A central challenge in microbial ecology is to understand the underlying mechanisms driving community assembly, particularly in the continuum of species sorting and dispersal limitation. However, ...little is known about the relative importance of species sorting and dispersal limitation in shaping marine microbial communities; especially, how they are related to organism types/traits and water depth. Here, we used variation partitioning and null model analysis to compare mechanisms driving bacterial and protist metacommunity dynamics at the basin scale in the East China Sea, based on MiSeq paired-end sequencing of 16S ribosomal DNA (rDNA) and 18S rDNA, respectively, in surface, deep chlorophyll maximum and bottom layers. Our analyses indicated that protist communities were governed more strongly by species sorting relative to dispersal limitation than were bacterial communities; this pattern was consistent across the three-depth layers, albeit to different degrees. Furthermore, we detected that bacteria exhibited wider habitat niche breadths than protists, whereas, passive dispersal abilities were not appreciably different between them. Our findings support the 'size-plasticity' hypothesis: smaller organisms (bacteria) are less environment filtered than larger organisms (protists), as smaller organisms are more likely to be plastic in metabolic abilities and have greater environmental tolerance.
1. The biodiversity-ecosystem functioning debate is a central topic in ecology. Recently, there has been a growing interest in size diversity because body size is sensitive to environmental changes ...and is one of the fundamental characteristics of organisms linking many ecosystem properties. However, how size diversity affects ecosystem functioning is an important yet unclear issue. 2. To fill the gap, with large-scale field data from the East China Sea, we tested the novel hypothesis that increasing zooplankton size diversity enhances top-down control on phytoplankton (H1) and compared it with five conventional hypotheses explaining the top-down control: flatter zooplankton size spectrum enhances the strength of top-down control (H2); nutrient enrichment lessens the strength of top-down control (H3); increasing zooplankton taxonomic diversity enhances the strength of top-down control (H4); increasing fish predation decreases the strength of top-down control of zooplankton on phytoplankton through trophic cascade (H5); increasing temperature intensifies the strength of top-down control (H6). 3. The results of univariate analyses support the hypotheses based on zooplankton size diversity (H1), zooplankton size spectrum (H2), nutrient (H3) and zooplankton taxonomic diversity (H4), but not the hypotheses based on fish predation (H5) and temperature (H6). More in-depth analyses indicate that zooplankton size diversity is the most important factor in determining the strength of top-down control on phytoplankton in the East China Sea. 4. Our results suggest a new potential mechanism that increasing predator size diversity enhances the strength of top-down control on prey through diet niche partitioning. This mechanism can be explained by the optimal predator–prey body-mass ratio concept. Suppose each size group of zooplankton predators has its own optimal phytoplankton prey size, increasing size diversity of zooplankton would promote diet niche partitioning of predators and thus elevates the strength of top-down control.
This study evaluates the rarely observed phenomenon of the simultaneous occurrences of phytoplankton blooms, hypoxia, and upwelling along the Zhejiang coast in the East China Sea. Results show that ...the upwelling uplifted bottom water to 5–10 m below the surface. In the upwelling region, phytoplankton blooms (Chl a = 10.9 μg L−1) occurred and hypoxia or low-oxygen appeared below the surface water. High concentrations of nitrate and phosphate were regenerated in the hypoxic regions, corresponding with mean values (± SD) of 16.9 (± 1.5) and 0.90 (± 0.14) μM, respectively. The upwelling expanded the region of hypoxic water, which nearly reached the surface, thereby increasing the threat to marine life. In addition to fluvial nutrients, the upwelling of water with high nutrient levels, especially phosphates, can enhance phytoplankton blooms. The results suggest that hypoxia can become more severe due to further decomposition of bloom-derived organic matter after blooms crash.
The importance of biodiversity effects on ecosystem functioning across trophic levels, especially via predatory-prey interactions, is receiving increased recognition. However, this topic has rarely ...been explored for marine microbes, even though microbial biodiversity contributes significantly to marine ecosystem function and energy flows. Here we examined diversity and biomass of bacteria (prey) and nanoflagellates (predators), as well as their effects on trophic transfer efficiency in the East China Sea. Specifically, we investigated: (i) predator diversity effects on prey biomass and trophic transfer efficiency (using the biomass ratio of predator/prey as a proxy), (ii) prey diversity effects on predator biomass and trophic transfer efficiency, and (iii) the relationship between predator and prey diversity. We found higher prey diversity enhanced both diversity and biomass of predators, as well as trophic transfer efficiency, which may arise from more balanced diet and/or enhanced niche complementarity owing to higher prey diversity. By contrast, no clear effect was detected for predator diversity on prey biomass and transfer efficiency. Notably, we found prey diversity effects on predator-prey interactions; whereas, we found no significant diversity effect on biomass within the same trophic level. Our findings highlight the importance of considering multi-trophic biodiversity effects on ecosystem functioning in natural ecosystems.
The substantial increase in plastic pollution in marine ecosystems raises concerns about its adverse impacts on the microbial community. Microorganisms (bacteria, phytoplankton) are important ...producers of exopolymeric substances (EPS), which govern the processes of marine organic aggregate formation, microbial colonization, and pollutant mobility. Until now, the effects of nano- and micro-plastics on characteristics of EPS composition have received little attention. This study investigated EPS secretion by four phytoplankton species following exposure to various concentrations of polystyrene nano- and microplastics (55 nm nanoparticles; 1 and 6 μm microparticles). The 55 nm nanoparticles induced less growth/survival (determined on a DNA basis) and produced EPS with higher protein-to-carbohydrate (P/C) ratios than the exposure to microplastic particles. The amount of DNA from the four marine phytoplankton showed a higher negative linear correlation with increasing P/C ratios, especially in response to nanoplastic exposure. These results provide evidence that marine phytoplankton are quite sensitive to smaller-sized plastics and actively modify their EPS chemical composition to cope with the stress from pollution. Furthermore, the release of protein-rich EPS was found to facilitate aggregate formation and surface modification of plastic particles, thereby affecting their fate and colonization. Overall, this work offers new insights into the potential harm of different-sized plastic particles and a better understanding of the responding mechanism of marine phytoplankton for plastic pollution. The data also provide needed information about the fate of marine plastics and biogenic aggregation and scavenging processes.
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•High levels of nano-/micro-plastics can decrease the survival of phytoplankton.•High concentrations of nano-/micro-plastics can trigger protein-rich EPS release.•A negative correlation between cell survival and P/C ratio was established.•Protein-rich EPS can facilitate the aggregate formation.
Upwelling water generally transports abundant nutrients to fertilize the euphotic zone and promotes larger phytoplankton to thrive. In contrast, knowledge about the composition of prokaryotic ...picoplankton associated with the scale of upwelling is limited. In this study, the population compositions of prokaryotic picoplankton, with particular focus on Synechococcus, under two diverse hydrographic conditions in the shelf-margin upwelling system were compared in detail. During the study period of 2009, an upwelling event was observed. In contrast to conventional upwelled water, the surface of this upwelling was covered with a thin layer of nutrient-depleted water. Although the water exchange created a low-nutrient stock environment, which fell below traditional chemical detection limits, its flux was likely sufficient to support the growth of the Synechococcus clade-II lineage. In comparison with the hydrography in 2009, no obvious upwelling occurred, and oligotrophic water primarily occupied the upper layer during the study period of 2010. The abundance of Synechococcus significantly declined to approximately half its numbers observed in 2009. While the Synechococcus clade-II were still the predominant population, their proportion in the 16S rRNA gene library decreased to approximately 50%. The remaining part was replaced with α-Proteobacteria and various heterotrophic bacteria. The results of the present study, combined with those obtained in previous studies, yield a more comprehensive understanding of the phytoplankton community dynamics in this varied ecosystem.
Spatial variation of communities composition (metacommunities) results from multiple assembly mechanisms, including environmental filtering and dispersal; however, whether and why the relative ...importance of the assembly mechanisms in shaping bacterial metacommunity changes through time in marine pelagic systems remains poorly studied. Here, we applied the elements of metacommunity structure framework and the variation partitioning framework to examine whether temporal variation of hydrographic conditions influences bacterioplankton metacommunity dynamics in the southern East China Sea (ECS). The spatiotemporal variation of bacterial communities composition was revealed using 454 pyrosequencing of 16S rDNA. In addition to the whole bacterial community, we analyzed four dominant taxonomic groups (Cyanobacteria, Alphaproteobacteria, Gammaproteobacteria, and Actinobacteria) separately. Our analyses indicate that, considering the whole community level, the determinism of metacommunity structure varied among seasons. When the degree of connectivity was low (December), the metacommunity exhibited random distribution and was explained mainly by the environmental component. However, Clementsian metacommunity was found at intermediate connectivity (May), during which the environmental and spatial predictors were both significant. When connectivity was high (August), a random distribution pattern was found and no significant effect of environmental filtering or dispersal limitation was detected. Nevertheless, when considering different taxonomic groups, the differences in metacommunity dynamics among groups were found. Our results suggest that the driving forces of metacommunity dynamics varied depending on hydrography, as the degrees of environmental heterogeneity and connectivity among habitat patches were determined by circulation pattern. Moreover, mechanisms varied among different taxonomic groups, suggesting that differential dispersal capacity among taxonomic groups should be integrated into community assembly studies.
•Microplastics can be transferred by bubble bursting at the water–air interface.•First study on plastic-gel enhancement of microplastic transfer from water to air.•High salinity, gel concentration, ...and viscosity induced microplastic transfer to air.•Plastic-gel formation via cation-linking bridges modulates microplastic transfer capacity.
The pervasiveness of microplastics (MPs) in global oceans is raising concerns about their adverse impacts on ecosystems. The mechanistic understanding of MP transport is critical for evaluating its fate, flux, and ecological risks specifically. Currently, bubble bursting is believed to represent an important route for MP transfer from sea surfaces to the atmosphere. However, the detailed mechanisms of the complex physico-chemical interactions between MPs, water composition, and gel particles in the air–sea interface remain unknown. Our results suggested three steps for MP transfer between air–sea phases: (1) MPs incorporating into gel aggregates in the water column; (2) further accumulation of plastic-gel aggregate in the surface layer phase; finally (3) ejection of aggregates from the sea when bubbles of trapped air rise to the surface and burst. The water composition (e.g., high salinity, gel concentration and viscosity) can modulate plastic-gel aggregation and subsequent transport from water to the atmosphere. The possible mechanism may be closely tied to the formation of plastic-gel via cation-linking bridges, thereby enhancing plastic-gel ejection into air. Collectively, this work offers unique insights into the role of marine plastic-gels in determining MP fate and transport, especially at air–sea interfaces. The data also provide a better understanding of the corresponding mechanism that may explain the fates of missing plastics in the ocean.
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It has been documented that the global proliferation of dam construction on the major river has reduced nutrient and sediment loading to coastal environments. As a consequence, dams can impact marine ...ecological systems by changing nutrient concentrations and ratios in the coastal zone. From 1998–2004, we conducted a high resolution oceanographic investigation of the East China Sea (ECS) before and after the first filling phase (June 2003) of the Three‐Gorges Dam (TGD). We found that the Si:N ratio in the River affected region changed from 1.5 in 1998 to 0.4 in 2004 with sediment loading significantly reducing (about 55%) at the Datong station after June 2003. Most importantly, we found that the PP had declined by 86% between 1998 and 2003, both measured during the high flood season. The results suggest that the ECS ecosystem may respond sensitively to changes in the nutrient supply arising from the TGD project.
Prey availability plays an important role in determining larval fish survival. Numerous studies have found close relationships between the density of mesozooplankton and larval fishes; however, ...emerging studies suggest that small-size zooplankton are more important prey for some larval fish species. One arising question is whether the size of zooplankton determines the relationship between zooplankton and larval fish community in natural environments. To address this question, we collected small-size (50-200 μm) zooplankton, mesozooplankton (> 330 μm), and larval fish using three different mesh-size (50, 330, 1000 μm, respectively) nets in the East China Sea, and examined their relationships in density. Both meso- and small-size zooplankton densities showed positive relationships with larval fish density, while the relationship is much stronger for the small-size zooplankton. Specifically, the smallest size classes (50-75 and 75-100 μm) of small-size zooplankton showed the highest positive relationships with larval fish density. Temperature, salinity, and chlorophyll-a concentration did not significantly explain larval fish density. Based on these findings, we demonstrate the importance of considering prey size when investigating prey availability for larval fishes.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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