10 research outputs found
Chapter 5 Feeding and Food Processing in Antarctic Krill (Euphausia superba Dana)
Euphausia superba is exceptional among euphausiids for the large
filtering surface of the feeding basket and its fine mesh size (2–3 μm), which remain
into adulthood. This enables them to feed efficiently on nano- and microplankton,
and to reach substantial growth rates with food concentrations as low as 0.5 μg
Chlorophyll a L
�1. Even though phytoplankton – in particular diatoms – are their
staple food, protozoans and small copepods are ingested simultaneously and represent
an important supplementary food source year-round. However, krill feeding
behaviour is more complex than just filter-feeding in the water column, it includes
raptorial capture of larger zooplankton, handling of ‘giant’ diatoms, scraping algae
from beneath sea ice and lifting detritus from the seabed. High mobility and
physiological robustness enable krill to explore three feeding grounds – the water
column, the sea ice and the benthos. Variability in access and productivity of these
feeding grounds leads to fundamental differences in krill overwintering across their
habitats. Gut passage time, absorption efficiency and fecal pellet density vary with
food concentration and nutritional needs. Therefore krill fecal pellets have a dual
role; some promote the export of carbon and nutrients while others facilitate the
recycling of material in the upper water column. Krill grazing can suppress phytoplankton
blooms, but this tends to be a localised phenomenon where krill abundances
are exceptionally high. Conversely, krill appear to have major conditioning
effects due to nutrient supply (e.g. ammonium, iron), although their role in Southern
Ocean biogeochemical cycles is only starting to be discovered