A Model of Seston Capture by Net-Spinning Caddisflies

Abstract

Six species of net-spinning caddisflies (Trichoptera) coexist in the headwater region of the Tallulah River, a rocky, high-gradient tributary of the Savannah River. These caddisflies feed on the suspended organic matter (seston) captured by their nets. We analyzed these species' nets, microhabitat preferences, and monthly abundances. These data, along with the particle size distributions and monthly abundances of seston, were incorporated into a model of seston capture by these net-spinning caddisflies.The resulting model permitted us to test the hypothesis that differences in capture net mesh sizes serve to partition, by size, the food available to coexisting net-spinning caddisflies. and thus reduce competition between them. The model predicted annual seston capture by the six species of 1300 g AFDW (ash free dry weight), over 1000 times their annual production. The seston captured per longitudinal meter of stream represents 0.005% of the total seston in transport. Resource overlap coefficients indicated that the instars of the five hydropsychid species do not partition the seston by particle size or food type in a manner that reflects competitive interactions. We hypothesize that these filter feeders are limited by the availability of high-quality food items (primarily drifting animals) rather than by the overall seston supply. Species with highly selective feeding habits must filter large volumes of water to permit them to specialize on rare items. High filtration rates require rapid current velocities, large nets, and coarse net meshes. Instars with coarse-meshed nets showed the largest proportionate declines in seston capture rates when the model was simulated using the lower current velocity and smaller seston panicles sizes typical for the larger Savannah River.

Production of net-spinning caddisflies (Hydropsychidae) and black flies (Simuliidae) on rock outcrop substrate in a small southeastern Piedmont stream

“…Gut content analyses have demonstrated the importance of carnivory and diatom ingestion in many hydropsychid species (Coffman et al, 1971 ;Benke & Wallace, 1980 ;Fuller & Mackay, 1980 ;Ross & Wallace, 1983), suggesting that the low hydropsychid production in headwater streams results from the limited availability of high quality food (Georgian & Wallace, 1981) . In Rose Creek, enrichment by agricultural runoff may contribute to hydropsychid productivity by subsidizing algal growth and production of potential prey species .…”

“…These animals collect and consume drifting material and thus slow the downstream loss of nutrients and energy from the stream system (Wallace et a!., 1977) . Although their impact on total seston quantity may be negligible, filter-feeders can decrease seston quality by removing easily assimilated material, thereby influencing food availability to downstream communities (Maciolek & Tunzi, 1968 ;Carlsson et al, 1977 ;McCullough et a!., 1979 ;Oswood, 1979 ;Benke & Wallace, 1980 ;Georgian & Wallace, 1981 ;Haefner & Wallace, 1981) . Filterfeeder production, defined as tissue elaborated over time (Waters, 1977), represents nutrients and energy Hydrobiologia 112, 3-15 (1984) .…”

Effects of Microhabitat Selection on Feeding Rates of Net‐Spinning Caddisfly Larvae

“…Stream filter feeders exhibit intra-and interspecific aggressiveness in both laboratory and field studies (Edington 1965, Glass and Bovbjerg 1969, Hemphill and Cooper 1983, Hart 1986, Gatley 1988, Hemphill 1988, Hershey and Hiltner 1988, and there exists indirect evidence that interspecific competition for suitable sites for nets may have driven the evolution of net-spinning caddisflies (Georgian and Wallace 1981, Alstad 1986, Thorp et al 1986). Gut analyses (Benke and Wallace 1980) and behavioral studies (Petersen 1985) have shown that the larger hydropsychid larvae feed selectively on high-quality food items such as diatoms and drifting animals, despite the fact that these materials compose only a very small portion of the particulate organic matter (POM) transported by streams (e.g., Parker and Voshell 1983).…”

Downstream Changes in Caddisfly Composition and Abundance in Relation to Changes in Water Conductivity and Oxygen in the River Butron Basin

“…Coexistence of species of thegenus Hydropsyche is a common feature in rivers (BOON, 1979;MALAS & WALLACE:, 1977;HILDREW & EDINGTON, 1979; ANDERSEN & KLVB- NES, 1983;HIGLER & TOLKAMP, 1983;GEORGIAN & WALLACE, 1981; HERRANZ 8r GARC~A DF: J A L~N , 1984). I n this basin Hydropsyche bulbifera, Hydropsyche pellucidula and Hydropsyche siltalai coexisted a t the sites which showed higher species richness such as sites 2 and 3 of the main river.…”