The influence of stream age and environmental variables in structuring meiofaunal assemblages in recently deglaciated streams

The influence of stream age and environmental variables on meiofaunal assemblages were examined for 15 streams across a temporal gradient of 200 yr in Glacier Bay National Park, southeast Alaska. Meiofaunal assemblages were found in all streams but varied in diversity and abundance. Copepod species found had a wide range of habitat affinities and good dispersal abilities; we argue that the observed copepod assemblage in a given Glacier Bay stream is determined by habitat availability rather than dispersal constraints. Two-way indicator species analysis (TWINSPAN) classified the meiofaunal assemblages largely according to stream age. Stepwise multiple regressions were performed on environmental variables and meiofaunal species richness or abundance, and predictors differed between taxa. The sorting coefficient, a measure of the diversity of particle sizes in the sediment, best explained the variation in both total harpacticoid copepod abundance and meiofaunal taxon richness (together with stream gradient). Harpacticoids were more abundant in relatively well-sorted streams and declined as the range of particle sizes within the streams increased; the opposite pattern to that found in the marine environment. The abundance of Bryocamptus spp. was best explained by models incorporating stream age and indicators of habitat complexity, whereas abundance of Tardigrada, Chaetogaster, and Moraria affinis increased with increasing substrate stability. A habitat templet was developed for the meiofaunal assemblages in Glacier Bay streams. Stream age (incorporating stream habitat complexity) formed one axis and the second axis was the sorting coefficient.