Microorganisms from the Volcano of Nea Kammeni Island (Santorini)

Forty taxa of microorganisms (16 blue-green algae, 17 diatoms, 2 bacteria, 5 green algae) were totally identified. The majority consisted of fresh-water and widely distributed species. A considerable number of blue-green algae are characterisric of hot habitats. The abundant and resistant diatoms found belong to the aerophil species. 

INTRODUCTION 

The microflora of Nea Kammeni island has not hitherto been investigated. Three old and new lava samples, collected by Geitler during the 6th scientific excursion of the University of Vienna in 1933 were found to be free of organisms. Geitler (1934) characteristically points out: "Bereits mit freiem Auge war die Nacktkeit der Laven und Aschen an allen besuchten Stellen auf-fallend... Jedenfalls besteht der allgemeine Eindruck trostloser Öde auch für die Mikroflora zu recht".

On the other hand, the macroflora of the island has become a subject of research since last century by the following scientists: first Dumont D'Urville in 1819 (9 species), later Heldreich in 1899 (20 species) and afterwards a staff of botanists - within the framework of the above-mentioned scientific excursions of the University of Vienna - in 1911 (75 species) and in 1933 (26 species)*. Recently Diapoulis (1971) has once more studied the macrophytes (34 species).

*  Data after Diapoulis (1971).

Our study is an attempt to determine the species composition - mainly blue-green algae, diatoms and bacteria, which play an essential role in soil formation - on recent lava after the strong eruptions of the volcano in 1939-41, resulting in the destruction of the flora. Further research on the colonization of microorganisms may contribute to the knowledge of the process of ecogenesis on a volcanic substrate (see also Schwabe 1975 and Surtsey/Iceland project publications).

MATERIAL AND METHODS

The material examined - two samples - was collected on May 14, 1977 from the slopes of the "twin funnel", which is composed of lava, erupted in 1939 - 1941 and consisted of quartz andesite and dacite (Liatsikas 1942, Georgalas & Papastamatiou 1953, Davis 1975).

The slopes of the funnel, bare of higher plants**, were completely covered by boulders, pebbles and fine granulated ashes, without real soil. Sampling biotopes were small aggregations (1 - 2 cm in diameter, 1 cm thick) of the bryophyte Tortella nitida (Lindb.) Broth., growing sporadically in narrow fissures of stones near steam exhalations.

**  [ Few phanerogams were collected far from the sampling biotopes: Asparagus spp. Avena barbata, A. sterilis, Bromus rubens, Crepis sp., Cymbopogon hirtus, Ficus carica, Helichrysum italicum, Hypochoeris radicata, Lagurus ovatus, Rumex bucephalophorus, Trifolium spp. Three of them (Avena sterilis, Cymbopogon hirtus, Hypochoeris radicata) are reported for the first time in Nea Kammeni.

The identification of bacteria, blue-green algae and green algae was exclusively based on culture material developed on agar in petri dishes. The surface of the agar was provided with fine granulated ashes, pebbles and dried pieces of Tortella nitida. The composition of the nutrient solution (pH 7) was: KNO₃ 5.Og, K₂HPO₄ 0.1g, MgSO₄, 7H₂O 0.05g, H₃C₆H₅O₇. H₂O 10 drops in 1% dilution; these components were added to 1000 ml dist. water and solidified with 15g agar. Diatoms, on the contrary, were immediately treated for investigation. First, pieces of bryophytes were placed in a collecting jar, then some volcanic ash and water were added and the contents were shaken vigorously to separate and concentrate the diatoms. The remaining treatment up to the preparation of permanent slides was made by means of the classical procedures (Hustedt 1930 -1966, Patrick & Reimer 1966). Rogallin was the mounting medium (index of refraction 1.66).

• I. Bacteriophyta

-   Siderocapsa major Molisch. Cells spherical or ellipsoid 1 - 1.5 μm large, numerous, embedded in a gelatinose, capsular, yellow-brownish mass.

This and the following species were both found forming yellow-brownish spots on the agar plate. As the difference between them is in fact, mainly the size of the cells, it is possible that they represent the same taxon (see Zavarzin, 1974). Besides, it was considered convenient to maintain, for the time being, the old name Siderocapsa instead of Arthrobacter recently proposed by Dubinina and Zhdanov (1975), Zhdanov and Dubinina (1975), because these microorganisms were not cultivated under specific culture conditions for iron bacteria.

-   Siderocapsa treubii Molisch. Cells spherical, colourless without iron sheath 0.4 - 0.6 μm in diameter, embedded in brown-yellowish zoogloeal masses, in large cell aggregations forming yellow-brownish spots on the surface of the agar.

• II. Cyanophyta

-   Anbaena variabilis Kütz. Filaments in 2 - 4 mostly parallelly arranged among proronemata. Trichomes pale blue-green, few celled, mainly with 10 - 20 cells, 3.2 - 4.2 μm broad. Cells without gas-vacuoles, mainly rounded as a string of pearls or barrel-shaped, with distinct cell bridge (plasma bridge). No characteristic differentiation in chromoplasma and centroplasma. Length of cells mostly 3.5 - 5 μm, sometimes 2.5 - 3 μm. Apical cell rounded conical. Heterocysts rare or completely absent, coloured, almost not distinctive from the vegetative cells, nearly spherical 5 - 6 μm in diameter, with thin wall. Breakage of trichomes often in the heterocysts. Resting spores few, away from the heterocycts mainly in five, spherical or ellipsoidal, 4 - 5 μm X 5 - 6.5 μm large. Outer wall smooth, colourless, unlamellated, about 0.5 μm thick.

-   Anabaena sp. 1. Solitary filaments of 10 - 30 - 40 barrel shaped or cylindrical cells with rounded ends, pale blue-green. Cells in a colourless, indistinct deliquescent slime. Cells without gas-vacuoles, 2.5 - 2.8 μm broad, 3 - 4 μm long; chromoplasma clear. Apical cell slightly conical, attenuated up to 2 μm. Heterocysts intercalary, ellipsoidal more or less 4 μm broad, 5 - 6 μm long, with colourless hyaline content. Resting cells not observed.

This organism - because of its features - is similar to Anabaena thermalis Vouk as well as to A. oscillarioides Bory and A. torulosa (Carm.) Lagerh. (see Anagnostidis 1961, 113 - 119; Komarek 1975, 615).

-   Anabaena sp. 2. Filaments variously bent. Sheaths very thin, colourless. Trichomes 4 - 5 μm broad, blue-green. Cells barrel-shaped, 2.5 - 3 μm long. Heterocysts intercalary 5 - 5.5 μm broad, 4 μm long. Apical cell rounded. Resting cells not observed.

-   Chroococcus turgidus (Kütz.) Näg. Cells in 2 -4, seldom in 8, blue-green, without sheath 9 μm large, 12 - 15 μm with sheath. Sheath not clearly lamelated or unlamellated, colourless.

Scattered mainly among filaments of Stigonema hormoides. The rarely observed 8 celled colonies are reminiscent of the vegetative cells or even sporangia (?) of Chroocoidiopsis.

-   Cyanothece minervae (Copel.) Kom. (Fig. 3). Plant mass bright blue-green. Cells single or following division in pairs, cylindrical, with rounded ends, till elliptical, sometimes lightly bent, pale blue-green (2.5) - 3 - 3.5 -4.2 μm broad, 4 - 10 μm long, during the division till 14 μm. Cell content mostly without, sometimes with longitudinal rows of fine granules.

-   Eucapsis minor (Skuja) Hollerb. (Fig. 1). Scattered on and among erected bundles of Symploca thermalis. These bundles occupy the upper parts of the agar substrate which touches the rounded walls of the petri dish. Colonies pale blue-green, moderate regularly cubic, seldom consisting of more than 128 cells, usually in packets of 4 ³ cells (length of edge 20 - 22 μm). Sometimes larger colonies are formed with irregular out-lines consisting of smaller more or less cubic colonies. Cells globular or semiglobular, 2.5 - 3 μm in diameter, in a slime.

The species of this genus are considered as cold stenotherm. However, our findings and the fact that E. alpina var. major - described as a new variety by Schwabe & Simonsen (1961) - was found on the crater oasis Wau en-Namus (Central Sahara) seem to cast some doubt on the former data. A microorganism with about the same dimensions (cells 8.2 X 9.2 -10.3 μm) has been already recorded in USSR as E. alpina f. major Poljansk (Hollerbach et al. 1953).

-   Nostoc punctiforme (Kütz) Hariot var. populorum Geitl. (Fig. 9). Colonies small, spherical, punctiform, dark blue-green or blackish, consisting mostly of growing hormogones in different forms extendend on the agar plate. Gelatine sheath mostly thin and colourless. Vegetative cells barrel-shaped or rounded, sometimes oblong also, (2.5) - 3 - 5 μm broad, just as long as broad, or a little larger. Heterocysts about the same size or smaller, spherical, oblong or compressed. Resting cells not seen.

This blue-green alga shows great similarities to Nostoc edaphicum Kondrat. However, according to the dimensions and appearance of the hormogones, this microorganism is, for the present, considered as Nostoc punctiforme var. populorum Geitl.

-   Phormidium tenue (Menegh.) Gom. (Fig. 7). Plant mass thin, bright blue-green, membranaceous and lamellated consisting of filaments variously bent, densely entangled, extended on and inside the agar. They are often parallelly arranged or in thick cords more or less regularly spirally twisted, scarcely coiled as a watch spring. Sheaths thin, firm, rarely mucilaginous. Trichomes 1.2 - 1.8 (2) μm broad, pale or bright blue-green, in the ends abruptly or gradually attenuated, mostly straight, seldom slightly hooked-curved. Most of the diaphanous cross-walls are usually slightly constricted without granules. Cells with a more or less characteristic differentiation in chromoplasma and centroplasma, mostly 2 - 5 times as long as broad, 1.5 - 6 μm long. Apical cell more or less conical, pointed, sometimes rounded.

About the problems on the taxonomy of this collective species see Anagnostidis (1961, 150 - 153).The watch-spring coiled forms correspond to Ph. tenue f circinatum Fremy.

-   Phormidium weedii (Tilden) Copel. (Fig. 10). Filaments variously and strongly bent. Sheaths not easily visible, very thin, mostly confluent. Trichomes 2.5 - 3 μm broad, in the apices gradually attenuated, slightly constricted at the cross-walls without granules. Cells usually almost quadrate or shorter than broad. Apical cell pointed conical.

This species was developed with Phormidium tenue to which it shows many similarities. On account of the great variability of Phormidium tenue which is characterized by swarms of forms or as a collective species (see Anagnostidis 1961, 150 - 152), it was initially identified as Phormidium tenue. However, the clearly broader trichomes and the relativelly short length of the cells are features which correspond better to Phormidium weedii. Drouet (1968) considers this species as Schizothrix calcicola.

-   Plectonema tenue Thur. (Fig. 6). Filaments very long, variously bent, in bright emerald green or green, densely entangled bundles, 5 - 6.5 μm broad. Pseudo-branches single or rarely in pairs. Sheaths thin colourless or yellowish. Trichomes pale blue-green 4 - 4.8 μm broad, clearly constricted at the cross-walls, attenuated in the apices. Cells almost quadrate or longer than broad, 3.5 - 6 μm long. Protoplasts with large granules. Apical cell attenuated, sharp conical or obtuse conical.

This organism, according to its features, is similar to Plectonema tenue. However, it differs in the dimensions (trichomes 5 - 10 μm broad) and in the clear constriction of the cross-walls. It must be noted that in the description of the species, Gomont (1892) writes: "genicula haud constrictis" while in the figure 6 (pl. 1) only one trichome of Plectonema tenue is not constricted at the cross-walls, the two others being slightly or clearly constricted. This figure has been differently transferred by Tilden (1910, pl. XI, fig. 2), Geitler (1932, fig. 448), Elenkin (1949, fig. 547), Hollerbach et al (1953, fig. 310, g), and Starmach (1966, fig. 1014).

-   Plectonema tomassinianum Born. (Fig. 5). Filaments entangled, 11 - 20 μm broad, mostly 15 μm, seldom to 25 μm, not forming thallus, mostly isolated on the bryophytes leaves, penetrating thallus of Phormidium tenue. Pseudo branches, sparse, single or in pairs. Sheaths till 2.5 μm thick, colourless, unlamellated, in old filaments yellow till brownish lamellated; sometimes with characteristic knots at the cross-walls. Trichomes mostly constricted at the cross-walls, (7) - 9 - 15 μm broad, not attenuated at the ends. Cells till 9 μm long, discoid or almost quadrate. Apical cell rounded.

-   Schizothrix delicatissima W. et G.S. West (Fig. 11). Filaments solitary, long, not in bundles but forming a network, variously bent, 4 - 6.5 μm broad. Sheaths colourless, distinct, not slimy, exterior smooth, gradually long attenuated, ending in a long tapered apex, seldom slightly rounded, sometimes opened or in places outside wavy, interrupted and wrinkled, containing mostly one, rarely two trichomes. Cells at the cross-walls not or slightly constricted, 0.8 - 1 μm broad, 3 - 8 times longer than broad, bright blue-green. Apical cell pointed conical.

-   Stigonema hormoides (Kütz.) Born. et Flah. (Fig. 8). Filaments strongly bent, densely woven, not very long, forming tiny brownish-black balls 1 mm in diameter, like fish eggs on the upper layer of agar, while in the lower layer protonemata are developed. Main filaments 7 - 14.5 μm broad, irregularly and sparsely branched. Lateral branches erected, nearly as thick as the main filament, variously curved. Sheath colourless, deliquescent, mostly invisible. Trichomes mostly of one row, sporadically in two, seldom in more rows, 7 - 13 μm broad, very often with large apical cells. Cell bright blue-green, discoid or barrel-shaped in one row trichomes, 4 - 7 μm long. Heterocysts lateral and intercalary, also terminal, mostly 5 X 7 μm large. Sometimes in a chroococcoid stage. In this material, the early stages are particularly developed, being distinctly marked in the growing parts of thallus.

-   Symploca thermalis (Kütz.) Gom. (Fig. 12). Emerald green erect bundles, densely arranged in tufts, about 1 mm high, developed at the margins of petri dishes. Bundles and filaments are densely entangled in the basis as a network, further up arranged almost parallel. Filaments 3 - 3.5 - 4 μm broad. Sheaths thin, colourless, dinstinct. Trichomes 1.5 - 1.8 μm broad, pale blue-green, not attenuated at the ends. Cross-walls visible, transparent, not constricted, without granules. Cells almost quadrate or longer than broad, 2 - 6 μm long. Apical cell rounded, without calyptra.

-   Synechococcus elongatus (Näg.) Näg. f. thermalis Geitl. (Fig. 2). Spots bright emerald green, scattered on the agar plate or among filaments and hormogones of Phormidium tenue. Cells straight, cylindrical or lightly curved, 2.5 - 3 μm broad, 4 - 8 - (12) μm long, bright blue-green or emerald green more or less with one prominent large refractile polar granule. Differentiation of protoplast in chromoplasma and centroplasma sometimes clear. Movement relatively slow, irregularly crawling. Mucilage present.

Considering the habitat as thermal biotope (steam exhalations) this microorganism was identified as f. thermalis and not as f. elongatus. However, and because of its similarities to var. amphigranulatus, it deserves a higher taxonomic evaluation, being in accordance with Komarek (1976).

-   Synechocystis diplococcus (Pringsh.) Bourr. (Fig. 4). Cells globular, solitary or in twos, 1.0 - 1.4 μm large, during division to 2.5 μm long, blue-green, with characteristic differentiation in centroplasma and chromoplasma, without mucilage, scattered among colonies of Eucapsis and filaments of Symploca.

• III. Bacillariophyta

-   Achnanthes coarctata (Bréb.) Grun. (Fig. 13) . Valve linear-elliptical, constricted at the centre, with broadly rounded ends. Raphe valve with linear axial area and a rectangular central area reaching the margins. Raphe recurved near the proximal ends. Striae radiate throughout, distinctly punctate, 13 - 14 in 10 μm. Pseudoraphe valve with submarginal narrow pseudoraphe. Striae distinctly punctate, 13 - 14 in 10 μm, irregularly parellel at the centre of the valve, becoming curved radiate near the ends. Length, 22 - 30 μm. Breadth, 6.5 - 8 μm.

-   Achnanthes coarctata var. elliptica Krasske. (Fig. 17). Valve linear-elliptical not constricted at the centre of the valve, with hardly protracted, rounded ends. Length, 12.5 - 15.5 μm. Breadth, 5.5 - 6.5 μm.

This taxon is considered as a boundary variety, including short forms (A. coarctata: 20 - 48 μm length). Its recorded length is about 20 μm (Cleveeuler 1953a).

-   Achnanthes microcephala (Kütz.) Grun. (Fig. 14). Valve linear or linear-lanceolate with capitate to subcapitate ends. Raphe valve with narrow, linear axial area. Central area more or less clearly orbicular and about one-half the valve breadth at the centre. Raphe filiform; distal ends indistinct. Striae slightly radiate, about 28 in 10 μm near the centre, becoming more numerous toward the ends; central striae slightly broader than the remaining striae. Pseudoraphe valve with narrow, linear pseudoraphe and small central area. Striae slightly radiate near the centre, about 26 in 10 μm, approaching parallel and becoming more numerous toward the ends. Length, 15 - 18 μm. Breadth, 2.5 - 3 μm.

-   Cymbella affinis Kütz. (Fig. 19). Valve semi-lanceolate, strongly unsymmemcal; ends short rostrate, obtuse rounded. Dorsal margin highly convex, ventral margin slightly convex or almost straight. Raphe eccentric, not the same width thoughout; terminal fissures dorsal curved. Axial area narrow, slightly widening toward the centre of the valve; a distinct isolated punctum present on the ventral side. Striae radiate, 9 in 10 μm at the dorsal side, 10 in 10 μm at the ventral side, becoming denser at the ends. Length, 35 - 42 μm. Breadth, 9 - 11 μm.

-   Diploneis papula var constricta Hust (Fig. 24). Valve linear-elliptical, constricted at the center, with broadly rounded ends. Central nodule small, apical-rectangular in shape. Siliceous rib enclosing the raphe, strong divergence at the base and convergence at the ends. Longitudinal canals thin lanceolate, gradually narrowing near the ends, with an outer row of fine pores; internal pores not existent. Costae strong, slightly radiate, 10 in 10 μm, crossed by a longitudinal rib. Length, 30 - 35 μm (the length of D. papula is given as 20 -30 μm); Breadth, 10 - 12 μm in the middle.

-   Gomphonema longiceps var. subclavata f. gracilis Hust. (Fig. 20). Valve club-shaped, strongly narrowed at the somewhat obtuse ends, accentuating the concave of the valve margins from the middle toward the ends. Axial area moderate wide, slightly widening toward the centre of the valve; a distinct isolated stigma, present at the end of a median stria. Striae slightly radiate, 10 in 10 μm. Length, 50 - 56 μm. Breadth, 10 - 11.5 μm.

-   Hantzschia amphioxys (Ehr.) Grun. (Fig. 21). Cells in girdle view rectangular slightly constricted in the middle; ends rounded. Valve concave on the ventral margin and slightly convex on the dorsal margin, strongly narrowed at the more or less rostrate or slightly capitate ends. Keel puncta 7 in 10 μm, the two median ones being more distant than the others. Valve surface punctate-striate. Striae 19 - 20 in 10 μm. Length, 35 - 45 μm. Breadth, 6 - 7 μm.

-   Melosira granulata (Ehr.) Ralfs. Cells cylindrical, united in long, firmly dosed chains. Valve with considerable developed cylindrical mantel part and flat discus. Pseudosulcus small. Sulcus present. Collar moderate long. Discus with short, distinct margin spines. Mantel surface with coarse pores, arranged in longitudinal, spiral and undulating striae. Striae 8 - 9 in 10 μm. End cell with long spines and folds; pores coarse, forming parallel longitudinal striae. Diameter of the valve 7 - 9 μm. Height 22 - 25 μm.

The height of this species is recorded as about 5 - 18 μm. In Cleve-Euler's (1951) figures it is given as about 30 μm.

-   Melosira granulata var. angustissima Müll. Cells long and narrow; diameter (4 μm) to height (28 μm) ratio 1 : 7. Pores 8 in 10 μm.

-   Melosira granulata var. muzzanensis Meister. Discus strongly arched. Pseudosulcus distinct. Sulcus weak. Pores fine, about 18 in 10 μm. Striae 12 - 13 in 10 μm. Diameter, 12 - 14 μm. Height, 8 - 9 μm.

-   Navicula mutica f. cohnii (Hilse) Grun. (Fig. 23). Valve linear-elliptical, with distinct protracted ends. Axial area linear, clear. Central area rectangular with an isolated punctum on one side. Striae distinctly punctate, 20 in 10 μm in the middle of the valve. Length, 12.5 - 17 μm. Breadth, 6 - 7 μm.

-   Navicula nivalis Ehr. (Fig. 22). Valve linear, with triundulate margins; ends broad rostrate, usually capitate rounded. Raphe straight; median ends and terminal fissures of the raphe turned in the same direction. Axial area narrow, linear-lanceolate. Central area a transverse fascia which does not reach the margins of the valve; a distinct isolated punctum present on one side. Striae radiate, 18 in 10 μm at the centre. Length, 18 -24 μm. Breadth, 6.5 - 7 μm.

-   Rhopalodia parallela (Grun.) O. Müll. Cells in girdle view linear or slightly widening toward the middle; ends flat truncated, not capitate. Valve cramp-shaped, slightly depressed at the ventral nodule; ventral margin straight; ends curved ventralwards. Valve surface costate, transverse, slightly radiate toward the ends, 6 in 10 μm. Between the costae are 2 - 3 lines of fine areolae. Length, 95 - 107 μm. Breadth, 30 - 33 μm.

-   Stephanodiscus astraea (Ehr.) Grun. Cells discoid. Valves circular, with concentrically undulate surfaces, the central part being slightly concave. Valve surface divided into a rather large central zone, a broad striated peripheral zone and an hyaline margin; central zone with scattered puncta; striae punctate, about 8 in 10 μm, radiating from a single punctum near the central zone to three or four puncta near the margin; intermediate spaces between the striae hyaline, with spines inserted at the ends of some of them. Diameter of the valve, 32 - 38 μm. 

-   Stephanodiscus astraea var. minutula (Kütz.) Grun. (Fig. 15) Membrane weak silicated. Striae, about 9 in 10 μm. Each stria near the margin includes 2 - 3 rows of puncta. Diameter of the valve 10 - 14 μm.

-   Stephanodiscus astraea var. indermedia Fricke. (Fig. 16). The radial striae near the margins are wider than those of the species; 2 - 3 rows of puncta in each stria. Striae about 6 - 7 in 10 μm. Diameter of the valve 20 - 22 in 10 μm.

-   Stephanodiscus dubius (Fricke) Hust. (Fig. 18). Cells discoid. Valves circular with concentrically undulate surfaces, the central part being slightly concave. Valve radial, punctate-striate. Puncta hardly recognizable, arranged in radiating short marginal ribs (9 - 10 in 10 μm). Central area radial punctate; puncta distinct; the lines form direct continuation to the ribs, in the transition place being distinct duplicate puncta. Diameter of the valve 11 - 15 μm.

• IV. Ghlorophyta

The following green algae were additionally found in the cultures: Bracteacoccus sp., Chlorella sp., Chlorococcum sp., Coelastrum sp., and Gloeocystis sp.

DISCUSSION

The material examined is comprised of 40 taxa of microorganisms: 16 blue-green algae, 17 diatoms, 2 bacteria and 5 green algae. Ten taxa are reported for the first time in Greece: Diploneis papula var. constricta, Eucapsis minor, Melisira granulata. var. muzzanensis, Nostoc punctiforme var. populorum, Phormidium weedii, Plectonema tenue, Plectonema tomassinianum, Stephanodiscus dubius, Stigonema hormoides, Synechocystis diplococcus (lit. in Anagnostidis 1968, Economou-Amilli 1976).

The majority of the microorganisms found consisted almost entirely of fresh-water species. Marine and halophilous species are lacking. The presence - in very few individuals - of Diploneis papula var. constricta, a marine diatom, is probably due to the vicinity of the sea.

The species found are mostly widely distributed. Seven species of blue-green algae (Anabaena sp. (cf. thermalis?), Chroococcus turgidus, Cyanothece minervae, Phormidium tenue, Ph. weedii, Symploca thermalis, Synechococcus elongatus f. thermalis) and two species of bacteria (Siderocapsa major, S. treubii) are thermobiont, thermophil or at least known from thermal springs. Their presence may be due to the stream exhalations (hot environment). The presence of Eucapsis minor (= E. alpina var. minor Skuja) was at first strange because of its restricted distribution (in winter plankton of a lake near Riga and elsewhere in USSR). However it must be taken into consideration that E. alpina also occurs in Africa and has been found in a crater oasis of Sahara (E. alpina var. major).

Anabaena variabilis and Nostoc punctiforme belong to the nitrogen fixing species. The presence of Plectonema and Schizothrix genera is worth noticing as several species of them are particularly important for both ecogenesis and soil formation.

The identified diatoms are sporadically distributed and rather limited in number in the same way as those which can live on dry rock habitats. The reduction in size in most of them, being in the lower limits of the type species, may also well be special adaptation to withstand drying out and increased salt concentrations or indicates wind transport of the pioneers (Hustedt, 1937 - 39, Patrick & Reimer 1966, Schwabe 1972).

It is also remarkable - although it is to be expected - that the more abundant diatoms found are aerophils (Hustedt 1957, Cholnoky 1966) for they live favourably in waters rich in oxygen content or are often found in aerial biotopes in large numbers: Achnanthes coarctata, A. coarctata var. elliptica, A. microcephala, Gomphonema longiceps var. subclavata f. gracilis, Hantzschia amphioxys, Navicula nutica f. cohnii, N. nivalis, Rhopalodia parallela.

In the cultures enriched with fine granulated ashes, pebbles and dried pieces of Tortella nitida, only a selection of germlings or resting stages was able to grow. Therefore, the existing microflora might probably be considered richer.

Only the forms which had found favourable conditions in the nutrient medium or were capbale of withstanding an abnormal environment, developed. The development in cultures of Siderocapsa treubii and S. major may be due to the fact that the quartz andesite and dacite contain a considerable amount of Fe₂O₃ (1.57 - 2.35 %), FeO (3.5 - 4.25 %) and MnO (0.09 - 0.14 %) (Georgalas & Kokoros 1940, Pichler & Kussmaul 1972, see also Puchelt et al 1973, Hanert 1973).

Besides, it is quite possible that tbe diatoms from tbe bryophyte mat may not accurately represent the existing community on the date of sampling. They are probably incorporated into the mat as cells die or they have been transferred there by air. Since it was impractical to separate living diatoms from dead frustules, the appearance of Hantzschia amphioxys in abundance on the agar plates probably represents the most common and resistant diatom at this extreme volcanic biotope.

Based on tbis preliminary sampling of material it is difficult to draw any conclusions about the microfloral composition. Further collections and research may record changes and probably show the colonization of microorganisms on this volcanic island. 

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