Substratum-Production Relationships in Net-Spinning Caddisflies (Trichoptera) in Disturbed and Undisturbed Hardwood Catchments

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Abstract
The effect of substratum on production of two species of net-spinning Trichoptera (Hydropsychidae), Parapsyche cardis Ross and Diplectrona modesta Banks, was examined in two second-order southern Appalachian streams: Hugh White Creek (HWC), a reference stream draining an undisturbed hardwood catchment, and Big Hurricane Branch (BHB), which drains a catchment that was clear cut during the first six months of the study. Surber samples were collected monthly for 21 months in four common substrata in each stream: moss-covered rock face, cobble riffle, pebble riffle, and sandy reach. Both hydropsychid species showed distinct substratum preferences. Abundances and production (size-frequency method) of P. cardis were significantly higher in rock face > cobble riffle > pebble riffle > sandy reach in both streams. Distribution of D. modesta was more uniform among substrata and differed between streams: highest abundances and production occurred in cobble riffle in HWC, but on rock face in BHB; the lower density of moss in HWC may not have provided sufficient microhabitats for Diplectrona compared with the thicker moss of BHB. Overall production (weighted according to the relative proportions of each substratum in each stream) of D. modesta was highest in HWC. Parapsyche cardis had higher substratum-specific production in BHB than in HWC for all substrata, but higher overall production in HWC; this difference was due to availability of preferred substrata in the two streams. Differences in production between streams may be related more to geomorphic differences (i.e., relative proportion of common substrata) between streams than to effects of logging on these two species. Comparisons between streams on a reach or catchment basis should consider carefully whether the streams differ in geomorphic characteristics such as the relative proportion of channel substrata.

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