No abstract

Foraminifera are abundant unicellular organisms that play an important role in marine element cycles. A large benthic foraminifer obligatory bearing photosymbionts is Heterostegina depressa. We studied potential impacts of sunscreens available on the market on the activity of photosymbionts on H. depressa by means of pulse-amplitude modulated (PAM) fluorescence microscopy. We included four different sunscreens, with two of them sold as “conventional” and two more stated as “eco-friendly”. Further, the impact of pure Ensulizole (phenylbenzimidazole sulfonic acid) was tested, which is a common agent of sunscreens. Foraminifera were incubated at varying concentrations (10, 50 and 200 mgL−1) of different sunscreens and the pure Ensulizole for 14 days. The photosynthetic performance was measured after 1,3, 7 and 14 days. Pure Ensulizole had a strong negative impact on the photobionts, which was reflected by a significant reduction of the areal fluorescence signal. “Eco-friendly” sunscreens affected the health of foraminifera more severely compared to “conventional” ones. We assume that metal nanoparticles like titanium dioxide or zinc oxide of “eco-friendly” sunscreens are causing this impact, because these substances were already classified as toxic for several microorganisms.

<p>Benthic foraminifera (marine protists) with a calcareous shell (test) show a variety of feeding strategies including detrivory, herbivory, bacterivory, carnivory or mixotrophic adaptations. However, little is known about the feeding habits of agglutinated foraminifera, which build there tests from sedimentparticles, embedded in organic cement secreted by the foraminifer. <em>Liebusella goesi</em> is a benthic foraminifer with an agglutinated test, which requires stable hydrographic conditions with low seasonal variation. In general, information on the biology or ecology of this species is very limited. Furthermore, there are no data available on foraminiferal metabolic rates and their feeding ecology  (energy consumption in calories/time, food consumption rates) of such foraminifera by now.</p><p>In this study, we compared the respiration rates of <em>L. goesi</em> at <em>in situ</em> conditions incubated in sterile seawater with or without 1.5 mM labelled glucose (33 atom% <sup>13</sup>C/<sup>12</sup>C) as a potential food source. Additionally, we estimated the individual metabolic rates of <em>L. goesi</em> specimens from their rate of glucose uptake over time.</p><p><em>Liebusella goesi</em> individuals were collected in August 2021 with the R/V Oscar von Sydow at the deepest spot of the Swedish Gullmar Fjord (Alsbäck deep, 120m), by sampling the surface layer of sediments recovered from multiple box corer hauls. Subsequently, specimens from the 5000 µm - 125 µm sediment fraction were picked under a stereo microscope, in the laboratory at the Sven Lovén Centre in Kristineberg. Seventy specimens were pooled in six replicates per treatment and incubated within glass vials (1.5 mL) filled with either plain sterile seawater or with seawater amended with <sup>13</sup>C-glucose, and sealed airtight. Finally, simultaneous non-invasive oxygen measurements were carried out over the course of 45 h. Foraminifera incubated with <sup>13</sup>C-glucose were prepared for elemental analysis and isotope ratio mass spectrometry to evaluate the amount of <sup>13</sup>C-glucose intake during the experimental period.</p><p>The respiration rates of <em>L. goesi</em> were in the range of previously observed rates of other foraminifera. <em>Liebusella goesi</em> actively feeded on dissolved organic carbon in the form of glucose and a significant increase of the respiratory activity of the specimens incubated with the <sup>13</sup>C-glucose was observed. Metabolic rates of <em>L. goesi</em> will be presented in comparison with those of other protists based on data synthesis from other available sources.</p><p>The results of this experiment enhance the knowledge about the metabolism of agglutinated foraminifera. However, further experimentation with other species and eventually further variation of incubation factors will be needed, to get a more comprehensive picture of the feeding strategies and metabolic adaptations of agglutinated foraminifera.</p>