Daily rations and growth of larval krill Euphausia superba in the Eastern Bellingshausen Sea during austral autumn

As the German contribution to the Southern Ocean Global Ocean Ecosystems Dynamics Study (SO GLOBEC), RV Polarstern visited the Eastern Bellingshausen Sea between 18 April and 1 May 2001. This paper examines in situ feeding cycles, ingestion rates and growth of larval krill Euphausia superba. Larval krill were exceptionally numerous, especially over the shelf break and continental slope: mean 8872 larvae m−2, maximum 30 084 larvae m−2. The developmental stage composition of krill larvae over the shelf was advanced compared to that at continental slope stations, which may have resulted from enhanced food availability over the shelf. Despite the season being late autumn, the feeding activity of larval krill was similar to published summer rates. The intermoult period of larval krill ranged from 6 to 17 days, with daily growth rates reaching 2.2% of body length, 8.7% of body wet mass and 5.7% of body carbon. Daily ingestion rates were 8.5–17.6 μg C ind−1 d−1 for calyptopis 3 to furcilia 2 and 35.1–57.4 μg C ind−1 d−1 for furcilia 3–5, and were positively correlated with ambient chlorophyll a concentrations. Daily rations showed the same tendency, ranging from 21.5 to 44.5% of body C d−1 (calyptopis 3 to furcilia 2) and from 17.8 to 29.2% of body C d−1 (furcilia 3–5). Comparison of daily rations between open water and sea ice stations supports the notion that larval krill at low pelagic food supply under the sea ice have to exploit ice biota to sustain their metabolic demands.