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DECOMPOSITIONS OF NANO g^sup #^-CONTINUITY VIA IDEALIZATION
A subset E of an ideal nano topological space (U,xR(X), J) is called: 1. ag#-nJ-open if G c a-nJ-int(E) whenever G c E and G is nag-closed in U. 2. 7#-nJ-open if G c p-nJ-int(E) whenever G c E and G is nag-closed in U. 3. /i#-nJ-open if G c s-nJ-int(E) whenever G c £\" and G is nag-closed in //. [...]we have, G c a-nO-int(E) whenever G c E and G is nag-closed in U. Now, G c E n nint (ncl* (nint (E))) c £\" n nint(ncl(nint(E))) = na-int(E). [...]we have, G c p-nO-int(E) whenever G c £\" and G is nag-closed in //. [...]G c £\" n nint (ncl* (Ey) c £\" n nint(ncl(E)) = np-int(E). [...]we have, G c s-nO-int(E) whenever G c £\" and G is nag-closed in U. Now, G c £\" n ncl*(nint(E~)~) c £\" n ncl(nint(E)) = s-int(E). [...]we have, G c int(E) whenever G c £\" and G is nag-closed in U. Now, G c nint ((nint (E))*) U nint(E) = nint ((nint (E))*) U nint (nint (Ey) c runt [(runt (£\"))* U nint^)] = nint (ncl* (nint (E))). [...]we have, G c a-nO-int(E) whenever G c £\" and G is nag-closed in //. [...]G c £\" n nint (ncl* (nint (E))) c £\" n nint (ncl* (E)) = p-nJ-int(E). [...]we have, G c a-nO-int(E) whenever G c E and G is nag-closed in U. Now, G c E n nint(ncl*(nint(E))) c £\" n ncZ*(nint(E~)~) = s-nJ-int(E). Assume that E is 7#-nJ-open and g\\-nJ-set in U. Let G c E and G be nag-closed in U. Since £\" is a gf-nJ-set in U, E = P n Q, where P is ng#-open and Q is a t-nJ-set. [...]G is nag-closed and P is ng#-open implies G c nint(P). Since £\" is 7#-nJ-open, G c p-nJ-nint(E) = E C\\ nint(ncl*(E)) = (P r\\Q) n nint{ncl\\P n (?)) c (P n (?) n nint{ncl\\P) n ncl\\Q)) = PnQ n nint{ncl\\P)) n nint(ncl*(Q)).
Journal Article
Plankton networks driving carbon export in the oligotrophic ocean
The biological carbon pump is the process by which CO
2
is transformed to organic carbon via photosynthesis, exported through sinking particles, and finally sequestered in the deep ocean. While the intensity of the pump correlates with plankton community composition, the underlying ecosystem structure driving the process remains largely uncharacterized. Here we use environmental and metagenomic data gathered during the
Tara
Oceans expedition to improve our understanding of carbon export in the oligotrophic ocean. We show that specific plankton communities, from the surface and deep chlorophyll maximum, correlate with carbon export at 150 m and highlight unexpected taxa such as Radiolaria and alveolate parasites, as well as
Synechococcus
and their phages, as lineages most strongly associated with carbon export in the subtropical, nutrient-depleted, oligotrophic ocean. Additionally, we show that the relative abundance of a few bacterial and viral genes can predict a significant fraction of the variability in carbon export in these regions.
Plankton communities in the top 150 m of the nutrient-depleted, oligotrophic global ocean that are most associated with carbon export include unexpected taxa, such as Radiolaria, alveolate parasites, and
Synechococcus
and their phages, and point towards potential functional markers predicting a significant fraction of the variability in carbon export in these regions.
Oceanic plankton associated with carbon flux
Using environmental and metagenomic data collected during the
Tara
Oceans expedition, this study examines the plankton communities that are most strongly associated with carbon export in the top 150 metres of the nutrient-depleted, oligotrophic global ocean. This work highlights some unexpected taxa as lineages strongly associated with carbon export, including Dinophyceae and Rhizaria, and alveolate parasites, in addition to
Synechococcus
and their phages, and suggests that the relative abundance of just a few bacterial and viral genes can predict most of the variability in carbon export in these regions.
Journal Article
Diversity and temporal patterns of planktonic protist assemblages at a Mediterranean Long Term Ecological Research site
Abstract
We tracked temporal changes in protist diversity at the Long Term Ecological Research (LTER) station MareChiara in the Gulf of Naples (Mediterranean Sea) on eight dates in 2011 using a metabarcoding approach. Illumina analysis of the V4 and V9 fragments of the 18S rDNA produced 869 522 and 1 410 071 sequences resulting in 6517 and 6519 OTUs, respectively. Marked compositional variations were recorded across the year, with less than 2% of OTUs shared among all samples and similar patterns for the two marker tags. Alveolata, Stramenopiles and Rhizaria were the most represented groups. A comparison with light microscopy data indicated an over-representation of Dinophyta in the sequence dataset, whereas Bacillariophyta showed comparable taxonomic patterns between sequence and light microscopy data. Shannon diversity values were stable from February to September, increasing thereafter with a peak in December. Community variance was mainly explained by seasonality (as temperature), trophic status (as chlorophyll a), and influence of coastal waters (as salinity). Overall, the background knowledge of the system provided a sound context for the result interpretation, showing that LTER sites provide an ideal setting for high-throughput sequencing (HTS) metabarcoding characterisation of protist assemblages and their relationships with environmental variations.
Temporal diversity and community structure of the entire protist assemblage from the Gulf of Naples assessed using high throughput sequencing and light microscopy.
Journal Article
Response of the eukaryotic plankton community to the cyanobacterial biomass cycle over 6 years in two subtropical reservoirs
Although it is widely recognized that cyanobacterial blooms have substantial influence on the plankton community in general, their correlations with the whole community of eukaryotic plankton at longer time scales remain largely unknown. Here, we investigated the temporal dynamics of eukaryotic plankton communities in two subtropical reservoirs over a 6-year period (2010–2015) following one cyanobacterial biomass cycle—the cyanobacterial bloom (middle 2010), cyanobacteria decrease (late 2010–early 2011), non-bloom (2011–2014), cyanobacteria increase, and second bloom (late 2014–2015). The eukaryotic community succession that strongly correlated with this cyanobacterial biomass cycle was divided into four periods, and each period had distinct characteristics in cyanobacterial biomass and environments in both reservoirs. Integrated co-occurrence networks of eukaryotic plankton based on the whole study period revealed that the cyanobacterial biomass had remarkably high network centralities, and the eukaryotic OTUs that had stronger correlations with the cyanobacterial biomass exhibited higher centralities. The integrated networks were also modularly responded to different eukaryotic succession periods, and therefore correlated with the cyanobacterial biomass cycle. Moreover, sub-networks based on the different eukaryotic succession periods indicated that the eukaryotic co-occurrence patterns were not constant but varied largely associating with the cyanobacterial biomass. Based on these long-term observations, our results reveal that the cyanobacterial biomass cycle created distinct niches between persistent bloom, non-bloom, decrease and increase of cyanobacteria, and therefore associated with distinct eukaryotic plankton patterns. Our results have important implications for understanding how complex aquatic plankton communities respond to cyanobacterial blooms under the changing environments.
Journal Article
Das Universum, die Tiefsee und wir
[...]Is Where We Start From sind sie neben den wieder-kehrenden Pflanzen die einzigen lebendigen Entitäten. Auf den ersten Blick wirkt die Wahrneh-mung von Raum und Arbeiten \"blurry\": recycelte Robotertiere auf Podesten, kinetische bzw. mechanische Skulpturen, die sich auf den vagen Konturen einer Landschaft versammeln. Diese versammelt eine atmende Maschine, zwei Liegestühle sowie die Zwei-Kanal-Videoarbeit Staying With The Trouble - eine Art Chillout-Environment, das Makro-aufnahmen von Monarchfaltern, Bakterien und Pilzen zeigt.
Journal Article
Distinct patterns and processes of abundant and rare eukaryotic plankton communities following a reservoir cyanobacterial bloom
Plankton communities normally consist of few abundant and many rare species, yet little is known about the ecological role of rare planktonic eukaryotes. Here we used a 18S ribosomal DNA sequencing approach to investigate the dynamics of rare planktonic eukaryotes, and to explore the co-occurrence patterns of abundant and rare eukaryotic plankton in a subtropical reservoir following a cyanobacterial bloom event. Our results showed that the bloom event significantly altered the eukaryotic plankton community composition and rare plankton diversity without affecting the diversity of abundant plankton. The similarities of both abundant and rare eukaryotic plankton subcommunities significantly declined with the increase in time-lag, but stronger temporal turnover was observed in rare taxa. Further, species turnover of both subcommunities explained a higher percentage of the community variation than species richness. Both deterministic and stochastic processes significantly influenced eukaryotic plankton community assembly, and the stochastic pattern (e.g., ecological drift) was particularly pronounced for rare taxa. Co-occurrence network analysis revealed that keystone taxa mainly belonged to rare species, which may play fundamental roles in network persistence. Importantly, covariations between rare and non-rare taxa were predominantly positive, implying multispecies cooperation might contribute to the stability and resilience of the microbial community. Overall, these findings expand current understanding of the ecological mechanisms and microbial interactions underlying plankton dynamics in changing aquatic ecosystems.
Journal Article
Marked changes in diversity and relative activity of picoeukaryotes with depth in the world ocean
Microbial eukaryotes are key components of the ocean plankton. Yet, our understanding of their community composition and activity in different water layers of the ocean is limited, particularly for picoeukaryotes (0.2–3 µm cell size). Here, we examined the picoeukaryotic communities inhabiting different vertical zones of the tropical and subtropical global ocean: surface, deep chlorophyll maximum, mesopelagic (including the deep scattering layer and oxygen minimum zones), and bathypelagic. Communities were analysed by high-tthroughput sequencing of the 18S rRNA gene (V4 region) as represented by DNA (community structure) and RNA (metabolism), followed by delineation of Operational Taxonomic Units (OTUs) at 99% similarity. We found a stratification of the picoeukaryotic communities along the water column, with assemblages corresponding to the sunlit and dark ocean. Specific taxonomic groups either increased (e.g., Chrysophyceae or Bicosoecida) or decreased (e.g., Dinoflagellata or MAST-3) in abundance with depth. We used the rRNA:rDNA ratio of each OTU as a proxy of metabolic activity. The highest relative activity was found in the mesopelagic layer for most taxonomic groups, and the lowest in the bathypelagic. Altogether, we characterize the change in community structure and metabolic activity of picoeukaryotes with depth in the global ocean, suggesting a hotspot of activity in the mesopelagic.
Journal Article
Marine mixotrophy increases trophic transfer efficiency, mean organism size, and vertical carbon flux
Mixotrophic plankton, which combine the uptake of inorganic resources and the ingestion of living prey, are ubiquitous in marine ecosystems, but their integrated biogeochemical impacts remain unclear. We address this issue by removing the strict distinction between phytoplankton and zooplankton from a global model of the marine plankton food web. This simplification allows the emergence of a realistic trophic network with increased fidelity to empirical estimates of plankton community structure and elemental stoichiometry, relative to a system in which autotrophy and heterotrophy are mutually exclusive. Mixotrophy enhances the transfer of biomass to larger sizes classes further up the food chain, leading to an approximately threefold increase in global mean organism size and an ∼35% increase in sinking carbon flux.
Journal Article
Diel transcriptional response of a California Current plankton microbiome to light, low iron, and enduring viral infection
Phytoplankton and associated microbial communities provide organic carbon to oceanic food webs and drive ecosystem dynamics. However, capturing those dynamics is challenging. Here, an in situ, semi-Lagrangian, robotic sampler profiled pelagic microbes at 4 h intervals over ~2.6 days in North Pacific high-nutrient, low-chlorophyll waters. We report on the community structure and transcriptional dynamics of microbes in an operationally large size class (>5 μm) predominantly populated by dinoflagellates, ciliates, haptophytes, pelagophytes, diatoms, cyanobacteria (chiefly
Synechococcus)
, prasinophytes (chiefly
Ostreococcus)
, fungi, archaea, and proteobacteria. Apart from fungi and archaea, all groups exhibited 24-h periodicity in some transcripts, but larger portions of the transcriptome oscillated in phototrophs. Periodic photosynthesis-related transcripts exhibited a temporal cascade across the morning hours, conserved across diverse phototrophic lineages. Pronounced silica:nitrate drawdown, a high flavodoxin to ferredoxin transcript ratio, and elevated expression of other Fe-stress markers indicated Fe-limitation. Fe-stress markers peaked during a photoperiodically adaptive time window that could modulate phytoplankton response to seasonal Fe-limitation. Remarkably, we observed viruses that infect the majority of abundant taxa, often with total transcriptional activity synchronized with putative hosts. Taken together, these data reveal a microbial plankton community that is shaped by recycled production and tightly controlled by Fe-limitation and viral activity.
Journal Article