PHOTOSYNTHESIS AND RESPIRATION IN FIVE SPECIES OF BENTHIC FORAMINIFERA THAT HOST ALGAL ENDOSYMBIONTS

Oxygen production and consumption were measured in five species of benthic foraminifers using a "Clark-type" oxygen electrode. Net photosynthesis and respiration were calculated and normalized to mu g chlorophyll a for the chlorophyte-bearing soritid foraminifers Archaias (Ar.) angulatus and Cyclorbiculina compressa, and the diatom-bearing amphisteginids Amphistegina gibbosa, Am. lessonii, and Am. radiata. Chlorophyll a concentrations were 40-50% lower in C. compressa than in the four other species. Photosynthesis/Irradiance (PIE) curves were generated by fitting data to the hyperbolic tangent equation, P = P-max tanh (alpha E/ P-max), yielding the derived photosynthetic parameters, P-max, alpha, and E-k. Calculated maximum oxygen production (P-max), when normalized to chl a, was 3-4X higher in the soritids than in the amphisteginids. Photosynthetic efficiency (alpha) was approximately two-fold higher in Am. gibbosa and similar to 50% higher in Am. lessonii than in the soritids. Calculated PIE data for Am. radiata were too variable to estimate an alpha. Median Ek, which indicates approaching light saturation, was 13 mu mol photon m(-2) s(-1) for Am. gibbosa and Am. radiata, 26 mu mol photon m(-2) sec(-1) for Am. lessonii, and 86 and 122 mu mol photon m(-2) sec(-1) respectively for Ar. angulatus and C compressa. These values are consistent with the habitats occupied by these foraminifers and with results of previous studies that used other methods. Median factorial metabolic scope, which is the ratio of respiration rate under normal activity to resting metabolic rate, was 2-4 for the amphisteginids versus 9-10 for the soritids. Archaias angulatus, C. compressa and Am. lessonii appear to be net primary producers, whereas Am. gibbosa and Am. radiata are net consumers.