Frontiers in Marine Science

Rapid detection methods and field applications for two types of red tide algae in Fujian coastal areas

2026-04-02

Zhang Kang, Haoyuan Zhang, Shanxiu Duan, Changgong Zhang, Pengze Zhong, Guangming Ding, Yiwen Huang, Kefu Zhou

Red tides in Fujian’s coastal waters—dominated by Prorocentrum donghaiense and Skeletonema costatum—are increasing in frequency and impact, yet prevailing detection methods (microscopy, molecular assays) are labor-intensive, time-consuming, and instrument-dependent, limiting rapid field deployment. We generated species-specific monoclonal antibodies against P. donghaiense and S. costatum and established a colloidal gold immunochromatographic (GIC) test strip workflow for on-site detection. The assay provides semi-quantitative readouts (10–15 minutes) without complex instrumentation, using standardized visual interpretation (control-line validity; test-line positivity) and image analysis for optional T/C-based trend estimation. Field applicability was evaluated at fixed sites in Yundang Lake, with strip results compared against routine microscopic enumeration to assess sensitivity, specificity, and agreement. The GIC strips enabled rapid, on-site identification of the target species within 10–15 minutes and showed strong discrimination against non-target algae under standardized conditions. Operational detection limits were suitable for near-threshold early warning, and test-line intensities reflected spatial differences in algal abundance across sites. Field results closely matched microscopy, supporting reliable tracking of site-level density trends and confirming practical performance in a real-world lagoon environment.This GIC-based approach addresses a key monitoring gap by coupling speed, simplicity, and field portability with species-level specificity, enabling near-real-time decision support for harmful algal bloom management. The method reduces reliance on specialized personnel/equipment and can be integrated into routine surveillance as a rapid screening tool; future work can extend species coverage (panelization), strengthen early-detection capability (e.g., preconcentration, reader-based quantification), and validate robustness across broader aquatic matrices.

Correction: Allocation and adaptation in China’s blue carbon policy: a quantitative textual analysis based on a “theme-instrument-stage” framework

2026-04-01

Lili Li, Xiaochen Zhang

Spatio-temporal variations of heavy metal(loid)s and their influencing factors in surface sediments of Daya Bay, South China Sea

2026-04-01

Zeming Wang, Nan Zheng, Man Hao, Yahui Xu, Jinmei Li

To elucidate the spatiotemporal dynamics and driving mechanisms of heavy metal (loid)s (HMs) in coastal systems, this study investigated the surface sediments from Daya Bay across four seasons. Results indicated that the average HM concentrations (mg/kg) decreased in the order of Zn (65.35) > Pb (28.66) > Cu (13.19) > As (7.06) > Hg (0.073) > Cd (0.058), with Pb, As and Hg exhibiting significant seasonal heterogeneity (p spring (2.49) > autumn (2.39) > summer (2.27). Crucially, Redundancy Analysis revealed that the distribution of Cu, Zn, Cd, and Pb was primarily governed by natural physicochemical binding to fine-grained, organic-rich matrices. In contrast, the accumulation of Hg and As exhibited a stronger dependency on dynamic biogeochemical factors, notably dissolved oxygen and anthropogenic nutrient inputs. These findings highlight the necessity of distinct management strategies that account for the coupling between sediment matrices and water column biogeochemistry.

Phylogenetically distinct Vibrio mediterranei lineages confer robust protection under thermal stress against oyster pathogens

2026-04-01

Steph Smith, Ami Wilbur, Jaypee S. Samson, Yesmarie De La Flor, Marta Gomez-Chiarri, Blake Ushijima, Rachel T. Noble

IntroductionMarine bivalve mortality events cause substantial economic losses in aquaculture and threaten global food security. While pathogenic Vibrio species are frequently implicated, growing evidence suggests that loss of beneficial microbes can increase host susceptibility to disease. We previously observed that Vibrio mediterranei was consistently isolated from healthy oysters but systematically disappeared prior to mortality events, coinciding with proliferation of pathogenic Vibrio species. Here, we test whether this pattern reflects a protective functional role.MethodsScreening eleven V. mediterranei strains against eastern oyster (Crassostrea virginica) larvae revealed three distinct virulence phenotypes – avirulent, pathogenic, and intermediate – that correspond to monophyletic phylogenetic clades.ResultsPre-colonization with the avirulent strain Vm02 increased larval survival from 10–19% (pathogen-only controls) to 94–97% when challenged with V. harveyi or V. coralliilyticus, representing near-complete protection maintained at both ambient (28 °C) and thermal stress (32 °C) temperatures. Protection was rapid, effective even under simultaneous co-inoculation with the pathogen, and durable through >96 hours post-exposure. Fluorescence microscopy confirmed persistent association of fluorescently tagged Vm02 with larval digestive tissues. Phylogenomic analysis of 33 V. mediterranei genomes placed the three phenotypic groups within well-supported clades separated by 97.1–97.8% average nucleotide identity, approaching species-level thresholds. Pangenome analysis revealed that protective-clade strains harbor 230 unique orthogroups encoding regulatory systems, stress tolerance, metabolic versatility, and a conserved bacteriocin biosynthetic operon. These same strains do not encode the Type I secretion system, Type VI secretion system variants, and TCP pathogenicity island found in pathogenic lineages.DiscussionTogether, these findings demonstrate that beneficial and pathogenic phenotypes are phylogenetically constrained within distinct V. mediterranei lineages, providing a framework for probiotic development and disease forecasting in shellfish aquaculture.

Blubber under stress: ex vivo cortisol exposure induces an anti-inflammatory state in precision-cut adipose tissue slices from humpback whales

2026-04-01

Veslemøy Mantor, Derrick Kwame Odei, Audun Håvard Rikardsen, Jasmine Nahrgang, Aurélien Warnant, Cathy Debier, Kimberley Ann Bennett, Pierre Blévin, Laura Pirard

Cetaceans are exposed to multiple anthropogenic stressors that may disrupt hormonal balance, notably through elevated release of circulating stress hormones, such as catecholamines and glucocorticoids. While stress response mechanisms are vital in the short term, prolonged stress can have serious health implications including impaired immunity. Yet, cause-effect relationships and mechanistic understanding about the impacts of elevated stress hormones on large cetacean health remain poorly understood due to the ethical and logistical challenges of studying free-ranging whales. To address this knowledge gap, the present study established an ex vivo precision-cut adipose tissue slice (PCATS) model from blubber biopsies collected from 13 humpback whales (Megaptera novaeangliae) in Norway. Metabolic viability of PCATS was assessed and confirmed by measuring ΔO2 saturation in the culture medium, as a proxy for mitochondrial respiration. PCATS of humpback whales were further used to investigate the effects of stress hormone exposure on the relative mRNA levels of a set of 5 stress and immunoregulatory genes: heat-shock protein 70 (HSP70), toll-like receptor 4 (TLR4), peroxisome proliferator activated receptor gamma (PPARG), interleukin 10 (IL10) and tumor necrosis factor alpha (TNF). PCATS were incubated for 48 hours with 400 nM cortisol introduced every 12 hours to mimic a chronic stress response alone and combined with 10 µM epinephrine in the final 12 hours to simulate an acute stress response. Relative gene expression assessed through RT-qPCR, revealed that both cortisol alone and combined with epinephrine significantly upregulated PPARG and downregulated TNF and TLR4 expression, suggesting that cortisol induces an anti-inflammatory state. The present findings call for in-depth transcriptomic analyses to identify which biological pathways may be compromised by stress hormones in cetaceans. Our study also opens new research avenues for using PCATS as an ex vivo model to investigate the effects of multiple stressors on free-living cetaceans.

A robust UV–Vis spectral method for seawater COD detection based on principal component turbidity correction and ensemble variable selection

2026-03-31

Yingying Zhang, Shiwei Hou, Da Yuan, Xiandong Feng, Yilin Wang

Reliable assessment of chemical oxygen demand (COD) in coastal seawater is essential for monitoring organic pollution and protecting marine ecosystems. However, turbidity-induced spectral interference and high-dimensional redundancy in UV–Vis spectra hinder the accuracy of conventional modeling methods. This study presents an integrated approach that combines a novel Principal Component Disturbance Feedback Turbidity Compensation (PC-FDTC Hybrid) with a Stacking-based Variable Selection (SBVS) strategy to enhance COD prediction. The PC-FDTC Hybrid introduces the first principal component as a feedback correction term to improve spectral baseline stability in the 200–400 nm range. Meanwhile, the SBVS strategy integrates CARS, MC-UVE, and Random Frog algorithms via meta-learning to identify robust and informative wavelengths. A total of 646 seawater samples from Jiaozhou Bay, China, were analyzed using a self-developed UV–Vis multi-parameter sensor system. Experimental results show that the proposed SBVS-PLSR model, combined with Savitzky–Golay smoothing and PC-FDTC compensation, achieved superior prediction accuracy (R² = 0.993, RMSEP = 0.340), significantly outperforming traditional full-spectrum and single-method models. Overall, the proposed methodology enhances model robustness, reduces spectral complexity by over 96%, and provides a compact, accurate, and field-deployable solution for real-time COD monitoring in turbid marine environments.

Challenges and recommendations for marine waste management in European fishing ports

2026-03-31

Cristina Pita, Gillian B. Ainsworth, Marina Astudillo-Pascual, Priscila M. Silva, Angel Gutierrez, Sebastian Villasante

The fishing sector plays a crucial role in the effective management of marine litter, emphasising the importance of facilitating waste collection for fishers and ensuring its subsequent management in port reception facilities (PRFs). EU Directive 2019/883/EU provides a unified sector-specific legal framework for managing ship-generated waste within EU ports, but harmonising PRFs and waste management remains challenging across Member States. Key areas for improving waste management include streamlining the regulatory framework (policies and processes), enhancing economic viability, fostering partnerships, promoting knowledge sharing, improving infrastructure, and increasing stakeholder awareness. The measures taken should consider the context, including port characteristics and the country in which it operates.

Binary reformulation for marine debris detection in Sentinel-2 imagery: an empirical study on extreme class imbalance using the first benchmarks on combined MARIDA and MADOS datasets

2026-03-31

Soufyane Bouchelaghem, Lahcene Mamen, Marco Balsi, Ahmed Tibermacine, Monica Moroni, Imad Eddine Tibermacine

IntroductionMarine debris detection from satellite imagery is challenged by two major factors: extreme class imbalance, with debris pixels accounting for less than 0.01% of image content, and the need for robust generalization across diverse geographic and temporal domains for operational deployment. Although existing methods often report strong within-dataset performance, cross-dataset generalization, where models trained on one dataset are applied to entirely different geographic regions, remains insufficiently investigated.MethodsTo address this limitation, we conducted rigorous bidirectional cross-dataset validation experiments using the MARIDA and MADOS datasets. The problem was reformulated as a binary segmentation task and addressed using a standard U-Net architecture combined with a composite imbalance-aware loss and a rarity-aware sampling strategy. Two experimental settings were considered: training on MARIDA and testing on MADOS, and training on MADOS and testing on MARIDA.ResultsThe experiments revealed asymmetric cross-dataset generalization. Models trained on the geographically diverse MADOS dataset achieved an F1-score of 0.890 when tested on MARIDA, corresponding to only a 1.25% decrease from the within-dataset baseline of 0.901. In contrast, models trained on MARIDA achieved an F1-score of 0.833 on MADOS, representing a 7.55% decrease. The average cross-dataset degradation was 4.38%, which is substantially lower than the typical 10--25% performance drops reported in remote sensing domain-shift scenarios. Despite comparable patch counts (2,529 for MADOS versus 2,173 for MARIDA), the superior transferability of MADOS-trained models indicates that geographic diversity across globally distributed tiles is more beneficial than exhaustive annotation within concentrated regions. Moreover, the MADOS-to-MARIDA cross-dataset F1-score of 0.890 exceeded MAP-Mapper's within-dataset F1-score of 0.880 and closely approached MariNeXt's reported performance of 0.891.DiscussionThese findings show that careful data formulation and training design can enable standard architectures to achieve strong cross-domain performance under extreme class imbalance, approaching or even surpassing more specialized models in realistic deployment conditions. The results provide practical guidance for operational marine debris monitoring systems: spatially stratified sampling across diverse marine environments should be prioritized, F1-scores in the range of 0.86--0.89 can be expected when deploying on previously unseen regions without fine-tuning, and a two-stage strategy should be considered in which models are first trained on geographically diverse data and then optionally adapted for region-specific applications. To the best of our knowledge, this is the first systematic cross-dataset validation study involving both MARIDA and MADOS, demonstrating that binary reformulation supports generalization-preserving marine debris detection across geographic and temporal domain shifts.

Adaptive energy-efficient and secure clustering-based routing architecture for underwater wireless sensor networks in marine environmental and ecosystem monitoring

2026-03-31

Jyoti Sharma, Salil Bharany, Abdulrahman Mohammed Alamoudi, Heba G. Mohamed, Abdul Khader Jilani Saudagar, Ateeq Ur Rehman

IntroductionReliable long-term monitoring of coral reefs and other marine ecosystems is limited by the harsh underwater environment, restricted battery capacity of sensor nodes, and the high energy cost of acoustic communication. Underwater Wireless Sensor Networks (UWSNs) have emerged as a promising solution for marine environmental monitoring; however, challenges related to energy efficiency, secure communication, and reliable data collection remain significant.MethodsThis study proposes an integrated architecture for UWSNs that enhances energy efficiency, security, and data reliability. The framework combines a hybrid Adaptive Swarm Fitness Optimization–Golden Eagle Optimizer with K-Medoids clustering (ASFO–GEO–KM) for optimal cluster head selection, a Tiny Security (TinySec)-enabled Energy-aware Coral-Environmental Reliable Path (E-CERP) routing protocol, and Autonomous Underwater Vehicle (AUV)-assisted data collection. The ASFO–GEO–KM algorithm selects cluster heads based on residual energy, underwater link quality, and node density to improve load balancing and cluster stability. TinySec-enabled E-CERP provides authenticated, energy-aware multi-hop routing while accounting for underwater path loss and propagation delay. AUVs periodically collect aggregated data from cluster heads to reduce long-range acoustic transmissions and conserve node energy.ResultsSimulation results conducted in a realistic 3D marine environment demonstrate that the proposed framework outperforms existing approaches, including DEDG, AP, ALP, HECRA, GSA, and CTRGWO-CRP. The proposed system achieves a longer network lifetime, a higher packet delivery ratio, and significantly reduced routing overhead.DiscussionBy enabling secure, energy-efficient, and reliable underwater sensing, the proposed architecture supports long-term coral reef monitoring and marine ecosystem observation. It facilitates early detection of environmental stressors, such as thermal anomalies and turbidity spikes, thereby improving marine ecosystem protection and supporting conservation-oriented decision-making.

Ocean literacy knowledge in informal education: a systematic literature review

2026-03-30

Lisa S.Y. Coe, Hada M. Herring, Bryndan P. Durham, Julie C. Brown

The health of the ocean is essential to human wellbeing, but increasing and compounding anthropogenic pressures are putting the ocean at risk. Recognizing the critical need for an ocean-literate society prepared to tackle changing complexities of ocean function, the Ocean Literacy Guide, comprised of seven Essential Principles and forty-five Fundamental Concepts, was developed as a resource for formal, K-12 educators to integrate key principles of ocean science into their curricula; however, informal learning experiences that take place outside of the structured classroom are equally important mechanisms to target ocean education. How informal initiatives connect to ocean literacy remains largely unknown. In response, we conducted a systematic literature review to characterize informal ocean science education efforts worldwide and examined how these efforts align with the principles and concepts defined within the Ocean Literacy Guide. Applying search, screening, and extraction processes guided by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) principles, we selected thirty-two empirical studies as data for this review. Results indicate that though informal programs are making connections between their educational efforts and the Ocean Literacy Guide, principles and concepts are unevenly represented in this space, with a particular bias towards the biodiversity of ocean life (Concept 5C) and the role of humans hurting (Concept 6E) or helping (Concept 6G) the ocean. While recognizing limitations of our study design with respect to our coding methodology, we also recommend changes to the Ocean Literacy Guide that are based on trends observed in informal ocean education. Specifically, we recommend the development of an eighth principle in order to capture the multi-faceted consequences of climate change on the ocean and the human contribution to such effects. The results of this study provide an initial framework to support informal educators as essential partners in reforming and reframing ocean education through effective ocean science learning experiences.