The above data clearly demonstrate selectivity in the Aureliu rmurita L. (Scyphozoa, Semaeostomae). Wiss. diets of the four colnrnon species that show predation Martin Luther Univ. HaBle-i$litter-aberg hfath. Naturwiss on other coelenterates. However. no predator was de- Reihe 33) : 479-482. M. pendent on a single prey species. Tt is difficult to evaluate HYMN, L. 2940. Ob5ervations and experiments on the physiology of medusae. Biol. Bull. (Woods Hole) 79: the degree of competition involved. Not only do the 282-296. four species vary in period of maximum abundance in LEBOUK,M. V. 1922. The food of plankton organisnas. J. Mar the bay but all four species will accept noncoelenterate Riol. Assoc. U.M. 12: 644-677. prey. This study will be extended to investigate preda- 1923. The food of plankton organisms HI. J. Mar. tion on other possible prey including fish larvae. Biol. Assoc. U.K. 13: 70-92. LC)C;INOVA,N. P., AND N. M. PERZOVA.1967. Some data on Acknowledgnie~zts- We are very grateful for the facil- ecology of feeding of pelagic Coelemterata in the White ities of the Pacific Biological Station, Nanaimo, B.C., where Sea. Issled. Fauny Morei 7415): 21-28. (In Russian) this study was carried out and the cooperation of the staff. ~~CCORMICK,J. M. 1969. Trophic relationships of hydro- Dr Z. Kabata kindly translated several Russian papers. Miss medusae in Yaquina Bay, Oregon. Northwest Sci. 43: Valerie Overend assisted in collection of specimens. The 207-2 14. project was supported by NRC Grant A2007 to M.N.A. PETIPA,T. S.? E. V. PAVLOVA,AND C;. N. MIRONOV.1970. The food web structure utilization and transport of energy by trophic levels in the planktonic communities, p. 142-167. It1 J. H. Steele [ed.] Marine food chains. Oliver and Boyd, AGASSIZ,L. 1862. Contribution to the natural history of the Edinburgh. 552 p. United States of America. Second Monograph. IV. PLOTNIKOVA,E. D. 1961. On the diet of medusae in the littoral MydroBdae 4: 183-372. pl. 16-35. of Eastern Murman, p. 153--156. I/? M. M. Kamshilov FOMBPS.E. 1848. A monograph of the British naked eyed [ed.] Hydrological and biological features of the shore medusae with figures of all the species. The Ray Society waters of Murman. Akad. Nauk USSR Kolsk. Fil. Publication, London. 104 p., pl. 1-13. (In Russian) FRASER,J. H. 1969. Experimental feeding of some medusae SOUTHWARD,A. 3. 1955. Observations on the ciliary currents and Chaetognatha. J. Fish. Res. Board Can. 26: 1743- of the jelly-fish AIIT~~~LIrmrifu L. 1. Mar. Biol. Assoc. U.K. 1762. 34: 201-216. C~REVE,W. 1970. Cultivation experiments on North Sea SVESPINIKOV,V. A. 1963. The feeding habits of jelly-fish as ctenophores. Helgol. Wiss. Meeresunters. 20: 304-317. possible rivals of the White Sca herring, Mosco\v Univ. 1971. Okologische U~~tersuchungenan Pleurobrtrcllitr Belmorsk. Biologichesk. Tr. 2: 246-249. (In Russian; piieus. 1. Freilanduntersuchurlgen. Helgol. Wiss. Meeie- English abstract) sunters 22: 303-325. ZELICKMAN,E. A. 1076. The biology of a little known neritic 1972. Okologische Untersuchungen an Pl~urobrctclriu hydromedusa Poi~.orchis kurufirroc~nsis (I'olyorchidae: pilrus. 2. Laboratoriumsuntersuchungen. Helgol. Wiss. Coelenterata). Tr. Inst. Okeanol. Altad. Nauk SSSR. 105: Meeresunters. 23 : 141-164. 210-213. (In Russian; English abstract) HUN~LEY,M. C., AND L. A. HOBSON.1978. Medusa predation ZELICKMAN,E. A., V. 1. GELFAND,AND M. A. SHIFKIN.1969. and plankton dynamics in a temperate fjord, British Growth, reproduction and nutrition of some Barents Sea Columbia. J. Fish. Kes. Board Can. 35: 257-261. hydromedusae in natural aggregations. Mar. Biol. (Berl.) HUSING,J. 0. 1956. Zur Frage der Ernahrung der Ohrenclualle 4: 167-173. Leaf Litter Processing in a Regulated Rocky Mountain Stream Depurtnzet~tof Zoology and en tor no log^, Coloru~loState Umivtlrsity, Fort Collins, CCd 80523, USA Snron~,W. A., AND J. V. WARD.1980. Leaf litter processing in a regulated Rocky Mountain stream. Can. J. Fish. Aquat. Sci. 37:123-127. Processing of alder (Alrurs tenuijbliu) was investigated during autumn and winter to determine the influence of stream regulation on leaf litter processing. Study sites were the Colorado River below Granby Dam and the Frasei. River, an unregulated tributary. Alder leaves (5-g units) were attached to bricks and placed in riffles. Lcaching controls were re- trieved after 48 h; thereafter five replicates were collected from each site after 17, 38, 52, and 66 d. There were significant differences (P < 0.05) in processing rates B-xtween sites. The loss rate coetiticient (X:) was much higher (X: = 0.0462) for leaves incubated in the regulated section 'Present address: Departmeiat of Biological Sciences, North 'Texas State University, Denton, TX 76203, USA. Printed in Canada (55676) Imprim6 au Canada (55676) CAN. J. FISH. AQUAT. SCI., VOL. 37, 1080 of the Colorado River than for those in the unregulated tributary (k = 0.0235 1. The hypothesis that reductions in macroinvertebrate shredders would decrease processing rates of leaf litter in regulated streams was not supported by the results. The "winter warm" thermal regime below the reservoir seems to compensate for the virtual absence of shredder species apparently by enhanced microbial processing. Kej, words: Colorado River. leaf litter, macroinvertebrates, Rocky Mountains, stream regula- tion, temperature SHORT,R. A., AND J. V. WAI~D.1980. Leaf litter processing in a regulated Rocky Mountain stream. Can. J. Fish. Aquat. Sci. 37: 123-127 Dans le but de determiner l'influence du contrdle d'un cours d'eau sur la transformation de la litikre de feuilles dans un cours d'eau des montagnes Kocheuses, nous avons 6tudiC la transformation de l'aulne (Alnus terrrl{f'oliu) en automne et en hiver. Les recherches ont Ctl eb'fectuCes sur le fleuve Colorado, en aval du barrage Granby et sur la rivikre Fraser, un tribu- taire non contrale. Bes feuilles d'aulne (unites de 5 g) furent attachees h des briques et plackes dans des .maigres)) le 29 septembre. Des temoins de lessivage furent enleves aprks 48 h; par la suite, 5 reproductions furent recueillies h chaque site aprks 17, 38, 52 et 66 jours. 11 y a des differences signiticatives (P < 0,05) de taux de transformation entre les sites. Le coeficient de taux de perte (k) est beaucoup plus Cleve (k - 0,0462) pour des feuilles incubees dans la section contrdlee du fleuve Colorado que celles placees dans le tributaire non contr816 (k = 0,0235). Les resultats de cette etude n'appuient donc pas l'hypothkse que la diminution des macroinver- tCbrCs dechiqueteurs ralentit la transformation de la litikre vCg6tale dans des cours d'eau con- trdlCs. LC regime thermique de xchaleur hivernale. en aval du reservoir semble compenser l'absence virtuelle d'espkces dechiqueteuses par une transformation microbienne plus active. Received June 15, 1979 Re~ule 15 juin 1979 Accepted October 4, 1979 Accept6 le 4 octobre 1979 DETERMINATIONSof leaf litter processing rates have stream bottom was predominantlgl rubble in both study generated a great deal of information concerning stream sections. During the study period, discharge averaged 0.54 ecosystem strrlcture and function (e.g. Petersen and m"/sin the Colorado River and 0.53 m.'/s in the Fraser River. Total dissolved solids (35.7 mdL: 65.4 mg/L) and Cumnlins 1974; et al. g75; Benfield et 1977) sedell methyl orange a1 kalinity ( I1.0 mg/L; 22.5 mg/L) values and have provided an experimental means to test vari- ,ere somewhat in the River. ous hypotheses (Reice 1974, 1977)- 'The leaf pack (53 .g/L; 43 rg/L) and pH (7.6: 7.4) exhibited similar method has also been used as a bioassay to determine values at both locations. There were, however, collsider- the effects of man's activities on streams (Triska and able differencs in water tenlperature (discused later) be- Sedell 1976; Gelroth and Marzolf 1978). One signifi- tween the regulated and unregulated streams. cant anthropogenic impact has been the construction Experimental procedures - Alder (Alties tenuifolia) leaves of numerous reservoirs on previously free-flowing were collected in September 1978 immediately prior to streams. Large dams may greatly physic'- abscissioll. The leaves were air-dried then oven-dried at chemical conditions of downstream reaches with re- 60°C for 48 h and weighed into 5-g units and strung on sultant changes in the diversity, density, and composi- monofilament line. A single- leaf nack was lashed to each tisn of the nlacrsinvertebrate fauna (Ward 1976a; brick and placed into a rime area of each stream on Sep- Ward and Stanford 1979). Since there is a selective tember 29. After 48 h, three replicate lcaf packs were re- elimination sf certain taxonomic and functional groups trieved from each site to serve as leaching controls. There- (Ward and short 19781, it was hypothesized that leaf after five replicates were collected from each site aAer 17, litter processing would be altered by stream regulation. 38, 52, and 66 d in the stream. At the time of collection the leaf pack was cut free of the brick and placed into a leaf pack The method was to determine the in- plastic bag containing 5% formalin. In the laboratory the fluence of stream regulation by dams on leaf litter pro- leaf Dack was thoroughlv rinsed with ta~water to remove cessing rate. accuiulated sedimen;, dried at 60°C for.48 h, and weighed (k0.1 g). Macroinvertebrates associated with the leaf pack Materials and nlethods - Study area - Study sites were were placed into 80% EtOH until identified and enumerated. on the Colorado River below Lake Granby and on the Dry weight of macroinvertebrates was determined follow- Fraser River, a major tributary unregulated by dams.