Microdistributional Variability of Larval Caddisflies in Mediterranean-Climate Streams in Northern California

Knowing how physical and biogenic habitat characteristics affect microspatial variability of larval caddisflies is important to understanding potential population distributions and local species assemblages. We show that larval caddisfly densities and assemblages vary between study reaches and streams on the Angelo Coast Range Reserve in northern California and that species abundance patterns are associated with specific habitat variables. Dicosmoecus gilvipes and Psychoglypha spp. were most dense in 4th-order reaches of the south fork of the Eel River (SFE) and rare or absent in shallow 2nd- and 1st-order reaches of the Elder and Fox Creek tributaries, respectively. Multidimensional scaling (MDS) suggested D. gilvipes densities were associated with water depth, as microdistributions were restricted to depths >40 cm. Microdistributions were also associated with Rivularia-dominated algal patches, but it is doubtful grazing D. gilvipes tracked these cyanobacteria. Psychoglypha spp. were typically found between roughness elements (stones) in relatively deep waters, and MDS suggested that densities of Psychoglypha spp. were related to current velocity Lepidostoma sp. was densest in Fox Creek, and densities of this detritivore were associated with benthic organic matter (BOM). Glossosoma spp. densities were similar among streams (∼25 larvae · m-2) and did not configure around any of the habitat variables used in MDS. Neophylax (likely rickeri), Heteroplectron, Ecclisomyia, and Hydatophylax hesperus were uncommon and found only in either Elder or Fox creeks. Our work shows that larval caddisfly assemblages are more diverse in SFE tributaries than in the mainstem and that species traits and microdistributions are related to local-scale habitat variables in these Mediterranean-climate streams.