Krill excretion and its effect on primary production

Abstract

During the austral summer, zooplankton excretion along the western Antarctic Peninsula was studied in a contrasting hydrographic regime including coastal and oceanic waters. In coastal waters, ammonium supply by mesozooplankton indicated a low contribution to fuel primary production. In oceanic waters, however, Antarctic krill Euphausia superba contributed a significant percentage to the nitrogen requirements of primary producers. Thus, the ontogenetic migration of adult krill during austral summer should be a key factor regulating the regenerated ammonium for primary production. A significant coupling of ammonium concentration in the water column and in situ krill biomass supported the significant role of krill excretion in the epipelagic realm. Results from short-term experiments with E. superba indicated that ammonium excretion rates were much higher than previously found. Because the use of experimental metabolic rates that are close to field rates would be more appropriate, we suggest to re-assess the ammonium supplied by the epipelagic marine biota. Moreover, the outcomes of experimental krill excretion rates, in situ measurements of ammonium and a review of data on primary production suggest that Antarctic krill sustain a high proportion of the daily phytoplankton production.

Short-term variation in the <i>Calanus sinicus</i> ammonium excretion rate during the post-capture period

“…No significant difference between the feeding and no-feeding incubations at t 6 -t 24 was observed. This result was consistent with that reported for Calanus pacificus (Miller & Landry 1984), although a number of authors reported higher excretion rates in fed animals than in non-fed animals (Atkinson & Whitehouse 2001, Gardner & Paffenhöfer 1982, Ikeda 1976, Lehette et al 2012, Vanderploeg et al 1986). Therefore, the contradictory results in this study may be attributed to the specific physiological characteristics of Calanus; for instance, the degree of starvation may not be evident at relatively low temperatures during 24 h in experimental animals that tend to store a large amount of lipid reserves under conditions of phytoplankton blooms (e.g.…”

“…On the basis of results from using a short-term incubation method, Lehette et al (2012) found that the field rate of ammonium excretion in Antarctic krill was two times higher than previously thought, while the effect of stress by experimental manipulation during short incubation times was negligible. On the other hand, our results demonstrate that starvation did not affect the excretion rates in C.…”

Zooplankton excretion metabolites stimulate Southern Ocean phytoplankton growth

“…The actual mechanism by which krill is implicated in NH 4 + regeneration may not be direct or obvious (Whitehouse et al 2011), and it has been suggested that krill excretion may enhance bacterial activity (Goeyens et al 1991;Aristegui et al 2014), fuelling phytoplankton growth, and thus stimulating periods of high productivity in the Southern Ocean (Smetacek 2008;Aristegui et al 2014). However, the direct excretion of dissolved ammonium can also be the primary boost to mixed layer NH 4 concentrations (Whitehouse et al 2011;Lehette et al 2012). High concentrations of krill may supply sufficient local excesses of nutrients to trigger enhanced uptake and phytoplankton turnover (Whitehouse et al 2011;Lehette et al 2012).…”

“…However, the direct excretion of dissolved ammonium can also be the primary boost to mixed layer NH 4 concentrations (Whitehouse et al 2011;Lehette et al 2012). High concentrations of krill may supply sufficient local excesses of nutrients to trigger enhanced uptake and phytoplankton turnover (Whitehouse et al 2011;Lehette et al 2012).…”

“…Amongst ammonia sources, zooplankton recycling of nutrients also plays an important role, conditioning the pelagic ecosystem in the Southern Ocean to maintain it at a high productivity level (Alcaraz et al 1998;Lehette et al 2012;Arístegui et al 2014).…”