BENTHIC DIATOMS OF THE RIVER DEEL: DIVERSITY AND COMMUNITY STRUCTURE

Abstract

This paper compares the diversity and structure of the benthic diatom assemblages on boulder and cobble substrata and examines the influence of site and seasonal factors on diatom diversity in the River Deel, Co. Limerick. One hundred and ten diatom species were identified from the River Deel, with 85 species found on boulders over a two-year period and 102 species found on cobbles over a one-year period. There was little difference in the composition of the diatom community on boulders between sites. Some differences were noted between sites for cobbles, with a small number of species being more associated with certain sites than others. The absence of marked differences between the sites was attributed to the lack of longitudinal variation in the main channel of the River Deel. On both substrates, indicator species analysis showed that the abundance of most diatom species was not related to sampling date. On boulders, only fourteen species in 1999 and twenty-one species in 2000 had a significant association with any sampling date. Twelve cobble species had a significant association with a sampling date (principally May). There was little correspondence between significant indicator species on cobbles and boulders. The patterns of dominance of diatom species differed between the boulder and cobble substrates over the sampling period, and Detrended Correspondence Analysis (DCA) showed that diatom samples formed two distinct groupings based on substrate.