Accurate benthic habitat mapping is essential for coastal ecosystem monitoring, biodiversity conservation, and marine spatial planning. Single-beam echosounders (SBES) are an affordable tool for acoustic habitat mapping, however prior studies have only used acoustic information from the first and second bottom echoes, while the potential contribution of higher-order echoes largely unexplored. The present study examined the effect of the inclusion of multi-echo acoustic parameters including the third-bottom echo information on benthic habitat classification from shallow waters, Kapota Atoll, Indonesia. Acoustic data were collected with an SBES Simrad EK15 and analyzed with Sonar5-Pro to get eight acoustic parameters (depth, BD, BP, E0, E1, AttDecSv1, E2, and E3) from sequential bottom echoes. We analyzed these parameters using a Random Forest classifier to identify three primary benthic habitat groups (coral, seagrass, and sand) and tested the classification performance using an independent validation dataset. The combination of multi-echo acoustic parameters enhanced significantly the habitat classification over traditional methods. The maximum overall accuracy (79.3%) was achieved when all eight acoustic parameters were used, which is better than the traditional two-parameter model based just on seabed roughness (E1) and hardness (E2) (63.3%). Variable importance analysis indicated E2, water depth and E1 as the most influential predictors, and information on third-bottom echo (E3) offered additional acoustic information that further improved classification accuracy when integrated with other variables. These findings demonstrate that exploiting multi-echo acoustic information improves the reliability of SBES-based benthic habitat mapping, providing a practical approach for benthic habitat mapping in shallow tropical coastal environments.
Mangroves, which are important to coastal ecosystems, are undergoing significant degradation driven by intensifying anthropogenic pressures. Our study was conducted across three mangrove areas in Lhokseumawe, encompassing five stations, to characterize spatial variability in epiphytic diatom abundance and community structure in relation to human activities. Epiphytic diatoms were collected by scraping sampling plots in mangrove stands, and environmental parameters were measured both in situ and in the laboratory. ANOVA was used to compare diversity indices and water quality among stations; SIMPER identified the key species contributing to diversity; and PCA evaluated correlations between environmental factors and diatom communities. The study identified 16 distinct genera of epiphytic diatoms from mangrove habitats, with Fragilaria sp. (22.77%), Pinnularia sp. (18.76%), and Melosira sp. (12.94%) among the most abundant taxa. Fragilaria sp. exhibited the highest abundance (695 cells/L) and an Important Value Index (IVI) of 28.13%, indicating its capacity to numerically dominate the assemblage under the prevailing physicochemical conditions of the strait. Niche breadth analysis revealed that Diploneis sp., Navicula sp., and Pinnularia sp. were the most adaptable species, with Shannon diversity indices ranging from 1.63 to 1.92 and Margalef taxonomic richness from 1.47 to 2.72. SIMPER analysis showed that Fragilaria sp. and Pinnularia sp. were the primary drivers of spatial community heterogeneity, contributing 24.26% (16.31% dissimilarity) and 18.65% (12.54% dissimilarity), respectively, to the overall dissimilarity among sections. PCA identified five principal components that explained 77.12% of the cumulative variance; PC1 (24.79%) was primarily driven by gradients in pH and phosphate; PC2 (19.88%) reflected salinity and turbidity; and PC3 (12.92%) was dominated by ammonia and conductivity. These findings demonstrate a strong structural interaction between local-specific environmental factors and diatom distribution, highlighting the value of epiphytic assemblages as reliable bioindicators of distinct anthropogenic land-use pressures.
This study presents the first coast-wide, integrated spatial characterisation of hard-substrate epibenthic biodiversity in shallow waters, based on a systematic sampling of 28 stations spanning 14 administrative regions from the western to the eastern extremity of the coast. The inventory records 276 faunal taxa (6,712 individuals) and 53 floristic taxa, dominated by Mollusca, Arthropoda and Annelida, and structured by macrophytes and meadows of Posidonia oceanica (Linnaeus) Delile, 1813. The mean species richness (34.4±9.0 species per station) places this coast in the upper range of the best-preserved sectors of the basin. The ecological status, assessed through a panel of complementary indicators (alpha diversity, faunal AMBI and phytobenthic EEI-c), reveals a coast in generally good condition, with all stations falling within the “undisturbed” to “slightly disturbed” categories. A significant longitudinal signal, carried by the functional indices (AMBI and EEI-c increasing from west to east) and not by the classical structural descriptors is consistent with a west-east ecological gradient that should be interpreted with caution, since the west-to-east sampling schedule (spring in the west, summer in the east) confounds season with geographical position. Superimposed on this regional structuring is a mosaic-like spatial organisation, in which substrate type and local habitat conditions prevail over geographical position. By virtue of its position at the interface between Atlantic and Mediterranean influences, the Algerian coast may constitute a useful observatory for tracking future biogeographical change, a perspective that remains to be tested with temporally synchronised surveys. This biodiversity inventory will contribute to the national Algerian database of marine biodiversity BANBIOM.
Seabed substrate mapping is essential for ecosystem-based management, fisheries regulation, and marine spatial planning. Yet, high-resolution characterization of the seafloor remains spatially limited because oceanographic surveys are costly and logistically demanding. Here, we present a low-cost and reproducible framework for integrating heterogeneous data sources, including fishing captains’ operational records, nautical charts, satellite imagery, sediment samples, multibeam acoustic data and underwater video observations, within a GIS environment. The approach was applied to the northern San Jorge Gulf in Patagonia, Argentina, a highly productive marine region subjected to intensive trawling yet lacking spatially explicit seabed information. Categorical substrate observations were converted into quantitative sediment descriptors and spatially interpolated to generate continuous seabed maps, which were subsequently refined using empirical fisheries information and validated with scientific datasets. Validation showed high agreement between rocky and sedimentary bottoms (95% agreement; κ = 0.47) and moderate agreement for the more detailed sedimentary classes (70% agreement; κ = 0.48). When scientific validation data were incorporated in the interpolation, close to 17% of the mapped pixels were modified, although large-scale geomorphological patterns remained stable. The resulting cartography represents the first integrative seabed substrate maps for the northern San Jorge Gulf and shows that operational fisheries information can substantially improve seabed characterization in data-limited marine regions, providing relevant baseline spatial information for fisheries management, marine spatial planning, and conservation in coastal systems.
Box jellyfishes (Class Cubozoa) have significant ecological and socioeconomic importance, as their potent venom can cause severe, and sometimes fatal, envenomation, affecting coastal fisheries and tourism worldwide. Cubozoa is a relatively small class comprising 51 described species from seven families. Box jellyfishes are predominantly found in tropical and subtropical waters, causing human fatalities and medical emergencies worldwide. This study reviews the diversity and distribution of box jellyfishes in the Northern Indian Ocean through a comprehensive assessment of published literature, taxonomic records, and distributional data. A total of 15 taxa (13 were identified upto species level and two upto genus level) were found from the records from Northern Indian Ocean.Among these 15 taxa, 10 taxa were observedwithin the Indian Exclusive Economic Zone (EEZ), while the eight taxa occur in adjacent waters in the northern Indian Ocean and the species distribution is not exclusive to the particular regions.Given the ecological and public health implications of cubozoan blooms, sustained long-term monitoring and effective management strategies are essential for assessing their distribution, understanding their seasonal and spatial dynamics, predicting bloom events, and mitigating associated risks in coastal areas. The integration of ecological monitoring, environmental data, and early-warning systems will improve preparedness and support evidencebased decisionmaking, thereby reducing the impacts of box jellyfish on public health, fisheries, tourism, and other coastal activities.
Continental shelf regions are characterized by strong physical and biogeochemical variability driven by both natural and anthropogenic forcing. In the northern East China Sea (nECS), seasonal changes in the relative influences of Changjiang Diluted Water (CDW) and Tsushima Surface Water (TSW) are associated with contrasting hydrographic conditions, yet surface nitrous oxide (N2O) and methane (CH4) dynamics remain poorly constrained. Here, we present seasonal observations of surface N2O and CH4 concentrations and air–sea fluxes based on four surveys conducted in May, August, and November 2022, and February 2023. Stations were classified into CDW– and TSW–influenced groups based on water–mass characteristics reported in previous studies. The CDW region generally showed higher nutrient availability and higher surface N2O and CH4 concentrations than the TSW region. Mean air–sea fluxes of both gases across the four seasonal surveys were higher in the CDW region than in the TSW region. First–order annual emission estimates for the sampled domain, based on four seasonal surveys, were 2.8×10-4 Tg yr-1 for N2O and 2.0×10-4 Tg yr-1 for CH4. Although limited to surface observations within a spatially restricted area, this study provides a regional baseline for understanding associations between seasonal hydrographic contrasts and the surface distributions of N2O and CH4 and their air–sea exchange in the nECS.
Diversity in fish migration across space and time can buffer populations against environmental variability and promote long-term resilience. Considerable effort has been focused on understanding anadromous mixed-stock populations of striped bass on the east coast of the United States; yet a key knowledge gap remains in identifying which spawning populations contribute to northern habitats during seasonal migrations. Here, we used acoustic telemetry and network analyses to investigate the migratory behavior of striped bass utilizing northern habitats. We compared fine-scale movements and broad coastal migrations of striped bass populations present within Southern Maine, USA. Our specific goals were to identify spawning populations present in Southern Maine, characterize estuarine habitat use, and compare migratory patterns among populations. Results revealed a mixed-stock assemblage in the Saco River Estuary composed primarily of Hudson River, New York, USA (42.3 - 59.6%) and Delaware Bay, Delaware and New Jersey, USA (5.7 - 32.6%) origin fish, with fewer fish from the Chesapeake Bay population, Maryland, USA (1.9 - 3.8%), and 3.8% of individuals whose spawning population origin could not be confidently estimated. Fine-scale habitat use varied among individuals and size classes and shifted seasonally, with fish exhibiting both long- and short-term residency. Despite overlapping seasonal residency within the estuary, network analyses indicated that Hudson River and Delaware Bay striped bass largely maintained distinct migratory pathways (8-20% network similarity) and habitat connections, converging within shared northern foraging habitats. These findings demonstrate that Maine provides important seasonal habitat for multiple Atlantic coast spawning populations and highlight population-specific differences in movement, habitat connectivity, and site fidelity.
Arid coastal wetlands frequently host hypersaline groundwater lenses, yet the hydrological dynamics governing these systems remain poorly studied. We investigated coastal groundwater-tidal interactions in a mangrove/sabkha aquifer in Exmouth Gulf, Western Australia, using three years (2022–2025) of high-frequency groundwater level, temperature, and salinity observations from a 415 m inland transect, combined with geochemical, isotopic, and ecohydrological measurements. Sediment analyses and slug tests revealed extremely low hydraulic conductivity (<10-9 m/s), indicating a semi-confined aquifer with limited vertical mixing. Spectral analysis showed rapid attenuation of the semidiurnal M2 tidal constituent inland, with an exponential damping length of ∼487 m and effective hydraulic diffusivity of ∼16.7 m2/s, demonstrating that tidal forcing propagates primarily through pressure diffusion rather than direct tidal pumping. Groundwater remained persistently hypersaline (40-90 ppt) and exhibited negligible response to tides or rainfall. Geochemical facies (NaCl dominated) and stable isotopes define an evaporation trend from seawater (δ18O/δ2H slope = 4.37), confirming that the hypersaline lens derives from progressive evaporative concentration of marine inputs. Logistic modelling suggests local, episodic outcropping of hypersaline groundwater (>70 ppt) at the sabkha surface when coastal water levels exceed ∼0.15 m above local ground level, indicating pressure-driven ground wetting rather than direct tidal inundation. Sap flow measurements in Avicennia marina showed reduced sap flux during periods of shallow hypersaline groundwater and elevated surface salinity. Arid sabkha aquifers behave as hydrologically isolated, evaporation-dominated systems that constrain groundwater exchange and impose strong ecohydrological controls on mangrove persistence and potential inland migration under sea-level rise.
Comau Fjord, located in northern Chilean Patagonia, is recognized as one of the most biodiverse fjord ecosystems in southern South America. Its complex geomorphology, environmental gradients, and stratified water column support diverse marine habitats and communities. Despite its ecological importance, knowledge of deep marine assemblages remains limited compared with shallow environments. This study aimed to characterize deep fish and benthic invertebrate assemblages associated with mesophotic and deep environments (50–200 m depth) throughout Comau Fjord, including Cahuelmó Fjord and Lilihuapi Island, and to evaluate their spatial and seasonal variability. Surveys were conducted at 12 stations using a remotely operated vehicle (ROV) during winter 2024 and summer 2025. A total of 13 fish taxa and 56 benthic invertebrate taxa were recorded during winter and summer, respectively. Fish assemblages were dominated by Sebastes oculatus and Prolatilus jugularis, with S. oculatus accounting for most records during both sampling periods. Multivariate analyses revealed no significant temporal or spatial differences in fish assemblage composition. In contrast, benthic invertebrate assemblages exhibited significant seasonal variation, with an average dissimilarity of 60.8% between winter and summer. Holothuroidea, Porifera, Psolus sp., Notaulax phaeotaenia, and Desmophyllum dianthus contributed most to these differences. Although diversity and abundance varied among stations, no significant differences were detected between assemblages located inside and outside the head of the fjord. Overall, these findings provide the first fjord-scale characterization of deep marine communities in Comau Fjord and establish a baseline for future monitoring and conservation of deep Patagonian fjord ecosystems.
