Importance of feeding for egg production in Calanus finmarchicus and C. glacialis during the Arctic spring

The vertical distribution and in situ egg production of Calanus finmarchicus and C. glacialis were studied in Disko Bay, western Greenland, from winter throughout the spring bloom. The 2 species entered the surface water simultaneously, but their spawning patterns differed significantly. Maximum egg production for C. glaciahs of 48 ± 8 eggs female-1 d -1 was measured on May 1, 2005 in association with the culmination of the bloom, while the highest egg production rate of C. finmarchicus of 44 ± 7 eggs female-1 d-1 was measured on May 25 after termination of the bloom.

During 3 phases of the spring bloom, the impact of starvation and saturating food conditions on the egg production rates of the 2 Calanus species was investigated in the laboratory. Experiments with starved and ad libitum fed females showed a significant difference in the egg production rate between the 2 species, depending on sampling time, i.e. gonad maturity and feeding history.

The results showed varying use of saturating food during the 3 phases of the bloom. For C. finmarchicus, no effect of food was observed during the first experiment in late April, whereas females collected in early May, during the peak of the spring bloom, responded strongly to changes in food concentration, with egg production which was 3 times higher than that of the starved controls.

In contrast, C. glaciahs responded strongly to food concentration in both late April and early May. The present investigations illustrate that Calanus females from the Disko Bay area continue to produce eggs without food more than twice as long as those reported from other northern populations. This observation could indicate an adaptation to the Disko Bay environment, which has unpredictable ice conditions and consequently large variations in the initiation of the spring bloom.