Search Results (208)

Benthic marine diatoms are speciose but vastly underexplored eukaryotic microbes. Diatoms are identified by their intricately ornamented silica cell walls known as frustules, following removal of all organic matter with acid or strong oxidants. When living samples of diatom communities are examined, it is impossible to detect all the species present, as rare ones are easily obscured among the other materials present, and taxonomic identification of living diatoms can be uncertain or impossible, even with isolated cells. These features of diatom taxonomy have important consequences for biogeography, which we illustrate and discuss using new observations from two species. Despite being the mainstay for diatom descriptions, species described by light microscopy (LM) alone may conflate two species or (as in the case presented) lead to spurious new species; both need ultrastructural study to ascertain taxonomic and geographical boundaries. The species studied with scanning electron microscopy (SEM) over the last 45 years by Stephens & Gibson, Pennesi et al., and Lobban under the name of Mastogloia hustedtii is shown to be synonymous with M. grunovii. The former became known in the SEM era to bear both pseudoconopea (longitudinal flaps parallel to the sternum, invisible in LM) and silica plaques on the inner margins of the partecta (chambers on the valvocopulae), with the latter supposedly bearing neither, but there is a single, pantropical/Mediterranean species encompassed in the original description of M. grunovii. A new ultrastructural feature for the genus is reported from this species: marginal chambers formed by laminae over the mantle areolae and the first 2–3 areolae on the valve face. The second species studied, M. meisteri, had been reported a few times from one region based on very rare frustules, which do not meet the first criterion for biogeography: where did they live? Although we, too, did not observe living cells, the number of specimens present is evidence for a living population epiphytic on a Virgin Islands coral reef. The ultrastructure of this species is also shown for the first time. Because absence of evidence is overwhelming in microbial biogeography, the best we can say is that this species is potentially a regional endemic. Full article

Based on an analysis of monitoring data from the Liaohe estuary, the distribution of inorganic nitrogen and active phosphate is related to the type of shoreline. The pollutant concentrations in the port area are 16% (inorganic nitrogen) and 59% (active phosphate) higher than those in the control area. The phytoplankton diversity index in the aquaculture area is 20% lower than in the mixed estuary area, which confirms the gradient effect of human disturbance. The constructed dual-mode distance effect model shows that, for a homogeneous shoreline, the goodness of fit is 40.1% in the non-estuary area, but radial basis function correction needs to be introduced for the estuary area. This study suggests that, in the port area, it is necessary to implement a combined policy consisting of ‘total nitrogen and phosphorus control + ecological compensation’, and artificial reefs should be built in the aquaculture area to maintain the number of benthic species. Full article

Citizen science approaches for monitoring, and even restoring, coral reefs have grown in popularity though tend to be restricted to those who have taken courses that expose them to the relevant methodologies. Now that cheap (~10 USD), waterproof pouches for smart phones are widely available, there is the potential for mass acquisition of coral reef images by non-scientists. Furthermore, with the emergence of better machine-learning-based image classification approaches, high-quality data can be extracted from low-resolution images (provided that key benthic organisms, namely corals, other invertebrates, & algae, can be distinguished). To determine whether informally captured images could yield comparable ecological data to point-intercept + photo-quadrat surveys conducted by highly proficient research divers, we trained an artificial intelligence (AI), CoralNet, with images taken before and during a bleaching event in 2015 in Chagos (Indian Ocean). The overall percent coral covers of the formal, “gold standard” method and the informal, “tourist diver” approach of 38.7 and 35.1%, respectively, were within ~10% of one another; coral bleaching percentages of 30.5 and 31.8%, respectively, were statistically comparable. Although the AI was prone to classifying bleached corals as healthy in ~one-third of cases, the fact that these data could be collected by someone with no knowledge of coral reef ecology might justify this approach in areas where divers or snorkelers have access to waterproof cameras and are keen to document coral reef condition. Full article

Coral life cycle dynamics are poorly understood in most reefs, especially at the large geographic scales commensurate with ocean transport, genetic flow, and other synoptic scale processes. We present a spatially explicit, large-scale, and multi-temporal study of coral settlement along a 30 km long reef system in the Southwest portion of Hawaiʻi Island. Here, we focused on interannual variability in coral recruitment from 2021 to 2024, a period without a major marine heatwave. We used stratified random site selection to place 320 coral settlement tiles at 32 sites (10 tiles per site) at 10 ± 3 m water depth annually to monitor recruitment of the three most common coral genera found in the region (Montipora, Pocillopora, Porites). Site-level interannual variability in coral recruitment was high yet the overall geographic distribution of recruits was consistent through time. This occurred despite a decrease in benthic temperature and recruitment rates during the study period. Persistent geographic patterns in coral recruitment strengthen our understanding of mechanisms and conditions that drive reef resilience. They also strongly suggest a need to protect areas of high recruitment while studying drivers of low recruitment in contrasting habitats. This approach will further increase support of coral production in an era of climate- and coastal pollution-driven declines in coral reefs. Full article

Coral reefs are crucial ecosystems for marine biodiversity but are increasingly threatened by anthropogenic pressures and climate anomalies. The 2016 global bleaching event resulted in widespread coral mortality, altering reef structure and benthic communities. Here, we examine the evolution of Maldivian reefs from 2015 to 2023 using long-term monitoring data to assess post-disturbance dynamics. Analyses of 26 benthic descriptors revealed severe impacts from thermal stress, with heterogeneous recovery patterns. Reef-building capacity, which reflects the reef’s accretion potential and is mainly sustained by primary (e.g., Acropora branching corals) and secondary constructors (e.g., Tridacna spp.), rebounded substantially, while binders (e.g., coralline algae) and bafflers (e.g., erect sponges) remained depleted. Among growth forms, fast-growing branching and digitate corals, despite substantial declines, drove rapid recovery. Massive corals were less affected and continued growing, while encrusting corals declined steadily over the period. Post-bleaching community composition shifted markedly toward increased abiotic cover and reduced coral dominance, with partial reversion by 2023. Despite the 2016 collapse in constructional capacity, most reefs exhibited notable recovery within seven years. These findings underscore the moderate yet promising resilience of Maldivian reefs, exceeding previous bleaching events, and emphasize the importance of long-term monitoring to understand ecosystem responses under accelerating climate stress. Full article

Coral reefs are increasingly impacted by marine heatwaves and global warming, with the 2023–2024 El Niño–Southern Oscillation (ENSO) event causing unprecedented thermal stress across the Eastern Tropical Pacific. This study assessed the effects of this event on coral reefs in the Gulf of Papagayo, Costa Rica. Sea surface temperatures exceeded the bleaching threshold for seven months, reaching a record 10.2 Degree Heating Weeks—twice the levels recorded during the 1997–1998 ENSO. Benthic and fish community surveys revealed severe coral mortality, particularly in Pocillopora-dominated reefs, with some sites losing over 90% of live coral cover. Resilience varied across sites, likely influenced by factors such as local water circulation, coral genetic diversity, symbiont type, and heterotrophic capacity. Reefs with higher genetic diversity and thermally tolerant Durusdinium symbionts showed partial recovery. Seasonal upwelling appeared to buffer thermal stress in some areas, potentially acting as a natural climate refuge. Bleaching also impacted reef fish communities, with a notable decline in invertebrate-feeding species on degraded reefs. These findings highlight the interplay between prolonged thermal stress, coral biology, and local oceanographic processes in shaping reef resilience. Identifying and protecting such climate refugia will be critical for coral conservation under future climate change scenarios. Full article

Accurate, scalable mapping of coral reef habitats is essential for monitoring ecosystem health and detecting change over time. In this study, we introduce a novel mathematically based nonlinear spectral unmixing method for benthic habitat classification, which provides sub-pixel estimates of benthic composition, capturing the mixed benthic composition within individual pixels. We compare its performance against two machine learning approaches: semi-supervised K-Means clustering and AdaBoost decision trees. All models were applied to high-resolution PlanetScope satellite imagery and ICESat-2-derived terrain metrics. Models were trained using a ground truth dataset constructed from benthic photoquadrats collected at Heron Reef, Australia, with additional input features including band ratios, standardized band differences, and derived ICESat-2 metrics such as rugosity and slope. While AdaBoost achieved the highest overall accuracy ($93.3\%$) and benefited most from ICESat-2 features, K-Means performed less well ($85.9\%$) and declined when these metrics were included. The spectral unmixing method uniquely captured sub-pixel habitat abundance, offering a more nuanced and ecologically realistic view of reef composition despite lower discrete classification accuracy ($64.8\%$). These findings highlight nonlinear spectral unmixing as a promising approach for fine-scale, transferable coral reef habitat mapping, especially in complex or heterogeneous reef environments. Full article

We adapt previous conceptual and numerical models of ciguateric food chains for the bioaccumulation of Pacific-ciguatoxin-1 (P-CTX-1) to a general model for bioaccumulation of P-CTX3C by parrotfish (Scarus frenatus, S. niger, and S. psittacus) that feed by scraping turf algae, and surgeonfish (Naso unicornis) that mostly feed on macroalgae. We also include the Indian Ocean parrotfish Chlorurus sordidus as a model for an excavator feeding parrotfish and include comparisons with the detritivorous surgeonfish Ctenochaetus striatus that brush-feeds on turf algae. Our food chain model suggests that, of the Gambierdiscus and Fukuyoa species so far analysed for ciguatoxin (CTX) production from the Pacific, only G. polynesiensis produces sufficient P-CTX3C to consistently produce parrotfish or N. unicornis with poisonous flesh. Our model suggests that insufficient CTX would accumulate into the flesh of parrotfish or N. unicornis to become poisonous from ingesting benthic dinoflagellates producing ≤0.03 pg P-CTX3C eq./cell, except from extended feeding times on high-density blooms and in the absence of significant depuration of CTX. Apart from G. polynesiensis, only G. belizeanus and possibly G. silvae and G. australes are thought to produce >0.03 pg P-CTX3C eq./cell in the Pacific. However, with relatively low maximum concentrations of ≤0.1 pg P-CTX3C eq./cell it is likely that their contribution is minimal. Our model also suggests that the differences between the area of turf algae grazed by parrotfish and similar sized C. striatus results in greater accumulation of CTX by this surgeonfish. This makes C. striatus a higher ciguatera risk than similar sized parrotfish, either directly for human consumption or as prey for higher trophic level fishes, consistent with poisoning data from Polynesia. It also suggests the possibility that C. striatus could bioaccumulate sufficient CTX to become mildly poisonous from feeding on lower toxicity Gambierdiscus or Fukuyoa species known to produce ≥0.02 P-CTX3C eq./cell. This indicates the potential for at least two food chain pathways to produce ciguateric herbivorous fishes, depending on the CTX concentrations produced by resident Gambierdiscus or Fukuyoa on a reef and the grazing capacity of herbivorous fish. However, only G. polynesiensis appears to produce sufficient P-CTX3C to consistently accumulate in food chains to produce higher trophic level fishes that cause ciguatera in the Pacific. We incorporate CTX depuration into our model to explore scenarios where mildly poisonous parrotfish or N. unicornis ingest CTX at a rate that is balanced by depuration to estimate the Gambierdiscus/Fukuyoa densities and CTX concentrations required for these fish to remain poisonous on a reef. Full article

Habitat complexity plays a critical role in coral reef ecosystems by enhancing habitat availability, increasing ecological resilience, and offering coastal protection. Structure-from-motion (SfM) photogrammetry has become a standard approach for quantifying habitat complexity in reef monitoring programs. However, a major bottleneck remains in the two-dimensional (2D) classification of benthic cover in three-dimensional (3D) models, where experts are required to manually annotate individual colonies and identify coral species or taxonomic groups. With recent advances in deep learning and computer vision, automated classification of benthic habitats is possible. While some semi-automated tools exist, they are often limited in scope or do not provide semantic segmentation. In this investigation, we trained a convolutional neural network with the ResNet101 architecture on three years (2015, 2017, and 2019) of human-annotated 2D orthomosaics from Kiritimati, Kiribati. Our model accuracy ranged from 71% to 95%, with an overall accuracy of 84% and a mean intersection of union of 0.82, despite highly imbalanced training data, and it demonstrated successful generalizability when applied to new, untrained 2023 plots. Successful automation depends on training data that captures local ecological variation. As coral monitoring efforts move toward standardized workflows, locally developed models will be key to achieving fully automated, high-resolution classification of benthic communities across diverse reef environments. Full article

Macroalgal–coral interactions (MCI) are an integral yet understudied component of coral reef ecology, particularly in healthy systems where they may represent stable coexistence rather than competition. This study provides the first comprehensive assessment of MCI diversity, abundance, and spatial patterns in the South West Lagoon of New Caledonia (SWLNC). Across 26 coral-dominated habitats, MCI accounted for an average of 16.4% of the benthic cover, with local values reaching 70% in high-interaction areas. A total of 43 unique macroalgal–coral genus pairings were documented, involving 16 macroalgal and 10 coral genera. Lobophora (47%), Halimeda (20%), and Hypnea (9%) were the dominant macroalgae, while Acropora (61%), Montipora (19%), Seriatopora (13%), and Porites (5%) were the most frequent coral interactants. The most abundant specific interactions were Lobophora–Acropora (29%), Hypnea–Acropora (15%), Halimeda–Montipora (10%), Lobophora–Seriatopora (10%), and Halimeda–Acropora (10%). MCI abundance varied markedly among habitat levels, differing across reef types, zonation, and benthic cover. Six recurrent typologies of physical association were identified, and the Coralgal Biotic Interaction Compass (CBIC) is introduced as a conceptual framework to distinguish the nature of macroalgal-coral associations. Overall, the study demonstrates that MCI in the SWLNC are diverse, structured, and non-random, shaped by both interactant identity and habitat filtering rather than ubiquity, providing a robust ecological baseline for future analyses of macroalgal-coral dynamics in Indo-Pacific reef systems. Full article

Coral reef ecosystems are biodiversity hotspots that provide essential ecological and environmental services but are increasingly threatened by anthropogenic pressure and climate change. Effective conservation of reef systems within Marine Protected Areas (MPAs) can be enhanced using spatially explicit approaches that integrate habitat mapping and ecological metrics at seascape scales. In this study, we characterized the benthic seascape of Cayo Arenas and identified optimal priority conservation zones in one of the core zones of the recently established Southern Gulf of Mexico Reefs National Park (SGMRNP). In July 2023, ground-truthing was performed to quantify the cover of sand, calcareous matrix, macroalgae, hard corals and octocorals. Cluster analysis of quantitative data and ecological similarity between classes was used to identify the main benthic habitat classes. Object-based and supervised classification algorithms on a PlanetScope image were used to construct a thematic map of the benthic reef system. Based on the thematic map, habitat connectivity, β-diversity, patch compactness, and availability for commercial species were estimated. In addition, a benthic change analysis (2017–2013), based on the spectral characteristics of PlanetScope images, was performed. The layers obtained were then used to perform an iterative weighted overlay analysis (WOA) using 126 combinations. Six main habitat classes, with different coverages of hard corals, calcareous matrix, macroalgae, and sand, were identified. Habitats with calcareous matrix and sandy substrates dominated the seascape. High habitat compactness, connectivity, and β-diversity values were observed, suggesting habitat stability and ecologically dynamic areas. Based on the WOA, eight optimal priority areas for conservation were recognized. These areas are characterized by heterogeneous habitats, moderate coral cover, and high connectivity. We provide a spatially explicit approach that can strengthen conservation planning within the SGMRNP and other MPAs, particularly by assisting zonation and sub-zonation processes. Full article

This study develops a geomorphological identification methodology for wall reefs in the microcontinental environment of Wangiwangi Island, Indonesia, using medium-resolution Landsat 8 satellite imagery and morphological analysis based on Maxwell’s geomorphological framework. The uniqueness of the wall reef landform lies in the fact that the lagoon elongates on limestone, resulting in a habitat and ecosystem that develops differently from those of other shelf reefs, namely, platform reefs and plug reefs. Using Optimum Index Factor (OIF) optimization and RGB image composites, four reef types were successfully identified: cuspate reefs, open ring reefs, closed ring reefs, and resorbed reefs. A field check was conducted at fifteen observation sites, which included measurements of depth, turbidity, and water quality parameters, as well as an in situ benthic habitat inventory. The analysis results showed a strong correlation between image composites, geomorphological reef classes, and ecological conditions, confirming the successful adaptation of Maxwell’s classification to the Indonesian reef system. This hybrid integrated approach successfully maps the distribution of reefs on a complex continental shelf, providing an essential database for shallow-water spatial planning, ecosystem-based conservation, and sustainable management in the Coral Triangle region. Policy recommendations include zoning schemes for protected areas based on reef landform morphology, strengthening integrative monitoring systems, and utilizing high-resolution imagery and machine learning algorithms in further research. Full article

Numerous studies have been conducted on the benthic stages of Medusozoa in Reunion Island, but none on the pelagic stages. This study is the first to investigate the shallow waters of the island for the diversity, abundance, and spatio-temporal distribution of jellyfish. During a one-year survey, samples were collected with a plankton net weekly or biweekly at four sites (two reef/two non-reef) and two depths (10/50 m). Of the 267 samples, 3450 medusae were sorted and 56 species identified. The meroplanktonic Hydroidolina (Antho- and Leptomedusae) were the most diverse (38 species), while the holoplanktonic Trachylinae (13 species) were the most abundant. Hydromedusa species richness was higher at coastal stations than offshore, but similar between reef and non-reef sites. There was no significant variation in species richness or abundance between months or seasons. Including some other catches, the total number of species reached 62. Eight species are new records for the Indian Ocean (all Anthomedusae). Indian Ocean literature references are given in the species list, and some photographs are provided. This initial study, which greatly expands the local hydrozoan fauna knowledge, will serve as a reference for future research, especially regarding climate change and coastal management in Reunion Island. Full article

This study investigates the taxon composition, seasonal variations, and diversity dynamics of macroinvertebrate communities associated with Mytilus galloprovincialis cultivated in mussel longline systems in the central Black Sea. Monthly sampling conducted between September 2023 and August 2024 yielded a total of 99,719 individuals representing 20 taxa. The communities were predominantly dominated by amphipods, particularly Jassa marmorata (71%) and Stenothoe monoculoides (28%). Individual abundance peaked in autumn, whereas taxon richness reached its highest levels in summer. ANOVA results revealed significant seasonal differences in diversity indices (p < 0.05). Multivariate analyses, including NMDS and RDA (PCA proxy), indicated distinct seasonal clustering, with pH (41%) and salinity (35 g/kg) identified as the primary environmental drivers of community composition. These findings demonstrate that offshore mussel longline systems function not only as aquaculture infrastructure but also as reef-like artificial habitats that support benthic diversity. The dominance of opportunistic and detritivorous amphipods, along with their sensitivity to environmental gradients, suggests their potential utility as bioindicators for ecological monitoring. Full article

Mediterranean rocky reef habitats are ecologically valuable yet increasingly degraded due to cumulative human pressures, necessitating efficient, large-scale ecological status assessments to inform management. Macroalgal communities are widely used as indicators of rocky reef conditions and are typically assessed via photoquadrat sampling. However, the manual annotation of benthic images remains time-consuming and costly. This study evaluates the performance of CoralNet (version 1.0), an AI-assisted image annotation platform, using a pre-annotated dataset of 2537 photoquadrat images from 89 rocky reef sites in the Aegean Sea, Greece, classified into 23 taxonomic and morphofunctional groups. Half of the dataset was used to iteratively train CoralNet classifiers, while the remainder was used to compute the reef-EBQI index and compare ecological status estimates with those derived from manual annotations. The classifier accuracy improved with training volume, reaching 67% using the entire dataset. Reef-EBQI scores derived from CoralNet showed 87% agreement with the manual classifications. Despite challenges and limitations, AI-assisted annotation proved effective in regional-scale ecological assessments based on broad taxonomic and morphofunctional categories. Automated tools like CoralNet can reduce post-processing bottlenecks and enable scalable, cost-effective monitoring, especially when integrated with standardized protocols and citizen science initiatives. Full article