Impact of the Introduced Rainbow Darter, Etheostoma caeruleum on the Microhabitat Use of Native Darters

Abstract

The Rainbow darter, Etheostoma caeruleum is an introduced species that has spread rapidly in the Potomac River drainage. However, the reason for this rapid spread and the impact of E. caeruleum on other species of both native and nonnative darters has not been determined. This study examines how the abundance E. caeruleum affects the microhabitat use of E. blennioides, E. flabellare, and E. olmstedi within the Monocacy River drainage. Snorkeling was used as a method to observe and measure the microhabitat use of darters across eight locations. Sites where E. caeruleum were present had significantly low population levels of E. olmstedi. E. flabellare experienced a habitat shift towards habitats with larger substrates, increased depths, and slower bottom velocities with an increasing proportion of E. caeruleum. The microhabitat use of E. blennioides remained consistent across all sites, regardless of the relative abundance of E. caeruleum. This study suggests E. caeruleum are outcompeting native species, specifically E. flabellare, for their preferred habitat.