ATOLL RESEARCH BULLETIN NO. 216

TERRESTRIAL AND FRESHWATER OF THREE WESTERN INDIAN OCEAN ISLANDS (ASTOVE, FARQUHAR AND ST. PIERRE) by B. A. Whitton and A. Donaldson

Issued by THE SMITHSONIAN INSTITUTION Washington, D. C., U.S.A. May 1977 TERRESTRIAL AND FRESHWATER ALGAE OF THREE WESTERN INDIAN OCEAN ISLANDS (ASTOVE, FARQUHAR AND ST. PIERRE)

By B. A. Whitton and A. Donaldson 1

Introduction

In contrast to the many studies of the marine algae of tropical limestone islands, the terrestrial and freshwater algae have received little attention. A preliminary account for Aldabra (Whitton, 1969) is apparently the only description of such algae from the Western Indian Ocean. This account emphasized the abundance of blue-green algae, and it was suggested that these might be of considerable ecologi- cal significance. The following note provides comparative observations made during brief visits (by B.A.W.) to Astove (10°6'S, 47O45'E) , Farquhar Atoll (lOO1l'S) and St. Pierre (9019'S1 50°43'E during March - April 1973.

The ecology and vascular plant species of Astove and Farquhar Atoll have recently been described in some detail (Astove: Bayne et -al. , 1970; Fosberg & Renvoize, 1970b; Farquhar Atoll: stoddarty Poore, 1970; Fosberg & Renvoize, 1970a), while the data known for St. Pierre have been summarized by Vesey-Fitzgerald (1942), Stoddart (1967) and Piggott (1969). The reader is referred to these accounts for general environmental information. Samples were either studied while still fresh, or dried down and re-wetted before viewing. In addition a few samples from each island were used as a source of inocula for subsequent growth in the laboratory using a range ofmedia

Observations

As the visits to each of these islands lasted only a few hours, the accounts are obviously very incomplete. Nevertheless it was rapidly obvious that while all three islands resembled Aldabra (Whitton, 1969) in having blue-green algae constituting the bulk of the algal vegetation, the overall abundance varied markedly between them, being most abundant on St. Pierre and least abundant on Farquhar. The species records are summarized in Table I.

l Department of Botany, University of Durham, Durham, England (Manuscript received June 1974--Eds.) Astove

(Visited 3 April 1973). The algal vegetation of the western side of this elevated atoll (the only region visited) rather closely resem- bled that of West Island, Aldabra. The rocks had a general cover of ~olypothrixbyssoidea, with sanguinea almost always closely associated with it. Tolypothrix byssoidea also sometimes formed small black patches on bare sand, and in such cases the principal alga associated with it was Schizothrix arenaria. Conspicuous growths of (typical) Nostoc commune colonies were sometimes present on the lime- stone, while N. commune var. flagelliforme was frequent in the coconut plantations. Small freshwater pools were quite common, especially towards the lagoon. These were mostly 2-4 m diameter and reached (at the time of visit) up to 0.6 m deep. These had an attached algal cover, a plankton, and usually also a partial surface cover of flocs or filaments buoyant as a result of associated oxygen bubbles. Species almost always present at the sides of these pools included: Calothrix parietina, Lyngbya spp., Gongrosira sp. and Oedogonium sp. The plank- ton consisted of varying proportions of blue-green algae (including Anabaena variabilis, Phacotus lenticularis, Chlorella sp., Scenedesmus quadricauda, Tetraedron minimum and Euglena sp. Floating flocs mostly consisted of Closterium sp., Oedogonium sp., Spirogyra sp.

Only one species was recorded on Astove which has so far (the authors, unpublished) not been found on Aldabra. This was Stigonema hormoides, which was locally frequent in an area about 1 km south of the settlement, occuring on shaded concavities on rocks. As this species is easily visible to the naked eye, and relatively distinctive, its presence on Astove may represent a genuine difference from Aldabra.

Farauhar Atoll

(Visited 16 March and 6 April 1973; North Island only). The algal vegetation was relatively inconspicuous. This was no doubt largely due to the general cover of coconut trees over most of the island, and to the rarity of standing freshwater. Nevertheless it seems possible that these are not the only explanations since typical Nostoc commune colonies were not recorded anywhere, and N. commune var. flagelliforme occurred only very rarely. Exposed rock surfaces did however resemble those of Astove in having a thin cover of Tolypothrix byssoidea and Gloeocapsa sanguinea .

One small area of freshwater was found, apparently identical with the marshy area referred to by Stoddart and Poore (1970, p.16). Its general appearance and algal species composition was rather similar to that of a saline pool, so it seems possible that it may not remain fresk water throughout the year. This pool overlay a dark-coloured fine silt, and lacked exposed rock surfaces. The only algae found were blue-green algae, these mostly occurring as floating granules or mucilaginous lumps. Such flocs taken from deeper layers in the pool contained many purple photosynthetic , which together with some forms of Aphanocapsa were often sufficient to colour the granules pink. The blue-green algae included: Aphanocopsa spp., Chroococcus minutus, Synechococcus elongatus, Lyngbya spp.

St. Pierre

(Visited 17 March 1973). This island is sufficiently small (417 acres) for an impression of the whole area to have been obtained during the visit, which occurred a year after mining for guano had finally been completed.

Observations on the algal flora of St. Pierre are of particular interest in view of the high levels of phosphate likely still to be available in many microhabitats. In spite of the large literature published in recent years on the effect of phosphate eutrophication in freshwaters, there have been no previous accounts of the algae of naturally occurring very phosphate-rich environments.

At the time of the visit there was much standing water, with hundreds of small freshwater pools. About one-sixth of the island is covered with young trees of Casuarina (up to 4m high). In addition there were about 20 much older trees of this species and 5 coconut palms. The open part of the island is deeply dissected by thousands of crevices. The solitary Pisonia grandis found in 1960 by Piggott (1969) is apparently dead, and the angiosperm vegetation of this region consisted of Ipomoea and various herbs, especially Stachytarpheta jamaicensis, Turnera ulmifolia, Vernonia cinerea and Lippia nodiflora (all names based on field observations only).

Both blue-green algae and lichens were very conspicuous. As with the other islands, the more exposed parts of the rock were dominated by Tolypothrix byssoidea. Epilithic lichens were much more abundant here than on any of the other islands (including Aldabra). Crustose lichens were especially abundant on the lips of the rocks adjacent to fissures. Small blue-green alga containing lichens were also often evident, especially where the covering of free-living epilithic blue-green algae was particularly thick. Recent observations have shown that the latter phenomenon occurs also on Aldabra.

No large Nostoc commune colonies were seen, but a thin film of Nostoc was common in rock concavities. The small pools were sometimes completely filled by growths of Rhizoclonium, mixed with numerous small blue-green algal colonies. In the young Casuarina woodland, Oscillatoria animalis was abundant. Samples from this region cultured on agar with mineral medium developed, in addition to algal colonies, a particularly rapid and vigorous growth of actinomycetes.

Discussion

Although Table I is merely a preliminary list of the algal floras of these atolls, nevertheless they probably give a fair indication of the relative proportions of the main algal groups represented. Blue- green algae are by far the most important group, and free-living eukaryotic algae are largely restricted to the pools. Tolypothrix byssoidea was the most widespread alga on all three islands, being ubiquitous on rocks and widespread on sand. This species has a similar distribution both on Aldabra (the authors, unpublished) and the Bikini islands (Taylor, 1950). The Indian Ocean islands do however show a marked contrast to the latter in that neither Porphyrosiphon nor Symploca have so far been found on them, whereas Taylor reports them to be major constituents of the vegetation of sand on Bikini.

Acknowledgements

This survey was carried out while the authors were in receipt of a grant from the Royal Society and Natural Environment Research Council for research on Aldabra. The authors are most grateful to both these bodies and to Dr. D. R. Stoddart for a guide to the literature about St. Pierre. TABLE 1. Terrestrial and freshwater algal floras

Astove Farquhar St. Pierre

MYXOPHYTA

Chroococcales

Aphanocapsa fusco-luted Hansg. A. grevillei (Hass. ) Rabenh. A. muscicola (Menegh. ) Wille Aphanothece castagneii (~r6b.) Rabenh. A. pallida (Kiitz.) Rabenh. Gloeocapsa magma (~r6b.) Hollerbach. emend. G. sanguinea (Ag. ) Kiitz. Gloeothece rupestris (Lyngbye) Barnet Chroococcus minutus (Kiitz.) NSg. C. turgidus (Kiitz. ) NSg. C. turicensis (NSg . ) Hansg . Synechococcus aeruginosus NZg. S. elongatus NSg.

Chamaesiphonales

Pl eurocapsa minor Hansg . em. Geitler Hyella fontana Huber et Jadin

Hormogonales

~a~~losiphonwelwitschii W. et G. S. West Westiellopsis prolifica Janet Stigonema hormoides (Kiitz.) Born. et Flah. Calothrix marchica Lernm. C. parietina Thuret Gloeotrichia sp. Microchaete tenera Thuret Plectonema bor yanum Gomont P . gloeophil um Borzi P. gracillimum (Zopf .) Hansg . P. notatum Schmidle P. terebrans Born. et Flah. Tolypthrix byssoidea (Hass. ) Kirchn. T. tenuis Kiitz Cylindrospermum muscicola Kiitz. Nostoc carneum Ag. N. commune Vaucher N. commune Vaucher var. flagelliforme (Berk et Curtis) Born. et Flah. N. microscopicum Cam. sec. Harvey, in Hook 6

TABLE 1. (Cont. )

Astove Farquhar St. Pierre

N. paludosum KUtz. N. piscinale KUtz. N. punctiforme (Kiitz. ) Hariot N. piscinale Kiitz. N. sphaericum Vaucher Anabaena variabilis Kiitz Oscillatoria animalis Ag. 0. pseudogeminata G. Schmid 0. tenuis Ag. Phormidium africanum Lemm. P. angustissimum W. et G. S. West P. tenue Lyngbya allorgei Fr6my L. digueti Gom. L. erebi W. et G. S. West L. martensiana Menegh L. nordqardhii Wille L. perelegans Lemm Schizothrix arenaria (Berk.) Gom S. calcicola (Ag . ) Gom

CONJUGATOPHYTA

Spiroqyra sp . Closterium sp. Cosmarium subcostatum Nordst. Cosmarium sp.

CHLOROPHYTA

Phacotus lenticularis (Ehr . ) Stein Ankistrodesmus minutissimus Korschik. Chlorella sp . Scenedesmus quadricauda (Turp.) Br6b. Tetraedron minimum (A.Br.) Hansg. Gongrosira sp . Trentepohlia iolithus (L. ) Wallroth Oedogonium sp . (? p . ) Rhizoclonium sp. c. 40 pm broad

EUGLENOPHYTA

Euglena sp. c. 30 pm long Euglena sp. c. 75 pm long

XANTHOPHYTA

Akanthochloris sp. Astove Farquhar St. Pierre

BACILLAR IOPHYTA

~itzschiapalea (Kiltz.) W. Smith it zschia sp .

Total References

Bayne, C. J., Cogan, B.H., Diamond, A. W., Frazier, J., Grubb, P., Hutson, A., Poore, M. E. D., Stoddart, D. R. and Taylor, J. D. 1970 Geography and ecology of Astove. Atoll. Res. Bull. 136: 83-99.

Desikachary, T. V. 1959 Cyanophyta. 686 pp. Indian Council of Agricultural Research, New Delhi, India.

Fosberg, F. R. and Renvoize, S. A. 1970a Plants of Farquhar Atoll. Atoll Res. Bull. 136: 27-33.

Fosberg, F. R. and Renvoize, S. A. 1970b Plants of Astove Island. Atoll Res. Bull. 136: 101-111.

Geitler, L. 1932 Cyanophyceae. In: Rabenhorstrs Kryptogamen-Flora, Vol. 14. Akademische Verlagsgesellschaft, Leipzig.

Piggott, C. J. 1969 A Report on a Visit to the Outer Islands of Seychelles between October and November 1960. Land Resources Division of Overseas Surveys, Tolworth, Surrey, England.

Stoddart, D. R. 1967 Summary of the ecology of coral islands north of Madagascar (excluding Aldabra). Atoll Res. Bull. 118: 53-61.

Stoddart, D. R. and Poore, M. E. D. 1970 Geography and ecology of Farquhar Atoll. Atoll Res. Bull. 136: 7-26.

Taylor, W. R. 1950 Plants of Bikini and other northern Marshall Islands. Ann Arbor, Michigan: University Press.

Vesey-Fitzgerald, L. D. E. F. 1942 Further studies on the vegetation on islands in the Indian Ocean. J. Ecol. 30: 1-16.

Whitton, B. A. 1969 Terrestrial and freshwater algae of Aldabra. Phil. Trans. R. Soc. Lond. B. 260: 249-255.