Great Basin Naturalist
Volume 57 Number 2 Article 1
5-7-1997
Freshwater sponges (Porifera: Spongillidae) of western Montana
Susan H. Barton Carrol College, Helena, Montana
John S. Addis Carrol College, Helena, Montana
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Recommended Citation Barton, Susan H. and Addis, John S. (1997) "Freshwater sponges (Porifera: Spongillidae) of western Montana," Great Basin Naturalist: Vol. 57 : No. 2 , Article 1. Available at: https://scholarsarchive.byu.edu/gbn/vol57/iss2/1
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ISSN 0017-3614
VOLUME 57 30 APRIL 1997 NO.2
Greal Basin NaturaList 57(2), el997, pp. 93-103
FRESHWATER SPONGES (PORIFERA: SPONGILLIDAE) OF WESTERN MONT A
Susan H. Barton l and John S. Addis l ,2
ABSTRACT.-Between May 199'2 and ApnLl996, freshwater sponges (Porifera: Spongillidae) were collected at 24 sites, distributed among 6 sub-major drainage basins in western Montana, to determine the species present. Water samples also were analyzed from 16 of these sites and from 9 sites at which no sponges were detected to characterize sponge habitats chemically. Three species ofsponges were identified: Ephydatia muelleri (Em), Etltlapiusfragilis (Ef), and SpoMgilia lacus tris (51). A4th type of specimen was present at 2 sites but could not be identified because of the absence of gemmules and gemmoscleres. At 46% ofthe sites containing sponges, more than 1 specimen type was present. Sponges were most com monly found near outlets of lakes, attached to sides or undersides of submerged rocks and logs. They appeared as encrusting (Em, Ef, 81), lobate (Em), and fingerlike (81) growths, varying in color from light tan to green. Dimensions of the spicules varied greatly within each species and expanded previously recorded ranges. No factors limiting sponge djs~ lributioo were identified, but ranges ofconductivity (Em) and ofsilica (Em, SO, calcium (Em), and magnesium (Em) con centrations were expanded beyond those reported previously.
Key words: freshwater sponges, Porifera, Spoogillidae, Ephydatia mueUeri, Eunapius fragilis, $pongiLIa lacustris, Montana.
Although freshwater sponges form part of 1932, Jewell 1935, 1939, Poirrier 1969, Harrison the benthic community in many of the world's 1974). In addition, some attempts have been lentic and lotic habitats, they are among the made to identify factors that affect species dis least understood ofanimal groups. Basic ques hibulion (Old 1932, Jewell 1935, 1939, Poirrier tions about their biogeography and ecology 1969, Strekal and McDiffett 1974). Freshwater remain unanswered (Frost 1991). Their distri sponges of the West, in contrast, have received butions have not been completely determined, much less attention. This is unfortunate since and their habitat requirements have not been water quality is an important issue in the west fully defined. ern United States and since sponges are poten Freshwater sponges in the United States tially valuable bioindicators of water quality have been studied most extensively in the East (Harrison 1974, Francis and Harrison 1988, and Midwest. Species present in these regions Richelle-Maurer et al. 1994). have been described and their habitats charac In the Mountain West only freshwater terized in chemical and physical terms (Old sponges of Colorado have been studied in
lDepartment of Bio! 93 94 GREAT BASIN NATURALIST [Volume 57 detail (Williams 1977, 1980). Fresh""dter sponges taries, Upper Clark Fork, Lower Clark Fork, have been collected in Montana (sec, for ex Kootenai, and Flathead (Water Quality Bureau ample, Ynung 1935, Poirrier et al. 1987), but no 1991). Sites included lakes and ponds, man studies focusing on the fi'eshwater sponges of made as well as natural. and in some cases the this statc have heen published. In tllis paper first 50 m ofrivers or stremns draining lakes and we repOit results of a survey of fresl1water ponds. Most sites were within 2 km ofa road. sponges in western Montana. The survey was In most cascs we collected samples by wad conducted to identifY the species present and to ing near tbe shore and handpicking likely determine chemical anu physical ranges for substrata (submcrged rocks or logs). Most each species' habitat. The latter is a necessary samples were ohtained from substrata sub step in defining factors that influence sponge merged at depths of less tban 1 m. In 1 lake distribution. (Blanchard Lake), samples werc collected by diving. Substratum depth in this case was MATERIALS AND METHODS approximately 3 m. We attempted to collect gemmules (asexual propagules) with the sam Sampling plcs by scraping the substratum with a knife Between May 1992 and Ap"i! 1996, we ob or gathering a piece of the substratum itself. tained sponge samples from 24 sites in western For transport to the laboratory, samples were Montana (listed in Table 1). Thcsc sites were placed ill small containers \vith lake water. distributed among 6 sub·major dminage hasins: Between June and August 1994, surface Missouri-Sun-Smith, Upper Missouri Tribu- water grab samples were taken from 16 sites at TABLE 1. Surveyed hIkes in we~tern Montana containing fr~shwatcrsponges. Species Lake County Locality prcscnt:l MISSOUJU-SUN-SMITJJ BASIN I-loiter Lake Lewis and Clark 49°59'NlIl2°00'\V 1,.'3 Upper Holter Llke Ll~wis ilnd Clark 46°50'N/112°OCY\V 1 U PI'ER M ISSOUIU TllllllJ'TARIF:S BASIN Lower Miner Lake Beaverhead 45°20'N/113°34'W 1.3 Hock Island Lake Beaverhead 45°IS'N/113°41'\V 2,3 Upper Miner Lake Beaverhead 45°t6'N/113°41'W 2 Hehgcn Lake Madison 44°52'NIJ W20'W 1,3 JerOine Ilock Lake Madisol\ 45°23'1'/lll°2i(\V 2 Pond below Blue Panl.di.~ we Madison 44°57'. /IW26'W 2 Quake Lake Madison 44°50', /lW26'\V 2,3 Willow Creek Reservoir Madison 45°43'N/I1lD42'\V I UPPER CLARK FORK BASIN Blanchard Lake Missoula 47DOJ'N/I13°23'V{ 2,3,4 Salmon Lake Missoula 47"06'NIJ 13°~!4'W 1.2,3 Coopers Lake Powell 47"05'N/l 12°55W 3,4 Pond nellr West Fork of Hilterroot River Ravalli 46°06'N/IJ401 nv 1 loWEn CLAHK FOUK BASIN Diamond Lake Mineral 47°09'N/115°11'W 1.,3 ),\'Iooro L'lkc \1ineral 47° ll'N/115°15'W 3 KOOTENAI BASIN Kilbrennan Lake Lincoln 48 D35'N/115°53'W 1,3 Loon Lake Lincoln 48°OS'1'/1l5°tJ'W 2.:3 FLATJIEAIJ BASIN I)ond near Railey Lakt' Flathead 48°28'N/114°OB'W 1 Spoon Lake Flathead 48°29'N/114°09'W 2 Ce N ~ ~~~ ~'"'--'-""" $eoll ...... 40 eo _ "._•• i.3 i I I;""".ji·.. '-.I >. ."----..--.. .\ ...... -...... ; - Fig. 1. Distribution of sponge species in western Montana. Eunapius jragilis, .; Spongilla lacustris, .... ; EphydaUa muelleri, .; unidentified ~"ponge, *. Sub-major drainage basins, outlined by thick lines, are as follows: 1, Missouri-Sun Smith Basin; 2, Upper Missouri Tributaries Basin; 3, Upper Clark Fork Basin; 4, Lower Clark Fork Basin; 5. Kootenai Basin; 6, Flathead Basin. to 550 llJIl, were either arranged in a distinc Spongilla lacustris (Linnaeus 1758) tive pavement layer or clustered in groups of Collection Numbers, 1099-1100, 1103, 3--5. Cemmoscleres, oriented tangentially in 1108-9, 1122, 1124-25, 1132, the pneumatic layer of the gemmule, had 1137--38,1140-41, 1149, 1152, 1154, blunt, rounded ends, were slightly to strongly 1156-57, 1161-63, 1165 curved, and were covered with thick spines, (Fig. 4) concentrated at the ends. Spicule dimensions are given in Table 2. SpongiU" laeustris was collected at 11 sites. One specimen of E. fragills from Diamond It was the only species collected at6 sites, and Lake, an oligotrophic mountain lake located in at the 5 other sites it was collected with E. the Lower Clark Fork Basin, was unique in that muelleri or with E. muelleri and either E. frag almost every megasclere contained at least 1 ilis or the unidentified sponge (Table I). More expanded bulb along its length (Fig. 3). Normal than the other species, S. lacust1'i$ varied in specimens of E. fragilis and E. muelleri were gross morphology. While often encrusting, it also collected from the same region ofDiamond occasionally extended long (>10 em), cylindri Lake. cal branches (Fig. 4). It was usually found at 1997] FRESHWATER SPONGES OF WESTERN MONTANA 97 Fig. 2. Eunapius fragilis on the uoderside of a log (pond adjacent to Bailey Lake). Note conspicuous oscula in upper specunen. TABLE 2. Spicule dimensions ofwestern Montana sponges. Mean ± standard error (range). Dimensions in ~m. Species E·f...guis S. lacu8tris E. muelleri Spicule dimensiona (n ~ 13) (n = 20) (n = 23) Megascleres Length 275 + 27 (90-392)' 287 ± 35 (120-408)' 269 + 19 (150-391)' Width 9.5 + 1.5 (2.0-14.0)b 11.0 ± 2.0 (2.5--19.0)' 10.5 + 1.5 (3.0-18.0)b Microscleres Length 67 ± 7 (35-120) Width 3.5 ± 0.5 (1.5--7.5) Gemmosc1eres Length 79 ± 13.5 (30-148)" 89 ± 24 (25--177)" 14.5 + 1.5 (9.5--25.0) W;dth 6.0 + 1.0 (3.5-1l.O) 4.5 ± 1.5 (3.0-9.5) 4.0 ± 0.5 (1.5--7.5) Ratule diameter 17.5 + 2.0 (9.5--27.5) "las and greater tbl) previously .eported; see terl bLess than prev.iouny recorded; _l:&t «;~ lb:;m previously 1e outlets of lakes Or ponds, but the branching curved. Megascleres, however, were smooth form of the sponge occurred in quiet water at while microsc1eres were covered with small sites distant from the outlet or at sites near the spines. Spicule dimensions are given in Table 2. lake outlet that were not noticeably affected Gemmules were small, ranging in diameter by the current. Usually, S. 1aroshls was found from 250 to 500 ~m, and were typically scat growing on the sides or tops of rocks or logs. tered throughout the sponge. As others have The hranching form also was found growing observed (Gilbert and Simpson 1976), gemmo directly out of bottom sediments. The sponge scleres were not consistently present. Those was either light tan or green. that were found had pointed or rounded ends, Both megasc1eres and microscleres were were slightly to strongly curved, and were cov sharply pointed at both ends and slightly ered with prominent spines. 98 GREAT BASIN NATURALIST [Volume 57 Fig. 3. Abnormal megasclere ofEunapius!ragilis showing expanded "bulbs" (Diamond Lake). Bar = 50 11m. Ephydatia muelleri (Lieberkuhn 1855) had 1 or more spines extending from their Collection Numbers: 1106, 1112-13, 1115, shafts, and misshapen rays were often present 1118, 1126-27, 1129-30, 1139, 1143-46, (Figs. 7b,c). 1148,1150-51,1158-60,1167-68,1170 (Figs. 5-7) Unidentified Sponge Collection Numbers: 1119, Ephydatia muelleri was collected from 14 1155, 1172-75 sites. At 11 sites it was collected with at least 1 (Fig. 8) other sponge type (E. fragilis, S. lacustris, or the unidentified sponge; Table 1). 11 was found Some specimens collected from undersides most often on sides or undersides of logs or of rocks and logs in Blanchard and Coopers rocks. The sponge varied in morphology from lakes lacked gemmules and gemmoscleres and thin «0.5 em) encrustations to lobate forms in could therefore not be positively identified. which rounded masses (approximately 2 em tall) Although collected from 2 different sites, these extended from basal mats (Fig. 5). Large oscula specimens exhibited similar morphologies. At were sometimes present. Its color varied from both locations sponges were light tan and light tan to green. formed hard, disc- or cushion-shaped masses. This species, which like E. fragilis lacks Megascleres were slightly curved, sharply microscleres, contained megascleres that were pointed at both ends, and covered with short sharply pointed at their ends and slightly curved. spines except at their tips, Many megascleres Although they were often covered with small also had a slight midregion expansion (Fig. 8). spines except at their tips, many were smooth The megascleres bore an overall resemblance or had few spines (Fig. 6). Both smooth and to the spined megascleres of E. muelleri but spined megascleres were frequently present in were substantially wider (21.0 + 1.5 ~m versus the same specimen. Spicule dimensions are 10.5 + 1.5 ~m for E. muelleri). Normal speci given in Table 2. mens of E. muelleri also were present in both Gemmules, ranging in diameter from 350 to lakes. Specimens collected during return visits 450 ~m, were scattered throughout the sponges to Coopers Lake in November 1995 and Feb or were concentrated at the base. A distinct ruary 1996 did not contain gemmules. In fact, pavement layer was not present, however. The specimens of this sponge collected at these gemmoscleres were birotulate (Fig. 7a). Rotules times resembled specimens collected during had similar diameters within each gemmo summer months, In contrast, E. muelleri had sclere and had irregular and deeply iucised rays died back and occurred only as mats of gem numbering no more than 12. Shafts connect mules held within skeletal frameworks. The ing the rotules were moderately thick, their unidentified sponge might be a species ofEphy lengths usually not exceeding the diameters of datia, Trochospongilla, or Anheteromeyenia. Fur the rotules. Gemmoscleres were arranged in a ther studies ofthis sponge are underway. single layer perpendicular to the gemmule and Chemical and Physical Factors were embedded in a well-developed pneumatic layer. Chemical and physical ranges characteriz Slight malformations ofgemmoscleres were ing habitats of the identified species are given not uncommon, but those present in sponges in Table 3, These ranges were determined from Cedar Lake and au adjoining pond (Flat from data collected at 16 of the sites that con head Basin) were extreme. Many birotulates tained sponges. The table also includes ranges 1997] FRESHWATER SPONGES OF WESTERN MONTANA 99 Fig. 4. Spongilla lacustrls with 6ngerlike projections growjng from beneath a rock (Salmon Lake). Flg. 5. Ephydati4 muelleri exhibiting encrusting and lobate growth (Salmon Lake). derived from data collected at 9 lakes that did were wider than those determined for E. not contain sponges. Although there was over mueUeri or S. lacustris. In addition, S. lacustris lap among the ranges detennined for the 3 had the narrowest ranges of alkalinity, calcium species, widths of the ranges varied. Chemical and magnesium concentrations, and total hard ranges determined for E. fragilis, except for ness. Differences between variances of data the ranges of total organic carbon and silica, obtained from sites containing the different 100 GREAT BASIN NATURALIST [Yolume 57 Fig. 6. Smooth and sparsely spined megascleres ofEphyd-atia muelleri. Bar = 50 !-lrn. Fig. 7. GemmoscIeres ofEphydatia muelleri: a, normal birotulate gemmoscleres, top and side views; band c, malfonned gemmoscleres, top view (b) and side view (c) (Cedar Lake). Bar = 251lm. Fig. 8. Megasclere ofunidentified sponge (Coopers Lake). Note slight rnidregion swelling (dark band). Bar = 50 /lm. sponge species, however, were not statistically DISCUSSION significant at a = 0,05 (Levene's test for equal ity of variances, one-tailed), although at a = The small number ofsponge species found in 0.10 the variance of the data for magnesium western Montana is consistent with results of concentration from lakes containing E. jragilis other surveys ofsponges ofthe Mountain West was significantly greater than the variance and seems to reflect an overall paucity ofsponge detennined from lakes containing S. lacustris. species in this region. In his listing of the sponges ofAlberta, Clifford (1991) reports only Differences among the means ofthe data were 3 species, the same 3 reported by us: Ephyda also not statistically significant at a = 0,05 tia muelleri, Eunapius fragilis, and Spongilla (one-way ANOYA). lacustris. Williams (1980) reports 4 species Some sites that lacked sponges had values from Colorado: the previously mentioned 3 plus for chemical and physical factors that lay out Ephydatia jluviatilis, found at 1 location on side the ranges determined from sponge-con the eastern plains, That these 3 species of the taining lakes, but others had chemical and 27 reported for the United States and Canada physical profiles that were very similar to lakes (Frost 1991) were found in western Montana is that contained sponges, The difference between not surprising when their distributions are con means of the data obtained from lakes contain sidered. All 3 species are \videspread. Eunapius ing sponges and lakes lacking sponges was not fragilis is truly cosmopolitan, being present significant at a = 0,05 (pooled t test). on every continent, whereas E. muelleri and 1997] FRESHWATER SPONGES OF WESTERN MONTANA 101 TABLE 3. Chemical and physical ranges ofwestern Montana sponges. Lakes containing sponges Lakes without E·fragilis S.lacwtrn E. muelleri sponges Variable (n ~ 9) (n ~ 7) (n ~ 10) (n ~ 9) Methyl orange al~...linity (mgIL) 11.2-139.0 15.0-80.0 11.2-106.0 0.0-244.0 Calcium (mgIL) 2.0-39.4 4.3-21.4 2.0-30.1" 0.4-47.9 Total hardness as C.CO, (mglL) 6-151 11-81 6-112 2-231 Total organic carbon (TOe) (mglL) 0.7-5.1 0.5-6.5 0.0-6.5 0.6-14.4 Magnesium (mglL) 0.8-12.8 0.0-6.7 0.0-9.0b 0.2-27.0 pH 7.06-ll.83 7.62-5.39 7.06-5.26 6.11-5.26 SiO, (mgIL) 3.2-17.1 2.1-37.9" 2.1-37.9" 4.9-15.4 Conductivity ("S/cm) 21-3$5 26-237 38-2.:17a 9-420 Elevation (m) 884-2124 1006-2911 884-2537 646-2926 TemperatuTe rC) 15.8-23.4 13.6-23.4 15.6-23.4 13.6-23.4 ll(;ruler than pre-ioody recorded; _ text bLe.l5 tm.u pr~\l~ly recorded: see text S. lawstris are present throughout the cold of the measured chemical factors in Diamond temperate region of the northern hemisphere Lake were not unusual although values for (Penny and Racek 1968). hardness. calcium, and magnesium were near Although only 3 species were identified, each the upper ends of the ranges we determined showed considerable morphological variation. from E. fragilis-containing sites. The variation encompassed spicule size in all 3 Another type of malformation occurred in identified species, spicule shape in E. fragilis gemmoscleres of the specimens of E. muelleri and E. muelleri, and spine development in E. collected from Cedar Lake and a nearby pond. muelleri. Variations of spicule morphology are Here, gemmoscleres had misshapen rays, and of concern since taxonomic classification rests at least 1 spine extended from their shafts. largely on this feature. Poirrier (1974) described similar malforma Spicule size ranges for each species identi tions in a related species, Ephydatia. fluviatilis, fied were expanded beyond those reported pre and observed that they can be induced by viously (Penny and Racek 1968, Ricciardi and altering environmental conditions, suggesting Reiswig 1993). The broader range of mega that the presence of malformed gemmoscleres sclere lengths in E. fragilis was especially pro in Cedar Lake might be due to the environ nounced. Some megascleres observed were ment. Since no chemical or physical data are > 120 /lm longer and others were > 70 /lm available for Cedar Lake, we do not know shorter than those previously recorded. Short, whether unusual conditions exist in this lake. thin megascleres and long megascleres were Finally, smooth megascleres or megascleres sometimes found in the same specimen. having few spines were common in E. muelleri Atypical spicules with bulbs along their throughout western Montana. Both Penny and lengths were present in 1 specimen of E. frag Racek (1968) in their taxonomic revision of the ilis collected from Diamond Lake. Simpson Spongillidae and Ricciardi and Reiswig (1993) and Vaccaro's (1974) report that germanium in their description of the sponges of eastern inhibits silica deposition during spicule forma Canada state that E. muelleri only rarely has tion and can cause spicules with bulbs to form smooth megascleres. Williams (1977), however, suggests that these malformations might have reported that in Colorado, E. muelleri frequent an environmental basis. Since other specimens ly has smooth megascleres. A high frequency of of E. fragilis in the same area of the lake had smooth megascleres therefore might be char normal megascleres, however, the malforma acteristic ofthis species in the Mountain West. tions must either be due to highly localized Most chemical and physical ranges deter conditions or have a genetic basis. The levels mined from sponge-containing lakes fell within 102 GREAT BASIN NATURALIST [Volume 57 limits established in previous reports (Jewell technical assistance, and Dr. Jean Smith for 1939, Harrison 1974, Williams 1977). Excep her encouragement and many suggestions. tions were the ranges of conductivity and of calcium, magnesium, and silica concentrations LITERATURE CITED determined for E. muelleri and the range of silica concentration for S. Wcustris. CLIFFORD, H. F 1991. Porifera: sponges. Pages 17-33 in Aquatic invertebrates ofAlberta. University ofAlberta In her study of Colorado sponges, Williams Press, Edmonton, Alberta, Canada. (1977) observed that broadest chemical ranges FRANCIS, J. C., AND F W. HARRISON. 1988. Copper and were associated with E. fragilis, whereas the zinc toxicity in Ephydatia fiuviatilis. Transactions of ranges of alkalinity, calcium and magnesium the American Microscopical Society 107; 67-78. FROST, T. M. 1991. Porifera. Pages 95-124 in J. H. Thorp concentrations, and total hardness determined and A. P Covieh, editors, Ecology and classification for S. lacustris were significantly narrower than of North American freshwater invertebrates. Acade those for E. fragilis or E. muelleri. Even though mic Press, New York. SI~PSON. the chemical ranges determined for these GILBERT, J. J., AND T. L. 1976. Gemmule polymor phism in the freshwater sponge, Spongilla lacustris. species were, in several cases, broader in west Archiv flir Hydrobiologie 78: 268--277. ern Montana than in Colorado, similar rela HARRISON, F. W. 1974. Sponges (Porifiera: Spongillidae). tionships among the widths oftheir ranges were J;'ages 29-66 in C. W Hart, Jr., and S. L. H. Fuller, edi observed: E. fragilis, in western Montana as in tors, Pollution ecology of freshwater invertebrates. Academic Press, New York. Colorado, had the widest chemical ranges JEWELL, M. E. 1935. An ecological study of the fresh overall (in western Montana, total organic car water sponges ofnortheastern Wisconsin. Ecological bon and silica were exceptions), and S. lacus Monographs 5: 463-504. ___. 1939. An ecological study of the fresh-water tris had the narrowest ranges of alkalinity, cal sponges of Wisconsin. II. The influence of calcium. cium and magnesium concentrations, and total Ecology 33: 11-28. hardness. From the 2 studies, it appears as if OLD, M. C. 1932. Environmental selection of the fresh E. fragilis in the Mountain West is less con water sponges (Spongillidae) of Michigan. Transac tions of the American Microscopical Society 51: strained by chemical factors than the other 2 129-136. species are and that S. lacustris is more lim PENNAK, R. W. 1978. Porifera (sponges). Pages 80-98 in ited by such factors. These conclusions need to Freshwater invertebrates of the United States. 2nd be substantiated by analyses involving larger edition. John Wiley and Sons, Inc., New York. PEN!\EY, J. T., AND A. A. RACEK. 1968. Comprehensive revi sample sizes. sion of a worldwide collection offreshwater sponges The fact that sponges were absent from some (Porifera: Spongillidae). United States Natural His lakes having measured chemical and physical tory Museum Bulletin 272: 1-184. POIRRIER, M. A. 1969. Louisiana fresh-water sponges: tax profiles almost identical to those of lakes con onomy, ecology, and distribution. Unpublished dis taining sponges suggests that sponge distribu sertion, Louisiana State University, Baton Rouge. tion is influenced by more factors than those University Microfilms, Inc., Ann Arbor, MI. 110 pp. we examined. In fact, as Williams (1977) pointed . 1974. Ecomorphic variation in gemmoscleres of --E"phydatiafluviatilis Linnaeus (Porifera: Spongillidae) out, distribution is probably controlled by chem with comments upon its systematics and ecology. ical, physical, and biological factors acting syn Hydrobiologia 44: 337-347. ergistically. The identification of species of POIRRIER, M. A., P. S. MARTIN, AND R. J. BAERWALD. 1987. freshwater sponges in western Montana and Comparative morphology ofmicrosclere structure in Spongilla alba, S. cenota, and S. lacustris (Porifera; the initial chemical and physical characteriza Spongillidae).Transactions of the American Micro tion of their habitats lay the foundation for scopical Society 106; 302-310. investigations of the effects of additional fac RICCIARDI, A., AND H. M. REISWIG. 1993. Freshwater tors on sponge distribution. sponges (Porifera, Spongillidae) of eastern Canada: taxonomy, distribution, and ecology. Canadian Jour nal ofZoology 71: 665-683. ACKNOWLEDGMENTS RrcHELLE-MAURER, E., Y. DEGOlJDENNE, G. VAN DE VYVER, A.' STREKAL, T. A" AND w: .r. McDwFETI: 1974. Factors affect WUJ.TA;-"{S, R. E. 1977. Distribution, ecolah,)" and reproduc ing germination, growth, ,mel disb'ibution ofthe &-e5h tive cycles of Colorado freshwater sponges (Porifera: water sponge, SpongiUa fragilis Leidy (Porifera). Bio Spongilllidae). Unpublished dissertation, University of logical Bulletin 146: 267-278. Colorado, Boulder. University MicroBlms, Inc., Ann U:-.IITED STATES ENVIRONME;../TAL PROTECTION AGENCY. 1983. Arbor, MI. 155 pp. Standard methods for chemical analysis ofwater and --7' 1980. The freshwater sponges (Porifera: Spongilli wastes. Cincinnati, OR. 275 pp. dae) of Colorado. Natural Ilistory Inventory of Colo ___. 1991. Methods for the determination of metals in rado 4: 1-12. environmental samples. OfBce ofResearch ,mel Devel YOUNG, R. T. 1935. The life of Flathead Lake, Montana. opment, Washington, DC. 339 pp. Ecological Monographs 5: 93-163. WATER QUALITY BUREAU, 1991. Ficld procedure manuaL Montana Department of Health and Environmental Received 5 August 1996 Sciences, Helena. Pages .3.1-3.21. Accepted 31 January 1997