Distribution of sponges (Porifera: Spongillidae) in southern Irish rivers and streams

Abstract

Surveys of southern Irish rivers and streams confirmed the presence of five sponge species: Ephydatia fluviatilis, Racekiela ryderi, Spongilla lacustris, Ephydatia muelleri and Eunapius fragilis, in order of decreasing frequency of occurrence. The putative ‘amphiatlantic’ species R. ryderi, which is largely absent from Europe, was found to be of relatively common occurrence in south-western rivers, at unpolluted sites (Ecological Quality Ratio ≥ 0.7) with soft water, where it largely replaces Ephydatia fluviatilis, the most common species found throughout the whole study area in a wide range of water-quality conditions. Spongilla lacustris, the commonest species in Irish lakes, was found at 16% of Spongillidae river sites, while the uncommon but relatively widely distributed E. muelleri was identified from some 10% of these sites. Identification, by analysis of spicule morphology, was carried out using optical microscopy with SEM performed on some samples, and the identity of the very rare Irish species E. fragilis confirmed by DNA gene sequencing. The findings signify that while freshwater sponges could, because of their large filtration rate, have a role as sentinel bioaccumulators in monitoring toxic pollution of aquatic ecosystems, the wide tolerances of Spongillidae to water-quality conditions may militate against their use as indicator species to measure ecological integrity.