Processing of 13C-labelled diatoms by a bathyal community at sub-zero temperatures

Abstract

) of the total processed C, with meiofauna contributing only ~1% to the total metazoan uptake. The bacterial response was characterised by varying bacterial growth efficiency (BGE). During the first half of the experiment, low respiration and high bacterial uptake of the 13 C-labelled substrate resulted in particularly high BGE, while the opposite was observed in the second half of the incubation. We postulate that the high BGE at the start of the experiment represents the absorption and metabolism of the readily available labile components of the added organic matter (OM). The decrease in BGE possibly corresponds to the initiation of the energetically costly hydrolytic processes necessary for the consumption of more recalcitrant OM.KEY WORDS: Stable isotope labelling · Benthos · Bacterial growth efficiency · Bathyal sediments · Faroe-Shetland Channel · δ 13 C · PLFA Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 421: [39][40][41][42][43][44][45][46][47][48][49][50] 2011 nutrients in 2 ways: by producing new biomass (bacterial secondary production, BP) and by remineralizing OC and nutrients (bacterial respiration, BR) (del Giorgio & Cole 1998). The relative magnitudes of BR and BP are expressed by the bacterial growth efficiency (BGE), which represents the amount of new bacterial biomass produced per unit of substrate assimilated and hence the efficiency with which C is made available to higher trophic levels (del Giorgio & Cole 1998). The factors that influence BGE are currently not well understood, and as a result the real magnitude of OC flow through bacteria in the world's oceans remains largely unknown (del Giorgio & Cole 2000). The bacterial response to naturally occurring, seasonal inputs of POC has been documented in various studies (Lochte 1992, Pfannkuche 1993, Pfannkuche et al. 1999. It is first detectable as an intensification of metabolic activity, reflected in adenosine triphosphate concentration (Graf 1989) and extracellular enzyme production (Boetius & Lochte 1994). The extracellular hydrolysis of OM is a prerequisite for bacterial cells to gain access to macromolecules, since only low molecular weight compounds can be transported across bacterial membranes (Benz 1985). Bacterial growth may follow enzyme production provided that the exploitable energy of the substrate is sufficiently high (Boetius & Lochte 1994. Other small-sized organisms, such as protozoa and foraminifera, are also highly responsive to food pulses and may undergo changes in density (Gooday & Rathburn 1999) and species composition (Lambshead & Gooday 1990) or show episodic recruitment of opportunistic species (Ohga & Kitazato 1997). The response of benthic metazoans in terms of population dynamics has been more difficult to establish, perhaps because of their slower turnover rates (Gooday 2002). On the timescale of several months, however, metazoan communities show shifts in their structure in relation to upper-ocean conditions and food supply (Ruhl & Smith 2004, Sellanes et ...

Resource quality affects carbon cycling in deep-sea sediments

“…Biomass and carbon uptake in all of our experiments were dominated by bacteria, in accordance with previous 13 C-labelled diatom addition experiments conducted on deep-sea benthic communities (see, for example, Moodley et al, 2005;Woulds et al, 2007;Gontikaki et al, 2011b). A notable exception to this pattern is the rapid macrofaunal response and retarded bacterial uptake of 13 C-tracer observed at 4850 m on the Porcupine Abyssal Plane, Northeast Atlantic, using an automated lander system (Witte et al, 2003).…”

“…Mineralization rates in the different treatments did not differ between months, illustrating that the benthic community at our experimental location is capable of rapidly capitalizing on sporadic food inputs whenever they occur, irrespective of background levels of biological activity: the SCOC rate in May was significantly greater than that in October, likely reflecting seasonal activity patterns that relate to the productivity regime and hence food supply from the overlying waters (Ruhl et al, 2008). Resource-quality effects on SCOC were not discernable, which agrees well with previous studies in which relatively small quantities of organic carbon tracers have been introduced to deep-sea benthic communities (Moodley et al, 2005;Gontikaki et al, 2011b). Indeed, the observed SCOC rates were an order of magnitude greater than would be expected from the 13 C mineralization data alone, illustrating that the majority of oxygen consumption was fuelled by substrates other than those introduced experimentally.…”

“…A previous, 6-day study at the same experimental location documented a temporal shift from high to low BGE following the addition of diatoms. This was attributed to a switch from labile to refractory respiratory substrates as the former became exhausted (Gontikaki et al, 2011b). However, this interpretation is not consistent with the relatively high BGE observed in our faecal pellet treatment.…”

“…These contrasting substrates can have similar bulk elemental stoichiometry, yet differ considerably at the biochemical level: the former are rich in labile compounds such as sugars, lipids and amino acids, whereas the latter are largely devoid of these, instead containing large quantities of insoluble carbohydrates (Cowie and Hedges, 1996;Mayor et al, 2011). An influx of diatom-derived organic matter to deep seabed communities initiates the rapid uptake and mineralization of carbon by the benthos (Moodley et al, 2005;Gontikaki et al, 2011b). A similar, rapid response has been proposed to occur in response to the arrival of zooplankton faecal material (Graf, 1989).…”

Negative Priming Effect on Organic Matter Mineralisation in NE Atlantic Slope Sediments

“…Benthic C cycling studies using artificial pulses of isotopically-labelled marine algae, have repeatedly demonstrated the “awakening” of benthic communities at the arrival of this labile material as an overall increase in benthic metabolism [23], [24], [25], [26]. However, whether this increase in sediment metabolism was coupled with priming phenomena is unknown.…”