The Potential Indicator Value of Rare Taxa Richness in Diatom-Based Stream Bioassessment1

Abstract

Despite their recognized contribution to species richness, the importance of rare taxa richness in bioassessment is unclear. This study aimed to characterize the environmental factors affecting the number of rare diatom taxa in western U.S. streams and rivers, and to evaluate whether this number can be used to differentiate streams with contrasting human disturbance. Three different categories of rare taxa were used: satellite (taxa with low occurrence and low abundance), rural (taxa with high occurrence and low abundance), and urban (taxa with low occurrence and high abundance). Common taxa were included as a separate category of core taxa (taxa with high occurrence and high abundance). We analyzed 987 diatom samples collected over the period of 5 years (2000-2004) for the U.S. Environmental Protection Agency's (EPA) Western Environmental Monitoring and Assessment Program (WEMAP). The results showed that rural taxa richness (number of rural taxa per site) increased along a longitudinal gradient from mountainous, fast-flowing oligotrophic streams with fewer fine substrates to large, slow-moving, nutrient-rich rivers with abundance of fine substrates. Rural taxa richness was the only rarity metric that distinguished least disturbed (reference) sites from the most disturbed (impacted) sites, but it was significantly different only in the mountains ecoregion. Core taxa richness distinguished reference from impacted sites in the West and in each one of the three ecoregions (mountains, plains, and xeric). Our findings revealed that rural taxa richness can be used as an indicator of human disturbance in streams/rivers, especially in the mountains ecoregion, and that rarity definition is important in bioassessment.

Comparative responses of dominant and subordinate periphytic diatom species to environmental gradients in Donghu Lake, China

“…Relative abundance is widely used in research on environmental assessments (Maraslioglu et al, ; Schuch et al, ; Tan et al, 2015). Gillett et al () separated all species into four groups: core species (high abundance and high occurrence) and satellite/rare species (low abundance and low occurrence), urban species (low abundance and high occurrence) and rural species (high abundance and low occurrence). Jain et al () defined species rarity from the three key properties of geographic range, habitat specificity, and local abundance, and found that the way rare species are defined changed how functional diversity is assessed.…”

The distribution of centric diatoms in different rivercatchments in the Anatolian Peninsula, Turkey

“…In many cases rare taxa are not recorded in the results of different publications about Turkish inland waters. However, these taxon records are important to biodiversity assessments (Gillett et al, 2011). We recommend that the species occurrences should be noted in water quality monitoring studies.…”

Three new records for diatoms from the Nišava River and its tributary, the Jerma River (Southern Serbia)

“…Evaluation of the floristic richness of diatoms in the river is a necessary, further step. These new and rare taxa significantly contribute to diatom biodiversity of the Nišava River and Serbia, though the importance of rare diatom taxa in bioassessment studies is still unclear (Potapova & Charles 2004, Gillett et al 2011. This new information increases our knowledge of the river system and the relationship between diatom species and chemical parameters, which is important for further predictions of the water quality based on the occurrence of diatoms as bioindicators, and monitoring programs.…”