Diel vertical migration and the haemocyanin of krill Meganyctiphanes norvegica

Abstract

Changes in environmental factors (PO 2 , temperature, salinity and food availability) influence the concentration of the respiratory pigment haemocyanin ([Hc]) present in many crustaceans. We investigated the possibility that [Hc] and HcO 2 affinity altered during the diel vertical migration (DVM) of Nordic krill Meganyctiphanes norvegica in the Gullmarsfjord, Sweden. The [Hc] decreased with increasing depth, for individuals both trawled and caged at different depths. Laboratory experiments indicated that this pattern could not be explained by differences in PO 2 , temperature or salinity. Alternatively, starvation had a significant effect on [Hc] over the course of a few h (≤10), i.e. a much shorter time scale than found for other crustacean species. Starved individuals showed a dramatic decrease in [Hc] compared with fed individuals. This decrease was exacerbated by an increase in temperature. We suggest that when M. norvegica migrates into deep water during the day, for whatever reason (predator avoidance or reduced prey abundance, or reduced ability to locate and capture prey), they cannot secure enough energy to meet routine metabolic demands; they therefore break down Hc and use it as an energy source. We conclude that there is likely to be a trade-off between the respiratory function of Hc and its importance in nutrition when krill migrate into deeper, nutritionally poorer waters during their DVM.

Physiology and Metabolism of Northern Krill (Meganyctiphanes norvegica Sars)

“…He found that at 5 C, M. norvegica haemolymph had a very low affinity for oxygen (P 50 or half saturation value ¼ 50.1 mmHg [6.66 kPa], at pH ¼ 7.9). This was very similar to P 50 values of 6.12-6.31 kPa, pH ¼ 7.80, T ¼ 7 C, recorded by Spicer and Strömberg (2002) for dialysed haemolymph from individuals collected from the Gullmarsfjord, Sweden. Brix et al (1989) also found that the cooperativity (the 'sigmoidness' of the O 2 binding curve) was high, but not exceptional (n 50 ¼ 2.5-3.0) although the haemolymph did exhibit a marked Bohr effect Physiology and Metabolism of Northern Krill (Dlog PO 2 /Dlog pH ¼ À1.99), amongst one of the highest recorded for crustaceans.…”

“…To our knowledge, M. norvegica, and krill generally, utilises just the one extracellular respiratory pigment, the copper-based haemocyanin (Hc), that is found in some crustaceans and some molluscs (Brix et al, 1989;Spicer and Strömberg, 2002). Brix et al (1989) was the first to characterise the O 2 binding properties of M. norvegica haemocyanin (Fig.…”

“…Concentrations of Hc ([Hc]) in individuals of M. norvegica collected from the Gullmarsfjord, Sweden, were extremely variable (0.39-0.89 mmol l À 1 ), but at the upper end are some of the highest recorded in aquatic crustaceans (Spicer and Strömberg, 2002). Spicer and Strömberg (2002) found that [Hc] varied during DVM.…”

“…Spicer and Strömberg (2002) found that [Hc] varied during DVM. This is one of the most exciting findings of their study, that [Hc] could and did change over a timescale of hours, rather than days, as generally believed.…”

“…However, starvation had a dramatic effect on Hc concentration over <10 h, and this was exacerbated by an increase in temperature. Spicer and Strömberg (2002) suggested that when M. norvegica migrates into deep water during the day, for whatever reason, they cannot secure enough energy to meet routine metabolic demands and so they resort to breaking down Hc and using it as an energy source. This notion, that there could be a trade-off between the respiratory function of Hc and its importance in nutrition when krill migrate into deeper, nutritionally poorer water during DVM, was further supported by Dawdry (2004) …”