Changes in Coral Skeleton Growth Recorded by Density Band Stratigraphy, Crystalline Structure, and Hiatuses

Next-generation high resolution brightfield microscopy, x-radiography, and microcomputed tomography (microCT) analyses indicate that coral skeleton high density band (HDB) and low density band (LDB) stratigraphic sequences record dynamic changes in coral growth history. HDB-LDB sequences were studied within three small heads of Orbicella annularis, an ecological keystone species in the Caribbean Sea, collected from the leeward fringing reefs on Curaçao. Results indicate that HDB layers are formed by the thickening of exothecal and endothecal dissepiments, costae, and theca located at the margin and external to individual skeletal cups (corallites). Conversely, septa and columellas located inside individual corallites do not change in thickness. HDB-LDB stratigraphic sequences were laterally traced from the center to the margins of individual coral heads, demonstrating that shifts took place in the trajectory of coral skeleton growth. Normal HDB layers in the center of individual coral heads are formed at the same time (age-equivalent) as surfaces of erosion and no skeleton growth (hiatuses) on the margins of the heads. These hiatus surfaces within HDB-LDB stratal geometries indicate that multiple marine ecological and environmental processes affect the orientation, size, shape, and geometry of coral skeletons during coral growth history. The presence of these hiatus surfaces in other large coral heads would strongly impact sclerochronology and the interpretation of multiple environmental factors including sea surface temperature (SST).

The Importance of Ecological Accommodation Space and Sediment Supply for Cold-Water Coral Mound Formation, a Case Study From the Western Mediterranean Sea

The formation of cold-water coral (CWC) mounds is commonly seen as being the result of the sustained growth of framework-forming CWCs and the concurrent supply and deposition of terrigenous sediments under energetic hydrodynamic conditions. Yet only a limited number of studies investigated the complex interplay of the various hydrodynamic, sedimentological and biological processes involved in mound formation, which, however, focused on the environmental conditions promoting coral growth. Therefore, we are still lacking an in-depth understanding of the processes allowing the on-mound deposition of hemipelagic sediments, which contribute to two thirds of coral mound deposits. To investigate these processes over geological time and to evaluate their contribution to coral mound formation, we reconstructed changes in sediment transport and deposition by comparing sedimentological parameters (grain-size distribution, sediment composition, accumulation rates) of two sediment cores collected from a Mediterranean coral mound and the adjacent seafloor (off-mound). Our results showed that under a turbulent hydrodynamic regime promoting coral growth during the Early Holocene, the deposition of fine siliciclastic sediments shifted from the open seafloor to the coral mounds. This led to a high average mound aggradation rate of >130 cm kyr–1, while sedimentation rates in the adjacent off-mound area at the same time did not exceed 10 cm kyr–1. Thereby, the baffling of suspended sediments by the coral framework and their deposition within the ecological accommodation space provided by the corals seem to be key processes for mound formation. Although, it is commonly accepted that these processes play important roles in various sedimentary environments, our study provided for the first time, core-based empirical data proving the efficiency of these processes in coral mound environment. In addition, our approach to compare the grain-size distribution of the siliciclastic sediments deposited concurrently on a coral mound and on the adjacent seafloor allowed us to investigate the integrated influence of coral mound morphology and coral framework on the mound formation process. Based on these results, this study provides the first conceptual model for coral mound formation by applying sequence stratigraphic concepts, which highlights the interplay of the coral-framework baffling capacity, coral-derived ecological accommodation space and sediment supply.

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.

Current and sea level control the demise of shallow carbonate production on a tropical bank (Saya de Malha Bank, Indian Ocean)

Carbonate platforms are built mainly by corals living in shallow light-saturated tropical waters. The Saya de Malha Bank (Indian Ocean), one of the world’s largest carbonate platforms, lies in the path of the South Equatorial Current. Its reefs do not reach sea level, and all carbonate production is mesophotic to oligophotic. New geological and oceanographic data unravel the evolution and environment of the bank, elucidating the factors determining this exceptional state. There are no nutrient-related limitations for coral growth. A switch from a rimmed atoll to a current-exposed system with only mesophotic coral growth is proposed to have followed the South Equatorial Current development during the late Neogene. Combined current activity and sea-level fluctuations are likely controlling factors of modern platform configuration.

Diversity of Coral Genus Scleractinia in Tidung Island Waters, Seribu Islands, DKI Jakarta Province

Coral reefs are one of the most productive and diverse ecosystems on earth and provide ecosystem services. One of the islands of the Seribu Islands that has a coral reef ecosystem is Tidung Island. It is strategic and developing location makes this island used as a residential area, conservation area, and tourist destination. But the utilization has an impact on the damage of coral reefs through environmental and anthropogenic pressures. This study aims to determine coral diversity by identifying the coral genus Scleractinia and the factors that affect coral diversity. Observations were done on three different stations include 2 snorkeling areas and 1 natural area. The method used is LIT (Line Intercept Transect) and coral genus identification with Coral Finder Toolkit Indo Pacific 3.0. The results of identification obtained 16 coral genera namely genus Acropora, Montipora, Isopora, Favites, Leptastrea, Favia, Goniastrea, Montastrea, Platygyra, Echinopora, Porites, Pocillopora, Stylophora, Ctenactis, Pavona, dan Symphyllia, with the value of Diversity Index (H') in the waters of Tidung Island ranges from 0.94 – 2.34 in the category of low to moderate diversity. The parameters of water quality in Tidung Island, temperature, salinity, and acidity (pH) are relatively good for coral growth, but brightness is still relatively poor for coral growth. The impact of human activities such as snorkeling, ship anchors, fishing with destroyers, oil and waste pollution, and rock mining are factors that affect coral growth and diversity.Keywords: Coral Scleractinia; Limiting Factors; Coral Finder; Tidung IslandAbstrakTerumbu karang adalah salah satu ekosistem yang paling produktif dan beragam di bumi serta menyediakan jasa ekosistem. Salah satu pulau dari gugusan Kepulauan Seribu yang memiliki ekosistem terumbu karang yaitu Pulau Tidung. Letaknya yang strategis dan berkembang menjadikan pulau ini dimanfaatkan sebagai kawasan permukiman, daerah konservasi, dan kawasan tujuan wisata. Namun dari pemanfaatan tersebut memberikan dampak terhadap kerusakan pada terumbu karang melalui tekanan-tekanan lingkungan maupun antropogenik. Penelitian ini bertujuan untuk mengetahui keanekaragaman karang dengan mengidentifikasi genus karang Scleractinia dan faktor yang mempengaruhi keanekaragaman karang. Pengamatan di tiga stasiun berbeda yaitu di antaranya 2 kawasan wisata snorkeling, dan 1 kawasan yang masih alami. Metode yang digunakan yaitu LIT (Line Intercept Transect) dan identifikasi genus karang dengan Coral Finder Toolkit Indo Pasific 3.0. Hasil identifikasi didapatkan 16 genus karang yaitu genus Acropora, Montipora, Isopora, Favites, Leptastrea, Favia, Goniastrea, Montastrea, Platygyra, Echinopora, Porites, Pocillopora, Stylophora, Ctenactis, Pavona, dan Symphyllia, dengan nilai Indeks Keanekaragaman (H’) di perairan Pulau Tidung berkisar 0,94 – 2,34 berada pada kategori keanekaragaman rendah hingga sedang. Parameter kualitas perairan di Pulau Tidung, suhu, salinitas, dan derajat keasaman (pH) tergolong baik bagi pertumbuhan karang, namun kecerahan masih tergolong kurang baik bagi pertumbuhan karang. Dampak aktivitas manusia seperti snorkeling, jangkar kapal, penangkapan ikan dengan alat perusak, pencemaran minyak dan sampah, serta penambangan batu karang menjadi faktor yang mempengaruhi pertumbuhan dan keanekaragaman karang.

Scaling the effects of ocean acidification on coral growth and coral–coral competition on coral community recovery

Ocean acidification (OA) is negatively affecting calcification in a wide variety of marine organisms. These effects are acute for many tropical scleractinian corals under short-term experimental conditions, but it is unclear how these effects interact with ecological processes, such as competition for space, to impact coral communities over multiple years. This study sought to test the use of individual-based models (IBMs) as a tool to scale up the effects of OA recorded in short-term studies to community-scale impacts, combining data from field surveys and mesocosm experiments to parameterize an IBM of coral community recovery on the fore reef of Moorea, French Polynesia. Focusing on the dominant coral genera from the fore reef, Pocillopora, Acropora, Montipora and Porites, model efficacy first was evaluated through the comparison of simulated and empirical dynamics from 2010–2016, when the reef was recovering from sequential acute disturbances (a crown-of-thorns seastar outbreak followed by a cyclone) that reduced coral cover to ~0% by 2010. The model then was used to evaluate how the effects of OA (1,100–1,200 µatm pCO2) on coral growth and competition among corals affected recovery rates (as assessed by changes in % cover y−1) of each coral population between 2010–2016. The model indicated that recovery rates for the fore reef community was halved by OA over 7 years, with cover increasing at 11% y−1 under ambient conditions and 4.8% y−1 under OA conditions. However, when OA was implemented to affect coral growth and not competition among corals, coral community recovery increased to 7.2% y−1, highlighting mechanisms other than growth suppression (i.e., competition), through which OA can impact recovery. Our study reveals the potential for IBMs to assess the impacts of OA on coral communities at temporal and spatial scales beyond the capabilities of experimental studies, but this potential will not be realized unless empirical analyses address a wider variety of response variables representing ecological, physiological and functional domains.

Micro-CT 3D reconstructions reveal coral growth pattern and parameter

Colony is the basic geometric construction of coral reef. However, both the forming regulations of colony and reef are still obscure. In this study, we reconstructed 21 important samples by high-resolution micro-computed tomography to investigate coral growth pattern and parameter. Our skeleton and canal reconstructions revealed characteristics of different coral species and we further visualized the growth axes and growth rings to reveal coral growth directions. We drew a skeleton gray-scale map and calculated coral skeleton void ratios to reveal skeletal diversity, devising a method to quantify coral growth. On the bases of the 3D reconstructions and growth parameters, we investigated growth strategies of different coral species. This work extends the knowledge of how reef-building corals grow their colonies, giving a hint on reef forming regulation. The data of this paper contain large amount of coral growth information, and can be used in further research on reef forming patterns under different conditions. The method used in this study can also be applied in animals with porous skeletons.