An Assessment of Photosynthetic Activity in Large Benthic Foraminifers and the Optimization of Light Intensity for Lab-scale Cultivation

Abstract

We assessed the photosynthetic efficiency of the lab-cultured large benthic foraminifers (LBFs), Calcarina gaudichaudii and Baculogypsina sphaerulata, by means of a pulse-amplitude-modulated (PAM) fluorometer for representative photosynthetic activity; and identified an optimal light intensity and water temperature for the lab-scale cultivation. It is known that in the actual environment, the convex side of LBFs exhibit higher photosynthetic efficiency [Y(II)] than concave one. However, our experimental results from the lab setting showed that Y(II) values apparently did not differ on the basis of their having convex and concave sides. This was due to the condition between the position of the LBFs within the glass vial and light irradiation. The LBFs were exposed to eleven different light conditions for a period of 72 h. The LBFs exhibited relatively higher Y(II) at 40−120 and 240 lum/ft 2 , compared with that at 1150−1800 lum/ft 2 . Using a light intensity of 80 lum/ft 2 and water temperature of 20°C to inhibit epiphyte infestation due to the growth of suspended microalgae released by the LBF hosts, LBFs were able to be cultured for 120 d under laboratory conditions, while B. sphaerulata could be cultured for 57 d under the on-site conditions in a previous study.