Microphytobenthic Communities Research Articles

Chromium removal by microbial mats: understanding the effect of salinity and pH.

Environmental contamination by chromium represents a serious public health problem. Therefore, it is crucial to develop and optimize remediation technologies to reduce its concentration in the environment. The aims of this study were to evaluate the uptake of chromium by live and complete microbial mats in experimental mesocosms under different pH and salinity conditions to understand how these factors affect the microphytobenthic community and, consequently, how chromium removal process is influenced. Microbial mats from the estuarine environment were exposed to 15mg Cr/L under different pH (2, 4, and 8) and salinity (2, 15, and 33) conditions. Salinity, redox potential, and pH were measured throughout the trial in solutions and in microbial mats, while total Cr determinations were performed at the end of the assay. The results demonstrated that the removal efficiency of Cr by microbial mats was significantly improved in solutions at pH 2, remaining unaffected by variations in salinity. Notably, both cyanobacteria and diatoms showed remarkable resistance to Cr exposure under all conditions tested, highlighting their exceptional adaptability. Microbial mats have proved to be effective filters for reducing the concentration of chromium in aqueous solutions with varying pH and salinity levels.

Functional and compositional responses of stream microphytobenthic communities to multiple stressors increase and release in a mesocosm experiment

Field observations form the basis of the majority of studies on microphytobenthic algal communities in freshwater ecosystems. Controlled mesocosm experiments data are comparatively uncommon. The few experimental mesocosm studies that have been conducted provide valuable insights into how multiple stressors affect the community structures and photosynthesis-related traits of benthic microalgae. The recovery process after the stressors have subsided, however, has received less attention in mesocosm studies. To close this gap, here we present the results of a riparian mesocosm experiment designed to investigate the effects of reduced flow velocity, increased salinity and increased temperature on microphytobenthic communities. We used a full factorial design with a semi-randomised distribution of treatments consisting of two levels of each stressor (2 × 2 × 2 treatments), with eight replicates making a total of 64 circular mesocosms, allowing a nuanced examination of their individual and combined influences. We aimed to elucidate the responses of microalgae communities seeded from stream water to the applied environmental stressors. Our results showed significant effects of reduced flow velocity and increased temperature on microphytobenthic communities. Recovery after stressor treatment led to a convergence in community composition, with priority effects (hypothesized to reflect competition for substrate between resident and newly arriving immigrant taxa) slowing down community shifts and biomass increase. Our study contributes to the growing body of literature on the ecological dynamics of microphytobenthos and emphasises the importance of rigorous experiments to validate hypotheses. These results encourage further investigation into the nuanced interactions between microphytobenthos and their environment and shed light on the complexity of ecological responses in benthic systems.

Succession, composition and structure of microphytobenthic communities of the large eutrophic Oka River in Russia, before its confluence with the Volga River

Succession, composition and structure of microphytobenthic communities of the large eutrophic Oka River in Russia, before its confluence with the Volga River

Are Toxic Substances Always Toxic? Case Studies of Different Organismal Responses Based on Brackish-Water Microphytobenthic Communities from the Baltic Sea

In this manuscript, we present the results of ecotoxicological tests conducted on the Baltic microphytobenthos community consisting largely of cosmopolitan species showing the responses at the community (taxonomic composition and structure), population (abundance), and cellular (chloroplast shape) levels. The tests were carried out for three chemicals with different modes of action on photosynthetic organisms, i.e., copper (II) chloride (at concentrations of 2·10−5 g·dm3 and 2·10−3 g·dm−3), glyphosate in the form of Roundup® (concentrations ranging from 4.2·10−2 to 8.5 g·dm−3), and the ionic liquid [BMIM]Cl (at concentrations of 1.13·10−3 g·dm−3 and 1.75·10−2 g·dm−3). The results of the study indicate that the responses of microphytobenthos at each level analysed are highly variable and difficult to predict a priori based on experiments performed on single strains. In addition, it was shown that microphytobenthic communities are relatively resistant to the substances tested, which is due to taxonomic richness and the resulting potential for substitution of sensitive taxa by more resistant taxa. The results obtained in the tests also indicate that the number of cells of individual taxa can remain at a similar level or increase over short periods of time despite the deformation of chloroplasts in a numerous group of cells.

Microscale imaging sheds light on species-specific strategies for photo-regulation and photo-acclimation of microphytobenthic diatoms.

Intertidal microphytobenthic (MPB) biofilms are key sites for coastal primary production, predominantly by pennate diatoms exhibiting photo-regulation via non-photochemical quenching (NPQ) and vertical migration. Movement is the main photo-regulation mechanism of motile (epipelic) diatoms and because they can move from light, they show low-light acclimation features such as low NPQ levels, as compared to non-motile (epipsammic) forms. However, most comparisons of MPB species-specific photo-regulation have used low light acclimated monocultures, not mimicking environmental conditions. Here we used variable chlorophyll fluorescence imaging, fluorescent labelling in sediment cores and scanning electron microscopy to compare the movement and NPQ responses to light of four epipelic diatom species from a natural MPB biofilm. The diatoms exhibited different species-specific photo-regulation features and a large NPQ range, exceeding that reported for epipsammic diatoms. This could allow epipelic species to coexist in compacted light niches of MPB communities. We show that diatom cell orientation within MPB can be modulated by light, where diatoms oriented themselves more perpendicular to the sediment surface under high light vs. more parallel under low light, demonstrating behavioural, photo-regulatory response by varying their light absorption cross-section. This highlights the importance of considering species-specific responses and understanding cell orientation and photo-behaviour in MPB research.

Understanding the Role of Macroalgal Complexity and Allelochemicals Production in Invasive and Non-Invasive Macroalgae in the North-Western Adriatic Sea: Effect on the Associated Communities

Highly diverse microphyto and meiobenthic communities are associated with large-sized marine macroalgae. Both morphological traits and allelochemical responses of macroalgae affect the composition of these communities, but the relative importance of these factors remains incompletely understood. In this study we investigated the microphytobenthic and meiobenthic communities associated with some native macroalgae and a non-indigenous species (Sargassum muticum) of the north-western Adriatic Sea. These seaweeds were sampled in two coastal sites subjected to different impacts. The possible effects of the structural complexity of the macroalgae and the potential role of allelochemicals (specifically polyunsaturated aldehydes, PUAs) on the associated communities were examined using univariate and multivariate analyses. The results indicate that distinct assemblages were associated with the macroalgae collected at the two different sites. Differences in microphytobenthic communities could be ascribed to differences in the macroalgal morphological traits and in their PUAs production. Conversely, variation of the meiobenthic community seemed to be related mainly to differences in the macroalgal communities at the two sites. This apparent inconsistency between the two analyzed communities suggests that microphytobenthos and meiofauna were differently shaped by the environmental habitat provided by macroalgae in the two sites, that are subjected to different environmental conditions and human activities. Overall, these results indicate that interactions between organisms belonging to different trophic groups (e.g., microphytobenthos and meiofauna) should be investigated in detail to better understand the global role of macroalgae as habitat formers on coastal ecosystems, especially in the case of large-sized introduced species.

Preliminary assessment of microbial mats in seawater metal remediation.

Microbial mats have a special role in the removal of metals in marine environment. This study aimed to experimentally determine the efficiency of Cr removal from seawater by microbial mats. The effect of Cr on the microphytobenthic community and the influence of an aerated condition on the removal of metal and microorganisms were also considered. Hence, microbial mat samples were subdivided in 4 groups: submerged in Cr (chromium 2mg/L without aeration), Cr + O2 (chromium 2mg/L with aeration), SW + O2 (filtered seawater with aeration), and a control: SW (filtered seawater with neither chromium nor aeration). Water and microbial mat subsamples were used to determine Cr concentrations, organic matter content, granulometry, physicochemical parameters, chlorophyll a, phaeopigments, and quantitative analysis of the microphytobenthic community. Cr removal efficiency from seawater was 95% for the Cr treatment and 99% for the Cr + O2 treatment. The abundance of cyanobacteria tended to decrease between the initial and final days of the assay, whereas the opposite trend was observed for diatoms. Two aspects are worth noting in the paper: microbial mats efficiently removed Cr from seawater at a concentration of 2mg Cr/L and the removal of Cr by microbial mats was more efficient with water aeration.

Invasive Vaucheria aff. compacta (Xanthophyceae) and its distribution over a high Arctic tidal flat in Svalbard

The high Arctic Svalbard tidal flat ecosystem is impacted by global warming, which could allow invasion by additional species with changes in the environment supporting their growth. The transport of additional species to Svalbard could be aided by an increase in the numbers of people traveling there. Anthropogenic activities related with global warming create opportunities for organisms to move across previously isolated regions, thus advancing biotic homogenization and extinctions. Our study focused on essential quantitative and qualitative information about the occurrence of widespread mats of the invasive siphonaceous yellow-green alga Vaucheria aff. compacta in the Adventfjorden tidal flat. We outline the present ecological state of V. aff. compacta mats (land cover estimation) and discuss the origin and future development of this microphytobenthic community. Phylogenetic analyses based on rbcL genes confirmed that the studied alga is closely related to V. compacta, inside the section Piloboloideae. With the help of a drone mapping survey, we estimated that V. aff. compacta area cover was about ca 231.1 m2 ( ± 10.55%, n = 11) across the drone mapped tidal flat area of 2475 m2. We confirmed that invasive V. aff. compacta is a coastal cosmopolitan species widely disseminated on shores in both hemispheres. Invasive V. aff. compacta is an important component of the Adventforden sea-land ecotone, which affects large-scale changes within the intertidal system, stabilizes the sediment coming in with the regular tides and protect the seashore ecosystem against erosion. As a result of global warming in the Arctic, invasive V. aff. compacta facilitates the greening of the Arctic.

Effects of the Ionic Liquid [BMIM]Cl on the Baltic Microphytobenthic Communities

Ionic liquids (IL) are regarded as the solution to the modern world’s need to create and use compounds that exhibit a range of desirable properties while having a low environmental impact. However, recent reports are shattering the image of ionic liquids as environmentally friendly substances, especially in relation to the aquatic environment, revealing their potentially toxic effects. To assess the potential environmental impact of ILs, we conducted an experiment involving 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), a substance considered to be the least hazardous among the imidazolium chloride ILs, on Baltic microphytobenthic communities. Microphytobenthos collected from the environment was tested under controlled laboratory conditions, and both the cell counts and the chloroplast condition were used as endpoints. It was shown that [BMIM]Cl at concentrations of 10−3 and 10−2, considered safe based on a cumulative impact assessment, has a negative effect on the condition of the microalgal cells and causes a reduction in population size. Although, under the influence of [BMIM]Cl, only a small proportion of the species was eliminated from the communities, only two species among those important to the communities showed resistance to this compound and eventually began to dominate the communities.

Photosynthetic, Respirational, and Growth Responses of Six Benthic Diatoms from the Antarctic Peninsula as Functions of Salinity and Temperature Variations.

Temperature and salinity are some of the most influential abiotic parameters shaping biota in aquatic ecosystems. In recent decades, climate change has had a crucial impact on both factors—especially around the Antarctic Peninsula—with increasing air and water temperature leading to glacial melting and the accompanying freshwater increase in coastal areas. Antarctic soft and hard bottoms are typically inhabited by microphytobenthic communities, which are often dominated by benthic diatoms. Their physiology and primary production are assumed to be negatively affected by increased temperatures and lower salinity. In this study, six representative benthic diatom strains were isolated from different aquatic habitats at King George Island, Antarctic Peninsula, and comprehensively identified based on molecular markers and morphological traits. Photosynthesis, respiration, and growth response patterns were investigated as functions of varying light availability, temperature, and salinity. Photosynthesis–irradiance curve measurements pointed to low light requirements, as light-saturated photosynthesis was reached at <70 µmol photons m−2 s−1. The marine isolates exhibited the highest effective quantum yield between 25 and 45 SA (absolute salinity), but also tolerance to lower and higher salinities at 1 SA and 55 SA, respectively, and in a few cases even <100 SA. In contrast, the limnic isolates showed the highest effective quantum yield at salinities ranging from 1 SA to 20 SA. Almost all isolates exhibited high effective quantum yields between 1.5 °C and 25 °C, pointing to a broad temperature tolerance, which was supported by measurements of the short-term temperature-dependent photosynthesis. All studied Antarctic benthic diatoms showed activity patterns over a broader environmental range than they usually experience in situ. Therefore, it is likely that their high ecophysiological plasticity represents an important trait to cope with climate change in the Antarctic Peninsula.

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 Gdańsk). The applied copper ion concentrations reflected permitted copper values established for waters of a good ecological status (2·10-5g Cu·dm-3), and the maximum copper concentrations which, according to the current environmental regulations, are allowed to be discharged into the environment (2·10-3g 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.

Dark survival in biofilm-forming microalgae: potential for colonizing benthic ecosystems.

The biofilm-forming microalgae are known to experience periods of continuous darkness (upto several days), in addition to the natural day-night cycle, especially in the intertidal sediment regions (when transported to deeper sediments) and the ships' ballast water tanks (during voyages). However, the information on community and physiological responses to different periods of darkness is limited. Here, the survival capability of biofilm-forming microalgae to varying periods of darkness (7-35 days) and the growth patterns upon resumption of normal 12 hlight:dark photocycle has been addressed through simulation experiments. Diatoms dominated the seawater biofilms, but the dark survival period varied and was species-specific. Of the 25 diatoms, only Amphora, potential toxin producer, followed by Navicula remained viable and photosynthetically healthy under darkness without undergoing asexual reproduction. Both diatoms are essential contributors to fouling and microphytobenthic community. Upon re-exposure of dark-adapted biofilms to 12 hlight:dark photocycle, the improvement in photosynthetic efficiency and resumption of growth via asexual-reproduction was observed. However, the lag-phase duration increased with a long dark history. Nevertheless, eurytolerant nature and high dark survival capability (with its quick response to light) of Amphora and Navicula indicated that they have the potential to colonize benthic-ecosystems thus impacting the benthic and fouling community.

Best available technique for the recovery of marine benthic communities in a gravel shore after the oil spill: A mesocosm-based sediment triad assessment

Ecotoxicological effects of spilled oils are well documented, but study of recovery of marine benthic communities is limited. Long-term recovery of hard bottom communities during physical and biological remediations after a spill was monitored. A 60-day experiment was conducted using a mesocosm with monitoring of eight endpoints by use of the sediment quality triad (SQT). First, physical treatment of hot water + high pressure flushing maximally removed residual oils (max=93%), showing the greatest recovery among SQT variables (mean=72%). Physical cleanup generally involved adverse effects such as depression of the microphytobenthic community during the initial period. Next, biological treatments, such as fertilizer, emulsifier, enzyme and augmentation of the microbes, all facilitated removal of oil (max=66%) enhancing ecological recovery. Analysis of the microbiome confirmed that oil-degrading bacteria, such as Dietzia sp. and Rosevarius sp. were present. A mixed bioremediation, including fertilizer + multi-enzyme + microbes (FMeM) maximized efficacy of remediation as indicated by SQT parameters (mean=47%). Natural attenuation with “no treatment” showed comparable recovery to other remediations. Considering economic availability, environmental performance, and technical applicability, of currently available techniques, combined treatments of physical removal via hand wiping followed by FMeM could be most effective for recovery of the rocky shore benthic community.

Antarctic Glacial Meltwater Impacts the Diversity of Fungal Parasites Associated With Benthic Diatoms in Shallow Coastal Zones.

Aquatic ecosystems are frequently overlooked as fungal habitats, although there is increasing evidence that their diversity and ecological importance are greater than previously considered. Aquatic fungi are critical and abundant components of nutrient cycling and food web dynamics, e.g., exerting top-down control on phytoplankton communities and forming symbioses with many marine microorganisms. However, their relevance for microphytobenthic communities is almost unexplored. In the light of global warming, polar regions face extreme changes in abiotic factors with a severe impact on biodiversity and ecosystem functioning. Therefore, this study aimed to describe, for the first time, fungal diversity in Antarctic benthic habitats along the salinity gradient and to determine the co-occurrence of fungal parasites with their algal hosts, which were dominated by benthic diatoms. Our results reveal that Ascomycota and Chytridiomycota are the most abundant fungal taxa in these habitats. We show that also in Antarctic waters, salinity has a major impact on shaping not just fungal but rather the whole eukaryotic community composition, with a diversity of aquatic fungi increasing as salinity decreases. Moreover, we determined correlations between putative fungal parasites and potential benthic diatom hosts, highlighting the need for further systematic analysis of fungal diversity along with studies on taxonomy and ecological roles of Chytridiomycota.

Allelopathic interactions between phytobenthos and meiofaunal community in an Adriatic benthic ecosystem: Understanding the role of aldehydes and macroalgal structural complexity

Macroalgae produce several allelopathic substances, including polyunsaturated aldehydes (PUAs), which may inhibit photosynthesis and growth rates of other algal species, and grazing. Additionally, macroalgal structural complexity is an important factor in determining abundance patterns and size structure of epiphytic organisms.In this study the PUAs production of two Mediterranean macroalgae, Dictyopteris polypodioides, (DP, Phaeophyceae, Dictyotales) and Cystoseira compressa (CC, Phaeophyceae, Fucales), was characterized to clarify the relationships between the meiobenthic and microphytobenthic communities. Results showed a higher PUAs production and a diverse qualitative profile for DP, which reported long-chain compounds (i.e. C14-C16) as main aldehydes, than CC, with the short-chain C6:2 as the main compound, as well as variability among sampling times. A clear separation of the meiofauna and microphytobenthos assemblages was found for the macroalgae, but with different temporal trends. Dissimilarities were due to five microalgal orders, namely Naviculales, Lyrellales, Gonyaulacales (i.e. Ostreopsis), Bacillariales, and Licmophorales, and to the meiofaunal groups nematodes, copepods, and copepod nauplii, which were more abundant on DP than on CC. Results indicate that macroalgal complexity is a major determinant of the meiofaunal community structure (accounting for 26% of the variation), rather than PUAs production itself (17%). PUAs effects seem species-specific, thus affecting some grazers instead of the entire community. Conversely, microphytobenthos affected the meiofauna assemblages, particularly harpacticoids, confirming the role of these organisms as the primary food source of all marine food chain producers. Since PUAs are produced also by several epiphytic diatoms, the understanding of their effects on the community structure and on the relationships among taxa in the field is complicated and requires further in-depth investigations in simplified systems (i.e. microcosms).

Functional adaptations of benthic communities to organic matter enrichment at the edge of an allowable zone of effect (AZE)

In a changing environment, it is important to understand the contribution of faunal and microbial communities to ecosystem functioning. In this context, the present study aimed to explore the effect of organic matter inputs due to aquaculture on the interaction between microphytobenthos and macrofaunal traits related to bioturbation. The study was conducted in the vicinity of a fish farm in a semi-enclosed bay in Cephalonia (Eastern Mediterranean). Two different disturbance zones were compared – a control area and an area close to fish cages and, more specifically, at the edge of the Allowable Zone of Effect (AZE) subject to intermediate stress from aquaculture waste discharge. Bioturbation potential was the main driver shaping microphytobenthic community composition. While Euglenophytes prevailed in the benthic communities close to fish farms, Cyanobacteria were more abundant in the control area, indicating a shift from a microbially driven functioning to a more macrofaunal one near fish cages. Indeed, a shift from suspension feeding to predation and scavenging was recorded close to fish cages. This shift was caused by the interaction of different trophic groups, food availability, as well as the interference of the increased bioturbation in suspension feeding near fish cages. High bioturbation and bioirrigation potentials recorded near fish cages probably acted as moderators of the negative effects of organic matter deposition caused by fish farming. In conclusion, the benthic community close to fish cages was more diverse in terms of biological traits than at the control sites. This indicated the co-existence of species with different ecological strategies near fish cages.

Exploring Multiple Aspects of Taxonomic and Functional Diversity in Microphytobenthic Communities: Effects of Environmental Gradients and Temporal Changes.

Biodiversity has traditionally been quantified using taxonomic information but the importance of also considering its functional characteristics has recently gained an increasing attention among microorganisms. However, studies exploring multiple aspects of taxonomic and functional diversity and their temporal variations are scarce for diatoms, which is one of the most important microbial groups in aquatic ecosystems. Here, our aim was to examine the taxonomic and functional alpha and beta diversities of diatoms in a coastal rock pool system characterized by a naturally high environmental heterogeneity. We also investigated the temporal differences in the diversity patterns and drivers. The relationship between the species richness and functional dispersion was temporally coherent, such that species-poor communities tended to be functionally clustered. The trend between the species richness and taxonomic uniqueness of community composition was temporally inconsistent, changing from negative to non-significant over time. Conductivity or distance to the sea or both were key determinants of species richness, functional dispersion, and uniqueness of community composition. The increase of community dissimilarity with an increasing environmental distance was stronger for the taxonomic than the functional composition. Our results suggest that even minor decreases in the species richness may result in a lowered functional diversity and decreased ecosystem functioning. Species-poor ecosystems may, however, have unique species compositions and high contributions to regional biodiversity. Despite changing the species compositions along the environmental gradients, communities may remain to have a high functional similarity and robustness in the face of environmental changes. Our results highlight the advantage of considering multiple biodiversity metrics and incorporating a temporal component for a deeper understanding of the effects of environmental changes on microbial biodiversity.

Succession pattern and phylotype analysis of microphytobenthic communities in a simulated oil spill seagrass mesocosm experiment

Microphytobenthic communities play a significant role in nutrient modulation, sediment stabilization, and primary production in seagrass beds, which provide various ecosystem services. We hypothesized that microphytobenthic communities in sediments of chronically oil-exposed seagrass beds will exhibit increased resiliency to stressors associated with oil exposure as opposed to seagrass beds never exposed to oil spills. We prepared 14-liter seawater mesocosms, each containing a submersed macrophyte Ruppia maritima collected from the Chandeleur Islands, Louisiana, and Estero Bay, Florida. Mesocosms were initially exposed to 50% water-accommodated oil fractions (WAF) and subsequently diluted by 50% with daily artificial seawater exchanges over 8 days to simulate tidal dilution. High-throughput amplicon sequencing based on 23S rRNA gene targeting cyanobacteria and chloroplasts of eukaryotic microphytobenthos was conducted to assess the impact of oiling on microphytobenthic communities with additional assessment via microscopy. High-throughput sequencing in combination with traditional microscopic analysis provided a robust examination in which both methods roughly complemented each other. Distinct succession patterns were detected in benthic algal communities of chronically oil-exposed (Louisiana) versus unexposed (Florida) seagrass bed sediments. The impact of oiling in microphytobenthos across all samples showed that benthic diatoms dominated all algal communities with sample percentages ranging from 42 to 97%, followed by cyanobacteria (2 to 50%). It is noteworthy that drastic changes in microphytobenthic community structure in terms of the larger taxonomic level were not observed, rather change occurred at the phylotype level. These results were also confirmed by microscopy. Similarity percentages (SIMPER) analysis identified seven phylotypes (Cyanobacteria, Bacillariophyceae, and Mediophyceae) in the Louisiana samples and one phylotype (Bacillariophyceae) in the Florida samples that increased in relative sequence abundance after oil exposure. The detailed phylotype analysis identifying sentinel microphytobenthic indicators provides a base for future research on benthic microalgae response to ecosystem disturbance.

Ecophysiological and Cell Biological Traits of Benthic Diatoms From Coastal Wetlands of the Southern Baltic Sea.

The German Baltic Sea coastline is characterized by sea-land transitions zones, specifically coastal peatlands. Such transition zones exhibit highly fluctuating environmental parameters and dynamic gradients that affect physiological processes of inhabiting organisms such as microphytobenthic communities. In the present study four representative and abundant benthic diatom strains [Melosira nummuloides, Nitzschia filiformis, Planothidium sp. (st. 1) and Planothidium sp. (st.2)] were isolated from a Baltic Sea beach and three peatlands that are irregularly affected by Baltic Sea water intrusion. Ecophysiological and cell biological traits of the strains were investigated for the first time as function of light, temperature and salinity. The four strains exhibited euryhaline growth over a range of 1–39 SA, surpassing in situ salinity of the respective brackish habitats. Furthermore, they showed eurythermal growth over a temperature range from 5 to 30°C with an optimum temperature between 15 and 20°C. Growth rates did not exhibit any differences between the peatland and Baltic Sea strains. The photosynthetic temperature optimum of the peatland diatom isolates, however, was much higher (20–35°C) compared to the Baltic Sea one (10°C). All strains exhibited light saturation points ranging between 29.8 and 72.6 μmol photons m–2 s–1. The lipid content did not change in response to the tested abiotic factors. All data point to wide physiological tolerances in these benthic diatoms along the respective sea-land transitions zones. This study could serve as a baseline for future studies on microphytobenthic communities and their key functions, like primary production, under fluctuating environmental stressors along terrestrial-marine gradients.

Influence of microphytobenthos on the sedimentary organic matter composition in two contrasting estuarine microhabitats.

The influence of microphytobenthic community on the composition of sedimentary organic matter was evaluated in two Bahía Blanca estuary microhabitats contrasting in vegetation and hydrodynamic conditions; namely, S1 located in a Sarcocornia perennis saltmarsh with macroscopic microbial mats and S2 in a mudflat without macroscopic microbial mats or vegetation. Moisture, organic matter, chlorophyll a, phaeopigments, carbohydrates (CH), proteins (PRT), and abundance and structure of microphytobenthic community were evaluated in surface sediments. Higher moisture was observed at S2 and was related to the proximity of this site to the subtidal zone and the effect of the environmental variables temperature and rain. No significant differences were found in organic matter content between sites; however, at S1, a higher concentration was registered during winter and early spring associated to the period of higher microphytobenthic biomass. Chlorophyll a and phaeopigments were higher at S1, attributed to the higher microphytobenthos abundance at this site. Differences in microphytobenthos were observed not only in quantity but also in community structure since at S1 filamentous cyanobacteria dominated the community, whereas at S2, higher abundance of centric diatoms and the absence of cyanobacteria were observed during most of the study. S1 showed higher concentration of proteins and carbohydrates which could be attributed to the higher production of fresh organic matter by microphytobenthos. The total protein and carbohydrate concentrations allowed us to classify both microhabitats into the meso-oligotrophic category, contrasting with the classification made by other authors using water column proxies.