CIRCULATION OF FLUIDS IN THE GASTROVASCULAR SYSTEM OF THE REEF CORAL <i>ACROPORA CERVICORNIS</i>

Abstract

Circulation of fluids in the gastrovascular system of A. cervicornis was determined by observing the movement of fluorescein dye injected via a lateral polyp and viewed in the dark under ultra-violet light. Scanning electron microscopy and petrographic thin sections were used to describe the general morphology of the gastrovascular system. This consists of two functional units: an axial unit composed of the coelenteron of the axial polyps and a peripheral unit composed of tubes oriented axially ramifying through the skeleton lying just beneath the outer ectoderm. These units are connected by radially oriented tubes including the coelenterons of the lateral polyps. The entire gastrovascular system is lined by flagellated endoderm cells. Flow in the axial unit is always proximal. Flow in the peripheral unit is both distal and proximal and the velocity is always less than the flow in the axial unit. Light does not appear to change the rate of flow. Rates of flow in the peripheral unit show a diel cycle, with increased flow rates occurring between 2100 and 0600.