Reference: liinl. Mull., 146: 267-278. (April, 1974) FACTORS AFFECTING GERMINATION. GROWTH, AND DISTRIBU-TION OF THE FRESHWATER SPONGE, SPONGILLA FRAG1LIS LEIDY (PORIFERA) THOMAS A. STREKAL AND WAYXE F. McDIFFETT Department nf Binlni/y, linckncll University, Lc'icishur;/, Pcnnsylrnnui 17S37 Various field surveys have been conducted to determine which physicochemical parameters affect the distribution of freshwater sponges (Old, 1932; Jewell, 1935, 1939; Cheatum and Harris. 1953; Penney. 1954). Old (1932) concluded that perhaps sponge distribution is influenced by the interaction of environmental factors rather than a single factor, while Jewell (1939) emphasized the role of calcium. Wurtz (1950) summarized the range of values for various parameters affecting individual species distribution. The general biology of the freshwater sponges has been reviewed by 1 lyman (l ( >4(h and Pennak (1 ( )53), although there have been few ecological studies dealing with them. Xo annual survey of a system has been attempted although seasonal fluctuations of important parameters may affect species distribution. More recent investigations have been devoted to rearing freshwater sponges from gemmules in the laboratory ( Kasmont. 1 ( >(>1 ) to elucidate the physiology of gem-mulation and germination, and, more generally, the process of dormancy ( Rozen-feld, 1970. 1971; Rasmont. 1 ( K>2. 1 ( ><,3. 1970; ka.Miioiit and Schmidt. 1 ( Y>7). This study was initiated to determine ( 1 ) the effects of physicochemical factors on sponge gemmule germination and earlv sponge growth in the laboratory, and (2) which of these tactors mav be limiting during the vear to atiect species distribu-tion. MATKRIAI.S AND MKTHODS Tlic species studied The freshwater sponge Spongilla Irai/dis inhabits a narrow range in Rapid Run, a mountain stream within 1\. l'>. Winter State I 'ark, I nion County, Pennsylvania. It is found immediately behind Ilalfwav I )am and in the pool below it attached to smooth concrete surfaces, on submerged twigs, within moss mats, and on the under-sides of rocks. It occupies the facing of large rocks at the end of the spillway below the pool and it may be found beyond the spillway for (.).(> mile on the undersides of rocks within the moderately flowing stream. It is not found in the remaining 9 mile course, nor in the stream anywhere above the dam. Exposed sponges tend to be gray in color; although green sponges (indicating the presence of symbiotic algae) have been reported, none were found during 1972. A white color is characteristic of sponges touiid under stones. Germination e.vperiincnts Gemmules of .S". frat/His were collected below the spillway in April, 1972 ( one month before germination) by scraping brown mats of them from the underside^ of 267
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