So Kawaguchi

Circumpolar occurrence of eugregarinid protozoan Cephaloidophora pacifica associated with Antarctic krill, Euphausia superba

Abstract The geographical distribution of protozoan parasite Cephaloidophora pacifica Avdeev (Order Eugregarininda) associated with Antarctic krill, Euphausia superba, was examined in samples collected from the vicinity of the Antarctic Peninsula, near Syowa Station, and Pacific and Indian sectors of the Southern Ocean. Cephaloidophora pacifica was found at all stations around the Antarctic, with 96.4% of the euphausiids infected (n = 195). The numbers of C. pacifica per krill ranged from 0 to 8089 krill-1, and the average was 350.0 ± 787.8 (mean ± SD). The frequency distributions of C. pacifica showed an overdispersed parasite population (i.e. the variance was greater than the mean) at all locations. Statistical analysis showed that whilst the geographical location did not have a significant effect on intensity of C. pacifica the maturity stage of krill did, with an increasing intensity of infection as krill matures. The infestation of E. superba by eugregarinid protozoan is considered to be a circum-Antarctic phenomenon, and it occurs equally throughout the Southern Ocean.

Structural changes in the digestive glands of larval Antarctic krill (Euphausia superba) during starvation

The effects of starvation on ultrastructure of digestive gland cells were studied in furcilia larvae of Antarctic krill (Euphausia superba: hereafter krill). Under laboratory conditions, larvae were starved for 0, 5, 10, 15, 20 and 25xa0days, and their R-cells were investigated by transmission electron microscope. R-cells are thought to play a role in the storage and absorption of nutrients. In fed larvae, numerous mitochondria scattered homogenously, and densely packed microvilli were observed on the apical surface of R-cells. After 5xa0days of starvation, mitochondria were swollen and were found concentrated in the apical region in R-cells. A decrease in cell volume and an increase in thickness of the basal lamina with many irregular infoldings were observed after 10–15xa0days of starvation. Lipid droplets were rarely found in the R-cells regardless of whether larvae had been fed or starved suggesting an inability to store lipid. Without the ability to store energy in the form of lipid, survival would be dependant on sourcing continuous food until maturation.