Effect of Black Fly Ingestion and Assimilation on Seston Transport in a Quebec Lake Outlet

Abstract

Ingestion and assimilation rates of simullid (Diptera) larvae feeding on natural seston were estimated in an artificial stream and used to predict the impact of simuliids on seston transport in a 40-m section of the outlet stream of Petit Lac Fraser in southern Quebec. This prediction was then compared with changes in the seston flux above and below the population. Finally, we selectively killed simuliids with a larvicide (Bacillus thuringiensis serovar. israelensis) to observe changes in seston transport after removal of simuliids. The stream population of simuliid larvae ingested between 32 and 55% of the seston flux and assimilated between 17 and 25% of the dry mass of ingested seston. The change in assimilation of seston in the stream section before and after the larvicide treatment was similar to that predicted from assimilation rate of larvae and standing stock. Larvae ingested 0.8–1.4% of the seston per linear meter of stream, about 10–1000 times more than what has been reported for other populations of stream filter-feeders. The high values observed can be explained by high specific ingestion rates, high standing stock, and low discharge. Our results suggest that simuliid populations can be food limited and may help to explain the downstream decrease in abundance and growth rates of filter-feeders in lake outlets.

The influence of filter‐feeding benthic macroinvertebrates on the transport and deposition of particulate organic matter and diatoms in two streams

“…Large standard error terms associated with the nonlinear regressions (as 95% CI in Table 1), lack replication in our field experiments, and small relative changes in k P all contributed to the low statistical power of our analysis. However, considering that POM capture rates (mg Ϫ1 filter-feeder dry mass) derived by back-calculating from the nonsignificant changes in k P were in close agreement with published values (e.g., Wotton 1978;McCullough et al 1979a,b;Morin et al 1988), we speculate that the observed changes in k P may have been real despite their lack of statistical significance.…”

“…These rates were higher than those observed by Morin et al (1988; particles Ͼ0.2 m; 1.13-1.53 g mg DM Ϫ1 min Ϫ1 ) and McCullough et al (1979a,b; diatoms and detritus of unreported size 0.2-1.33 g OM mg DM Ϫ1 min Ϫ1 ) but were similar to the range observed by Wotton (1978; powdered charcoal 10.1 m; 10.8-14 g OM mg DM Ϫ1 min Ϫ1 ).…”

“…Likewise, filter-feeder capture of POM also may result in significant depletion or alteration of their own food resource. Such effects may be local (Fréch-ette and Bourget 1985) or propagated downcurrent (Maciolek and Tunzi 1968;Peterson and Black 1987;Morin et al 1988), thereby limiting resource availability to other filterfeeders.…”

Fecal pellets from a dense aggregation of suspension‐feeders in a stream: An example of ecosystem engineering

“…Blackfly larvae are thus "allogenic ecosystem engineers" (Lawton and Jones 1995) and were probably responsible for the significant reduction in very small particles we recorded. Removal of particles < 11 pm in diameter was 0.06% m ' linear stream length, a much lower figure than the 0.8-1.4% m i of suspended matter recorded by Morin et al (1988) for a lake-outlet stream of similar depth (5-25 cm) in Canada.…”

“…Shallow streams that support very high densities of suspension-feeders have a higher retention of suspended particles than do those without, and spiralling is a more important process as a result (Morin et al 1988;Wotton et al 1996). The highest population densities and production of suspension-feeders in fresh waters are found in shallow lake-outlet streams (Wotton 1994;Malmqvist and Eriksson 1995).…”