Benthic foraminiferal responses to anthropogenic manipulation on a wild oyster reef

Benthic foraminifera are known to respond quickly to environmental changes. Biological indices are used in marine subtidal areas (Barras et al., 2014) to monitor impacted marine environments (Mojtahid et al., 2006, 2008). Such indices could be useful in transitional marine environments such as estuaries and mudflats where no accurate indices are available. To develop such to ols and to improve our knowledge on b enthic foraminifera in intertidal environments, we followed the spatial and temporal distribution of b enthic foraminifera in Bourgneuf Bay, a coastal bay with a large mudflat situated south of the Loire estuary on French west coast. At this location, wild oyster reefs are present. Partial release of organic and inorganic nutrients through oyster excretion enriches the nutrients flow leading to microphytobenthos bloom around the reef. To show this relation and to understand the relation between the different biological compartments,we analysed the foraminiferal composition of the sediment around the reef before and after ananthrop ogenic manipulation. In July 2014, the oysters of the reef were removed in order to assess their impact on microphytob enthos and meiofauna. In this study, we showed a strong impact of this anthrop ogenic manipulation on benthic foraminiferal densities and species composition. These results confirmed the strong and quick responses of benthic foraminifera from intertidal areas to environmental changes and showed that intertidal benthic foraminifera can be used as an index to monitor transitional marine environments

Locomotion speed of the benthic foraminifer Ammonia tepida exposed to different nitrogen and carbon sources

Ammonia tepida is a dominant benthic foraminifer colonizing intertidal mudflat sediments. Horizontal locomotion speeds were monitored using time-lapse image analysis over 6 and 24 h. Experimental conditions were based on foraminifera exposed to dry sediment re-suspended in artificial sea water (ASW) without any nutrient addition (condition DS), to combusted sediment re-suspended in in ASW also without any nutrient addition (condition CS), or to combusted sediment re-suspended in ASW enriched with either: nitrate, urea, glucose, soil extract (SE), extracellular polymeric substances (EPS), benthic diatoms (Entomoneis paludosa) or natural microphytobenthic assemblages (MPB). Significant differences were already measured after 6 h between A. tepida mean locomotion speeds at the different experimental conditions. However, differences were clearer after 24 h where the slowest A. tepida mean locomotion speed was measured in specimens placed in CS (1.00 ± 0.30 mm h− 1) and the highest mean locomotion speed in DS (2.99 ± 0.22 mm h− 1). Three different groups were defined according to their locomotion speed, (1) foraminifera exposed to DS had a locomotion speed significantly higher than all other conditions, (2) foraminifera placed in conditions enriched in SE, Glucose, Urea and EPS had intermediary locomotion speeds (1.8–2.5 mm h− 1), and (3) conditions with foraminifera showing the lowest locomotion speeds (1–1.6 mm h− 1) were CS, nitrate, MPB and E. paludosa. Thus, foraminifera exposed to organic matter (DS, SE, Glucose and Urea) showed faster locomotion speeds than foraminifera exposed to inorganic matter (CS, nitrate) or live preys (E. paludosa, MPB). Dissolved organic matter enrichment enhanced foraminifera locomotion speed, which might be a behavioural response to satisfy their carbon and/or nitrogen requirements, and the lowest locomotion speed observed when feeding on live preys might be a consequence of longer time required for live prey phagocytosis

What happened to my plastids? - Persistence of functionality in diatom plastids stolen by grazer intertidal benthic foraminifera

International audienc

Effect of bacteria on growth and biochemical composition of two benthic diatoms Halamphora coffeaeformis and Entomoneis paludosa

Benthic diatoms are the dominant microalgae in intertidal mudflats and are in constant interaction with their surrounding bacteria. This study was designed to investigate the effect of bacteria on growth, biomass, elemental (C & N) and biochemical composition, and extracellular polymeric substances (EPS) excretion by two marine benthic diatoms, Halamphora coffeaeformis and Entomoneis paludosa. The experiments were conducted on diatom cultures previously exposed or not to antibiotics. The treatment with antibiotics caused a decrease of bacterial abundance from 24 to fewer than 1 bacteria per algal cell. In non-treated cultures of E. paludosa and H. coffeaeformis, the bacteria phylogenetic affiliation was equally distributed between Bacteroidetes (Flavobacteriia) and Proteobacteria (alpha- and gammaproteobacteria). After treatment with antibiotics, the residual bacterial community was ~ 37% Flavobacteriia (Winogragskyella genus), 34% for the alphaproteobacteria (mainly Roseibacterium sp and Antarctobacter sp.) and 29% for the gammaproteobacteria (mainly Methylophaga sp. and Stenotrophomonas sp.). Growth of H. coffeaeformis and E. paludosa in non-treated cultures was enhanced by the abundance of the associated bacteria, with mean growth rate of 1 day− 1 compared to 0.7 for antibiotic treated cultures. In E. paludosa, maximal cell abundance was higher in the presence of bacteria while the final carbon biomass did not vary, but in H. coffeaeformis maximal cell abundance did not vary significantly while final carbon biomass was higher in the presence of bacteria. By contrast, for both diatoms, cellular content of protein and lipids decrease significantly, as did extracellular carbon (EPS fraction) in the presence of bacteria. However, only a minor effect was observed on cellular carbohydrates, C/N ratio, and pigments (Chl a). Diatoms carbon fluxes towards the main biochemical components were also modified, with the protein carbon fraction significantly lower relative to other carbon compounds in the presence of high bacterial biomass. These results showed the complex interactions between diatoms and their associated bacteria. Promotion of diatoms growth by the presence of bacteria appears linked to change in microalgae biochemical composition that will modify the biofilm. Our results might help understanding the regulation of benthic biota in mudflat ecosystems

Enrichment of intracellular sulphur cycle –associated bacteria in intertidal benthic foraminifera revealed by 16S and aprA gene analysis

Benthic foraminifera are known to play an important role in marine carbon and nitrogen cycles. Here, we report an enrichment of sulphur cycle -associated bacteria inside intertidal benthic foraminifera (Ammonia sp. (T6), Haynesina sp. (S16) and Elphidium sp. (S5)), using a meta barcoding approach targeting the 16S rRNA and aprA -genes. The most abundant intracellular bacterial groups included the genus Sulfurovum and the order Desulfobacterales. The bacterial 16S OTUs are likely to originate from the sediment bacterial communities, as the taxa found inside the foraminifera were also present in the sediment. The fact that 16S rRNA and aprA -gene derived intracellular bacterial OTUs were species-specific and significantly different from the ambient sediment community implies that bacterivory is an unlikely scenario, as benthic foraminifera are known to digest bacteria only randomly. Furthermore, these foraminiferal species are known to prefer other food sources than bacteria. The detection of sulphur-cycle related bacterial genes in this study suggests a putative role for these bacteria in the metabolism of the foraminiferal host. Future investigation into environmental conditions under which transcription of S-cycle genes are activated would enable assessment of their role and the potential foraminiferal/endobiont contribution to the sulphur-cycle.Peer reviewe

Effect of light on photosynthetic efficiency of sequestered chloroplasts in intertidal benthic foraminifera (<i>Haynesina germanica</i> and <i>Ammonia tepida</i>)

Some benthic foraminifera have the ability to incorporate functional chloroplasts from diatoms (kleptoplasty). Our objective was to investigate chloroplast functionality of two benthic foraminifera (<i>Haynesina germanica</i> and <i>Ammonia tepida</i>) exposed to different irradiance levels (0, 25, 70 µmol photon m⁻² s⁻¹) using spectral reflectance, epifluorescence observations, oxygen evolution and pulse amplitude modulated (PAM) fluorometry (maximum photosystem II quantum efficiency (Fv/Fm) and rapid light curves (RLC)). Our results clearly showed that <i>H. germanica</i> was capable of using its kleptoplasts for more than 1 week while <i>A. tepida</i> showed very limited kleptoplastic ability with maximum photosystem II quantum efficiency (Fv/Fm  =  0.4), much lower than <i>H. germanica</i> and decreasing to zero in only 1 day. Only <i>H. germanica</i> showed net oxygen production with a compensation point at 24 µmol photon m⁻² s⁻¹ and a production up to 1000 pmol O₂ cell⁻¹ day⁻¹ at 300 µmol photon m⁻² s⁻¹. <i>Haynesina germanica</i> Fv/Fm slowly decreased from 0.65 to 0.55 in 7 days when kept in darkness; however, it quickly decreased to 0.2 under high light. Kleptoplast functional time was thus estimated between 11 and 21 days in darkness and between 7 and 8 days at high light. These results emphasize that studies about foraminifera kleptoplasty must take into account light history. Additionally, this study showed that the kleptoplasts are unlikely to be completely functional, thus requiring continuous chloroplast resupply from foraminifera food source. The advantages of keeping functional chloroplasts are discussed but more information is needed to better understand foraminifera feeding strategies

Isolation, Structure Elucidation, Relative LC-MS Response, and in Vitro Toxicity of Azaspiracids from the Dinoflagellate Azadinium spinosum

We identified three new azaspiracids (AZAs) with molecular weights of 715, 815, and 829 (AZA33 (3), AZA34 (4), and AZA35, respectively) in mussels, seawater, and Azadinium spinosum culture. Approximately 700 mu g of 3 and 250 mu g of 4 were isolated from a bulk culture of A. spinosum, and their structures determined by MS and NMR spectroscopy. These compounds differ significantly at the carboxyl end of the molecule from known AZA analogues and therefore provide valuable information on structure-activity relationships. Initial toxicological assessment was performed using an in vitro model system based on Jurkat T lymphocyte cytotoxicity, and the potencies of 3 and 4 were found to be 0.22- and 5.5-fold that of AZA1 (1), respectively. Thus, major changes in the carboxyl end of 1 resulted in significant changes in toxicity. In mussel extracts, 3 was detected at low levels, whereas 4 and AZA35 were detected only at extremely low levels or not at all. The structures of 3 and 4 are consistent with AZAs being biosynthetically assembled from the amino end

Heterocapsa cf. bohaiensis (dinoflagellate): identification and response to nickel and iron stress revealed through chlorophyll a fluorescence

Metal toxicity in marine ecosystems is a growing issue owing to terrestrial runoff and anthropogenic pollution. Heterocapsa cf. bohaiensis, a newly isolated dinoflagellate from New Caledonia, was cultivated in photobioreactors operating continuously with high concentrations (10-3 M) of nickel (Ni2+) and/or iron (Fe2+) and their photosynthetic efficiency was assessed. The photosynthetic measurements indicated that H. cf. bohaiensis was tolerant to Ni2+ but sensitive to Fe2+ high concentrations. In the presence of Fe2+, maximum quantum efficiency and maximal relative electron transport rate decreased from 0.62 to 0.47 and from 156 to 102, respectively. The JIP-tests suggested a reduction of the photosynthesis in response to Fe2+ due to a disruption in the electron transport chain rather than a defect in the light absorption and trapping capacity which were on the contrary enhanced by Fe2+. These results bring new knowledge on the impact of nickel and iron on microalgae photosynthetic pathways