Search Results (43)

In this study, a Boussinesq-type wave model, namely FUNWAVE-TVD, was employed to explore solitary wave processes over coral atolls in two horizontal dimensions. First, a typical solitary wave propagation process over an idealized atoll in a field scale is simulated and analyzed. Then the effects of reef flat water depth, reef flat width, reef surface roughness, fore-reef slope, and lagoon water depth on the distribution of maximum surface elevations over atolls are investigated. Moreover, the effect of a channel on the reef flat is also studied. It is found that during solitary wave propagation, the coral reefs of an atoll can provide effective shelter for the lagoon inside; however, there will be an area of wave height enhancement near the lagoon edge at the lee side of an atoll. The maximum surface elevations over the entire atoll increase significantly with the rise in reef flat water depth, or reduced reef flat width and reef surface roughness, while the lagoon water depth and fore-reef slope have minimal influence. As the reef flat water depth increases or the reef surface roughness decreases, the extent of the wave height enhancement area at the lee side also undergoes an expansion. The presence of a channel in the reef flat mainly leads to two regions of increased wave height. The more the position of the channel deviates from the front of the atoll, the smaller the increase effect and range of the two regions will be. As the channel width increases, the increase effect and range of the two regions will also increase. Full article

Remote sensing monitoring and geomorphologic change analysis of coral reefs are of great practical significance for the ecological protection and sustainable development of coral reef area resources. A WBMD scheme is proposed to better extract coral reef information from island environments of Xisha, China. Satellite imagery, after preprocessing, is subjected to water depth correction to mitigate the influence of water depth on reflectance. A maximum likelihood classification model is then used for geomorphological classification, followed by refinement through a decision tree classification model, forming the WBMD scheme. The overall accuracy of geomorphological classification for Xisha Chau and Zhaoshu Island based on the WBMD scheme was 97.07% and 95.07%. Using this scheme to analyze the geomorphology of Xisha Chau and Zhaoshu Island from 2014 to 2018 reveals that the degradation of coral reef on Xisha Chau is mainly distributed in the lagoon slope and around the lagoon, and the lagoon area on Zhaoshu Island has been shrinking year by year, while the area of the gray sand island has increased, and the areas of other geomorphological types exhibit fluctuating changes. Previous studies on coral reefs have indicated that coral reefs are mainly distributed in the lagoon slope area, where significant coral reef degradation has also been observed, raising an alarm for coral reef conservation efforts in China. Full article

The Ayla Oasis in Aqaba, Jordan, is a major tourism and residential development project in Aqaba, Jordan, containing three artificial lagoons. This study explores the ecological sustainable development of Ayla Lagoons, focusing on the seawater and bottom sediment quality, and the bottom habitat, in addition to coral conservation and restoration initiatives. The flushing time, averaging 3.7 days for the Upper Lagoon and 2.4 days for the Middle Lagoon, plays a crucial role in maintaining water quality. These measures secure the well-being of all visitors and residents, while also preserving the marine biodiversity. The Upper, Middle, and Tidal Lagoons exhibit physiochemical properties in alignment with seawater characteristics of the Gulf of Aqaba. Sediment quality analysis shows organic carbon levels and grain size distribution vary among lagoons, indicating expected different energy conditions and a healthy environment. The lagoons support a diverse range of species, with a total of 2343 fish individuals belonging to 22 species across 17 families recorded. The comprehensive analysis of the Ayla Oasis lagoons’ seawater and sediment quality revealed a dynamic and resilient ecosystem. Ayla’s coral conservation and restoration initiative within its lagoons feature 166 reef balls, 5 coral nurseries, and 2 metal structures, all designed to foster marine biodiversity. The project demonstrates the effectiveness of Ayla Oasis’ environmental resilience and monitoring strategies, showcasing a commitment to sustainable management and environmental stewardship. These efforts reflect Ayla’s ongoing dedication to protecting and preserving the marine ecosystem, ensuring the long-term health of its coral reefs and surrounding marine life. Full article

The seismic safety evaluation of artificial reef islands is of great significance for ensuring their long-term stable operation and the safety of residents’ lives. However, due to an insufficient understanding of coral reefs’ basic characteristics, current research on coral reef seismic stability neglects the influence of pore water pressure and abnormal reef layers formed during geological evolution. To further study the impact of earthquakes on coral reefs in the South China Sea, this paper takes Meiji Reef as the research object, establishes a 3-D model containing a saturated coral reef–seawater–seabed coupling system, and considers the influence of abnormally high-porosity weathered layers to study the seismic response of the coupling system in the frequency domain. The results show that ignoring the influence of pore water pressure will underestimate the impact of earthquakes on coral reefs. The seismic waves with a frequency of 4.1 Hz in the horizontal direction have a significant impact on the reef, and the side parallel to the direction of wave propagation is more affected, while the side perpendicular to the direction of wave propagation is less affected. The reef flat near the seawater side is less affected by earthquakes, while that on the lagoon side is more affected. Highly porous, weathered layers increase the seismic impact on reef flats. Full article

We studied the Jafnayn Formation’s lithostratigraphy, microfacies, depositional environment, and uncertain presence of the Paleocene/Eocene boundary and present the first detailed analysis of a 127-m-thick section using the standard microfacies (SMF)/facies zone (FZ) system. The formation is dominated by foraminiferal grainstones and packstones of SMF 18-FOR, followed by peloidal grainstones and packstones of SMF 16. Coral-red algae floatstones of SMF 8 occur sporadically. SMF 18-DASY appears only once. SMF 16 and 18-FOR suggest a restricted lagoon, whereas SMF 8 and 18-DASY reflect episodic open marine lagoonal conditions. The section consists of four lithostratigraphic units. Considerable detrital quartz near the base (Unit 1: 22%; sand, sandstone, conglomerate) and top (Unit 4: 40%; sand) coincides with a restricted lagoon affected by near-shore processes (base) and near-shore conditions (top). Open marine conditions show an elevated bioclast diversity in units 3 and 4. Unit 2 displays very thickly-bedded limestones of the restricted lagoon. The lagoon barriers likely consist of foraminifera and other allochems that were reworked from the lagoon to form shoals. Coral remains in units 3 and 4 suggest that coral build-ups in the upper part of the formation protected the lagoon as well. The early Eocene age of several basal Alveolina species in the lowermost 9 m of the studied section indicates that the section is incomplete, with the late Paleocene part and meters-thick basal yellow marl missing. The Paleocene/Eocene boundary is unexposed. Full article

Subtropical coral reefs such as the lagoonal reefs of Norfolk Island in the remote South Pacific are vastly understudied, with many benthic species unrecorded in the scientific literature. Here we report on ascidian populations from 2021 to 2023 at Norfolk Islands inshore reefs. Quantitative assessments spanning that period were conducted to assess ascidian presence, cover, and benthic interactions. We show ascidian cover remained persistently low and stable across the lagoonal reefs during the study period. We find adjacent reef site, Cemetery Bay showed variation in ascidian cover over time, where we measure a 3.2-fold increase in cover over 2 years. Ascidians were associated primarily with sand and sediment substrates at all reef locations. Recorded interactions between hard corals and ascidians were low. This study provides valuable insights into the population dynamics of ascidians within subtropical reef ecosystems. Ongoing ascidian population monitoring can provide a comprehensive understanding of ascidian dynamics whilst also providing insight of theimpact of anthropogenic stressors on benthic communities. Together, this can aid in informing management and conservation strategies for subtropical reefs. Full article

Marine aerosol particles can act as cloud condensation nuclei and influence the atmospheric boundary layer by scattering solar radiation. The interaction of ocean waves and coral reefs may affect the distribution and size of marine aerosol particles. Measuring this effect has proven challenging. Here, we tested the hypothesis that the distribution and size of marine aerosol particles would vary over three distinct zones (i.e., coral lagoon, surf break, and open water) near One Tree Island in the Great Barrier Reef, which is approximately 85 km off the east coast of Australia. We used a modified DJI Agras T30 drone fitted with a miniaturised scanning electrical mobility sizer and advanced mixing condensation particle counter to collect data on aerosol size distribution between 30 and 300 nm at 20 m above the water surface. We conducted 30 flights over ten days during the Austral summer/autumn of 2023. The fitted bimodal lognormal curves indicate that the number concentrations for aerosols below 85 nm diameter are more than 16% higher over the lagoon than over open water. The average mean mode diameters remained constant across the different zones, indicating no significant influence of breaking waves on the detected aerosol size modes. The most influential explanatory variable for aerosol size distribution was the difference between air temperature and the underlying sea surface, explaining around 40% of the variability. Salinity also exhibited a significant influence, explaining around 12% of the measured variability in the number concentration of aerosols throughout the campaign. A calculated wind stress magnitude did not reveal significant variation in the measured marine aerosol concentrations. Overall, our drone-based aerosol measurements near the water surface effectively characterise the dynamics of background marine aerosols around One Tree Island Reef, illustrating the value of drone-based systems for providing size-dependent aerosol information in difficult-to-access and environmentally sensitive areas. Full article

The Great Barrier Reef lagoon is a large, relatively shallow area of the Australian continental shelf, isolated from the open ocean by a dense matrix of coral reefs. As the lagoon is generally vertically well mixed by strong tidal currents and wind, it is perhaps not surprising there is no mention in the open literature of the occurrence of internal waves there. Nevertheless, high-resolution satellite imagery is shown in this article to reveal the characteristic surface expressions of nonlinear internal waves in the lagoon. The waves are confined to periods of low winds in austral spring and summer, making them a potentially important mechanism for the dispersal of algae and planktonic larvae. The imagery suggests a link between the waves and tidally forced submesoscale jets and vortices, but the actual mechanism generating the internal waves is unclear and requires investigation. Full article

Nearshore coral reefs at Teahupo’o, Tahiti, are currently threatened by destruction from proposed plans to build a new judging tower in the reef lagoon for the 2024 Olympic surfing event. Local community members were trained to utilize 3D photogrammetry techniques to create high-resolution habitat maps of three sites that will be impacted by dredging and tower construction. The resulting orthomosaics were analyzed to quantify and characterize the coral community structure at each study site. Species diversity, coral colony count, coral colony size, and percent cover of live coral and living benthos were extracted from all survey plots. The resulting data show these sites support healthy and diverse coral communities that contribute to the ecological function of the larger reef system at Teahupo’o. The Hawai’i State Division of Aquatic Resources Penalty Matrix was used to estimate the USD value of the live corals and algae identified among the study sites and the total area that will be impacted by the planned development project. This study highlights the utility of 3D photogrammetry for effective citizen science as well as the large economic and ecological impacts that may occur if this proposed construction occurs. Full article

The Belize Barrier Reef system (BBR) in the western Caribbean’s Gulf of Honduras contains a large region of lagoon coral reef, seagrass and mangrove habitat. As the largest lagoon habitat within the Caribbean, this region experiences differing oceanographic and temperature conditions as compared to deeper offshore areas. The occurrence of several endemic species within the Gulf of Honduras area and inside the Belize lagoon supports the hypothesis that this area is a unique biogeographic region. Consequently, the ecological effects of temperature increase due to global climate change may have a long-term adverse impact on this region’s unique marine species. This study reports an in situ temperature record over a ten-year period (2004–2014) collected from a coral reef offshore of Wee Wee Cay within the South Water Cay Marine Reserve of Belize. There was a steady increase in temperature during the decade. Full article

The oceanic waters of the Southwest Tropical Pacific occupy a vast region including multiple Pacific Island Countries. The state of these waters is determinant for fisheries and the blue economy. Ocean color remote sensing is the main tool to survey the variability and long-term evolution of these large areas that are important for economic development but are affected by climate change. Unlike vast oligotrophic gyres, tropical waters are characterized by numerous archipelagos and islands, with deep and shallow lagoons subjected to the large impacts of the land. Strikingly large dendritic phytoplankton (Trichodesmium) blooms with high levels of chlorophyll, developing within archipelagos, as well as coastal enrichments from various origins may be observed. Algorithms to detect the presence of Trichodesmium have been developed or adapted, as well as algorithms to estimate the chlorophyll concentration ([Chl-a)]. Adapting existing [Chl-a] algorithms does not always yield high, i.e., sufficient, accuracy. A review of published regional bio-optical algorithms developed taking into account the specific phytoplankton composition and minimizing the adverse impacts of particles and the seabed bottom on [Chl-a] determination is presented, as well the bio-optical database that allowed their development. The interest of such algorithms for a variety of applications and scientific accomplishments is highlighted, with a view to further addressing the main biology and biogeochemistry questions, e.g., to determine the true impact of diazotrophs and assess lagoon [Chl-a] variability with the highest confidence. This work anticipates the use of future coarse and high-spatial-resolution and multi- and hyper-spectral satellite imagery in the Pacific. Full article

The Caribbean is one of the world’s most vulnerable regions to the projected impacts of climate change, and changes in coral reef ecosystems have been studied over the last two decades. Lately, new technology-based methods using satellites and unmanned vehicles, among others have emerged as tools to aid the governance of these ecosystems by providing managers with high-quality data for decision-making processes. This paper addresses the development of a Google Earth Engine (GEE)-based application for use in the management processes of shallow coral reef ecosystems, using images acquired with Remotely Piloted Aircraft Systems (RPAS) known as drones, at the Old Providence McBean Lagoon National Natural Park; a Marine Protected Area (MPA) located northwest of Old Providence Island, Colombia. Image acquisition and processing, known as drone imagery, is first described for flights performed using an RTK multispectral drone at five different monitoring stations within the MPA. Then, the use of the GEE app is described and illustrated. The user executes four simple steps starting with the selection of the orthomosaics uploaded to GEE and obtaining the reef habitat classification for four categories: coral, macroalgae, sand, and rubble, at any of the five monitoring stations. Results show that these classes can be effectively mapped using different machine-learning (ML) algorithms available inside GEE, helping the manager obtain high-quality information about the reef. This remote-sensing application represents an easy-to-use tool for managers that can be integrated into modern ecosystem monitoring protocols, supporting effective reef governance within a digitized society with more demanding stakeholders. Full article

In 2015, the communities of reef-associated motile macrocrustaceans (decapods and stomatopods) were compared between two coral reefs with contrasting levels of degradation in Puerto Morelos (Mexican Caribbean), “Limones”, less degraded, with a healthy live coral cover, and “Bonanza”, more degraded, with less live coral and more macroalgae. Since then, several stressors have impacted Puerto Morelos. Massive influxes of floating Sargassum, which reached record levels in 2018, 2021, and 2022, have exacerbated the already high eutrophication of the reef lagoon. An outbreak and rapid propagation of the Stony Coral Tissue Loss Disease in 2018 changed the functionality of reefs. Three back-to-back hurricanes struck the coast close to Puerto Morelos in October 2020 and another one in August 2021. We repeated the study in 2022 to examine the potential changes in the habitat and communities of reef-associated crustaceans since 2015. Reef degradation did not increase significantly between 2015 and 2022, but crustacean species richness, diversity, evenness, and dominance, which differed between reefs in 2015, became similar between reefs in 2022, as did the crustacean community composition. The abundance of herbivore crabs increased in Limones, displacing the coral- and hydrocoral-mutualistic crabs and the abundance of detritivore hermit crabs increased in Bonanza. These results suggest a taxonomic homogenization between reefs, apparently related to subtle ecological changes not necessarily captured by standard metrics of reef condition. Full article

Herbicides used for weed management on agricultural land in Australia’s Great Barrier Reef catchments are a key concern for its ecosystem, including the lagoon’s marine plants and corals, whose productivity has been found to decline. The most reliable way to assess herbicide risk is by monitoring a site regularly, but this is costly and time-consuming, so numerical simulations and computer models are an alternative method. Despite the availability of low-cost and less labor-intensive modelling methods, they have been limited in their effectiveness due to a lack of specific herbicide usage data and an inadequate understanding of the breakdown and transport processes of herbicides after application. This paper reviews current findings regarding herbicide risk in all Great Barrier Reef catchments according to their agricultural land use, and the most recent Reef Water Quality Protection Plan recommendations. The various pathways for fate and transport of the herbicides were also examined, and a list of critical parameters was developed to help with computer simulations. The accuracy and reliability of modelling can be improved by including aerial drifts, interceptions by crop residues, mechanisms within the root zone, and subsurface and groundwater contributions to the herbicide load in the GBR lagoon. Moreover, the findings will provide new directions for management practices adoption data with the fate and transport model from paddock to reef and improve the reliability of model results. Full article

Owing to climate change and anthropogenic stressors, the abundance and diversity of reef fishes have globally decreased. However, we know little about the long-term change in reef fishes in the South China Sea (SCS). To reveal the response of reef fishes to these threats in the SCS, based on the fish specimens at Yongshu Reef lagoon collected in 1999 and 2016–2019, this study investigated variations in fish composition and community structure. Additionally, we inferred the changes in the coral cover of Yongshu Reef based on the change of the coral cover of near Meiji Reef in the SCS, sea surface temperature (SST) in Yongshu Reef, and total annual catch of Epinephelinae from China in the SCS. We found that compared with 1999, the number of dominant species in 2016–2019 decreased. The relative dominance of the first dominant species increased from 24.46 in 1999 to 39.44 in 2016–2019. Indices of catch per unit effort, species diversity and richness declined from 1999 to 2016–2019. Community pattern changed with some species with a higher trophic level (3.7–4.5) decreased, while those with lower trophic level (2.2–4.1) increased greatly. Some species with high economic value and important ecological functions decreased or disappeared locally. Correlation analysis indicated that declining coral cover, increasing fishing and rising SST were clearly associated with changes in fish community structure at Yongshu Reef. We speculated that declining coral cover and increasing fishing had a direct impact on the degradation of fish communities at Yongshu Reef lagoon, but increasing SST had an indirect impact on that. To conserve coral reef fish, it is recommended to take rigorous measures for improving habitat and protecting resource. Full article