Ultrastructure, morphology and flux of microzooplankton faecal pellets in an east Antarctic fjord

Abstract

Small copepods and protozoa are major contributors to heterotrophic biomass in Antarctic waters. They produce small (< 300 µm) faecal pellets, the fates of which are largely unknown. We examined the distribution and abundance of microzooplankton and small faecal pellets in Ellis Fjord, east Antarctica. We determined statistical relationships between the abundance of microzooplankton and pellets, and examined pellet morphology and ultrastructure using light and scanning electron microscopy. Our results indicate species-specific differences in the morphology and fate of pellets produced by small copepods: Oithona similis and harpacticoid pellets were retained in upper waters, while Oncaea curvata and Paralabidocera antarctica pellets sank to depth. Protozoan pellets did not sink to depth irrespective of their source or morphology and despite the fact they can be larger than those produced by small copepods. The majority of microzooplankton pellets, composed of phytoplankton that otherwise may have directly sedimented to depth, was retained in near surface waters and probably recycled and remineralised. Despite producing faecal aggregates, heterotrophic activity of most microzooplankton do not contribute to vertical flux but instead support respiration of matter in upper waters. This may reduce the vertical flux of particulate matter to depth, thereby reducing the capacity of Antarctic waters to act as a carbon sink, with implications for global climate.

Size and biomechanic properties of diatom frustules influence food uptake by copepods

“…This transfer can take place either by sloppy feeding (Møller 2005) or faecal pellets (e.g. Turner & Ferrante 1979, Bathmann et al 1990, González & Smetacek 1994, Smetacek 1999, Beaumont et al 2002.…”

Role of heterotrophic dinoflagellates in the fate of diatoms released from fast ice in coastal water of Lützow-Holm Bay, East Antarctica

“…and oligotrich ciliates were dominant taxa (Table 1). HD and ciliate communities were similar to those in other Antarctic coastal areas (Archer et al 1996, Beaumont et al 2002, but differed from the predominance of thecate dinoflagellates Protoperidinium spp. at a nearby site reported in a previous study (Ishikawa et al 2001).…”

“…In the Antarctic seas, HD have also been observed abundantly in the Weddell Sea (Nöthig et al 1991), Ross Sea (Fonda Umani et al 2005), and coastal waters near Davis Station (Archer et al 1996) and Signy Island (Clarke & Leakey 1996). However, little is known about their grazing on diatoms under fast ice cover (Beaumont et al 2002, Pearce et al 2008. To understand the fate of the diatoms, we investigated HD grazing on diatoms, sinking loss of diatoms, and HD growth as a function of prey abundance.…”

Heterotrophic dinoflagellate fecal pellet production: grazing of large, chain-forming diatoms during upwelling events in Monterey Bay, California

“…Relatively intact siliceous frustules and girdle bands, in a relatively tightly packed fecal pellet surrounded by a peritrophic membrane, are egested. Previous reports of small dinoflagellate fecal pellets have been from disparate environments: Antarctic sea-ice (Buck et al 1990), Antarctic water column (Nothig & von Bodungen 1989, Gonzalez 1992, Gowing et al 1998, Beaumont et al 2002 and a small protected embayment in Washington state (Buck & Newton 1995); however, there is a remarkable consistency in the morphology of the pellets.…”