Response of Baetis Mayflies (Ephemeroptera) to Catchment Logging

Abstract

Following clear-cutting of a southern Appalachian hardwood catchment, standing stock densities and biomass of Baetis spp. increased in four stream substrate types (rock face, cobble riffle, pebble riffle and sandy reach) compared to those of a nearby undisturbed reference stream. Baetis production in the stream draining the clear-cut catchment averaged 17.6 X higher than that of the reference stream, and up to 27.6 X that of the reference stream in the more physically stable rock-face substrates. Food preferences and food-specific bioenergetic efficiencies were used to estimate the amount of food consumed and the amount of Baetis production attributable to each food category. Diatoms comprised the most important food in each stream. Analyses of gut contents of Baetis following logging indicate a significant increase in diatom consumption in the stream draining the clear-cut catchment. Diatom consumption in the reference stream (0.234 g ash-free dry mass [AFDM]/m2) and treatment stream (5.788 g AFDM/m2) comprised 9.0 and 7.4%, respectively, of the net primary production of each stream during the 1st year following the clear cut. These suggest that a similar proportion of net primary production was harvested by Baetis in each stream. Although the two Baetis populations consumed the same proportion of net primary production, Baetis in the clear-cut catchment stream had 1.22.0 X more diatoms in their guts while maintaining a standing stock biomass that exceeded that of the reference stream by 10-30 X, suggesting a much higher rate of periphyton harvesting in the clear-cut catchment. Sampling 4 and 5 years following the clear cut indicates significant declines in Baetis populations of the clear-cut stream that coincided with a 10-fold decrease in primary productivity. Although characterized by short, multivoltine life cycles and high fecundity, Baetis spp. comprise a minor component of the standing stock biomass in most headwater streams of the region. However, with disturbances such as clear-cutting, they respond quickly to exploit increases in autochthonous production, and assume major roles in energy processing. In contrast, larger, less fecund univoltine and semivoltine species lack the ability to respond quickly and exploit the relatively short-lived increases in primary production.