Carbon flows in the benthic food web of the Porcupine Abyssal Plain: The (un)importance of labile detritus in supporting microbial and faunal carbon demands

Dick van Oevelen, Karline Soetaert and Carlo Heip

Limnol. Oceanogr., 57(2), 2012, 645-664 | DOI: 10.4319/lo.2012.57.2.0645

ABSTRACT: Carbon flows in the benthic food web of the Porcupine Abyssal Plain (4850 m, northeast Atlantic) were reconstructed using linear inverse modeling based on mass balances of the various compartments, biomass data, carbon flux measurements, physiological constraints, and data from a previously published 13C-phytodetritus pulse-chase experiment. Food web compartments consisted of bacteria, Foraminifera, three feeding types of nematodes and of macrofauna, and four feeding types of megafauna. Three lability classes of detritus were defined to clarify especially the possible role of labile detritus in this abyssal plain food web. Total detritus inputs to the food web were 0.56 mmol C m-2 d-1, with only a minor (3.8%) contribution of labile detritus. The dominant pathway in the food web was dissolution of more refractory detritus, uptake by bacteria, and subsequent respiration (0.36 mmol C m-2 d-1, 80% of the community respiration). Lower contributions to community respiration were found for surface-deposit-feeding macrobenthos (5.6%), Foraminifera (4.9%), predatory macrobenthos (3.8%), and other deposit-feeding macrobenthos (3.1%). Contributions by other benthic compartments were < 1%. 13C-phytodetritus transfer data strongly constrained the carbon source for bacteria, Foraminifera, and the nematode and macrobenthic compartments. Surprisingly, labile detritus contributed < 5% of the total carbon requirements for all these compartments. Carbon sources were much less constrained for the megabenthic compartments because for these compartments no 13C pulse-chase data were available. The carbon flow model evidently shows a limited role of labile detritus in the food web.

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