[[p. 239]] Brock, T. D. 1973. Primary colonization of Surtsey, with special reference to the blue-green algae.--Oikos 24: 239-243. Blue-green algae were sought in the pioneer plant communities of Surtsey but were found to be extremely minor in importance. The algal mats found in a few locations were composed of coccoid chlorophytes. The primary colonizers of Surtsey are mosses and lichens on hard substrata and vascular plants on ash. The results are compared with those of Krakatau, where blue-green algae were primary colonizers, and Katmai, where they were not. Prof. T. D. Brock, Dept of Bacteriology, Univ. of Wisconsin, Madison, Wisconsin 53706, USA.

[[p. 240]] 1. Introduction

    The formation of Surtsey, a new volcanic island off the south coast of Iceland, is providing scientists from many nations with an unparalleled opportunity to study the processes and factors involved in the establishment of living organisms and ecosystems on pioneer substrata. The Surtsey eruption commenced in November 1963 and continued sporadically until 1967, by which time an island of about 220 ha had been formed. Surtsey is the last in a chain of off-coast islands and is about 5 km from the closest island, Geirfuglasker, and is about 30 km from the main coast of Iceland (Thorarinsson et al. 1964). The surface of Surtsey has now cooled to ambient temperature except for a few areas of fumaroles and heat vents, which seem to have no significant effect on the island as a whole. Some changes in shore-line topography are occurring as a result of erosion and deposition (Norman 1972), but the island is essentially stabilized and plant colonization is occurring.

    An idea widely current is that blue-green algae are pioneer forms in the colonization of new substrata (Fritsch 1945: 769). This idea apparently derives mainly from the observations made of the colonization of Krakatau after its explosive eruption of 1883 which completely destroyed all visible forms of life (Docters van Leeuwen 1936). However, to generalize from Krakatau to other situations is not warranted, especially since at Katmai, Alaska, the only other location at which it has been possible to study colonization by plants of a fresh volcanic substratum, blue-green algae were completely absent and the primary colonizing plants were liverworts (Griggs 1933). It is the purpose of this paper to report that as far as Surtsey is concerned, blue-green algae are not primary colonizers, and that mosses, vascular plants, and chlorophytan algae are the dominant pioneers. Only in thermal habitats adjacent to fumaroles are blue-green algae present in significant numbers.

2. Results

    Over the past seven years I have visited Surtsey four times, and on each trip I have made surveys of pioneer plant communities for the presence of blue-green algae. My visits in 1965 and 1966 coincided with extensive ash eruptions, and no favorable habitats for the development of any plants existed. Eruption ceased in 1967; already by 1968 visible patches of moss were present (Schwabe 1969) and by 1969 they had become conspicuous (Bjarnason and Fridriksson 1972). The first lichens appeared in 1970 (Kristinsson 1972) and thermophilic blue-green algae were present adjacent to fumaroles (Castenholz 1972). However, a survey I made of visible green patches in 1970 revealed that in nonthermal sites blue-green algae were virtually absent (Brock 1972a).

    During my visit in the summer of 1972 I found that plant colonization had proceeded much further than in 1970, and that mosses, lichens, and vascular plants were established in a wide variety of locations. In a few places thin layers of algae were seen, but almost invariably these were coccoid green algae. A summary of my 1972 data is presented in Tab. l. Samples were taken in a wide variety of locations where plant material was visible to the eye. The plant material was either scraped directly into a vial or plastic bag or a core of material was taken with a cork borer. The samples were examined within a day or two of collection using a Zeiss RA phase-contrast microscope.

    It is of considerable importance when considering establishment of plant communities on Surtsey to consider the nature of the substrata available for colonization. Surtsey was formed as a result of eruption of both ash-like tephra and rock-forming lava. In most places the tephra is weakly consolidated, and consists of loose, drifting sand, although in some of the higher locations the tephra has already consolidated into a stable rock-like substratum. The drifting tephra is unfavorable for algal growth but areas of hard tephra provide fairly good moisture-holding capacity and a firm substratum upon which algae have developed (see Tab. 1). The areas of loose tephra are also unfavorable habitats for moss and lichens, but are becoming colonized by several vascular plants, of which the most frequent is Minuartia (Honckenya) peploides, also common on sand beaches on the southern coast of Iceland.

    About 2/3 of the island is composed of lava flows, which provide a firm stable substratum of rough

Fig. 1. Sketch map of Surtsey. The dotted lines outline the areas of established moss communities. The grid system locates the sites of samples studied, as listed in Tab. 1. Based on Fridriksson et al. (1972a).

[[p. 241]]

Tab. 1. Plant types on nonthermal habitats.

Frequency of plant communities in this table does not reflect the frequency on Surtsey. Mosses and lichens were in great dominance.

surface but poor moisture-holding capacity. Some of these lava areas are unevenly covered with drifting sand-like tephra, blown by the wind, and are devoid of plant life, but in the bare lava areas plants are becoming well established. Mosses and lichens are very common, although rarely were patches greater than 2 cm in diameter seen. At least three species of lichens (Kristinsson 1972) and over 16 species of mosses (Fridriksson et al. 1972) were recorded on Surtsey by 1970 and many more species of moss were seen by 1972 (Fridriksson, pers. comm.).

    Mosses and lichens were the most common nonvascular plants seen, and are now in great dominance on Surtsey lava flows. After I had established this dominance, I made a special effort to locate mats or layers of algae. Algal layers were found in a few places, either on lava surfaces which had received fertilization from roosting birds, or on hard tephra. Virtually all of these algae were coccoid green algae (Chlorophyta), rather than blue-green algae. Only one blue-green algal mat was found in all of my searches, a mat of Oscillatoria (sample 91-7). The location of this blue-green algal mat is of some interest. Dr Bassett Maguire from the University of Texas had placed a series of plastic buckets on Surtsey, with the aim of studying algal colonization. These buckets filled with rainwater and provided the only standing freshwater on Surtsey. Sea birds were attracted to these buckets in great numbers, and large amounts of bird excrement were deposited. When it

[[p. 242]]

Fig. 2. Surtsey habitats (Upper left) General view looking north from the eastern crater. The hill in the distance (location I 12-13 on Fig. 1) was one of the sites where eucaryotic algae had become established (sample 96-5). (Lower left) Minuartia peploides plant growing in lava crevice. Horizontal distance of clump about 10 cm. Moss patches nearby were often less than 1 cm in diameter. (Right) Plastic bucket left by Maguire which filled with freshwater and attracted many birds. Photographed in 1970. In 1972 this same bucket was broken and filled with sand, but bird excrement was plentiful and a small Oscillatoria mat had developed, the only blue-green mat found at a nonthermal site on Surtsey (sample 91-7). The lava field here is typical of areas on the eastern side of Surtsey where tiny moss patches were fairly common (see dotted outline on Fig. 1).

became obvious that these buckets were not serving their original purpose but were acting only as a magnet for sea birds, they were removed. One bucket which had broken and had become filled with sand remained in the summer of 1972 and it was in a white zone of bird excrement next to this bucket that the Oscillatoria mat was found.

3. Discussion

    We thus see that blue-green algae are quite unimportant as primary colonizers of Surtsey. Mosses and lichens are of greatest importance, and coccoid green algae (Chlorophyta) are of lesser importance. Some algae are found in association with the moss plants, but these are always in the minority and are more often diatoms than blue-green algae. Even the algal members of the lichen symbioses ate not blue-green algae but chlorophytes. It might be noted that Schwabe and Behre (1972) have isolated by enrichment culture techniques a wide variety of blue-green algae from Surtsey soils. Thus, blue-green algae are becoming readily dispersed to Surtsey; they simply are not becoming established as dominant members of the developing plant communities.

    Why have blue-green algae not successfully colonized Surtsey when from Treub's work (Treub 1888) it is clear that they were successful in Krakatau? Both Surtsey and Krakatau probably have high rainfall (according to Fridriksson et al. (1972b), the mean annual rainfall at Heimaey, the closest town to Surtsey, is 1937 mm). However, temperatures at Surtsey should be much lower than at Krakatau (the mean annual temperature at Heimaey is 5.4ºC, Fridriksson et al. 1972b). It is noteworthy that at Katmai, an area probably more similar to Surtsey than to Krakatau, blue-green algae were also unimportant as pioneers, and liverworts dominated [[p. 243]] (Griggs 1933). This was true despite the fact that the Katmai volcanic ash was very low in combined nitrogen and the liverworts were unable to fix nitrogen gas (Griggs 1933).

    Much further work will be necessary to determine the exact environmental factors influencing the development and distribution of plant communities on Surtsey. The virtual absence of blue-green algal communities suggests that these organisms are not always the primary colonizers they have been thought to be. Indeed, as I have discussed in some detail elsewhere (Brock 1972b), blue-green algae are in general not nearly as adaptable to environmental extremes as has often been asserted by phycologists.

4. Acknowledgements

    This work was supported in part by a grant from the US National Science Foundation. The assistance of Dr Katherine M. Brock in the field work is greatly appreciated. The Surtsey Research Society generously provided research space on Surtsey and assisted in making arrangements for the visits. The microscope was provided by the Brinkmann Instrument Co., Chicago, Illinois.

References

BJARNASON, A. H. and FRIDRIKSSON, S. 1972. Moss on Surtsey, Summer 1969.--Surtsey Res. Progr. Rep. 6: 9-10.

BROCK, T. D. 1972a. Microbiological observation on Surtsey, 1970.--Surtsey Res. Prog. Rep. 6: 11-13.

_____ 1972b. Evolutionary and ecological aspects of the cyanophytes.--In Whitton, B. and Carr, N. (eds.) The Blue-green Algae. Blackwell, Oxford. 487-500.

CASTENHOLZ, R. W. 1972. The occurrence of the thermophilic blue-green alga, Mastigocladus laminosus, on Surtsey in 1970.--Surtsey Res. Prog. Rep. 6: 14-19.

DOCTERS VAN LEEUWEN, W. M. 1936. Krakatau, 1883 to 1933.--Ann. Jard. Bot. Buitenzorg, 46-47: 1-506.

FRIDRIKSSON, S., SVEINBJORNSSON, B. and MAGNUSSON, S. 1972a. Vegetation on Surtsey-Summer 1970.--Surtsey Res. Prog. Rep. 6: 54-59.

_____ 1972b. On the vegetation of Heimaey, Iceland II.--Surtsey Res. Prog. Rep. 6: 36-53.

FRITSCH, F. E. 1945. The Structure and Reproduction of the Algae.--Vol. 2. Cambridge University Press. 939 pp.

GRIGGS, R. F. 1933. The colonization of the Katmai ash, a new and inorganic "soil"--Amer. J. Bot. 20: 92-113.

KRISTINSSON, H. 1972. Studies on lichen colonization in Surtsey 1970.--Surtsey Res. Prog. Rep. 6: 77.

NORMAN, J. O. 1972. Coastal changes in Surtsey Island, 1969-1970.--Surtsey Res. Prog. Rep. 6: 145-149.

SCHWABE, G. H. 1969. Pioniere der Besiedlung auf Surtsey.--Umsch. Wiss. Tech. 2/69: 51-52.

_____ and BEHRE, K. 1972. Algae on Surtsey in 1969-70.--Surtsey Res. Prog. Rep. 6: 85-89.

THORARINSSON, S., EINARSSON, T., SIGVALDASON, G. E., and ELISSON, G. 1964. The submarine eruption off the Westman Islands 1963-64.--Bull. Volc. 27: 435-445.

TREUB, M. 1888. Notice sur la nouvelle flore de Krakatau.--Ann. Jard. Bot. Buitenzorg, 7: 213-223.

Bibliographic note

    The Surtsey Research Progress Report, now in its sixth volume, is published by the Surtsey Research Society, Reykjavik, Iceland, and is available from that organization.

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