Hastigerina pelagica (d'Orbigny, 1839)

This rare species (Fig. 31) is restricted to the North Atlantic in the analysed data where it occurs in northern tropical and subtropical environments. Most obvious are the narrow tolerances for sea surface salinities and seasonal change in salinity, and the distinct preference for warm water at 200 m depth (compare to the subtropical G. truncatulinoides). Some narrower tolerance for vertical temperature contrasts in summer seems to exist but depends on data from only three samples and may, therefore, not be significant. H. pelagica shows a clear restriction to water masses with salinities above about 35.5 psu. Maximum salinities in the Indian Ocean do not exceed 36 psu (Fig. 3) and may explain the rare occurrence of H. pelagica in a very restricted area east of Madagascar in the Indian Ocean. Bé and Hutson (1977) found H. pelagica with relative abundances of up to 10% in plankton from the Agulhas Current and the Gulf of Aden, but not in sediments of this area. The sea surface temperatures and salinites reported with these occurrences match the optimum conditions extracted from the sediment data in this paper. The short reproduction cycle of this species and effects of preservation of the dissolution susceptible tests limit comparisons of plankton and sediment data for this species (Bé and Hutson, 1977; Hutson, 1977; Hemleben et al., 1989).

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Figure 31: Hastigerina pelagica (d'Orbigny, 1839). Plots of relative abundance vs. selected physical parameters and latitude. For preferences in numeric form see appendix.

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