Limnology and Oceanography最新文献

The North Sea has been undergoing long-term transformations driven by shifts in human activities and climate change, which have jointly reshaped the composition of marine communities. Despite existing studies, the functional mechanisms driving community changes remain poorly understood. Here, we analyzed a 43-year time series of meso- and macro-zooplankton (> 500 μm) monitored at Helgoland Roads to assess long-term changes in functional biodiversity. We applied functional diversity indices and trait-based uni- and multivariate analyses to (1) investigate the temporal variability in functional biodiversity components, (2) relate structural community changes to environmental drivers, and (3) interpret patterns in the context of community assembly mechanisms. Our results reveal asynchronous changes across biodiversity components, with pronounced structural shifts occurring in the early 2000s. These shifts were tightly linked to modifications in the food web: feeding traits together with predation-risk traits contributed most to diversity changes, shaped by the abundance of diatoms and fish biomass. Environmental filtering processes could be identified as key mechanisms driving the reorganization of the community, leading to a significantly altered functional structure after 2005, with potential implications for food web dynamics and energy transfer to higher trophic levels. Our findings underscore the value of trait-based approaches in gaining a comprehensive understanding of the mechanistic processes driving community change and support their integration into ecological models to improve projections of ecosystem responses under future conditions.

Open ocean ecosystems represent the largest habitat on Earth and are highly dynamic in time and space. Mesoscale eddies are a primary driver of this variability and serve a key structural role in ocean ecosystems. Eddies modulate marine biodiversity beyond their impacts on plankton, influencing many ecologically and commercially important predators that may preferentially occupy anticyclonic eddies. However, how animal-eddy interactions scale across predator species and the mechanistic drivers of these relationships remain an area of active research. We integrated satellite tracking data for sharks with observations of mesoscale eddies to determine how four shark species interact with eddies in the Gulf Stream region. Based on over 24,000 tracking days, we found that blue, white, and shortfin mako sharks selected for the cores of anticyclones while the use of eddies by tiger sharks was less conspicuous. Some particularly large and long-lived anticyclones were occupied by tagged sharks for multiple weeks suggesting that these eddies may serve as hotspots for pelagic predators.

Experimental research on aquatic communities in changing environments is challenging. Controlled laboratory experiments can neatly tie cause to effect and allow for a mechanistic understanding of physiological as well as genome-based processes, but can be of limited ecological relevance. In situ observations can address more complex scenarios but often remain descriptive and difficult to replicate. These challenges have recently led to renewed interest in mesocosm (enclosures of water or benthic areas) research. The use of small-scale, large-scale, and in situ mesocosms has provided vital insights into the responses of aquatic communities to climate change and its repercussions, from streams and lakes to coastal and polar ecosystems. Mesocosm experiments have also proven a crucial tool to address how results from individual laboratory experiments on single organisms can translate to the community or ecosystem scale.

Gut microbiota influence the expression of traits during host growth and development, and are increasingly recognized as the critical driver of host fitness. However, their role in the host's inducible anti-predator defense in response to predation pressure remains unclear. Here, we investigated how the assembly of the early-life gut microbiota affects the induced anti-predation morphological, behavioral, and life-history defenses of Daphnia magna. The results show that different types of bacterial inoculations specifically altered the gut microbial community of D. magna and further mediated the differential expression of its morphological and life-history defenses, rather than behavioral defenses, to cope with subsequent predation risk. Specifically, early life inoculation with probiotics such as Escherichia coli significantly enhanced the reproductive output and spine length of D. magna under subsequent predation risk, whereas early life inoculation with pathogenic bacteria such as Aeromonas hydrophila significantly reduced the body size, spine length, and reproductive output of D. magna under subsequent predation risk. Behavioral defense, that is, negative phototaxis, did not exhibit significant variation due to changes in the gut microbiota. Furthermore, the growth–survival trade-off of D. magna under predation risk may be mediated by specific bacteria present in its gut microbiota, such as Staphylococcus. These results reveal the role of the gut microbiota in shaping prey defenses and deepen our understanding of host–microbiota co-adaptation to complex environmental stressors.

Barnacles capture prey with a cirral fan filter that is swept through the water. As the barnacles grow, the cirral fan experiences changing flow regimes, both at the level of the filter elements (Reynolds number ~ 0.01 to ~ 1) and of the cirral fan (~ 1 to ~ 100). Here, we examined the implications of barnacle size on feeding current and clearance rate as a function of filter characteristics and prey size in the barnacle Amphibalanus improvisus. The feeding current is near fore-aft symmetric in newly settled individuals but becomes increasingly asymmetric with size. Thus, in large specimens, most flow arrives from the sides, uninterrupted by the beating fan, while in small individuals most incoming flow passes the beating fan, warning evasive prey. This change is consistent with reports of an ontogenetic change in the diet from passive phytoplankton to inclusion of evasive prey. The leakiness of the filter increases during development, from 52% to 83%, and it thus functions both as a paddle that moves water, and as a filter that strains prey from the water. Clearance rates increase with the size of the barnacle, from 20 to > 500 mL ind⁻¹ h⁻¹, orders of magnitude higher than reported earlier for similarly sized barnacles. Clearance rates also increase with prey size, saturating at particle sizes of about 80 μm or more. Barnacles thus occupy a different niche than most other co-occurring benthic suspension feeders that retain prey down to a few microns in size.

The United Nations' “Biodiversity Beyond National Jurisdiction” (BBNJ) Agreement establishes a broad framework regulating activities—including scientific research—in marine Areas Beyond National Jurisdiction (ABNJ), with the aim of advancing long-term conservation and sustainable use. Here, we offer a practical guide for researchers hoping to understand how the BBNJ Agreement will impact their work upon entry into force, highlighting relevant requirements, recommendations, and opportunities. Researchers will be required to submit pre- and post-cruise reports to a centralized online repository, as well as information about downstream research and development, including commercialization. Capacity building efforts to bolster the scientific proficiency of developing countries will also be required, though the guidance on precise modalities is broad and allows for customization. The BBNJ Agreement recommends a range of activities around capacity building and technology transfer that individual researchers could initiate, including research exchanges and infrastructure improvement. There are also many opportunities for researchers to support the Agreement's conservation and sustainability objectives through, for example, proposing marine protected areas, conducting environmental impact assessments, or joining technically oriented subsidiary bodies that will add practical detail to the Agreement's implementation in the years to come. Overall, many of the BBNJ Agreement's prescriptions align well with current best practices regarding collaboration, cruise operation, and data sharing. Given the deep integration of science into the BBNJ Agreement, marine scientists aiming to work in ABNJ are poised to both benefit and benefit from the Agreement's forward-looking objectives.

Climate change has significantly altered the energy dynamics of lakes; however, little is known of how the temporal and spatial variation in energy fluxes impacts the structure and function of lake ecosystems. This study combined long-term (2011–2018) measurements of lake energy fluxes with environmental, nutrient, and phytoplankton data at five stations to investigate the effects of variably energy fluxes on phytoplankton production and composition in a large, shallow, eutrophic lake (Lake Taihu, China). Overall, atmospheric warming increased heat storage and water temperatures, with energy fluxes exhibiting significant spatial heterogeneity. Specifically, faster rates of energy input and higher energy budgets increases were observed in the clear macrophyte-rich regions of the lake compared to turbid hypereutrophic habitats. Temporal variation in energy fluxes was a strong predictor of primary production (as chlorophyll a), the spatial extent of cyanobacterial blooms, and phytoplankton biodiversity at the whole-lake level, whereas 42.4% of the variation in phytoplankton community composition was explained by a combination of energy fluxes, nutrients, and other environmental factors. Cyanobacterial taxa were significantly correlated with nutrients (total nitrogen and phosphorus), while green algal abundance was associated mainly with variations in the energy budget. These findings highlight the spatial variability of energy fluxes driven by local environmental conditions, underscoring the need for climate adaptation and mitigation strategies to account for heterogeneous energy effects on lake production and structure.

Nitrogen fixers can enhance nitrogen availability for seagrass communities that may be nitrogen limited. However, the role of epiphytic diazotrophs, particularly cyanobacteria, in seagrass communities is not well understood. We measured nitrogen fixation rates, epiphyte biomass, and relative abundances of epiphytic diazotrophs on the leaves of Thalassia testudinum and Halodule wrightii in the northern Gulf of Mexico. Greater accumulation of epiphyte biomass and diazotrophs may occur in T. testudinum due to lower leaf turnover than found in H. wrightii, particularly during periods of seagrass dormancy. Nitrogen fixation rates were determined using the acetylene reduction assay, while quantitative polymerase chain reaction was used to measure relative abundances of three cyanobacterial diazotroph groups in epiphyte DNA. Nitrogen fixation and epiphyte biomass were higher on T. testudinum leaves than on H. wrightii leaves. The lowest average fixation rates occurred in August when leaf turnover was high. Three phylotypes of nifH genes were detected in most samples, but overall, Crocosphaera-like Group B cyanobacteria (UCYN-B) were present on all leaves during all seasons. Relative abundance of this group was positively correlated with nitrogen fixation rates on both species (r = 0.59, p = 0.02). At one of the four study sites, heterocystous cyanobacterial symbionts in the Richelia-like (Het-1) and Calothrix-like (Het-3) groups accounted for similar relative abundances to those observed with UCYN-B nifH genes. Because T. testudinum and H. wrightii are dominant in shallow tropical and subtropical ecosystems, understanding the role that diazotrophic epiphytes play in providing nitrogen to these vital ecosystems is critical.

Methylotrophic methanogenesis has recently been recognized as a key process driving cryptic methane cycling within sulfate-reducing sediments. Here we conducted biogeochemical analyses of methanogenic substrates, activity, and communities in two sediment cores (4–5 m) from the East China Sea, to constrain the dynamics and controls of methylotrophic methanogenesis in coastal sediments. We detected micromolar concentrations of methane in the presence of sulfate and high methane concentrations (up to 4.2 mM) below the sulfate–methane transition zone (~ 150–170 cm). Stable isotope composition of methane was strongly depleted (−77‰ to −91‰), indicating its biological production. Methanogenic substrates including H₂/CO₂, acetate, and methylated compounds were detected in the porewaters and/or sediments. Radiotracer experiments indicated methane production from various substrates, and the presence of sulfate did not inhibit methanogenesis at either site. At the coastal site with the dominance of marine organic matter (total organic carbon: 0.6%; C/N ratio: ~ 6.4; δ¹³C-total organic carbon: −22‰), methane was primarily produced from hydrogenotrophic methanogenesis, consistent with the progressive enrichment of ¹³C in dissolved inorganic carbon with depth below the sulfate–methane transition zone. However, methylotrophic methanogenesis from methanol and trimethylamine contributed significantly to methane production (up to 30.2%) at the estuarine site (total organic carbon: 0.5%; C/N ratio: 7.4, δ¹³C-total organic carbon: −23‰) with elevated terrestrial organic matter input, also reflected from the predominance of long chain odd carbon n-alkanes. These findings suggested that organic carbon source and composition, instead of sulfate, control methanogenic activity, providing evidence that high terrestrial organic inputs could significantly enhance methylotrophic methanogenesis in coastal sediments.