Coral Growth Forms Research Articles

Coral Health and Benthic Composition of Reefs in an MPA and Open-access Site in Western Calatagan, Batangas

Monitoring hard coral health and diversity is essential in assessing their resilience to disturbances such as coral bleaching. This study gathered baseline data on the health and benthic composition of coral reefs in western Calatagan, Batangas, the Philippines. Coral health in two sites – Buntong Gasang and the Quilitisan Marine Protected Area (MPA) – was assessed using the CoralWatch citizen science Coral Health Chart method. The average color score of more than 200 coral colonies was compared between sites and coral growth forms (i.e. branching, boulder, and plate). In addition, benthic composition in both sites was determined using photoquadrats. Buntong Gasang Point and Quilitisan MPA had mean coral scores that are 4.4 (± 1.0 SD) and 3.6 (± 1.0 SD), respectively, thus indicating normal symbiont densities. The analysis also showed little differences in mean color scores among coral growth forms ranging from 3.8–4.3. Both sites had relatively high coral cover (mean = 52.3% ± 4.3% SD in Buntong Gasang, mean = 49.7% ± 8.7% SD in Quilitisan MPA) despite having different benthic compositions [PERMANOVA, F(1,8) = 8.87, p = 0.006]. Branching coral cover was about six times higher in Buntong Gasang Point (17%), whereas encrusting corals dominated at Quilitisan MPA (~ 39%). In addition, algal cover was higher in Quilitisan (45.0%) than in Buntong Gasang (35.5%). Although other studies show that branching corals are less resistant than massive or encrusting forms to coral bleaching, examining coral color suggests that reefs in both Buntong Gasang and Quilitisan MPA appeared to have comparably recovered from the mass bleaching events in 2020–2021. However, regular monitoring is needed to assess the responses of these reefs to future thermal stress. This study shows the potential of monitoring coral color in assessing coral reef health in the Philippines.

Bioecological Comparison of Angelfish (Pomacanthus sp.): Diversity of Habitat, Sex Ratio, Growth and Production Status in Coral Triangle Waters

Angelfish (Pomacanthus sp.) is an ornamental fish that inhabits lush coral reefs. Despite requiring a healthy coral environment to grow and develop, this fish species is often hunted for its high price in the international market. This research aimed to determine the bio-ecology of angelfish, including its habitat, activity, size, structure, growth, and sex ratio, as well as to provide insights into its production status in the last nine years in South Sulawesi, especially in the waters of Pangkajene dan Kepulauan (Pangkep). The angelfish population was observed in waters adjacent to coral reefs in the coastal area of Pangkep. For this research, we used locally caught samples and determined their age using Gulland plot analysis. This study shows that the presence of angelfish does not have a positive correlation with live coral cover. However, their existence is influenced by coral growth forms, such as branching, sub-massive, and massive coral fissures. The samples of the caught angelfish were young, and their gonads were undeveloped. The allometric relationship between the weight and length of angelfish is slow, with them reaching a maximum length of 41.7 cm at 13 years. Based on the results of the study, we found that angelfish with a length of 10.1cm to 15cm are still relatively young and their gonads are still not developed. This size is in great demand in the market. This research also shows a decline in angelfish production. Thus, it is necessary to control the amount of catch and the minimum size of the first catch or provide a catch quota system for each year. The findings of this research can serve as a reference for policymakers, fishermen, and aquascape experts who wish to protect the angelfish population in their natural habitat.

Analysis of Coral Reef Conditions in the Waters of Panjang Island, Central Bangka Regency

Coral reefs are organisms that live at the bottom of the water and take the form of sturdy limestone formations capable of withstanding the force of ocean waves. Ecologically, coral reefs serve as habitats where various animal and plant organisms seek food and shelter. This research aims to analyze the coral reef ecosystem conditions in the waters of Panjang Island and provide recommendations for sustainable management of marine biodiversity in the waters of Panjang Island, Central Bangka Regency. The Underwater Photo Transect (UPT) method involves underwater photography using a digital or regular digital camera equipped with a waterproof housing to withstand seawater exposure. The research results indicate that the percentage of live coral cover in the waters of Panjang Island ranges from 70.07% to 14.07%, categorizing it as fair to poor according to the Minister of Environment Decree No. 4 of 2001 on the Standard for Coral Reef Damage. Fourteen coral growth forms were identified in the waters of Panjang Island, belonging to 17 coral genera. Recommendations for managing marine resources on Panjang Island include sustainable tourism development. Environmentally based tourism development can serve as a solution for sustainably utilizing coral reefs and promoting improving coastal and fisheries management based on Marine Conservation Areas.

Host specificity of coral-associated fauna and its relevance for coral reef biodiversity

Coral-associated fauna predominantly consists of invertebrates and constitutes an important component of coral reef biodiversity. The symbionts depend on their hosts for food, shelter and substrate. They may act as parasites by feeding on their hosts, by overgowing their polyps, or by excavating their skeletons. Because some of these species partly reside inside their hosts, they may be cryptic and can easily be overlooked in biodiversity surveys. Since no quantitative overview is available about these inter-specific relationships, this present study adresses variation in host ranges and specificity across four large coral-associated taxa and between the Atlantic and Indo-Pacific oceans. These taxa are: coral barnacles (Pyrgomatidae, n = 95), coral gall crabs (Cryptochiridae, n = 54), tubeworms (Serpulidae, n = 31), and date mussels (Lithophaginae, n = 23). A total of 335 host coral species was recorded. An index of host specificity (STD) was calculated per symbiont species, based on distinctness in taxonomic host range levels (species, genus, family, etc.). Mean indices were statistically compared among the four associated taxa and the two oceanic coral reef regions. Barnacles were the most host-specific, tubeworms the least. Indo-Pacific associates were approximately 10 times richer in species and two times more host-specific than their Atlantic counterparts. Coral families varied in the number of associates, with some hosting none. This variation could be linked to host traits (coral growth form, maximum host size) and is most probably also a result of the evolutionary history of the interspecific relationships.

Suitability Index of Snorkeling Tourism In Sepulu District, Bangkalan, Indonesia

Bangkalan is one of the districts in Madura with a coastal area that can be developed as a marine tourism location for snorkelling, and their northern coast facing the Java Sea has only been used for coastal tourism. This research aimed to assess the suitability index of snorkelling tourism in Sepulu waters, Bangkalan. The research was carried out during September–October 2021. Coral cover, fish diversity, water conditions, and an analysis of tourism suitability and the carrying capacity of snorkelling tourism were assessed. Hard coral cover in Sepulu waters ranges from 22-38%, while the per cent of coral cover (including soft corals) ranges from 34-55.5%. The number of coral growth forms found in Sepulu waters ranged from 6-8 forms. Reef fish found in Sepulu district water were between 7-12 species. The tourism suitability index of Sepulu Waters, Bangkalan, which ranges from 61.40 – 75.44%, is included in the category of quite suitable. The area’s carrying capacity for snorkelling tourism activities is 152-500 people daily. Sepulu waters, especially Tengket and Labuhan waters, have a high potential to be used as snorkelling tourism objects.

Symbiodiniaceae Density Pattern in Relation To Colony Morphology of Scleractinian Corals in Pulau Tioman and Pulau Bidong, Malaysia

A healthy coral reef is linked to the mutualistic relationship between scleractinian coral and the symbiotic Symbiodiniacea (SD). However, there is limited research on SD in Malaysia, despite its important role in reef-building coral. In this study, the SD density of scleractinian corals from the family Acroporidae was evaluated to (i) examine the pattern of SD density and (ii) comprehend the regulation of the SD density by the host. The mean SD density ranged between 0.46 ± 0.01 × 106 cell cm-2 and 2.98 ± 1.17 × 106 cell cm-2. It is hypothetically proven that the SD density differed significantly between genera and morphological factors such as colony surface area (CSA) and dry weight coral tissue per unit colony surface area (DWCT/CSA) were significantly correlated with the SD density. The results show that the significant variation in SD density among coral genera can be influenced by coral growth forms and tissue biomass. There was a significant relationship between SD density and CSA as well as DWCT/CSA. Coral genera with a wider CSA and lower DWCT/CSA such as Anacropora and Acropora with branching, digitate and tabulate growth forms contained lower SD density than massive, laminar, and encrusting such as Montipora and Astreopora which hold more DWCT/CSA at lower CSA, resulting in higher SD density. The findings provide valuable information on SD density in different types of corals from the southern part of the South China Sea and reveal the coral host’s SD regulation.

Sea urchins of Peninsular Malaysia: Spatial distribution and species-habitat association

Sea urchins are keystone herbivores in coral reefs that can prevent coral-algae phase shifts and promote coral resilience in the Caribbean. However, knowledge of sea urchin populations in the Indo-Pacific region is less extensive and their role in marine ecosystems remains uncertain. To fill this knowledge gap, this study examined the spatial distribution and species-habitat association of sea urchins in Peninsular Malaysia as a first step in exploring their potential for promoting reef resilience. Firstly, geographical information on the population characteristics of sea urchins in Peninsular Malaysia (Sunda Shelf and Malacca Strait Marine Ecoregions) was gathered. Using literature, questionnaire, and field surveys, ten species of sea urchins from six families were identified in the species record for Peninsular Malaysia. Prionocidaris bispinosa represents the first record for Malaysia, documented in the intertidal seagrass meadow at Tanjung Kupang, Johor. Combining density data from literature and field surveys, sea urchin density for Peninsular Malaysia was estimated to be 46.94 ± 66 individuals/100 m2. Secondly, the species-habitat association of Diadema setosum and Echinothrix calamaris were determined in belt-transect surveys (n=57), with transects laid parallel to shore at Pulau Rawa, Johor. Multivariate regression analysis identified D. setosum to be more associated with live coral cover and coral growth form, while E. calamaris distribution was driven by habitat rugosity, water depth and live coral cover. These findings suggest contrasting species-habitat associations for the two co-existing species. Given the limited information about sea urchins in Malaysia, this study appears to be the first in-depth study of its kind in the country, deepening our knowledge of sea urchin distribution and the importance of habitat in shaping that distribution. This baseline data serves as valuable information in the planning and management of natural habitats for biodiversity and conservation in Malaysia’s marine ecosystem.

Intertidal seawall communities in Singapore: Are they all one and the same?

Ecological rehabilitation of seawalls requires a good understanding of the underlying community structure, which is still poorly known in the tropics where coastal urbanization is rapidly taking place. In this study, we compared intertidal sessile biota on sloping (20°) and vertical (90°) seawalls on a small, reclaimed offshore island in the Singapore Strait and examined the pattern of heterogeneity of sessile assemblages within each seawall type. Cover of sessile organisms, abundance of hard coral species as well as their growth forms across two tidal height ranges in the low littoral region (−0.2 to +0.3 m Chart Datum (CD) and + 0.3 to +0.8 m CD) were assessed. Seawalls had high biotic cover (mean cover of 91 ± 15%), comprising a variety of sessile organisms ranging from algae and non-colonial organisms including oysters and barnacles to colonial organisms such as cnidarians and sponges. Turf algae comprising coralline and non-coralline rhodophytes dominated the intertidal zone below +0.8 m CD. A moderate negative correlation was detected between crustose coralline and non-coralline algae (Spearman coefficient = −0.56). Coralline algae were relatively conspicuous on several vertical seawall sites. Seawall type was a significant factor differentiating sessile cover composition (p < 0.05) even though within-type site variability was significant (p < 0.005). Coral species diversity and growth form abundance were also significantly differentiated by seawall type (respectively p < 0.05). Tidal height (+0.3 m CD) was another significant factor for sessile cover composition and growth form abundance (p < 0.05). In general, sloping seawalls showed higher within-site variability and less obvious tidal stratification of sessile cover composition compared to vertical seawalls. In contrast, vertical seawalls showed lower within-site variability but higher site-to-site variation, as well as significant tidal stratification of coral growth form. These differences in community structure on apparently uniform seawall surfaces suggest the need for nuanced approaches to rehabilitate and enhance biodiversity in the intertidal zone.

On the fate of dead coral colonies

Abstract Carbonate budgets dynamically balance production and loss of calcium carbonate (CaCO3) on coral reefs. To sustain or expand the coral reef framework, CaCO3 production by calcifying organisms must be higher than erosion. However, global climate change has been negatively impacting carbonate production, with bleaching events causing widespread coral mortality. Although bleaching and coral mortality are well documented, the fate of coral colonies after their death, including their erosion rates, are still poorly known. We followed the fate of 143 recently dead individual coral colonies with complex growth forms (arborescent, caespitose, corymbose, digitate and tabular), whose mortality was triggered by two consecutive bleaching events. These colonies, spread over 16 km2 of the Lizard Island reef complex, were tracked for up to 5 years, allowing detailed examination of erosion rates and post‐mortality structural persistence. We also tested how variables that are commonly used in coral reef erosion studies relate to spatial and temporal variability in the erosion rates of dead coral colonies. We revealed rapid erosion of dead coral colonies, with an average of 79.7% of dead colonies completely disintegrating within 60 months. The predicted half‐life of a dead coral colony was 40 months, with limited variation among wave exposure levels. Remarkably, we found no effect of estimated parrotfish bioerosion, wave exposure, nor coral growth form, on observed erosion rates. Our results suggest that our understanding of the erosion of dead corals may be more limited than previously thought. The rapid loss of coral colonies on our study sites calls for a re‐evaluation of the role of corals with complex growth forms in reef growth and of parrotfishes in reef erosion. Read the free Plain Language Summary for this article on the Journal blog.

The Association of Waminoa with Reef Corals in Singapore and Its Impact on Putative Immune- and Stress-Response Genes

Waminoa spp. are acoel flatworms mainly found as ectosymbionts on scleractinian corals. Although Waminoa could potentially represent a threat to their hosts, not enough information is available yet regarding their ecology and effect on the coral. Here, the Waminoa sp.–coral association was analyzed in Singapore reefs to determine the prevalence, host range, and preference, as well as the flatworm abundance on the coral surface. Moreover, the impact of Waminoa sp. on the expression of putative immune- and stress-response genes (C-type lectin, C3, Hsp70 and Actin) was examined in the coral Lobophyllia radians. The association prevalence was high (10.4%), especially in sites with lower sedimentation and turbidity. Waminoa sp. showed a wide host range, being found on 17 coral genera, many of which are new association records. However, only few coral genera, mostly characterized by massive or laminar morphologies appeared to be preferred hosts. Waminoa sp. individuals displayed variable patterns of coral surface coverage and an unequal distribution among different host taxa, possibly related to the different coral growth forms. A down-regulation of the expression of all the analyzed genes was recorded in L. radians portions colonized by Waminoa individuals compared to those without. This indicated that Waminoa sp. could affect components of the immune system and the cellular homeostasis of the coral, also inhibiting its growth. Therefore, Waminoa sp. could represent a potential further threat for coral communities already subjected to multiple stressors.

Coralliths of tabulate corals from the Devonian of the Holy Cross Mountains (Poland)

Tabulates, an extinct Palaeozoic group of corals, developed diverse colony morphologies during the Silurian to Devonian peak of reef development. Coralliths, or circumrotatory colonies, are passively motile coral colonies constantly overturned by wave action or currents. Such overturning allows tissue growth on all sides of the colony. They are among the most rarely reported growth forms. Recent corallith-forming scleractinian corals mostly inhabit the shallowest reef environments, but coralliths can also develop at greater depths in areas of low topographic relief, unconsolidated substratum, low coral cover and high water movement. Here, we report on Devonian (Givetian Favosites goldfussi and Frasnian Alveolites ? tenuissimus ) coralla from the Holy Cross Mountains, Poland. Our analysis suggests these colonies are coralliths, although less mature than usually reported. These corals, unlike previously described growth forms of this kind, lived in relatively deep environments: probably the upper mesophotic (Givetian, Miłoszów), or deep reef fore-slope (Frasnian, Jaźwica and Kowala). Microfacies analysis of the Jaźwica site suggests unconsolidated substratum and high hydrodynamic energy. We conclude that these corals lived in deeper environments where bottom currents caused their autorotation. A good modern analogue for such a corallith-forming environment is the Wistari Channel (Southern Great Barrier Reef), where bottom tidal currents at nearly 30 m of depth are strong enough to overturn colonies of Stylocoeniella cf. guentheri reaching 15 cm in diameter. Our discovery shows that the spectrum of coral growth forms during the Devonian peak of reef development was broader than previously assumed, and that tabulate corals displayed numerous adaptive strategies to various environments. • Coralliths are unattached coral colonies passively rotated by water movement. • Recent and Palaeozoic coralliths were described from shallow-water environments. • Givetian and Frasnian tabulate coralliths are described here from deeper habitats. • The coralliths were moved by strong bottom currents, as shown by microfacies analysis. • We propose modern analogue, a corallith from ~28 m-deep channel near Heron Island.

Mapping coral reef using photogrammetry technique: A preliminary study at Pulau Udar Besar, Sabah, Malaysia.

Mapping of coral reefs is useful for understanding, monitoring and tracking their development. However, studies on reef mapping in the Southeast Asian region are limited. The main objectives of this study were to 1) map the coral reefs using photogrammetry in order to create a 3D map of the reef, and 2) determine the coral growth forms and identify the corals to the lowest possible taxa from the images. Data collection was conducted on 19 and 24 January 2018. All images were captured by applying photogrammetry technique using a digital camera with waterproof housing. Image reconstruction process was performed in Agisoft Photoscan and Blender, using the structure-from-motion (SfM) algorithms to reconstruct the 2-Dimensional images into a 3D model. The reef map generated from Agisoft Photoscan is of medium quality. Coral growth forms were determined and identified to the lowest possible taxa through the images. From the images, free-living corals of the family Fungiidae were the most common coral observed in the study site. In conclusion, the output of this study shows that reef mapping is possible using a photogrammetry approach and images can be used to identify coral growth forms.

Reef fish community structure and its association with Lifeform coral in the core zone of the Anambas islands Marine Tourism Park (MTP)

Reef fish are one of the biotas that live in coral reef ecosystems, and their lives depend on the condition of coral reefs. Reef fish communities have a close relationship with coral reefs as their habitat. Collecting data on reef fish and coral growth forms using the underwater visual census (UVS) method and methods point intercept transect (PIT). The results of the identification of coral growth forms found 10 growth forms. The most abundant group of fish in the core zone waters of the Anambas Islands was the omnivorous group of fish found as many as 14,924 ind/250m2. The uniformity index value is obtained by the criteria for a stable uniformity index. The cluster analysis results showed that the similarity index of 43% was found in three groups of entities. The correspondence analysis results found three groupings of reef fish based on their association with coral growth forms.

An assessment of small islands coral cover and coral-reef fish diversity at Oba Sub-district, Halmahera Island

Study on the percentage of coral cover four small islands of Oba Sub-district, Halmahera Island of North Maluku Utara Province was carried out in April 2021.The four small islands of Oba Sub-district studied are Woda Island, Raja Island, Tamin Island, and Guratu Island. The study applied systematic sampling method that included collecting coral reef data using UPT (Underwater Photo Transect) method and coral fish data collection using visual census method. Study results showed that live coral coverage of reefs on the four small islands of Oba Sub-district had the highest value of 5.415% and the lowest value of 4.29%. There was positive relationship between coral growth form diversity and fish diversity. High diversity of coral growth forms was significantly related to high diversity of target reef fish.

Tutupan Terumbu Karang pada Kedalaman Berbeda di Perairan Pantai Batu Sungu, Desa Les, Kabupaten Buleleng

Bali island has many magnificent underwater coral reef gardens that attract tourists. Besides Pemuteran and Menjangan island waters, Batu Sungu water has also potential to be a new tourist destination. Thus, to determine the potency and management plan in Batu Sungu waters, this research aimed to examine the overall coral cover, coral growth forms, other benthic forms, and each of their components in 5 and 10 m depths. The overall coral cover, coral growth forms, other benthic forms, and each of their components were counted by using the Line Intercept Transect (LIT) method. Before collecting data, study sites were observed by using the Manta Tow method. Data were collected in 2 depths (5 dan 10 m) with 5 sites each (replicates) that separates within 50 to 150 m. A 25 m LIT was spread parallel to the coastline above the reefs. Live coral colonies, other benthic forms below the transects were measured for the number, length, and growth forms. Water quality was measured in situ (temperature, current, and clarity) and ex situ (pH). Results showed that the category of coral coverage in Batu Sungu water is "good” in 5 m and "moderate” in 10 m whereas there was no significant difference among each component of the overall coral cover. The most dominant coral growth form among the 2 depths was Coral Massive whereas significantly abundant in 5 m. Moreover, the number of Coral Foliose was found significantly high in the same depth. Other coral growth forms were relatively similar in numbers in two depths. As likewise, the cover of other benthic forms and its component were not significantly different among two depths, except Dead Coral with Algae which significantly plentiful in 5 m. Sand was dominantly found in two depths with no significant difference. Furthermore, Coraline Alga was only observed in 5 m, however, there were no Macroalga and Alga Assemblages found at this depth. It is assumed that the similarity number of the overall coral cover, coral growth forms, other benthic forms, and each of their components is related to the alikeness of water quality among the two depths.

Quantifying the shelter capacity of coral reefs using photogrammetric 3D modeling: From colonies to reefscapes

Structural complexity plays a key role in the functioning of coral reef ecosystems. Reef-building corals are major contributors to this complexity, providing shelter and food for numerous invertebrates and fish species. Both structural complexity and shelter capacity of reefscapes are determined by several components such as spurs and grooves, slope, caves and holes, vegetation and coral colonies. Quantifying the shelter capacity from coral colonies to reefscapes is a fundamental step to estimating ecosystem potential to support biodiversity. Here, we applied underwater photogrammetry to quantify shelter volumes provided by individual coral colonies. Overall, 120 3D models of coral colonies from branching, massive, columnar and tabular growth forms were studied. Three reefscapes were also 3D modeled. The study encompasses three Indo-Pacific Islands: Reunion, Europa and New Caledonia. At the colony level, measurements of diameter, planar area, surface and shelter volume were computed. At the reefscape, the diameter and planar area of each colony were extracted from orthomosaics and then used to estimate shelter capacity. Linear models had high accuracy for predicting shelter volume (a 3D metric) from 2D metrics: the diameter= 83.1%, R2= 0.95; the planar area= 87.5%, R2= 0.95 and the colony surface= 87.3%, R2= 0.96. The surface complexity and the shelter volume of the colonies allowed inferring the size of shelters provided by coral growth forms. Quantitative descriptors (i.e. relative percentage of shelter by growth form, the abundance of coral colonies, “Shannon-Shelter Index”) revealed reefscape-scale shelter differences.Our major finding is that planar area and diameter of coral colonies are satisfactory proxies for estimating shelter volume. These new proxies allow 2D metrics to quantify 3D shelter provision, which can support scientists and managers in conservation actions since such metrics are widely used in monitoring programs. Future investigations on the relationships between shelter provision and reef biodiversity will improve the understanding of these complex ecosystems.

Frequent hydrodynamic disturbances decrease the morphological diversity and structural complexity of 3D simulated coral communities

Scleractinian corals, which create complex three-dimensional carbonate structures, are the foundation of coral reef ecosystems. There are a variety of coral growth forms or ‘morphologies’ that have distinct advantages and disadvantages when corals compete for space and light, and when they are exposed to hydrodynamic disturbances. We developed a novel three-dimensional functional-structural model, Coralcraft, to investigate how hydrodynamic disturbances (of different frequencies and intensities) influence coral communities. Using five common coral morphologies—encrusting, hemispherical, tabular, corymbose and branching—Coralcraft tracks the temporal dynamics of simulated coral communities. Six metrics are considered: (1) the number of colonies, (2) the percentage cover and (3) the volume of each morphology; (4) the structural complexity (rugosity) and (5) the total coral cover of the community; and (6) the diversity of morphologies in the community as calculated according to metrics (1)–(3). Frequent high intensity disturbances caused the greatest reduction to the structural complexity and morphological diversity of simulated communities, with some variation depending on the metric used to calculate diversity. Conversely, scenarios of no disturbance or infrequent disturbance (of low or high intensity) led to communities with higher structural complexity and a higher diversity of morphologies. These results indicate that disturbance frequency may play a greater role in eroding structural complexity and diversity than disturbance intensity. Importantly, given that the scientific coral reef literature generally uses percentage cover, the other metrics we considered—number of colonies, volume, rugosity and diversity—captured the dynamics of impact and recovery from disturbance in subtly different ways. While there are many models for corals, Coralcraft is the first to model the temporal dynamics of three-dimensional growth, competition and response to disturbance in a community with different coral morphologies.

Localized bleaching and quick recovery in Hong Kong's coral communities

During the summer of 2017 we visited 33 sites with substantial coral cover across Hong Kong waters. At six sites where coral bleaching was observed, video-transect surveys were conducted, which revealed 18.7% to 56.1% bleached colonies and 5.9% to 57.6% bleached coral covered area per site. Mainly affected were three plate-like and three massive coral species. Water quality parameters were analyzed, which indicated that hyposalinity might have triggered the bleaching event. Tagging and follow-up field observation revealed a pattern of recovery depending on coral growth form, with high recovery rates (>93%) at five sites dominated by massive and submassive corals, but moderate (70%) at a site dominated by plate-like corals. Our study shows that the corals of Hong Kong exhibit differential susceptibility to bleaching and ability to recover, therefore it is imperative to establish a long-term monitoring programme to detect the changes in community structure over time.

Growth responses of branching versus massive corals to ocean warming on the Great Barrier Reef, Australia

As oceans continue to warm under climate change, understanding the differential growth responses of corals is increasingly important. Scleractinian corals exhibit a broad range of life-history strategies, yet few studies have explored interspecific variation in long-term growth rates under a changing climate. Here we studied growth records of two coral species with different growth forms, namely branching Isopora palifera and massive Porites spp. at an offshore reef (Myrmidon Reef) of the central Great Barrier Reef (GBR), Australia. Skeletal growth chronologies were constructed using a combination of X-radiographs, gamma densitometry, and trace element (Sr/Ca) analysis. General additive mixed-effect models (GAMMs) revealed that skeletal density of I. palifera declined linearly and significantly at a rate of 1.2% yr−1 between 2002 and 2012. Calcification was stable between 2002 and 2009, yet declined significantly at a rate of 12% yr−1 between 2009 and 2012 following anomalously high sea surface temperatures (SST). Skeletal density of massive Porites exhibited a significant non-linear response over the 11-year study period (2002−2012) in that density was temporarily reduced during the 2009–2010 anomalously hot years, while linear extension and calcification showed no significant trends. Linear extension, density and calcification rates of I. palifera increased to maximum growth of 26.7–26.9 °C, beyond which they declined. In contrast, calcification and linear extension of Porites exhibited no response to SST, but exhibited a significant linear decline in skeletal density with increasing SST. Our results reveal significant differences in coral growth patterns among coral growth forms, and highlight both the resistant nature of massive Porites and sensitivity of branching I. palifera. Future research should target a broad range of coral taxa within similar environments to provide a community-level response of ocean warming on coral reef communities.

Endolithic Algae Affect Modern Coral Carbonate Morphology and Chemistry

While burial diagenetic processes of tropical corals are well investigated, current knowledge about factors initiating early diagenesis remains fragmentary. In the present study we focus on recent Porites microatolls, growing in the intertidal zone. This growth form represents a model organism for elevated sea surface temperatures and provides important but rare archives for changes close to the seawater/atmosphere-interface with exceptional precision on sea level reconstruction. As other coral growth forms, microatolls are prone to the colonization by endolithic green algae. In this case the algae can facilitate earliest diagenetic alteration of the coral skeleton. Algae metabolic activity not only results in secondary coral porosity due to boring activities, but may also initiate reprecipitation of secondary aragonite within coral pore space, a process not exclusively restricted to microatoll settings. In the samples of this initial study, we quantified a mass transfer from primary to secondary aragonite of around 4% within endolithic green algae bands. Using δ18O, δ13C, Sr/Ca, U/Ca, Mg/Ca, and Li/Mg systematics suggest that the secondary aragonite precipitation followed abiotic precipitation principles. According to their individual distribution coefficients the different isotope and element ratios showed variable sensitivity to the presence of secondary aragonite in bulk samples, with implications for microatoll-based sea surface temperature (SST) reconstructions. The secondary precipitates formed on an organic template, presumably originating from endolithic green algae activity. Based on laboratory experiments with the green algae Ostreobium quekettii we propose a conceptual model that secondary aragonite formation is potentially accelerated by an active intracellular calcium transport through the algal thallus from the location of dissolution into coral pore spaces. The combined high-resolution imaging and geochemical approach applied in this study shows that endolithic algae can possibly act as a main driver for earliest diagenesis of coral aragonite starting already during a coral’s life span.