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

摘要

Ammonia tepidais 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 withA. tepidacollected at the German Wadden Sea, to investigate the response ofA. tepidato 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) ofA. tepidaspecimens 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 livingA. tepidain 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,Ammoniapopulations can account for more than 11% of phytodetritus processing in intertidal benthic communities.