Massive Coral Porites Research Articles

Genomic data reveals habitat partitioning in massive Porites on Guam, Micronesia

Corals in marginal reef habitats generally exhibit less bleaching and associated mortality compared to nearby corals in more pristine reef environments. It is unclear, however, if these differences are due to environmental differences, including turbidity, or genomic differences between the coral hosts in these different environments. One particularly interesting case is in the coral genus Porites, which contains numerous morphologically similar massive Porites species inhabiting a wide range of reef habitats, from turbid river deltas and stagnant back reefs to high-energy fore reefs. Here, we generate ddRAD data for 172 Porites corals from river delta and adjacent (<0.5 km) fore reef populations on Guam to assess the extent of genetic differentiation among massive Porites corals in these two contrasting environments and throughout the island. Phylogenetic and population genomic analyses consistently identify seven different clades of massive Porites, with the two largest clades predominantly inhabiting either river deltas or fore reefs, respectively. No population structure was detected in the two largest clades, and Cladocopium was the dominant symbiont genus in all clades and environments. The perceived bleaching resilience of corals in marginal reefs may therefore be attributed to interspecific differences between morphologically similar species, in addition to potentially mediating environmental differences. Marginal reef environments may therefore not provide a suitable refuge for many reef corals in a heating world, but instead host additional cryptic coral diversity.

Coral geochemical response to uplift in the aftermath of the 2005 Nias–Simeulue earthquake

On 28 March 2005, the Indonesian islands of Nias and Simeulue experienced a powerful Mw 8.6 earthquake and coseismic uplift and subsidence. In areas of coastal uplift (up to ~ 2.8 m), fringing reef coral communities were killed by exposure, while deeper corals that survived were subjected to habitats with altered runoff, sediment and nutrient regimes. Here we present time-series (2000–2009) of Mn/Ca, Y/Ca and Ba/Ca variability in massive Porites corals from Nias to assess the environmental impact of a wide range of vertical displacement (+ 2.5 m to − 0.4 m). High-resolution LA-ICP-MS measurements show that skeletal Mn/Ca increased at uplifted sites, regardless of reef type, indicating a post-earthquake increase in suspended sediment delivery. Transient and/or long-term increases in skeletal Y/Ca at all uplift sites support the idea of increased sediment delivery. Coral Mn/Ca and Ba/Ca in lagoonal environments highlight the additional influences of reef bathymetry, wind-driven sediment resuspension, and phytoplankton blooms on coral geochemistry. Together, the results show that the Nias reefs adapted to fundamentally altered hydrographic conditions. We show how centuries of repeated subsidence and uplift during great-earthquake cycles along the Sunda megathrust may have shaped the modern-day predominance of massive scleractinian corals on the West Sumatran reefs.

Sea surface temperature reconstruction in the Pacific Ocean using multi-elemental proxy in Porites and Diploastrea corals: Application to Palau Archipelago

Massive reef-building Porites corals are commonly studied to obtain long-term reconstructions of past sea surface temperature (SST) using temperature-sensitive elemental proxies, such as Sr/Ca or Li/Mg ratios. Most recently, a multi-proxy approach combining these two ratios (e.g. D'Olivo et al., 2018) and the SrU method (DeCarlo et al., 2016) have proved to be more robust to reconstruct paleo-temperatures. To date, no study has been carried out on the application of these new approaches on the Diploastrea heliopora coral, another massive reef-building genus that can potentially provide longer temperature records. Moreover, only a few studies have assessed coral SST calibrations at the scale of the Indo-Pacific basin and compared SST reconstructions obtained from two massive coral genera from the same site.In this study, we investigated the elemental composition of the topmost portion of 34 modern tropical Porites and 6 Diploastrea colonies collected during the Tara Pacific expedition (2016–2018) from various hydrological contexts in the Pacific Ocean. We derived and discussed annual Sr/Ca, Li/Mg, combined Sr/Ca-Li/Mg and Sr/Ca-Li/Ca-Mg/Ca and SrU vs. SST calibrations as well as potential intra-colonial and genus specific effects and evaluated the use of these basin-wide calibration equations. Overall, multi-ratio and multi-genera SST calibrations perform better than single-ratio calibrations and seem to improve temperature reconstructions.These new SST calibrations were applied to two colonies of Porites and Diploastrea collected from the same site in the North-West of the Palau archipelago located in the western Pacific Ocean to evaluate the applicability of universal calibrations based on different proxies and their combination. Coral-based SST records spanning the last 141 years show decadal changes and recent warming episodes that are related to major El Niño Southern Oscillation events. However, differences in reconstruction remain between both genera in the long-term trends, amplitudes, and absolute temperatures, depending on which genus or temperature proxy is considered.

Depth‐independent phenotypic variation of massive Porites coral color morphs

AbstractAs coral reefs continue to decline due to anthropogenic stressors, community characterizations will reveal both historical selection processes and adaptive potential to environmental change. To address the potential role of color in the distribution and resilience of massive Porites corals, we surveyed the distributions of two dominant color morphs (brown and purple), and a unique intermediate state, across a depth gradient in Guam, Micronesia. We found that brown colonies dominated populations across all depths, and larger colonies had higher rates of partial tissue mortality and active disease lesions. Despite the dominance of brown colonies, both brown and purple color morphs showed a high similarity in susceptibility, as indicated by the colony sizes, the severity of partial tissue mortality, and the prevalence of active disease lesions. This is a non‐intuitive result given the presence of phenotypic plasticity between color morphs, evident by an intermediate, transitionary stage between brown and purple colonies that suggests a functional divergence between one color over the other. The study also revealed the dominance of small colonies at depth, which provides some insight into the ecological impacts that may have shaped Guam's current massive Porites population size structure over the past several decades. With this, we provide foundational insight into the adaptive strategies and historical pressures that have shaped the modern massive Porites population.

Porites' coral calcifying fluid chemistry regulation under normal- and low-pH seawater conditions in Palau Archipelago: Impacts on growth properties

Ongoing ocean acidification is known to be a major threat to tropical coral reefs. To date, only few studies have evaluated the impacts of natural long-term exposure to low-pH seawater on the chemical regulation and growth of reef-building corals. This work investigated the different responses of the massive Porites coral living at normal (pHsw ~ 8.03) and naturally low-pH (pHsw ~ 7.85) seawater conditions at Palau over the last decades. Our results show that both Porites colonies maintained similar carbonate properties (pHcf, [CO32−]cf, DICcf, and Ωcf) within their calcifying fluid since 1972. However, the Porites skeleton of the more acidified conditions revealed a significantly lower density (~ 1.21 ± 0.09 g·cm−3) than the skeleton from the open-ocean site (~ 1.41 ± 0.07 g·cm−3). Overall, both Porites colonies exerted a strong biological control to maintain stable calcifying fluid carbonate chemistry that favored the calcification process, especially under low-pH conditions. However, the decline in skeletal density observed at low pH provides critical insights into Porites vulnerability to future global change.

Hot spots of bleaching in massive Porites coral colonies

Coral bleaching events have become more frequent and severe due to ocean warming. While the large-scale impacts of bleaching events are well-known, there is growing recognition of the importance of small-scale spatial variation in bleaching and survival probability of individual coral colonies. By quantifying bleaching in 108 massive Porites colonies spread across Lizard Island, Great Barrier Reef, during the 2016 bleaching event, we investigated how hydrodynamic exposure levels and colony size contribute to local variability in bleaching prevalence and extent. Our results revealed that exposed locations were the least impacted by bleaching, while lagoonal areas exhibited the highest prevalence of bleaching and colony-level bleaching extents. Such patterns of bleaching could be due to prolonged exposure to warm water in the lagoon. These findings highlight the importance of considering location-specific factors when assessing coral health and emphasize the vulnerability of corals in lagoonal habitats to rapid and/or prolonged elevated temperatures.

High Heterotrophic Plasticity of Massive Coral Porites pukoensis Contributes to Its Tolerance to Bioaccumulated Microplastics.

Scleractinian corals have been observed to be capable of accumulating microplastics from reef environments; however, the tolerant mechanism is poorly known. Here, we examined the response of Porites pukoensis to microplastic pollution by analyzing algal symbiont density, energetic metabolism, and caspase3 activities (representing the apoptosis level) in the coral-Symbiodiniaceae association. The environments of three fringing reef regions along the south coast of Sanya City, Hainan Province of China, were polluted by microplastics (for example, microplastic concentrations in the seawater ranged from 3.3 to 46.6 particles L-1), resulting in microplastic accumulation in P. pukoensis (0.4-2.4 particles cm-2). The accumulation of microplastics was negatively correlated to algal symbiont density in the corals but not to caspase3 activities in the two symbiotic partners, demonstrating that P. pukoensis could tolerate accumulated microplastics despite the decrease of algal symbiont density. Furthermore, results from the carbon stable isotope and cellular energy allocation assay indicated that P. pukoensis obtained energy availability (mainly as lipid reserves) using the switch between heterotrophy and autotrophy to maintain energy balance and cope with accumulated microplastics. Collectively, P. pukoensis achieved tolerance to microplastic pollution by maintaining energy availability, which was largely attributed to its high heterotrophic plasticity.

Recovery patterns of the coral microbiome after relief of algal contact

Interactions between macroalgae and corals are omnipresent on eutrophied and overfished reefs worldwide. Contact with macroalgae can disrupt corals and their microbiomes through diverse mechanisms, including shading, abrasion, and the release of algal exudates. However, changes in the coral microbiome after algal contact ceases have not been studied. We investigated the recovery of the microbiome of massive reef-building Porites corals following experimental removal of the overgrowing green macroalga Halimeda macrophysa. We followed changes in the microbiome of macroalgal-removed and adjacent healthy-looking tissue of coral colonies over 40 days. Coral tissue was predominantly bleached underneath the macroalgae but regained almost its full pigmentation by day 40. Despite this recovery in pigmentation, the bacterial microbiome of macroalgal-removed coral tissue did not return to that of adjacent healthy-looking tissue (control). Overall, macroalgal contact led to the suppression of Gammaproteobacteria and increased diversity and dominance of Alphaproteobacteria, a shift that persevered for 40 days after algal removal. Causal effect analysis showed a positive effect of influential OTUs in healthy-looking tissue assigned to Gammaproteobacteria and Bacteroidia on the relative abundance of other OTUs within these classes. The effect of influential OTUs assigned to Alphaproteobacteria in macroalgal-removed tissue on the relative abundance of other OTUs was more diverse. Despite the high heterogeneity of coral microbiomes, differences in the relative abundance of main bacterial classes and orders between control/healthy and macroalgal-removed tissue showed temporal patterns. Differences in the Alpha-, Gamma-, Deltaproteobacteria and Bacteroidia between control/healthy and macroalgal-removed tissue increased after cessation of macroalga contact and stabilized or declined towards day 40. Acidimicrobiia, Deltaproteobacteria, Rhodospirillales and Rhodovibrionales returned to average relative abundances in the adjacent control/healthy tissue after 40 days. Nevertheless, Rhizobiales and Rhodobacterales (Alphaproteobacteria) still dominated the macroalgal-removed microbiome on day 40. We conclude that macroalgal overgrowth induces changes in the coral microbiome, and that algal removal did not lead to full recovery of the microbiome in 40 days. Return of pigmentation and distinct shifts in bacterial groups over time appear a possible pathway to the recovery of the coral microbiome after macroalgal removal.

Diversity and Ecology of Lobophora Species Associated with Coral Reef Systems in the Western Gulf of Thailand, including the Description of Two New Species

The brown macroalgal genus Lobophora plays important ecological roles in many marine ecosystems. This group has received much attention over the past decade, and a considerable number of new species have been identified globally. However, our knowledge of the genus diversity and ecology along south-east Asian coasts are still limited. Given the growing body of research that uses a combination of molecular and morphological data to identify cryptic species, this study investigates the diversity of Lobophora in the western Gulf of Thailand using morphological and molecular data, as well as their interactions with scleractinian corals. A total of 36 Lobophora specimens were collected from 15 sites in the western Gulf of Thailand and used for molecular and morphological analyses. One mitochondrial (cox3) and two chloroplast (psbA and rbcL) genes were amplified and sequenced for molecular phylogenetic analyses. Based primarily on phylogenetic evidence, two new species were formally described, L. chumphonensis sp. nov. and L. thailandensis sp. nov. Additionally, L. lamourouxii was newly recorded from Thailand. Two new lineages of Lobophora obscura were identified, L. obscura12 and L. obscura13. Among the Lobophora species identified, three were found in interaction with corals, the most notable of which was the massive coral Porites. Lobophora chumphonensis sp. nov. only interacted with Porites by growing on bare coral skeleton between Porites colonies. Furthermore, L. obscura13 was observed under the branching coral Pocillopora. Our findings revealed that Lobophora presented both effects and absence of effects on coral. A thorough understanding of Lobophora diversity and ecology is essential for ongoing and future research on coral-macroalgal ecological relationships.

Assessing the intercolony δ18O proxy calibration in a coral microatoll and its implication for ENSO reconstruction in the northern South China Sea

Massive Porites corals are widely used for paleoclimate reconstruction, however the potential of Porites coral microatoll δ18O as high-resolution archive of paleoclimate has only been recognized recently, and the systematic chemistry-climate relationship has yet to be well characterized in the western Pacific. In this study, we examined the reproducibility of microatoll δ18O records against two adjacent Porites corals from the Xisha Islands in the northern South China Sea (SCS) and evaluated the reliability of microatoll δ18O as a proxy for reconstructing regional climate and El Niño-Southern Oscillation (ENSO) variability. The seasonal to interannual variability in microatoll δ18O was primarily controlled by local sea surface temperature (SST), while the δ18O signal might be suppressed by sea surface salinity (SSS) variations on interannual timescale. Despite the overlapping coral δ18O records exhibited similar patterns of variability, the mean values were consistently offset by ~0.2‰ and the sensitivity of δ18O proxy to climate also varied across different coral colonies. The microatoll δ18O exhibited relatively high proxy-SST sensitivities and amplitude of the seasonal variabilities. These results suggested that intercolony δ18O variability was a significant source of uncertainty in coral-based paleoclimate reconstructions. Microatoll δ18O anomaly appeared to serve as a sensitive and relatively reliable proxy for ENSO variability, although the imprints of weak-to-moderate ENSO events could not be fully captured due to the complex relationship between the East Asian Monsoon and ENSO, as well as the local seawater salinity changes. This study further strengthened the evidence for microatoll as an alternate climate archive in the SCS and highlighted its potential in helping resolve poorly understood paleoclimate before instrumental observations.

Evaluation of coral skeletal δ88Sr as a paleoclimate proxy in the northern South China Sea

The climate and environmental significance of the stable strontium isotope composition (δ88Sr) in coral skeletons deserves further investigation. To improve our understanding of stable strontium isotope fractionation during the biomineralization process, correlations between monthly coral skeletal δ88Sr values and climatic and environmental variables (along with their corresponding geochemical proxies) between 2008 and 2009 were studied using a massive zooxanthellae Porites coral head from Sanya Bay on the south coast of Hainan Island in the northern South China Sea. Sea surface temperature and its corresponding geochemical proxies (Sr/Ca and δ18O), pH and its proxy δ11B, and precipitation (representing river runoff) show clear annual cycles, but their correlations with coral δ88Sr were not significant during 2008 and 2009. However, both total solar irradiance (TSI) and coral δ88Sr values followed a gradually increasing trend over the study period and showed a statistically significant correlation. These results indicate that the fractionation associated with coral skeleton δ88Sr is not temperature-dependent, but TSI may play a major role in controlling coral δ88Sr values at our study site. The underlying mechanism of TSI-induced 88Sr/86Sr fractionation in coral skeletons may be similar to that associated with coral δ13C. That is, symbiotic zooxanthellae preferentially uptakes 86Sr during photosynthesis leaving the internal strontium reservoirs enriched in 88Sr; consequently, increased uptake of 88Sr by the coral skeleton occurs when photosynthetic rates increase. However, the correlation between coral δ88Sr and δ13C values may be masked by the carbon input from terrestrial river runoff and the kinetic isotope fractionation effect during the calcification process.

A Century long of coral records of heavy metals in coastal water of Wakatobi Marine National Park, South East Sulawesi

Scleractinian corals absorb heavy metals in their skeletons; therefore, corals can be used as environmental recorders due to incorporating certain metals for centuries. The research was conducted in Wakatobi Marine National Park (WMNP) using a core of massive coral Porites Sp. to determine heavy metals’ concentrations and assess the possible impact on the coastal water. The sample was collected by drilling the coral vertically using a pneumatic tool. Annual banding was determined by using x-ray radiography, continued with sub-sampled from each band, and analyzed using an Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES) for heavy metals determination. Enrichment Factor (EF) and Principal Component Analysis (PCA) were applied for assessing possible impact and differentiating between the heavy metals, respectively. The concentrations of heavy metals fluctuated during the period of the year 1917 to 2016, with the average concentration were 0.55 %, 0.07 %, 2.46 ppm, 3.86 ppm, 5.70 ppm, 63.22 ppm, 0.66 ppm, 3.16 ppm, 0.66 ppm, and 42.59 ppm for Sr, Mg, Mn, Ba, Cu, K, Pb, Zn, Cr, and Al, respectively. EF for all heavy metals showed that the coastal area was at the level of very small pollution (EF<2); therefore, it can be used as baseline data.

Physiological Responses of Pocillopora acuta and Porites lutea Under Plastic and Fishing Net Stress

Marine debris has become a global problem affecting coral health around the globe. However, the photophysiological responses of corals to marine debris stress remain unclear. Therefore, this study firstly investigated transparent and opaque plastic bag shading and fishing nets directly contacting the coral. Photosynthetic performance, pigment content, symbiont density, and calcification rate of a branching coral Pocillopora acuta and a massive coral Porites lutea were investigated after 4 weeks of exposure to marine debris. The results show that the maximum quantum yield of PSII significantly decreased in P. lutea with all treatments, while P. acuta showed no effect on the maximum quantum yield of PSII from any treatments. Transparent plastic bag shading does not affect P. acuta, but significantly affected the maximum photochemical efficiency of P. lutea. Photoacclimation of cellular pigment content was also observed under opaque plastic bag shading for both species at week 2. Fishing nets had the strongest effect and resulted in P. acuta bleaching and P. lutea partial mortality as well as a decline in zooxanthellae density. Calcification rate of P. acuta significantly decreased with treatments using opaque plastic bag and fishing net, but for P. lutea only the treatment with fishing net gave any observable effects. This study suggests that the sensitivities of corals to marine debris differ strongly by species and morphology of the coral.

Dangerous demographics in post-bleach corals reveal boom-bust versus protracted declines

Thermal-stress events have changed the structure, biodiversity, and functioning of coral reefs. But how these disturbances affect the dynamics of individual coral colonies remains unclear. By tracking the fate of 1069 individual Acropora and massive Porites coral colonies for up to 5 years, spanning three bleaching events, we reveal striking genus-level differences in their demographic response to bleaching (mortality, growth, and recruitment). Although Acropora colonies were locally extirpated, substantial local recruitment and fast growth revealed a marked capacity for apparent recovery. By contrast, almost all massive Porites colonies survived and the majority grew in area; yet no new colonies were detected over the 5 years. Our results highlight contrasting dynamics of boom-and-bust vs. protracted declines in two major coral groups. These dangerous demographics emphasise the need for caution when documenting the susceptibility and perceived resistance or recovery of corals to disturbances.

Field measurements of a massive Porites coral at Goolboodi (Orpheus Island), Great Barrier Reef

An exceptionally large coral Porites sp. has been identified and measured at Goolboodi (Orpheus Island), Great Barrier Reef (GBR). This coral was measured in March 2021 during citizen science research of coral reefs in the Palm Islands group. We conducted a literature review and consulted scientists to compare the size, age and health of the Porites with others in the GBR and internationally. This is the largest diameter Porites coral measured by scientists and the sixth highest coral measured in the GBR. The health of the Porites was assessed as very good with over 70% live coral cover and minor percentages of sponge, live coral rock and macroalgae. An estimated age of 421–438 years was calculated based on linear growth models. Manbarra Traditional Owners were consulted and suggested that the Porites be named Muga dhambi (big coral) to communicate traditional knowledge, language and culture to indigenous, tourists, scientists and students.

El Niño–Southern Oscillation and internal sea surface temperature variability in the tropical Indian Ocean since 1675

Abstract. The dominant modes of climate variability on interannual timescales in the tropical Indian Ocean are the El Niño–Southern Oscillation (ENSO) and the Indian Ocean Dipole. El Niño events have occurred more frequently during recent decades, and it has been suggested that an asymmetric ENSO teleconnection (warming during El Niño events is stronger than cooling during La Niña events) caused the pronounced warming of the western Indian Ocean. In this study, we test this hypothesis using coral Sr∕Ca records from the central Indian Ocean (Chagos Archipelago) to reconstruct past sea surface temperatures (SSTs) in time windows from the mid-Little Ice Age (1675–1716) to the present. Three sub-fossil massive Porites corals were dated to the 17–18th century (one coral) and the 19–20th century (two corals). Their records were compared with a published modern coral Sr∕Ca record from the same site. All corals were subsampled at a monthly resolution for Sr∕Ca measurements, which were measured using a simultaneous inductively coupled plasma optical emission spectrometer (ICP-OES). Wavelet coherence analysis shows that interannual variability in the four coral records is driven by ENSO, suggesting that the ENSO–SST teleconnection in the central Indian Ocean has been stationary since the 17th century. To determine the symmetry of El Niño and La Niña events, we compiled composite records of positive and negative ENSO-driven SST anomaly events. We find similar magnitudes of warm and cold anomalies, indicating a symmetric ENSO response in the tropical Indian Ocean. This suggests that ENSO is not the main driver of central Indian Ocean warming.

Habitat specialisation and overlap in coral reef gobies of the genus Eviota (Teleostei: Gobiidae)

On coral reefs, many small coral-associated fishes exhibit high levels of habitat specialisation, which can contribute to their susceptibility to habitat loss. However, high levels of habitat partitioning may buffer communities from the loss of particular habitat types. This study provides a quantitative evaluation of habitat specialisation, substratum selectivity and habitat overlap of 9 Eviota (Gobiidae) species in Kimbe Bay, Papua New Guinea. All but 1 locally common Eviota species were strongly associated with scleractinian coral substrata, and species ranged from habitat generalists to obligate coral specialists with some of the most extreme fine-scale patterns of habitat specialisation known for coral reef fishes. Patterns of substratum selectivity varied greatly within the genus, but many species showed distinct preferences for particular corals, most notably the scleractinian genera Acropora and Porites. Most species exhibited low habitat overlap and partitioned habitat on a fine spatial scale, but there were notable exceptions. Two Acropora coral specialists and some species with strong preference for massive Porites coral exhibited high overlap. Overall, the local abundance of Eviota species varied in relation to the degree of habitat specialisation, with the most generalised species more abundant than the habitat specialists. Habitat structure and species-specific differences in habitat specialisation, substratum selectivity and habitat overlap are likely to be key drivers explaining the distribution and abundance of Eviota species and the local community structure. Most importantly, many coral-dependent and less abundant species of Eviota may be vulnerable to habitat loss as a result of the ongoing degradation of coral reefs.

Highly variable taxa-specific coral bleaching responses to thermal stresses

Complex histories of chronic and acute sea surface temperature (SST) stresses are expected to trigger taxon- and location-specific responses that will ultimately lead to novel coral communities. The 2016 El Niño-Southern Oscillation provided an opportunity to examine large-scale and recent environmental histories on emerging patterns in 226 coral communities distributed across 12 countries from East Africa to Fiji. Six main coral communities were identified that largely varied across a gradient of Acropora to massive Porites dominance. Bleaching intensity was taxon-specific and was associated with complex interactions among the 20 environmental variables that we examined. Coral community structure was better aligned with the historical temperature patterns between 1985 and 2015 than the 2016 extreme temperature event. Additionally, bleaching responses observed during 2016 differed from historical reports during past warm years. Consequently, coral communities present in 2016 are likely to have been reorganized by both long-term community change and acclimation mechanisms. For example, less disturbed sites with cooler baseline temperatures, higher mean historical SST background variability, and infrequent extreme warm temperature stresses were associated with Acropora-dominated communities, while more disturbed sites with lower historical SST background variability and frequent acute warm stress were dominated by stress-resistant massive Porites corals. Overall, the combination of taxon-specific responses, community-level reorganization over time, geographic variation, and multiple environmental stressors suggest complex responses and a diversity of future coral communities that can help contextualize management priorities and activities.

Macroborer presence on corals increases with nutrient input and promotes parrotfish bioerosion

Bioerosion by reef-dwelling organisms influences net carbonate budgets on reefs worldwide. External bioeroders, such as parrotfish and sea urchins, and internal bioeroders, including sponges and lithophagid bivalves, are major contributors to bioerosion on reefs. Despite their importance, few studies have examined how environmental (e.g., nutrients) or biological drivers (e.g., the actions of other bioeroders) may influence bioeroder dynamics on reefs. For example, internal bioeroders could promote external bioerosion by weakening the coral skeletal matrix. Our study investigated: (1) whether nutrient supply influences the dynamics between internal and external bioeroders and (2) how the presence of a boring bivalve, Lithophaga spp., influences parrotfish bioerosion on massive Porites corals. We hypothesized that nutrient supply would be positively correlated with Lithophaga densities on massive Porites colonies, and that as bivalve density increased, the frequency and intensity of parrotfish bioerosion would increase. To test these hypotheses, we analyzed six time points over a 10-yr period from a time series of benthic images and nitrogen content of a dominant macroalga from the fringing reefs around Moorea, French Polynesia. We found Lithophaga densities were positively correlated with nitrogen availability. Further, massive Porites that are more infested with Lithophaga had both a higher probability of being bitten by parrotfish and a higher density of bite scars from parrotfishes. Our findings indicate that increasing nutrient availability may strengthen the relationship between internal and external bioeroders, suggesting that colonies at more eutrophic sites may experience higher bioerosion rates.

Bioerosion in massive porites at reef flat area of the south Java Sea

Scleractinian coral as the main builder of the reef contributes to building a complex reef framework through produce growing aragonite in their skeleton. In shallow water area (reef flat) the reef constructional process will be equal with erosional one, can be caused by mechanical damage such as storm or water motion and biological way (bioerosion). This research focused on the biological agent that influence on bioerosion process on massive Porites. 3 types of bioerosion they were grazing, boring, and etching. We monitored 10 massive Porites coral that was abundant at Pantai Kondang Merak, where each coral colony was segmented into 12 parts and then photographed to record data grazing and boring in massive Porites coral, while for etching was observed using Scanning Electron Microscopy (SEM). The result showed the number of bioerosion from grazing was 581 and boring was 1,155. The etching process was dominated by cyanobacteria Planobola macrogata that live inside of coral skeleton. The grazing process caused by parrotfish and triggerfish, boring caused by polychaetes, bivalves, and sponge. Bioerosion process not only weakening reef structures but also increase habitat complexity of reef-associated biota and expand coral occupy in space with natural propagation.