The Influence of Symbiotic Dinoflagellates on Respiratory Processes in the Giant Clam Tridacna squamosa

Abstract

Several aspects of respiratory gas exchange are distinctive in the giant clam Tridacna squamosa, which obtains nutrients from symbiotic dinoflagellates found in the mantle. During the day, when more oxygen is produced than consumed by the host and its symbionts, oxygen extraction is negative. Exhalant water P02 is higher than inhalant water P02, and prebranchial blood P02 is higher than heart blood P02. Ventilation of the mantle cavity and the gills continues, which rids the system of much excess oxygen and, possibly, prevents the formation of gas bubbles in the blood, which is supersaturated. In the dark, when the oxygen balance shifts to a rate of uptake that is unexceptional among lamellibranchs, the ventilation rate remains low and oxygen extraction high relative to species that rely exclusively on an exogenous food source. On a 24-hr basis, the total oxygen uptake exceeded the total oxygen production.