A nine-year study of the macroinvertebrate fauna of a chalk stream

Abstract

Abstract:The macroinvertebrate fauna of a 50 m site on a partially shaded perennial section of the River Lambourn in Berkshire was studied intensively between 1971 and 1979. This period included a minor drought in 1973 and a major drought in 1976.A quantitative sampling programme for macroinvertebrates was undertaken on each of ®ve distinct biotopes (Berula, Callitriche, Ranunculus, gravel and silt). Each one was sampled in March, June, September and December of 1971 and thereafter in June and December from 1972 to 1979. Five replicate sampling units from each biotope were processed separately prior to determination of density estimates, except in 1972 and 1973, when time constraints necessitated bulking and subsampling.Family richness per sampling unit and per sample was higher in December than June, and higher on the three macrophytes than on gravel and silt. Nevertheless, over nine years, a high proportion of the 59 families recorded on the site were collected on each biotope.During the extreme drought of 1976, there was no evidence of loss of family richness on the site, but some biotopes supported unusually high densities of macroinvertebrates from a limited number of families. By combining information on the density of invertebrates per biotope and the area of each biotope, the weighted mean density of invertebrates on the site was calculated for each sampling occasion.Seasonal and between-year changes in the densities of numerically important families were observed and a variety of responses to discharge regime were noted. Overall, the macroinvertebrate fauna appeared to be capable of rapid recovery after an extreme drought event on this unpolluted perennial site.

Variability in the response of amphipods and macroinvertebrate assemblage structure to prolonged drought in forested upland streams

“…Our findings are similar to several previous studies of drought in UK chalk streams which showed significant changes to assemblage structure, driven by alterations to taxon abundance alone (Wright and Symes 1999) and both taxon richness and abundance Petts 1994, Wright et al 2002). For example Wright and Symes (1999) observed a significant decrease in the density of Simulidae and an increase in the densities of Chironomidae and Ceratopogonidae during drought. Similarly, Woods and Petts (1994) observed the loss of Elmidae, Simulidae and Ephydridae during drought, but also a significant decline in Lymnaeidae and G. pulex.…”

Macroinvertebrate community responses to a dewatering disturbance gradient in a restored stream

“…5). This response is similar to that shown in English chalk streams, where maintaining submerged macrophytes is critical to minimizing the ecological effects of droughts (Wright and Berrie, 1987;Wright and Symes, 1999). In contrast to the hydrophyte-associated taxa, however, the most mobile, swimming taxa at Timberlake actually responded positively to the dewatering.…”

Macroinvertebrate community dynamics in a temperate European Atlantic river. Do they conform to general ecological theory?

“…Therefore, we believe that the seasonal dynamics of macroinvertebrate number of taxa in the Pas river basin is primarily driven by the temporal segregation of taxa in relation Macroinvertebrate abundance increased downstream and was almost four times higher in the low flow period (summer) compared to the high one (winter), what is consistent with our second prediction. Similar spatial and temporal patterns have been reported for macroinvertebrate communities of other Atlantic rivers from northern Spain (Riaño et al, 1993;Basaguren et al, 1996;Otermin et al, 2002) and England (Wright & Symes, 1999). Both Riaño et al (1993) and Basaguren et al (1996) suggested that macroinvertebrate abundance is lower in headwaters due to higher hydraulic stress, which can reduce macroinvertebrate food resources such as periphytic biomass (Clausen & Biggs, 1997;Izaguirre & Elosegui, 2005) and the concentration of organic matter (Giller & Malmqvist, 1997).…”