Staghorn Acropora Research Articles

Nocturnal substrate association of four coral reef fish groups (parrotfishes, surgeonfishes, groupers and butterflyfishes) in relation to substrate architectural characteristics.

Although numerous coral reef fish species utilize substrates with high structural complexities as habitats and refuge spaces, quantitative analysis of nocturnal fish substrate associations has not been sufficiently examined yet. The aims of the present study were to clarify the nocturnal substrate associations of 17 coral reef fish species (nine parrotfish, two surgeonfish, two grouper and four butterflyfish) in relation to substrate architectural characteristics. Substrate architectural characteristics were categorized into seven types: (1) eave-like space, (2) large inter-branch space, (3) overhang by protrusion of fine branching structure, (4) overhang by coarse structure, (5) uneven structure without large space or overhang, (6) flat and (7) macroalgae. Overall, fishes were primarily associated with three architectural characteristics (eave-like space, large inter-branch space and overhang by coarse structure). The main providers of these three architectural characteristics were tabular and corymbose Acropora, staghorn Acropora, and rock. Species-specific significant positive associations with particular architectural characteristics were found as follows. For the nine parrotfish species, Chlorurus microrhinos with large inter-branch space and overhang by coarse structure; Ch. spilurus with eave-like space and large inter-branch space; Hipposcarus longiceps with large inter-branch space; Scarus ghobban with overhang by coarse structure; five species (Scarus forsteni, S. niger, S. oviceps, S. rivulatus and S.schlegeli) with eave-like space. For the two surgeonfish species, Naso unicornis with overhang by coarse structure; N. lituratus with eave-like space. For the two grouper species, Plectropomus leopardus with eave-like space; Epinephelus ongus with overhang by coarse structure. For the four butterflyfish species, Chaetodon trifascialis with eave-like space and large inter-branch space; C. lunulatus and C. ephippium with large inter-branch space; C. auriga showed no significant associations with any architectural characteristics. Four species (Ch. microrhinos, H. longiceps, S. niger and N. unicornis) also showed clear variations in substrate associations among the different fish size classes. Since parrotfishes, surgeonfishes and groupers are main fisheries targets in coral reefs, conservation and restoration of coral species that provide eave-like space (tabular and corymbose Acropora) and large inter-branch space (staghorn Acropora) as well as hard substrates with coarse structure that provide overhang (rock) should be considered for effective fisheries management in coral reefs. For butterflyfishes, coral species that provide eave-like space (tabular Acropora) and large inter-branch space (staghorn Acropora) should also be conserved and restored for provision of sleeping sites.

Performance of ecological restoration in an impaired coral reef in the Wuzhizhou Island, Sanya, China

Coral restoration is becoming popular to help restoring degraded coral reefs. However, few studies have tried to monitor the long-term recovery of coral reefs, which makes it difficult to assess the performance of the restoration. We monitored the growth of three transplanted Acropora corals and naturally-attached Pocillopora damicornis on artificial reefs (ARs) from October 2014 to September 2018 during which there were several attacks of typhoons. Results show that two staghorn Acropora species had the highest growth rates (11.0–12.1 cm/a), followed by table coral A. divaricate (5.6 cm/a) and P. damicornis (4.8 cm/a). A linear growth pattern was found for the three Acropora species; the pattern gradually slowed in P. damicornis. There was a strong interspecific competition for space among the corals on ARs, and it led to the sharply declined occurrence of slow-growing P. darmicornis colonies in 2017. Coral recovery was successful at the Wuzhizhou Island and quickly increased AR complexity. However, the ARs made of metal frames fail to resist the direct attack from a catastrophic typhoon. Therefore, concrete and environmental-friendly materials should be used in future restoration. This study is the first report on long-term monitoring and assessment of coral reef restoration in China. The results offer future guide of reef restoration for impaired coral reefs in regions easily affected by typhoons.

Successive bleaching events cause mass coral mortality in Guam, Micronesia

The reefs of Guam, a high island in the Western Pacific, were impacted by an unprecedented succession of extreme environmental events beginning in 2013. Elevated SSTs induced severe island-wide bleaching in 2013, 2014, 2016, and 2017. Additionally, a major ENSO event triggered extreme low tides beginning in 2014 and extending through 2015, causing additional coral mortality from subaerial exposure on shallow reef flat platforms. Here, we present the results of preliminary analyses of environmental and biological data collected during each of these events. Accumulated heat stress in 2013 was the highest since satellite measurements began, but this record was exceeded in 2017. Overall, live coral cover declined by 37% at shallow reef flat sites along the western coast, and by 34% at shallow seaward slope sites around the island. Staghorn Acropora communities lost an estimated 36% live coral cover by 2017. Shallow seaward slope communities along the eastern windward coast were particularly devastated, with an estimated 60% of live coral cover lost between 2013 and 2017. Preliminary evidence suggests that some coral species are at high risk of extirpation from Guam’s waters. In light of predictions of the near-future onset of severe annual bleaching, and the possibility that the events of 2013–2017 may signal the early arrival of these conditions, the persistence of Guam’s current reef assemblages is in question. Here, we present detailed documentation of ongoing changes to community structure and the status of vulnerable reef taxa, as well as a critical assessment of our response protocol, which evolved annually as bleaching events unfolded. Such documentation and analysis are critical to formulating effective management strategies for the conservation of remaining reef diversity and function.

Managers, modelers, and measuring the impact of species distribution model uncertainty on marine zoning decisions.

Marine managers routinely use spatial data to make decisions about their marine environment. Uncertainty associated with this spatial data can have profound impacts on these management decisions and their projected outcomes. Recent advances in modeling techniques, including species distribution models (SDMs), make it easier to generate continuous maps showing the uncertainty associated with spatial predictions and maps. However, SDM predictions and maps can be complex and nuanced. This complexity makes their use challenging for non-technical managers, preventing them from having the best available information to make decisions. To help bridge these communication and information gaps, we developed maps to illustrate how SDMs and associated uncertainty can be translated into readily usable products for managers. We also explicitly described the potential impacts of uncertainty on marine zoning decisions. This approach was applied to a case study in Saipan Lagoon, Commonwealth of the Northern Mariana Islands (CNMI). Managers in Saipan are interested in minimizing the potential impacts of personal watercraft (e.g., jet skis) on staghorn Acropora (i.e., Acropora aspera, A. formosa, and A. pulchra), which is an important coral assemblage in the lagoon. We used a recently completed SDM for staghorn Acropora to develop maps showing the sensitivity of zoning options to three different prediction and three different uncertainty thresholds (nine combinations total). Our analysis showed that the amount of area and geographic location of predicted staghorn Acropora presence changed based on these nine combinations. These dramatically different spatial patterns would have significant zoning implications when considering where to exclude and/or allow jet skis operations inside the lagoon. They also show that different uncertainty thresholds may lead managers to markedly different conclusions and courses of action. Defining acceptable levels of uncertainty upfront is critical for ensuring that managers can make more informed decisions, meet their marine resource goals and generate favorable outcomes for their stakeholders.

Anomalous temperatures and extreme tides: Guam staghorn Acropora succumb to a double threat

Anomalous temperatures and extreme tides: Guam staghorn Acropora succumb to a double threat

Structural complexity mediates functional structure of reef fish assemblages among coral habitats

Coral community composition varies considerably due to both environmental conditions and disturbance histories. However, the extent to which coral composition influences associated fish assemblages remains largely unknown. Here an ecological trait-based ordination analysis was used to compare functional richness (range of unique trait combinations), functional evenness (weighted distribution of fishes with shared traits), and functional divergence (proportion of total abundance supported by species with traits on the periphery of functional space) of fish assemblages among six distinct coral habitats. Despite no significant variation in species richness among habitats, there were differences in the functional richness and functional divergence, but not functional evenness, of fish assemblages among habitats. Structural complexity of coral assemblages was the best predictor of the differences in functional richness and divergence among habitats. Functional richness of fish assemblages was highest in branching Porites habitats, lowest in Pocillopora and soft coral habitats, and intermediate in massive Porites, staghorn Acropora, and mixed coral habitats. Massive and branching Porites habitats displayed greater functional divergence in fish assemblages than the Pocillopora habitat, whilst the remaining habitats were intermediate. Differences in functional richness and divergence were largely driven by the presence of small schooling planktivores in the massive and branching Porites habitats. These results indicate that differential structural complexity among coral communities may act as an environmental filter, affecting the distribution and abundance of associated species traits, particularly those of small-bodied schooling fishes.

Community-based, low-tech method of restoring a lost thicket of Acropora corals

Abstract Due to unregulated blast fishing and episodic bleaching events, the back-reef zone near Barangay Lucero in Bolinao, Pangasinan, Philippines, was reduced to a barren area of unconsolidated sand and coral rubble. Anecdotal accounts from local inhabitants, scientific reports, and examination of rubble on the substratum revealed that the area had been dominated by staghorn Acropora corals prior to degradation. With no significant signs of natural recovery, a low-tech restoration method that is both transferable to the community and cost-effective was devised and implemented. Through the help of local inhabitants, 450 fragments of two staghorn coral species (Acropora intermedia and A. pulchra) were transplanted, without using SCUBA equipment, in a total of six 4 × 4 m plots. There were two transplant density treatments: low and high, receiving 25 and 50 fragments of each coral species, respectively. Survivorship and growth of transplants, as well as the assemblage of fishes and macroinvertebrates inside the transplantation and control plots, were monitored periodically for up to 19 months. Transplant survivorship was generally high (68–89%) at the end of the study. There was also an average of a 15-fold increase in ecological volume of the transplants (from 1784.25 ± 162.75 to 26 540.765 ± 4547.25 cm3). Consequently, a significantly higher number of fish and of macroinvertebrates was recorded inside the transplantation plots than in the control plots, indicating signs of restoration success with the reintroduction of the two coral species. Exhibiting significant differences in coral cover, fish biomass and abundance, high-density is more cost-effective than low-density treatment, attaining optimal effects on key reef recovery parameters. The total cost of restoring a thicket of Acropora in a sandy-rubble field using this low-tech rehabilitation method with community participation was estimated to be US$9198.40 ha−1 (US$0.90 m−2), and thus ∼60% cheaper than without community involvement. Community involvement not only reduced the cost of the restoration activity but also provided the community with a sense of ownership and responsibility for their resources, thus ensuring the long-term success of the intervention.

Microhabitat association in white-streaked grouper Epinephelus ongus: importance of Acropora spp.

Microhabitat associations are considered to be important for juvenile survivorship and growth of coral reef fishes. The aim of the study was to quantify microhabitat associations between juvenile and adult white-streaked grouper Epinephelus ongus, which supports important fisheries in coral reef areas. Underwater observations revealed that most juveniles were found in bottlebrush Acropora spp., staghorn Acropora spp. and coral rubble and there was a significant positive use of bottlebrush Acropora spp. and a significant negative use of coral rubble. For adults, most individuals were found in bottlebrush Acropora spp. and staghorn Acropora spp., and there was a significant positive use of staghorn Acropora spp. and significant negative use of coral rubble. A habitat choice experiment by using pre-settlement individuals revealed that both bottlebrush Acropora spp. and staghorn Acropora spp. were used as settlement sites, whereas coral rubble was rarely used as a settlement site. Results of the study suggest that juvenile and adult E. ongus showed significantly positive microhabitat associations with bottlebrush Acropora spp. and staghorn Acropora spp., respectively, in the field. Bottlebrush Acropora spp. has smaller inter-branch spaces than staghorn Acropora spp., which could drive patterns of microhabitat associations. In addition, post-settlement processes such as predation may influence the spatial distribution of juveniles. Because Acropora corals are very susceptible to coral bleaching, we predict that rising temperatures from climate change will negatively impact populations of E. ongus.

Spatiotemporal patterns of coral disease prevalence on Heron Island, Great Barrier Reef, Australia

Despite increasing research effort on coral diseases, little is known about factors driving disease dynamics on the Great Barrier Reef (GBR). This is the first study to investigate the temporal patterns of coral disease prevalence and potential drivers of disease around Heron Island, in the southern Capricorn Bunker sector of the GBR. Surveys were conducted in two austral summers and three winters between November 2007 and August 2009 on six sites around the island. Six diseases were detected: brown band syndrome (BrB), growth anomalies (GA), ulcerative white spots (UWS), white syndrome (WS), skeletal eroding band disease (SEB) and black band disease (BBD). The lowest overall mean disease prevalence was 1.87 ± 0.75% (mean ± SE) in November 2007 and the highest 4.22 ± 1.72% in August 2008. There was evidence of seasonality for two diseases: BrB and UWS. This is the first study to report a higher prevalence of BrB in the winter. BrB had a prevalence of 3.29 ± 0.58% in August 2008 and 1.53 ± 0.28% in August 2009, while UWS was the most common syndrome in the summer with a prevalence of 1.12 ± 0.31% in November 2007 and 2.67 ± 0.52% prevalence in January 2008. The prevalence of GAs and SEB did not depend on the season, although the prevalence of GAs increased throughout the study period. WS had a slightly higher prevalence in the summer, but its overall prevalence was low (<0.5%). Sites with high abundance of staghorn Acropora and Montipora were characterised by the highest disease prevalence (12% of Acropora and 3.3% of Montipora species were diseased respectively). These results highlight the correlations between coral disease prevalence, seasonally varying environmental parameters and coral community composition. Given that diseases are likely to reduce the resilience of corals, seasonal patterns in disease prevalence deserve further research.

Community‐level density dependence: an example from a shallow coral assemblage

While density dependence is a popular topic of research in population ecology, it has received much less attention at the community level. Using 27 years of data from Heron Island, on Australia's Great Barrier Reef, we develop a matrix model of coral community dynamics that shows that community-level density dependence does occur and that it is fairly common, being found in 38% of the model parameters for which it was tested. In particular, colonization of free space (through either recruitment or growth of existing colonies) was nearly always density dependent. There were no consistent patterns in the results for mortality, persistence, or species interactions. Most transitions were found to be dependent on the cover of the incoming species group, with only a few dependent on that of the outgoing species group. In addition, few of the transitions representing species interactions were dependent on the amount of free space present, suggesting that the cover of other species does not influence encounters. When these results were combined into a model of community dynamics, it was found that density dependence resulted in a moderate increase in coral cover, which was spread over most species groups. The dynamics of the density-dependent assemblage were also a lot noisier than those of an assemblage without density dependence. Sensitivity analysis indicated that it was density dependence in the colonization probabilities, particularly of encrusting acroporids, bushy Acropora and staghorn Acropora, which had the main influence on the model, although persistence of free space was also important. Transitions representing mortality were only of minor importance, and those representing species interactions were of no importance.

Dynamics of shallow-water assemblages in the Saipan Lagoon

The Saipan Lagoon (Northern Mariana Islands) was first examined for benthic compo- sition and habitat distribution in the late 1940s. Here, we employ a 4-stage approach to evaluate and explain change in the distribution of the 9 habitats previously demarcated. We show that there have been considerable reductions in seagrass, staghorn Acropora, and Acropora palifera dominated habi- tats (-3.72, -1.26, and -1.37 km 2 , respectively) that were replaced by 6.16 km 2 of sand (~20% of the lagoon area). Multiple regressions showed that the spatial extent of Enhalus seagrass was positively related with, and best predicted by, the adjacent watershed area and lagoon width. Although the interaction was not as strong, Enhalus also increased in accordance with human development. The size of the Halodule seagrass and macroalgal habitat was negatively related to water-flow velocities and positively related to human development, while its integrity (i.e. the density of seagrass within a given habitat) decreased with human development. Taken together, the results suggest Enhalus and Halodule respond differently to proxies of watershed pollution, and contradict contemporary doctrine linking pollution with reduced seagrass density. This study found no relationship between offshore habitats and watershed characteristics, but suggests their expansion and contraction on relatively short time scales is a result of large-scale disturbances such as typhoons. We posit that, while habitat integrity can be altered by human disturbances, habitat identity is only altered under extreme condi- tions. In summary, this study advances habitat mapping by increasing resolution and accuracy, which, in turn, improves the texture at which reef ecology is used by management.

Latitudinal variation in coral communities in eastern Australia: a qualitative biophysical model of factors regulating coral reefs

The processes underlying the distributional limits of both corals and coral reefs can be elucidated by examining coral communities at high latitudes. Coral-dominated communities in eastern Australia cover a latitudinal range of >2,500 km, from the northern Great Barrier Reef (11°S) to South West Rocks (31.5°S). Patterns of coral species richness from 11 locations showed a clear separation between the Great Barrier Reef and subtropical sites, with a further abrupt change at around 31°S. Differences in community structure between the Great Barrier Reef and more southern sites were mainly attributable to higher cover of massive corals, branching Acropora, dead coral and coralline algae on the Great Barrier Reef, and higher cover of macroalgae and bare rock at more southern sites. The absence of some major reef-building taxa (i.e., staghorn Acropora and massive Porites) from most subtropical sites coincided with the loss of reef accretion capacity. Despite high cover of hard corals in communities at up to 31°S, only Lord Howe Island contained areas of reef accretion south of the Great Barrier Reef. Factors that have been hypothesized to account for latitudinal changes in coral community structure include water temperature, aragonite saturation, light availability, currents and larval dispersal, competition between corals and other biota including macroalgae, reduced coral growth rates, and failure of coral reproduction or recruitment. These factors do not operate independently of each other, and they interact in complex ways.

An experimental assessment of survival, re-attachment and fecundity of coral fragments

Many branching corals are routinely broken apart into live fragments, mainly by physical disturbances. Fragments have the potential to survive independently and reproduce sexually, but until these processes are better understood, it is unclear when and where fragmentation is adaptive. In this study, we assess variation in rates of survivorship, reattachment and fecundity of fragments as a function of species, fragment size and habitat. We investigated three common Indo–Pacific corals (the staghorn Acropora intermedia, bushy A. millepora and tabular A. hyacinthus), using 900 artificially generated fragments of two sizes, deployed in the reef flat, crest and slope habitats. Fragments of A. intermedia had the highest survivorship, with 32% remaining alive after 17 months, compared to 15% for A. millepora and 8% for A. hyacinthus. Larger fragments survived substantially better than small ones (30 vs 8%). Fragments deployed on the reef flat also survived better (32%), compared to the reef crest (14%) and reef slope (10%). The amount of reattachment varied from 0 to 50% depending on species, size and habitat, and was greatest for staghorn A. intermedia, on the relatively protected reef flat, and for larger fragments. Experimental fragments had substantially reduced fecundities, relative to intact control colonies. Collections of natural fragments upon the reef crest revealed that bushy Acropora millepora produced the most fragments relative to the percent cover of established colonies, but these were small and (based on our experiments) have a high mortality schedule. Tabular Acropora hyacinthus produced the fewest fragments, which had the highest rate of mortality of the three species. The staghorn A. intermedia generated relatively large fragments at an intermediate rate, which survived well in all habitats. Consequently, asexual reproduction by fragmentation is likely to be a more important life-history trait for A. intermedia than A. millepora or A. hyacinthus. Depending on circumstances, the considerable costs of fragmentation (high mortality and low fecundity) may outweigh the advantages, in corals and other clonal organisms.

Long-term effects of destruction of hermatypic corals by Acanthaster plana infestation on reef fish communities at Iriomote Island, Japan

Long-term changes in structure of fish communities on coral reefs infested by the coralfeeding starfish Acanthasterplanci were determined using 20 mZ visual transects. We censused a living coral reef consisting mainly of staghorn Acropora spp. at Saluyama Bay and a dead coral reef with low structural complexlty of coral branches (about 2 yr after A. planci infestation) at Amitori Bay, Iriomote Island (Ryukyu Islands, Japan) in September 1984. Two yr later, we recensused the dead coral reef, which had changed into a flat plain of unstructured coral rubble ('rubble reef'). Mean numbers of species and individuals per transect severely decreased in the following order of reef types: (1) living reef (1984). (2) dead reef (1984), and (3) rubble reef (1986). Correlated with these decreases in numbers were several patterns: (1) coral-polyp feeders completely s (2) numbers of resident species and individuals decreased on the dead reef, perhaps due to decrease in living space or shelter associated with the reduction in structural complexity of coral branches; and (3) numbers of species and individuals of both resident and visitor fishes declined on the unstructured rubble reef, likely due to shortage of living space and food.