SYMBIOSIS OF HYDRA AND ALGAE. II. EFFECTS OF LIMITED FOOD AND STARVATION ON GROWTH OF SYMBIOTIC AND APOSYMBIOTIC HYDRA

Abstract

1. When fed daily on Artemia nauplii, green and albino C. viridissima grew at nearly identical logarithmic rates. With limited food, growth of green hydra always exceeded that of albinos. This difference was not the result of a quantitative difference in food intake.2. Green hydra survived starvation for about four weeks, gradually diminishing in size. Albinos survived only 10-12 days, succumbing to starvation by relatively sudden disintegration.3. The relationship between survival ability and algal content was non-linear. Animals with 20% of the normal flora survived nearly as well as those with a full complement of algae.4. Turnover rate of sulfur-labeled protein during starvation showed the relationship albino > pale green > green, among the groups tested. The presence of symbiotic algae appears to depress the rate of protein catabolism.5. It is concluded that symbiotic algae augment growth, budding, and survival of C. viridissima (Carolina strain 1960) by a mechanism which does not appear to involve gas exchange or waste removal by the algae.6. Evidence is presented in support of the hypothesis that algal metabolic products augment growth and survival of C. viridissima.