THE GREEN HYDRA SYMBIOSIS: ANALYSIS OF A FIELD POPULATION

¹ School of Biological Sciences, University of Nebraska, Lincoln, Nebraska 68588-0118

Green hydra were abundant on the alga Vaucheria taylorii in a shallow woodland stream near Lincoln, Nebraska, from March to June 1985. Green hydra were also found in low numbers throughout the winter. The algal-animal biomass characteristics of field populations of green hydra are compared to those of cultures established from the field populations and maintained under defined laboratory conditions. Although of similar protein biomass, freshly collected hydra contained greater numbers of symbiotic algae than did cultured hydra. Algae in field hydra were larger and contained more chlorophyll than algae in cultured hydra. Field populations of green hydra were highly productive; 16 µg C·h^-1·mg hydra protein^-1 were fixed by the endosymbiotic algae at an irradiance of 28 µE·m^-2·s^-1.