Food supply and size class depending variations in phytodetritus intake in the benthic foraminifer Ammonia tepida.

Julia Wukovits,Petra Heinz,Maximillian Gerg,Annekatrin Julie Enge,Patrick Bukenberger,Wolfgang Wanek,Margarete Watzka

doi:10.1242/bio.030056

Abstract

ABSTRACTAmmonia tepida is a common and abundant benthic foraminifer in intertidal mudflats. Benthic foraminifera are primary consumers and detritivores and act as key players in sediment nutrient fluxes. In this study, laboratory feeding experiments using isotope-labeled phytodetritus were carried out with A. tepida collected at the German Wadden Sea, to investigate the response of A. tepida to varying food supply. Feeding mode (single pulse, constant feeding; different incubation temperatures) caused strong variations in cytoplasmic carbon and nitrogen cycling, suggesting generalistic adaptations to variations in food availability. To study the influence of intraspecific size to foraminiferal carbon and nitrogen cycling, three size fractions (125–250 µm, 250–355 µm, >355 µm) of A. tepida specimens were separated. Small individuals showed higher weight specific intake for phytodetritus, especially for phytodetrital nitrogen, highlighting that size distribution within foraminiferal populations is relevant to interpret foraminiferal carbon and nitrogen cycling. These results were used to extrapolate the data to natural populations of living A. tepida in sediment cores, demonstrating the impact of high abundances of small individuals on phytodetritus processing and nutrient cycling. It is estimated that at high abundances of individuals in the 125–250 µm size fraction, Ammonia populations can account for more than 11% of phytodetritus processing in intertidal benthic communities.

Highlights

Benthic foraminifera have existed since the Paleozoic and colonize a variety of marine sediments, ranging from shallow water environments to the deep sea
Noticeable is the increase in total cytoplasmic organic carbon (TOC) and total nitrogen (TN) at constant feed 2 (25:23°C) in comparison with the stable patterns at constant feed 1 (20:18°C) and the generally highest TOC and TN values for the single pulse approach at day 4 and 7
Response to different feeding modes in A. tepida Generally, empirical studies show that foraminiferal feeding behavior and phytodetritus intake varies between species according to the primary productivity of the habitat or their adaptations (Moodley et al, 2002; Witte et al, 2003; Enge et al, 2011, 2014, 2016)

Summary

Introduction

Benthic foraminifera (eukaryotic single-celled organisms) have existed since the Paleozoic and colonize a variety of marine sediments, ranging from shallow water environments to the deep sea. Many species produce an inorganic shell (test), which is preserved in accumulating sediment layers after their death. Based on these attributes, benthic foraminifera serve as important tools for paleoenvironmental reconstructions, including estimations of organic matter fluxes in marine sediments and paleoproductivity studies Bradshaw, 1961; Goldstein and Corliss, 1994; Lee et al, 1966) and their response to variations in phytodetritus fluxes can be observed on foraminiferal community compositions (Heinz and Hemleben, 2006) or metabolic activities (Graf and Linke, 1992; Linke, 1992). There is still a lack of studies quantifying foraminiferal carbon and nitrogen metabolism to improve the understanding of the connection between foraminiferal biomass and sediment organic matter fluxes

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Conclusion