Factors affecting germination, growth, and distribution of the freshwater sponge, Spongilla fragilis Leidy (Porifera).

Abstract

Gemmules of the freshwater sponge Spongilla fragilis were germinated and grown under a number of conditions in the laboratory using an artificial medium similar to stream water: germination was similar under conditions of light-dark and total dark; germination was prompted by temperatures between 6-8° C; development of the young sponge was supported by ion concentrations as low as 0.2 mg/l for Mg and Ca, 0.05 mg/l for K and Na, and 0.06 mg/l for SiO2; sponge development was inbhibted by the absence of Ca and Mg, but not Na, K, or SiO2, although no spicules were formed without SiO2.An annual survey was conducted to determine which physico-chemical parameters might limit the distribution of the species. As little difference with respect to chemical characteristics was noted among sampling stations and since sponges appear to tolerate low ion concentrations, it is suggested that distribution of sponges in the stream was affected by the interrelationship between current flow, suspended material, and substratum.