This dataset contains measurements of photosynthetic efficiency, expressed as maximum quantum yield (Fv/Fm), of the endosymbiotic diatoms of benthic the foraminifera Amphistegina lobifera, exposed to electric currents for a one-month period. The data were collected in April 2023 using Imaging Pulse-Amplitude Modulated (PAM) fluorometry during the first of a two-part experiment. This dataset provides insights into the effects of electric currents on the physiology of the endosymbionts of Amphistegina lobifera.