Using Geomorphic and Geologic Parameters to Identify Optimal Endemic Wēkiu Bug Habitat on the Summit of Maunakea, Hawai‘i

Abstract:

The upper summit region 3700-4205 m of the dormant post shield volcano Maunakea, located on the Big Island of Hawai‘i, is home to the endemic Wēkiu bug (WB) (Nysius wekiuicola), an arthropod species that lives within the cinder layer and feeds on the hemolymph and organs of aeolian deposited insects. Areas of the summit are undergoing environmental and anthropogenic changes, including accelerated erosion and land modification due to increased foot and vehicle traffic, road maintenance, and large telescope construction, which may be altering WB habitat. Although first studied over 30 years ago, little is known about the optimal habitat or spatial distribution of the WB. Possible environmental characteristics that influence WB persistence include elevation, mineralogy, cinder size, aspect, slope, cinder depth to the ash layer, and surface roughness. The aim of this study is to determine if measurable geomorphic and geologic parameters can be used to identify and differentiate viable WB habitat. For example, cinder depth is thought to be an important variable in WB thermoregulation, but this has never been established. We used a terrestrial lidar scanner to collect high resolution topographic data over 3750 acres at the summit in order to derive slope, aspect, surface roughness and elevation information. These data also provide a topographic baseline that can be used to quantify contemporary erosion rates. 20 m resolution AVIRIS hyperspectral data were used to classify summit surface mineralogy. We collected field data across the study area, including measurements of cinder size, gradation, and depth to the underlying ash layer. We compared the results from these diverse datasets with 15 years of annual arthropod survey data, sampled at over 1000 locations on Maunakea from 2001-2015. Preliminary results show that elevation and mineralogy play significant roles in WB capture rates, although WB sampling efforts were not evenly distributed amongst classes. No apparent trends were found for cinder depth, aspect, or slope. Surface roughness and cinder size measurements and analyses are ongoing. The results of this study will aid in defining optimal WB habitat and will be incorporated into efforts to return the substrate to pre-disturbance conditions during the future decommissioning of structures on the summit of Maunakea.The upper summit region 3700-4205 m of the dormant post shield volcano Maunakea, located on the Big Island of Hawai‘i, is home to the endemic Wēkiu bug (WB) (Nysius wekiuicola), an arthropod species that lives within the cinder layer and feeds on the hemolymph and organs of aeolian deposited insects. Areas of the summit are undergoing environmental and anthropogenic changes, including accelerated erosion and land modification due to increased foot and vehicle traffic, road maintenance, and large telescope construction, which may be altering WB habitat. Although first studied over 30 years ago, little is known about the optimal habitat or spatial distribution of the WB. Possible environmental characteristics that influence WB persistence include elevation, mineralogy, cinder size, aspect, slope, cinder depth to the ash layer, and surface roughness. The aim of this study is to determine if measurable geomorphic and geologic parameters can be used to identify and differentiate viable WB habitat. For example, cinder depth is thought to be an important variable in WB thermoregulation, but this has never been established. We used a terrestrial lidar scanner to collect high resolution topographic data over 3750 acres at the summit in order to derive slope, aspect, surface roughness and elevation information. These data also provide a topographic baseline that can be used to quantify contemporary erosion rates. 20 m resolution AVIRIS hyperspectral data were used to classify summit surface mineralogy. We collected field data across the study area, including measurements of cinder size, gradation, and depth to the underlying ash layer. We compared the results from these diverse datasets with 15 years of annual arthropod survey data, sampled at over 1000 locations on Maunakea from 2001-2015. Preliminary results show that elevation and mineralogy play significant roles in WB capture rates, although WB sampling efforts were not evenly distributed amongst classes. No apparent trends were found for cinder depth, aspect, or slope. Surface roughness and cinder size measurements and analyses are ongoing. The results of this study will aid in defining optimal WB habitat and will be incorporated into efforts to return the substrate to pre-disturbance conditions during the future decommissioning of structures on the summit of Maunakea.