Carbon Budgets for Two Species of Benthonic Symbiont-Bearing Foraminifera.

Carbon budgets are presented for two symbiont-bearing foraminifera: Amphistegina lobifera, a perforate species, and the imperforate species Amphisorus hemprichii. Both species have a potential for autotrophy with respect to carbon, because the translocation from symbionts to host is sufficient to account for the increase in measured biomass. Experimentally determined feeding rates exceed the supposed amount of food retained as calculated by balancing the budget by a factor of up to ten. When feeding does not occur, the carbon budget of A. lobifera is almost exactly balanced, whereas the budget of A. hemprichii can be balanced within the precision of the measurements. Carbon for calcification by A. lobifera is initially concentrated in an internal pool that derives approximately 10% of its content from organic matter respired by the host. Carbon of organic origin was not incorporated into the skeleton of A. hemprichii.