Southern Marine Science and Engineering Guangdong Laboratory

Accurate monitoring of fish movement is essential for understanding behavioral patterns and group dynamics in aquaculture systems. Underwater scenes-characterized by dense populations, frequent occlusions, non-rigid body motion, and visually similar appearances-present substantial challenges for conventional multi-object tracking methods. We propose an improved CenterTrack-based framework tailored for multi-fish tracking in such environments. The framework integrates three complementary components: a multi-branch feature extractor that enhances discrimination among visually similar individuals, occlusion-aware output heads that estimate visibility states, and a three-stage cascade association module that improves trajectory continuity under abrupt motion and occlusions. To support systematic evaluation, we introduce a self-built dataset named Multi-Fish 25 (MF25), continuous video sequences of 75 individually annotated fish recorded in aquaculture tanks. The experimental results on MF25 show that the proposed method achieves an IDF1 of 82.5%, MOTA of 85.8%, and IDP of 84.7%. Although this study focuses on tracking performance rather than biological analysis, the produced high-quality trajectories form a solid basis for subsequent behavioral studies. The framework's modular design and computational efficiency make it suitable for practical, online tracking in aquaculture scenarios.

Seaweed mariculture represents a promising blue-carbon strategy, but its carbon-sequestration dynamics and resilience to warming remain insufficiently constrained. Here, we conducted a comprehensive field assessment at a representative Porphyra (nori) mariculture farm in coastal China, where we monitored multisphere carbon pools across the water-column, sediments, atmosphere, and biomass. Multivariate statistical analysis and machine-learning models were used to identify stage-specific drivers and project carbon-pool responses under multiple warming scenarios. Our results demonstrate that Porphyra cultivation delivers substantial carbon-sequestration benefits, as it significantly enhances atmospheric CO2 sequestration and sedimentary carbon burial. Concurrently, the system consistently releases dissolved organic carbon (DOC), of which 48-54% was transformed into long-lived refractory DOC. High-temporal-resolution monitoring reveals highly dynamic carbon pools across cultivation stages, with dominant controls on net sequestration shifting from inorganic-carbon uptake and hydrodynamics during early growth to biologically mediated processes at peak biomass. Simulations across climate-change scenarios indicate that although inorganic pools were more temperature-sensitive than organic pools, changes across all major pools under projected warming over the coming decades remain within 5%, underscoring strong resilience to warming. Together, these process-based insights support the integration of macroalgal mariculture into blue-carbon action plans and carbon-offset initiatives.

Eukarya resemble Archaea in DNA replication. Analysis of the DNA replication machinery of Asgard archaea may provide a valuable test of the hypothesis that this phylum is the origin of Eukarya. Among the replication proteins, primase, which comprises the catalytic subunit PriS and the non-catalytic subunit PriL, synthesizes primers for extension by DNA polymerase. Here, we show that Asgard primases fall into two major groups, denoted the Heimdall group and the Loki group, which are phylogenetically and structurally more closely related to eukaryotic primases and to primases from non-Asgard archaea, respectively. Notably, like human PriL, PriL of the Heimdall group possesses an extra C-terminal domain, which, absent in archaeal PriL of the non-Heimdall group, presumably serves to enhance the stability of the conserved iron–sulfur cluster in PriL. We overproduced and purified the PriS and PriL subunits of the Heimdall group from the Candidatus Gerdarchaeota archaeon B18_G1 in Escherichia coli. Biochemical characterization reveals that the B18_G1 primase is capable of primer synthesis and extension, preferentially using dNTPs as substrates, as shown for primases from non-Asgard archaea; however, unlike non-Asgard archaeal primases, it produces short primers, a feature typical of eukaryotic primases. These results shed significant light on the evolutionary pathway of primase and are consistent with the hypothesis of the Asgard origin of Eukarya.

Abstract The pan-Arctic region is experiencing rapid climate change under global warming, with Arctic Amplification occurring at a rate 2-3 times faster than the global average. This study investigates the climate responses in the Pan-Arctic region under carbon dioxide removal (CDR) scenarios using nine CMIP6 models from the Carbon Dioxide Removal Model Intercomparison Project (CDRMIP). Our results reveal significant hysteresis and asymmetric responses in both temperature and precipitation during CO₂ increase and decrease phases. The multi-model mean shows that when CO₂ concentrations return to pre-industrial levels, the pan-Arctic region retains a warming of approximately 1.5°C and increased precipitation of about 0.1 mm/d compared to initial conditions. Notably, temperature and precipitation changes in the pan-Arctic at peak CO₂ are approximately twice the global average. We identify substantial inter-model uncertainties, primarily driven by divergent representations of Atlantic Meridional Overturning Circulation (AMOC) responses and associated North Atlantic cooling patterns in the ramp-up period. Two models (CESM2 and NorESM2-LM) simulate particularly strong AMOC weakening during the ramp-up phase, resulting in reduced warming and wetting trends across the pan-Arctic. Similar persistence of warmer and wetter conditions is found under the moderate CDR scenario SSP126. These findings highlight the irreversible nature of Arctic climate change even under aggressive CDR scenarios and emphasize the need for improved representation of Arctic processes in climate models to reduce uncertainties in climate projection and mitigation strategy design.

Abstract Coupled with the Antarctic Slope Front (ASF), the Antarctic Slope Current (ASC) mostly encircles Antarctica and has variable structures. Two regimes of the ASC/ASF have been identified in the Ross Sea, but the spatial characteristics of the ASC/ASF have not been depicted in detail, and the dynamical mechanisms of the two ASC/ASF regimes are still unclear. Using an eddy‐permitting coupled regional ocean‐sea ice‐ice shelf model, we investigate the spatial characteristics and energetics of the ASC/ASF in the Ross Sea. Based on the simulated results, two distinct structures of the ASC/ASF have been identified in two regimes: (a) in Regime I, the westward ASC is characterized by a surface‐intensified flow, predominantly driven by the barotropic pressure gradient; (b) in Regime II, the ASC is characterized by a bottom‐intensified westward flow, dominated by the baroclinic pressure gradient, especially prominent where Dense Shelf Water (DSW) overflows. Furthermore, by conducting an energy budget analysis in the framework of the Lorenz Energy Cycle, we found that in Regime I the ASC is maintained by Ekman transport that piles up water against the slope and drives a conversion from Mean Kinetic Energy (MKE) to Mean Available Potential Energy (MAPE), whereas in Regime II the ASC is strengthened as a bottom‐intensified current through DSW overflows, which release MAPE into MKE.