Investigations on the ecology of Calanus spp. in the Labrador Sea. I. Relationship between the phytoplankton bloom and reproduction and development of Calanus finmarchicus in spring

Abstract

During mid-May-early June 1997 observations of hydrography, phytoplankton and nitrate concentrations, and abundance and stage distribution of Calanus finmarchicus populations were made in the Labrador Sea and south of Greenland. Egg production rates were also measured for isolated C. finmarchicus females. Surface nitrate and integrated phytoplankton concentrations indicated that, in the deep water, the phytoplankton bloom had ended in the north and east, was in progress in the north central Labrador Sea and near the basin margins, and had not yet become established in an area stretching from the central Labrador Sea to the south of Greenland. C. finmarchicus egg production rates and stage distributions at stations in the 3 areas designated as early, mid-and late/post-bloom zones, suggested that development rates of the overwintered GO generation into mature adults (females and males) were probably low before the bloom, but accelerated during its development. Individual and area1 rates of egg production were highest in the early bloom zone, whereas nauplii were more abundant in the bloom and late/post-bloom zones. Differences in naupliar abundance may have been related to food limitation, or predation. Following development through to the young copepodite stages (CI-111), which were most abundant in the late/post-bloom zone, morality rates were apparently lower and growth rates less dependent on high phytoplankton concentrations and perhaps more dependent on temperature. In the Labrador Sea, where the annual growth season is relatively short and C. finmarchicus produces only 1 generation per year, the timing of the spring bloom may have a significant impact on recruitment of the new year's generation. In areas where the bloom is early and intense, maturation of the overwintered adults will be rapid and egg-laying will occur when phytoplankton concentrations are high. Subsequent survival success of eggs through to later stages will also probably be relatively high and individuals from the new year's generation will have ample time to reach stages capable of overwintering. By contrast, if the bloom is late or of low intensity, adult maturation wdl be delayed and egg-laying may occur when phytoplankton concentrations are low. Under these condtions relatively few eggs may survive and individuals that do survive will have a shorter period in which to attain stages which can overwinter.

Physical controls and interannual variability of the Labrador Sea spring phytoplankton bloom in distinct regions

“…Climatological variations in timing in the north bloom were due to stratification, while in the central Labrador Sea, were controlled by the annual cycle of light. Maps of buoyancy anomaly indicate that haline stratification is responsible for the early north bloom and explains the reversal of the overall northward progression of bloom onset, first identified by Head et al (2000).…”

“…Interestingly, while the general pattern of bloom timing in the North Atlantic tends to be earlier at lower latitudes and later at higher latitudes (Siegel et al, 2002), this pattern is reversed within the Labrador Sea (Head et al, 2000). An early explanation of the reversal was offered by Head et al (2000), that ice melt from icebergs in the north Labrador Sea resulted in high stratification. A more recent study using a numerical model highlighted the importance of stratification for bloom timing patterns (Wu et al, 2008).…”

“…Recruitment of copepods, the most abundant mezozooplankton in the region, depends on the supply of food (Head et al, 2000). Interestingly, while the general pattern of bloom timing in the North Atlantic tends to be earlier at lower latitudes and later at higher latitudes (Siegel et al, 2002), this pattern is reversed within the Labrador Sea (Head et al, 2000). An early explanation of the reversal was offered by Head et al (2000), that ice melt from icebergs in the north Labrador Sea resulted in high stratification.…”

“…Labrador Sea food chains tend to be short, enabling a description of the relationship between higher consumers such as cod, whale and bird populations to primary production (Conover et al, 1995;Laidre et al, 2007Laidre et al, , 2008. Recruitment of copepods, the most abundant mezozooplankton in the region, depends on the supply of food (Head et al, 2000). Interestingly, while the general pattern of bloom timing in the North Atlantic tends to be earlier at lower latitudes and later at higher latitudes (Siegel et al, 2002), this pattern is reversed within the Labrador Sea (Head et al, 2000).…”

Physical controls and mesoscale variability in the Labrador Sea spring phytoplankton bloom observed by Seaglider

“…The 1997 spring bloom in the Labrador Sea was observed by Head et al (2000) from shipboard observations. They found two distinct bloom regions: the north bloom, which had ended by their sampling period (May-June), and the central Labrador Sea bloom, which was actively blooming.…”