Enzymatically hydrolysed protein and carbohydrate pools in deep-sea sediments:estimates of the potentially bioavailable fraction and methodological considerations

Abstract

In this study we developed existing protocols for the enzymatic digestion of protein and carbohydrate pools in deep-sea sedments in order to estimate the organic fraction potentially bioavailable for benthic consumers. Sedunent samples were collected m an abyssal locality (Porcupine Abyssal Plain, 4800 m depth) of the NE Atlantic in September 1996, and March and October 1997, and vertically divided into 5 layers down to a depth of 15 cm. Protein and carbohydrate concentrations released enzyrnatically were highest after 2 h of incubation for both organic pools. The release of enzymatically hydrolysed proteins from the deep-sea sediments was significantly higher using Tris+EDTA and sonication instead of a simple sediment homogenisation in Na-phosphate buffer. Hydrolysed carbohydrate concentrations were higher utilising a-amylase, P-glucosidase, Proteinase K and lipase instead of only a-arnylase and P-glucosidase. Hydrolysed proteins and carbohydrates accounted for a small fraction of the total protein and carbohydrate pools (on average 15 and 13%, respectively), indicating that total protein and carbohydrate concentrations do not represent the actual available fraction of the sedirnentary organic matter in this deep-sea environment. Hydrolysed protein pools changed significantly between sampling periods whereas carbohydrate pools appeared to be more conservative both spatially and temporally. Hydrolysed protein and carbohydrate concentrations were characterised by different vertical patterns and carbohydrate concentrations were much hgher in deeper sediment layers. These results indicate that the 2 classes of organic compounds might play different roles in different sediment layers with important trophodynarnic implications for benthic organisms living at different sediment depths.

Persistence of labile organic matter and microbial biomass in Antarctic shelf sediments: evidence of a sediment ‘food bank’

“…This assay measures an enzymatically degradable fraction of protein in sediments, which can comprise a relatively small percentage of the total protein pool (Dauwe et al 1999, Dell'Anno et al 2000. EHAA is thought to measure the pool of protein readily available as a food source for deposit-feeders (Mayer et al 1995).…”

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

“…Such an approach, despite its intrinsic limitations, has been extensively used across a wide range of benthic ecosystems to provide quantitative information on food availability for heterotrophic consumers (Mayer et al, , 2008Dauwe et al, 1999a;Dell'Anno et al, 2000;Danovaro et al, 2001a;Pusceddu et al, 2003;Grémare et al, 2005;Bourgeois et al, 2011).…”

“…aminoacids) for heterotrophic metabolism (Mayer et. al., 1995;Dell'Anno et al, 2000), and (ii) the relative importance of enzymatically digestible organic matter fractions to their total pools (Danovaro et al, 2001a). …”

“…biomimetic approach, sensu Mayer et al, 1995), has been proposed for mimicking organic matter degradation steps in deposit feeding (George, 1964;Mayer et al, 1995;Dauwe et al, 1999a). The enzymatically hydrolyzed organic matter pools represent a reliable estimate of the food availability for heterotrophic consumers, thus providing insights on benthic trophodynamics (Dauwe et al, 1999b;Dell'Anno et al 2000;Pusceddu et al, 2003;Grémare et al, 2005;Mayer et al, 2008;Bourgeois et al, 2011).…”

“…However, assessing the trophic state of benthic deep-sea ecosystems is a difficult task since organic detritus is made of a complex array of compounds exhibiting different levels of bioavailability, i.e. from highly labile to refractory compounds (Mayer 1995;Middelburg et al, 1999;Dell'Anno et al, 2000;Middelburg and Meysman 2007;Pusceddu et al, 2009). This limits the use of total organic C and N pools as suitable quantitative descriptors of food availability for consumers (Dell'Anno et al, 2002;Pusceddu et al, 2009), especially for sediments in continental margins receiving large inputs of land-derived organic material, which is potentially more recalcitrant to biodegradation than organic compounds of marine origin (Wakeham and Canuel, 2006;Sanchez-Garcia et al, 2009).…”