Coral Areas Research Articles

Coral mortality and fish abundance in the Marine Nature Reserve of the Eastern Coast of Weh Island, Sabang, Aceh

Coral reefs play an important role in marine ecosystems as habitats for various species of fish and other marine organisms, as well as protecting the coast from erosion and storms. However, climate change, pollution, human activities, and bleaching have resulted in declining coral conditions. The purpose of this study was to analyze the level of coral mortality and its effect on the abundance of coral fish. The study was conducted in the coastal nature reserve area of East Weh Island. Data collection was carried out at two depths using the Belt Transect method and the Underwater Visual Census technique. The results showed that the level of coral mortality in the coastal nature reserve area of East Weh Island reached 0.82 ± 0.05% at Reuteuk station. These results show that coral conditions in the protected area have a very high mortality rate. However, the high coral mortality in the area did not affect the abundance of coral fish (p-value > 0.05). This value indicates that coral fish can be found abundantly in damaged coral areas. The average results of coral mortality and abundance of coral fish at depths of 3 meters and 7 meters showed no significant difference. These results illustrate that at shallow or deep depths, coral and coral fish mortality can be found at high/abundant values.

Different bacterial communities of the coral area and its surrounding sediments in Daya Bay, South China Sea

Sediment in coral reef habitats has a tight interaction with coral reefs. Bacterial communities are a critical part of sediments and play a vital role in marine ecosystems, as well as coral reef habitats. To determine whether the bacterial structure of sediments differs between the inside and surrounding coral area, we compared the bacterial community on the surface of the dead coral skeleton (CS) and three soft sediment sites (SS, SS10, SS50) in and around the coral reef distribution of Dalajia Island in Daya Bay. Our results showed that bacterial diversity and composition of the coral skeleton had a significant difference with that of surrounding soft sediments. Proteobacteria and Actinobacteria were dominant in CS, and Proteobacteria and Bacteroidetes were dominant in SS, SS10, and SS50. Substrate type and environmental parameters are the main factors in the separation between coral skeletons and sediment. Salinity and pH were largely negatively correlated with CS, indicating they are primary factors that potentially impact coral mortality and revival. Heavy metals were positively related to sediments and they are potential threats to coral growth. Our work provides updated data on bacterial structure in the coastal coral area, contributing to policy-making and management of coastal activities to minimize the degradation of coral reefs.

Potential for developing a sustainable fishing sector in Sukamara

This research explores the potential of a sustainable fisheries sector in Sukamara Regency, Central Kalimantan, which is rich in fisheries resources, both freshwater and marine. This study identified the potential for freshwater fish production of 10,000 tons annually and marine fish of 8,000 tons yearly, with superior species such as snakehead fish, baung, catfish, snapper, grouper, and tuna. Although the fishing sector has an essential role in the local economy, unsustainable fishing practices have led to overfishing, environmental degradation, infrastructure problems, and limited technological knowledge. This research emphasizes the importance of sustainable fisheries practices through ecosystem-based management, the use of environmentally friendly technology, and education and training programs to increase the capacity of fishermen. The economic impact shows an increase in the average income of fishermen by 25%, while the social impact includes an increase in the welfare of coastal communities by 20%. Environmental impacts include the restoration of mangrove and coral reef ecosystems with increased area and cover of live coral. The main challenges include overfishing, environmental degradation, lack of infrastructure, and limited technological knowledge. Proposed strategies to overcome these challenges include strengthening policies and regulations, improving infrastructure, education and training, multi-stakeholder collaboration, and research and development. By implementing this strategy, the potential of the sustainable fisheries sector in Sukamara can be optimized, providing significant economic, social, and environmental benefits and becoming a model for other regions in sustainable natural resource management.

The distribution of coral reef fish biodiversity on Bontosua Island, Spermonde Archipelago, South Sulawesi Province

Background: Bontosua Island, located in the Spermonde Archipelago, is one of the strategic and historical islands in the region. The island plays a vital role in ecosystem conservation efforts by the local community, who are committed to preserving their natural environment. With dynamic ecosystem conditions, it is essential to understand the seabed cover and biodiversity on the island to support more effective conservation efforts. Methods: This study was conducted from March to September 2022 to mark the seabed cover of Bontosua Island and understand the relationships between coral reef fish species and the ecosystem. The method used was a stationary visual census, followed by descriptive analysis and one-way ANOVA to assess the biodiversity and diversity of coral reefs. Findings: The results showed a total of 1,306 coral reef fish from 9 families with 63 species identified, including the families Chaetodontidae, Serranidae, Lutjanidae, Haemulidae, Lethrinidae, Scaridae, Acanthuridae, and Siganidae. The families with the highest citations were Scaridae, Acanthuridae, and Siganidae. The highest coral reef fish were found in the north, west, and southwest of the island, where live coral areas are more dominant. Conclusion: This study shows that Bontosua Island has significant coral reef diversity, and certain areas, such as the north and southwest sides, have higher reported fish. These findings indicate the importance of these areas in conservation efforts. Novelty/Originality: This study provides a comprehensive picture of the seabed cover and coral reef fish diversity in Bontosua Island, which has yet to be widely discussed in previous studies. These findings provide a scientific basis for more targeted conservation strategies and help improve understanding of the dynamics of coral reef ecosystems in the Spermonde Islands.. Novelty/Originality of this article: This study proposes developing a community-based coral reef monitoring system that integrates local knowledge with digital mapping technology, aiming to increase the effectiveness of conservation and management efforts of marine resources on small islands.

Ecological drivers of parrotfish coral predation vary across spatial scales

Parrotfishes (Labridae: Scarini) are widely recognized for their important functional role in reducing coral-algae competition by grazing algae, yet some species are also coral predators (corallivores) and thereby have direct negative impacts on corals they prey upon. To better understand the ecological drivers of parrotfish corallivory intensity, we compared patterns of relative predation scar size and abundance across spatial scales from individual coral colonies (<1 to several meters in size), to reefs within islands (1 to 10s of km), to 4 regions across the Greater Caribbean (100s to 1000s of km) including Panamá, Florida, St. Croix, and Bonaire. Across reef sites, there was a positive correlation of both parrotfish density and biomass with the relative coral area preyed upon, but not predation scar abundance. While there was no apparent site-level effect of coral cover on corallivory intensity, we found that the abundance of colonies preyed upon was positively correlated with both coral diversity and the proportional cover of frequently targeted coral taxa within localized 30 m2 reef areas. At the scale of individual coral colonies, we found that while numerous coral taxa were preyed upon, corallivory was concentrated on a few species across regions, such as Orbicella spp., Porites spp., and Stephanocoenia intersepta. Our findings suggest that while increased parrotfish densities may result in an increased coral area preyed upon across reefs, corallivory intensity within reefs may decrease in response to declines in the cover of frequently targeted coral taxa and overall coral diversity.Spanish and Papiamentu versions of the abstract are provided in the Supplement at www.int-res.com/articles/suppl/m740p145_supp.pdf

Influence of different substrates on bacterial communities in coral reefs and surrounding environments of a coastal bay

Substrate types are diverse in coastal coral reefs, which can determine the distribution pattern of marine benthic organisms. Coastal coral reefs are also increasingly influenced by activities from the intertidal zone. However, the variation of bacterial communities on different substrates from the intertidal zone to coastal coral reefs have been seldom discussed. Here, we collected 12 samples of different substrate (rock, sand, live coral, and dead coral) from three environments (i.e., intertidal zone, coral distribution area, and no-coral distribution area) in Daya Bay of the South China Sea, and investigated the influence of substrates on bacterial communities. The results showed that the bacterial diversity (Shannon and Chao 1 index) in sand substrates was higher than those in stone/hard substrates. However, a more complex co-occurrence network of bacterial communities were observed in intertidal sand samples than sand samples from the coral area. Principal coordinate analysis and taxonomic analyses of bacterial composition showed that substrate type can shape the variations in bacterial communities from different environments in the Daya Bay region. Bacteroidetes and Chloroflexi were more abundant in sand substrates, while Cyanobacteria and Planctomycetes were more abundant in rock substrates. Redundancy analysis revealed that environmental factors, such as gravel, heavy metals, salinity, and pH regulated the bacterial community in the coastal region. Furthermore, the shared operational taxonomic units (OTUs) from different substrates in the coral distribution area were identified, and most of the top 20 shared OTUs (core bacteria) were identical to the bacteria associated with coral reef ecosystems in previous studies; thus, indicating that core bacteria exist in coral reefs from Daya Bay. This study broadens the understanding of the effect of substrates on bacterial distributions in coral reefs and surrounding environments from a coastal bay.

Variations in benthic coverage and diversity of shallow water coral reefs in Eastern coast of Sri Lanka: A combined analysis from Allen Coral Atlas and ground surveys

AbstractMonitoring changes in coral reef ecosystems for their conservation and management is important as they are frequently subject to various natural and anthropogenic threats. However, in Sri Lanka, the attention in this regard is to be further concerned for their well‐being. Therefore, this study focused on the selected shallow water (<5 m) coral reefs as Pigeon Island (PIR), Adukkuparu (AR), Salli Beach (SBR), Kayankerni (KR), and Passikuda (PR) on the Eastern coast of Sri Lanka to estimate their changes over 2020, 2021, and 2022. The remote sensing demarcations with the composition of reef ecosystems were done through the analysis of the Allen Coral Atlas data followed by field surveys. Higher accuracy levels for corals were obtained for each site due to field verifying all individual polygons and omitting unmatched polygons of the initial maps from the Allen Coral Atlas. Then, the in‐situ reef surveys were conducted over randomly selected permanent transects at each site. From 2020 to 2022, the live coral percentages have increased in PIR, AR, and SBR while reduced in KR and PR. Dead corals have facilitated the overgrowth of macroalgae. The combined area of live coral on all five reefs has slightly gone up. This increase is primarily due to the rise in live coral cover in AR and SBR. Also, prominent increments of coral diversity have resulted from those sites. Therefore, it is suggested that AR and SBR be designated as Marine Protected Areas to safeguard the newly emerging live corals.

Pemetaan Terumbu Karang Berbasis Citra Unmanned Aerial Vehicle (UAV) Dan Satelit Sentinel-2A Dengan Metode Object Based Image Analysis (OBIA) Di Perairan Pulau Menjangan Bali

There is still little research on mapping benthic habitats on Menjangan Island, so the availability of spatial data in this area is still limited. This research aimed to map coral reefs using UAV imagery and Sentinel-2A imagery with the object-based/OBIA classification method and calculate the level of accuracy of classification results in the waters of Menjangan Island. This research was conducted in 4 water areas, especially waters where diving and snorkeling activities often occur. This research used Sentinel-2A satellite data acquired on March 17, 2022, and UAV data acquired on March 30, 2022. Area 1 live coral (KH) with an area of 0.76 Ha for UAV imagery, live coral (KH) on Sentinel imagery -2A, namely 0.64 Ha. Region 2, the area of live coral (KH) in the UAV image is 0.67 Ha, and live coral (KH) in the Sentinel-2A image is 0.49 Ha. Region 3, the area of live coral (KH) in the UAV image is 0.77 Ha; in the Sentinel-2A image, it is 0.60 Ha. The 4 live coral (KH) areas in the UAV image have an area of 0.83 Ha, and the live coral (KH) in the Sentinel-2A image covers an area of 0.62091 Ha. UAV imagery can produce an overall accuracy in each region of 97.96% in Region 1. 98.21% in Region 2, 98.84% in Region 3, and 96.77% in Region 4. The overall accuracy level of Sentinel-2A imagery is 85.71% in Region 1, 83.93% in Region 2, 86.05% in Region 3, and 83.87% in Region 4.

Status of Coral reef around Swaraj Dweep (Havelock Island), Andaman, India

The study was carried out in selected reef sites at Swaraj Dweep (Havelock Island) to assess the status of live coral diversity with related fauna by using the line intercept transects (LIT) survey method. Three sites were selected for this study viz (1) Vijayanagar beach, (2) Elephant beach and (3) Radha Nagar Beach. The average length of entire LIT and reef area of each site were 1098 m, 141.3m and 215 m & 675.3 m, 103.3m and 133m respectively. The average of live corals was found dominant in the entire LIT at site 2 (37.7%) followed by site 1 (16.2%), and site 3 (14%) and dead corals were found dominant at site 3 (44.7%) followed by site 2 (33.2%) and site 1 (13.8%). Similarly reef area of live coral was found dominant at site 2 (50.8±2.5%) followed by site-1 (26.9±0.2%) and site 3 (23.7±6.2%). Altogether 80 species of live coral were recorded under 31 genera and 11 family at all LIT in which the family Poritidae was dominant in site 1 (55.1±4.9%) and site 2 (55.2±2.5%). The family Acroporidae was dominant in site 3 (35.2±4.1%). The environmental parameters of all three sites were analyzed that there were little variations observed except CO2 which remained consistent (0) during the study period.

Quantifying the Loss of Coral from a Bleaching Event Using Underwater Photogrammetry and AI-Assisted Image Segmentation

Detecting the impacts of natural and anthropogenic disturbances that cause declines in organisms or changes in community composition has long been a focus of ecology. However, a tradeoff often exists between the spatial extent over which relevant data can be collected, and the resolution of those data. Recent advances in underwater photogrammetry, as well as computer vision and machine learning tools that employ artificial intelligence (AI), offer potential solutions with which to resolve this tradeoff. Here, we coupled a rigorous photogrammetric survey method with novel AI-assisted image segmentation software in order to quantify the impact of a coral bleaching event on a tropical reef, both at an ecologically meaningful spatial scale and with high spatial resolution. In addition to outlining our workflow, we highlight three key results: (1) dramatic changes in the three-dimensional surface areas of live and dead coral, as well as the ratio of live to dead colonies before and after bleaching; (2) a size-dependent pattern of mortality in bleached corals, where the largest corals were disproportionately affected, and (3) a significantly greater decline in the surface area of live coral, as revealed by our approximation of the 3D shape compared to the more standard planar area (2D) approach. The technique of photogrammetry allows us to turn 2D images into approximate 3D models in a flexible and efficient way. Increasing the resolution, accuracy, spatial extent, and efficiency with which we can quantify effects of disturbances will improve our ability to understand the ecological consequences that cascade from small to large scales, as well as allow more informed decisions to be made regarding the mitigation of undesired impacts.

The cold-water coral province of the eastern Ligurian Sea (NW Mediterranean Sea): historical and novel evidences

Several bathyal cold-water coral provinces, characterized by a lush growth of habitat-forming scleractinians, have been recognized in the Mediterranean Sea. However, the search for this biogenic habitat only marginally targeted the Italian coast of the Ligurian Sea (NW Mediterranean basin) despite historical and a few recent local studies in the region reporting the presence of corals. This study used bathymetry maps, side-scan sonar profiles, historical charts, and trawling routes to identify sites that could potentially host coral habitats in the eastern sector of the Ligurian Sea. Remotely operated vehicle video footage from various projects (2015-2021, 20 dives) was then used to characterize four sub-areas (Genoa Plateau, Portofino, Deiva Marina, and Monterosso) where corals were detected between 450 m and 750 m depth. Radiocarbon dating was used to trace back the geological history of the coral structures. A small coral mound, impacted by trawling activities, was found on the Genoa Plateau, while four massive coral structures were found in the other sub-areas, mainly located in a morphologically complex and highly energetic canyon region. High levels of megafaunal biodiversity, including rarely reported alcyonaceans as Placogorgia coronata, were observed together with moderate fishing impact. Overall, the identified coral areas potentially account for 9 km2 of both subfossil mounds (as old as 13300 years BP), dominated by Desmophyllum pertusum, and living reefs, dominated by Madrepora oculata, the latter representing up to 23% of the substrate coverage. The few living colonies of D. pertusum in the area represent the first documented records for the Ligurian Sea. These data support the presence of a distinct eastern Ligurian cold-water coral province.

TINGKAT PEMANFAATAN UDANG KARANG (Panulirus spp) BERDASARKAN PENDEKATAN MODEL PRODUKSI SURPLUS DI PERAIRAN KABUPATEN PANGKEP

Crayfish (Panulirus spp) is one type of Indonesian marine fishery resources that is very potential and has long been caught by fishermen in coral areas to find out the description of fishing gear, methods, and crayfish fishing areas (Panulirus spp) in the waters of Pangkep Regency and to find out the estimated utilization rate of crayfish using the MSY approach in Pangkep Regency. This research has been carried out by taking data in the form of primary data carried out from March 1, 2022 – April 30, 2022 and secondary data in the form of catch production data and fishing efforts (units) obtained from the Marine and Fisheries Service of Pangkep Regency for the 2016-2021 time period. The results of this study showed that the fishing gear used to catch crayfish (Panulirus spp) was a fixed gill net using a canoe boat as a tool. The process of catching crayfish includes setting, soaking and hauling. Coral fishing grounds are in rocky areas with the fishing season occurring from November to January. Based on the results of research using three surplus production models, it was concluded that the most suitable surplus production model for crayfish fisheries in Pangkep Regency is the Gulland model by showing a large (R2) and a small standard deviation. The maximum sustainable catch is 16,783.58 kg/year and the attempted catch is 12,496 units. The Utilization Rate (TP) and Capability Rate (TPU) have exceeded (yJTB) and (fJTB) with overexploited status.

Control efforts of crown‐of‐thorns starfish outbreaks to limit future coral decline across the Great Barrier Reef

AbstractCrown‐of‐thorns starfish (CoTS) naturally occur on coral reefs throughout the Indo‐Pacific region. On Australia's Great Barrier Reef (GBR), outbreaks of CoTS populations are responsible for ecologically significant losses of corals, and while they have been documented for decades, they now undermine coral recovery from multiple stressors, especially anthropogenic warming. Culling interventions are currently the best approach to control CoTS outbreaks on the GBR, but assessing control effectiveness under multiple stressors is complicated. Using an ensemble of two reef community models simulating the temporal and spatial dynamics of CoTS and corals under future climate scenarios, we evaluate the present‐day and future effectiveness of the current implementation of the GBR CoTS Control Program. Specifically, we determine the culling effort needed (i.e., number of vessels) to achieve the maximum ecological benefits as predicted by the models under possible warming futures. Benefits were measured by comparing projections of coral cover and CoTS densities under scenarios of increasing control effort and baseline scenarios where no control was simulated. Projections of present‐day control efforts (five vessels) show that the number of individual reefs subject to CoTS outbreaks is reduced by 50%–65% annually, yielding a benefit of 5%–7% of healthy GBR coral area per decade, equivalent to gaining 104–150 km2 of live corals by 2035. A threefold increase in current control efforts is sufficient to reach more than 80% of the maximum coral benefits predicted by each model, but the future amount of effort required to control CoTS effectively depends on the intensity of warming and the early detection of CoTS outbreaks. While culling CoTS across the entire GBR is unfeasible, we provide a framework for maximizing ecosystem‐wide benefits of CoTS control and guide management decisions on the required culling effort needed to reduce CoTS outbreaks to levels that may ensure coral persistence in the face of future climate change impacts.

Coral reef degradation at an atoll of the Western Colombian Caribbean.

Coral reef decline is an issue of concern around the globe. Remote and uninhabited coral areas are not exempt from facing changes in species composition and functionality due to global drivers. Quitasueño is a remote atoll within the Seaflower Biosphere Reserve, in the Southwestern Caribbean Sea. To evaluate the current status of the coral reefs in Quitasueño we sampled 120 stations through Rapid Ecological Assessment and evaluated four stations through Planar Point Intercept to compare the current percent cover of benthic groups with previous studies in the area. We found pronounced changes in coral and macroalgae covers in time, and great conspicuousness of multiple conditions of deterioration along Quitasueño, including diseases, coral predation, and aggression and invasion of coral colonies by macroalgae and sponges. The reef ecosystem seems to be facing a phase shift, in which the benthic cover previously dominated by hard corals is currently dominated by fleshy macroalgae. It is essential to evaluate the possible drivers of the extent of degradation of Quitasueño to understand the process of deterioration and mitigate the impacts.

Coral Reefs Detecting with Artificial Neural Network Classification and PlanetScope Imagery in Cu Lao Xanh Island, Binh Dinh province

Coral reefs are a vital component of coastal and marine ecosystems. They are now under strong environmental challenges and are being harmed by human activities and rising sea surface temperatures, which are reducing the living coral cover. The purpose of this research was to evaluate the mapping accuracy of coral covers using PlanetScope satellite pictures with the Artificial Neural Network (ANN) method surrounding Cu Lao Xanh Island in Binh Dinh province. To adjust for the sunglint effect, the bands were corrected using the Hedley technique. After that, the Depth-Invariant Index technique was utilized to reduce the influence of the water column, and the ANN algorithm was employed for mapping. Hard coral, soft coral, seagrass, deep water, and bare bottom were identified as the five kinds of benthic habitat. The accuracy of the classification results was assessed using field data collected on May 10 and 11, 2022. The results indicated that the artificial neural network (ANN) technique had a higher accuracy, with a total classification accuracy of 89.55% and a kappa value of 0.87. Cu Lao Xanh’s coral area is around 68 hectares, with soft corals mostly found west and southwest of the island and hard corals in the east. This finding demonstrates that Planetscope satellite imagery is effective at monitoring shallow coral reefs on small islands, providing a scientific foundation and reliable data for the development of a more comprehensive coral reef ecological monitoring and management.

Late Holocene pteropod distribution across the base of the south-eastern Mediterranean margin: the importance of the > 63 µm fraction

Abstract. Euthecosomata pteropods were analysed in core sediments collected in the framework of the 2016 EUROFLEETS2 SEMSEEP cruise, offshore of Israel, in the eastern Mediterranean Sea. The investigated cores were retrieved in a deep-sea coral area at 690 m depth, an actively methane-seeping pockmark area at 1038 m depth, and a deep-sea channel area at 1310 m water depth. We identified and documented the pteropod species belonging to the families Heliconoididae, Limacinidae, Creseidae, Cavoliniidae, Cliidae, and Hyalocylidae and to some heteropods. Our study highlights the importance of investigating pteropods in the size fractions > 63 µm instead of the > 125 µm only. In particular, neglecting the small size fraction may result in a remarkable (up to 50 %–60 %) underestimation of the relative abundance of the epipelagic species Creseis acicula and Creseis conica and the mesopelagic species Heliconoides inflatus. This may significantly affect palaeoenvironmental reconstructions. The observed presence of tropical species supports the suggestion that the eastern Mediterranean is a refugium for these species. This study provides a basic benchmark for the late Holocene evolution of pteropod and heteropod distribution over 5800–5300 cal BP across the base of the south-eastern Levantine margin.

Dictyota defense: Developing effective chemical protection against intense fish predation for outplanted massive corals.

The incorporation of coral species with massive (e.g., boulder, brain) morphologies into reef restoration is critical to sustain biodiversity and increase coral cover on degraded reef ecosystems. However, fragments and colonies of massive corals outplanted in Miami-Dade County, Florida, US, can experience intense predation by fish within the first week of outplanting, resulting in >70% mortality. Here, we tested for the first time the potential benefit of feeding corals powdered Dictyota, a brown reef alga that is chemically defended against grazing, to determine if exposure to Dictyota can confer chemical protection to coral fragments and reduce the impacts of fish predation after outplanting. We found that feeding corals every 2 to 3 days for 2 months with dried and powdered Dictyota prior to outplanting significantly reduced predation levels on Orbicella faveolata and Montastraea cavernosa fragments (with less than 20% of the fragments experiencing predation up to 1-month post-outplanting). We also found that a single exposure to Dictyota at a high concentration 1 to 2 days prior to outplanting significantly reduced predation for six coral species within the first 24 h following outplanting. Thus, feeding corals dry Dictyota ex situ prior to outplanting appears to confer protection from fish predation during the critical first days to weeks after outplanting when predation impacts are commonly high. This simple and cheap method can be easily scaled up for corals kept ex situ prior to outplanting, resulting in an increase in restoration efficiency for massive corals in areas with high fish predation.

Mapping coral cover using Sentinel-2A in Karimunjawa, Indonesia

Abstract. Satya ED, Sabdono A, Wijayanti DP, Helmi M, Widiaratih R. 2023. Mapping coral cover using Sentinel-2A in Karimunjawa, Indonesia. Biodiversitas 24: 827-836. Coral reefs in the Karimunjawa National Park (KNP) have their own charm, especially for snorkeling and divers, it can be seen from the number of tourist visits which tends to increase every year, except for 2020 to 2021 due to the COVID-19 pandemic. This study aims to determine the impact of tourism on coral reef cover in KNP, with islands selected as representatives of high, medium and low level of tourist visits using Sentinel-2A. Comparison of Sentinel-2A coral cover area in 2020 with previous research which used Landsat 8 data in 2018 showed decrease in coral cover area by 16.5% and an increase in sand area by 24.1% for island of high tourist visits. It can be seen that tourism activities have significant impact on coral cover area, especially snorkeling and diving activities that are intentional or not potentially damaging to coral reefs. Sentinel-2A's ability to detect coral area is reliable, since field data is needed as input for data processing to identification locations in detail as needed. Coral area in 2020 using Sentinel-2A obtained for Menjangan Besar Island and Menjangan Kecil, Sintok Island, Tengah Island and Seruni Island were 1.88 km2, 0.303 km2, 0.318 km2, 0.237 km2 respectively.

Can black coral forests be detected using multibeam echosounder “multi-detect” data?

The black coral Anthipatella wollastoni forms marine animal forests in the mesophotic zone. The spatial extent of black coral forests is not well known in many regions. Due to its protein and chitin skeleton, the coral is difficult to image using acoustic remote sensing techniques compared to corals with carbonate skeletons. Several manufacturers have recently introduced an additional data type to their multibeam echosounders, called “multi-detection,” which provides additional target detections per beam in addition to the primary bottom detection. In this study, we used a Norbit chirp multibeam echosounder in multi-detect mode to acquire up to three targets in each beam in an area of black coral below 45 m depth off the coast of Lanzarote (Canary Islands, Spain). Multi-detect allows features above and below the primary bottom detection to be identified without the need to store and process water-column data. Black coral can be detected by comparing “multi-detection” data with ground truthing by technical divers and underwater cameras. However, the repeatability of the detections is limited and further sensitivity studies are required.

Coral recruitment and its relationship to hard coral cover in the Derawan Islands, East Kalimantan

Coral recruitment is the process when coral larvae settle to the substrate and establish themselves as a reef community. The success of coral recruitment is very important for the sustainability of coral reefs in an area, including the Derawan Islands which develop underwater tourism. Observations on coral reef recruitment were carried out in the Derawan Islands. This study aimed to determine the density of coral recruitment, hard coral cover, and the relationship between coral recruitment and hard coral cover. Data were collected using the Underwater Photo Transect method at 11 stations in the Derawan Islands. The results showed that coral recruitment in the Derawan Islands was low, ranging from 1.41 to 3.13 colonies.m−2. Hard coral cover was categorized as “moderate” with an average of 28.04% (+SE=3.63%). The relationship between coral recruitment and hard coral cover occurred for medium-sized juvenile corals (3-6 cm). Their negative relationship was shown by the presence of more medium-sized juvenile corals in areas with lower hard coral cover. The large availability of stable substrates such as DCA in areas with low hard coral cover can increase the potential for coral reef ecosystems to recover naturally.