Riparian Bryophytes: An Overlooked Yet Important Habitat for Aquatic Macroinvertebrates in Interior Pacific Northwest (USA) Salmonid-Bearing Streams.

Restoration of riparian vegetation is an objective for recovery of threatened salmonids in the interior Pacific Northwest (PNW; USA). However, bryophytes (mosses, liverworts, and hornworts) are overlooked despite their capacity to provide stream habitat for invertebrates, an important salmonid food. The role of bryophytes as invertebrate habitat is little studied in the PNW. We investigated macroinvertebrate communities in bryophytes across three aquatic habitat types (headwaters, mid-order streams and wetlands) in a salmonid-bearing stream system in the Blue Mountains, northeastern Oregon (USA). We sampled paired bryophyte and non-bryophyte benthic (streambed) substrates from 12 sites (headwaters, n = 3; mid-order streams, n = 6; wetlands, n = 3) during spring, summer and fall, 2022-2023. Bryophytes, regardless of habitat, enhanced invertebrate density per square meter, by ~11 times, on average, compared to streambeds without bryophytes. Bryophytes increased the abundance of most functional groups and hosted unique invertebrate communities dominated by Chironomidae (midges) and detritivores. Bryophytes did not serve as nursery habitat; however, invertebrates were smaller (mean length ~12% shorter) in bryophytes compared to streambeds, primarily because bryophytes were dominated by smaller taxa. Non-metric multidimensional scaling indicated that the dominant gradient in invertebrate composition was related to separation between bryophytes and streambeds (R 2 = 0.70). This gradient was driven by the dominance of midges in bryophytes compared to streambeds regardless of season or habitat type. Bryophytes harbored high densities of most functional groups of macroinvertebrates, particularly midges, a highly productive food for many stream and riparian organisms. These results suggest that bryophytes are important habitat for macroinvertebrates across most aquatic habitat types in salmonid-bearing stream systems of the Blue Mountains. By considering bryophytes in stream-riparian restoration and management plans, practitioners can enhance an important vegetation component and support conservation of highly productive aquatic invertebrate communities and consumers that depend on them for food.