Time series of vertical flux of zooplankton fecal pellets on the continental shelf of the western Antarctic Peninsula

Abstract

Zooplankton fecal pellet contribution to particulate organic carbon (POC) flux over the continental shelf of the western Antarctic Peninsula (WAP) was investigated to better understand the possible effects of changes in zooplankton community structure, due to climate change, on carbon export. Fecal pellets were collected at 170 m depth in a moored sediment trap from January 2004 to January 2009. Fecal pellet shape and size (i.e., carbon content) were quantified to assess flux of pellets from different zooplankton taxa and compared between seasons and years. Fecal pellet POC constituted the dominant proportion of total POC flux, with summer (November to April) pellet POC flux (67%) significantly higher than winter (May to October) pellet POC flux (34%), while phytodetritus or fecal 'fluff' constituted the remainder. Cylindrical euphausiid pellets contributed to a monthly mean of 72% of total fecal pellet flux; ovoid copepod and tabular salp pellets contributed significantly less (22 and 6%, respectively). Cylindrical and ovoid pellet export was significantly higher in summer, while 48% of tabular pellet flux occurred in winter. Tabular pellets had the highest carbon content (median = 1.03 µgC pellet ) and ovoid (0.04 µgC pellet −1 ) pellets. As krill fecal pellets are the dominant component of particle export in the WAP, we hypothesize that a decrease in krill and increase in salps in the region could alter the export of POC to the deep sea.KEY WORDS: Southern Ocean · Particle flux · Sediment trap · Krill · Salp · Copepod · Climate Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 471: [23][24][25][26][27][28][29][30][31][32][33][34][35][36] 2012 variable sinking rates of 16 to 1218 m d −1 (Turner 2002, Atkinson et al. 2012). Copepods produce ellipsoid or ovoid pellets. They have round or pointed ends and are encased in a peritrophic membrane that makes the pellets more resistant to bacterial degradation and breakage (Gauld 1957, Yoon et al. 2001, Köster et al. 2011. Copepod fecal pellet sinking rates range from 5 to 220 m d −1 (Turner 2002, Møller et al. 2011, Patonai et al. 2011. Salps are indiscriminate feeders that produce very large, fast-sinking (42 to 2700 m d −1 ) 'fecal flakes' that greatly enhance the efficiency of POC transport to depth (Anderson 1998, Madin & Deibel 1998, Yoon et al. 2001, Phillips et al. 2009).Long-term zooplankton time series from a variety of environments indicate that climate is changing zooplankton community structure (Richardson 2008 and that these changes can lead to changes in the efficiency of the biological pump . The western Antarctic Peninsula (WAP) is experiencing one of the most rapid rates of warming on Earth; since 1950, the annual mean air temperature has increased by 2°C, with average mid-winter temperatures rising by 6°C (Vaughan et al. 2003, Ducklow et al. 2012. As a result, the WAP is changing from a cold, dry, polar climate to a warm, humid, maritime climate (Ducklow et al. 2012), with a 40% decrease in s...

First Evaluation of the Role of Salp Fecal Pellets on Iron Biogeochemistry

“…The daily egestion rate per S. thompsoni individual and the carbon content from salp FPs measured at our sampling site were 0.33 FP ind −1 h −1 (resulting in a daily production of 310 ± 126 FPs m −2 for the upper 250 m) and 17.6 ± 27 µg C FP −1 , (n = 33), respectively ; Table 1). Those values are comparable to the average values reported from salp individuals and their respective FPs collected at the Western Antarctic Peninsula (WAP) of 0.25 FP ind −1 h −1 and 3.62 µg C FP −1 , respectively (Phillips et al, 2009;Gleiber et al, 2012). According to calculated sinking rates, salp FPs take about 4-24 h to travel the 100 m upper meters .…”

“…The hypothesized increase in salp dominance in the SO due to a depletion of sea-ice (Atkinson et al, 2004) could enhance their annual contribution to carbon vertical flux. Compared to krill, salps consume more food more effectively (Perissinotto and Pakhomov, 1998), produce larger and denser FPs with high carbon content (Gleiber et al, 2012) and have higher sinking velocity (Phillips et al, 2009;Turner, 2015). Increasing abundances of salps over krill could imply important changes to the lower and higher trophic levels (Fraser and Hofmann, 2003) with strong implications for the biological pump activity and associated carbon sequestration.…”

Carbon fluxes and pelagic ecosystem dynamics near two western Antarctic Peninsula Adélie penguin colonies: an inverse model approach

“…obs.). Salps are efficient grazers of small phytoplankton, bacteria and microzooplankton, which they repackage into rapidly sinking fecal pellets that are exported out of the euphotic zone (Gleiber et al 2012). With around 40% of ingested nitrogen and 49% of ingested carbon excreted (Pakhomov et al 2002), salps also increase the pool of dissolved organic matter available for bacterial production.…”

“…Cope pods can be the dominant phytoplankton grazer in areas where, or at times when, krill are scarce, and copepod fecal pellets can occasionally contribute significantly to export flux (Gleiber et al 2012). However, in austral summer, krill are the dominant grazers especially in water influenced by sea ice (Bernard et al 2012, and krill fecal pellets dominate export flux (Gleiber et al 2012).…”

“…If phytoplankton populations become dominated by small phytoplankton, it will reduce the importance of the diatom−krill food chain and favor salps, changing the food web further (e.g. increased but more sporadic export, Gleiber et al 2012; weakening of apex predators, Loeb et al 1997).…”