The response of four lotic macroinvertebrate taxa to burial by sediments

Sedimentation is widely acknowledged as a major cause 4 degradation of instream habitats. However, macroinvertebrate burial by sediment has been poorly studied. Ex situ experiments were undertaken to examine the response of four common and abundant macroinvertebrate taxa (Baetis rhodani, Nemoura cambrica, Hydropsyche pellucidula, and Asellus aquaticus) to burial by six sediment size classes (range = 125 mu m - 10 mm in size) and two depths of burial (5 mm and 10 mm). The nymphs of the ephemeropteran, Baetis rhodani, were unable to excavate themselves from any of the sediments. In contrast, the plecopteran nymphs of Nemoura cambrica were able to excavate themselves from all sediment classes and burial depths. Adults of the isopod, Asellus aquaticus, were able to excavate themselves rapidly from finer sediment classes (< I mm) but took significantly longer to escape from sediment > 1 mm in size and became trapped in coarser sediments (> 4 mm in size at 5 mm burial depth and > 2 mm at 10 mm. burial depth). The larvae of the trichopteran, Hydropsyche pellucidula, were able to excavate their heads from all sediment classes and both burial depths, but became trapped in particles < 500 mu m in size when buried under 10mm of sediment. The results demonstrate that the response of individual taxa to burial with sediments is highly variable. Consequently, many of the documented changes to benthic macroinvertebrate community composition due to sedimentation probably mask a variety of individual faunal responses.