Population Dynamics and Standing Biomass of the Freshwater Sponge Spongilla Lacustris
1982
Frost, Thomas M. | De Nagy, George S. | Gilbert, John J.
In a sphagnum bog—pond in central New Hampshire, USA, the common freshwater sponge Spongilla lacustris exhibits a high growth rate and reaches a large standing biomass (ash—free dry biomass is 1.7 g/m²) by the end of its growing season in October. The sponge overwinters as gemmules, and the conversions between these dormant forms and active sponge tissue in the spring and fall are very conservative in terms of biomass. With the high growth rate and efficiency of these transfers, 10 mg of gemmulated sponge (AFDM) in the spring could eventually produce 18 g upon resting stage formation in the fall. S. lacustris does not require a hard substratum. The greatest part of this population grows as upright branches from the pond bottom or attached to aquatic macrophytes. In winter, the gemmulated sponges, including those attached to macrophytes, collapse into the bottom sediments. There is a high mortality during this period, resulting from the accumulation of sediments over the gemmulated sponges, which prevents their successful hatching. It appears that sponges derived from sexually produced larvae would be particularly unlikely to survive the winter. A sexual growth processes are thus of primary quantitative importance in this system and must be considered in evaluating reproductive effort.
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