Search Results (25)

Corals in the Galápagos present diverse reef configurations from biogenic coral reefs to coral communities growing on rocks and sand. These corals have experienced decades of disturbances including recurring El Niño and mass bleaching events. However, traditional methods in ecology have limited capacity in describing coral demographic trends across large spatial scales. Photogrammetry—a form of 3D imaging, has emerged over the past decade as a popular method for benthic surveys. However, the majority of protocols in the field utilize the 2D products of photogrammetry, ignoring overhangs and leaving significant information unexploited. We surveyed seven reef sites across the archipelago using underwater photogrammetry and developed new methods for 3D annotation and fractal dimension calculation. Our findings reveal variation in coral cover, diversity, and structural complexity across the archipelago. Our results align with previous studies in the region and add important information on reef structural complexity which was not measured here before. We release a unique dataset: Galápagos_3D, including seven 3D models and over 17,000 annotated images. This study establishes an important baseline for long-term monitoring, research, and conservation in the Galápagos, potentially informing evidence-based policies and advancing our understanding of coral resilience and recovery. Full article

Coralligenous bioconstructions are priority habitats crucial for the protection of Mediterranean marine biodiversity. Among these bioconstructions, the mesophotic biogenic reefs of the northern Adriatic are of particular concern due to their ecological relevance and the high levels of human pressure in the region. Thus, effective monitoring strategies are vital for the conservation and management of these fragile environments. In this study, we investigated the multivariate spatial and temporal patterns of sessile macrobenthos on biogenic reefs within two areas of a Natura 2000 site in the northern Adriatic over a four-year period. We also classified the ecological status of reefs based on the NAMBER index, specifically tailored for these peculiar bioconstructions. Our findings revealed that temporal trajectories of assemblages significantly differed between the two investigated areas, mostly due to larger fluctuations in algal turf abundance in the area closest to the coast, which is putatively more exposed to human impacts. In this area, the index identified a “Moderate” status during the period of peaking turf abundance, while the reef status consistently remained “Good” in other periods and in the area located further from the coast. This highlights the index sensitivity in reflecting actual changes in assemblages potentially associated with reef degradation. Full article

The development pattern of the high-quality reservoir in the Changxing Formation in the Wolonghe-Yangduxi area of southeastern Sichuan is complex. To clarify its evolution, genetic mechanisms, and distribution patterns, this study integrates data from profiles, cores, thin sections, and well logs. It reveals the distribution mechanisms of the bio-reef and shoal reservoirs in the Changxing Formation and discusses the controlling effects of tectonic, sedimentary, and diagenetic processes on reservoir development. The results show the following: (1) The Changxing Formation mainly develops open platform facies, platform margin facies, and slope-basin facies, which can be further subdivided into subfacies of platforms, intra-platform depressions, intra-platform depressions marginal reefs, and intra-platform depressions marginal shoals. The intra-platform margin reefs and the reefs at the edge of the platforms are favorable microfacies for reservoir development. (2) The high-quality reservoirs of the Changxing Formation are dominated by medium-thick-layered biogenic reef limestone and bioclastic limestone, with secondary porosity as the main reservoir space. (3) Sedimentary conditions, sea level fluctuations, and diagenesis are crucial factors for reservoir development. Paleogeomorphological conditions provide the foundation for reservoir development, while sea level fluctuations control the internal structure of the reef–shoal and the cyclical variations in the reservoir. Full article

Biogenic reefs support marine biodiversity and play a key role in a healthy marine environment. Protecting and enhancing reef-building species, such as Sabellaria spinulosa, require mapping and monitoring strategies. A multi-scale and multi-sensor mapping campaign, including a multi-beam echosounder, side-scan sonar (SSS), box corer and ROV with an attached video camera, has been carried out in the northern Brown Bank (Dutch Continental Shelf) in August 2023. A semi-automated classification workflow, based on a support vector machine (machine learning), was developed to map Sabellaria reefs using SSS and video data. Elevated Sabellaria reefs were classified with a precision and sensitivity of 52% and 49%, respectively. The classified SSS images were merged into full-coverage percentage maps of Sabellaria reef coverage. Located between the swales of the tidal ridges, it was estimated that the reefs cover an area of 3.8 to 5.7% within the surveyed areas. The maps indicate (1) on the large-scale a preference of Sabellaria spinulosa for settlement to the east of the deepest part of the swale and (2) on the small-scale a preference for the troughs towards the stoss side of the megaripples. The employed survey strategy and the developed classification workflow can be extended to other environmental areas and further developed into a standard monitoring procedure. Full article

The beneficial or detrimental effects of human-built marine structures (piers, breakwaters, and seawalls) on macrozoobenthic assemblages and diversities are currently underexplored. The present study investigated the enhancement of β-diversity of oysterbed-associated species on breakwaters constructed along sandy beaches. We compared habitat complexities and species assemblages among artificial breakwater shores (ABS), a natural rocky shore (NS), and an embayment shore (ES). Oysterbed habitat complexity was found to be greatest on the ABS due to the successional colonization of the reef-forming estuarine oyster, Saccostrea echinata, followed by the colonization of boring bivalves and burrowing annelids. High-resolution taxonomic data revealed that the ABS supports the greatest species richness, including 48.1% unique species and 33.3% species shared with the embayment shore. The other shores uniquely or in combination with ABS support up to 11.1% of the total species richness associated with the oysterbeds (n = 81). Taxonomic dominance in terms of species number was Mollusca > Annelida > Arthropoda. This study reveals that ABS enhances β-diversity by ~91% (Jaccard dissimilarity index), which is driven by the sequential cascading events of (1) sheltering of shores, (2) colonization of novel habitat-forming oysters, (3) novel macrozoobenthic species recruitment from adjacent shores and sheltered embayments, including habitat-forming bivalves and annelids, and (4) the recruitment of macrozoobenthic species to boreholes. ABS habitat complexity derives from a spatially distinct, three-tiered ecological engineering system, involving (1) breakwater construction (100 m), (2) reef-forming oysters (10 m), and (3) boring bivalves and burrowing annelids (<10 cm). Irrespective of the purpose of their construction, breakwaters along extended sandy shores can potentially increase the resilience (β-diversity) and regional interconnectivity of hard surface macrozoobenthic species. Full article

The Trabocchi Coast in the Chieti district of the mid-Adriatic (Italy) is one of the few rocky areas within the General Fisheries Commission GSA 17, alongside Mount Conero (Ancona 43°00′01″ N 13°52′13″ E) and the small San Nicola Rock (Ascoli Piceno; 43°32′0″ N 13°36′0″ E). This coastline is known for its biodiversity-rich bays, inlets, and submerged cliffs. Since 2015, annual biodiversity surveys have been conducted in the area, focusing on marine species richness and the identification of non-native species. In September 2024, a juvenile ornate wrasse (Thalassoma pavo) was documented for the first time in the middle Adriatic during an underwater visual survey at Trabocco Punta Torre, a key site along the Trabocchi Coast near artificial and biogenic reefs. This record extends the known distribution of T. pavo, a thermophilic species previously reported only along the southern Adriatic coast of Puglia. This is the first confirmed sighting on the middle and northern Adriatic coast of Italy. The discovery highlights the importance of ongoing biodiversity monitoring to track changes in marine ecosystems, particularly as the Adriatic Sea faces environmental shifts linked to climate warming. The presence of T. pavo in this area suggests the potential for the species to establish populations in previously uninhabited northern regions. Further research is needed to explore the role of biotic and abiotic factors—such as water temperature, current patterns, and habitat availability—in the survival and potential reproduction of T. pavo in the middle Adriatic. The observation contributes to the broader understanding of the meridionalization process in the Adriatic Sea, where rising water temperatures are facilitating the northward expansion of thermophilic species. Continuous monitoring is recommended to assess the long-term viability of T. pavo populations in the Adriatic Sea and better predict the impacts of ongoing climate change on marine biodiversity. Full article

The karst landforms in northeastern Sichuan Basin are widely developed, but the understanding of the geological characteristics, controlling factors, and spatiotemporal evolution process of karst caves is still unclear. The research object of this study is the Panlongdong karst cave in the northeastern Sichuan Basin. An outcrop geological survey was carried out, ¹⁴C isotope dating of stalactite was performed, carbon and oxygen isotope analysis was completed, and the formation process was identified. The interior of this cave is covered with karst sediments, and its original rocks are the Permian Wujiaping and Changxing formations, with secondary dissolution that has developed. The rock types, geological structure (fault, joint), and climate are the main factors behind the formation of the Panlongdong karst cave. The sedimentation of biogenic reefs and carbonate rocks is a fundamental geological condition for the development of karst processes. The geological structures provide channels for the dissolution of atmospheric precipitation. From 43.5 ka.B.P., six continuous changes in climate have intensified the formation of karst landforms. Warm, humid, and cold dry climate conditions have repeatedly occurred, and carbonate rocks have experienced varying degrees of karstification under the influence of climate. Through the four stages of structural breakup and surface dissolution, secondary cranny dissolution, selective dissolution, and detachment of rock mass and karst sediment formation, the Panlongdong karst cave was ultimately formed. The formation process of the Panlongdong karst cave is of great significance for understanding the evolution of the paleoenvironment in the northeastern Sichuan Basin. Full article

The symbiosis between cnidarians and dinoflagellates underpins the success of reef-building corals in otherwise nutrient-poor habitats. Alterations to symbiotic state can perturb metabolic homeostasis and thus alter the release of biogenic volatile organic compounds (BVOCs). While BVOCs can play important roles in metabolic regulation and signalling, how the symbiotic state affects BVOC output remains unexplored. We therefore characterised the suite of BVOCs that comprise the volatilome of the sea anemone Exaiptasia diaphana (‘Aiptasia’) when aposymbiotic and in symbiosis with either its native dinoflagellate symbiont Breviolum minutum or the non-native symbiont Durusdinium trenchii. In parallel, the bacterial community structure in these different symbiotic states was fully characterised to resolve the holobiont microbiome. Based on rRNA analyses, 147 unique amplicon sequence variants (ASVs) were observed across symbiotic states. Furthermore, the microbiomes were distinct across the different symbiotic states: bacteria in the family Vibrionaceae were the most abundant in aposymbiotic anemones; those in the family Crocinitomicaceae were the most abundant in anemones symbiotic with D. trenchii; and anemones symbiotic with B. minutum had the highest proportion of low-abundance ASVs. Across these different holobionts, 142 BVOCs were detected and classified into 17 groups based on their chemical structure, with BVOCs containing multiple functional groups being the most abundant. Isoprene was detected in higher abundance when anemones hosted their native symbiont, and dimethyl sulphide was detected in higher abundance in the volatilome of both Aiptasia-Symbiodiniaceae combinations relative to aposymbiotic anemones. The volatilomes of aposymbiotic anemones and anemones symbiotic with B. minutum were distinct, while the volatilome of anemones symbiotic with D. trenchii overlapped both of the others. Collectively, our results are consistent with previous reports that D. trenchii produces a metabolically sub-optimal symbiosis with Aiptasia, and add to our understanding of how symbiotic cnidarians, including corals, may respond to climate change should they acquire novel dinoflagellate partners. Full article

Red calcareous algae create bio-aggregations ecosystems constituted by carbonate calcium, with two main morphotypes: geniculate and non-geniculate structures (rhodoliths may form bio-encrustations on hard substrata or unattached nodules). This study presents a bibliographic review of the order Corallinales (specifically, rhodoliths), highlighting on morphology, ecology, diversity, related organisms, major anthropogenic influences on climate change and current conservation initiatives. These habitats are often widespread geographically and bathymetrically, occurring in the photic zone from the intertidal area to depths of 270 m. Due to its diverse morphology, this group offers a special biogenic environment that is favourable to epiphyte algae and a number of marine invertebrates. They also include holobiont microbiota made up of tiny eukaryotes, bacteria and viruses. The morphology of red calcareous algae and outside environmental conditions are thought to be the key forces regulating faunistic communities in algae reefs. The impacts of climate change, particularly those related to acidification, might substantially jeopardise the survival of the Corallinales. Despite the significance of these ecosystems, there are a number of anthropogenic stresses on them. Since there have been few attempts to conserve them, programs aimed at their conservation and management need to closely monitor their habitats, research the communities they are linked with and assess the effects they have on the environment. Full article

Coral reefs are three-dimensional biogenic structures that provide habitat for plenty of marine organisms; yet, coral reefs are deteriorating worldwide. Hence, it is essential to identify suitable substitutes for such coral services. This study examines reef fishes’ behavior and reactions to three-dimensional-printed (3DP) corals based on scanned Stylophora pistillata, as well as modified 3DP models. In particular, fishes’ unresponsiveness to the color, shape, morphology, and material of 3DP models both in vitro and in situ experiments was investigated. Coral reef fishes responded to the 3DP corals and demonstrated their usage in a range of services. Moreover, a greater number of fish species interacted more with 3DP models than they did with live corals. Furthermore, specific reef fish species, such as Sea Goldies (Pseudanthias squamipinnis), showed a preference for specific 3DP coral color, and other species demonstrated preferences for specific 3DP model shapes. The current study results show that three-dimensional-printed coral models can substitute for live corals for certain types of reef fish services. Full article

Remote sensing is a relevant method to map inaccessible areas, such as intertidal mudflats. However, image classification is challenging due to spectral similarity between microphytobenthos and oyster reefs. Because these elements are strongly related to local geomorphic features, including biogenic structures, a new mapping method has been developed to overcome the current obstacles. This method is based on unmanned aerial vehicles (UAV), RGB, and multispectral (four bands: green, red, red-edge, and near-infrared) surveys that combine high spatial resolution (e.g., 5 cm pixel), geomorphic mapping, and machine learning random forest (RF) classification. A mudflat on the Atlantic coast of France (Marennes-Oléron bay) was surveyed based on this method and by using the structure from motion (SfM) photogrammetric approach to produce orthophotographs and digital surface models (DSM). Eight classes of mudflat surface based on indexes, such as NDVI and spectral bands normalised to NIR, were identified either on the whole image (i.e., standard RF classification) or after segmentation into five geomorphic units mapped from DSM (i.e., geomorphic-based RF classification). The classification accuracy was higher with the geomorphic-based RF classification (93.12%) than with the standard RF classification (73.45%), showing the added value of combining topographic and radiometric data to map soft-bottom intertidal areas and the user-friendly potential of this method in applications to other ecosystems, such as wetlands or peatlands. Full article

Seasonal oscillations in the partial pressure of carbon dioxide (pCO₂) in the Earth’s atmosphere, stronger in northern latitudes, are assumed to show that terrestrial photosynthesis exceeds respiration in summer, reducing the pCO₂ in air but increasing its value in winter when respiration exceeds photosynthesis. We disagree, proposing that variation in the temperature of the surface mixing zone of seawater also reversibly regulates the pCO₂ in air as a non-equilibrium process between air and seawater. We predict by thermal modelling that carbonate (CO₃²⁻) concentration in the surface mixed layer seawater declines in winter by conversion to bicarbonate with CaCO₃ (calcite or aragonite) becoming more soluble and, proportional to the fall of temperature, calcite decalcifying more strongly, allowing more CO₂ emission to air. Paradoxically, the increasing CO₂ concentration in seawater favoring photosynthesis peaking in mid-summer declines simultaneously in autumn and early winter, forced by boundary layer fugacity into phase transfer to the atmosphere, supporting peak atmospheric pCO₂ by late winter. These physico-chemical processes reverse in late winter and spring as seawater warms favoring calcification, fugacity forcing CO₂ from the atmosphere as bicarbonate declines and carbonate increases, augmenting suspended calcite particles by several percent. Our numerical computation predicts that the larger range of thermal fluctuations in the northern hemisphere could reversibly favor absorption from air of more than one mole of CO₂ per square meter in summer with calcite formation potentially augmenting shallow limestone reefs, despite falling pH, if there is a trend for increasing seawater temperature. Another assumption we challenge is that upwelling and advection from deeper water is the sole cause of increases in dissolved inorganic carbon (DIC) and alkalinity in surface waters, even in the southern hemisphere. Instead, some calcite dissolution is favored as water temperature falls near the surface. Standard enthalpy analysis of key DIC reactions indicates why this oscillation is more obvious in the northern hemisphere with seasonal variations in water temperature (ca. 7.1 °C) being almost twice those in the southern hemisphere (ca. 4.7 °C) with a greater depth of the surface mixing zone of seawater in the southern oceans. Questions remain regarding the relative rates of biotic and abiotic inorganic precipitation and dissolution of CaCO₃ in the mixing zone. In summary, rapid biogenic calcification is favored by summer photosynthesis, but slower abiotic calcification is also more likely in warmer water. We conclude that the relative significance of terrestrial biotic and seawater abiotic processes in seawater on the seasonal oscillation in the atmosphere can only be assessed by direct seasonal measurements in seawater. Full article

Large amounts of anthropogenic CO₂ in the atmosphere are taken up when the ocean alters the seawater carbonate system, which could have a significant impact on carbonate-rich sediments. Coral reef limestone is a special biogenic carbonate, which is mainly composed of calcium carbonate. When carbonate-rich rocks are brought into contact with a CO₂ weak acid solution, they will be dissolved, which may affect the physical and mechanical properties of the rock. In this paper, the physical and chemical interactions between CO₂, seawater and the framework structure reef limestone were studied based on an experiment conducted in a hydrothermal reactor. The solution was analyzed for dissolved Ca²⁺ concentration during the reaction, and the rock mass, effective volume (except for the volume of open pores), permeability, images from electron microscopy and X-ray microtomography were contrasted before and after immersion. The uniaxial compressive and tensile strength tests were conducted, respectively, to clarify the mechanical response of the rock after the reaction. The results indicate that dissolution occurred during the reaction, and the calcium ions of the solution were increased. The physical properties of the rock were changed, and the permeability significantly increased. Because the rocks were soaked for only 15 days, the total cumulative amount of calcium carbonate dissolved was less, and the mechanical properties were not affected. Full article

Biogenic habitats often form hot spots of biodiversity. However, the role of epibiosis and the ‘habitat cascades’ phenomenon in enhancing structural heterogeneity and biodiversity in biogenic habitats in remote and difficult-to-access areas is little known. In this work, we provide the first insight by exploring epibiosis across remote habitats that often support high levels of biodiversity, i.e., cold-water coral reefs and marine caves. The present study acts as a stepping-stone for the further exploration of ‘habitat cascades’ in habitats where scientific knowledge about this phenomenon is limited. Full article

In temperate coastal regions of Western Europe, the polychaete Sabellaria alveolata (Linné) builds large intertidal reefs of several hectares on soft-bottom substrates. These reefs are protected by the European Habitat Directive EEC/92/43 under the status of biogenic structures hosting a high biodiversity and providing ecological functions such as protection against coastal erosion. As an alternative to time-consuming field campaigns, a UAV-based Structure-from-Motion photogrammetric survey was carried out in October 2020 over Noirmoutier Island (France) where the second-largest known European reef is located in a tidal delta. A DJI Phantom 4 Multispectral UAV provided a topographic dataset at very high resolutions of 5 cm/pixel for the Digital Surface Model (DSM) and 2.63 cm/pixel for the multispectral orthomosaic images. The reef footprint was mapped using a combination of two topographic indices: the Topographic Openness Index and the Topographic Position Index. The reef structures covered an area of 8.15 ha, with 89% corresponding to the main reef composed of connected and continuous biogenic structures, 7.6% of large isolated structures (<60 m²), and 4.4% of small isolated reef clumps (<2 m²). To further describe the topographic complexity of the reef, the Geomorphon landform classification was used. The spatial distribution of tabular platforms considered as a healthy stage of the reef in contrast to a degraded stage was mapped with a proxy that consists in comparing the reef volume to a theoretical tabular-shaped reef volume. Epibionts colonizing the reef (macroalgae, mussels, and oysters) were also mapped by combining multispectral indices such as the Normalised Difference Vegetation Index and simple band ratios with topographic indices. A confusion matrix showed that macroalgae and mussels were satisfactorily identified but that oysters could not be detected by an automated procedure due to their spectral complexity. The topographic indices used in this work should now be further exploited to propose a health index for these large intertidal reefs. Full article