Intertidal microphytobenthic primary production and net metabolism of a tropical estuary.

Tidal flats are inhabited by benthic microalgae (microphytobenthos, MPB) supporting important ecosystem functions and services. Studies on MPB have been conducted mainly in temperate systems, despite that the majority of tidal flats on Earth are found in the tropical zone (∼55%). To fill this gap of knowledge and evaluate the contribution of tidal flat MPB in one of the most productive estuaries worldwide, sediment cores were collected from 14 stations along the inner Gulf of Nicoya (Costa Rica) at different tidal heights or sea levels (SL) from October 2013 to April 2014. MPB abundance, using chlorophyll a (Chla) biomass as a proxy, and net primary production (PN) and dark respiration (RD), using O2 microsensors, were measured together with other sediment biogeochemical variables in muddy and sandy sediments. Landsat-8 satellite images were used to map the extension of tidal flats and the abundance of MPB using Normalized Difference Vegetation Index (NDVI) as a proxy. Chla ranged from 0.45 to 7.45 µg cm-2, with higher concentrations observed closer to the river mouth. There was no significant correlation between Chla and SL nor with any other sediment physicochemical variable. MPB abundance estimated by remote sensing displayed considerable spatial heterogeneity, both within and among tidal flats, and clear seasonal differences with higher abundance during the rainy season. PN ranged between 0.8 and 8.6 mmol O2 m-2 h-1, being positively correlated to SL and to the accumulated rain during 30 days prior to the sampling date and inversely to the mean irradiance at noon during the previous month. Daily net community metabolism estimated from PN and RD data and converted to carbon fixation rates indicates that the unvegetated tidal flats of the gulf contribute as much as the total input of allochthonous C from the Tempisque River. However, the results presented here have to be confirmed with direct measurements of C transfer, including the contribution of the adjacent mangrove system. Such studies are crucial to assess the local, regional and global importance of production and other ecosystem services by MPB in tropical areas.

High-resolution temporal NDVI data reveal contrasting intratidal, spring-neap and seasonal biomass dynamics in euglenoid- and diatom-dominated biofilms.

Intertidal microphytobenthos (MPB) are a major contributor to primary production in estuarine ecosystems. While their biomass is highly variable at multiple spatial and temporal scales, the underlying drivers are as yet little understood. Both in situ sampling and remote-sensing techniques often lack the temporal resolution or coverage to simultaneously capture short-term (intratidal to daily) and longer-term (weekly to annual) biomass changes. Our field setup with in-situ NDVI sensors allowed us to study MPB surface biomass variability at high temporal resolution (10 mins) for up to two years in a freshwater euglenoid dominated mudflat, and a brackish and a marine diatom dominated mudflat. MPB biomass showed marked periodicities at multiple temporal scales: seasonal, spring-neap and intratidal. The diatom-dominated MPB community showed a seasonal biomass peak in winter, while the euglenoid-dominated community showed biomass peaks during spring and summer, probably caused by underlying divergent responses to mainly irradiance, temperature and wind-induced resuspension, and macrobenthos grazing. Spring-neap periodicity likely resulted from differential migratory responses of the MPB communities to variation in timing and duration of daylight exposure. In the freshwater community, upward migration only occurred when exposure duration was sufficiently long (≥4 h). In the diatom-dominated community, morning daylight exposure resulted in highest NDVI values. This study highlights the differences in MPB biomass dynamics between MPB communities within estuarine ecosystems, and underscores the great potential of high-resolution temporal NDVI monitoring for more accurate estimates of MPB biomass and primary production.

Benthic diatom diversity in microtidal mangrove estuaries.

Mangrove habitats support taxonomically diverse benthic communities, yet their effects on microphytobenthos remain understudied. This study investigated the benthic diatom community structure of 17 microtidal mangrove estuaries situated along the east coast of South Africa. High sediment organic content (≤ 18.1 %) and clay fraction (≤ 17.5 %) measured in the Avicennia marina and Rhizophora mucronata habitats favoured diverse communities (H' > 3) and the presence of unique benthic diatom species such as Gyrosigma balticum. The habitat complexity and stabilisation provided by the mangrove forests served as microrefugia for colonisation of benthic diatoms. Taxa displayed a broad range of nutrient tolerance, with some nutrient tolerant species (e.g., Halamphora acutiuscula, Navicula clausii, Navicula gregaria, and Navicula radiosa) dominating the communities in the Mbashe and Mnyameni estuaries. The presence of these nutrient tolerant taxa in relatively pristine systems serves as an early warning for possible anthropogenic nutrient enrichment.

Linking microphytobenthos distribution and mudflat geomorphology under varying sedimentary regimes using unoccupied aerial vehicle (UAV)-acquired multispectral reflectance and photogrammetry.

Microphytobenthic (MPB) biofilms play significant roles in the ecology of coastal mudflats, including provision of essential food resources to shorebird species. In these ecosystems, water-divergence structures like jetties and causeways can drastically alter sedimentation patterns and mudflat topography, yet their effects on MPB biofilm biomass and distribution are poorly understood. Here, we used a combination of unoccupied aerial vehicle (UAV) technologies, photogrammetric processing, and sediment field samples to compare biofilm and mudflat characteristics between areas of the Fraser River Estuary with varying sedimentary regimes and shorebird use. Our aims were to: (1) demonstrate the use of fine spatial resolution UAV-acquired multispectral imagery (cm2) with extensive spatial coverage (>km2) and a co-alignment photogrammetric processing techniques to survey MPB biofilm and mudflat topography at spatial scales and detail relevant to foraging shorebirds; and, (2) investigate the effects of water-divergence structures on mudflat elevation and microtopography, as well as MPB biofilm biomass, distribution, and spatial patterning. From a technical perspective, co-alignment allowed us to analyze aligned and continuous fine-resolution elevation models and orthomosaics for large areas of the estuary, while the normalized difference vegetation index was a good predictor of sediment chlorophyll-a (R2 = 0.9). Using these data products, we found that mudflats in close proximity to water-divergence structures have cross-shore profiles characteristic of low sediment supply as well as decreased microtopographic variability. At disturbed sites, elevation and microtopography had a weaker influence on biofilm biomass compared to intact estuarine ecosystem sites. Analysis of biofilm patch showed that sites either had a relatively small number of large, contiguous patches, or a large number of smaller, isolated patches; however, less disturbed sites did not necessarily have larger biofilm patches than more disturbed sites. We conclude that UAV-acquired multispectral imagery and co-alignment-based workflow are promising new tools for ecologists to map, monitor, and understand MPB biofilm dynamics in ecologically sensitive estuaries.

Nitrogen enrichment changed the biogeochemical role of sesarmid crabs by shifting their diets in tropical mangrove ecosystems.

Sesarmid crabs modulate nutrient dynamics of tropical mangroves through their leaf-eating habit. How N enrichment may alter this regulatory role, and the implications for mangrove nutrient dynamics, remain unclear. Using a mesocosm experiment, we tested how N enrichment could change the microphytobenthos (MPB) communities, thus modifying the crabs' diet and their role in nutrient dynamics. The factorial experiment combined with field investigation revealed a significant increase in the relative abundance of cyanobacteria. Stable isotope analysis suggested that the main carbon source of crabs shifted from leaf litter to cyanobacteria in mesocosms under both high (20×) and low (2×) N enrichment treatments. The significantly lower total cellulase activity of crabs in the mesocosms might explain the decreased carbon assimilation from leaf litter. The changes in the MPB and the microbiome with N enrichment in the presence of crabs may drive significantly higher carbon processing rate in tropical mangroves.

The Photoprotective Behavior of a Motile Benthic Diatom as Elucidated from the Interplay Between Cell Motility and Physiological Responses to a Light Microgradient Using a Novel Experimental Setup.

It has long been hypothesized that benthic motile pennate diatoms use phototaxis to optimize photosynthesis and minimize photoinhibitory damage by adjusting their position within vertical light gradients in coastal benthic sediments. However, experimental evidence to test this hypothesis remains inconclusive, mainly due to methodological difficulties in studying cell behavior and photosynthesis over realistic spatial microscale gradients of irradiance and cell position. In this study, a novel experimental approach was developed and used to test the hypothesis of photosynthesis optimization through motility, based on the combination of single-cell in vivo chlorophyll fluorometry and microfluidic chips. The approach allows the concurrent study of behavior and photosynthetic activity of individual cells of the epipelic diatom species Craspedostauros britannicus exposed to a light microgradient of realistic dimensions, simulating the irradiance and distance scales of light microgradients in benthic sediments. Following exposure to light, (i) cells explored their light environment before initiating light-directed motility; (ii) cells used motility to lower their light dose, when exposed to the highest light intensities; and (iii) motility was combined with reversible non-photochemical quenching, to allow cells to avoid photoinhibition. The results of this proof-of-concept study not only strongly support the photoprotective nature of photobehavior in the studied species but also revealed considerable variability in how individual cells reacted to a light microgradient. The experimental setup can be readily applied to study motility and photosynthetic light responses of other diatom species or natural assemblages, as well as other photoautotrophic motile microorganisms, broadening the toolset for experimental microbial ecology research.

Ecological interruption on food web dynamics by eutrophic water discharge from the world's longest dike at Saemangeum, Yellow Sea.

The man-made sea dike has disrupted the natural link between riverine and marine ecosystems and caused eutrophication within the aquatic ecosystem. The eutrophic water discharge has also raised concerns. As a representative tidal flat with the longest dike in the world, Saemangeum has experienced the problem of eutrophication. To elucidate the discharge water effects on the benthic food web dynamics, a four-year round sampling was conducted in/outside of the Saemangeum sea dike. Stable isotope analysis was applied to benthos (a total of 54 species) and their potential diets. Water discharge tripled in period II (2021-2022) compared to the period I (2019-2020). However, there were no significant impact changes in food web structure between the two periods due to improved lake water quality in period II. A positive correlation of nutrient concentration between the inner and outer areas of the dike revealed a direct effect of the water discharge on the outer tidal flat. The water discharge altered the spatial environmental conditions and the food web structure of the outer tidal flat. High TN concentrations stimulated the biomass of microphytobenthos (MPB) near the water gates, which in turn increased MPB consumption by benthos, demonstrating the in/direct impacts of water discharge on the food web. Furthermore, filter feeders exhibited a more sensitive response to spatial organic matter distribution compared to deposit feeders in diet utilization. Overall, our novel findings on food web dynamics in a representative tidal flat with artificial structures emphasize the necessity of continuous monitoring to ensure the sustainability of coastal ecosystems.

The metabolites of light: Untargeted metabolomic approaches bring new clues to understand light-driven acclimation of intertidal mudflat biofilm.

The microphytobenthos (MPB), a microbial community of primary producers, play a key role in coastal ecosystem functioning, particularly in intertidal mudflats. These mudflats experience challenging variations of irradiance, forcing the micro-organisms to develop photoprotective mechanisms to survive and thrive in this dynamic environment. Two major adaptations to light are well described in literature: the excess of light energy dissipation through non-photochemical quenching (NPQ), and the vertical migration in the sediment. These mechanisms trigger considerable scientific interest, but the biological processes and metabolic mechanisms involved in light-driven vertical migration remain largely unknown. To our knowledge, this study investigates for the first time metabolomic responses of a migrational mudflat biofilm exposed for 30 min to a light gradient of photosynthetically active radiation (PAR) from 50 to 1000 µmol photons m-2 s-1. The untargeted metabolomic analysis allowed to identify metabolites involved in two types of responses to light irradiance levels. On the one hand, the production of SFAs and MUFAs, primarily derived from bacteria, indicates a healthy photosynthetic state of MPB under low light (LL; 50 and 100 PAR) and medium light (ML; 250 PAR) conditions. Conversely, when exposed to high light (HL; 500, 750 and 1000 PAR), the MPB experienced light-induced stress, triggering the production of alka(e)nes and fatty alcohols. The physiological and ecological roles of these compounds are poorly described in literature. This study sheds new light on the topic, as it suggests that these compounds may play a crucial and previously unexplored role in light-induced stress acclimation of migrational MPB biofilms. Since alka(e)nes are produced from FAs decarboxylation, these results thus emphasize for the first time the importance of FAs pathways in microphytobenthic biofilms acclimation to light.

Abundance, biomass and species richness of macrozoobenthos along an intertidal elevation gradient.

Ecology aims to comprehend species distribution and its interaction with environmental factors, from global to local scales. While global environmental changes affect marine biodiversity, understanding the drivers at smaller scales remains crucial. Tidal flats can be found on most of the world's coastlines and are particularly vulnerable to anthropogenic disturbances. They are important transient ecosystems between terrestrial and marine ecosystems, and their biodiversity provides important ecosystem services. Owing to this unique, terrestrial-marine transition, strong environmental gradients of elevation, sediment composition and food availability prevail. Here, we investigated which regional and local environmental factors drive the spatio-temporal dynamics of macrozoobenthos communities on back-barrier tidal flats in the East Frisian Wadden Sea. On the regional level, we found that species composition changed significantly from west to east on the East Frisian islands and that total abundance and species richness decreased from west to east. On the local abiotic level, we found that macrozoobenthos biomass decreased with higher elevation towards the salt marsh and that the total abundance of organisms in the sediment significantly increased with increasing mud content, while biodiversity and biomass were not changing significantly. In contrast to expectations, increasing Chl a availability as a measure of primary productivity did not result in changes in abundance, biomass or biodiversity, but extremely high total organic carbon (TOC) content was associated with a decrease in biomass and biodiversity. In conclusion, we found regional and local relationships that are similar to those observed in previous studies on macrozoobenthos in the Wadden Sea. Macrozoobenthos biomass, abundance and biodiversity are interrelated in a complex way with the physical, abiotic and biotic processes in and above the sediment.

Influence of nutrient enrichment on colonisation and photosynthetic parameters of hard substrate marine microphytobenthos.

This study aimed to assess the influence of nutrient enrichment on the development of microalgal biofilm on concrete and PVC cubes. Three mesocosms were utilized to create a nutrient gradient over a period of 28 days. Various parameters including biomass, photosynthetic activity, microtopography, and extracellular polymeric substances (EPS) were measured. Imaging PAM techniques were employed to obtain surface-wide data. Results revealed that nutrient availability had no significant impact on Chl a biomass and the maximum quantum efficiency of PSII (Fv/Fm). The photosynthetic capacity and efficiency were minimally affected by nutrient availability. Interestingly, the relationship between microphytobenthic (MPB) biomass and photosynthesis and surface rugosity exhibited distinct patterns. Negative reliefs showed a strong correlation with Fv/Fm, while no clear pattern emerged for biomass on rough concrete structures. Overall, our findings demonstrate that under conditions of heightened eutrophication, biofilm photosynthesis thrives in the fissures and crevasses of colonized structures regardless of nutrient levels. This investigation provides valuable insights into the interplay between nutrient availability and surface rugosity.

The Impact of MOSE (Experimental Electromechanical Module) Flood Barriers on Microphytobenthic Community of the Venice Lagoon.

MOSE is a system of mobile gates engineered to temporarily isolate the Venice Lagoon from the Adriatic Sea and to protect the city from flooding during extreme high tides. Within the framework of the Venezia2021 program, we conducted two enclosure experiments in July 2019 (over 48 h) and October 2020 (over 28 h) by means of 18 mesocosms, in order to simulate the structural alterations that microphytobenthos (MPB) assemblages might encounter when the MOSE system is operational. The reduced hydrodynamics inside the mesocosms favored the deposition of organic matter and the sinking of cells from the water column towards the sediment. Consequently, MPB abundances increased over the course of both experiments and significant changes in the taxonomic composition of the community were recorded. Species richness increased in summer while it slightly decreased in autumn, this latter due to the increase in relative abundances of taxa favored by high organic loads and fine grain size. By coupling classical taxonomy with 18S rRNA gene metabarcoding we were able to obtain a comprehensive view of the whole community potential, highlighting the complementarity of these two approaches in ecological studies. Changes in the structure of MPB could affect sediment biostabilization, water turbidity and lagoon primary production.

Feeding effects of the keystone deposit feeder Ilyanassa obsoleta (Neogastropoda, Gastropoda) on sedimentary diatoms.

Microphytobenthos (MPB), typically comprised mainly of diatoms, is a key contributor to nearshore energy flow and nutrient cycles. Deposit-feeding invertebrates are known to alter the structure and activity of MPB. The eastern mud snail Ilyanassa obsoleta can reach extremely high densities in estuaries of the northwestern Atlantic, and their deposit-feeding and locomotion strongly influence other invertebrates and microbes. Our objective was to explore quantitative and qualitative effects of this keystone deposit-feeder on diatoms of intertidal sediments. We gathered snails from mudflat and sandflat habitats and collected their fresh fecal pellets in the laboratory. DNA metabarcoding allowed us to characterize diatom assemblages of ingested sediments and feces. We noted selective feeding such that reduction in MPB biomass with gut passage was difficult to quantify. Diatom α-diversity was reduced with gut passage in snails from both sedimentary regimes. Mudflat and sandflat diatom assemblages were distinct and differed markedly between feces and sediment in mud-feeding snails, whereas the difference in sand-feeding snails was minor. The sandy habitat was dominated by a mix of epipelic and epipsammic diatoms. In contrast, mudflat samples were dominated by epipelic and planktonic diatoms. Compositional differences between sediment and feces reflected preferential removal of planktonic taxa. Our results suggest the importance of phytodetritus to the mud snail diet, particularly in hydrodynamically quiescent environments. Due to the natural spatial patchiness of the snails and the capacity for rapid microbial recolonization, field experiments are recommended to determine whether MPB community changes attributed to gut passage are manifested at the landscape scale.

Long chain fatty acids analysis of intertidal biofilm by direct injection liquid chromatography time of flight mass spectrometry.

The critical importance of mono- and polyunsaturated fatty acids (FAs) in a variety of biological functions, including animal nutrition and as an environmental stress monitor, is well recognized. However, while methods exist for monitoring of fatty acids, few are specific either to the profile of a microphytobenthos matrix or practical in application to multiple, diverse intertidal biofilm sample sets. In the current study, a sensitive liquid chromatography (LC) quadrupole time of flight mass spectrometry (QTOF) method was developed for the quantitative analysis of 31 FAs specific to intertidal biofilm, a thin mucilaginous layer of microalgae, bacteria, and other organisms on the surface of coastal mudflats, which provide a rich source of FAs for migratory birds. Preliminary screening of diverse biofilm samples collected from shorebird feeding grounds highlighted eight saturated (SFA), seven monounsaturated (MUFA), and sixteen polyunsaturated FAs (PUFA) that were selected for analysis. Improved method detection limits in the range 0.3-2.6 ngmL-1 were achieved, excepting for stearic acid at 10.6 ngmL-1. These excellent results were obtained without use of complex sample extraction and clean-up procedures undertaken by other published methods. An alkaline matrix of dilute aqueous ammonium hydroxide with methanol was shown to be selective for extraction and stability of the more hydrophilic fatty acid components. The direct injection method showed excellent precision and accuracy both during validation and application to hundreds of real-world intertidal biofilm samples from the Fraser River estuary (British Columbia, Canada) and other areas of the region frequented by shoreline birds.

Short-term stability of rocky intertidal biofilm to nitrogen and phosphorus pulses.

Coastal environments experience both natural and anthropogenic inputs of nitrogen (N) and phosphorus (P). Agricultural fertilisers, organic run-offs, and edaphic characteristics of coastal environments may generate mosaics of nutrient concentrations that ultimately influence the coastal primary productivity. Here, we experimentally assessed the effects of repeated pulses of N and P on multiple components of ecological stability (sensitivity, resilience, temporal stability and recovery) of phototrophic rocky intertidal biofilm. We performed a repeated-pulses factorial experiment crossing increasing N and P concentrations chosen to reflect a range of nutrient enrichment conditions, from oligotrophic to eutrophic. N and P, regardless of concentration or whether they occurred in isolation or combination, enhanced biofilm's sensitivity (increased biomass or physiological performance compared to controls) without altering resilience. Our experiment illustrates how the stability of an essential coastal primary producer responds to increasing N and P supply levels. Furthermore, notwithstanding the importance of decomposing the multiple dimensions of stability, the transitory increase of the sole sensitivity indicated that rocky shore biofilm is robust against a wide range of nutrient enrichment.

The response of microphytobenthos to physical disturbance, herbicide, and titanium dioxide nanoparticle exposure.

The microphytobenthos that form transient biofilms are important primary producers in intertidal, depositional habitats, yet we have only a limited understanding of how they respond to the cumulative impacts of the growing range of anthropogenic stressors to which they are exposed. We know even less about how the temporal alignment of exposure - such as duration and exposure sequence - may affect the response. Estuarine biofilms were cultured in mesocosms and exposed to the herbicide glyphosate and titanium dioxide (TiO2) nanoparticles in different sequences (glyphosate-first or TiO2-first), as well as in the presence and absence of physical disturbance. We found that at environmentally realistic chemical concentrations, the order of exposure was less important than the total stressor scenario in terms of impacts on key functional attributes and diatom community structure. Physical disturbance did not have an impact on functional attributes, regardless of exposure sequence.

Assessment of the Chronic Toxicity and Interactions between Arsenic and Riverbed Biofilms.

The toxic effect of exposure to arsenic, As(V), at concentrations of 0 to 30 mg L-1, for 49 days, on epipsammic biofilms, was evaluated in a microcosm experiment. The growth and composition of biofilms developed on sediments containing As concentrations of 31 mg kg-1 and 85 mg kg-1 were compared, using photosynthetic parameters and Live/Dead stains as end points. A toxic effect of arsenic could not be demonstrated; however, biofilm growth was higher over the sediment with higher arsenic concentrations, suggesting the development of pollution-induced community induced tolerance (PICT). Nevertheless, PICT was not observed after exposure to high arsenic concentration in the laboratory, as there were no differences in algal growth between the previous 0 and 30 mg L-1 systems exposed to new 30 mg As L-1 dissolution over 29 days. The algal composition was affected by the added arsenic, and brown algae were the most tolerant compared to green algae and cyanophyceae, as their percentage increased from 25 and 33% in the control samples to 57 and 47% in the samples with the highest added As concentration. In turn, the biofilm development influenced arsenic redistribution and speciation. Arsenic concentration in water decreased with time during the incubation experiment, retained by the sediment particles and the biofilm. In the biofilm, extracellular As was significantly higher (up to 11 times) than intracellular arsenic. As(V) was the predominant species in water and in the biofilm, but products of biotic transformation, namely As(III), DMA(V) and MMA(V), were also found in the solution and in the biofilm in some systems, demonstrating reduction and methylation by the organisms. As a conclusion, a toxic effect was not detected for the concentrations evaluated. Biofilms naturally exposed in the river system to high As concentrations acquire pollution-induced tolerance; however, tolerance was not acquired by exposure to 30 mg L-1 for 29 days in the laboratory.

Altered nitrogen transformation pathways and a legacy of sediment organic matter enrichment.

Estuaries are ecologically valuable ecosystems that process nutrients through complex biogeochemical processes. Here we identify drivers and inhibitors of nitrogen removal in unvegetated intertidal sandflats at six sites in Manukau Harbour (37° 2.00'S 174° 42.00'E) to quantify the exchange of solutes across the sediment-water interface, with nitrogen removal rates (NRR) measured at two contrasting sites (PI and CB) near and far, respectively, from an historical wastewater treatment plant. Solute fluxes were paired with sediment and macrofauna community data to identify drivers of ecosystem function. Fluxes of oxygen, nitrogen and phosphorous were found to vary among sites, with differences attributed to variation in sediment characteristics (grain size, chlorophyll a, organic content) and macrofauna community structure. Mean NRR was found to vary between sites (PI = 32.2 vs CB = 217.9 µmol N2/m2/h), with bioturbating macrofauna (bivalves Austrovenus stutchburyi and Macomona liliana), microphytobenthic biomass, and exposure to nutrients likely key contributing drivers.

Colonisation of artificial structures by primary producers: competition and photosynthetic behaviour.

Colonisation of artificial structures by primary producers is an important determinant for eco-engineering projects. In this context, interactions between the colonisation by microphytobenthic biofilm and macroalgae were explored on 48 samples of marine infrastructures (MI) immersed for one year in the English Channel. Marine infrastructures samples with smooth and rough surface were compared to evaluate the influence of surface micro-scale rugosity. Microphytobenthos biomass (MPB), macroalgal diversity and photosynthetic parameters of both were assessed during colonisation. No significant differences were found as a function of the surface rugosity of MI samples, which was unexpected, but can be explained by biogenic rugosity provided by barnacles. Marine infrastructures were largely colonised by a red encrusting alga, Phymatolithon purpureum, which showed poor photosynthetic capacity compared to the microphytobenthos present next to it. Colonisation by monospecific encrusting algae tended to reduce the primary productivity of hard substrate.

Copper chloride (II) effect on the composition and structure of marine microphytobenthic communities.

To assess the temporary effects of the increased copper ion inflow on estuarine microphytobenthic communities, ecotoxicological tests were conducted using natural microphytobenthic assemblages obtained from an artificial substratum exposed to the waters of the southern Baltic Sea (Gulf of Gdansk). The applied copper ion concentrations reflected permitted copper values established for waters of a good ecological status (2·10-5 g Cu·dm-3), and the maximum copper concentrations which, according to the current environmental regulations, are allowed to be discharged into the environment (2·10-3 g Cu·dm-3).In the studied communities, diverse responses of single species to CuCl2 exposure were recorded, including both growth inhibition and stimulatory effects as well. Despite the shift in the community composition and structure, total cell number remained at a similar level. The results of our investigations suggest that microphytobenthic assemblages are resistant to CuCl2 which is facilitated by the shift in the community composition resulting from the increasing cell number of copper tolerant species.

Epibenthic microbial mats behavior as phosphorus sinks or sources in relation to biological and physicochemical conditions.

Microbial mats are complex microecosystems that have shown promise as possible green filters to remediate polluted seawater. This usage would possibly require changing the natural conditions under which these microbial mats prosper in order to maximize their contact with the water. Thus, it is necessary to evaluate the adaptation of the mats to different environmental conditions, while monitoring their short-term efficiency at nutrient removal. To that aim, epibenthic microbial mats collected from a tidal flat in the Bahía Blanca Estuary, were incubated under different flooding conditions (periodically exposed to the air or continuously flooded), with and without the addition of a high phosphorus concentration (5 mg PO43- L-1), and with and without the presence of penicillin. This last condition was added to understand the influence of penicillin-sensitive microbes on cyanobacteria and diatom communities and their importance for P remediation. The presence of high P concentrations as well as the continual flooding of the mats resulted in the decrease of the dominant cyanobacterium, Coleofasciculus (Microcoleus) chthonoplastes, giving rise to the dominance of other genera such as Arthrospira sp. Or Oscillatoria sp., depending on the presence or absence of the antibiotic, respectively. Water P removal was highly efficient (60-87%) when the mats were treated with the high-P water. However, microbial mat behavior changed from P sink to source when mats where incubated in seawater with no P addition, suggesting that mats can both function as P sinks and sources, depending on the condition of the water they come in contact with.