Globigerinoides ruber (D'Orbigny, 1839)
This species occurs in two varieties. One produces white shells and occurs in all oceans while the other variety produces pink shells and is restricted to the Atlantic (Figs 15a-c). Globigerinoides ruber (pink) and G. ruber (white) have been counted as separate categories. Pink forms are common but are never dominating the assemblages. White forms belong to the dominating species in tropical and subtropical planktic foraminifera.
The most obvious relationships exist with sea surface temperature. Both forms show a clear distribution pattern somewhat skewed towards higher temperatures with a distinctly narrower range in summer temperatures. Pink variants prefer warmer
habitats than white variants (Bé & Hamlin, 1967). The relation of sea surface salinity and relative abundance is unique in G. ruber (white). At sites where the relative abundance does not exceed 10-15% the species has a narrow
tolerance and occurs only where salinities do no deviate by more than about 0.5 psu from average marine conditions (about 35.5 psu). When the species relative abundance exceeds 10-15% it demonstrates a markedly higher salinity tolerance and
occurs over the entire range above about 34 psu. A similar but less pronounced relationship exists with the temperature at 200 m. Globigerinoides ruber (pink) shows relationships that are noteably different from those of G. ruber (white)
which suggest distinctly different adaptations. This is also expressed in the biogeographic distribution evident from the plots of relative abundance vs. latitude. G. ruber (white) shows clear maxima in northern and southern warm subtropical
areas. G. ruber (pink) is most abundant in the tropics. It seems both forms are not simple ecophenotypes which increase in their relative abundance along environmental gradients.
Figure 15a: Globigerinoides ruber (D'Orbigny, 1839), differentiated for white and pink varieties. Plots of relative abundance vs. selected physical parameters and latitude. For preferences in numeric form see appendix. Continued in Figs. 15b
Figure 15b: G. ruber continued. Plots of relative abundance vs. selected physical parameters and latitude. For preferences in numeric form see appendix. Continued in Fig. 15c.
Figure 15c: G. ruber continued. Plots of relative abundance vs. selected physical parameters and latitude. For preferences in numeric form see appendix.