Importance of Instream Habitat to Recruitment and Community Structure of Aquatic Invertebrates

This thesis investigates how mechanisms of colonization by aquatic insects, both by ovipositing adults and or larval drift, operate at either micro-, meso-, or macro-scales to influence larval community assemblage in streams. Our study took place in a forested floodplain stream characterized by uniform soft clay and loose detritus substrate. Within this study reach we built three sets of riffles, with each set comprised of three identical riffles built either 15, 10, or 5 m apart. We examined microscale influences on community assemblage by studying recruitment of egg masses to our constructed riffles. We found that riffle habitat additions were used by ovipositing insects and that oviposition behavior and habitat preferences varied across taxa. Mesoscale impacts on community assemblage were addressed by studying how riffle habitat isolation might impact total invertebrate abundance, along with aquatic insect taxa with different oviposition behaviors and larval mobility, within and below isolated riffle habitats. We found that impacts of habitat isolation in our stream were masked at the community level, as total invertebrate abundance did not vary significantly within or below isolated riffles; however, community composition varied by location. Oviposition behavior and larval mobility might be responsible for differences in community structure within and below isolated riffles, but discerning population dynamics requires further investigation. Finally, we focused on the macroscale impacts of habitat diversity on community assemblage by comparing invertebrate communities from mud habitat that was 2 characteristic to our study reach prior to our experiment with communities from our constructed riffles. We documented a 79% increase in taxa richness at the reach scale after adding riffle habitats to our study reach. We found mud and riffle habitats supported equally abundant and diverse communities of macroinvertebrates but with distinct taxonomic differences based on oviposition behavior and larval habitat preferences. The results of these three studies suggest that benthic invertebrate communities in streams are influenced by processes operating at multiple life stages. In addition, abundance, distribution, and diversity of instream habitat directly influences abundance and composition of benthic invertebrate communities. Consequently, impairment of habitats preferred by adult or larval invertebrates could present barriers to colonization or population persistence within a stream. Therefore, stream restoration efforts aimed at recruiting and supporting diverse macroinvertebrate communities should include instream habitat diversity, including habitat for oviposition, amongst other primary concerns, such as water quality and best land-use practices. Furthermore, recovery of macroinvertebrate communities following restoration efforts that target improvements in water quality may not be fully observed if instream habitat quality and diversity remain low