Spread of Elodea canadensis in Lake Baikal

Hydrobiologia 259: 203-211, 1993. 0 1993 Kluwer Academic Publishers. Printed in Belgium. 203

Spread of Eludea canadensis in Lake Baikal

0. M. Kozhova & L. A. Izhboldina ScientiJic Research Institute of Biology, Irkutsk State University, 664003 Irkutsk, Russia

Received 27 September 1991; revised 12 January 1992; accepted 6 February 1992

Abstract

Elodea canadensis Michx. was first observed in Lake Baikal at the end of the 70’s. E. canadensis was probably introduced to Baikal by aquarists or by transport vehicles and transport

together with fishes taken from lakes of the Urals, where mass development of the plant was observed at the beginning of the present century. The spread of E. canadensis along lake Baikal may be due to navigation, but natural factors also affect its spread.

The fast spread of E. canadensis, its high competitive quality and metabolic properties for purifying sewage waters are of interest.

The expansion of E. canadensis may be considered a catastrophic phenomenon; its effect now cov- ers practically the whole perimeter of Lake Baikal.

Introduction

Between the mid-1970’s and early-1980’s our attention was drawn to the appearance of Elodea canadensis Michx., first in the River An- gara and its reservoirs, then in Lake Baikal. This phenomenon needs investigation on the following grounds: first, there is a strong ecological spread of this species on the Euro-Asian continent; second, it is a major anthropogenic factor able to cause changes to the unique ecosystem of Lake Baikal; third, it is a possible factor in water puri- fication.

The traditional habitat of Elodea canadensis is North America, from which it was brought to England. In less than two centuries it spread in Europe. It was also found in the lakes of the Urals.

Historical aspects of spread in Baikal

Elodea canadensis appeared in the Irkutsk Reser- voir (filled in 1956) after 1959, as in 1956-59

when Kozhova investigated plant periphyton it was not observed. In 1974 it expanded its habitat vigorously. Between the Irkutsk and Bratsk reservoirs an abundant development of Elodea canadensis was described in 1976, when it was established that Elodea canadensis and other aquatic plants (Cladophora spp., Myriophyllum spp., Potamogeton spp.) clogged up the gratings of water intakes in the region of the town of Angarsk.

Abundant growth of these plants was observed in small lakes on the shores of the Angara river and particularly in a special channel along the shore of Angarsk, where the temperature of the water was some 3-4 “C higher than in the An- gara River. Evidently, this factor has contributed to the development of Elodea canadensis and other plants (Kozhova et al., 1985).

In Bratsk Reservoir, where plant periphyton was examined 1962- 1967 (Kozhova, 1970), Elodea canadensis occurred neither in the flowing part of the reservoir nor in its bays. But in 1974 floating fragments of its stem occurred in mass

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not only along navigable waterways but also in the upper part of the reservoir.

This is an indication of the probable spread of Elodea canadensis both in the Bratsk Reservoir and in lower-located reservoirs. In Lake Baikal Elodea canadensis was first observed at the end of the ’70s in the Selenga River shallows (Neronov & Maistrenko, 198 1).

There are several hypotheses regarding the ways of penetration of Elodea canadensis into Lake Baikal. One of them is an expansion in different ways from the Irkutsk Reservoir, where a mass growth was observed earlier than in the lake (1974) (Neronov & Maistrenko, 1981). The second source might be the Selenga River, as stated by Neronov & Maistrenko. But in 1972-3 Pautova (1973, 1974) investigated the Selenga shoal of Lake Baikal and did not observe Elodea canadensis in the Selenga River delta. Hence, Elodea canadensis must have appeared after 1973, most probably in 1974-1977 (Kozhova & Time- feeva, 1986), as at the end of the ’70s it was discovered there en masse.

To explain the above, assumptions have been made on the bringing of Elodea canadensis to Baikal by aquarists (though they use another species of Elodea) or by transport vehicles. One more way may be added - transport of Elodea canadensis together with fishes from lakes of the Urals, where mass development of the plant was observed at the beginning of the present century.

After comparison of all dates concerning the discovery of Elodea canadensis in Lake Baikal and the River Angara, it is evident it has hap- pened almost simultaneously - in the middle of the ’70s. This suggests that the appearance of the plant in these waters occurred by ‘natural’ ways, as in Europe.

After Elodea canadensis was observed in the Selenga shallows, it was found in the southern part of the Maloye More strait, in Posolsky Sor (a shallow lagoon), and in the Chivyrkuisky Bay (Azovsky et al., 1983; Kuzmich et al., 1985). In 198 1 it formed closed communities with complete cover of the bottom in the southern part of the Maloye More strait, the Mukhor and Sarmin shallow bays. In 1982-3 it existed in many bays

of the Maloye More (Khuzhir-Nugo, Kurkut, Bazar, Tutay, Zagly). It was found not only in undisturbed bays that deeply indent the coast and in Mukhor, but in the shoreline zone near capes. The phytomass (fresh weight) of Elodea canadensis reached 2-5 kg me2 in July-August (Kozho- va & Timefeeva, 1986). Elodea canadensis co- occurs here with typical plants for this region.

Environmental control of biomass development

As is well-known for the shoreline zone, shallow bays and streams of Baikal are relatively warm and protected from wave disturbance; their vegetation is rather diverse and includes widely spread species of aquatic plants. The most frequent communities are dominated by Potumo- geton perfoliatus (Meyer, 1930; Kozhov, 1931, 1947; Kozhov & Spelit, 1958; Pautova, 1974; Azovsky et al., 1983). In such regions, endemic algae of Baikal - that constitute the main part of the flora - are absent, but during summer such widely spread genera as Cladophora, Spirogyra, Oedogonium, and Mougeotia are abundant. In some places Elodea canadensis develops mono- specific growths, with other plants absent. This is an indication that it inhibited the Potamogeton spp. communities in the southern part of the Mal- oye More strait (Kozhova et al., 1986). Neronov & Maistrenko (198 1) pointed out the inhibitory effect of Elodea canadensis on local species of higher waterplants in Posolsky Sor, though in the ’80s it grew here under a cover of Potamogeton spp. Sometime later it appeared along open coasts of the lake, where vegetation is slow to develop and mainly includes Potamogeton pectinatus, P. perfoliatus, Ranunculus trichophyllum, and Myriophyllum spicatum (Kuzmich et al., 1985). Bottom algae are the main phytomass in the flora.

On the south-east coast, Elodea canadensis was found in the regions of Utulik settlement (Kozho- va & Timefeeva, 1986) Kluevka station, and on the north-west coast of south Baikal between the Bolshiye Koty river mouth and Zhilish stream (Izhboldina et a1.,1984; Zueva, 1987). The roots that serve to fix plants in the surf zone make it

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possible for Elodea canadensis to grow in open parts of the lake. Its present distribution along Lake Baikal is shown in Fig. 1. As can be seen, it spreads to deep-cut shallow bays, including harbours for ships, where its phytomass can reach several kg m- *, and its weighted-mean phytomass is 200-300 g m-*.

The process of spreading of Elodea canadensis from shallow closed parts into more open zones has been studied at the Bolshiye Koty settlement (south-west coast of Baikal). At the beginning of the ’80s it was found here at the biological station pier. In 1983 thinned growths were observed beyond the pier at a depth of 3-6 m on silted sand, where it grew together with charophyte algae. Its phytomass at the pier reached 200 g m - * and

0 PA a.sdw

SOT POSOPSk~

X0

a

/h&44 s%wdt-

O-f, o-2

Fig. 1. Scheme of Elodea canadensis distribution in Lake Baikal. 0, Points of discovery; 0, points free of Elodea canadensis.

beyond the pier, in the open, 24 g m-*. In 1986 it was found in this region over a depth range of 1 to 16 m. The height of its shoots reached 20- 25 cm, the area of growth 0.5 ha and the mean phytomass 260 g m - * (Zueva, 1987). In 1989- 1990, according to Gombraih, a thin growth of Elodea canadensis made its appearance on the sites between Chemaya ravine (3 km south of the Bolshiye Koty settlement) and the Kadilny cape (12 km north of Bolshiye Koty). E. canadensis is now growing in the littoral zone, on silted sand devoid of other higher water plants (Fig. 2). But on the sites of the coasts protected by capes, on silt or silted sand alongside typical macrophytes (Azovsky et al., 1983; Izhboldina et al., 1984), it forms heavy growths too (Fig. 3). In those places where branched forms of Baikal sponge (Lubo- mirskia baicalensis Dyb.) occur, the shoots of Elodea canadensis entwine the sponge. Thus, Elodea canadensis assimilates these typical Baikal biotopes. A negative response of Baikal sponges to Elodea canadensis has not been directly recorded, but, supposedly, does exist, at least due to insufficient quantity of light for the photosyn- thesizing zoochlorellae responsible for the green colour of the sponge. Elodea canadensis occurs most frequently along the west coast of the lake (Fig. 1).

In 1984- 1986 quantitative estimates of Elodea were made in places of mass growth (Posolsky Sor, Olkhonsky Gates strait, southern part of the Maloye More strait). Besides determining the limits of its distribution, an examination of the whole coast of the lake was carried out in July- August 1988 (Fig. 1). The samples were collected in summer using a dredge (area 0.025 m*), and in the regions with abundant Elodea canadensis by aqualung divers aided by a special diving bell with 0.25 m* inlet. The divers selected samples, and determined the distribution and degree of cover of the bottom, average height, and viability of the plants. The samples were fixed with formalin. The weight of the algae was later determined in the laboratory. The surface moisture was removed on filter paper; 400 quantitative samples were ana- lyzed. The annual production (P) of Elodea canadensis was calculated by a formula proposed

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Fig. 2. Along the open shallows of Lake Baikal Elodea canadensis inhabits silted sands devoid of higher plants.

Fig. 3. Elodea canadensis and Potamogeton perfoliatus growing in a shallow place well protected from waves.

by Raspopov (1973): P = 1.2 B, where B is the canadensis, quantative estimates were made in maximum overground phytomass. Posolsky Sor in June 1984, at the beginning of

To determine the production of EZodea vegetation, and in September, at the period of

maximum phytomass. In July Elodea canadensis was observed on silt and silted sand in the central part of the coast along spits separating the coast from the open Baikal (Fig. 4). It co-occurred with macrophytes typical of this region. The height of the branches of Elodea canadensis and Potamogentonpefiliatus did not exceed lo- 15 cm in June, but in central deeper parts of the coast, on viscous grey silt with a large admixture of organic material, the height of juvenile branches was greater and reached 20-25 cm. The phytomass (fresh weight) of Elodea canadensis in different parts of the coast varied from 0.2 to 68 g m - 2. The weighted mean value was 15.6 g m - 2, which implies 166 tons fresh (air-wet) weight or 27.7 tons of dry substance or 10 tons of carbon per unit area (1063.8 ha). In September the height of the branches was greater and reached 60 cm. At different parts of the coast the phytomass var-

Fig. 4. Distribution of sediments and plants according to Kozhova & Spelit (1958) (A) and of Elodea canadensis phytomass (B - June 1984, C - September 1984) in the Posolsky Sor. 1-isobaths, 2-sands, 3-silted sands, 4-silts, 5-Potamogeton perfoliatus. Myriophyllum sp., Ceratophyllum sp., 6-Carex sp., 7-Polygonum sp., Sparganium sp., Nuphar sp.; B, C fresh (wet) weight of Elodea canadensis (g mm*): 8-0.1-10, 9-10-100, lo- 100-1000, 11-transects.

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ied from 0.9 to 437 g m - 2. The weighted mean value was 40 g m - 2, 2.5 times higher than in June. Thus, seasonal changes in the increase of biomass are due to the growth of branches; their length, like the mean phytomass, increased from June (to 20-25 cm) to September (60 cm) by 2.5 times. The total weight of Elodea canadensis in Posolky Sor was 425.4 tons, with an estimated annual production of 510 tons of air-wet weight. This corresponds to 71 tons of absolute dry weight or 25.7 tons of carbon (Figs 4, 5, 6).

Analysing the spread of Elodea canadensis in Lake Baikal, in the years after its discovery, Kozhova & Timefeeva (1986) suggested that in future there is a possibility of a cardinal change of the vegetation of the coastal-sor zone of Baikal where the conditions most favour this plant. In this connection it is of interest to compare data on distribution and intensity of vegetation of Elodea canadensis in Posolky Sor, where a mass development, preventing fish from spawning, was observed in 198 1. In September 1989 the growth of Elodea canadensis could hardly have prevented fish from spawning. Moreover it is difficult to believe that the species had an inhibitory effect on the common plants of the sor.

Elodea canadensis grew under the cover of Potamogeton perfoliatus, the height of which reached 34 m. Kuzmich et al. (1985) note that the phytomass of Potamogeton sp. was twice greater than that of Elodea canadensis, and its phytomass (fresh weight) was 700 g m - 2. Evidently, in 1984 there was a decline in the development of Elodea canadensis in Posolky Sor, as compared with data from the late ’70s to early ’80s. However, the difference in the data obtained in September 1984 and by Kuzmich may be due to interannual changes of biomass typical of Baikal. These are affected by fluctuations of the water level and upwelling of the river. Also, the average time for mass development of Elodea canadensis in Euro- pean reservoirs is 40 years, and in the lakes of the Urals 22 years (Mishin & Gribovskaya, 1960). It is hard to believe that duration of mass development in the region of the Baikal basin can be much shorter.

The spread of Elodea canadensis in the Olkhon-

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Fig. 5. Scheme of the distribution of Elodea canadensis in the Olkhonsky Gates strait and southern part of Maloye More strait in July (A) and in August (B) 1985. Fresh weight of Elodea canudensis (g m-*): l-l-10, 2-10-100, 3-100-1000, 4-> 1000.

sky Gates strait and in the southern part of the Maloye More strait was studied in July 1984, in August 1985 and in 1986. In July 1984 heavy growths of the plant were found in interior parts of the Khuzhir-Nugo and Shide bays, where complete bottom cover was loo%, and mean phytomass 1800 and 4260 g m - *, respectively (Fig. 5). In such communities of Elodea canadensis other higher water plants are absent or grow under the cover of the Elodea canadensis, the height of which reaches l- 1.5 m. Algae typical of these regions in association with the dominant Elodea canadensis are constant species (occurrence 50%), but their share in the total phytomass is extremely low. Along shores of the Olkhonsky Gates strait the growths of Elodea canadensis have been examined from the Mukhor bay to Jubuhan capes, where its phytomass did not exceed 10 g m - *. On the shores of the Olkhonsky strait thin growths were observed only in the regions of an old pier, in the inner part of the Zagly bay. The total area of Elodea canadensis in this region of Baikal in July was 963 ha, with a phytomass of 2894 tons, which amounts to 474 tons dry weight and 172 tons of carbon (Table 1). More than half of the area (56%) was occupied by Elodea canadensis with

phytomass from 10 to 100 g m-*. The weighted mean phytomass on the whole area was 294 g m - *, i.e. 7.5 times greater than at the Posolsky lake shore. In August 1985 further spread of Elodea canadensis at the Olkhonsky Gates strait was observed. It was met east of the Jubukhan cape in a small bay. On the Olkhonsky shore it was found in Perevozhnaya bay. There is a pas- senger ferry between these capes due to which it was probably brought. In Maloye More strait Elodea canadensis continued to take over new habitats. In the southern part of the Maloye More, communities were found, except for Khuzhir- Nugo and Shide bays, a small bay at Antukhai cape, where its phytomass was 1150 g m- 2. The total area of Elodea canadensis in August 1985 as compared with that in July had increased from 963 ha to a 1260 ha, and the air-wet phytomasss was 3794 tone (229.3 tons of carbon) (Table 1).

In August 1986 along the shoreline in the Olkhonsky Gates strait the development of Elodea canadensis, as in previous years in Kurkutsky bay and at Shibete cape (1724 g m - *), had become more massive (1575 and 1724 g m - * respectively), and in individual samples the weight reached 10600 g m-*. The area of Elodea

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Fig. 6. Scheme of the distribution of Elodea canadensis in the Olkhonsky Gates strait and southern part of Maloye More strait in August 1986. Symbols in as Fig. 5.

Table I. Area occupied and phytomass of Elodea canadensis in different sites of Lake Baikal.

Month 5-a

General area 04

Phytomass (t)

Fresh Dry C

Areas with phytomass Average phytomass density (g m), per cent density (g m)

0.1-10 10-100 loo- 1000 Fresh wt Drywt C

In Posolsky Sor

June, 1984 1064 166 28 10 35 65 - 15 2 0 September, 1984 1064 425 68 24 45 43 12 40 I 2

In Olkhonsky Gates and Maloe More straits

June, 1984 963 2840 414 172 32 41 15 294 49 18 August, 1985 1261 3795 634 230 29 56 10 300 50 18 August, 1986 1189 3344 558 202 30 35 26 281 47 17

canadensis had increased with phytomass density north to Kurminsk gulf, where detached floating from 100 to 1000 g m- *. A movement of Elodea branches were found. Along the Olkhonsky shore canadertsis towards open Baikal to Oboin cape is of the Maloye More strait it was observed at Lake also observed. Ugungoi and in the region of the Shibeteisky bay.

In Maloye More strait, the spread of Elodea The total area in both straits was, in August 1986, canadensis has been examined along the shoreline 1189 ha, and the phytomass 3344 g (air-wet

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weight) m - 2. The weighted mean phytomass was 280-300 g rnp2 in 1984-1986, much higher than in Posolky Sor (40 g m- 2), and can be compared with that along the open coast of Lake Baikal at the Bolshiye Koty settlement.

Discussion

The above is an indication of a wide spread of Elodea canadensis in Baikal. The communities of Elodea canadensis with complete bottom cover are densest in harbours and in shallow bays and sors, where it co-occurs with widely spread higher water plants and algae. In the evolutionary process these plants did not become adapted to the conditions typical for open coasts of the lake, and at present occupy zones free of endemic species of algae (Azovsky et al., 1982). Elodea canadensis is a recent invader and its ecological niche has not yet been determined. Taking these features into consideration, it may be supposed that for some time, abundant growth of the plant will take place in shallow bays. The spread of thin stands is quite possible along the open coasts of Baikal, as con- firmed by the observations at the Bolshiye Koty settlement. According to the map of distribution it is limited by the 5 m isobath, though in the open Baikal at the Bolshiye Koty settlement Elodea canadensis is observed down to 16 m depth. The outer limit of its distribution appears to be determined by transparency, as it is known to be sen- sitive to light, and according to Mishin & Gribovskaya (1960) it spreads to a depth close to twice the transparency determined by Secchi disk. Likewise, to such depth plant periphyton spreads, as reported by Kozhova for the Bratsk and Irkutsk reservoirs. Elodea canadensis is not observed at the very edge of the water. In the Maloye More strait it appears at a depth of 2 m, in Posolsky Sor 1 m, and in the harbour at the Bolshiye Koty settlement. It inhabits both silt and sand bottoms, including those with a great quantity of organic substance (centre of Posolsky Sor), and stony ones that are the habitat of Baikal sponges. It co-occurs with Potamogeton perfoliatus and other higher plants and algae.

Elodea canadensis has a high competitive quality. It can survive frozen in ice, and prefers waters with a low mineral content and high transparency. It can accumulate and metabolise toxic substances, and is highly toxic-resistant, e.g. to phenolic compounds. It contains /I-cyanoalanine synthetase, the substrates of which are mercapto combinations, particularly methyl-, ethyl-, and butyl-mercaptans. When using mercaptoethanol as substrate, Elodea canadensis can eliminate it at the rate of 3 mol min - ’ mg - ’ of plant protein. At a high natural density (air-wet weight 5 kg m - ‘) and a protein content of up to 6% dry weight, it can become a powerful agent of purifying mercapto compounds. The same is true for phenols (Kozhova et al., 1985; Kozhova & Timefeeva, 1986).

The spread of Elodea canadensis along Lake Baikal must be due to navigation, which is con- firmed by the above description of the regularities of its distribution in the Olkhonsky Gates strait. However, natural factors, currents in particular, also affect its spread. In late summer at the west coast branches were met in the water together with other objects, indicating the Selenga River current.

When making a prognosis about changes in the ecosystem of Lake Baikal, the fast spread of Elodea canadensis, its high competitive quality, and metabolic capacities for purifying sewage waters should be taken into account. The intru- sion of this plant into Baikal is an example of an unforeseen effect of eutrophication of the lake, with deviation from the ‘normal’ functioning of continental aquatic communities. Such expansion may be referred to as a catastrophic phenomenon, which had not been anticipated, though its effect has now covered practically the whole perimeter of Lake Baikal.

References

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Spread of Elodea canadensis in Lake Baikal