Abstract
Traditional methods of collecting, sorting, and identifying benthic macroinvertebrate samples are useful for stream biomonitoring and ecological studies, however, these methods are time consuming, expensive, and require taxonomic expertise. Estimating larval densities through collection of post-emergent exuvia can be a practical and time efficient alternative. We evaluated the use of multiple pass depletion techniques of the post-emergent exuvia of Pteronarcys californica to estimate larval densities at ten sites in three Colorado rivers. Exuvia density was highly correlated with both final-instar larval density (R2 = 0.90) and total larval density (R2 = 0.88) and the multiple pass removal technique performed well. Exuvia surveys found P. californica at three low density sites where benthic sampling failed to detect it. At moderate and high density sites the exuvia surveys always produced lower density estimates than benthic surveys. Multiple pass depletion estimates of exuvia proved to be an accurate and efficient technique at estimating larval densities and provided an effective alternative for traditional benthic sampling when objectives are detecting and monitoring P. californica, especially at low density sites.
Highlights
Evaluating the condition of freshwater ecosystems through benthic macroinvertebrate communities is a common approach for stream health assessment and biomonitoring [1,2,3]
We evaluated this by correlating density estimates of shed exuvia from multiple pass removal models from the riparian area with densities of larvae from benthic samples
Larvae from the Colorado and Fraser Rivers separated into four year classes; mature female larvae were 39 mm total length (TL) and males 35 mm TL (Table 1)
Summary
Evaluating the condition of freshwater ecosystems through benthic macroinvertebrate communities is a common approach for stream health assessment and biomonitoring [1,2,3]. These methods characterize and compare aquatic invertebrate communities among sites using regionally developed standards. While useful, are labor and time intensive, expensive, sensitive to sampling techniques, and require taxonomic expertise. The costs can be justified by the valuable data used by government agencies, researchers, and water managers to monitor water quality and to describe and understand the function of river ecosystems. If sampling objectives are more specific and budgets are limited, whole community benthic sampling may not be necessary or the most appropriate technique.
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