Letteratura scientifica selezionata sul tema "Haynesina germanica"

Abstract. Some benthic foraminifera have the ability to incorporate functional chloroplasts from diatoms (kleptoplasty). Our objective was to investigate chloroplast functionality of two benthic foraminifera (Haynesina germanica and Ammonia tepida) 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 H. germanica was capable of using its kleptoplasts for more than 1 week while A. tepida showed very limited kleptoplastic ability with maximum photosystem II quantum efficiency (Fv/Fm = 0.4), much lower than H. germanica and decreasing to zero in only 1 day. Only H. germanica 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. Haynesina germanica 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.

The combination of lower diet quality and increased metabolic rates is assumed to cause cascading effects on organismic C cycling. Future changes in CO2 levels or terrestrial nutrient discharges in marine ecosystems can lead to increased phytoplankton C:N ratios relative to consumer C:N ratios, lowering the quality of the food source. In this study, we compared the single and interactive effects of diet quality and temperature on the feeding behavior and C and N intake and release of a common and abundant intertidal mixotrophic protist, the foraminifer Haynesina germanica. Two batches of artificially produced and dual isotope-labeled (13C/15N) chlorophyte detritus with different C:N ratios (5.6 and 7.1) were fed to the foraminifer at 3 different temperatures (15, 20, 25°C). We observed a strong interactive effect of temperature and diet. A very strong increase in feeding rates was observed at 20°C for the low-quality food source. Respiration rates of carbon derived from the low-quality diet (C:N ratio of 7.1) were lower than those of the high-quality diets and increased at 25°C. This indicates that a high C content of the diet might be of advantage in calcifying mixotrophs, since respired excess C could be advantageous for test calcification. Additionally, respired excess C could be a useful resource of CO2 for kleptoplast photosynthesis and functionality in the mixotrophic lifestyle of H. germanica. Further, the observed effects of diet and temperature could impact nutrient fluxes in the habitat of H. germanica, possibly leading to food-web shifts in the future.

Monthly samples retrieved from the previously unstudied Plym Estuary, from January 1994 to November 1994, were analysed for living and dead Foraminifera. An assemblage composed of three hyaline species; Haynesina germanica, Elphidium williamsoni and Ammonia beccarii var. batavus, was identified. Further samples were taken to assess depth distribution, microdistribution and lateral distribution, to compliment the original sample suite. A comparison of the dead assemblage to the live assemblage revealed similar species proportions in both assemblages, reduced test abundance in the dead assemblage, and the presence of rare estuarine and marine species in the dead assemblage. This study has revealed a complex interplay of species resulting in several foraminiferal blooms throughout the year; the largest occurring in May.

Abstract. Benthic foraminifera are abundant marine protists which play an important role in the transfer of energy in the form of organic matter and nutrients to higher trophic levels. Due to their aquatic lifestyle, factors such as water temperature, salinity and pH are key drivers controlling biomass turnover through foraminifera. In this study the influence of salinity on the feeding activity of foraminifera was tested. Two species, Ammonia tepida and Haynesina germanica, were collected from a mudflat in northern Germany (Friedrichskoog) and cultured in the laboratory at 20 ∘C and a light–dark cycle of 16:08 h. A lyophilized algal powder from Dunaliella tertiolecta, which was isotopically enriched with 13C and 15N, was used as a food source. The feeding experiments were carried out at salinity levels of 11, 24 and 37 practical salinity units (PSU) and were terminated after 1, 5 and 14 d. The quantification of isotope incorporation was carried out by isotope ratio mass spectrometry. Ammonia tepida exhibited a 10-fold higher food uptake compared to H. germanica. Furthermore, in A. tepida the food uptake increased with increasing salinity but not in H. germanica. Over time (from 1–5 to 14 d) food C retention increased relative to food N in A. tepida while the opposite was observed for H. germanica. This shows that if the salinity in the German Wadden Sea increases, A. tepida is predicted to exhibit a higher C and N uptake and turnover than H. germanica, with accompanying changes in C and N cycling through the foraminiferal community. The results of this study show how complex and differently food C and N processing of foraminiferal species respond to time and to environmental conditions such as salinity.

Abstract. Benthic foraminifera are highly abundant heterotrophic protists in marine sediments, but future environmental changes will challenge the tolerance limits of intertidal species. Metabolic rates and physiological processes in foraminifera are strongly dependent on environmental temperatures. Temperature-related stress could therefore impact foraminiferal food source processing efficiency and might result in altered nutrient fluxes through the intertidal food web. In this study, we performed a laboratory feeding experiment on Ammonia tepida and Haynesina germanica, two dominant foraminiferal species of the German Wadden Sea/Friedrichskoog, to test the effect of temperature on phytodetritus retention. The specimens were fed with 13C and 15N labelled freeze-dried Dunaliella tertiolecta (green algae) at the start of the experiment and were incubated at 20, 25 and 30 °C respectively. Dual labelling was applied to observe potential temperature effects on the relation of phytodetrital carbon and nitrogen retention. Samples were taken over a period of 2 weeks. Foraminiferal cytoplasm was isotopically analysed to investigate differences in carbon and nitrogen uptake derived from the food source. Both species showed a positive response to the provided food source, but carbon uptake rates of A. tepida were 10-fold higher compared to those of H. germanica. Increased temperatures had a far stronger impact on the carbon uptake of H. germanica than on A. tepida. A distinct increase in the levels of phytodetrital-derived nitrogen (compared to more steady carbon levels) could be observed over the course of the experiment in both species. The results suggest that higher temperatures have a significant negative effect on the carbon exploitation of H. germanica. For A. tepida, higher carbon uptake rates and the enhanced tolerance range for higher temperatures could outline an advantage in warmer periods if the main food source consists of chlorophyte phytodetritus. These conditions are likely to impact nutrient fluxes in A. tepida/H. germanica associations.

The assessment of behavioural traits of marine organisms is increasingly recognized as a key issue to understanding their role in ecosystem processes such as bioturbation and nutrient cycling. The movement ability of intertidal foraminifera suggest that they may have a role, yet to be quantified, in benthic-pelagic coupling through their movement on the sediment surface, at the sediment-water interface and within the sediment. In this context, we investigated the behavioural traits of 5 benthic foraminiferal species typical of European temperate mudflats under standardized trophic light and temperature conditions. Behavioural traits related to motion of Ammonia tepida, Haynesina germanica, Cribroelphidium williamsoni, Miliammina fusca and Quinqueloculina seminula were assessed through their travelled distance, velocity, tortuosity of the path, position in the sediment and activity index. By analogy with macrofauna bioturbation functional groups, we describe the studied foraminifera as biodiffusor species with 3 sub-groups defined according to their vertical position in the sediment. C. williamsoni belongs to the epifaunal-biodiffusors, A. tepida and H. germanica belong to the surficial-biodiffusors, and Q. seminula and M. fusca are considered gallery-biodiffusors. Our results further suggest that features such as velocity, activity and tortuosity may mediate sediment-mixing intensity. Therefore, Q. seminula, H. germanica and C. williamsoni, which are the most active species, would have a larger effect on particle reworking rates than the less active A. tepida and M. fusca. Our results suggest that benthic foraminifera may play an underestimated role in bioturbation processes.

L’objectif de cette thèse est de décrire le rôle des foraminifères benthiques dans les processus de bioturbation en se focalisant sur les flux sédimentaires à l’interface eau-sédiment. Plus spécifiquement, les objectifs sont (i) de caractériser le comportement de déplacement à l’interface eau-sédiment des espèces dominants les vasières intertidales des côtes Est de la Manche pour notamment les classer dans les groupes fonctionnels de bioturbation, (ii) de quantifier le remaniement sédimentaire de surface de ces espèces, (iii) de comprendre comment les facteurs biotiques et abiotiques vont moduler le mode et l’intensité du remaniement sédimentaire de l’espèce Haynesina germanica, enfin, (iv) de décrire la dynamique du déplacement verticale, des structures biogéniques et de quantifier le taux de bioturbation de H. germanica. Pour cela, les paramètres suivants ont été mesurés : la distance parcourue, la vitesse de déplacement, la position, l’indice d’activité et la complexité de la trajectoire. La dynamique du déplacement a été étudiée sur les espèces suivantes : Haynesina germanica, Cribroelphidium williamsoni, Quinqueloculina seminulum, Ammonia tepida et Miliammina fusca. Bien que toutes identifiées comme appartenant au groupe fonctionnel des biodiffuseurs, les espèces occupent des positions verticales distinctes dans la colonne sédimentaire. Ainsi, C. williamsoni est un biodiffuseur épifaune, Q. seminulum, M. fusca et H. germanica sont des biodiffuseurs de galeries tandis que A. tepida est un biodiffuseur de surface. Ceci suggère ainsi des effets différents sur la redistribution spatiale des particules. L’intensité du remaniement sédimentaire est contrôlée par les traits spécifiques ainsi que par les facteurs biotiques et abiotiques. En effet, la distance parcourue, la vitesse, le niveau d’activité et la complexité de la trajectoire varient à la fois entre et au sein des espèces. Par conséquent, les taux de remaniement sédimentaire varient aux échelles spécifiques, individuelles et fonctionnelles. Spécifiquement, l’étude d’H. germanica montre que la taille du test, la densité, la température et la concentration en matière organique sont des éléments clefs structurant son activité de bioturbation. Ce travail illustre la capacité des foraminifères benthiques à contribuer au processus de remaniement sédimentaire à l’interface eau-sédiment mais également en profondeur. Il ouvre de nouvelles perspectives sur la compréhension de l’écologie des foraminifères et leur rôle non négligeable dans la bioturbation des écosystèmes intertidaux
The aim of this PhD is to describe the role of benthic foraminifera in bioturbation processes focusing on particulate fluxes at the sediment-water interface. Specifically, the objectives are fourfold: (i) characterising the motion behaviour of key benthic foraminiferal species inhabiting intertidal mudflats from the Eastern English Channel at the sediment water interface to further classify them into functional groups of bioturbation, (ii) quantifying surface sediment reworking rates of the above-mentioned species, (iii) understanding how biotic and abiotic parameters may drive the mode and the intensity of surface sediment reworking of the dominant species Haynesina germanica, and (iv) further describing the vertical burrowing dynamics and the biogenic structures built by Haynesina germanica to quantify its bioturbation rates. To do so, the following parameters are described: the travelled distance, the velocity, the vertical position, the activity level and the tortuosity of the path. The motion-behaviour is described for the following species: Haynesina germanica, Cribroelphidium williamsoni, Quinqueloculina seminulum, Ammonia tepida and Miliammina fusca. Although they are all classified in the functional group of biodiffusors, these species differ in their preferential vertical position within the sediment. Specifically, C. williamsoni is an epifaunal-biodiffusor, Q. seminulum, M. fusca and H. germanica are gallery-biodiffusors while A. tepida is a surficial biodiffusor. This therefore means that the mode of sediment reworking is species-specific in benthic foraminifera. Its intensity is mediated by specific traits as well as biotic and abiotic factors. Indeed, travelled distance, velocity, activity level and tortuosity of the path would vary between and within species. As a consequence, the rate and the mode of sediment reworking are species-, individual- and functional group-dependant. Specifically, the surface area of the test, the species density, the temperature and the organic matter concentration are key parameters that control the bioturbation activity of H. germanica. The present work highlights the role of benthic foraminifera in sediment reworking processes taking place at the sediment-water interface and in the sediment column. It opens new perspectives on the understanding of the ecology of foraminifera and their putative non-negligible role in bioturbation processes in intertidal ecosystems