotic zooxanthella. The gradients of water turbidity were simulated using a solution containing different concentrations of inactivated Escherichia coli. The results revealed that the photosynthetic efficiency and density of the symbiotic zooxanthella were both restricted by the water turbidity, and that high turbidity corresponds to high inhibitory action. The results also showed that the tolerance of the five symbiotic zooxanthella to water turbidity differed, with the massive corals Galaxea fascicularis and Porites lutea having strong tolerance, and that of the branching corals Acropora millepora, Acropora nasuta and Pocillopora damicornis being relatively weak.

Recruitment hotspots: consistent spatial patterns in the relative abundance of coral recruits at One Tree Island, Australia

On coral reefs, sites that receive consistently high levels of recruitment relevant to other sites (“recruitment hotspots”) may be crucial to the persistence of populations. However, few studies of coral recruitment have the necessary replication in space and time required to detect recruitment hotspots. The aim of this study was to detect recruitment hotspots at One Tree Reef (southern Great Barrier Reef) and to explore associations between hotspots, hydrodynamics, adult abundance and reef benthos. Recruitment hotspots were detected on the reef slope and in the lagoon. Almost all hotspots were located on the leeward side of the reef, however, there was little congruence among hotspots for different families of coral recruits. Recruitment hotspots in some taxa in some habitats were correlated with water flow or adult abun-dance. A clear recruitment hotspot for two families (Pocilloporidae and Poritidae) in the lagoon had medium levels of water flow (∼4 cm s-1), but there was no re-lationship with water flow on the slope. In experimental aquaria, Acropora nasuta settlement was six to 10 times greater under low (2.1 cm s-1) compared to medium water flow (4.6 cm s-1). Abundance of pocilloporid and poritid, but not acroporid, recruits at each site was often correlated with adult cover indicating either aggregative settlement or limited dispersal. Recruitment hotspots are likely to be both sources and sinks for some taxa, and therefore identifying and protecting hotspots should be a high priority in marine reserve design.

The durability of bioclastic sediments and implications for coral reef deposit formation

AbstractThe generation and composition of carbonate sediment within tropical carbonate settings is controlled by the skeletal production of CaCO3 in conjunction with physical, biological and chemical processes which act to break down and disperse skeletal remains. Using the results of detailed tumbling barrel experiments, this paper discusses the role the physical durability of common constituents of reef sediment plays in the composition of coral reef deposits. The durability of the skeletal remains of six reef sediment constituents was determined experimentally using tumbling barrels. Results indicate that constituent durability varies considerably amongst common reef sediment constituents. Calcareous algae Halimeda was the least durable constituent tested, followed by larger benthic foraminifera Baculogypsina sphaerulata and Marginopora vertebralis and the pelecypod Fragum fragum. Two species of branching coral (Acropora sarmentosa and Acropora nasuta) were found to be the most resistant to physical destruction. These findings provide increased power to interpret reef and island deposits and the potential role skeletal durability plays in the retention of constituent skeletons within coral reef associated sedimentary systems.