AQUATIC HYPHOMYCETES OF 21 RIVERS IN SOUTHERN IRELAND

Foam was collected fromn 21 nrvers in southern and westem Ireland in autumn 1993 and 1994 and early spring 1994, and aquatic hyphomycete spores were enumerated and identified. Sixty-eight aquatic hyphomycete species were identified, with a significantly greater number of species being recorded from nrvers with a riparian vegetation of woodland than from rivers with a more herbaceous vegetation. The number of species recorded in this study was comparable to numbers recorded from Europe and North America. However, the mean number of taxa recorded per river (26.5) was comparatively low. Detrended correspondence analysis showed that rivers of contrasting water hardness and conductivity could be differentiated on the basis of differences in the composition of their aquatic hyphomycete spora. Assemblages of associated species were also detected, such as those confined to soft-water rivers. TWINSPAN analysis also distinguished a core assemblage of species that were widely distributed. T.J. Harrington, Life Sciences Department, University of Limerick, Ireland. Received 25 July 1996. Read 30 October 1997. Published 31 October 1997. INTRODUCTION The distribution of aquatic hyphomycete spores in rivers has been investigated in a number of temperate countries but apart from the work of Fenton (1950), who recorded the occurrence of aquatic hyphomycetes in a number of rivers in Northern Ireland, little work has been done on the distribution of these fungi in Irish rivers. While there is a good deal of information from other European countries about the influence of ripanran vegetation, water cheniistry and other factors on the ecology of aquatic hyphomycetes (Iqbal and Webster 1977; Blirlocher and Rosset 1981; Wood Eggenschwiler and Birlocher 1983; Shearer and Webster 1985; Engblom et al. 1986; Gdnczdl 1989; Chauvet 1991), there is an absence of such information for Ireland. This work attempts to address this deficit and to provide at least prelimi nary answers to the following questions: (i) is the range of aquatic hyphomycetes found in Irish riv ers similar to that found in other European coun tries of comparable climate, and (ii) are there differences in the aquatic hyphomycete spora of Irish rivers of contrasting water chenmistry and riparian vegetation such as those described in-stud ies of European rivers? Aquatic hyphomycetes (also known as In goldian fungi or amphibious fungi) were first dis covered as an ecological group in a British stream by Ingold (1942). Since then over 300 species have been described from rivers and lakes in most parts of the world. Many aquatic hyphomycetes have cosmopolitan distributions, while others show lati tudinal or altitudinal distributions that are largely determnined by water temperature (Koske and Duncan 1974; Suberkropp 1984). In general, spe cies diversity seems to be greater in circumneutral than in acidic or alkaline rivers (Wood-Eggen schwiler and Barocher 1983). Their ecology and physiology have been studied extensively. They are known to play an essential role in mediating energy transfer in food chains in woodland streams and rivers. They accomplish this by degrading the large amount of leaf litter and other woody debris that falls into these rivers and converting it into fungal biomass, which in turn supports many in vertebrate detritivores (Triska 1970; Kaushik and Hynes 1971). Leaves that fall into rivers in autumn are rapidly colonised by aquatic hyphomycetes and prolific sporulation follows. The majority of aquatic hyphomycetes pro duce spores (conidia) xvith distinctive tetraradiate shapes that allow many taxa to be identified with some degree of confidence from spore nmorphology alone. A smaller number produce signmoid spores, while some species have spores of more conven tional shape. The mature spores become detached from colonised leaves and are carred passively ownstream in large numbers. The tetraradiate spore form is thought to be an adaptation to minimise downstream transport and to facilitate attachment to leaves (Webster 1959). On attach ment to a suitable substratum, the spores germinate rapidly. Tetraradiate spores are captured very effi ciently by air bubbles rising through the water and they collect in foam where they can remain in a viable, ungerminated state for considerable periods of time. BI()LOGC,Y AN) ENVIRONMENT: PFoCEEIuNcS OF THE LOYAL 1IPSH AC-Ai)EMY, VOL. 97B, No. 2, 139-148 (1997) 0 ROYAL IRuSH ACA)EMY 139 This content downloaded from 207.46. 13.148 on Sun, 11 Sep 2016 04:27:55 UTC All use subject to http://about.jstor. org/terms BIOLOGY AND ENVIRONMENT MATERIALS AND METHODS