Resource Quantity Affects Benthic Microbial Community Structure and Growth Efficiency in a Temperate Intertidal Mudflat

Estuaries cover <1% of marine habitats, but the carbon dioxide (CO2) effluxes from these net heterotrophic systems contribute significantly to the global carbon cycle. Anthropogenic eutrophication of estuarine waterways increases the supply of labile substrates to the underlying sediments. How such changes affect the form and functioning of the resident microbial communities remains unclear. We employed a carbon-13 pulse-chase experiment to investigate how a temperate estuarine benthic microbial community at 6.5°C responded to additions of marine diatom-derived organic carbon equivalent to 4.16, 41.60 and 416.00 mmol C m−2. The quantities of carbon mineralized and incorporated into bacterial biomass both increased significantly, albeit differentially, with resource supply. This resulted in bacterial growth efficiency increasing from 0.40±0.02 to 0.55±0.04 as substrates became more available. The proportions of diatom-derived carbon incorporated into individual microbial membrane fatty acids also varied with resource supply. Future increases in labile organic substrate supply have the potential to increase both the proportion of organic carbon being retained within the benthic compartment of estuaries and also the absolute quantity of CO2 outgassing from these environments

Relationships between biodiversity and the stability of marine ecosystems: comparisons at a European scale using meta-analysis.

The relationship between biodiversity and stability of marine benthic assemblages was investigated using existing data sets (n = 28) covering various spatial (m-km) and temporal (1973-2006) scales in different benthic habitats (emergent rock, rock pools and sedimentary habitats) through meta-analyses. Assemblage stability was estimated by measuring temporal variances of species richness, total abundance (density or % cover) and community species composition and abundance structure (using multivariate analyses). Positive relationships between temporal variability in species number and richness were generally observed at both quadrat (<1 m2) and site (100 m2) scales, while no relationships were observed by multivariate analyses. Positive relationships were also observed at the scale of site between temporal variability in species number and variability in community structure with evenness estimates. This implies that the relationship between species richness or evenness and species richness variability is slightly positive and depends on the scale of observation, suggesting that biodiversity per se is important for the stability of ecosystems. Changes within community assemblages in terms of structure are, however, generally independent of biodiversity, suggesting no effect of diversity, but the potential impact of individual species, and/or environmental factors. Except for sedimentary and rock pool habitats, no relationship was observed between temporal variation of the aggregated variable of total abundances and diversity at either scale. Overall our results emphasise that relationships depend on scale of measurements, type of habitats and the marine systems (North Atlantic and Mediterranean) considered

Proliferation of purple sulphur bacteria at the sediment surface affects intertidal mat diversity and functionality

Funding provided by French National Centre for Scientific Research/INSU program EC2CO-MicroBien (Microbiologie Environnementale -BIOPOURPRE Project), European Community (ASSEMBLE grant agreement n° 227799), Region Pays de la Loire (France), Marine Alliance for Science and Technology for Scotland and the Scottish Funding Council and participating institutions.There is a relative absence of studies dealing with mats of purple sulphur bacteria in the intertidal zone. These bacteria display an array of metabolic pathways that allow them to disperse and develop under a wide variety of conditions, making these mats important in terms of ecosystem processes and functions. Mass blooms of purple sulphur bacteria develop during summer on sediments in the intertidal zone especially on macroalgal deposits. The microbial composition of different types of mats differentially affected by the development of purple sulphur bacteria was examined, at low tide, using a set of biochemical markers (fatty acids, pigments) and composition was assessed against their influence on ecosystem functions (sediment cohesiveness, CO2 fixation). We demonstrated that proliferation of purple sulphur bacteria has a major impact on intertidal mats diversity and functions. Indeed, assemblages dominated by purple sulphur bacteria (Chromatiaceae) were efficient exopolymer producers and their biostabilisation potential was significant. In addition, the massive growth of purple sulphur bacteria resulted in a net CO2 degassing whereas diatom dominated biofilms represented a net CO2 sink.Publisher PDFPeer reviewe

Impacts of biogenic structures on benthic assemblages: microbes, meiofauna, macrofauna and related ecosystem functions

Species that modify their surroundings are known as ecosystem engineers. For example, patches of polychaete tubes enhance soft-bottom intertidal habitat complexity, modifying water flow, promoting sediment accretion and affecting nutrient fluxes at the water-sediment interface. Understanding how such structures affect the benthic ecosystem's functioning requires the assessment of their influence on all benthic components and how the related ecosystem services may be modified. We performed an in situ experimental study, involving the use of artificial mimics of polychaete tubes, to investigate the purely physical impacts of the structures without the complexity of worm activity. Benthic chambers of different mimic densities were used, and their effect on the recolonisation of defaunated natural sandy sediments by microorganisms, meiofauna and macrofauna was monitored. We also measured air-sediment CO2 fluxes and sediment stability as they constitute crucial ecosystem services provided by benthic habitats. We showed that the biogenic structures stimulated the development of diatom biofilms (microphytobenthos) and their associated extracellular polymeric substances (EPS). Impacts of tubes on meiofaunal and macrofaunal assemblages were significant; in most cases, species and groups were more abundant in treatments with few or no tubes. In response to the tube density increase, the whole system tended towards heterotrophy and higher sediment stability, probably as a consequence of the development of the diatom biofilm. Biogenic structures are, therefore, of critical importance for soft-bottom intertidal communities in terms of both structure and function.</p

Impacts of biogenic structures on benthic assemblages: microbes, meiofauna, macrofauna and related ecosystem functions

International audienceSpecies that modify their surroundings are known as ecosystem engineers. For example, patches of polychaete tubes enhance soft-bottom intertidal habitat complexity, modifying water flow, promoting sediment accretion and affecting nutrient fluxes at the water–sediment interface. Understanding how such structures affect the benthic ecosystem’s functioning requires the assessment of their influence on all benthic components and how the related ecosystem services may be modified. We performed an in situ experimental study, involving the use of artificial mimics of polychaete tubes, to investigate the purely physical impacts of the structures without the complexity of worm activity. Benthic chambers of different mimic densities were used, and their effect on the recolonisation of defaunated natural sandy sediments by microorganisms, meiofauna and macrofauna was monitored. We also measured air–sediment CO2 fluxes and sediment stability as they constitute crucial ecosystem services provided by benthic habitats. We showed that the biogenic structures stimulated the development of diatom biofilms (microphytobenthos) and their associated extracellular polymeric substances (EPS). Impacts of tubes on meiofaunal and macrofaunal assemblages were significant; in most cases, species and groups were more abundant in treatments with few or no tubes. In response to the tube density increase, the whole system tended towards heterotrophy and higher sediment stability, probably as a consequence of the development of the diatom biofilm. Biogenic structures are, therefore, of critical importance for soft-bottom intertidal communities in terms of both structure and function

Role of bacterial communities in the annual benthic community production and respiration of two contrasted intertidal sediments (Roscoff Aber Bay, France),

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Physiological versus behavioral photoprotection in intertidal epipelic and epipsammic benthic diatom communities

Physiological and behavioral photoprotection are the two major mechanisms by which natural microphytobenthic assemblages protect themselves against high light. These mechanisms were investigated with high vertical resolution in intertidal epipelic (mud) and epipsammic (sand) benthic diatom communities. Photophobic cell migration was found in epipelic communities when exposed to high light, detected using pigment analysis of 200 μm sediment depth layers and Low Temperature Scanning Electron Microscopy. In the mud, significant differences between migratory and non-migratory (Latrunculin A-treated) biofilms were observed in the photosynthetic activity measured using rapid light curves: after exposure to high light, non-migratory biofilms showed lower light use efficiency (lower α) and lower maximum photosynthetic capacity (lower rETRmax). Increased de-epoxidation state (DPS) was observed in both epipelic and epipsammic diatom assemblages after exposure to high light: in the surface 400 μm for mud and throughout the sediment profile up to 1 mm for sand. The two diatom communities showed different photoregulatory strategies: the epipelic community of muddy sediments photoregulated using both physiological and behavioral photoprotection, while the epipsammic community of sandy sediments used exclusively physiological mechanisms.publishe