Increased degradation of copepod faecal pellets by co-acting dinoflagellates and Centropages hamatus

Abstract

Copepod faecal pellets (FP) are carbon-rich particles possibly of great importance for the biological pump. However, most FP are degraded within the euphotic zone, by processes not yet fully understood. In a series of experiments conducted in Gullmarsfjorden, Sweden, we investigated degradation rates (r, d ) was higher than the sum of the degradation rates measured under each individual condition (bacteria + dinoflagellates + C. hamatus). We suggest an interactive effect of dinoflagellates and copepods acting together -that the copepods were mechanically breaking up large FP, making the FP more available for further degradation by the dinoflagellates. This finding may have implications for understanding FP fluxes and carbon export in the ocean and points to a more complex 'coprophagous filter' (sensu González & Smetacek 1994; Mar Ecol Prog Ser 113:233−246)

The role of particle associated microbes in remineralization of fecal pellets in the upper mesopelagic of the Scotia Sea, Antarctica

“…Ploug et al () conducted experiments on small copepod FP (over 500 times smaller volume than analysed here) at 15°C, and measured much higher rates of carbon‐specific respiration (0.08–0.20 d −1 ). FP size may in part explain differences between studies (Svensen et al ), however we observed no relationship between FP ESD and carbon‐specific respiration rate over the small size range of FP measured here (0.33–0.85 mm ESD). A clear trend of increasing respiration rate (in terms of oxygen flux per FP) with increasing FP ESD and FP volume (Fig.…”

“…This study presents the first direct measurements of respiration rates in euphausiid FP in an attempt to understand the key processes driving flux attenuation in the mesopelagic. A few studies have measured microbial respiration of copepod FP (Hansen et al 1996;Ploug et al 2008;Shek and Liu 2010;K€ oster et al 2014;Svensen et al 2014), only one of which utilizes the direct methods used here (Ploug et al 2008).…”

“…Conversely, FP incubations performed by Poulsen and Iversen (2008) demonstrated that protozooplankton were the main driver of FP remineralization. More recently, it has been suggested that interactive effects must be considered, with the mechanical break up of large FP by copepods supporting further degradation by dinoflagellates (Giering et al 2014;Svensen et al 2014).…”

Downward particle flux and carbon export in the Beaufort Sea, Arctic Ocean; the role of zooplankton

“…This is in contrast to the findings by Forest et al (2012), who found good agreement between maximum phytoplankton abundance and copepods, which were by far the most abundant grazers around 60 m depth. It follows that, either grazing activity at this depth was low despite the relatively high food availability or the produced pellets were subject to enhanced coprophagy and/or coprohexy (Svensen et al, 2014), a process, which has already been reported from the nearby Baffin Bay (Sampei et al, 2004) and which we cannot exclude although we do not have direct evidence. Another possibility for this observation could be that defecation from these grazers took place above the 40 m depth horizon.…”

The potential role of Antarctic krill faecal pellets in efficient carbon export at the marginal ice zone of the South Orkney Islands in spring

“…Faecal pellets can also be broken up and remineralised by zooplankton and prokaryotes as they sink, decreasing the efficiency of export to the deep sea (e.g., Poulsen and Kiørboe 2005;Iversen and Poulsen 2007;Svensen et al 2012Svensen et al , 2014 and fragmentation has been suggested to explain high retention of krill FP in the study of González (1992). González (1992) suggests that where krill FP production is high relative to abundances of the zooplankton recycling community, a large percentage of krill FP can pass undisturbed through the mesopelagic zone and reach deep sediment traps.…”