Production of chromophoric dissolved organic matter (CDOM) in the open ocean by zooplankton and the colonial cyanobacterium Trichodesmium spp.

Abstract

Chromophoric (or colored) dissolved organic matter (CDOM) has been identified as a major determinant of the optical properties of oligotrophic oceans. The factors controlling distribution of CDOM far from the direct influence of land are not well known, as CDOM abundance and distribution does not directly correlate with phytoplankton productivity or biomass, or with dissolved organic matter (DOM) concentration. As part of a larger study of the dynamics of CDOM in the open ocean, we investigated direct release from plankton as a factor contributing to distribution patterns of CDOM. We measured the production of CDOM by zooplankton (copepods, euphausiids, amphipods, salps, polychaetes), protozoans (colonial radiolaria), and by the colonial cyanobacterium Trichodesmium spp. in the North Atlantic subtropical gyre. Groups of individual species of plankton were incubated and absorption spectra were obtained for their release products. CDOM was produced by all organisms examined, and absorption spectra varied by taxa, with major taxa exhibiting characteristic absorption peaks. Plankton-produced DOM is a source of labile carbon and thus facilitates microbial activity, and CDOM may also serve as photoprotection for near-surface-living organisms. Zooplankton likely play an important role in the CDOM cycle in the Sargasso Sea, directly through release/excretion of CDOM and indirectly by providing a labile substrate (excretia) for microbial-mediated production of CDOM.KEY WORDS: Zooplankton · Trichodesmium · Chromophoric dissolved organic matter · CDOM · Excretion · Sargasso Sea · North AtlanticResale or republication not permitted without written consent of the publisher

Marine CDOM accumulation during a coastal Arctic mesocosm experiment: No response to elevated pCO2 levels

“…These include processing of organic matter into CDOM by bacteria [Nelson et al, 1998Rochelle-Newall et al, 1999;Steinberg et al, 2004], excretion from zooplankton , lysis of heterotrophic bacteria by viruses [Balch et al, 2002;Lønborg et al, 2013], release by phytoplankton [Vernet and Whitehead, 1996;Rochelle-Newall and Fisher, 2002], and phytoplankton degradation [cf. Zhang et al, 2011].…”

The microbiome of North Sea copepods

“…They are key components of the food web as grazers of primary production and as food for higher trophic levels, such as fish (Cushing 1989;Møller and Nielsen 2001). Copepods contribute to the microbial loop (Azam et al 1983) due to ''sloppy feeding'' (Møller and Nielsen 2001) and the release of nutrients and DOM from faecal pellets (Hasegawa et al 2001;Møller et al 2003;Steinberg et al 2004). Similarly, their moults and carcasses can be populated and decomposed by bacteria (Tang et al 2009b;Tang et al 2006a, b).…”

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“…This interest sprang from concurrent advances in both satellite-based estimates of oceanic CDOM and optical instrumentation for in situ CDOM measurements as well as recent indications that changes in open-ocean CDOM signatures reflect local ecological processes (Nelson et al 1998Steinberg et al 2004). Improvements in satellite instrumentation (McClain et al 1998) and retrieval algorithms (Roesler and Perry 1995;Garver and Siegel 1997;Maritorina et al 2002) now enable remote estimates of surface seawater CDOM on a global scale , and long-pathlength liquid core waveguide cells enable CDOM measurements in oligotrophic environments.…”

“…Recent work has shown the potential use of CDOM as a tracer of water circulation processes (Coble et al 1998;Blough and Del Vecchio 2002;Nelson et al 2007;Boehme, J. and M.L. Wells, unpublished observations), and correlation between CDOM and ecological processes (Nelson et al 1998Coble et al 2004 and references within; Steinberg et al 2004). …”