Bull. Natl. Mus. Nat. Sci., Ser. B, 44(3), pp. 115–120, August 22, 2018

Waterfoam Mycobiota collected in Kita-Iwojima Island,Ogasawara Islands
Tsuyoshi Hosoya*, Kentaro Hosaka and Yoshihito Ohmura
Department of Botany, National Museum of Nature and Science,
Amakubo 4–1–1, Tsukuba, Ibaraki 305–0005, Japan* E-mail: hosoya@kahaku.go.jp(Received 8 May 2018; accepted 28 June 2018)

Abstract A water foam sample formed in an ephemeral stream was obtained in Kita-Iwojima
Island, one of the Volcano Islands south of the Ogasawara Islands, and its mycobiota was enumerated on a morphological basis. In total, 15 species among 13 genera and ﬁve unidentiﬁed fungi
were recognized. The sample was characterized by the paucity in biodiversity, and the majority of
species producing coiled spores, partially due to the lack of stable aquatic environment. This is theﬁrst report of Ingoldian and other water foam-associated microfungi from the Island.
Key words : Aquatic fungi, Bonin Islands, distribution, Ingoldian fungi, microfungi.

Introduction
Kita-Iwojima Island (latitude +25.4333, longitude +141.2833) is a small island with an area of
5.57 km2, 3.3 km from south to north, 2.1 km
from east and west, and 8 km in the periphery.
The island is one of the three islands to form Volcano Island, under the jurisdiction of the Ogasawara Islands, and is about 1,200 km away fromthe main islands of Japan (Fig. 1). While
Minami-Iwojima has been uninhabited sincerecorded history, Kita-Iwojima was once colonized in 1899, but uninhabited since 1944 due tothe evacuation during the war. Because of theirgeographical isolation and the relative lack ofhuman activity, the natural life on both islands
has been receiving attention from researchers.
However, due to severe geographical and environmental conditions, approaching these islands
has been extremely difﬁcult. Nevertheless, some
explorations have been carried out on bothislands. Fortunately, the authors of this paper
were able to accompany one biota assessment
exploration activity in Kita-Iwojima Island, andpart of the result has been published (Hosoya etal., 2011).
Aquatic hyphomycetes are the ecologicalgroup of fungi that have characteristic morphology like tetraradiate or coiled spores, considered
to be an adaptation to aquatic habitats. The groupis also known as “Ingoldian fungi” or “freshwater
hyphomycetes”. Because of the characteristic
morphology of the spores, they accumulate inwater foams, which makes the collection of samples easy. Within the water foams, however,spores of terrestrial fungi associated with humid
environments are sometimes found due to thephysical properties of the water foam, which capture particles.
Although the study of Ingoldian fungi started
in Europe (Ingold, 1975), the fungal group is distributed worldwide, and the fungal diversity ofthis group has been enthusiastically studied intropical areas (e.g. Nawawi, 1985; Goh, 1997;
Marvanová,1997; Hosoya et al., 2006; Graça etal., 2016), but never in Volcano Islands. In Japan,
Miura (1974) provided a survey, but large partsof Japan remain unsurveyed. In the Kita-Iwojima

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Tsuyoshi Hosoya et al.

Fig. 1. Map of Kita-Iwojima Island and the collection site. A. Large-scale map showing the location of KitaIwojima Island (arrow). B. Map of Kita-Iwojima Island showing the collection site (●). The numbers in theﬁgure shows the elevation in meters.

Fig. 2. Materials observed in the present study. A. Water foam formed in the tentative lotic water. B. Water foam
sample collected in the site. C. Insect exoskeleton and ﬁlamentous plant material captured in the foam. D.
Conidiophore of a dematiaceous fungus observed in the water foam. Scales＝10 µm.

Island, no perennial streams are known, with
only ephemeral streams forming after heavy rain.
The island also receives severe sunlight and hightemperature. Despite such a harsh environment,

the authors fortunately found an ephemeral
stream where water foam was found. The present
paper reports the analysis of the fungal elementsin the water foam sample.

Waterfoam mycobiota in Kita-Iwojima Isl.

Materials and Methods
The sample was obtained on June 19, 2009, in
an ephemeral stream (latitude +25.43700, longitude +141.2873889, elevation 186 m) that formed
due to the heavy rain in the previous night (Fig. 2).
The site was just below the campsite in the exploration from June 16–19 (Hosoya et al., 2011). Several spoonfuls of water foam were collected by aspoon and immediately ﬁxed by formalin in a
50 ml plastic vial and brought back to the laboratory. Part of the sample was transferred to a 1.5 ml
Eppendorf tube and centrifuged (12,000 rpm,
30 sec) to obtain the concentrated sediment. A dropof the sediment was added to a drop of Hoyerʼs
medium (distilled water 50 ml, Arabic gum 30 g,chloral hydrate 200 g and glycerin 20 g; Martin andAlexopulos, 1969) on the slide glass, and examined for fungal spores under light microscopyusing an Olympus BX51 microscope. Identiﬁcation of the fungi was made based on morphology.
Because some spores have complex threedimensional structure, adjusting focus in a single
frame in the photograph was difﬁcult. To obtain
photo image of these spores, digital photographs
were taken by Nikon Digital Sight DS-Fi2 anddepth synthesized using Combine ZP software(http://www.hadleyweb.pwp.blueyonder.co.uk).
For supportive purpose, line drawings were prepared using the Olympus BX-51 microscope
equipped with U-DA drawing tubes and 40 or
100 objective lens.
To analyze the tendency of spore frequency
based on the spore morphology, numbers of thespores were counted by choosing 20 ﬁelds at 10
objective lens, and spores were counted on themorphological categories based on the typicalspore morphology in aquatic fungi (see explanation of the categories in the legend of Fig. 6).
Results and Discussion
The spores observed and identiﬁed are listed
in Table 1, the representative of which are shownin Figs. 3–5. In total, 15 species among 13 genera and ﬁve unidentiﬁed fungi were recognized.

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Table 1. List of species found in the water foam
*Anguillospora crassa Ingold*Anguillospora longissima (Sacc. & P. Syd.) Ingold
Camposporium sp.
Chaetospermum sp.
Cylindrocladium sp.
Diplocladiella scalaroides G. Arnaud ex M.B. Ellis*Filosporella aquatica Nawawi*Flabellospora multiradiata Nawawi*Flabellospora verticillata Alas.
Helminthosporium sp.
*Isthmotricladia laeensis Matsush.
Pestalotiopsis sp.
Speiropsis pedatospora Tubaki
Wiesneriomyces javanicus Koord.
Unidentiﬁed #1 (Helicoid 1)
Unidentiﬁed #2 (Helicoid 2)
Unidentiﬁed #3 (Helicoid 3)
Unidentiﬁed #4 (Helicoid 4)
Unidentiﬁed #5 (Spore type #79 of Nawawi (1985))

Fig. 3E, 5I
Fig. 3I, 5G
Fig. 4H
Fig. 4F
Fig. 4G
Fig. 4E, 5B
Fig. 3H, 5A
Fig. 4A
Fig. 4D, 5C
Fig. 4I
Fig. 4B, 5D
Fig. 4J
Fig. 3J, 5F
Fig. 3K, 5E
Fig. 3A, 5H
Fig. 3B
Fig. 3C, 5J
Fig. 3D
Fig. 4C

Fungi with asterisk (*) are to be regarded as typical Ingoldian
fungi.

All of them have been recorded for the ﬁrst timefrom Kita-Iwojima Island.
The sediment also contained a number ofsmall particles of insect exoskeletons, plantdebris, and conidiophores (Fig. 2), because of thefoamʼs physical ability to capture particles, but
no diatoms were found indicating the water was
lotic and tentatively formed.
The water sample had some remarkable features to be noted as below.
The majority of the spores were ﬁliform andcurved (Fig. 6). Coiled spores consisted of morethan 50% of the observed spores. Together with sigmoid and curved spores, ﬁliform spores occupied
almost 80% of the Ingoldian fungal spores. Coiled
spores are known as an adaptation to intermediate
environments between terrestrial and submergedareas (Michaelides and Kendrick, 1982). A numberof coiled spores are known in terrestrial fungi fromhighly humid environments (Ellis, 1971).
Some fungal spores derived from terrestrial environments were also recognized (Fig. 4). In fact,some of these have been recognized in aquatic
environment, e.g. Diploceras and Camposporium(Gonczol and Revay, 2003). Yet, the speciﬁc diversity seemed low, again indicating the limited occurrence of aquatic environments on the island.
The paucity of typical Ingoldian fungi having

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Tsuyoshi Hosoya et al.

Fig. 3. Representative spores (helicosporous, sigmod or curved, and connected) observed in the water foam. A.
Unidentiﬁed #1 (Helicomyces?). B. Unidentiﬁed #2 (Helicomyces?). C. Unidentiﬁed #3 (Helicomyces?). D.
Unidentiﬁed #4 (Helicomyces?). E. Anguillospora crassa. F. A. longissima (?). G. A. longissima (?). H. Filosporella aquatica. I. A. longissima. J. Speiropsis pedatospora. K. Wiesneriomyces javanicus. B, D, E, G and J:
depth synthesized. Scales＝10 µm.

Fig. 4. Representative spores (radiating or terrestrial) observed in the water foam. A. Flabellospora crassa. B.
Isthmotricladia laeensis. C. Unidentiﬁed #5 [Spore type #79 in Nawawi (1985)]. D. F. verticillata. E. Diplocladiella scalaroides. F. Chaetospermum sp. G. Cylindrocladium sp. H. Camposporium sp. I. Helminthosporium sp. J. Pestalotiopsis sp. K. Jaculispora sp. B, D and E: depth synthesized. Scales＝10 µm.

Waterfoam mycobiota in Kita-Iwojima Isl.

119

Fig. 5. Line drawings of representative spores observed in the water foam. A. Filosporella aquatica. B. Diplocladiella scalaroides. C. Flabellospora verticillata. D. Isthmotricladia laeensis. E. Wiesneriomyces javanicus. F.
Speiropsis pedatospora. G. Anguillospora longissima. H. Unidentiﬁed #1 (Helicoid 1). I. Unidentiﬁed #2(Helicoid 2). J. A. crassa.

radiating morphology was also remarkable. Only
Flabellospora spp., Isthimotricladia, and unidentiﬁed #5 (Nawawi, 1985) possessed the typicalradiating morphology of Ingoldian fungi.
It is also notable that the sample contained
very few dematiaceous spores, basidiomycetous
spores, and terrestrial-aquatic fungal spores. All
these spores usually occur in samples in tropicalenvironments, but not in this case, suggesting thepaucity of fungal biodiversity in Kita-Iwojima.
Although Kita-Iwojima was once colonized in
1899, it has been uninhabited since 1944 when
the inhabitants were forced to evacuate during
the war. Some plants and animals were introduced to the island, but the vegetation in theisland has remained relatively low diversity.

Tsuyoshi Hosoya et al.

120

edged for their help during the exploration. The
authors show their gratitude to Dr. Joey Tanney,
Institut de Biologie Intégrative des Systèmes,Université Laval, Québec City, QC, Canada, for
critically reviewing the manuscript. The current
study was partially supported by Grant-in-Aid
for Scientiﬁc Research (C) 20570087, “Clarifying the species diversity of bryophytes in theoceanic island, and researching for the importroute and the speciation to the solitary island”.
Fig. 6. Pie chart showing the frequency ratio of
the observed spores based on the major morphological categories. Coiled: spores are curved>360 degrees in the same plain loosely ortightly or forming three-dimensional coils.
Curved: spores are gently to strongly curved,
but not reaching 360 degrees. Sigmoid: sporesare curved twice to give “S”-like structure.
Radiating: spores composed of linear hyphalelements that radiating into three or more directions. Connected: spores are constructed bysmall cells, connected by a thin connective
structure (Speiropsis pedatospora and Wiesneriomyces javanicus). Note spore morphology ofcoiled, curved, and sigmoid are continuous.

Together with the extremely isolated environment in the middle of the ocean and its origin(volcanic island formed by mid-ocean eruption),
inhabitation of fungi associated with freshwateraquatic environments may be limited.
Acknowledgments
The authors wish to express their gratitude to
the members of the exploratory team. In particular, we are deeply indebted to Drs T. Yamaguchi
and H. Kato for providing a very precious occasion to visit Kita-Iwojima Island. We would also
like to thank Mr. T. Shumiya and M. Munakata,
The Nature Conservation Society of Japan, andS. Uchida, Hiroshima University for their help
during the exploration. Mr. Y. Sakurai, Ogasawara Subprefecture, is greatly acknowledged for
obtaining the permission to carry out the exploration. Mr. H. Suzuki and other members of Institute of Boninology are also greatly acknowl-

References
Ellis, M. B. 1971. Dematiaceous Hyphomycetes. 608 pp.
Commonwealth Mycological Institute, Kew.
Goh, T. K. 1997. Tropical Freshwater Hyphomycetes. In:
Hyde, K. D. (ed.), Biodiversity of topical microfungi,
pp. 189–227. Hong Kong University Press., Hong Kong.
Gonczol, J. and Revay, A. 2003. Treehole fungal communities: aquatic, aero-aquatic and dematiaceous hyphomycetes. Fungal Diversity 12: 19–34.
Graça, M. A. S., Hyde, K. and Chauvet, E. 2016. Aquatic
hyphomycetes and litter decomposition in tropical–
subtropical low order streams. Fungal Ecology 19:
182–189.
Hosoya, T., Hosaka, K. and Ohmura, Y. 2011. Preliminary
mycobiota assessment on Kita-Iwojima Island, Ogasawara Islands. Memoir of the National Museum of
Nature and Science (47): 405–410.
Hosoya, T., Tanaka, C., Yamada, A. and Baharuddin, S.
2006. Survey of stream spora of Penang Island and the
Malay Peninsula. Bulletin of the National Science
Museum, Tokyo, Series B 32: 123–127.
Ingold, C. T. 1975. An illustrated guide to aquatic andwater-borne hyphomycetes (Fungi Imperfecti) with
notes on their biology. Freshwater Biological Association Scientiﬁc Publication 30: 1–96.
Martin, G. W. and Alexopoulos, C. J. 1969. The Myxomycetes. University of Iowa Press. pp. 477＋pl. 41.
Marvanová, L. 1997. Freshwater Hyphomycetes: a survey
with remarks on tropical taxa. In: Janarhanan, K. K.,
Rajendran, C., Natarajan, K. and Hawksworth, D. L.
(eds.), Tropical Mycology, pp. 169–226. Science Publishers, Inc., New Hampshire.
Michaelides, J. and Kendrick, B. 1982. The bubble-trap
propagules of Beverwykella, Helicoon and other aeroaquatic fungi. Mycotaxon 14: 247–260.
Miura, K. 1974. Stream spora of Japan. Transactions of
the Mycological Society of Japan 15: 289–308.
Nawawi, A. 1985. Aquatic hyphomycetes and otherwater-borne fungi from Malaysia. Malayan Nature
Journal 39: 75–134.