Oviposition site selectivity of some New Zealand aquatic macroinvertebrate taxa and implications for stream restoration

In many stream restoration projects, macroinvertebrates characteristic of natural conditions do not return despite habitat improvements. One contributing factor may be lack of oviposition sites for some taxa. To understand oviposition requirements of five taxa, we investigated their egg mass distributions on rocks in streams in the Waikato region, New Zealand. We compared insect taxa with aerial adults (caddisfly families Hydrobiosidae and Hydropsychidae, and blackfly species Austrosimulium australense and Austrosimulium sp.) to the fully aquatic limpet Latia neritoides. Egg masses of all taxa were highly aggregated, indicating strong site selection. Hydrobiosidae and both Austrosimulium species preferred ovipositing on emergent rather than submerged rocks. When ovipositing on submerged rocks, Hydropsychidae, Hydrobiosidae and A. australense preferred rocks <70 mm deep. Latia preferred large rocks (as did all taxa except Austrosimulium sp.) in reaches with low riparian shade. To allow recolonisation and/or persistence of these taxa, restored stream reaches need at least some rocks (or other features) with these characteristics.