First evidence of an extant freshwater sponge fauna in Jackson Lake, Grand Teton National Park, Wyoming (USA)

Abstract

Skeletal remains of freshwater sponges are important microfossils that may be preserved in the sediments of inland waters. Yet, much is still unknown about the sponge fauna of the Nearctic, which limits their use in paleoenvironmental reconstructions. Here, we report the first evidence of an extant freshwater sponge fauna in Jackson Lake, Grand Teton National Park, Wyoming (USA). Two sponge species were identified living in shallow littoral and shoreline environments: Eunapius fragilis (Leidy, 1851) and Ephydatia muelleri (Lieberkühn, 1856). The spicules of E. fragilis present high morphological variability, in contrast to gemmuloscleres reported in specimens from lakes and rivers in southern South America and eastern North America. Ephydatia muelleri also exhibits morphological differences in comparison to published examples, chiefly related to the spines on megascleres. The megascleres of E. muelleri are straight or slightly curved, sharpening gradually towards the apices, with completely smooth surfaces (13%), surfaces with minimal spines (65%), or highly spined surfaces in the central area (22%). These morphological differences in the E. muelleri megascleres suggest the potential for ecophenotypic effects in Jackson Lake. Furthermore, the morphological and ecological variability of E. fragilis and E. muelleri observed in Jackson Lake suggest the need for further studies of the Nearctic to understand if a species complex exists or if morphological dissimilarities are indicative of true taxonomic differences and therefore multiple new species. This study expands the biogeography of freshwater sponges and provides the first documentation of benthic sessile filter feeders in Jackson Lake, a key source of ecosystem services.