Transparent Exopolymer Particles Formation Research Articles

Spatio-temporal variations in organic carbon composition driven by two different major phytoplankton communities in the Ross Sea, Antarctica

The compositions of organic carbon could be important in determining biological carbon pump efficiency. However, little information on them in relation to each algal assemblage is currently available in the Ross Sea. Here, we investigated the seasonal variations in organic carbon composition and the relative abundance of each organic carbon, including particulate organic carbon (POC), dissolved organic carbon (DOC), and transparent exopolymer particles (TEPs), characterized by different algal groups in the Ross Sea. The average POC and DOC contributions to the total organic carbon (TOC = POC + DOC) were 13.8 ± 3.7 % and 86.2 ± 3.7 % in mid-January 2019 and 20.9 ± 4.1 % and 79.1 ± 4.1 % in February–March 2018, respectively. The carbon content of TEP (TEP-C) contributed 19.6 ± 11.7 % and 4.6 ± 7.0 % of POC and TOC in mid-January and 36.2 ± 14.8 % and 9.0 ± 6.7 % in February–March, respectively. We found that the organic carbon compositions were affected by seasonal variations in the phytoplankton bloom phase, physical characteristics, and phytoplankton community structure. DOC concentrations and contributions to the TOC increased as phytoplankton cells became senescent in mid-January and decreased in February–March when phytoplankton were relatively active. From February–March, the deepened mixed layer depth encouraged TEP formation, subsequently increasing the TEP contributions. Regardless of the sampling season, all organic carbon concentrations per unit Chl-a were significantly higher in P. antarctica–abundant groups. The DOC contributions to the TOC were correspondingly higher at the P. antarctica–abundant stations in mid-January, which indicates that P. antarctica could be also important in the DOC contributions in the Ross Sea. The rapid alteration in environmental characteristics and phytoplankton community structures in the Ross Sea due to climate change could affect the organic carbon pool at the euphotic layer which consequently could determine the efficiency of the biological pump.

Transparent Exopolymer Particles in Drinking Water Treatment-A Brief Review.

Transparent exopolymer particles (TEP) have been described as a class of particulate acidic polysaccharides, which are commonly found in various surface waters. Due to their unique physicochemical characteristics, they have recently been receiving increasing attention on their effects in water treatment. Currently, TEP are commonly known as clear, gel-like polysaccharides. This review first introduced the definition of TEP in water treatment and the relationship between TEP and algal organic matter (AOM). Further, in the review, the authors attempt to offer a holistic view and critical analysis concerning the research on TEPs in source water reservoirs, water plants and membrane treatment processes. It was clearly demonstrated in this review that the formation of TEP in source water reservoirs is largely related to water quality and phytoplankton, and the seasonal water stratification may indirectly affect the formation of TEP. In the waterworks, the relationship between TEP and water treatment process is mutual and there is limited research on this relationship. Finally, the mechanism of TEP-induced membrane fouling and the effect of alleviating TEP-induced membrane fouling is discussed in this review. The TEP removed by ultrafiltration can be recombined after membrane, and the recombination mechanism may be an important way to reduce reverse osmosis membrane contamination.

Effect of Temperature on the Release of Transparent Exopolymer Particles (TEP) and Aggregation by Marine Diatoms (Thalassiosira weissflogii and Skeletonema marinoi)

The presence of diatoms is accompanied by the production of a large amount of extracellular polymeric substances, which are mainly composed of carbohydrates. Transparent exopolymer particles (TEP) are a large class of extracellular polymeric substances with high stickiness that promotes the formation of aggregates and marine snow, which affects marine bio-carbon pump efficiency. The purpose of this research was to determine how temperature increases affect the allocation of cellular carbohydrates and the formation and aggregation of TEP. The results showed that the responses of two different diatom species (Thalassiosira weissflogii and Skeletonema marinoi) differed according to temperature. The cell density and chlorophyll a concentration of the former were not significantly correlated with temperature, while those of the latter were significantly decreased with increasing temperature. This indicates that the two species of diatom may have different heat tolerance ranges. A temperature increase will promote significant formation of TEP by both types of diatoms, including aggregation of S. marinoi as the temperature rises, meaning that the high temperature will produce an aggregate with a larger particle size and thus may increase the sedimentation rate of organic carbon. Moreover, the TEP aggregation of T. weissflogii did not increase; therefore, its particle size was smaller, and so it may remain on the sea surface at high temperatures for longer periods. These influences have a profound impact on the biogeochemical cycling of carbon.

Enhanced formation of transparent exopolymer particles (TEP) under turbulence during phytoplankton growth

AbstractSmall-scale turbulence in the surface ocean is ubiquitous, influencing phytoplankton dynamics with consequences for energy flow. The underlying mechanisms that drive changes in phytoplankton dynamics under turbulence are not well constrained. We investigated growth of four phytoplankton species at different turbulence levels in oscillating grid tanks. We also measured transparent exopolymer particles (TEP) from phytoplankton exudates, which play a major role in biogeochemical fluxes in the ocean. Turbulence levels in the tanks reflected in situ conditions in surface waters from the open ocean to higher turbulent environments such as estuaries. Growth rates were unaffected by turbulence while TEP concentrations as xanthan gum (XG) equivalents normalized to algal cells showed generally higher levels in the high turbulence compared to the low turbulence treatments particularly during initial algal growth. Results from a mixing experiment without algal cells and XG also revealed enhanced formation of TEP-like particles under high mixing conditions, indicating that TEP formation in the phytoplankton turbulence treatments was mainly driven by physical processes, such as enhanced encounter rates of TEP-precursors under high mixing. Our results underline the importance of small-scale turbulence on TEP formation with possible consequences for particle aggregation and vertical carbon fluxes in the ocean.

Concentrations and distribution of transparent exopolymer particles in a eutrophic coastal sea: a case study of the Changjiang (Yangtze River) estuary

Transparent exopolymer particles (TEPs) contribute to carbon export and can represent a significant part of the carbon pool, most notably in eutrophic systems. This study represents the first investigation of the concentrations and distribution of TEPs in the Changjiang (Yangtze River) estuary, one of the most eutrophic coastal seas in the world. The concentration of TEPs was determined on a seasonal basis (spring, summer and autumn), and the distribution patterns of TEPs were studied with respect to physical, chemical and biological conditions. Spatially, TEP concentrations exhibited a significant positive correlation with chlorophyll-a concentrations in spring and summer, which implies a consistent production of TEPs by phytoplankton cells. Vertically, TEP concentrations decreased gradually from the surface layer to the bottom layer in spring and summer, but were distributed homogenously in the water column in autumn. Values of nitrogen:phosphorus ratio (N:P) were found to have a significant positive correlation with TEP concentrations in summer, indicating that a P limitation would probably accelerate production and formation of TEPs. TEP-carbon (TEP-C) concentration was found to be similar to phytoplankton-C in the study area, highlighting the fact that TEP-C could represent a significant fraction of the particulate organic carbon pool in the Changjiang (Yangtze River) estuary.

Enhanced formation of transparent exopolymer particles (TEP) under turbulence during phytoplankton growth

Enhanced formation of transparent exopolymer particles (TEP) under turbulence during phytoplankton growth

Prochlorococcus as a Possible Source for Transparent Exopolymer Particles (TEP).

Transparent exopolymer particles (TEP), usually associated with phytoplankton blooms, promote the formation of marine aggregates. Their exportation to deep waters is considered a key component of the biological carbon pump. Here, we explored the role of solar radiation and picocyanobacteria in the formation of TEP in oligotrophic surface waters of the Atlantic and Pacific Oceans in ten on-deck incubation experiments during the Malaspina 2010 Expedition. TEP concentrations were low on the ocean’s surface although these concentrations were significantly higher on the surface of the Pacific (24.45 ± 2.3 μg XG Eq. L-1) than on the surface of the Atlantic Ocean (8.18 ± 4.56 μg XG Eq. L-1). Solar radiation induced a significant production of TEP in the on-deck experiments from the surface water of the Pacific Ocean, reaching values up to 187.3 μg XG Eq. L-1 compared with the low production observed in the dark controls. By contrast, TEP production in the Atlantic Ocean experiments was lower, and its formation was not related to the light treatments. Prochlorococcus sp. from the surface ocean was very sensitive to solar radiation and experienced a high cell decay in the Pacific Ocean experiments. TEP production in the on-deck incubation experiments was closely related to the observed cell decay rates of Prochlorococcus sp., suggesting that this picocyanobacteria genus is a potential source of TEP. The evidence to propose such potential role was derived experimentally, using natural communities including the presence of several species and a variety of processes. Laboratory experiments with cultures of a non-axenic strain of Prochlorococcus marinus were then used to test TEP production by this genus. TEP concentrations in the culture increased with increasing cell abundance during the exponential phase, reaching the highest TEP concentration at the beginning of the stationary phase. The average TEP concentration of 1474 ± 226 μg XG Eq. L-1 (mean ± SE) observed at the stationary phase of P. marinus cultures is comparable with the values reported in the literature for diatom cultures, also growing in non-axenic as well as axenic cultures. Our results identify Prochlorococcus sp. as a possible relevant source of TEP in the oligotrophic ocean.

Experimental evidence of formation of transparent exopolymer particles (TEP) and POC export provoked by dust addition under current and high pCO2 conditions.

The evolution of organic carbon export to the deep ocean, under anthropogenic forcing such as ocean warming and acidification, needs to be investigated in order to evaluate potential positive or negative feedbacks on atmospheric CO2 concentrations, and therefore on climate. As such, modifications of aggregation processes driven by transparent exopolymer particles (TEP) formation have the potential to affect carbon export. The objectives of this study were to experimentally assess the dynamics of organic matter, after the simulation of a Saharan dust deposition event, through the measurement over one week of TEP abundance and size, and to evaluate the effects of ocean acidification on TEP formation and carbon export following a dust deposition event. Three experiments were performed in the laboratory using 300 L tanks filled with filtered seawater collected in the Mediterranean Sea, during two ‘no bloom’ periods (spring at the start of the stratification period and autumn at the end of this stratification period) and during the winter bloom period. For each experiment, one of the two tanks was acidified to reach pH conditions slightly below values projected for 2100 (~ 7.6–7.8). In both tanks, a dust deposition event of 10 g m-2 was simulated at the surface. Our results suggest that Saharan dust deposition triggered the abiotic formation of TEP, leading to the formation of organic-mineral aggregates. The amount of particulate organic carbon (POC) exported was proportional to the flux of lithogenic particles to the sediment traps. Depending on the season, the POC flux following artificial dust deposition ranged between 38 and 90 mg m-2 over six experimental days. Such variability is likely linked to the seasonal differences in the quality and quantity of TEP-precursors initially present in seawater. Finally, these export fluxes were not significantly different at the completion of the three experiments between the two pH conditions.

Transparent exopolymer particles (TEP) are driven by chlorophyll a and mainly confined to the euphotic zone in a deep subalpine lake

Microgels such as transparent exopolymer particles (TEP) can be as important in freshwater as they are in the ocean because they constitute microenvironments of unique physical, chemical, and biological properties. Previous studies have shown that TEP concentrations can significantly contribute to the organic carbon pool in both marine and freshwater. Despite the relevance of TEP as a microbial substrate in aggregate formation, their fate within the hypolimnion has not been studied in deep lakes. This work is the first extensive analysis on the TEP space–time distribution and their role in the carbon cycle of Lake Maggiore, a subalpine deep lake where the presence of TEP became macroscopically evident in recent times. Our study demonstrated that in oligotrophic Lake Maggiore, characterized by low total organic carbon (TOC) concentration (summer max ~1.8 mg L−1), TEP can reach 36% of TOC in the photic layer while its weighted average in the hypolimnion below 100 m depth is 1.7%. We therefore hypothesised that most TEP is recycled in the upper layers, and that its contribution as carbon burial in the sediment may be lower than expected. TEP concentration exhibited a clear seasonal variability mirroring that of the autotrophic plankton. The models explain TEP variability as a function of chlorophyll a, a proxy for phytoplankton biomass, and a weaker effect of picocyanobacteria. TOC, but not TEP, influenced the abundance of bacterial aggregates, leaving open the role of bacteria and phytoplankton association in TEP formation.

Transparent exopolymer particles (TEP)-associated membrane fouling at different Na+ concentrations

Membrane filtration has been widely applied for water treatment, wastewater reclamation and seawater desalination. Although extensive research work has been conducted to better understand the fouling mechanism under various conditions, little has been known about the transparent exopolymer particles (TEP)-associated membrane fouling at different Na+ concentrations. In this study, the influence of Na+ concentration on the TEP formation as well as the filtration behaviors of alginate blocks was investigated. Results showed that increasing Na+ concentration substantially reduced the TEP formation from all types of alginate blocks, thus preventing the cake layer development on the membrane surface. As a result, the TEP-associated membrane fouling was found to be kinetically slower and much less at higher Na+ level. Furthermore, filtration tests of alginate blocks at freshwater and seawater conditions were also conducted, showing that TEP-associated fouling in freshwater is much server than that in seawater at the defined conditions. This study reveals that the TEP formation is significantly influenced by the chemistry condition of bulk solution and membrane fouling is profoundly affected by the TEP levels in feed water.

Exopolymer production as a function of cell permeability and death in a diatom (Thalassiosira weissflogii) and a cyanobacterium (Synechococcus elongatus).

Exopolymer particles are found throughout the ocean and play a significant biogeochemical role in carbon cycling. Transparent exopolymer particles (TEP) are composed of acid polysaccharides, and Coomassie staining particles (CSP) are proteins. TEPs have been extensively studied in the ocean, while CSP have been largely overlooked. The objective of this research was to determine the role of stress and cell permeability in the formation of TEP and CSP. The diatom Thalassiosira weissflogii and cyanobacterium Synechococcus elongatus were grown in batch cultures and exposed to hydrogen peroxide (0, 10, and 100μM) as an environmental stressor. There was no correlation between TEP and CSP concentrations, indicating that they are different populations of particles rather than different chemical components of the same particles. CSP concentrations were not affected by hydrogen peroxide concentration and did not correlate with indicators of stress and cell death. In contrast, TEP concentrations in both taxa were correlated with a decrease in the effective quantum yield of photosystem II, increased activity of caspase-like enzymes, and an increase in the proportion of the population with permeable cell membranes, indicating that TEP production was associated with the process of cell death. These data show that different environmental factors and physiological processes affected the production of TEP and CSP by phytoplankton. TEP and CSP are separate populations of exopolymer particles with potentially different biogeochemical roles in the ocean.

Dynamics of transparent exopolymer particles (TEP) during the VAHINE mesocosm experiment in the New Caledonian lagoon

Abstract. In the marine environment, transparent exopolymeric particles (TEP) produced from abiotic and biotic sources link the particulate and dissolved carbon pools and are essential vectors enhancing vertical carbon flux. We characterized spatial and temporal dynamics of TEP during the VAHINE experiment that investigated the fate of diazotroph-derived nitrogen and carbon in three replicate dissolved inorganic phosphorus (DIP)-fertilized 50 m3 enclosures in the oligotrophic New Caledonian lagoon. During the 23 days of the experiment, we did not observe any depth-dependent changes in TEP concentrations in the three sampled depths (1, 6, 12 m). TEP carbon (TEP-C) content averaged 28.9 ± 9.3 and 27.0 ± 7.2 % of total organic carbon (TOC) in the mesocosms and surrounding lagoon respectively and was strongly and positively coupled with TOC during P2 (i.e., days 15–23). TEP concentrations in the mesocosms declined for the first 9 days after DIP fertilization (P1 = days 5–14) and then gradually increased during the second phase. Temporal changes in TEP concentrations paralleled the growth and mortality rates of the diatom–diazotroph association of Rhizosolenia and Richelia that predominated the diazotroph community during P1. By P2, increasing total primary and heterotrophic bacterial production consumed the supplemented P and reduced availability of DIP. For this period, TEP concentrations were negatively correlated with DIP availability and turnover time of DIP (TDIP), while positively associated with enhanced alkaline phosphatase activity (APA) that occurs when the microbial populations are P stressed. During P2, increasing bacterial production (BP) was positively correlated with higher TEP concentrations, which were also coupled with the increased growth rates and aggregation of the unicellular cyanobacterial Group C (UCYN-C) diazotrophs that bloomed during this period. We conclude that the composite processes responsible for the formation and breakdown of TEP yielded a relatively stable TEP pool available as both a carbon source and facilitating aggregation and flux throughout the experiment. TEP were probably mostly influenced by abiotic physical processes during P1, while biological activity (BP, diazotrophic growth and aggregation, export production) mainly impacted TEP concentrations during P2 when DIP availability was limited.

New insights into transparent exopolymer particles (TEP) formation from precursor materials at various Na+/Ca2+ ratios.

Transparent exopolymer particles (TEP) are planktonic, organic microgels which play significant roles in cycling of carbon and trace elements, aggregation of particles, feeding and accommodating microbes as well as development of biofilms. However, few studies are available on the mechanism of TEP formation in various water environments. Here we investigate the formation of TEP with alginate blocks as precursors at various Na+/Ca2+ ratios to simulate the situations in different aquatic environments (e.g. freshwater and seawater). We found that the formation of TEP from precursor materials studied was essentially determined by the Ca2+ concentration at a fixed sodium concentration, while Na+ at high Na+/Ca2+ ratio out-competed Ca2+ for the binding sites on the precursor molecules, leading to a significantly decreased trend of TEP formation. Our results indicate that a more abundant TEP could be expected in freshwater than in seawater, and we also discuss the engineering implications of the findings.

Transparent exopolymer particle production and aggregation by a marine planktonic diatom (Thalassiosira weissflogii) at different growth rates.

Transparent exopolymer particles (TEP) play an important role in the ocean carbon cycle as they are sticky and affect particle aggregation and the biological carbon pump. We investigated the effect of growth rate on TEP production in nitrogen limited semi-continuous cultures of the diatom Thalassiosira weissflogii (Grunow) G. Fryxell & Hasle. Steady-state diatom concentrations and other indicators of biomass (chl a, and total carbohydrate) were inversely related to growth rate, while individual cell volume increased with growth rate. There was no change in total TEP area with growth rate; however, individual TEP were larger at high growth rates and the number of individual TEP particles was lower. TEP concentration per cell was higher at higher growth rates. SYTOX Green staining showed that <5% of the diatom population had permeable cell membranes, with the proportion increasing at low growth rates. However, TEP production rates were greater at high growth rates, refuting our hypothesis that TEP formation is dependent on dying cells with compromised cell membranes in a diatom population. Measurements of particle size distribution in the cultures using laser scattering showed that they were most aggregated at high growth rates. These results indicate a coupling between TEP production and growth rate in diatoms under N limitation, with fast growing T.weissflogii producing more TEP and aggregates.

Natural oil slicks fuel surface water microbial activities in the northern Gulf of Mexico.

We conducted a series of roller tank incubations with surface seawater from the Green Canyon oil reservoir, northern Gulf of Mexico, amended with either a natural oil slick (GCS-oil) or pristine oil. The goal was to test whether bacterial activities of natural surface water communities facilitate the formation of oil-rich marine snow (oil snow). Although oil snow did not form during any of our experiments, we found specific bacterial metabolic responses to the addition of GCS-oil that profoundly affected carbon cycling within our 4-days incubations. Peptidase and β-glucosidase activities indicative of bacterial enzymatic hydrolysis of peptides and carbohydrates, respectively, were suppressed upon the addition of GCS-oil relative to the non-oil treatment, suggesting that ascending oil and gas initially inhibits bacterial metabolism in surface water. Biodegradation of physically dispersed GCS-oil components, indicated by the degradation of lower molecular weight n-alkanes as well as the rapid transformation of particulate oil-carbon (C: N >40) into the DOC pool, led to the production of carbohydrate- and peptide-rich degradation byproducts and bacterial metabolites such as transparent exopolymer particles (TEP). TEP formation was highest at day 4 in the presence of GCS-oil; in contrast, TEP levels in the non-oil treatment already peaked at day 2. Cell-specific enzymatic activities closely followed TEP concentrations in the presence and absence of GCS-oil. These results demonstrate that the formation of oil slicks and activities of oil-degrading bacteria result in a temporal offset of microbial cycling of organic matter, affecting food web interactions and carbon cycling in surface waters over cold seeps.

Abundance and patterns of transparent exopolymer particles (TEP) in Arctic floodplain lakes of the Mackenzie River Delta

The Mackenzie River Delta is a lake‐rich arctic floodplain that receives high inputs of dissolved organic matter (DOM) and suspended particulates from allochthonous and autochthonous sources, and may transfer carbon from dissolved to particulate phase via in situ formation of transparent exopolymer particles (TEP). TEP provides food for grazers, surfaces for bacteria, and increased potential for aggregation and sedimentation of organic matter. During open water 2006, we tracked TEP abundances in three Delta lakes representing gradients that include declining river‐to‐lake connection times, increasing levels of dissolved organic carbon (DOC), and declining chromophoric‐DOM (CDOM). Unexpectedly, TEP abundances were highest immediately after the flood, when autochthonous autotrophic production was at a seasonal low and CDOM a seasonal high. Moreover, the lake with the strongest riverine influence and lowest levels of autochthonous autotrophic production had the highest mean TEP‐carbon (TEP‐C) concentrations among the lakes. The mean proportion of particulate organic carbon (POC) represented by TEP‐C increased with increasing river connection time, and appears to represent a substantial proportion of POC in Mackenzie Delta Lakes. Unexpectedly, the TEP gradient was most strongly related to CDOM (river water source) rather than overall DOC. Variations in CDOM accounted for 53% of TEP‐C variation among the lakes, indicating allochthonous matter was the most important source of TEP. DOC release from in situ macrophytes during periods of high photosynthesis may contribute to TEP formation in the lake with lowest riverine influence, but pH levels &gt;9.5 driven by the high photosynthetic rates complicate the interpretation of results from this lake.

Distribution characteristics of transparent exopolymer particles in the Pearl River estuary, China

Distribution of Transparent Exopolymer Particles (TEP) in the Pearl River estuary, China, was investigated during two cruises in August 2009 and January 2010. TEPcolor concentrations were 521.5–1727.4 μg Xeq.L−1 (μg Gum Xanthan equivalent liter−1) in August 2009 and 88.7–1586.9 μg Xeq.L−1 in January 2010, respectively. The size of TEP generally increased in the seaward along the longitudinal section with the dominant size of 2–40 μm during the cruises. Experimental work suggested that both concentration and size of TEP increased with Ca2+ concentration (from 0.8 mmol L−1 to 10 mmol L−1). In the field study, Ca2+ concentration had a positive correlation with TEPcolor concentration in the surface layer with salinity &lt;16. Decrease of TEP concentration seaward from intermediary salinity was partly due to dilution of seawater as well as enhanced aggregation and sedimentation of TEP via increasing divalent cation concentration. TEP concentration and turbidity maximum coexisted at the tip of salt wedge in the bottom layer during the wet season, and positive correlation between TEP and turbidity was observed in the winter. Relationships between TEP and turbidity suggested the important contribution of TEP aggregation to flocculation and sedimentation of particles in estuaries. Different pattern of TEP during two cruises can be attributed to physical process (i.e., mixing type) in estuaries. These findings indicated that formation and distribution of TEP were largely influenced by interaction between physical and biogeochemical processes in the Pearl River estuary. A conceptual model for TEP formation and distribution in the Pearl River estuary was developed.

Release of dissolved carbohydrates by Emiliania huxleyi and formation of transparent exopolymer particles depend on algal life cycle and bacterial activity

The coccolithophore Emiliania huxleyi plays a pivotal role in the marine carbon cycle. However, we have only limited understanding of how its life cycle and bacterial interactions affect the production and composition of dissolved extracellular organic carbon and its transfer to the particulate pool. We traced the fate of photosynthetically fixed carbon during phosphate-limited stationary growth of non-axenic, calcifying E. huxleyi batch cultures, and more specifically the transfer of this carbon to bacteria and to dissolved high molecular weight neutral aldoses (HMW NAld) and extracellular particulate carbon. We then compared the dynamics of dissolved carbohydrates and transparent exopolymer particles (TEP) between cultures of non-axenic and axenic diploid E. huxleyi. In addition, we present the first data on extracellular organic carbon in (non-axenic) haploid E. huxleyi cultures. Bacteria enhanced the accumulation of dissolved polysaccharides and altered the composition of dissolved HMW NAld, while they also stimulated the formation of TEP containing high densities of charged polysaccharides in diploid E. huxleyi cultures. In haploid E. huxleyi cultures we found a more pronounced accumulation of dissolved carbohydrates, which had a different NAld composition than the diploid cultures. TEP formation was significantly lower than in the diploid cultures, despite the presence of bacteria. In diploid E. huxleyi cultures, we measured a high level of extracellular release of organic carbon (34-76%), retrieved mainly in the particulate pool instead of the dissolved pool. Enhanced formation of sticky TEP due to bacteria-alga interactions, in concert with the production of coccoliths, suggests that especially diploid E. huxleyi blooms increase the efficiency of export production in the ocean during dissolved phosphate-limited conditions.

Effects of nutrients and turbulence on the production of transparent exopolymer particles: a mesocosm study

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 419:57-69 (2010) - DOI: https://doi.org/10.3354/meps08840 Effects of nutrients and turbulence on the production of transparent exopolymer particles: a mesocosm study M. L. Pedrotti1,*, F. Peters2, S. Beauvais1, M. Vidal3, J. Egge4, A. Jacobsen4, C. Marrasé2 1Marine Microbial Ecology Group, Laboratoire d’Océanographie de Villefranche, CNRS-UMR 7093, BP 28, 06234 Villefranche-sur-mer, France 2Institut de Ciències del Mar, CMIMA (CSIC), Passeig Marítim de la Barceloneta 37-49, 08003 Barcelona, Catalunya, Spain 3Departament d’Ecology, Universitat de Barcelona, Barcelona, Spain 4Department of Fisheries and Marine Biology, University of Bergen, HIB, 5020 Bergen, Norway *Email: pedrotti@obs-vlfr.fr ABSTRACT: The production of transparent exopolymer particles (TEP) in response to several environmental variables was studied in 2 mesocosm experiments. The first (Expt 1) examined a gradient of 4 nutrient levels; the second (Expt 2) examined different conditions of silicate availability and zooplankton presence. Tanks were separated in 2 series, one subjected to turbulence and the other not influenced by turbulence. In tanks with nutrient addition, TEP were rapidly formed, with net apparent production rates closely linked to chl a growth rates, suggesting that phytoplankton cells were actively exuding TEP precursors. High nutrient availability increased the absolute concentration of TEP; however, the relative quantity of TEP produced was found to be lower, as TEP concentration per unit of phytoplankton biomass was inversely related to the initial nitrate dose. In Expt 1, an increase in TEP volume (3 to 48 µm equivalent spherical diameter) with nutrient dose was observed; in Expt 2, both silicate addition and turbulence enhanced TEP production and favored aggregation to larger TEP (>48 µm). The presence of zooplankton lowered TEP concentration and changed the size distribution of TEP, presumably by grazing on TEP or phytoplankton. For lower nutrient concentrations, the ratio of particulate organic carbon (POC) to particulate organic nitrogen (PON) followed the Redfield ratio. At higher nutrient conditions, when nutrients were exhausted during the post-bloom, a decoupling of carbon and nitrogen dynamics occurred and was correlated to TEP formation, with a large flow of carbon channeled toward the TEP pool in turbulent tanks. TEP accounted for an increase in POC concentration of 50% in high-nutrient and turbulent conditions. The study of TEP dynamics is crucial to understanding the biogeochemical response of the aquatic system to forcing variables such as nutrient availability and turbulence intensity. KEY WORDS: Transparent exopolymer particles · TEP production · Phytoplankton · Particulate organic carbon · POC · Turbulence · Nutrients · Mesocosms Full text in pdf format PreviousNextCite this article as: Pedrotti ML, Peters F, Beauvais S, Vidal M, Egge J, Jacobsen A, Marrasé C (2010) Effects of nutrients and turbulence on the production of transparent exopolymer particles: a mesocosm study. Mar Ecol Prog Ser 419:57-69. https://doi.org/10.3354/meps08840 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 419. Online publication date: November 30, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Diatom-associated bacteria are required for aggregation of Thalassiosira weissflogii

Aggregation of algae, mainly diatoms, is an important process in marine systems leading to the settling of particulate organic carbon predominantly in the form of marine snow. Exudation products of phytoplankton form transparent exopolymer particles (TEP), which acts as the glue for particle aggregation. Heterotrophic bacteria interacting with phytoplankton may influence TEP formation and phytoplankton aggregation. This bacterial impact has not been explored in detail. We hypothesized that bacteria attaching to Thalassiosira weissflogii might interact in a yet-to-be determined manner, which could impact TEP formation and aggregate abundance. The role of individual T. weissflogii-attaching and free-living new bacterial isolates for TEP production and diatom aggregation was investigated in vitro. T. weissflogii did not aggregate in axenic culture, and striking differences in aggregation dynamics and TEP abundance were observed when diatom cultures were inoculated with either diatom-attaching or free-living bacteria. The data indicated that free-living bacteria might not influence aggregation whereas bacteria attaching to diatom cells may increase aggregate formation. Interestingly, photosynthetically inactivated T. weissflogii cells did not aggregate regardless of the presence of bacteria. Comparison of aggregate formation, TEP production, aggregate sinking velocity and solid hydrated density revealed remarkable differences. Both, photosynthetically active T. weissflogii and specific diatom-attaching bacteria were required for aggregation. It was concluded that interactions between heterotrophic bacteria and diatoms increased aggregate formation and particle sinking and thus may enhance the efficiency of the biological pump.