Underwater noise pollution is a known anthropogenic threat to marine wildlife as it can cause an assortment of auditory, behavioral, and physiological issues. Although concerns about low-frequency ship noise have resulted in some mitigation measures, such as seasonal vessel slowdowns in designated areas, less research effort has been undertaken to understand the prevalence and potential impacts of high-frequency sounds on marine life. The Salish Sea is home to a diverse array of marine mammals with hearing sensitivities in the higher frequencies, including endangered Southern Resident killer whales (SRKW). Ultrasonic antifouling (UA) signals were detected in passive acoustic recordings collected in the U.S. waters of the Salish Sea from 2019 to 2023, and their spatio-temporal occurrence and potential overlap with SRKW presence was investigated. The vessel types emitting UA signals in SRKW critical habitat were identified with Automatic Identification System (AIS) data, and a negative relationship was found between vessel speed and UA event duration. Many UA events were concentrated near the commercial shipping lanes, including sites with relatively high SRKW presence. Although seasonal cruise ships contributed many of the UA events, cargo ships, tankers, and pleasure craft operated these systems year-round, which highlights the prevalence of these signals and how they may be altering the soundscape within the SRKW critical habitat and the highly productive Salish Sea ecosystem in general. Potential impacts of UA on protected species that rely on underwater high-frequency sounds are an emerging concern for conservation measures that seek to reduce disturbance from noise generated by vessels.
Rapid urbanization and high intensity land development may aggravate ecosystem service degradation and the accumulation of landscape ecological risk (LER). Clarifying the spatiotemporal relationship between ecosystem service value (ESV) and LER and their underlying drivers is essential for optimizing territorial spatial patterns and ensuring regional ecological security. Taking the Guangxi Beibu Gulf Urban Agglomeration as the study area, this study analyzed the spatiotemporal dynamics of ESV and LER using land use data from 2000 to 2020, established an ESV–LER coupling-based ecological zoning framework to identify ecological functional heterogeneity, and applied the XGBoost-SHAP model to quantify the nonlinear driving effects and thresholds of natural and anthropogenic factors. The results showed that: (1) Built-up land expanded significantly from 2000 to 2020, with bidirectional conversion between cropland and forestland dominating land use change. ESV remained generally stable, displaying higher values in peripheral areas and lower values in urban cores. LER was mainly low to medium-low, while high-risk areas exhibited patchy distributions, and ESV and LER showed a significant negative spatial correlation. (2) Based on the coupling characteristics of ESV and LER, the study area was classified into four ecological zones (ecological protection, control, improvement, and conservation) with control and conservation zones predominating and forming a mountain conservation and plain development spatial pattern. (3) Land use structure, especially cropland and forestland proportions, made the largest contributions to the fitted ESV and LER patterns, while topography (DEM) imposed fundamental constraints. Key drivers exhibited clear nonlinear threshold and interval sensitivity effects on both ESV and LER, and human activity factors (population density and road proximity) exerted stronger marginal impacts in low elevation plains. Differentiated zoning regulation based on ESV–LER coupling, together with threshold oriented management of key drivers, can provide a scientific basis for refined ecosystem governance and sustainable regional development.
Microplastics (MPs) and antibiotics frequently co-occur in aquatic environments and jointly influence the dissemination of antibiotic resistance genes (ARGs). However, the modulatory role of salinity, a highly dynamic factor in estuarine and coastal regions, remains underexplored. This study investigated the effects of erythromycin (ERY) on biofilm development and RP4 plasmid conjugative transfer on poly(vinyl chloride) (PVC) MPs across varying salinity levels (5‰, 10‰, and 15‰). Results demonstrated that MP hydrophobicity increased with salinity, while the ERY adsorption capacity followed the order: 5‰ > 15‰ > 10‰. A higher salinity (15‰) promoted biofilm biomass and extracellular polymeric substance (EPS) secretion on MPs. Notably, conjugative transfer frequencies within MP-associated biofilms were consistently higher than those in planktonic cultures. Under varying salinities, the conjugation frequencies in biofilms displayed a U-shaped trend, with higher rates observed at 5‰ and 15‰ compared to 10‰. Crucially, the impact of ERY on plasmid transfer was highly salinity-dependent, i.e., the addition of ERY promoted conjugation at 5‰ and 10‰ but significantly inhibited it at 15‰. Physiological assessments revealed that exposure to varying salinities and ERY induced non-lethal oxidative stress, evidenced by elevated reactive oxygen species and upregulated antioxidant enzymes (CAT and SOD), while lipid peroxidation (MDA) remained relatively low. Concurrently, intracellular proline accumulation and cell membrane permeability increased significantly with rising salinity. These findings provide direct experimental evidence that salinity fluctuations and antibiotic residues jointly alter bacterial physiological states and antibiotic resistance dissemination on MPs, which highlights the necessity of considering dynamic environmental variables in ecological risk assessments.
Biogenic acidification is a growing concern in large-scale bivalve aquaculture. To investigate its drivers and mitigation strategies, oysters were incubated in a continuous flow-through system with five chambers in series to simulate upstream-to-downstream water flow in a large-scale long-line oyster aquaculture system. Four stocking densities (1, 3, 6, and 9 ind. Chamber−1) and three water exchange rates (3.6, 5.4, and 7.2 L h−1) were tested. The mitigation potential of macroalgal photosynthesis was then evaluated. Results showed that biogenic acidification was observed in experimental waters and higher oyster stocking density intensified seawater acidification, with downstream chambers exhibiting more pronounced acidification than upstream chambers. Compared with the blank control, the terminal chamber at the highest density showed a pH decrease of 0.85 units, a pCO2 increase of 2698 μatm, and decreases in total alkalinity (TA) and TA − DIC of 333 and 349 μmol kg−1, respectively. Lower water exchange rate also exacerbated biogenic acidification. In the terminal chamber at the lowest water exchange rate, pH decreased by 0.52 units, pCO2 increased by 976 μatm, and TA and TA − DIC decreased by 140 and 188 μmol kg−1, respectively. Negative effects were observed: correlation analysis revealed a significant negative correlation between seawater pCO2 and the weight-specific CO2 excretion rate (P < 0.05), alongside a significant positive correlation between Ωcal and the weight-specific calcification rate (P < 0.05). Adding Ulva Lactuca L. to the acidified seawater progressively raised pH (7.75 to 8.06) and Ωcal (2.3 to 4.3) and lowered pCO2 (1306 to 585 μatm) over five days, approaching ambient levels, whereas TA remained at its post-acidification level despite a DIC drawdown of 133 μmol kg−1. CO2 removal therefore raises the pH and saturation -state caused by biogenic acidification but not the TA deficit, indicating that TA must be included when the mitigating effect of macroalgal photosynthesis is evaluated and that supplementary alkalinity sources may be required in large-scale bivalve aquaculture.
