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Fusion, fission, and scrambling of the bilaterian genome in Bryozoa
No full textGroups of orthologous genes are commonly found together on the same chromosome over vast evolutionary distances. This extensive physical gene linkage, known as macrosynteny, is seen between bilaterian phyla as divergent as Chordata, Echinodermata, Mollusca, and Nemertea. Here, we report a unique pattern of genome evolution in Bryozoa, an understudied phylum of colonial invertebrates. Using comparative genomics, we reconstruct the chromosomal evolutionary history of five bryozoans. Multiple ancient chromosome fusions followed by gene mixing led to the near-complete loss of bilaterian linkage groups in the ancestor of extant bryozoans. A second wave of rearrangements, including chromosome fission, then occurred independently in two bryozoan classes, further scrambling bryozoan genomes. We also discover at least five derived chromosomal fusion events shared between bryozoans and brachiopods, supporting the traditional but highly debated Lophophorata hypothesis and suggesting macrosynteny to be a potentially powerful source of phylogenetic information. Finally, we show that genome rearrangements led to the dispersion of genes from bryozoan Hox clusters onto multiple chromosomes. Our findings demonstrate that the canonical bilaterian genome structure has been lost across all studied representatives of an entire phylum, and reveal that linkage group fission can occur very frequently in specific lineage
Hindsight informs foresight: revisiting millennial forecasts of impacts and status of rocky shores in 2025
No full textRocky shorelines are characterised by vulnerability to both land- and sea-derived impacts. They face acute impacts such as pollution from shipping accidents, chronic pollution from point sources, run-off and catchments plus disturbances by food gathering, recreation and sediment deposition in sheltered areas. Coastal urbanisation can both impact natural shores and create impoverished artificial rocky shores. Superimposed upon local and regional scale impacts are global environmental changes including warming, sea-level rise, increasing storm frequency, ocean acidification and non-native invasive species. Rocky shores are, however, amenable to long-term ecological monitoring and ecological experimentation. Thompson, Crowe and Hawkins (2002) reviewed anthropogenic impacts on rocky intertidal habitats and forecasted their status for the next 25 years. The paper was critiqued by invited experts (Branch, Castilla) at a subsequent conference in 2003 (Environmental Future of Aquatic Ecosystems, Zurich, 23-27 March 2003), culminating in a consensus chapter in Aquatic Ecosystems: Trends and Global Prospects (Branch et al., 2008). Nearly 25 years later, we revisit and evaluate their predictions to explore implications for the next 25 years as new potential impacts emerge in parallel with societal attempts to transition to net zero carbon outputs. An update is provided on what was largely correct (oil-spills, food harvest, invasive species, sedimentation/run-off, organotins, global-change, artificial habitats, recreation/research/education) and what was partially/completely wrong (eutrophication, aquaculture/GMOs, renewable energy, UV radiation) or omitted (coastal mining, ocean acidification, plastic, light, noise pollution). We also consider the challenges and uncertainties inherent in predicting impacts of environmental changes by using hindsight to inform foresigh
Marine Biogeochemical Control on Ozone Deposition Over the Ocean
Full text linkThe ocean is a large but uncertain sink of tropospheric ozone. Ozone deposition is controlled partly by its reactions with marine substances, but in situ evidence of this marine biogeochemical control remains sparse. Here we report a novel measurement of ozone uptake efficiency (OUE) from a trans‐Atlantic cruise (50°N to 45°S). Observed OUE for surface waters varied two‐fold and the implied chemical deposition velocity varied from 0.012 to 0.034 cm s
− 1 . Iodide accounted for on average 2/3 of total OUE, with generally higher contributions in tropical waters. The residual OUE, generally higher in temperate waters and positively correlated with biological proxies, was likely due to marine organics. OUE was also measured for 1,000 m
waters, which were likely devoid of iodide but contained biologically refractory organics. Unexpectedly, these
waters were rather reactive toward ozone, suggesting that surface organics that affect ozone uptake are not all
freshly produced by marine biot
Seasonally migrating zooplankton strongly enhance Southern Ocean carbon sequestration
Full text linkHigh‐latitude zooplankton can sequester millions of tons of carbon due to their seasonal migration from the surface ocean to depth, and their respiration and mortality during overwintering. This seasonal vertical migration pump (SVMP) efficiently removes carbon but not limiting nutrients such as iron from the surface layers. However, this process is not included in Earth System Models and whole Southern Ocean estimates are still lacking. Here, we compile large datasets of Southern Ocean zooplankton biomass and physiology to estimate that the SVMP transports 65 Mt carbon annually to sequestration‐achieving depths of > 500 m. Mesozooplankton are the main agents (80%), followed by krill (14%), and salps (6%), with respiration and mortality at depth contributing a similar share. This SVMP adds greatly to existing modeled or measured estimates of Southern Ocean carbon sequestration, equating to 38–56% of particulate organic carbon flux at 500 m and 78–103% of the flux at 1000 m. Given their large biomass but projected change under polar warming, understanding how zooplankton transport carbon and nutrients will underpin improved model projections of ocean carbon storage in a warmer world
Application of a theoretical simulator to the optimisation of risk-based invasive species surveillance
Full text linkEarly detection and rapid response are critical to the successful management of non-indigenous species (NIS) and rely on effective surveillance programmes. Risk-based surveillance, where surveillance targets high risk locations, is the most efficient form of NIS surveillance. However, further research is required on the impact of different levels of emphasis on risk, in sampling designs and on surveillance efficacy. This study implements a theoretical surveillance simulator to model the relative merit of different surveillance strategies with different levels of focus on NIS risk for NIS detection at one or more sites. Three potential surveillance scenarios were modelled: random, risk-based and heavy risk-based surveillance, each with three distributions of combined NIS risks of introduction and establishment: exponential, random and uniform. An example analysis using model derived NIS risk data is also provided. Sensitivity and elasticity analyses were conducted to identify variables which influence model outputs. The interaction between sampling method detection probability and changes in NIS abundance was modelled. It was found that NIS risk distribution influences the relative performance of different surveillance strategies and that risk- and heavy risk-based surveillance have lower times to detections and, generally, higher surveillance probabilities of detection compared to random surveillance at more skewed NIS risk distributions. However, there was a trade-off between short detection time and detection failure in risk-based and particularly heavy risk-based surveillance. Therefore, an over-emphasis on risk-based surveillance could provide suboptimal NIS detection. Sensitivity and elasticity analysis showed that the number of NIS seed sites, mean site visit rate and method detection probability had the largest effects on detection time, highlighting the complexity of designing surveillance programmes. In conclusion, the optimal surveillance strategy is conditional on the risk distribution and this study highlights the value of model-based simulators to guide decision-making in the design of NIS surveillance programmes
Anaerobic decomposition dynamics of three kelp species from the North-east Atlantic: implications for blue carbon storage
No full textrobic decomposition of 3 North-east Atlantic canopy-forming kelp species was investigated using ex situ decomposition chambers. Thallus parts (stipes, holdfasts and blades) of Laminaria hyperborea, Saccharina latissima and L. digitata were incubated in still seawater in temperature-controlled dark conditions. Refractory potential (Rp), first-order decomposition rate (k) and associated half-life (t1/2) were calculated. Dissolved organic and inorganic carbon (DOC and DIC, respectively) were measured in the incubation water at 0, 7, 14 and 21 d, and thermal gravimetric profiles were determined at each decomposition stage. Oxygen depletion occurred within 24 h. Approximately 5 times as much DOC was released than DIC. Holdfast material produced the most DIC, while blade material released the greatest amounts of DOC. S. latissima released less DOC than L. hyperborea and L. digitata. The mean (SD) Rp of fragments increased from 0.46 ± 0.05 to 0.50 ± 0.04 throughout the 21 d incubations. S. latissima had the highest Rp throughout. First-order decomposition rates, averaged across the 3 kelp species, gave half-lives (t1/2) for blade fragments of 27.8 ± 2.9 d, (k = 0.025 ± 0.002) and stipes as 113.2 ± 21.1 d (k = 0.006 ± 0.001). This experiment clarifies the fate of macroalgal carbon during early decomposition and thus the processes that govern blue carbon pathways of macroalgae, highlighting the differences in breakdown among different species and thallus part
Giants in the cold: Morphological evidence for vascular heat retention in the viscera but not the skeletal muscle of the basking shark (Cetorhinus maximus)
No full textFewer than 50 of the over 30,000 extant species of fishes have developed anatomical specializations facilitating endothermy in specific body regions. The plankton-feeding basking shark (Cetorhinus maximus), traditionally classified as an ectotherm, was recently shown to have regionally endothermic traits such as centralized red muscle (RM) along its body trunk and elevated (white) muscle temperatures. However, key anatomical features essential for classification as a regional endotherm, such as the presence of vascular rete mirabile, could not be confirmed in this cold-water giant. This study compared the morphology of heat-generating and heat-retaining tissues – associated with skeletal RM, the cranium and viscera – in the basking shark with those of a confirmed regional endotherm, the porbeagle (Lamna nasus), and a polar ectotherm, the Greenland shark (Somniosus microcephalus). Despite the presence of more medial RM in the basking shark's trunk, the absence of paired lateral vessels and a perfusing rete strongly suggests a lack of RM endothermy in this species. However, the presence of small arterial plexuses in the orbit, along with the discovery of visceral retia associated with the stomach, spleen and valvular intestine, in addition to distinct vascular arrangements in the liver and kidney, indicates potential for cranial and, particularly, visceral endothermy in C. maximus. These specializations, combined with reduced conductive heat loss from partial RM internalization and large body size, may enable C. maximus to maintain regionally elevated body temperatures, facilitating their active lifestyle also in cold-water environments. Enhanced sensory perception and digestive efficiency may aid prey acquisition and processing in the dimly lit meso- and bathypelagic zones, as well as high-latitude regions. Our findings provide initial insights into the thermal adaptations of these circum-globally distributed, highly migratory ram filter feeders. Further research is needed to better understand the eco-physiological implications of these adaptations, especially in the context of rapid ocean warming across their range, including Atlantification in the Arctic, and other anthropogenic pressures in the Anthropocen
Global tracking of marine megafauna space use reveals how to achieve conservation targets
No full textThe recent Kunming-Montreal Global Biodiversity Framework (GBF) sets ambitious goals but no clear pathway for how zero loss of important biodiversity areas and halting human-induced extinction of threatened species will be achieved. We assembled a multi-taxa tracking dataset (11 million geopositions from 15,845 tracked individuals across 121 species) to provide a global assessment of space use of highly mobile marine megafauna, showing that 63% of the area that they cover is used 80% of the time as important migratory corridors or residence areas. The GBF 30% threshold (Target 3) will be insufficient for marine megafauna’s effective conservation, leaving important areas exposed to major anthropogenic threats. Coupling area protection with mitigation strategies (e.g., fishing regulation, wildlife-traffic separation) will be essential to reach international goals and conserve biodiversit
Revealing two decades of chlorophyll-a dynamics in arid oligotrophic lakes of Xinjiang, China using a deep recurrent approach
No full textOligotrophic lakes in arid and semi-arid regions are vital to local livelihoods and ecosystems, yet research has primarily focused on water levels and volumes in these areas, with limited attention to water quality. As a sensitive indicator of ecological change, chlorophyll-a (Chl-a), which is detectable via remote sensing, can provide valuable insights into subtle variations in water quality. To address this research gap, we investigated Chl-a concentrations in lakes larger than 100 km2 across the expansive Xinjiang region of China using two decades (2002–2023) of MODIS imagery. A robust deep learning model was developed to accurately estimate spatiotemporal Chl-a dynamics, overcoming the limitations of conventional algorithms for oligotrophic lakes. Unlike existing machine learning models that treat remote sensing spectra as static multi-dimensional points, our approach models wavebands as dynamic sequences with a Recurrent Neural Network (RNN) framework. A comparative evaluation with four conventional Chl-a inversion models, four machine learning and five deep learning models demonstrated the superiority of the RNN model with an RMSE of 0.75 mg m−3 and R2 of 0.72. Results over the ice-free period revealed that Chl-a concentrations in major lakes of Xinjiang generally remained below 6 mg m−3, with annual averages below 3 mg m−3, and manifested a slight declining trend in recent years. Further analysis of environmental variables revealed that Chl-a variability in lakes influenced by anthropogenic activities was primarily driven by solar radiation, vegetation cover, and runoff. In contrast, alpine lakes with minimal human disturbance exhibited dynamics largely shaped by lake expansion. This study presents a robust framework for Chl-a estimation, potentially extendable to other water parameters, and advances the understanding of long-term ecological dynamics in arid environments of Xinjiang
Icelandic intertidal fish communities and effects of knotted wrack (Ascophyllum nodosum) harvesting
No full textIn Iceland, sheltered rocky intertidal zones like Breiðafjörður bay are dominated by monospecific stands of Ascophyllum nodosum, providing key habitats for marine organisms. Increasing demand for A. nodosum has led to its commercial exploitation, yet impacts on fish assemblages remain poorly known. Using a novel multi-mesh netting approach, we characterised seasonal patterns in fish composition, abundance, size structure, age, and diet. Additionally, to assess the local effects of seaweed harvesting, commercial harvesting was conducted, with comparisons being made between treatment and control unharvested areas during different seasons. Nine fish species were identified, with Pollachius virens, Myoxocephalus scorpius, and Gadus morhua being the most common. Fish abundance peaked in summer, and declined the following spring, suggesting cohort turnover with juvenile gadoids relying on these habitats as nurseries. P. virens showed increased length through seasons, whereas no trends in length or abundance were observed for M. scorpius. Effects of seaweed harvesting were minimal, although fish diversity was slightly higher and G. morhua significantly larger in control plots. Stomach contents exhibited a greater diversity of prey types in harvested sites, suggesting potential impacts on trophic dynamics. These findings underscore the importance of A. nodosum-dominated habitats as nursery grounds for commercially valuable gadoids and highlight the need for a precautionary approach to seaweed harvesting to maintain ecosystem healt