Salinity tolerance of the gemmules of Eunapius fragilis (Leidy) and the inhibition of germination by various salts

Abstract

Gemmules of the freshwater sponge, Eunapius fragilis (Leidy), survived exposure to 30 ppt natural sea water at 20 °C for up to 27 days and to 37 ppt Instant Ocean sea water for up to at least 9 days. This high salinity tolerance may have made possible the dispersal of the sponge on the hulls of ocean-going ships that frequented freshwater ports. The gemmules also survived 9-day exposures to 5% NaCl, 20% NaCl and some artificial sea waters containing only a few of the major ions. All of these solutions inhibited germination of the gemmules during the period of exposure, and treatment with 30 ppt natural sea water, 37 ppt Instant Ocean sea water, 20% NaCl and a solution containing Na⁺, Cl⁻ and SO ^sup2−_inf4 had a persisting inhibitory effect on gemmule germination after the gemmules were returned to pond water at 20 °C. Many of the gemmules that did not germinate under favorable conditions following treatment could be stimulated to germinate after they were chilled at 4 °C for 4 or more months. Such gemmule inhibition mimics natural diapause which also is broken by exposure to low temperature.