Abstract. Benthic foraminifera play a major role as primary consumers and detrivores redistributing organic carbon and nitrogen in intertidal environments. Here we compared the differences of phytodetrital carbon and nitrogen intake and turnover of two dominant intertidal foraminifera, Ammonia tepida and Haynesina germanica. Their lifestyles in relation to feeding behavior (feeding preferences, intake and turnover of phytodetrital carbon and nitrogen) and temperature adaptations were compared to obtain a closer definition of their specific roles in intertidal organic matter processing. For this comparison, we carried out a series of short-term laboratory incubations with stable-isotope-labeled (13C and 15N) detritus as the food source. We compared the response of the two species to diatom detritus at three different temperatures (15, 20, 25 ∘C). Ammonia tepida showed a very high, temperature-influenced intake and turnover rates with more excessive carbon turnover, compared to nitrogen. The fairly low metabolic nitrogen turnover in H. germanica was not affected by temperature and was higher than the carbon turnover. This might be related with the chloroplast husbandry in H. germanica and its lower demands for food-derived nitrogen sources. Ammonia tepida prefers a soft chlorophyte food source over diatom detritus, which is harder to break down. In conclusion, A. tepida shows a generalist behavior that links with high fluxes of organic matter (OM). Due to its high rates of OM processing and abundances, we conclude that A. tepida is an important key player in intertidal carbon and nitrogen turnover, specifically in the short-term processing of OM and the mediation of dissolved nutrients to associated microbes and primary producers. In contrast, H. germanica is a highly specialized species with low rates of carbon and nitrogen budgeting.

<p><strong>Abstract.</strong> Benthic foraminifera play a major role as primary consumers and detrivores redistributing organic carbon and nitrogen in intertidal environments. Here we compared the differences of phytodetrital carbon and nitrogen intake and turnover of two dominant intertidal foraminifera, <i>Ammonia tepida</i> and <i>Haynesina germanica</i>. Their lifestyles in relation to feeding behaviour (feeding preferences, intake and turnover of phytodetrital carbon and nitrogen) and temperature adaptations were compared to obtain a closer definition of their specific roles in intertidal organic matter processing. For this comparison, we carried out a series of short-term laboratory incubations with stable isotope labelled (<sup>13</sup>C & <sup>15</sup>N) detritus as food source. We compared the response of the two species to diatom detritus at three different temperatures (15 °C, 20 °C, 25 °C). The quite low metabolic nitrogen turnover in <i>H. germanica</i> was higher than the carbon turnover, and in contrast to the latter, not affected by temperature. This might be related with the chloroplast husbandry in this species and lower demands of food derived nitrogen sources. In contrast, <i>A. tepida</i> showed a very high, temperature-influenced intake and turnover rates with more excessive carbon turnover. Further, the latter species prefers a soft chlorophyte food source over diatom detritus, which is harder to break down. In conclusion, <i>H. germanica</i> is a highly specialized species with low rates of carbon and nitrogen budgeting. In contrast, <i>A. tepida</i> shows a generalist behaviour that links with high fluxes of organic matter (OM). Due to its high rates of OM processing and abundances, we conclude that <i>A. tepida</i> is an important key-player in intertidal carbon and nitrogen turnover, specifically in the short-term processing of OM and the mediation of dissolved nutrients to associated microbes and primary producers.</p>