Trochospongilla horrida (Porifera, Spongillidae) was the dominant freshwater sponge in the Rhine between Karlsruhe and Bonn between 1992 and 1995 are reported. It showed an annual life cycle, with an inactive phase during winter. The life cycle was controlled by temperature. Gemmules were produced in high numbers, and played a significant role as resting bodies. Their role as distribution units was negligible because they were tightly fixed to the substratum. Trochospongilla horrida preferred relatively stable habitats, not affected by fluctuations in water level; it was restricted to habitats with a slightly alkaline pH. Laboratory experiments showed a delayed germination of the gemmules, which explains why the highest abundance of the species occured considerably after the first hatching colonies.
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