Production of Parapsyche cardis Ross and Diplectrona modesta Banks was estimated in two first-order southern Appalachian streams. One stream drains a natural undisturbed hardwood watershed and the other a watershed subjected to several disturbances, including clearcutting. Since 1968 the latter has been allowed to undergo natural succession. Both hydropsychid species were univoltine in each stream. Production estimates were higher for both species in the stream draining the disturbed watershed. This was attributed to: (1) More suitable habitat in the disturbed watershed consisting primarily of rock face habitat with large amounts of moss; (2) Higher densities of prey species in the disturbed watershed; and, (3) Potentially enhanced food quality resulting from a 200 fold greater NO 3 -N concentration in the disturbed stream. The estimates of animal food consumption required to support the combined production of P. cardis and D. modesta were 11.59 and 3.33 g/m 2 /yr on the disturbed and undisturbed watersheds respectively. These two species use <0.019% and <0.0063% of the total organic seston passing over each m 2 /yr on the disturbed and undisturbed watersheds respectively. However, estimates of animal tissue consumption are several times higher than the invertebrate drift from each watershed. The latter suggests that the major impact of these net spinners is on the animal fraction of the seston.
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Haefner et al. (1981) studied this question.