Abstract Trans‐regional green tides dominated by Ulva prolifera exert significant impacts on coastal ecosystems. While the mechanisms of early‐stage proliferation are well documented, the specific physiological and molecular drivers governing the transition from bloom persistence to terminal decline during this trans‐regional drift remain unresolved. Using in situ physiological and transcriptomic data collected across a 300‐km latitudinal gradient in the Yellow Sea, we found that a dominant molecular type (5S‐II) within the sampled 2021 U. prolifera population showed phenotypic plasticity, with its physiological and transcriptional traits varying across environmental conditions. Physiological observations showed declines in photosynthetic performance ( F v /F m and rETR) and pigment content along the northward drift path, marking a transition from active growth to physiological decline. Transcriptomic and physiological evidence further indicated that the intermediate drifting phase was characterized by a compensatory photoprotective state, potentially involving cyclic electron flow. By contrast, terminal‐phase stress was associated with reduced expression of G‐protein‐signaling‐related genes and patterns suggesting that PSII repair could no longer compensate for photodamage as energy metabolism declined. This bioenergetic failure coincided with a shift toward endogenous catabolism and a transition from vegetative growth toward sporulation. Together, these findings provide insight into bloom termination and suggest that ocean warming may accelerate late‐stage senescence, whereas acidification may intensify photosynthetic inhibition under multiple stressors, potentially increasing coastal hypoxia risk.
Abstract The Portuguese man‐o'‐war, Physalia physalis , regularly washes ashore on the US East Coast, but the physical and biological processes that determine when and where these animals strand are not well understood. Here we integrate iNaturalist observational data with a biologically‐informed particle‐tracking model to investigate the origins, dispersal, and stranding dynamics of P. physalis in the northwest Atlantic Ocean, building on recently reported population genomic structure. We find that juvenile P. physalis largely appear in Florida and on the Gulf of Mexico coast in winter months, and we use these findings to initialize particle‐tracking simulations based on observed juvenile distributions. Using models that incorporate Physalia drift hydrodynamics and high‐resolution forcing data, we show that P. physalis undergo rapid Gulf Stream transport along the US East Coast, with seasonal reproduction and onshore wind patterns shaping distinct regional stranding peaks, consistent with observed stranding data from iNaturalist. Our results suggest that seasonal Gulf Stream dynamics, including eddy activity, influence P. physalis transport in offshore regions and modulate strandings north of Cape Hatteras. Our study highlights the Gulf Stream's critical role in structuring planktonic distributions in the northwest Atlantic and reveals the transport dynamics that allow sailing species like P. physalis to disperse across vast regions of the ocean.
Abstract Lipids are central to animal physiology, underpinning energy storage, membrane architecture, and cell signaling. Targeted lipid studies in wild animals have already demonstrated that lipid adjustments, such as shifts in energy storage and membrane composition, are key molecular responses to environmental stressors. Yet, in situ lipidome‐wide responses remain virtually unexplored in marine invertebrates, particularly in systems affected by chronic environmental deoxygenation. Here, we characterized for the first time the whole‐body lipidome of the benthic marine annelid Neoleanira tetragona collected from sites across a naturally occurring deoxygenation gradient, with over 1700 lipids identified and quantified via untargeted high‐resolution lipidomics. Individuals from less oxygenated areas exhibited an enrichment in triacylglycerols, indicating increased lipid storage, and membrane lipids with lower fatty acid unsaturation. In contrast, an enrichment of acylcarnitines in individuals from more oxygenated areas suggests increased lipid catabolism and turnover. We interpret these findings as a display of moderate capacity for lipidome‐wide remodeling under chronic deoxygenation. We propose that this remodeling is due to physiological trade‐offs between energy conservation, cellular protection and membrane architecture. Finally, by applying a breakpoint analysis we identify a potential molecular tipping point of O 2 availability (~ 56.6 ± 8.7 μ M), providing a first step toward mechanistically explaining a previously identified biogeochemical and community‐level tipping point (~ 63 μ M) to environmental change. Our work demonstrates that lipid‐wide remodeling represents a chronic physiological response to deoxygenation, detected in situ, offering a link between biochemical and community‐level tipping points in a naturally exposed marine invertebrate.
Abstract Typhoons disrupt upper‐ocean dynamics through wind‐driven mixing and upwelling, often producing cross‐track asymmetry in the Northern Hemisphere. However, how such asymmetric physical forcing reshapes phytoplankton size structure remains poorly understood. This study integrates multi‐sensor satellite observations with in situ size‐fractionated chlorophyll a (Chl a ) and nutrient measurements to examine the impacts of Typhoon Yagi (2024) in the northwestern South China Sea. Post‐typhoon satellite observations showed cross‐track physical contrasts: the right‐of‐track side exhibited stronger surface cooling (~ 3–4°C). In situ sampling on September 10 revealed strong biogeochemical contrasts across the track. Mean surface and concentrations were higher on the right side, with the most robust cross‐track contrast observed for . Total surface Chl a was approximately 2.7‐fold higher on the right side when all three left‐side stations were included. At T6, elevated Chl a co‐occurred with an independently identified frontal and hydrographic anomaly. Size‐fractionated Chl a indicated that fractions > 2 μ m dominated on the right side, whereas the 0.2–2 μ m fraction contributed approximately 70% at left‐side Stas. T2 and T4. Notably, near‐bottom total Chl a on the left side peaked at T6, coincident with an intensified offshore sea surface temperature front. Satellite imagery on September 11–12 captured a delayed surface Chl a enhancement. These results are consistent with cross‐track differences in nutrient availability and upper‐ocean physical structure associated with asymmetric typhoon forcing, while lateral advection and frontal convergence may have further modulated the observed Chl a distribution. These findings provide new insight into post‐typhoon ecosystem restructuring.
Abstract The Eastern Indian Ocean exhibits a gradient from eutrophic nearshore to oligotrophic offshore conditions. The trophic structure of the planktonic food web in this region was investigated in spring 2022 using stable isotopes (δ 13 C, δ 15 N), biomass, and piecewise structural equation models (PSEM). Regional comparisons based on grouped stations showed that the equatorial zone was highly oligotrophic with the shortest food‐chain length (FCL = 3.12), while the Bay of Bengal had the highest δ 15 N baseline and widest trophic range (0.10–4.0). The Sumatra upwelling and seamount area were nutrient‐rich, supporting high particulate organic matter (POM), phytoplankton biomass, and top predators with longer food chains (FCL = 4.26 and FCL = 4.73, respectively). Isotopic niches were broadest in nearshore and upwelling zones but most constrained in oligotrophic waters. Using station‐level data, the PSEM revealed that nitrite and chlorophyll a influenced isotopic patterns and FCL through POM carbon‐to‐nitrogen ratio (C : N), while plankton C : N played a significant role in extending the FCL. These findings emphasize how gradients shape food webs and the importance of upwelling and seamounts in supporting high‐trophic‐level species and carbon sequestration in the face of climate change.
