Shedding a light on bryophyte distribution and facilitation: Exploring microhabitats and invertebrate interactions

Abstract

Bryophytes (mosses, liverworts, and hornworts) are underrepresented in conservation and restoration efforts, yet they play critical roles in maintaining ecosystem health. Globally, bryophytes have been shown to facilitate seed germination and seedling growth, as well as increase resources for invertebrates which may then pollinate plants or become food for other animals. This study is one part of a larger collaborative research project in Limahuli Stream in Hāʻena, Haleleʻa, Kauaʻi, which aims to understand the ecological foundations of Indigenous resource management, including the effects of management of riparian canopy cover on stream life. Specifically, we explored 1) how variation in daily mean light intensity affects bryophyte cover in the stream, and 2) if bryophytes are associated with the presence of invertebrates. We documented bryophyte identity and cover in four sites, using 8-22 transects per site and a total of 672 0.25x0.25 cm plots in order to capture the variation in bryophyte microhabitats. In total, 36 bryophyte species were recorded in the stream, including 23 mosses, 12 liverworts, and 1 hornwort. Bryophytes were found in 72.3% of all plots. The effect of mean daily light intensity on bryophyte cover varied across microhabitat types. In wet microhabitats (e.g., waterfall splash zones), bryophyte cover had a curvilinear relationship with increasing mean daily light intensity, from 0–12000 mean daily lux, then decreasing from 12000–15000 mean daily lux, but persisted even in areas with the highest light averages. The inverse relationship was seen in dry (e.g., dry rocks) and intermediate microhabitats (e.g., substrates at the water’s edge), where bryophyte cover declined from 0–9000 mean daily lux then increased from 9000–18000 mean daily lux. The effect of temperature on the probability of bryophyte presence showed a U-shaped pattern, and had minimal effect on bryophyte cover. Bryophytes forming dense, upright mats (“turfs”) were positively associated with mean daily light intensity. Across all microhabitat types except rock overhangs, the probability of invertebrate presence increased as a function of bryophyte cover. Additionally, mat-forming bryophytes were associated with invertebrate presence. These findings can guide restoration efforts, including outplanting decisions, canopy management, and reintroduction of bryophyte species to streams. As Hawai‘i faces threats from climate change and microhabitat loss, these insights are critical for addressing the urgent need to conserve biodiversity and restore degraded ecosystems.