Chapter 5 Feeding and Food Processing in Antarctic Krill (Euphausia superba Dana)

• Main Authors: Schmidt, K, Atkinson, A
• Other Authors: Siegel, V
• Format: Book Part
• Language: unknown
• Published: Springer 2016
• Subjects: Ecology and Environment; Marine Sciences; Oceanography; Antarctic; Southern Ocean; Antarc*; Antarctic Krill; Euphausia superba; Sea ice; Copepods
• Online Access: http://plymsea.ac.uk/id/eprint/7776/; http://www.springer.com/series/10290; https://doi.org/10.1007/978-3-319-29279-3_5

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.