Planktonic shelled protists (Foraminifera and Radiolaria Polycystina): Global biogeographic patterns in the surface sediments

BOLTOVSKOY, DEMETRIO; CORREA, NANCY

Zooplankton Ecology

CRC Press, Taylor & Francis

Lugar: Boca Raton; Año: 2020; p. 119 - 141

The Radiolaria Polycystina (or Polycystinea) and the Foraminifera (included recently in the Supergroup Rhizaria, Clade Retaria; Adl et al. 2018) are marine, free-living protists. All radiolarians are planktonic, whereas the Foraminifera include both planktonic and benthic species (the present chapter is restricted to the former only).The two groups share several traits, including their widespread distribution throughout the World Ocean, habitat, mode of life, size, trophic status, possession of a mineral shell (amorphous silica in Radiolaria, calcium carbonate in Foraminifera), and both often host symbiotic algae (Anderson 1983, Hemleben et al. 1989, Boltovskoy et al. 2017, Schiebel and Hemleben 2017). The possession of hard, skeletal structures makes them major contributors to open-ocean sediments, although carbonate deposits (chiefly represented by planktonic Foraminifera and Coccolithophorida), the dominant biogenic sediments, are scarce or absent below 3,500?5,000 m because calcium carbonate dissolves faster than it accumulates at these depths, whereas siliceous oozes (formed largely by diatoms and radiolarians), are less widespread, but their distribution is not affected by depth (Berger 1974). The presence of the remains of both protists is very common in open-ocean sediments worldwide, albeit their proportions and absolute abundance vary substantially (Lisitzin 1971a, b). This circumstance has fostered the use of Foraminifera and Radiolaria from sediment samples for biogeographic (surface sediments) and paleoceanographic (surface and downcore sediments) investigations (De Wever et al. 2001, Schiebel and Hemleben 2017).