The balance of autotrophy and heterotrophy in three freshwater sponges with algal symbionts
Magnitude and relative balance of autotrophy and heterotrophy were analyzed in three freshwater sponges with algal symbionts. The three species, Corvomeyenia everetti, Ephydatia muelleri, and Spongilla lacustris share a common habitat but exhibit distinct species-specific differences in their chlorophyll content. We tested three alternative models for the balance of autotrophy and heterotrophy: a null model in which heterotrophy and autotrophy are independent, a tradeoff model in which heterotrophy decreases as the potential return from autotrophy increases, and a mutualistic model in which heterotrophy is positively influenced by autotrophy. We found that Spongilla lacustris, with intermediate chlorophyll levels, consistently exhibited the highest levels of heterotrophy. Primary production per biomass of symbiotic association (sponge and algae) was also highest in S. lacustris. The efficiency of production (production/ chlorophyll) decreased among the three sponge species as chlorophyll increased. As a result we reject the null and tradeoff models and suggest a mutualistic interaction between sponges and their algal symbionts.
Smithsonian Institution Press