Disentangling phytoplankton regime shifts and ecosystem stability under water diversion: Insights from functional traits and trophic interactions in a mesocosm experiment.

The Arctic Ocean has undergone accelerated warming and a marked decline in sea ice over recent decades. Yet, the response of the biological pump—a critical mechanism for atmospheric carbon sequestration—remains poorly understood. Here, we develop a satellite-derived dataset (2003–2022) to identify a regime shift in the Arctic biological pump. Between 2003 and 2012, the strength and efficiency of the biological pump increased rapidly, primarily driven by sea ice decline. However, from 2013 to 2022, this trend plateaued, coinciding with stabilized sea ice conditions and increased phytoplankton biomass. Earth system model simulations (1850–2100) support the observed link between biological pump enhancement and sea ice loss, and project a future regime shift towards a weakened biological pump under nearly ice-free conditions, associated with shifts in phytoplankton community structure. These findings underscore the Arctic’s vulnerability to climate-driven changes, with far-reaching implications for Arctic carbon sequestration and ecosystem stability.

Impacts of climate change on methylmercury formation and bioaccumulation in the 21st century ocean

Phytoplankton phenology and community structure in the western North Pacific were investigated for 2001–2009, based on satellite ocean colour data and the Continuous Plankton Recorder survey. We estimated the timing of the spring bloom based on the cumulative sum satellite chlorophyll adata, and found that the Pacific Decadal Oscillation (PDO)‐related interannual SST anomaly in spring significantly affected phytoplankton phenology. The bloom occurred either later or earlier in years of positive or negative PDO (indicating cold and warm conditions, respectively). Phytoplankton composition in the early summer varied depending on the magnitude of seasonal SST increases, rather than the SST value itself. Interannual variations in diatom abundance and the relative abundance of non‐diatoms were positively correlated with SST increases for March–April and May–July, respectively, suggesting that mixed layer environmental factors, such as light availability and nutrient stoichiometry, determine shifts in phytoplankton community structure. Our study emphasised the importance of the interannual variation in climate‐induced warm–cool cycles as one of the key mechanisms linking climatic forcing and lower trophic level ecosystems.

Phytoplankton communities play an important role in marine food webs and biogeochemical cycles. The transition zones between ocean gyres and surrounding waters represent critical ecological boundaries where environmental gradients drive significant shifts in phytoplankton community structure. This study investigates how nutrient availability and temperature shape the size distribution and composition of small phytoplankton (< 5 [Formula: see text]m) communities across the North Pacific Subtropical Gyre (NPSG) boundaries, testing several ecological hypotheses that explain phytoplankton size distribution patterns in relation to environmental variability. We used high-resolution, underway flow cytometry data collected during eight oceanographic cruises from 2016 to 2021 to assess changes in phytoplankton biomass and growth rate across the gyre boundaries. The cyanobacterium Prochlorococcus dominated within the gyre, with biomass ranging from 3.2 to 13.1 [Formula: see text]gC L-1, and its relative contribution to total phytoplankton biomass varied among cruises (31% to 81%, average 60 [Formula: see text] 16%). Prochlorococcus growth rates were significantly higher within the gyre (0.43 [Formula: see text] 0.18 per day) than outside the gyre (0.28 [Formula: see text] 0.16 per day) (one-sided t-test, p < 0.001). Northward in the gyre, Prochlorococcus biomass and growth rates declined. Some variations in biomass and growth rates were observed southward and eastward, with biomass ranging from 3 to 10 [Formula: see text]gC L-1 and growth rate ranging from 0.2 to 0.6 per day. Outside the NPSG, total phytoplankton biomass increased, with nanoeukaryotes becoming the predominant contributors (up to 71%, 9.1 [Formula: see text] 7.3 [Formula: see text]gC L-1). Picoeukaryote biomass also increased outside the gyre (up to 28 [Formula: see text] 12% of total biomass). Nutrient concentrations increased by nearly two orders of magnitude outside the NPSG, coinciding with the shift towards larger phytoplankton. The dominance of Prochlorococcus within the gyre emphasizes its adaptation to oligotrophic conditions, while the shift towards larger size classes outside the gyre likely reflects the relatively higher nutrient availability. The relatively low abundance of Synechococcus even in nutrient-rich regions suggest that that factors beyond nutrient availability, such as grazing, may influence its distribution. These findings have implications for understanding how phytoplankton communities will respond to future changes in oceanographic conditions, such as warming and altered nutrient regimes.

Phytoplankton community variation and ecological health assessment for impounded lakes along the eastern route of China's South-to-North Water Diversion Project.

Appropriate water body diversion can improve the water quality of Tai Lake. Excessive diversion of water would, however, dramatically alter the local flow fields, which are not conducive to the growth of aquatic plants and the stability of ecosystems. The current “Diverting Water from the Yangtze River to Tai Lake (DWYRTL)” project uses a single water source, the Wangyu River, for diversion, a model that may significantly affect the nearby flow rate or uniformity of the lake and is not conducive to the long-term stability of the aquatic ecosystem in the Tai Lake district of the eastern part of the lake. In order to simulate the different situations of single- and dual-source water diversions (Wangyu-Xinmeng Rivers) in Tai Lake, we based this study on a three-dimensional hydrodynamic model coupled with the Euler method, which can accurately calculate the water exchange rates in the different districts of Tai Lake. The results show that (1) it is recommended that the total annual diversion of water should not exceed 20 × 108 m3; (2) the wind field is the most important factor determining the distribution of spatial water exchange; (3) under wind-free conditions, the flow rate of a single-source diversion of water is approximately 50% higher than that of dual-source diversion; and (4) water diversion under the prevailing conditions of the northwest wind in winter will reduce the semiexchange period of the eastern part of the lake area from 50 to 30 days, significantly changing the nearby district’s uniformity, leading to ecological risks. Therefore, it is recommended that the dual-source water diversion mode be used in winter and windless season, and single-source water diversion mode be used in other seasons.

Nuclear war would produce dire global consequences for humans and our environment. We simulated climate impacts of US‐Russia and India‐Pakistan nuclear wars in an Earth System Model, here, we report on the ocean impacts. Like volcanic eruptions and large forest fires, firestorms from nuclear war would transport light‐blocking aerosols to the stratosphere, resulting in global cooling. The ocean responds over two timescales: a rapid cooling event and a long recovery, indicating a hysteresis response of the ocean to global cooling. Surface cooling drives sea ice expansion, enhanced meridional overturning, and intensified ocean vertical mixing that is expanded, deeper, and longer lasting. Phytoplankton production and community structure are highly modified by perturbations to light, temperature, and nutrients, resulting in initial decimation of production, especially at high latitudes. A new physical and biogeochemical ocean state results, characterized by shallower pycnoclines, thermoclines, and nutriclines, ventilated deep water masses, and thicker Arctic sea ice. Persistent changes in nutrient limitation drive a shift in phytoplankton community structure, resulting in increased diatom populations, which in turn increase iron scavenging and iron limitation, especially at high latitudes. In the largest US‐Russia scenario (150 Tg), ocean recovery is likely on the order of decades at the surface and hundreds of years at depth, while changes to Arctic sea‐ice will likely last thousands of years, effectively a “Nuclear Little Ice Age.” Marine ecosystems would be highly disrupted by both the initial perturbation and in the new ocean state, resulting in long‐term, global impacts to ecosystem services such as fisheries.

Phytoplankton blooms have become a global concern due to their negative impacts on public health, aquaculture, tourism, and the economic stability of coastal regions. Therefore, elucidating the shifts in phytoplankton community structure and abundance, as well as their environmental drivers, is crucial. However, existing studies often fail to capture the detailed dynamics of phytoplankton blooms and their environmental triggers due to low temporal observation resolution. In this study, high temporal resolution (daily) samples were collected over 43 days to investigate the influence of environmental factors on phytoplankton in Qinhuangdao in the summer. During the observation period, a total of 45 phytoplankton species were identified, comprising 26 Bacillariophyta species, 16 Dinophyta species, 2 Euglenophyta species, and 1 Chromophyta species. Interestingly, a lag bloom pattern of phytoplankton behind freshwater input was observed across day-to-day samples. Phytoplankton blooms typically lagged 1–3 days behind periods of decreased salinity and nutrient input, suggesting that freshwater influx provides the foundational materials and benefits for these blooms. Moreover, the phytoplankton blooms were triggered by six dominant species, i.e., Chaetoceros spp., Pseudo-nitzschia delicatissima, Skeletonema costatum, Protoperdinium spp., Leptocylindrus minimus, Pseudo-nitzschia pungens, and Thalassiosira spp. Consequently, the succession of phytoplankton showed a predominant genera shift in the following sequence: Nitzschia, Protoperdinium, and Prorocentrum – Skeletonema – Pseudo-nitzschia – Gymnodinium – Leptocylindrus. Besides that, a deterministic process dominated phytoplankton community assembly across time series, and DIP is a key factor in shifting the phytoplankton community structures in this area. In summary, our study offers high-resolution observations on the succession of phytoplankton communities and sheds light on the complex and differentiated responses of phytoplankton to environmental factors. These findings enhance our understanding of the dynamics of phytoplankton blooms and their environmental drivers, which is essential for the effective management and mitigation of their adverse impacts.

Question: What is the relationship between plant diversity and species turnover in coastal dune vegetation plots? How is the long‐term change in species composition of vegetation plots related to shifts in functional traits, and what does it tell us about the dominant processes?Location: Coastal dunes, the Netherlands.Methods: Our data set comprised 52 years of vegetation data from 35 permanent plots in grassland/scrub/woodland vegetation. Vegetation dynamics were described in terms of changes in species composition and abundance, and shifts in 13 functional traits related to resources capture and forage quality, regeneration and dispersal.Results: Species turnover in the plots was high, because of local extinction and colonization. Species‐rich plots were more stable in terms of species abundance and composition compared with species‐poor plots. Over time, the plots converged with respect to their abiotic conditions, as reflected by Ellenberg indicator values – indicating that the prevailing process was succession. The high species turnover reflected high invasibility: accordingly, the relative importance of annuals increased. Most newcomer annuals, however, were competitive generalists of little conservation value. The functional trait analysis allowed us to unravel the complexity of effects of disturbances and succession, and yielded information on the processes driving the observed vegetation dynamics.Conclusions: In this study, small‐scale species turnover was negatively related to species diversity, indicating more stability in species‐rich communities. Regarding shifts in trait diversity, unifying filters appeared to be more dominant than diversifying filters. Counteracting this homogenization process poses a challenge for nature management.

Interannual phenological variability (IPV), a critical indicator of plant phenological sensitivity to climate variations, can determine ecosystem functions and stability. While the influence of climate on IPV has been recognized, the effects of biotic factors such as functional traits and diversity remain underexplored. We selected four temperate forest sites with similar intrasite climate variations to investigate the biotic regulatory mechanisms of IPV. For each site, we utilized IPV from time-series Harmonized Landsat Sentinel-2 data, foliar traits from airborne hyperspectral data, and structural traits from airborne Light Detection and Ranging data for the analysis. Our results reveal considerable IPV variations within and across forests. Functional traits and diversity are important for explaining intrasite IPV variation. Functional traits, particularly those related to resource use and productivity, have more explanatory power than functional diversity. Moreover, functional traits and diversity can regulate ecosystem productivity stability through their effects on IPV, with a strong negative association between IPV and ecosystem productivity stability (r = -0.71 to -0.86). These findings demonstrate significant contributions of functional traits to regulating IPV and ecosystem productivity stability, highlighting their critical role in determining plant phenological sensitivity and ecosystem stability in response to climate changes.

200 000 yr diatom records from Atlantic upwelling sites reveal maximum productivity during LGM and a shift in phytoplankton community structure at 185 000 yr

Urbanization may lead to changes in assemblage and result in shifts in trait distribution from natural habitats to highly urbanized habitats. The shift in functional traits can affect ecosystem functions in urban areas. This study explored the foraging period of ants over 72 h and determined the relationship between the behavioral, morphological, and physiological traits of local foragers ants and environmental conditions in urban and forest sites. In addition, this study examined the ants’ ecosystem functions and compared it with that of their forest counterparts. Our results revealed that the foraging period of ants (i.e., Cardiocondyla sp.1, Monomorium chinense, Paratrechina longicornis, Pheidole megacephala, and Solenopsis sp.1) in urban areas peaked between 0900 and 1500 and that of some ants (i.e., Carebara diversa, P. megacephala, Pheidole fervens, Plagiolepis longwang, and Nylanderia sp.1) in forest areas was constant over time. For urban ants, a weak correlation was observed between foraging period and body size traits (i.e., Weber’s length and head width). This finding indicates that the major factor underlying the change in the foraging period might not be related to body size. Rather, the change may be attributed to synchronization between food availability and human activity (waste disposal; i.e., between 0900 and 1800). The shift in the functional traits of ants affects ecosystem functions in urban areas. In urban areas, although only one predatory ant species (P. megacephala) was sampled, its activity density was high. Most of these individuals were active during the daytime, indicating that the predatory behavior of ants in the novel urban environment has decreased temporally and is limited to the daytime. Urban ants tended to choose smaller food particles, whereas forest ants preferred larger food particles and had a twofold higher food removal rate.

The adaptive value of functional and life-history traits across fertility treatments in an annual plant

Nutrient enrichment impacts grassland plant diversity such as species richness, functional trait composition and diversity, but whether and how these changes affect ecosystem stability in the face of increasing climate extremes remains largely unknown. We quantified the direct and diversity‐mediated effects of nutrient addition (by nitrogen, phosphorus, and potassium) on the stability of above‐ground biomass production in 10 long‐term grassland experimental sites. We measured five facets of stability as the temporal invariability, resistance during and recovery after extreme dry and wet growing seasons. Leaf traits (leaf carbon, nitrogen, phosphorus, potassium, and specific leaf area) were measured under ambient and nutrient addition conditions in the field and were used to construct the leaf economic spectrum (LES). We calculated functional trait composition and diversity of LES and of single leaf traits. We quantified the contribution of intraspecific trait shifts and species replacement to change in functional trait composition as responses to nutrient addition and its implications for ecosystem stability. Nutrient addition decreased functional trait diversity and drove grassland communities to the faster end of the LES primarily through intraspecific trait shifts, suggesting that intraspecific trait shifts should be included for accurately predicting ecosystem stability. Moreover, the change in functional trait diversity of the LES in turn influenced different facets of stability. That said, these diversity‐mediated effects were overall weak and/or overwhelmed by the direct effects of nutrient addition on stability. As a result, nutrient addition did not strongly impact any of the stability facets. These results were generally consistent using individual leaf traits but the dominant pathways differed. Importantly, major influencing pathways differed using average trait values extracted from global trait databases (e.g. TRY). Synthesis. Investigating changes in multiple facets of plant diversity and their impacts on multidimensional stability under global changes such as nutrient enrichment can improve our understanding of the processes and mechanisms maintaining ecosystem stability.

The present study reports the changes in the phytoplankton community structure in Taklong Island National Marine Reserve (TINMAR), Guimaras Island, Philippines. Quantification of PAH yielded undetectable results, whereas, primary productivity, phytoplankton density, and diversity values were higher as compared to samples before the oil spill and samples from the reference site. Sixty-nine genera representing 6 classes of phytoplankton were identified. Class distribution revealed that diatoms belonging to Coscinodiscophyceae, Bacillariophyceae and Fragilariophyceae were dominant in the area. Class Coscinodiscophyceae was the best represented class with 1,535 individuals/L seawater. The top-ranked diatom genera encountered were Chaetoceros, Skeletonema, Thalassionema, Rhizosolenia, and Bacteriastrum. The shifts in dominance of diatoms over dinoflagellates and fast-growing centric diatoms over pennate diatoms are indicative of a stressed phytoplankton community. Both the Simpsons (1/D’) and Shannon-Weiner (H’) values registered for the 2006 TINMAR samples (1/D’:11.23; H’:1.304) were higher than those obtained from pre-oil impacted samples (1/D’:8.83; H’:1.07) and samples from the reference site (1/D’:8.798; H’:1.039). The present findings provided information on the direct impact of a recent oil spill on phytoplankton community and demonstrate the suitability of using phytoplankton as bioindicators of environmental stress.