Fate of organic carbon released from decomposing copepod fecal pellets in relation to bacterial production and ectoenzymatic activity

Abstract

Fecal pellets were produced by Acartia tonsa fed 14 C-labeled diatom, cryptophyte, and dinoflagellate diets, and were incubated in 1.2 µm-filtered Long Island Sound seawater. Based on the 14 C label, the decrease in fpOC (fecal pellet organic carbon), the release and fate of dissolved organic carbon (DOC) and particulate organic carbon (POC), as well as bacterial production and enzymatic activity, were followed over a 96 h period. fpOC decreased by 9, 14, and 19% d -1 in diatom, cryptophyte, and dinoflagellate pellets, respectively. There was a fast, possibly passive, leakage of DOC from pellets from all 3 diets within a few hours after egestion, which may not have been utilized by attached bacteria. Bacterial production rates were 17, 12, and 31 pg C pellet -1 h -1, on diatom, cryptophyte, and dinoflagellate pellets, respectively. These were 5 orders of magnitude higher than production rates of free-living bacteria, indicating that copepod fecal pellets are hot spots of pelagic microbial production. The high production was caused primarily by high initial bacterial abundances. Accordingly, production and growth were entirely uncoupled in diatom pellets. There were no increases in abundance of attached bacteria on any of the 3 diets, indicating that the produced bacterial cells were released from the fecal pellets. Attached bacteria had a higher ectoenzymatic activity than free-living bacteria, but their production and ectoenzymatic activity were uncoupled and they only assimilated a minor fraction of the released DOC. DOC was therefore released favoring free-living microbes. The chitinase activity, which increased several-fold, was coupled to the production of attached bacteria; thus, chitin may play an important role in bacterial production on copepod fecal pellets.KEY WORDS: Copepod fecal pellets · Fecal pellet decomposition · Pelagic DOC flux · Pelagic POC flux · Attached bacterial production · Ectoenzymatic activity Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 33: [279][280][281][282][283][284][285][286][287][288] 2003 cycled (Wotton & Malmqvist 2001, Turner 2002 and that most carbon originating from these fecal pellets remains part of the long-lived organic carbon in the epipelagic (Legendre & Michaud 1998). Hence, the role of fecal pellets from small copepods is that of supplying nutrients to the epipelagic planktonic microbial community rather than maintaining the vertical flux of organic matter.Copepod fecal pellets host an extensive flora of attached bacteria (Gowing & Silver 1983, Bianchi et al. 1992, Delille & Razouls 1994, Hansen & Bech 1996. Breakdown of the fecal pellets is in part governed by microbial decomposition driven by the hydrolytic activity of these bacteria. The potential hydrolytic activity is generally high in pelagic aggregates of organic matter (Karner & Herndl 1992, Smith et al. 1992, and if this potential is fully exploited in fecal pellets, then decomposition and hence recycling of organic matter may occur rapidly....

Responses in Arctic marine carbon cycle processes: conceptual scenarios and implications for ecosystem function

“…The amount of DOC that leaches from copepod faecal pellets is dependent on their food source; amounts being higher when feeding on dinoflagellates compared to diatoms (Thor et al 2003), and when feeding on other heterotrophs compared to phytoplankton (Urban-Rich 1999). Diffusion of DOC from faecal pellets occurs on very short timescales of minutes to hours, in contrast to excretion of DOC from heterotrophs, which occurs over a relatively long timescale of hours to days (Jumars et al 1989;Urban-Rich 1999).…”

Sea urchin fecal production and accumulation in a rocky subtidal ecosystem

“…Resale or republication not permitted without written consent of the publisher (Povero et al 2003, Thor et al 2003. In turn, microbes increase the nutritional value of the feces by contributing to the labile organic matter fraction (González & Biddanda 1990, Fabiano et al 1994 through remineralization of dissolved organic matter (Urban-Rich 1999, Povero et al 2003) and uptake of dissolved inorganic nutrients from the water column , Povero et al 2003.…”

“…In a previous study at Splitnose Point, we observed an exponential loss of fecal mass after defecation (Eq. 2; Sauchyn & Scheibling 2009b), which we attributed to the dissolution of organic matter (DOM) and microbial hydrolysis of particulate organic matter (Urban-Rich 1999, Thor et al 2003). The release of DOM may stimulate microbial activity (Povero et al 2003, Thor et al 2003 and provide nutrients for kelp production (Bert- ) of several species of suspension feeding bivalves, gastropod molluscs, planktivorous reef fish, and blackfly larvae in comparison to the sea urchin Strongylocentrotus droebachiensis ness 1984, Kautsky & Evans 1987).…”

Coprophagy and coprorhexy in the copepods Acartia tonsa and Temora longicornis: clearance rates and feeding behaviour

“…However, the similarity of the clearance estimates when either copepod concentration or incubation time were varied (Type 1 and 2 experiments, respectively) suggests that this is a minor source of error, and that microbial degradation played a minor role in visibly removing the fecal pellets. Fecal pellets leak DOC rapidly after egestion, which is utilized primarily by non-attached bacteria (Jumars 1989, Urban-Rich 1999, Thor et al 2003. Leakage of DOM, however, does not change the appearance of the pellets beyond recognition and they may still be counted as intact pellets or fragments.…”

“…Fecal pellets produced during the diatom dominated spring bloom are larger, sink faster, are more persistent, and are cleared and degraded at lower rates by copepods due to handling difficulty than pellets produced during a flagellate dominated post-bloom situation (Hansen et al 1996, Feinberg & Dam 1998, Besiktepe & Dam 2002, Thor et al 2003.…”