Growth of the foraminifer <i>Nummulites venosus</i> in nature and culture

Abstract

Cultures of larger benthic symbiont-bearing foraminifers have been used for studying growth and reproduction by long term investigations taking several months. For getting results that can be interpreted as 'natural growth', the culture medium must represent the same environmental conditions like the sea at sampling time. Growth of Nummulites venosus specimens was tested where about 40 chambers have been built in the natural environment at the time of sampling. After exposition to cultures with the same environmental conditions as those at the sampling stations, growth in the culture was compared with 'natural growth' of the initial part. This was done calculating deviations of empirical data obtained in the culture from the Gompertz function established for the cell part constructed in the sea. Three reaction types could be detected: 1) strong (negative) deviations just after exposure to the culture; 2) continuing natural growth in the culture, starting deviation in later chambers; 3) throughout continuing natural growth. The chamber building rate, calculated by the Michaelis-Menten function as the second parameter determining growth, differs significantly between growth in the nature and culture, where the velocity of chamber building rates decrease immediately after exposure into the cultures. It must be concluded, that the culture medium, although approximating natural conditions rather perfectly, always impact growth, especially in the chamber building rate. Therefore, studies checking influences of environmental factors using cultures must be carefully interpreted.