Jar1 K. Hiltunen U.S. Bureau of Commercial Fisheries, Biological Laboratory, Ann Arbor, Michigan 48107

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1 DISTRI.BUTION OF OLIGOCHAETES IN WESTERN LAKE ERIE, 1961l Jar1 K. Hiltunen U.S. Bureau of Commercial Fisheries, Biological Laboratory, Ann Arbor, Michigan ABSTRACT A total of 52,390 oligochaetes were collected from 40 stations in western Lake Erie in spring The population was composed of two families, Naididae and Tubificidae. Only six species of naidids were found. One, Paranais frici, is apparently new to the list of North American freshwater Naididae. Among the 14 tubificids found, five species of Limnodrilus were most abundant; they contributed 90% or more of all oligochaetes at 33 of the 40 stations. Numbers of Limnodrilus were generally large near the mouths of the Detroit, Raisin, and Maumee rivers and decreased progressively lakeward. Stylodrilus heringianus, a pollution-intolerant species common in eastern Lake Erie, was not found in the western end of the lake. INTRODUCTION In late May and early June 1961, the U.S. Bureau of Commercial Fisheries Biological Laboratory conducted a study to compare the abundance and distribution of macrobenthos in extreme western Lake Erie with those reported by Wright ( 1955) for The results were reported by Carr and Hiltunen ( 1965), but the Oligochaeta and other invertebrates were discussed only as groups. This paper is an account of the distribution of the various species of oligochaetes. Station designation and area grouping ( Fig. 1) are the same as in the 1965 report. The study of species was conducted at the University of Liverpool, England, under the direction of R. 0. Brinkhurst; his instruction made this report possible. I am also grateful to the Department of Zoology of the University of Liverpool for making available its laboratory and library facilities. MATERIALS AND METIIODS Three bottom samples were taken with a Petersen dredge ( 743-cm2 sampling area) at each of 40 stations in western Lake Erie in late May and early June 1961 from the research vessel Musky II. Samples were placed in bags of No. 36 grit cloth (ca. 1 Contribution No. 385 of the Ann Arbor Biological Laboratory, U.S. Bureau of Commercial Fisheries. OS-mm mesh) and washed over the side of the boat. The material was then transfcrred to a wire screen (ca. 0.6~mm mesh), washed free of remaining sediment, placed in jars, and fixed in 10% formalin. The organisms were later separated under 15X magnification, and 52,390 oligochaetes were examined under 35x or greater magnification. Details of the field techniques were reported by Carr and Hiltunen (1965). The current study includes only those oligochaetes that could be identified to species, either by external features or by mature sex organs. Only sexually mature individuals of Limnodrilus cervix, L. clapare- dianus, L. hoffmeisteri, L. maumeensis, and Potamothrix moldaviensis were counted; hence, the numbers of these spccics given in comparisons of abundance are disproportionately low compared with the remaining species which were identifiable even when immature. The taxonomic interpretation of Limnod&us species follows that of Hiltunen ( 1967).for Lake Michigan. The two forms of L. cervix found in Ludington Harbor, Lake Michigan ( Hiltunen 1967)) were also present in western Lake Erie. The distri- bution and abundance of each is illustrated separately. The proper placement of one Limnodrilus taxon remains uncertain; its paired penis tubes (Fig. 2) resemble somewhat those of Eisen s ( 1885) Camptodrilus [ = Limnodrilus] spiralis. Because of this uncertainty I have included it with L. 260

2 OLIGOCHAETES IN WESTFXN LAKE ERIE 261 FIG. 1. Location of sampling stations in western Lake Erie. hoffmeisteri--the species which it most closely resembles. DISTRIBUTION Naididae Only 20 specimens of Naididae were collected (many were probably lost when the samples were sieved), but six species were represented: Nais elinguis, Ophidonais serpentina, Paranais f&i, Slavina appendiculata, U&n& uncinata, and Veidovskyella intermedia. The naidid species were present only at stations in the Detroit River except for V. intermedia, which was also taken at the mouth of the Raisin River (sta. 1R). A single specimen of P. f&i, from station 16D, apparently is the first record of that species from the freshwater of North America.. hoffmeisteri Tubificidae The tubificid genus Limnodrilus included the most common species (L. cervix, L. claparedianus, L. hoffmeisteri, L. maumeensis, and L. udekemianus) in western Lake Erie. Limnodrilus species composed 90% or more of all oligochaetes at 33 of the 40 stations. The most abundant was L. hoffmeisteri; its numbers were greatest near the mouths of the three major tributary rivers (Detroit, Raisin, and Maumee) and declined progressively A v toward the FIG. 2. Penis tube of Limnochilus?spiralis. In situ, exserted. Line equals 300 p. open lake (Fig. 3). A similar effect of enriched river water on the population of this species has been demonstrated in Lake Huron ( Brinkhurst 1967). The species was present at every station and was the only Limnodrilus at some stations in the open lake. When the comparison was restricted to mature Limnodrilus, the percentage made up by L. hoffmeisteri was also greatest in the Detroit River and the open lake areas but least near the mouth of the Raisin River ( Fig. 4). The second most abundant LimnodriZus was L. cervix (Figs. 5 and 6). The combined totals of the typical and atypical FIG. 3. Abundance ( Mo./m2) of Limnodrihs hens. lat.] in western Lake Erie.

3 262 JARL K. IIILTUNEN FIG. 4. Percentage of Limnodrilus hoffmeisteri hens. lat.1 among total mature Limnodrilus spp. in western Lake Erie. FIG. 5. Abundance (No./m ) of Limnodrilus cervix (typical) in western Lake Erie. forms exceeded the number of L. hoffmeisteri at only two stations ( 2R and 2M ). Like L. hoffmeisteri, L. cervix was abundant near the mouths of the rivers; however, it was not found in the open lake. The two L. cervix forms wcrc gcncrally sympatric but the atypical form was the more abundant at each station, The taxonomic relationship between the forms remains unexplained. Theoretically, one form could result from self-fertilization which could account for the morphological differenccs, but the existence elsewhere of apparently monotypic populations of the typical form (Kennedy 1965) casts doubt on that thesis; self-fertilization in one area but not in another is unlikely. Kennedy (1965) has reported the typical form of L. cervix from England, but its discontinuous distribution led him to conclude that the species may have been introduced from North America. The distribution of L. cervix in the Great Lakes also is apparently discontinuous. Although the species is well established in western Lake Erie, in Lakes Huron ( Brinkhurs t 1967 ), Michigan ( Hiltunen 1967), Ontario (Johnson and Matheson 1968), and Superior ( Hiltunen, in press) it has been reported only from inshore areas subject to organic pollution. Limnodrilus maumeensis, a species re- ccntly described from Maumee Bay, Lake Erie, and Lake St. Clair (Brinkhurst and Cook 1966)) was the third most abundant Limnodrilus in western Lake Erie. Except in the Detroit River area, the distribution of L. maumeensis (Fig. 7) was similar to that of L. cervix. The species was most abundant at the mouth of the Maumec and Raisin rivers, but the population was unexpectedly less abundant in the Detroit River area. Competition among species or some adverse effect by the river may have depressed it. The least plentiful of the sexually mature members of the genus was L. claparedianus. Like L. hoffmeisteri and L. cervix, this species also included a typical and an atypical form. The atypical form had a penis tube with a thicker wall than in the typical form, and the head of the tube had a distal digitate lobe (Fig. 8). The remaining margin of the head was rounded, in contrast to the triangular outline of the bilaterally symmetrical head on the typical form. The typical form was the more common; the atypical form was found in the mouth of the Raisin and Detroit rivers but not at the lakeward stations. Hunt ( 1962) recorded all tubificids from the lower Detroit River region as L. claparedianus, but my work shows that the area

4 OLIGOCIIAETES IN WESTERN LAKE ERIE 263 FIG. 8. Penis tube of atypical Limnodrilus claparedianus, facial aspect. FIG. 6. Abundance ( No./ma) of Limnodrilus cervix (variant) in western Lake Erie. has more than one species of LimnodriZus. Possibly his specimens were the very common L. hoffmeisteri, which in earlier studies has been mistaken for L. CZaparedianus ( Brinkhurst 1965a). Limnodrilus udekemianus was identified by cxtcrnal features, regardless of maturity; numbers of this species recorded wcrc disproportionate to the other Limnodrilus species that were identified only when sexually mature. The distribution of L. udekemianus was probably influenced by river discharge, but the effect was not as pronounced as it was on the other species. The distribution of L. udekemianus may have been affected more by depth, distance from shore, or both. All L. udekemianus were immature, suggesting that its reproductivc cycle may diffor from that of the other species of LimnodriZus. The distribution of PeZoscoZex multisetosus differed conspicuously from that of other tubificids. The species was poorly represented in western Lake Erie except in the mouth of the Detroit River where many were collected from a few stations (Fig. 9). Both subspecies, P. m. multisetosus and P. m. Zongidentus, were included in the population; the typical subspecies was always more abundant. The abundance of PeZoscoZex ferox was considerably below that of P. muztisetosus; only one specimen of P. ferox was found at each of three stations, all in the Detroit River area. All four species of AuZodriZus currently known from North America (Brinkhurst 1965a) were collected. Although A. Zimnobius and A. pigueti were relatively scarce, many of them probably passed through the sieve when the samples were washed. FIG. 7. Abundance ( No./ma) of Limnodrilus FIG. 9. Abundance (No./m ) of Peloscolex maumeensis in western Lake Erie. multisetosus [sens. lat.1 in western Lake Erie.

5 264 JARL K. 1 SILTUNEN Aulodrilus Zimnobius was found only in the mouths of the Raisin and Detroit rivers, The distribution of A. pigueti reflected no habitat preference except that it was the only Aulodrilus taken off the mouth of the Maumec River. Distribution of A. americanus and A. pluriseta showed no regional regularity, but the greatest number of each was found at the mouth of the Detroit River. Branchiura sowerbyi is the largest tubificid in the Great Lakes, where it is currently known only from Lake St. Clair (unpublished data) and Lake Erie. Only a few specimens were collected (at stas. ll, 2L, lr, and 2R), but in Sandusky Bay (Lake Erie) the species is abundant (Wolfert and Hiltunen 1968). Potamothrix moldaviensis and P. vejdovskyi were collected from scattered stations in western Lake Erie but neither was relatively abundant; 1,102 mature P. moldaviensis per m2 and 193 P. vejdovskyi per m2 were the maximum calculated densities of each, both from station 5D. The phenotypically similar species, Tubifex tubifex and Ilyodrilus templetoni, were present in some of the samples but these species were not separated from one another. Their distribution and relative abundance was not noteworthy. CONCLUSION The beneficial effect of river outflow on certain species of Tubificidae was clearly evident. The relative abundance of some species (e.g., L. hoffmeisteri, L. cervix, L. maumeensis, and P. multisetosus) was greatest near the mouths of the rivers. Conversely, the river outflows of western Lake Erie were not suitable to other speties, Sty Zodrilus heringianus, for example, has been reported from eastern Lake Erie (Brinkhurst, Hamilton, and Herrington 1968) but was not taken in the western end of the lake. This species is common in the other Great Lakes but only in areas that are relatively free of pollution (Brinkhurst 1967; Hiltunen 1969). In England, however, S. heringianus has been reported from polluted water ( Brinkhurst 1965b). This difference will bc understood further ecological research. only after REFERENCES BHINKHUIST, R a. Studies on the North American aquatic Oligochaeta. II. Tubificidae. Proc. Acad. Nat. Sci. Phila., ll7(4) : b. The biology of the Tubificidae with special reference to pollution, p In Clarence M. Tarzwell [ed.], Biological problems in water pollution, 3rd seminar, US. Public Health Serv., Publ. No. 999-WP The distribution of aquatic oligochaetes in Saginaw Bay, Lake Huron. Limnol. Oceanog., 12 : , AND D. G. COOK Studies on the North American aquatic Oligochaeta. III. Lumbriculidae and additional notes and records of other families. Proc. Acad. Nat. Sci. Phila., 118( 1) : , A. L. HAMILTON, AND H. B. HERRINGTON Components of the bottom fauna of the St. Lawrence Great Lakes. Univ. Toronto, Great Lakes Inst., Publ. No. PR p. CARR, J. F., AND J, K. IIILTUNEN Changes in the bottom fauna of western Lake Erie from 1930 to Limnol. Oceanog., 10: EISEN, G Oligochaetological researches. Rept. U.S. Comm. Fish Fisheries for 1883, Part XI, Appendix D, p HILTUNEN, J, K Some oligochaetes from Lake Michigan. Trans. Am. Microscop. Sot., 86: Benthic macroinvertcbratcs of Lake Ontario. Great Lakes Fish. Comm. Tech. Rcpt. No. 14, p In press. Invertebrate macrobenthos of western Lake Superior. Mich. Acad. HUNT, G. S Water pollution and the ecology of some aquatic invertebrates in the lower Detroit River. Proc. 5th Conf. Great Lakes Rcs., Univ. Mich., Inst. Sci. Tech., Great Lakes Res. Div., Publ. No. 9, p JOI-INSON, M. G., AND D. H. MATI-IESON Macroinvertebrate communities of the sediments of Hamilton Bay and adjacent Lake Ontario. Limnol. Oceanog., 13: KENNEDY, C. R The distribution and habitat of Limnodrilus Claparede ( Oligochacta: Tubificidac). Oikos, 16: WOLFERT, D. R., AND J. K. HILTUNEN Distribution and abundance of the Japanese snail, Viviparus jnponicus, and associated macrobenthos in Sandusky Bay, Ohio. Ohio J, Sci., 68: WRIGHT, S Limnological survey of western Lake Eric. U.S. Fish Wildlife Serv., Spcc. Sci. Rept., Fisheries, p.