Regulation of the Endosymbiotic Algae in Hydra by Digestive Cells and Tissue Growth

Endosymbiotic algae in hydra release photosynthetically fixed carbon to the host which augments the animals nutrition during starvation. The algae may acquire metabolites from hydra as a source of nutrition when the animals are maintained in the dark. The kind of algae acquired by aposymbiotic hydra is determined by a recognition phenomenon involving the hosts digestive cells and potential endosymbionts. The size of the algal population is related to the necessity of light for maximum algal multiplication, the rate of cell division in hydra, and the potential for heterotrophy by the algae.