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

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 13 C-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 22 d 21 , 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 22 d 21 , 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%. 13 C-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 13 C pulse-chase data were available. The carbon flow model evidently shows a limited role of labile detritus in the food web.

Trophic state of benthic deep-sea ecosystems from two different continental margins off Iberia

“…Previous studies have inferred the amount of labile organic matter in surface deep-sea sediments through the analysis of chlorophyll a concentrations (van Oevelen et al, 2011(van Oevelen et al, , 2012. However, chlorophyll a is rapidly converted into degradation products during particle sinking to the ocean floor (Fabiano et al, 2001) and rapidly decays in the sediments (Sun et al, 1991).…”

Lanice conchilega structures carbon flows in soft-bottom intertidal areas

“…Absolute values of the lower and upper bounds of the literature data (production rates, assimilation efficiencies, net growth efficiencies and respiration rates) were added to the model as inequalities since they are used to constrain single flows or linear combinations of flows to biologically realistic values. The complete model As in the majority of LIMs, the food webs in this study are under-sampled and the number of equalities (48 + 46) is insufficient to balance the number of unknown flows (727) (van Oevelen et al 2010). Therefore, the LIM is under-determined and the matrix equations have an infinite number of solutions (van Oevelen et al 2010).…”

“…The complete model As in the majority of LIMs, the food webs in this study are under-sampled and the number of equalities (48 + 46) is insufficient to balance the number of unknown flows (727) (van Oevelen et al 2010). Therefore, the LIM is under-determined and the matrix equations have an infinite number of solutions (van Oevelen et al 2010). This problem can be solved in 3 ways: (1) upgrading literature data (i.e.…”

“…By merging a variety of traditional data types and currently underexploited data sources, linear inverse models (LIMs) are used to quantitatively reconstruct pathways in systems as small as single cells up to entire food webs. This feature makes LIMs an effective tool to bridge the gap between incomplete and uncertain empirical data on natural food webs and the analysis of food web structures (van Oevelen et al 2010).…”

Improving the estimation of deep-sea megabenthos biomass: dimension to wet weight conversions for abyssal invertebrates

“…Our current understanding of the ecology of these assemblages is based on these techniques, including studies of community dynamics over time (Billett et al 2001) and space (Alt et al 2013), food web interactions (van Oevelen et al 2012), the potential links between resource availability and community dynamics (Ruhl et al 2014), and their contributions to large-scale and global assessments of standing stocks (Rex et al 2006, Wei et al 2010. Although trawling and similar approaches are necessary to obtain specimens for taxonomy, histology, and genet-ics, such samples have major quantitative uncertainty in terms of the seabed area sampled, and likely do not accurately represent the megabenthic community present (Rice et al 1979.…”