Cascade macroinvertebrate assemblages for in‐stream flow criteria and biomonitoring of tropical mountain streams

Abstract

Few comprehensive studies on stream assessment and biomonitoring have been conducted in tropical, freshwater watersheds. Currently under threat from climate change, urbanization and increasing freshwater demands, there is a need for innovative approaches to tropical watershed assessment and management. This study investigated cascade habitat macroinvertebrate communities among four tropical mountain streams with the goal of enhancing future efforts to identify flow biocriteria for watersheds of Polynesia. Cascade macroinvertebrate communities were compared between streams of differing size and magnitude of flow removal to evaluate the biological effects of water withdrawal on benthic communities. Two cascade microhabitats, identified as torrenticolous and amphibious, were evaluated for macroinvertebrate community differences and presence of native taxa among watersheds. Cascade habitat in general was reduced, by as much as 98%, in downstream reaches, having a significant impact on the stream ecosystem physical template important for native stream communities. In addition, two‐way ANOVA results revealed no main effects, but significant interactions of watershed size and flow removal on mean macroinvertebrate density for torrenticolous microhabitats; however, the opposite was true for the amphibious microhabitat. Diversity was significantly higher under undiverted flow conditions (t = 4.21, df = 272, p = 0.0004) and in torrenticolous microhabitats (t = 3.86, df = 272, p < 0.0001) over the entire study period. The amphibious microhabitat was composed of 39% native taxa, while the torrenticolous microhabitat contained <7%. This study provides new options for biomonitoring of native populations in Polynesian watersheds. Further studies that support the development of in‐stream flow criteria to preserve cascades are important to understanding the role of this habitat in tropical stream ecosystem function. Copyright © 2010 John Wiley & Sons, Ltd.

Benthic Community Responses to Water Removal in Tropical Mountain Streams

“…(, , ) and Shoda et al . (). We preserved all macroinvertebrate samples in 70–90% ethanol for laboratory sorting and identification.…”

“…We pooled members of Chironomidae, excluding Telmatogeton sp., which was easily identifiable as an endemic midge (Benbow, ; Shoda et al ., ) and verified identifications using voucher specimens identified by EcoAnalyst Inc. On the basis of the findings of previous studies (Williams, ; Polhemus, ; Englund et al ., ) and similar to Shoda et al . (), we classified all members of Procanace , Limonia , Ephydridae, Telmatogeton sp., Hyposmocoma sp., Megalagrion sp. and Atyoida bisulcata as endemic to the Hawaiian Islands.…”

“…(). On the basis of funding, logistical and accessibility constraints, all sites were sampled twice in August 2007 and once in May 2008, which was similar to sampling frequency for other published bioassessment studies of Hawaiian streams (McIntosh et al ., , , ; Brasher et al ., ; Wolff, ; Shoda et al ., ).…”

“…Cascade habitats and their corresponding microhabitats were analysed in full detail by Shoda et al . (). For purposes of this paper, cascade data from Shoda et al .…”

“…Although the impacts of dams have received some attention, few studies have assessed the direct physical and hydraulic effects of flow diversion on stream communities (Baker et al ., ) even though the construction of small low head dams has undergone substantial proliferation in tropical watersheds (Benstead et al ., ). Further, hydrologic alterations and subsequent ecosystem changes have been extensively studied in temperate regions, whereas far less is known about these impacts in tropical regions, especially islands, leaving these ecosystems poorly understood (Benke et al ., , ; Pringle et al ., ; March et al ., ; McIntosh et al ., ; Shoda et al ., ).…”