The rare planktonic diatom Eunotia zasuminensis in Canada

KENNETH H. NICHOLLS A N D ELAINE C. CARNEY Otrttrrio Mit~istr:)! of tile Enrirotrt?~ent, Litnt~ology crtrd Toxicity Sectiotr, Bos 213, Re,vd(rie, Otlt., Conudo M9W 5 L I

Received December 6, 1978

NICHOLLS, K. H., and E. C. CARNEY. 1979. The rare planktonic diatom Brtlotio ztr.sr~tnit~~rl.si.s in Canada. Can. J. Bot. 57: 1150-1 154.

The planktonic diatom Elrrroticr zcrslrrt~inc.nsis (Cab.) Korner is reported from eight locations in Ontario, Canada. It is previously known from only four other localities in Europe and Africa and from two rivers in the U.S.A. The taxonomy ofE. zcr~rrrnir~errsis is discussed relative to similar species. Observations on the rudimentary raphe in this species emphasize its proper taxonomic position within the Eunotiales. The distribution of E. zcrsrrrniir~r~.si.s seems to be controlled by its apparent preference for slightly acidic or dystrophic waters.

NICHOLLS, K. H., et E. C. CARNEY. 1979. The rare planktonic diatom Errnotic/ zcrs~rrnirler~sis in Canada. Can. J . Bot. 57: 1 150- 1 154.

La diatomee planctonique Errrrotio zu.slrmirr~rrsi.s (Cab.) Korner est rapportee de huit localites en Ontario (Canada). Elle etait connue auparavant de seulement quatre localites en Europe et en Afrique et d e deux rivi'eres aux Etats-Unis. La taxonomie d e I'E. ztr.s~rrnir~~rr.sis est discutee en rapport avec les espkces semblables. Des observations sur le mphe rudimentaire d e cette espkce souligne sa position taxonomique parmi les Eunotiales. L a distribution de I'E. zo.srrrnirrrnsi.s semble contr6lee par une preference pour des eaux Iegerement acides ou dystrophiques.

[Traduit par le journal]

Introduction The diatom genus Eunotia contains about 100

freshwater species, most of which are restricted to acidic waters (Bourrelly 1968). Eltnotia zaslt- minensis (Cab.) Korner is a very rare planktonic species having been reported only from Lake Zasuminskie in Poland (Cabejszekowna 1937; Cleve-Euler 1953), Lake Lillsjon and the lakes around Vittsjo, Sweden (Lundh-Almestrand 1954), the Plate River in the Transvaal, Africa (Cholnoky 1958), and Lake Keurusselki, Finland (Eloranta 1974). The only reports from the western hemi- sphere appear to be from Tobyhanna Creek, Penn- sylvania, and the Edisto River, South Carolina, U.S.A. (Korner 1970).

The taxonomy of this species was reviewed and revised by Korner (1970). Previously, E. zasLt- minensis had been reported as Fragilaria zas~tmin- ensis Cab., Asterionella gracillima var. ralfsii Cleve- Euler, A. lf i icana Chol., and A. zas~trninerlsis (Cab.) Lundh-Alm. Recently, Nauwerck (1978) questioned the separation of E. zas~trninensis from Astei.ionella in light of A . thornassonii Nauwerck, which he suggests has features of two related Asterionella species ( A . candelnbrltm Bourrelly and Manquin and A. ralfsii Smith) but also of E. zas~lminensis.

The purpose of this paper is to report E. zas~~minensis from Canada for the first time and to discuss its taxonomy and ecology relative to those of similar pennate diatoms.

Methods All lake samples containing E. zuslrr~~itr~rrsis were collected a s

composites of the euphotic zone, assumed to extend to 2 x the Secchi disc visibility, by lowering and raising a weighted I-L bottle through this depth. Lake sediment samples were also collected at some locations with an Ekman dredge. At one site (Ottawa River), plankton samples were obtained via the city of Ottawa's municipal water supply intakes at the Britannia and Lemieux Island plants. Except when living material was re- tained, samples were fixed in the field with Lugol's iodine solu- tion. Concentration (4 x or 10 x ) was by filtration orsedimenta- tion. Samples were counted prior to I974 with a compound microscope and Sedgewick-Rafter counting chambers and since then with an inverted microscope. All concentrated samples have been retained in the Ontario Ministry of the Environment's permanent sample repository.

For light microscopy, the diatom cells were combusted in boiling nitric acid, washed in distilled water, reconcentlxted by centrifugation, and mounted on glass slides in Hyrax. For elec- tron microscopy, cells were transferred with a micropipette to carbon-coated copper grids, dried, and examined with a Siemens Elmiskop model 102 and R.C.A. model EMU-3G transmission electron microscopes (TEM). Cells were also col- lected on 0.2-pm nucleopore filters, shadowcast with Au, and examined with a Joel model JXA 50 scanning electron micro- scope (SEMI.

0 bservations Occ~~rrence

E~tnotia zas~tminensis has been found in Ontario at eight locations (Table 1). It was most common during summer (July and August), and in this re- gard, its seasonal periodicity was similar to Tabel- laria fenestrata (Lyngb.) Kutz. with which it was always associated. Maximum recorded density was

0008:4026/79/10 1 150-05$01 .OO/O @ 1979 National Research Council of CanadalConseil national d e recherches du Canada

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NICHOLLS AND CARNEY

1030 cells/mL in Riley Lake on August 21, 1969. Other algae occurring with E. zas~rn7it7et7sis at all locations were Asterionella fortnosn Hass. and Chrysophaerella n7~rltispina Bradley. At least four of the lakes (Kashe, Riley, North Wildcat, and Chub) also contain the little-known but common prymnesiophyte Chrysochrom~llinn breuiturritn (Nicholls 1978). All waters except the OttawaRiver site are very poorly buffered with low alkalinity (Table 1) and are slightly acidic in reaction. 'They may be classified as mesotrophic to slightly eutro- phic. Riley and Kashe Lakes may be slightly dys- trophic.

Cell Morphology Cells were sufficiently abundant in samples from

four of the Ontario lakes to permit detailed measurements of cleaned material mounted in Hyrax. There were no important differences in cell dimensions among the samples from the Ontario lakes (Table 2).

The shape of a single cell is very distinctive and is reminiscent of a human humerus with its cordiform poles in valve view (Figs. 1, 2, 4). Although both poles appear similarly shaped, there is some lon- gitudinal asymmetry of the valve with one margin of the frustule (the dorsal side) appearing more convex than the ventral side, which is usually straight or slightly concave (Figs. 1,2,4).

Striae are faintly visible with the light micro- scope (Figs. 1,2) but are clearly resolved as rows of punctae with the electron microscope (Fig. 3). The axial area (pseudoraphe) is not visible with the light microscope, but in the electron microscope, a slight misalignment of the punctae appears near the ven- tral margin of the valve (Fig. 3). A wider space between punctae is common for other diatoms (e.g., Asterionella formosn).

A rudimentary raphe is present at both poles of one valve but is somewhat variable in position and length (2-5 pm long). It is always curved and sometimes traverses the valve mantle and hence only partly shows in either the valve or girdle views (Fig. 4). The raphe can often be seen with the light microscope (Figs. 2,5).

Small spines are present on the margins of both valves (Figs. 6, 7) and may be faintly visible with the light microscope, appearing as refractive dots. The spines are located singly on every third to fifth row of punctae along the main body of the frustule or in small groups of two or three (Fig. 6) but are more closely positioned (<0.5 pm apart) at the polar margins (Figs. 4,7).

Z Z Z Z Z Z Z Z

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1152 CAN. J. BOT. VOL. 57, 1979

FIGS. 1.2. Valve views ofE. zasuminensis (light microscope) showingstriaeand rudimentary raphes (arrows). Bar= 5 pm. FIG. 3. Valve view ofE. zasltminrnsis (TEM) showing rows ofpunctae and axial area (pseudoraphe, arrow). Bar= 5 pm. FIG. 4. Valve view ofE. zasuminrnsis (SEM) showinga rudimentary raphe near each pole (arrows). Marginal spines show a s white dots along the edge of the valve. Bar= 5 pm. Frcs. 5-7. Girdle view of frustule pole ofE. zrrsuminrnsis. Fig. 5. Rudimentary raphe (light microscope). Bar = 5 pm. Fig. 6. Marginal spines (arrows) and rows of punctae on valve mantle. Bar = 1 prn. Fig. 7. Polar spines. Bar = 1 pm. FIG. 8. Typical colony formation ofE. zasloninensis. Bar = 5 pm.

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TABLE 2. Measurements of 25 frustules of Elrr~oria znsrrt~~it~et~sis (Cab.) Korner from four Ontario Lakes. The median statistic is given in micrometres with the range in parentheses

Bala Bay Riley Lake Kashe Lake Harp Lake (Lake Muskoka)

Total frustule length 38(29-45) 40(29-57) 45(38-52) 45(39-53) Polar width, girdle 4.0(2.8-4.5) 4.0(3.0-5.0) 4.0(2.04.8) 4.0(3.0-5.2) Polar width, valve 3.4(3.0-4.0) 4.0(2.44.2) 3.5(3.0-4.0) 4.0(3 .O-4.1) Centre width, girdle 2.0(1.6-4.0) 3.0(2.0-3.5) 2.0(1.5-4.0) 2.2(1.6-4.0) Centre width, valve 1.7(1.2-2.0) l.S(l.3-2.2) l.S(l.4-2.2) l.S(l.4-2.2)

Transverse striae in 10 ~m 20-24 18-24 20-24 16-22

Colony shape is quite distinctive with both zigzag and radial patterns found in single colonies. There are rarely more than four cells in the radial portion of a colony. The median total number of cells in 41 colonies from Riley Lake was seven. The largest colony seen contained 13 cells (Fig. 8).

Discussion Morphology and Trrxonorny

Cell shape of the Ontario E. zascrtninensis agrees closely with those described from Europe, Africa, and the U.S.A. The cell size of the Ontario speci- mens, especially the length, is considerably greater. The South African specimens are the shortest of all at 20-30 pm. The next greatest in length come from Pennsylvania and South Carolina (U.S.A.), ranging from 26 to 35 pm, while the Polish and Swedish specimens are 20-45 pm long (Korner 1970). Several frustules in our collection exceeded 50 pm in length and the minimum length recorded (from Riley and Kashe Lakes) was 29 pm. No taxonomic significance should be attached to these apparently large differences in cell size as cell size in diatoms is very dependent upon the relative frequency of simple cell division and gamete for- mation, which in turn is controlled largely by nutri- ent status, light, and temperature.

The raphe in E~rnotia ~ascrrninensis is the most important taxonomic feature and its discovery (Korner 1970)justifies its removalfromAsterionella and placement in the order Eunotiales. As- terionellrr thotnassonii Nauwerck (Nauwerck 1978) would appear to be more closely related to some Actinella species than to E. zas~rrninensis with which it has few features in common. Asterionella thotnassonii would seem to be properly assigned to Asterionella with its lack of a raphe, its axial pseudoraphe, heteropolarity, and stellate colony formation.

Eunotia zasurninensis is closest to some species of Desrnogoni~rrn and Actinella, both of which possess raphes. Some authors (e.g., Patrick and

Reimer 1966) prefer to separate Destnogonirrtn from E~rtzotirr, the distinguishing character of Des- tnogoni~rrn being marginal spines on both margins while Eunotirr's marginal spines, if present, are re- stricted to only one valve face. If this system were strictly followed, E. zrrs~rnlinensis should be as- signed to Desmogonilrtn since it has spines on both valve faces. However, Bourelly (1968) views the separation of Desrnogonilrtn and Errnotirr as artifi- cial especially since there have been several "Desmogonium" species named as Errnoti~. In not transferring E. zas~rtninensis to Desmogonirrm, we are concurring with Boun-elly's si~ggestion that Desmogonirrm be considered synonymous with Elrnotia. The major taxonomic feature distin- guishing Eunotirr from Actinella is in the shape of the valve; Elrnotirr is isopolar, while Actinella is heteropolar.

Ecology The occurrence of E. zrrs~rrninensis in several

Ontario waters suggests that the species may be much more widespread than the few published records would suggest. Perhaps it has been mis- identified as Trrbellaria or as Aster.ionella if present only as single or double cells.

Little is known of the nutrient requirements of the species; however, it achieved highest densities (1030 cellsImL) in Riley Lake, which is also the highest of the lakes in nutrient content. Similarly, Eloranta (1974) reported it as a dominant species in the most eutrophic parts of Lake Keurusselka, Finland.

Elrnotia zasurninensis seems to prefer the warmer waters of midsummer, as do other eutro- phic diatom species (Fragilrrria crotonensis, Melosirrr grrrncrlrrtrr, M. atnbig~ra, and Tcrbellaria fenestratrr) with which it is often associated. Living cells have been obtained from the bottom sedi- ments of some of the Ontario lakes in October and November when the species was not present in the plankton so it is likely that E. zasurninensis over- winters on the lake bottom.

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I 1-54 CAN. J. BOT. VOL. 57, 1979

Korner (1970) points out that E. zus~!lninensis has been found in slightly acidic or dystrophic waters. Of the Ontario habitats, only Riley and Kashe Lakes may be considered dystrophic. The other waters, with the exception of the Ottawa River, although not dystrophic are all poorly buf- fered with euphotic zone pH during summer of 6.0-7.0. The occurrence ofE. zas~rminensis in the lower Ottawa River probably indicates wash-in from some soft-water areas in the upper drainage basin of the river. It has not been found in more alkaline waters even though the phytoplankton from several Ontario lakes with pH above 7 has been studied in recent years. Neither have we found E. zas~rminensis in the strongly acidic lakes nearsudbury (pH 4.0-5.5) in northeastern Ontario. If lakes of northern Europe and northeastern North America are being acidified by atmospheric input of Hf (Almer et al. 1974; Dillon et a/ . 1978), then it is conceivable that E. zas~rminensis will occur in many more lakes as their summer pH drops to the apparent optimum range of 6-7.

Acknowledgments We wish to thank Mr. R. Jaen, T. Pang, and D.

Fung for technical assistance with the electron mi- croscopes. Mr. C. Inniss translated portions of Korner's (1970) monograph and Nauwerck's (1978) paper. Mr. G. Hopkins and R. Strus assisted with photography. Mr. M. Michalski initiated the lim- nological studies on Riley Lake in 1968 and 1969

and made the first collections of phytoplankton containing E~rnotiu zus~rminensis (recorded as As- tel.ionella zas~rminensis (Cab.) Lundh-Alm.).

ALMER, B., W. DICKSON, E. EKSTROM, and E. HORNSTROM. 1974. Effects of acidification on Swedish lakes. Ambio, 3: 30-36.

BOURRELLY, P. 1968. Les Algues D'eau Douce. Tome 11. Les alguesjaunes et brunes. N. Boubee et Cie, Paris.

CABEJSZEKOWNA, I . 1937. Frrrgilrrrirr znstrtnitletlsis n.sp. w jeziorze Zasuminskim na Polesiu. Arch. Hydrobiol. Rybactwa, lO(4): 423-425.

CHOLNOKY, B. J . 1958. Beitrlge zur kenntnis der Siidafrikanis- chen Diatomeenflora. 11. Einige Gewasser irn Water- berggebiet (Transvaal). Port. Acta Biol., Ser. B, 6(2): 99-160.

CLEVE-EULER, A. 1953. Die Diatomeen von Schweden und Finnland. Teil 11. Araphideae, Brachyraphideae. K. Sven. Vetenskapsakad. Handl. 4(1): 1-158.

DILLON, P. J . , D. S. JEFFRIES, W. SNYDER, R. REID, N. YAN, D. EVANS, J. MOSS, and W. SCHEIDER. 1978. Acidic precipi- tation in south-central Ontario: recent observations. J . Fish. Res. Board Can. 35: 809-815.

ELORANTA, P. 1974. Studies on the phytoplankton in lake Keurusselkl, Finnish Lake District. Ann. Bot. Fenn. 11: 13-24.

KORNER, H. 1970. Morphologie und Taxonornie der Diato- meengattung Astrrionrlln. Nova Hedwigia Z. Krypto- garnenkd. 20: 557-723.

LUNDH-ALMESTRAND, A. 1954. Some remarks on Frrrgilrrrin zrrslrtnitzetlsis Cab. Bot. Not. 1954(2): 179-182.

NAUWERCK, A. 1978. Asterionrlln thotnrrssotrii, eine neue Kieselalge aus Afrika. Bot. Not. 131: 161-165.

NICHOLLS, K. H. 1978. Chrysochrornlrlinrr breaitrrmitn sp.nov., a new freshwater member of the Prymnesiophyceae. J. Phycol. 14: 499-505.

PATRICK, R., and C. W. REIMER. 1966. The diatoms of the United States. Vol. I. Acad. Nat. Sci. Philadelphia, Monogr. No. 13.

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