Heterosternuta sulphuria (Coloptera: Dytiscidae) Occurence in the Sulphur Springs Headwater System and in Buffalo National River Tributaries (Arkansas, USA): Current Distribution, Habitat Conditions, and Biomonitoring Framework

Abstract

Heterosternuta sulphuria is an endemic aquatic species of concern in Arkansas, with a priority score of 80 out of 100 and a conservation rank of S1and G1. A need of the Arkansas Wildlife Action Plan (AWAP) was to obtain baseline information on distribution and population status of H. sulphuria. Here, we report new H. sulphuria records for 39 sites across 10 counties in the Ozark Highlands and Boston Mountain ecoregions and a determined habitat type of shallow margins and small bedrock pools of perennial streams and spring seeps. Few habitat patches were observed per site because detection was typically rapid and (unconfirmed) field identifications were possible because of the unique coloration of the pronotum, therefore only a small portion of the total available habitat was surveyed. We conclude that from our surveys and information gathered from other sources that in Arkansas H. sulphuria is probably ubiquitous among permanently wet aquatic habitats (primarily in upland headwater systems) throughout the Ozark Highlands and Boston Mountain ecoregions. Based on the number of occurrences, we recommend a downgrade of conservation status to S3 or S4. While some locations provide protection for current H. sulphuria populations (e.g., Buffalo National River, Hobbs State Park – Conservation Area, Sherfield Cave effluent stream, and USFS Richland Creek Wilderness), populations on unprotected lands in urban and agricultural settings probably have a much greater risk of population decline. A final determination of conservation status should consider several factors including dispersal capacity, population sizes, and genetic differentiation among populations. Furthermore, determining if existing H. sulphuria populations are isolated subpopulations or an interacting metapopulation and the habitat area required for population persistence are key for developing effective conservation actions. Monitoring existing populations should involve revisiting current H. sulphuria sites, and this is especially important for potentially fragmented populations in unprotected streams. Bioassessment programs could benefit from monitoring these easily observed populations that might positively relate to the overall physical and biological integrity of permanent Ozark streams and riparian corridors