Transparent Exopolymer Particles Concentrations Research Articles

Depth is relative: the importance of depth for transparent exopolymer particles in the near-surface environment

Abstract. Transparent exopolymer particles (TEPs) are a major source for both organic matter (OM) and carbon transfer in the ocean and into the atmosphere. Consequently, understanding the vertical distribution of TEPs and the processes which impact their movement is important in understanding the OM and carbon pools on a larger scale. Additionally, most studies looking at the vertical profile of TEPs have focused on large depth scales from 5 to 1000 m and have omitted the near-surface environment. Results from a study of TEP enrichment in the sea surface microlayer (SML) in different regions (tropical, temperate) has shown that, while there is a correlation between TEP concentration and primary production (PP) on larger or seasonal scales, such relationships break down on shorter timescales and spatial scales. Using a novel small-scale vertical sampler, the vertical distribution of TEPs within the uppermost 2 m was investigated. For two regions with a total of 20 depth profiles, a maximum variance of TEP concentration of 1.39×106 µg XG eq2 L−2 between depths and a minimum variance of 6×102 µg XG eq2 L−2 was found. This shows that the vertical distribution of TEPs was both heterogeneous and homogeneous at times. Results from the enrichment of TEPs and Chl a between different regions have shown TEP enrichment in the SML to be greater in oligotrophic waters, when both Chl a and TEP concentrations were low, suggesting the importance of abiotic sources for the enrichment of TEPs in the SML. However, considering multiple additional parameters that were sampled, it is clear that no single parameter could be used as a proxy for TEP heterogeneity. Other probable biochemical drivers of TEP transport are discussed.

Effects of Phytoplankton Growth Phase on Settling Properties of Marine Aggregates

Marine snow aggregates often dominate carbon export from the surface layer to the deep ocean. Therefore, understanding the formation and properties of aggregates is essential to the study of the biological pump. Previous studies have observed a relationship between phytoplankton growth phase and the production of transparent exopolymer particles (TEP), the sticky particles secreted by phytoplankton that act as the glue during aggregate formation. In this experimental study, we aim to determine the effect of phytoplankton growth phase on properties related to aggregate settling. Cultures of the diatom Thalassiosira weissflogii were grown to four different growth phases and incubated in rotating cylindrical tanks to form aggregates. Aggregate excess density and delayed settling time through a sharp density gradient were quantified for the aggregates that were formed, and relative TEP concentration was measured for cultures before aggregate formation. Compared to the first growth phase, later phytoplankton growth phases were found to have higher relative TEP concentration and aggregates with lower excess densities and longer delayed settling times. These findings may suggest that, although particle concentrations are higher at later stages of phytoplankton blooms, aggregates may be less dense and sink slower, thus affecting carbon export.

Distribution of transparent exopolymer particles (TEP) in distinct regions of the Southern Ocean.

Transparent exopolymer particles (TEP) are an abundant class of suspended organic particles, mainly formed by polysaccharides, which play important roles in biogeochemical and ecological processes in the ocean. In this study we investigated horizontal and vertical TEP distributions (within the euphotic layer, including the upper surface) and their short-term variability along with a suite of environmental and biological variables in four distinct regions of the Southern Ocean. TEP concentrations in the surface (4 m) averaged 102.3 ± 40.4 μg XG eq. L-1 and typically decreased with depth. Chlorophyll a (Chl a) concentration was a better predictor of TEP variability across the horizontal (R2 = 0.66, p < 0.001) and vertical (R2 = 0.74, p < 0.001) scales than prokaryotic heterotrophic abundance and production. Incubation experiments further confirmed the main role of phytoplankton as TEP producers. The highest surface TEP concentrations were found north of the South Orkney Islands (144.4 ± 21.7 μg XG eq. L-1), where the phytoplankton was dominated by cryptophytes and haptophytes; however, the highest TEP:Chl a ratios were found south of these islands (153.4 ± 29.8 μg XG eq (μg Chl a)-1, compared to a mean of 79.3 ± 54.9 μg XG eq (μg Chl a)-1 in the whole cruise, in association with haptophyte dominance, proximity of sea ice and high exposure to solar radiation. TEP were generally enriched in the upper surface (10 cm) respect to 4 m, despite a lack of biomass enrichment, suggesting either upward transport by positive buoyancy or bubble scavenging, or higher production at the upper surface by light stress or aggregation. TEP concentrations did not present any significant cyclic diel pattern. Altogether, our results suggest that photobiological stress, sea ice melt and turbulence add to phytoplankton productivity in driving TEP distribution across the Antarctic Peninsula area and Atlantic sector of the Southern Ocean.

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.

Potential terrestrial influence on transparent exopolymer particle concentrations in boreal freshwaters

AbstractTransparent exopolymer particles (TEP) are ubiquitous in aquatic ecosystems and contribute, for example, to sedimentation of organic matter in oceans and freshwaters. Earlier studies indicate that the formation of TEP is related to the in situ activity of phytoplankton or bacteria. However, terrestrial sources of TEP and TEP precursors are usually not considered. We investigated TEP concentration and its driving factors in boreal freshwaters, hypothesizing that TEP and TEP precursors can enter freshwaters via terrestrial inputs. In a field survey, we measured TEP concentrations and other environmental factors across 30 aquatic ecosystems in Sweden. In a mesocosm experiment, we further investigated TEP dynamics over time after manipulating terrestrial organic matter input and light conditions. The TEP concentrations in boreal freshwaters ranged from 83 to 4940 μg Gum Xanthan equivalent L−1, which is comparable to other studies in freshwaters. The carbon fraction in TEP in the sampled boreal freshwaters is much higher than the phytoplanktonic carbon, in contrast to previous studies in northern temperate and Mediterranean regions. Boreal TEP concentrations were mostly related to particulate organic carbon, dissolved organic carbon, and optical indices of terrestrial influence but less influenced by bacterial abundance, bacterial production, and chlorophyll a. Hence, our results do not support a major role of the phytoplankton community or aquatic bacteria on TEP concentrations and dynamics. This suggests a strong external control of TEP concentrations in boreal freshwaters, which can in turn affect particle dynamics and sedimentation in the recipient aquatic ecosystem.

Rising bubbles enhance the gelatinous nature of the air–sea interface

AbstractBubbles rising through the water column are known to scavenge organic material and microorganisms, and transport them through the air–sea interface after bursting. This mechanism has important implications for air–sea exchange processes. However, little is known about how bubbles influence the chemical and biological properties of the sea‐surface microlayer (SML), a gelatinous film at the air–sea interface. We used floating mesocosms in the coastal Baltic Sea and a laboratory tank filled with seawater from the North Sea to study the effect of bubbling on the gelatinous nature of the SML. Bubbling was found to always increase concentrations of transparent exopolymer particles (TEP) in the SML. In the field, TEP in the SML already increased after 2 min (53% ± 63%) and 10 min (19% ± 12%) bubbling, respectively. During the tank experiment, TEP enriched in the SML by 312% (± 244%) after &gt; 3 h of bubbling. Therefore, bubbling is a highly efficient mechanism for TEP enrichment in the SML. Bubbling caused enrichment and depletion of microbial abundances (prokaryotes, flagellates, eukaryotes) in the SML. However, the incorporation of 3H‐thymidine (i.e., bacterial carbon production) was consistently stimulated after 10 min of bubbling in the field experiment, indicating a bubble‐induced import of unstressed bacteria and fresh organic substrates into the SML. Overall, our results suggest that the gelatinous matrix of the SML is re‐formed within min after disruption by bursting bubbles, and, thus, highlights the importance of biogeochemical interactions within the air–sea interface.

Do transparent exopolymeric particles (TEP) affect the toxicity of nanoplastics on Chaetoceros neogracile?

The potential presence of nanoplastics (NP) in aquatic environments represents a growing concern regarding their possible effects on aquatic organisms. The objective of this study was to assess the impact of polystyrene (PS) amino-modified particles (50 nm PSNH2) on the cellular and metabolic responses of the diatom Chaetoceros neogracile cultures at two essential phases of the growth cycle, i.e. exponential (division) and stationary (storage) phases. Both cultures were exposed for 4 days to low (0.05 μg mL-1) and high (5 μg mL-1) concentrations of PS-NH2. Exposure to NP impaired more drastically the major cellular and physiological parameters during exponential phase than during the stationary phase. Only an increase in ROS production was observed at both culture phases following NP exposures. In exponential phase cultures, large decreases in chlorophyll content, esterase activity, cellular growth and photosynthetic efficiency were recorded upon NP exposure, which could have consequences on the diatoms life cycle and higher food-web levels. The observed differential responses to NP exposure according to culture phase could reflect i) the higher concentration of Transparent Exopolymer Particles (TEP) at stationary phase leading to NP aggregation and thus, probably minimizing NP effects, and/or ii) the fact that dividing cells during exponential phase may be intrinsically more sensitive to stress. This work evidenced the importance of algae physiological state for assessing the NP impacts with interactions between NP and TEP being one key factor affecting the fate of NP in algal media and their impact to algal' cells.

Main drivers of transparent exopolymer particle distribution across the surface Atlantic Ocean

Abstract. Transparent exopolymer particles (TEPs) are a class of gel particles, produced mainly by microorganisms, which play important roles in biogeochemical processes such as carbon cycling and export. TEPs (a) are colonized by carbon-consuming microbes; (b) mediate aggregation and sinking of organic matter and organisms, thereby contributing to the biological carbon pump; and (c) accumulate in the surface microlayer (SML) and affect air–sea gas exchange. The first step to evaluate the global influence of TEPs in these processes is the prediction of TEP occurrence in the ocean. Yet, little is known about the physical and biological variables that drive their abundance, particularly in the open ocean. Here we describe the horizontal TEP distribution, along with physical and biological variables, in surface waters along a north–south transect in the Atlantic Ocean during October–November 2014. Two main regions were separated due to remarkable differences: the open Atlantic Ocean (OAO, n=30), and the Southwestern Atlantic Shelf (SWAS, n=10). TEP concentration in the entire transect ranged 18.3–446.8 µg XG eq L−1 and averaged 117.1±119.8 µg XG eq L−1, with the maximum concentrations in the SWAS and in a station located at the edge of the Canary Coastal Upwelling (CU), and the highest TEP to chlorophyll a (TEP:Chl a) ratios in the OAO (183±56) and CU (1760). TEPs were significantly and positively related to Chl a and phytoplankton biomass, expressed in terms of C, along the entire transect. In the OAO, TEPs were positively related to some phytoplankton groups, mainly Synechococcus. They were negatively related to the previous 24 h averaged solar irradiance, suggesting that sunlight, particularly UV radiation, is more a sink than a source for TEP. Multiple regression analyses showed the combined positive effect of phytoplankton and heterotrophic prokaryotes (HPs) on TEP distribution in the OAO. In the SWAS, TEPs were positively related to high nucleic acid-containing prokaryotic cells and total phytoplankton biomass, but not to any particular phytoplankton group. Estimated TEP–carbon constituted an important portion of the particulate organic carbon pool in the entire transect (28 %–110 %), generally higher than the phytoplankton and HP carbon shares, which highlights the importance of TEPs in the cycling of organic matter 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.

Sea cucumbers reduce nitrogen, bacteria and transparent exopolymer particles in Anemonia sulcata aquaculture tanks

Traditional aquaculture produces wastewater with high nutrient and organic matter concentrations. Poly-culture can improve this problem including “extractive species” such as sea cucumbers along with the primary species. The influence of sea cucumbers on transparent exopolymer particles (TEP) (i.e. biofilm precursors) has not been previously explored. Here, we monitored during 1 year the concentration of nutrients, total organic carbon (TOC), particulate organic matter (POM), TEP, chlorophyll-a and bacteria in two tanks of 50,000 L. One tank only contained Anemonia sulcata, whereas the other tank also included holothurians. To complement these time-series, we performed three short-term experiments in smaller (300 L) tanks. Three tanks contained A. sulcata plus Holothuria tubulosa (+H treatment) and other four tanks contained only A. sulcata (−H treatment). In the time-series, we found that the concentration of ammonium, nitrate, TOC, POM, TEP and bacteria in the effluent of the tank with holothurians was lower than in the effluent of the tank without holothurians. The three experiments confirmed that the holothurians reduced significantly nitrates, bacterial abundance and TEP concentration. Therefore, these invertebrates can control bacterial proliferation and prevent biofilm formation minimizing likely the risk of outbreak of pathogenic bacteria and improving the hygiene of the tanks.

Ammonia oxidizers in the sea-surface microlayer of a coastal marine inlet.

Planktonic archaea are thought to play an important role in ammonia oxidation in marine environments. Data on the distribution, abundance, and diversity of ammonia oxidizers in the coastal sea-surface microlayer (SML) are lacking, despite previous reports of high abundance of Thaumarchaeota in the SML of estuaries and freshwater lakes. Here, we failed to detect the presence of ammonia-oxidizing bacteria in any of our samples taken from a semi-enclosed marine inlet in Japan. Therefore, we shifted our focus to examine the archaeal community composition as well as the Thaumarchaeota marine group I (MG-I) and ammonia monooxygenase subunit A (amoA) gene copy numbers and composition in the SML and corresponding underlying water (UW, 20 cm). amoA gene copy numbers obtained by quantitative PCR were consistent with the typical values observed in the surface waters of oceanic and coastal environments where nitrification activity has been detected, but the copy numbers were two- to three-fold less than those reported from the surface layers and UW of high mountain lakes. Both amoA and MG-I 16S rRNA gene copy numbers were significantly negatively correlated with chlorophyll-a and transparent exopolymer particle concentrations in the SML. Communities of archaea and ammonia-oxidizing archaea in SML samples collected during low wind conditions (≤5 m s–1) differed the most from those in UW samples, whereas the communities in SML samples collected during high wind conditions were similar to the UW communities. In the SML, low ratios of amoA to MG-I 16S rRNA genes were observed, implying that most of the SML Thaumarchaeota lacked amoA. To our knowledge, our results provide the first comparison of ammonia-oxidizing communities in the coastal SML with those in the UW.

Effects of salinity and transparent exopolymer particles on formation of aquatic aggregates and their association with norovirus

Human noroviruses (NoVs) are responsible for 50% of food-related disease outbreaks and are notably associated with shellfish consumption. Despite the detrimental health impacts of human NoV-contaminated seafood to public health, there is a lack of knowledge on the physicochemical conditions that govern NoV transmission in aquatic ecosystems. In the present study, we investigated the propensity for NoVs to associate with aquatic aggregates, which have been shown to efficiently deliver nano-sized particles to shellfish. Specific physicochemical conditions characteristic of shellfish cultivation waters, specifically salinity and transparent exopolymer particles (TEP), were targeted in this study for investigating aggregate formation and NoV association dynamics. Murine norovirus (MNV) was used in aggregation experiments as a model surrogate for NoVs. Results demonstrate increased aggregate formation as a function of increasing salinity and TEP concentrations, as well as greater numbers of MNV genomes incorporated into aggregates under conditions that favor aggregation. As aggregate formation was enhanced in waters representing optimal conditions for shellfish production, specifically saline and high TEP waters, the implications to virus transport and shellfish food safety are profound: more aggregates implies increased scavenging of virus particles from surrounding waters and therefor greater risk for bivalve contamination with nano-sized pathogens. These novel data provide insight into where and when NoVs are most likely to be ingested by shellfish via contaminated aggregates, thereby informing best management and water quality monitoring practices aimed at providing safe seafood to consumers.

A laboratory study on the generation of estuarine negatively, neutrally and positively buoyant bio-mediated flocs

In estuaries and coastal areas, the mixing of inorganic and organic sediments results in the production of bio-mediated flocs. Their densities depend on the ratio between the light organic fraction and the mineral ballast. Transparent exopolymer particles (TEP) are ubiquitous in estuarine and marine environments. Because of their positive buoyancy, they form biofilms at the water surface. In order to investigate how the bio-mediated flocculation involving TEP impacts the sedimentation processes in the near surface layer of estuaries, we determined at the laboratory, the ascending/descending velocity of the mineral particles and their flocs size distributions (FSDs) of sediments sampled from the Cam River estuary (Vietnam), for concentrations ranging from 5 to 50 mg L−1, for two levels of turbulence representative to the slack water and mid ebb conditions of this estuary and for various TEP concentration and stickiness. The obtained results showed that the sediment velocity varied over two orders of magnitude depending of the conditions of the experiment. Ascending velocities were mostly measured for mid ebb conditions. The generated positively buoyant bio-mediated flocs were formed by microflocs coated by a TEP matrix. For the slack water conditions, FSDs were highly dependent of the TEP concentration and stickiness. Positively buoyant bio-mediated flocs were generated for specific concentrations and stickiness of TEP only. The corresponding FSDs were consistent with positively buoyant macroflocs, with TEP located mostly inside the flocs.

Small tropical islands with dense human population: differences in water quality of near-shore waters are associated with distinct bacterial communities.

Water quality deterioration caused by an enrichment in inorganic and organic matter due to anthropogenic inputs is one of the major local threats to coral reefs in Indonesia. However, even though bacteria are important mediators in coral reef ecosystems, little is known about the response of individual taxa and whole bacterial communities to these anthropogenic inputs. The present study is the first to investigate how bacterial community composition responds to small-scale changes in water quality in several coral reef habitats of the Spermonde Archipelago including the water column, particles, and back-reef sediments, on a densely populated and an uninhabited island. The main aims were to elucidate if (a) water quality indicators and organic matter concentrations differ between the uninhabited and the densely populated island of the archipelago, and (b) if there are differences in bacterial community composition in back-reef sediments and in the water column, which are associated with differences in water quality. Several key water quality parameters, such as inorganic nitrate and phosphate, chlorophyll a, and transparent exopolymer particles (TEP) were significantly higher at the inhabited than at the uninhabited island. Bacterial communities in sediments and particle-attached communities were significantly different between the two islands with bacterial taxa commonly associated with nutrient and organic matter-rich conditions occurring in higher proportions at the inhabited island. Within the individual reef habitats, variations in bacterial community composition between the islands were associated with differences in water quality. We also observed that copiotrophic, opportunistic bacterial taxa were enriched at the inhabited island with its higher chlorophyll a, dissolved organic carbon and TEP concentrations. Given the increasing strain on tropical coastal ecosystems, this study suggests that effluents from densely populated islands lacking sewage treatment can alter bacterial communities that may be important for coral reef ecosystem function.

Fouling of ultrafiltration membranes by organic matter generated by marine algal species

Controlling fouling in seawater reverse osmosis and ultrafiltration systems is a major challenge during algal blooms. This study investigates UF fouling potential of four marine algae and their algal organic matter (AOM): Chaetoceros affinis (Ch), Rhodomonas balthica (Rh), Tetraselmis suecica (Te), and Phaeocystis globulosa (Ph). Batch culture monitoring of the four different marine algal species showed remarkable differences in their production of biopolymers, transparent exopolymer particles (TEP) and their membrane fouling potential (MFI-UF10 kDa). MFI-UF10 kDa was linearly related to biopolymer concentration, and TEP during the growth and stationary/death phase of all four algal species. But the linear relation of MFI-UF10 kDa with algal cell density and chlorophyll-a concentration did not continue during the stationary/death phase. In experiments with capillary UF membranes, non-backwashable fouling of UF membranes varied strongly for the four different AOM solutions tested, and was linked to the presence of polysaccharides (stretching-OH) and sugar ester (stretching S˭O) groups in the AOM. The non-backwashable fouling coincided with MFI-UF150 kDa and TEP concentration. Therefore, determination of these parameters (MFI and TEP) and correlating with MODIS satellite data may generate useful information about the fouling potential of seawater at different locations during an algal bloom.

Seasonal dynamics of transparent exopolymer particles (TEP) and their drivers in the coastal NW Mediterranean Sea

Transparent Exopolymer Particles (TEPs) are a subclass of organic particles with high impact in biogeochemical and ecological processes, such as the biological carbon pump, air-sea interactions, or the microbial loop. However, the complexity in production and consumption makes TEP dynamics hardly predictable, calling for the need of descriptive studies about the in situ dynamics of these particles. We followed monthly TEP dynamics and combined them with a dataset of environmental variables during three years in a coastal site of the oligotrophic North Western Mediterranean (Blanes Bay). TEP concentration, ranging from 11.3 to 289.1μgXGeqL−1 (average 81.7±11.7μgXGeqL−1), showed recurrent peaks in early summer (June–July). TEP were temporally disconnected from chlorophyll a maxima, that occurred in late winter and early spring (maxima 1.21μgL−1), but they were significantly related to the abundance of specific phytoplankton groups (diatoms and dinoflagellates) and also coincided with periods of low nutrient concentrations. The fraction of particulate organic carbon in the form of TEP (the TEP:POC and TEP:PM ratios) were also highest in early summer, indicating that TEP-enriched particles of low density accumulate in surface waters during stratified periods. We hypothesize that the accumulation of these particles affects the microbial food web by enhancing the activity of specific prokaryotic extracellular enzymes (esterase, β-glucosidase and alkaline phosphatase) and promoting the abundance of heterotrophic nanoflagellates.

Comparison of Alcian blue and total carbohydrate assays for quantitation of transparent exopolymer particles (TEP) in biofouling studies

Transparent exopolymer particles (TEP) and their precursors are gel-like acidic polysaccharide particles. Both TEP precursors and TEP have been identified as causal factors in fouling of desalination and water treatment systems. For comparison between studies, it is important to accurately measure the amount and fouling capacity of both components. However, the accuracy and recovery of the currently used Alcian blue based TEP measurement of different surrogates and different size fractions are not well understood. In this study, we compared Alcian blue based TEP measurements with a total carbohydrate assay method. Three surrogates; xanthan gum, pectin and alginic acid; were evaluated at different salinities. Total carbohydrate concentrations of particulates (>0.4 μm) and their precursors (<0.4 μm, >10 kDa) varied depending on water salinity and method of recovery. As xanthan gum is the most frequently used surrogate in fouling studies, TEP concentration is expressed as xanthan gum equivalents (mg XGeq/L) in this study. At a salinity of 35 mg/L sea salt, total carbohydrate assays showed a much higher particulate TEP fraction for alginic acid (38%) compared to xanthan gum (9%) and pectin (12%). The concentrations of particulate TEP therefore may only represent ∼10% of the total mass; while precursor TEP represents ∼80% of the total TEP. This highlights the importance of reporting both particulate and precursor TEP for membrane biofouling studies. The calculated concentrations of TEP and their precursors in seawater samples are also highly dependent on type of surrogate and resulting calibration factor. A linear correlation between TEP recovery and calibration factor was demonstrated in this study for all three surrogates. The relative importance and accuracy of measurement method, particulate size, surrogate type, and recovery are described in detail in this study.

Temporal and spatial distribution of transparent exopolymer particles off the northern coast of Baja California, Mexico

Transparent exopolymer particles (TEP) have been reported as a significant fraction of organic microgels in different oceans. No TEP data have been published for the California Current region off Baja California that indicate the potential contribution of this reservoir to the carbon budget. We measured TEP in seawater samples, using the spectrophotometric method with alcian blue stain, and additional environmental and biological variables during 3 seasons at coastal stations between ~1.4 and 12.0 mi offshore, near 31ºN. Concentrations of TEP obtained with 0.45 µm pore size filters showed spatial and temporal distributions with a tendency to increase from offshore to nearshore and from winter to summer, respectively, ranging from undetectable values to 7.18 µg XG eq·mL–1 (median: 0.70). A significant positive correlation was observed between the concentration of TEP and bacterioplankton abundance (P &lt; 0.05), and between total organic carbon and bacterioplankton abundance (P &lt; 0.05). Transparent exopolymer particles also presented a negative correlation with community respiration (P &lt; 0.05), suggesting that TEP provided a physical substrate for settlement of prokaryotic microorganisms but probably did not supply labile carbon. We compared the concentration of alcian blue stainable particles retained by the standard 0.45 µm pore size with the concentration obtained with 0.22 µm filters; the latter showed 1.7 to 64.0 fold (median: 4.1) higher TEP concentrations. This strong dependence of TEP concentration on pore size makes it difficult to define the quantitative contribution of TEP and their precursors to particulate organic matter and their role in the carbon cycle. Further studies on TEP in the Mexican portion of the California Current must corroborate the observed spatial and seasonal trends, and estimate a TEP-to-carbon conversion factor that provides a better approximation to its contribution to the regional carbon budget.

Seagrass as major source of transparent exopolymer particles in the oligotrophic Mediterranean coast

Abstract. The role of seagrass, Posidonia oceanica, meadows as a source of transparent exopolymer particles (TEPs) to Mediterranean coastal waters was tested by comparing the TEP dynamics in two adjacent coastal waters in the oligotrophic NW Mediterranean Sea, one characterized by oligotrophic open-sea waters and the other accumulating seagrass leaf litter, together with an experimental examination of TEP release by seagrass litter. TEP concentrations ranged from 4.6 to 90.6 µg XG (xanthan gum) Eq L−1, with mean (±SE) values of 38.7 (± 2.02) µg XG Eq L−1 in the site devoid of seagrass litter, whereas the coastal beach site accumulating leaf litter had &gt; 10-fold mean TEP concentrations of 487.02 (± 72.8) µg XG Eq L−1. Experimental evaluation confirmed high rates of TEP production by P. oceanica litter, allowing calculations of the associated TEP yield. We demonstrated that P. oceanica is an important source of TEPs to the Mediterranean Sea, contributing an estimated 76 Gg C as TEPs annually. TEP release by P. oceanica seagrass explains the elevated TEP concentration relative to the low chlorophyll a concentration in the Mediterranean Sea.

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.