Investigations of planktonic foraminiferal population indicate that tropical species attain their largest test sizes in tropical waters, and polar species reach maximum sizes in polar waters. Species living in subtropical and subpolar waters decrease in test size with both increasing and decreasing temperature.
The proloculus (the first chamber) sizes of benthic forams are affected by sea water temperature and their mean has been used as proxy for paleoclimatic investigations.
Mean test diameters of the planktonic foraminifer Orbulina universa have been used to interpret sea surface temperature history in Somali Basin. R-mode factor and Q-mode cluster analyses define five significant factor assemblages and five clusters reflecting different environmental characteristics, including increased oxygenation, high surface productivity.