The excretion of nitrogen and phosphorus and changes in nitrogen content in the Antarctic amphipod Waldeckia obesa and isopod Glyptonotus antarcticus during long-term starvation

Seasonal food availability for benthic feeders in Antarctica can influence the level of excreted metabolites, which may then be a source of N and P for autotrophs. In this study, we examined the effects of starvation of Waldeckia obesa and Glyptonotus antarcticus on the excretion of both N and P, and the chemical composition of their bodies. N-NH4 (+) dominated in the pool of excreted nitrogen (93% and 77% of inorganic nitrogen, and 76% and 67% of total nitrogen, for W. obesa and G. antarcticus, respectively). Reactive phosphorus dominated in the pool of excreted phosphorus (72% and 65% of total phosphorus for G. antarcticus and W. obesa, respectively). The excretion of N-NH4 (+) (in mu mol N h(-1) 100 g(-1)) dropped from 3,687 (W. obesa) and 1,336 (G. antarcticus) in the first day to about 0.6 after 10 days of starvation (for both species). Phosphorus excretion was generally lower than that of nitrogen (on average 0.046 and 0.017 mu mol P h(-1) 100 g(-1) for G. antarcticus and W. obesa, respectively), but no clear trend appeared with N as a result of starvation. The greatest decrease in nitrogen and protein content in W. obesa was recorded on the 3rd day of starvation (nitrogen: from 1.30% to 0.93%; protein: 8.15% to 5.80%) and in G. antarcticus on the 5th day of starvation (nitrogen: from 2.22% to 1.43%; protein: from 13.86% to 8.94%). Conclusions: (i) nitrogen and phosphorus compounds released by crustaceans may be a supplementary source of biogenic salts for autotrophs, (ii) nitrates constituting approx. 20% nitrogen may be used by phytoplankton in the period of new production, (iii) starvation reduces the excretion of N and P and the content of nitrogen and protein in crustaceans.