Characteristics of egg production of the planktonic copepod, Calanus finmarchicus, in the Labrador Sea: 1997-2010

Abstract

Egg production rates (EPRs) were measured for Calanus finmarchicus from the Labrador Sea during annual cruises between May and July from 1997 to 2010. EPRs ranged between 0 and 91 eggs f-1 day-1 at 95 stations. Clutch size (CS) was related to female size (prosome length, PL) and both were smallest on the Greenland (2.76 mm, 55.2 eggs) and Labrador (2.86 mm, 60.1 eggs) shelves and largest in the central basin (2.94 mm, 73.0 eggs). CS and spawning frequency (SF, the proportion of females spawning during a 24 h experiment) both increased with increasing female nitrogen content and decreased with increasing C:N ratio. CS and SF were also positively correlated and both increased with an increasing in situ chlorophyll concentration. The relationships between SF (% day-1) and EPR (as eggs f-1 day-1 or % body C or N day-1) and in situ chlorophyll concentration were well described by Ivlev functions (r2 = 0.30-0.34). The residuals from the Ivlev correlations for EPR (but not SF) were significantly negatively correlated with temperature for the central basin (r2 = 0.14), but unrelated over all sub-regions. Over the course of the bloom, as in situ nitrate concentrations decreased, the female N content and the CS decreased and the female C content and C:N increased. Overall, the EPR was most influenced by (i) local feeding conditions (in situ chlorophyll concentration), (ii) the state of the bloom (via effects on female age/condition) and (iii) long-term feeding and temperature history (via effects on female size), although a significant amount of variability remains unexplained. © The Author 2013. Published by Oxford University Press. All rights reserved.