Abstract
The adaptation of sponges to freshwater environments was a major event in the evolutionary history of this clade. The transition from a marine environment to freshwater ecosystems entailed a great number of adaptations to more unstable habitats, such as the ability to form resistance gemmules as a defense mechanism against environmental adversity. However, data on the parameters that modulate hatching and growth of these animals are scarce. In the present study, the growth response capacity of Ephydatia fluviatilis (Porifera: Spongillidae) has been evaluated in relation to both water alkalinity and light intensity. The results obtained revealed a positive association between the growth capacity of this freshwater sponge and high alkalinity values. On the other hand, exposure to light, regardless of its intensity, affected the development and distribution of the symbionts, which in turn, corresponds to a higher growth rate of the sponge. The obtained data suggest an explanation for the greater distribution of this species in alkaline environments. The results of this work also shed light on the importance of the symbiosis phenomenon in E. fluviatilis .