Experimental Approaches in Marine Biogeosciences


Experimental Approaches in Marine Biogeosciences
Co-organized by OS3, co-sponsored by JpGU
Convener: Petra Heinz | Co-conveners: Hiroshi Kitazato, Christiane SchmidtECSECS, Takashi Toyofuku
vPICO presentations
| Thu, 29 Apr, 11:00–12:30 (CEST)

vPICO presentations: Thu, 29 Apr

Chairpersons: Hiroshi Kitazato, Christiane Schmidt, Takashi Toyofuku
Marco Sigovini, Luigi Tosi, Andrea Bergamasco, Sandra Donnici, Andrea Sabino, and Alessandro Bergamasco

Environments along the ocean-land continuum strictly interlink to each other both in horizontal and in vertical. Most of the acting processes require investigation through a multi looking observation approach, integrating coastal oceanography, hydrogeology and marine ecology. This can be achieved by simultaneously looking from different perspectives at the same environmental context and processes.
The present study focuses on the northern Adriatic Sea, where a number of peculiar, diverse and valuable coastal and marine ecosystems are localized, characterized by high biodiversity and productivity, such as the Lagoon of Venice and the underwater biogenic-geogenic rocky outcrops named tegnùe. Their structural complexity and habitat heterogeneity is increased by the role of habitat forming species, bioconstructors and biodemolitors. To understand the ecological and morphogenetic role of these organisms, selected biogenic formations and habitats, such as the fan mussel Pinna nobilis colonies on both the Lagoon of Venice and the rocky outcrops, were investigated. Innovative approaches are here presented to map and characterize these biogenic habitats at different hierarchical levels, in order to promote their conservation.

How to cite: Sigovini, M., Tosi, L., Bergamasco, A., Donnici, S., Sabino, A., and Bergamasco, A.: A multi-observer approach to promote the conservation of north Adriatic marine biogenic habitats, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13706,, 2021.

Kazuma Oikawa, Hideko Takayanagi, Kazuyoshi Endo, Masa-aki Yoshida, and Yasufumi Iryu

Carbon (δ13C) and oxygen (δ18O) isotope composition of Rhynchonelliformea brachiopods (hereafter, called ‘brachiopods’) have been regarded as useful paleoenvironmental indicators throughout the Phanerozoic. However, recent studies have revealed that the isotopic composition in modern brachiopod shells records not only environmental changes in ambient seawater but also is influenced by biological controls such as the chemical/isotopic composition of calcifying fluids and physiological processes (e.g., growth rates, metabolism). The latter is known as biological isotope fractionation effects, such as kinetic, metabolic, and pH effects. Recently, a new calcification mechanism in brachiopod shell formation, ion transport mechanism, was proposed. In this study, we measured δ13C and δ18O values of the primary (PL) and secondary (SL) shell layers of three Pictothyris picta (one male and two female specimens) collected at a water depth of~61 m off Okinoshima to improve our understanding of biological isotope fractionation effects during their shell secretion. We obtained ontogenetic-series δ13C and δ18O profiles from the PL (PL-Ont) and the uppermost SL (SL-Ont) at the sampling resolution of 3 days to 8 months per sample. We obtained inner-series δ13C and δ18O profiles from the innermost SL (SL-In) as well. The variations in the δ13C and δ18O profiles of the PL-Ont showed similar trends to those of the SL-Ont. However, the PL-Ont values mostly exhibited relatively lower δ18O values than those of the SL-Ont. Cross plots between the δ13C and δ18O values of the PL-Ont indicated a strong positive correlation and were lower than those of calcite precipitated in isotopic equilibrium with ambient seawater at the fast growth stage, suggesting the significant influence of the kinetic isotope fractionation effect. The SL was precipitated in oxygen isotopic equilibrium with ambient seawater regardless of the growth stage and/or the seasonal changes in living environments. Furthermore, the PL-Ont, SL-Ont, and SL-Inshowed similar δ18O values during the cold season, indicating negligible influences of the kinetic, pH, and magnesium effects on δ18O composition. The δ13C values of the PL-Ont formed at the cold season (= micro-portion formed under the least kinetic isotope fractionation effect) were lower than those of the SL, indicating the stronger metabolic effect on the PL secretion. Our isotopic data showed that the time lag of the PL and the SL formation varies among specimens.

How to cite: Oikawa, K., Takayanagi, H., Endo, K., Yoshida, M., and Iryu, Y.: High-resolution carbon and oxygen isotope record in modern brachiopod Pictothyris picta collected off Okinoshima, Japan, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14032,, 2021.

Bianca Lintner, Michael Lintner, Jutta Wollenburg, Erik Wurz, and Petra Heinz

This is the first study on the interactions between foraminifera and sponges. Although Cibicides and Hyrrokin are regarded as parasites on siliceous sponges, it is not yet clarified whether foraminifera specifically colonize sponges or are accidentally sucked in during the pelagic stage. To better elucidate these relationships, 12 sponges of different genera were examined and their foraminiferal communities analyzed. In 2018, the sponges for this study were collected with a ROV in water depths of 223 to 625 m in the Norwegian-Greenland Sea. Sponge parts were preserved in ethanol (96 %) and stained with Rose Bengal (2g l-1) to allow a differentiation between the living and dead foraminiferal fauna.

Each sponge sample contained several hundred live and dead foraminiferal individuals of up to 60 different species. Even on Geodia baretti, which is able to release barettin to avoid colonalisation of other organisms, few foraminiferal individuals were observed. On all sponges, the most abundant genus was Cibicides, with Cibicides lobatulus and Cibicides refulgens as the most common taxa. Other very common species were Discorbinella bertheloti or Epistominella nipponica. Also, Hyrrokkin sarcophaga was found on different sponges and following its lifestyle, penetrating the sponge surfaces. The fact that besides adult foraminifera splendid juvenile stages were found indicate that foraminifera reproduced while inside the sponges. This reproduction might be stimulated/triggered by enhanced food availability by the pumping sponge.

In summary, sponges are a special habitat for a high number of foraminiferal taxa. Their interaction ranges from parasitic lifestyle up to reproduction purposes. All these aspects highlight the importance of foraminifera-sponge interactions.

How to cite: Lintner, B., Lintner, M., Wollenburg, J., Wurz, E., and Heinz, P.: Foraminifera-sponge interactions – commensalism to parasitism in the Norwegian-Greenland Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12913,, 2021.

Christiane Schmidt, Katharina Neumüller, Raphael Morard, Hildegard Westphal, Gurjit Theara, Grace Vaughan, and John Burt

The Persian Gulf hosts corals reefs under the most extreme conditions in the world, where summer maxima reach >36°C in combination with high salinities >44 PSU. While high bleaching thresholds characterize corals on these reefs, knowledge of adaptation of other calcifiers to local conditions is lacking. Benthic foraminifera are important calcifiers for coral reefs ecosystems as they build calcium carbonate tests. To map the environmental envelopes and the physiological limits of dispersal of benthic foraminfera, we exposed adult and juvenile foraminifera to a range of temperature and salinity conditions. Samples were collected from two reefs in the southern Gulf of Abu Dhabi, UAE. The dominant symbiont-bearing foraminifera was Peneroplis planatus hosting the endosymbiotic red algae Porphyridium purpureum. This was a surprising finding of sampling in these extreme reefs, as other symbiont-bearing benthic foraminifera are normally more abundant, but were completely absent in the reefs investigated. In the laboratory, we exposed P. planatus to 27°C (control), 35°C local summer maxima, and 39°C, +4°C above summer maxima, each with and without sediment substrates. The ecophysiological parameters growth, survivorship and photophysiological performance were measured. Photosynthetic rates declined after one week of exposure to 35°C and symbionts were photoinhibited at 39°C. Conditions were clearly more hostile for the symbionts, as host survival was high and growth rates unaffected by temperature. We hypothesize that to sustain growth the holobionts gained energy through heterotrophy under these conditions. In a second experiment, we exposed asexually reproduced offspring to an orthogonal temperature and salinity stress treatment (27-39°C, x 34-42 PSU) for four weeks. Asexual reproduction occurred in several treatments but was reduced under high salinity and temperature and combination of both parameters. The higher rate of asexual reproduction at control conditions indicates that stressful conditions do not trigger asexual reproduction in P. planatus, but rather suppress it. The results indicate that P. planatus can resist temperatures above current summer maxima for short periods of time, but that reproduction is impaired. Such heat-adapted populations may be considered a refuge for colonizing an increasingly warming Indian Ocean. Reproductive declines in the local population with increased warming threatens the long-term viability of this uniquely adapted organism.

How to cite: Schmidt, C., Neumüller, K., Morard, R., Westphal, H., Theara, G., Vaughan, G., and Burt, J.: Red algae-bearing benthic foraminifera adapted to extremely warm temperatures and high salinity in the Persian Gulf, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16223,, 2021.

Laurie Charrieau, Katsunori Kimoto, Delphine Dissard, Beatrice Below, Kazuhiko Fujita, Yukiko Nagai, and Takashi Toyofuku

Ocean acidification is a consequence of current anthropogenic climate changes. The concomitant decrease in pH and carbonate ion concentration in sea water may have severe impacts on calcifying organisms. Coral reefs are among the first ecosystems recognized vulnerable to ocean acidification. Within coral reefs, large benthic foraminifera (LBF) are major calcium carbonate producers.

The aim of this study was to evaluate the effects of varying pH on survival and calcification of the symbiont-bearing LBF species Peneroplis spp. We performed culture experiments to study their resistance to ocean acidification conditions, as well as their resilience once placed back under open ocean pH (7.9).

After three days, small signs of test decalcification were observed on specimens kept at pH 7.4, and severe test decalcification was observed on specimens kept at pH 6.9, with the inner organic lining clearly appearing. After 32 days under pH 7.4, similar strongly decalcified specimens were observed. All the specimens were alive at the end of the experiment. This result demonstrates the resistance of Peneroplis spp. to an acidified pH, at least on a short period of time.

After being partially decalcified, some of the living specimens were placed back at pH 7.9. After one month, the majority of the specimens showed recalcification features, mostly by addition of new chambers. The trace elements concentrations of the newly formed chambers were analysed by LA-ICPMS. Interestingly, more chambers were added when food was given, which highlights the crucial role of energy source in the recalcification process. Moreover, the newly formed chambers were most of the time abnormal, and the general structure of the tests was altered, with potential impacts on reproduction and in situ survival. In conclusion, if symbiont-bearing LBF show some resistance and resilience to lowered pH conditions, they will remain strongly affected by ocean acidification.

How to cite: Charrieau, L., Kimoto, K., Dissard, D., Below, B., Fujita, K., Nagai, Y., and Toyofuku, T.: The coral reef-dwelling Peneroplis spp. shows calcification resilience to ocean acidification conditions - results from culture experiments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15029,, 2021.

Débora Silva Raposo, Raphaël Morard, Christiane Schmidt, and Michal Kucera

In recent decades the “Lessepsian” migration caused a rapid change in the marine community composition due to the invasion of alien species from the Red Sea into the Mediterranean Sea. Among these invaders is the large benthic foraminifera Amphistegina lobifera, a diatom-bearing species that recently reached the invasion front in Sicily. There it copes with colder winters and broader temperature than in its original source, the Red Sea. It is not yet known how (or if) the population from the invasion front has developed adaptation to this new thermal regime. Understanding the modern marine invasive patterns is a crucial tool to predict future invasive successes in marine environments. Therefore, in this study we aim to evaluate the physiological responses to cold temperatures of A. lobifera populations at three different invasive stages: source (Red Sea), early invader (Eastern Mediterranean) and invasion front (Sicily). For this, we conducted a culturing experiment in which we monitored the responses of the foraminifera (growth, motility) to temperatures of 10, 13, 16, 19°C + control (25°C) over four weeks. To address what is the role of their endosymbionts in the adaptation process, we also monitored their photosynthetic activity (Pulse Amplitude Modulation - PAM fluorometer) during the experiment. The growth rate of the foraminifera was reduced for all populations below 19°C as well as the motility, reduced until 16°C and dropping to zero below 13°C. The response of the endosymbionts was however different. There was a reduced photosynthetic activity of the Red Sea and Eastern Mediterranean populations at colder temperatures observed by the lower maximum quantum yield (Fv:Fm) and effective quantum yield (Y(II)), when compared to their initial levels and to the other treatments. In the meantime, the endosymbionts of the Sicily population stood out with the highest photosynthetic activity (Fv:Fm and Y(II)) in the treatments bellow 13 °C (P < 0.05). In conclusion, we observed that while the host responses were similar between the three populations, the endosymbionts from the invasion front population shows the best performance at colder temperatures. This suggests that the photo-symbiosis has an important role in adaptation, most likely being a key factor to the success of past and future migrations.

How to cite: Silva Raposo, D., Morard, R., Schmidt, C., and Kucera, M.: Local adaptation of a Lessepsian invader species to winter conditions in the Mediterranean Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14762,, 2021.

Anna E. Weinmann, Susan T. Goldstein, Maria V. Triantaphyllou, and Martin R. Langer

Benthic foraminifera are important indicators for ecological studies. The assemblage composition of local communities can be used to analyze influences of environmental variables such as temperature, salinity, pH, and others. In recent years, the experimental propagule method has emerged as an effective tool to evaluate the influence of these variables on assemblage dynamics of benthic foraminifera. Propagules (tiny juveniles) of benthic foraminifera are widespread and can survive outside of a species’ natural distribution range. Their ability to become dormant and be re-activated once local conditions become suitable, is an important driver behind the capacity of foraminiferal assemblages to react quickly to environmental changes. In the laboratory, the propagules are first separated from the coarser fractions by sieving and then cultured under different conditions.

In the present study, we analyzed the effect of ocean pH on the composition of shallow-water assemblages from Corfu Island (Greece). Like other calcifying organisms, assemblages of foraminifera are susceptible to pH variations and have revealed compositional shifts along natural or experimental pH gradients. Our experimental set-up included four pH treatments between 6.5 and 8.5 at constant temperature and salinity (22°C and 38 ppt) for 5 weeks.

At the conclusion of the cultivation experiment, we found high numbers of grown specimens (825–1564 per replicate) and a high survivability rate throughout all treatments (78–87%). Higher pH (7.8 and 8.5) resulted in assemblages that were dominated by monothalamous and porcelaneous species, whereas lower pH (6.5 and 7.2) lead to a reduction in porcelaneous and an increase in agglutinated species. Several taxa showed significant positive or negative correlations with decreasing pH values.

Our results are congruent with previous findings that reported compositional shifts from calcareous to agglutinated taxa with decreasing pH (both from culture and field observations). Our study also indicates that the activation of propagules is an important mechanism behind assemblage dynamics in shallow-water foraminifera. As such, it offers an improved insight into potential resilience and recovery mechanisms of foraminiferal assemblages with regard to local or seasonal pH variations as well as ongoing ocean acidification.

How to cite: Weinmann, A. E., Goldstein, S. T., Triantaphyllou, M. V., and Langer, M. R.: The propagule method as a tool to study assemblage dynamics in benthic foraminifera: An example with pH variations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7192,, 2021.

Julia Courtial, Edouard Metzger, Jérémy Lothier, Constance Choquel, Anis M. Limami, Caroline Cukier, and Emmanuelle Geslin

Foraminifera are single-celled organisms, and part of protists. They are present in all types of environments, though most foraminifera are marine benthic and are found from the deep ocean to the intertidal zone. Thus, foraminifera are subjected to various environmental stresses, (natural or anthropogenic). Because of their rapid response to stresses and their strong resistance, foraminifera are studied as paleo-environmental indicators. However, little is currently known about their biology, and specifically their metabolism and physiology. Some foraminifera species are notably known to retain, in their cytoplasm, chloroplasts from diatom preys. This phenomenon is called kleptoplasty. It has been shown that kleptoplasts remain intact and photosynthetically functional from a few days to several weeks, depending of the foraminiferal species and abiotic factors as light. In order to better understand this life strategy and the advantages provided to foraminifera by kleptoplasty in a coastal mudflat environment, we study metabolism of kleptoplastic and non-kleptoplastic species.

The “Mudsurv” (Mudflat survey, OSUNA) project initiated in 2016 a monitoring of the foraminiferal fauna and sediment geochemistry of Bourgneuf Bay (French Atlantic Coast). The main foraminiferal species observed were: Ammonia sp. T6, Elphidium oceanense and a kleptoplastic specie, Haynesina germanica. We therefore set up a monthly monitoring of respiration and photosynthesis of those kleptoplast and non-kleptoplast foraminifera species. The oxygen production or consumption is measured by microelectrodes in light and darkness. Preliminary results suggest a seasonality of photosynthesis in kleptoplast foraminifera. A second approach, using gas chromatography-mass spectrometry (GC-MS)-based experiments, provided us with the first’s foraminifera metabolomes highlighting kleptoplast species metabolic specificities.

How to cite: Courtial, J., Metzger, E., Lothier, J., Choquel, C., Limami, A. M., Cukier, C., and Geslin, E.: Kleptoplastic foraminifera: a trophic strategy of life, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15345,, 2021.

Christiane Schmidt, Geslin Emmanuelle, Bernhard Joan M., LeKieffre Charlotte, Roberge Helene, Svenning Mette Marianne, Schweizer Magali, and Panieri Guiliana

Foraminifera on the seafloor are known to have species-specific feeding habits. Among those are deposit feeders, eating organic detritus and bacteria. Little is known about the feeding habits of foraminifera from Arctic seep environments. That is, in particular, of interest as variable δ13C values in the tests of foraminifera have been suggested to be partly linked with a diet rich in bacteria, themselves lighter in δ13C values. As there is little information on the ecology of the foraminifer Nonionellina labradorica (Dawson, 1860), this study examined feeding habits on bacteria and compared them to in situ collected specimens, using Transmission Electron microscopy (TEM). As bacterial food, the marine methane-oxidizing bacterium Methyloprofundus sedimenti was chosen, which is an important representative of methanotrophs in the marine environment near methane seeps. Sediment samples containing living N. labradorica specimens collected in close vicinity(approx. 5 m) from an active methane seep in Storfjordrenna, Barents Sea (382-m water depth).  We performed a feeding experiment on N. labradorica (n=17 specimen), which were incubated in the dark at in situ temperature. Specimens were fed at the beginning of the experiment, except the un-fed controls, and incubations terminated after 4, 8 and 20 h. After fixation in epoxy resin the ultrastructure of all specimens and their food vacuoles was observed and compared using a TEM. All examined specimens were living at the time of fixation, based on observation of intact mitochondrial membranes. In all specimens, inorganic detritus was preserved inside food vacuoles. Closer observation of food vacuoles also revealed that in addition to inorganic debris, such as clay, occasionally bacteria were visible. This led us to conclude that our N. labradorica can  generally be classified as a deposit feeder, which is rather a generalist than a specialist. Regarding uptake of M. sedimenti, the timing of the experimentation seemed to be critical. We did not observe methanotrophs preserved in the resin at the 4 and 8 h incubations, but found two putative methanotrophs near the apertural region after the 20-h incubation. After closer observation, we could identify one of those two putative specimen as the menthanothroph M. sedimenti near the foraminiferal aperture, based on presence of a typical type I stacked intracytoplasmic membrane (ICM) and storage granules (SC). We concluded that N. labradorica may ingest M. sedimenti via “untargeted grazing” in seeps. Further studies must examine the exact relationship between diet and δ13C in foraminiferal test on several different paleo-oceanographically relevant species.

How to cite: Schmidt, C., Emmanuelle, G., Joan M., B., Charlotte, L., Helene, R., Mette Marianne, S., Magali, S., and Guiliana, P.: Feeding experiments of the seep-associated foraminifer Nonionellina labradorica with a marine methanotroph from the Arctic, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14673,, 2021.

Julia Wukovits, Nicolaas Glock, Johanna Nachbagauer, Petra Heinz, Wolfgang Wanek, Margarete Watzka, and Alexandra-Sophie Roy

Benthic foraminifera are highly abundant, ubiquitous marine protists, with many species feeding on microalgae or phytodetritus. Knowledge about carbon and nitrogen budgets and metabolic activities of benthic foraminifera can help to increase our understanding about their ecology and their role in aquatic biogeochemistry at the sediment-water interface. This can further increase their application as proxies for environmental changes. Shifts in the benthic foraminiferal communities of the Swedish Gullmars Fjord document the shift from well oxygenated bottom waters to seasonal hypoxia at its deepest location the Alsbäck Deep (125 m), during the last century.

So far there are only investigations available relating foraminiferal community composition with increased primary productivity and resulting hypoxia in this Fjord. In contrast, studies about the species-specific feeding ecology or food derived foraminiferal carbon and nitrogen fluxes are scarce.

Therefore, laboratory feeding experiments and respiration rate measurements were carried out with Bulimina marginata, Cassidulina laevigata and Globobulima turgida, abundant foraminifera in such environments, collected in August 2017.

Experiments were conducted to evaluate the carbon and nitrogen intake and turnover of dual (13C and 15N) isotope labelled Phaeodactylum tricornutum detritus; detritus of a common diatom in the Gullmar Fjord. For the feeding experiments, foraminifera were incubated at 9.1°C in the dark, in sterile filtered seawater at ambient oxygen concentrations. The foraminifera were fed for a period of 24 hours and subsequently incubated without food for another 24 hours. After each incubation cycle, foraminiferal respiration rates were measured. The individuals were analyzed via Elemental Analyzer-Isotope Ratio Mass Spectroscopy to evaluate 13C/12C and 15N/14N ratios and their bulk content of organic carbon and nitrogen.

Additionally, we present carbon and nitrogen to volume ratios for the foraminifera B. marginata, C. laevigata, G. turgida, G. auriculata and Nonionella turgida, as derived from elemental analysis and light microscopy imaging.

The results show, that B. marginata, an opportunistic species associated with high fluxes of organic matter, had the highest rate of specific carbon and nitrogen intake and turnover. Cassidulina laevigata, a species that co-occurs with fresh phytodetritus and does not tolerate very low oxygen concentrations, showed lower carbon and nitrogen intake rates. Globobulima turgida, a denitrifying infaunal species that thrives under hypoxia, showed the lowest specific carbon and nitrogen intake and turnover rates. Respiration rates of all species did not depend on incubation with or without a food source. The foraminifera showed similar carbon and nitrogen densities per test volume across all species.

Overall this study helps to improve the knowledge on the nutritional ecology of the investigated species, demonstrating the close relation between feeding/metabolic rates and their environmental niche and highlighting the need to introduce foraminiferal data in future marine carbon and nitrogen flux models.

How to cite: Wukovits, J., Glock, N., Nachbagauer, J., Heinz, P., Wanek, W., Watzka, M., and Roy, A.-S.: Carbon and nitrogen budgets and respiration rates of selected foraminifera of the Gullmar Fjord in Sweden, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12003,, 2021.

Michael Lintner, Bianca Lintner, Wolfgang Wanek, Nina Keul, Frank von der Kammer, Thilo Hofmann, and Petra Heinz

Foraminifera are unicellular organisms which are important for marine C and N processing. Feeding experiments showed that the food uptake and thus the turnover of organic matter are influenced by changes of physical parameters (e.g., temperature, salinity). Since many areas of the Baltic Sea are strongly affected by anthropogenic activity and therefore contaminated by heavy metals from shipping in the past, this study examined the effect of heavy metal pollution on the food uptake of the most common foraminiferal species of the Baltic Sea, Elphidium excavatum. In 2019, we collected water and sediment containing living E. excavatum in the Kiel Fjord. In laboratory experiments, Baltic Sea seawater was enriched with metals at various levels above normal seawater: Zn (9.2-, 144- and 1044-fold), Pb (2.4-, 48.5- and 557-fold) and Cu (5.6- and 24.3-fold), and the foraminiferal uptake of 13C- and 15N-labelled phytodetritus was measured by isotope ratio mass spectrometry. Significant differences in food uptake were observable at different types and levels of heavy metals in sea water. An increase in the Pb concentration did not affect food uptake, whereas strong negative effects were found for high levels of Zn and especially for Cu. Interestingly, experiments with short incubation periods (1 and 5 days) showed greater differences in food uptake from undisturbed conditions than those of longer incubation times (10 and 15 days). In summary, an increase in the heavy metal pollution in the Kiel Fjord will likely lead to a significant reduction in the turnover of organic matter by foraminifera such as E. excavatum.

How to cite: Lintner, M., Lintner, B., Wanek, W., Keul, N., von der Kammer, F., Hofmann, T., and Heinz, P.: Effects of heavy metals (Pb, Cu, Zn) on algal food uptake by Elphidium excavatum (Foraminifera), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12402,, 2021.

Haruka Takagi, Tetsuichi Fujiki, and Katsunori Kimoto

Photosymbiosis is one of the important features in planktonic foraminifera. The number of symbiont cells within one host is reported to be well over a few thousand, which means that photosynthesis by photosymbiosis might be a “hot spot” of primary production, especially in oligotrophic oceans. Information of photosynthetic activity of symbionts is also essential when interpreting the geochemical proxies recorded in foraminiferal tests because the microenvironmental condition in the vicinity of foraminifera is greatly affected by rapid biological activities such as photosynthesis and respiration. Recently, active chlorophyll fluorometry is increasingly being used as a useful and instant tool to estimate photosynthesis. However, the carbon assimilation rate is the only direct measure of photosynthetic carbon flow. Therefore, confirming the relationship between the active fluorometry-based photosynthetic rate (electron transport rate, ETR) and carbon assimilation rate (CAR) is required before utilizing ETR to understand the dynamics of carbon in the foraminifera-symbiont system.

Here, we compared CAR and ETR for two species, Trilobatus sacculifer (dinoflagellate-bearing) and Globigerinella siphonifera Type II (pelagophyte-bearing). CAR was estimated using 14C‐tracer experiment and ETR was estimated using active fluorometric measurement by fast repetition rate fluorometry.

The results showed that the CAR and ETR were correlated positively (p << 0.01) for both species. However, the regression slopes of the two species were largely different. The slope, representing the apparent electron requirement for carbon assimilation (e/C), was estimated to 28.5 for T. sacculifer and 101.1 for G. siphonifera. These values were strikingly high. Theoretically, under optimal growth conditions, phototrophs’ e/C should be 4 based on the minimum number of electrons derived from 2 water molecules to generate 1 oxygen molecule. So, we hypothesized that the observed high e/C in the foraminifera-algal consortia is partly attributable to the utilization of unlabeled respiratory carbon (resulting in underestimation of CAR). Considering the theoretical and empirically realistic e/C, we estimated the proportion of the carbon source for photosynthesis. The results showed that a considerable amount of carbon should be derived from the host’s respired CO2. The higher contribution of the respired CO2 was suggested in G. siphonifera than in T. sacculifer.

From the viewpoint of utilizing test geochemistry such as δ13C as paleoceanographic proxies, one should beware that the potential magnitude of the photosynthetic effect can differ between species. This study suggests that in G. siphonifera, photosynthetic carbon incorporation from seawater is smaller, and utilization of the host-derived carbon by symbionts is more efficient, indicating that G. siphonifera would be less susceptible to the alteration of geochemical composition by photosynthesis and respiration. This attempt to couple the ETR and CAR could comprehensively disclose an interesting perspective of these intimate interactions in the photosymbiotic system.

How to cite: Takagi, H., Fujiki, T., and Kimoto, K.: Photosynthetic carbon assimilation and electron transport rate in two symbiont-bearing planktonic foraminifera, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13839,, 2021.

Manuel F. G. Weinkauf, Michael Siccha, and Agnes K. M. Weiner

Understanding the biology of reproduction is important for retracing key evolutionary processes (e.g. speciation and adaptation) in any group of organisms, yet gaining detailed insights often poses a major challenge. Planktonic Foraminifera are a group of globally distributed marine microbial eukaryotes that are important contributors to the global carbon cycle and, due to their fossil record, are widely used as model organisms to investigate the responses of plankton to past environmental changes. The extant biodiversity of planktonic Foraminifera shows restricted distribution patterns and local adaptations of some species, whereas others are cosmopolitan in the world ocean. Hypotheses on their diversification and population dynamics so far entirely rely on the assumption of a nearly exclusively sexual reproduction.

So far, reproduction in culture has not been successful under laboratory conditions, and thus details on their life cycle and its influence on the evolution of the group remain unknown. Only the production of flagellated gametes has been observed and is taken as an indication for sexual reproduction. Yet, sexual reproduction by spawning of gametes in the open ocean relies on sufficient gamete encounters to maintain viable populations. This represents a problem especially for unflagellated protists like planktonic Foraminifera, which lack the means of active propulsion and are characterized by low population densities in large areas of the world ocean.

To increase the sparse knowledge on the reproductive biology of planktonic Foraminifera, we applied a dynamic, individual-based modelling approach with parameters based on laboratory and field observations. We tested if random gamete encounters under commonly observed population densities are sufficient for maintaining viable populations or if alternative strategies, such as asexual reproduction or synchronization in depth and time, are indispensable to achieve reproduction success. Our results show that a strict synchronization of gamete release in time and/or space seems inevitable for a successful maintenance of populations. We further argue that planktonic Foraminifera optimized their individual reproductive success at the expense of community-wide gene flow, which may explain their high degree of diversity as well as hampered evolvability. Our modelling approach helps to illuminate the ecology and evolution of this important marine calcifier and to predict the existence of necessary reproduction strategies, which may be detectable in future field and laboratory experiments.

How to cite: Weinkauf, M. F. G., Siccha, M., and Weiner, A. K. M.: Reproduction strategies in a marine protist: A digital experiment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9692,, 2021.

Hiroshi Kitazato

Foraminifers secrete various chemicals for chamber walls. They are calcium carbonates such as calcite, aragonite, Mg-calcite, organic compounds for agglutinated chambers and/or organic cemented test walls.  Foraminiferal test walls basically form according to genetic information.  However, same test group is tended to gather at specific microenvironments.  For instance, turf shaped algal microhabitat such as coralline algae at rocky shore is composed of both frond and thallus parts as microhabitat.  Frond part is open space where fresh seawater moves inbetween one frond and the other.  Elphidium crispum, Pararotalia nipponica and Patellina corrugate and other calcareous foraminifers dwell at frond surface.  In contrast, thallus part is muddy and high concentration of organic matters.  The thallus part shows less oxygenated than frondal part as the space is close.  Microbial cascades are developed at thallus part.  Minor elements such as Mg or Sr are relatively high in sediment.  Soft-shelled forms such as Allogromia, gromiid, agglutinated forms and miliolids groups with high magnesian calcite tests flourish at the thallus part.

Microhabitat segregation and microenvironmental differences may cause similar biomineralization of benthic foraminiferal tests.  I would like to stress that micro-seascape should be important to characterize benthic foraminiferal assemblages.

How to cite: Kitazato, H.: Seascape ecological view as a new insight of benthic foraminiferal community, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16505,, 2021.