The role of aquatic moss on community composition and drift of fish-food organisms

Abstract

Macroinvertebrate density, biomass and drift were studied from moss-covered and moss-free channels in the South Fork Salmon River, Idaho. Insect densities were compared for 10 different substrate types and locations involving moss (Fontinalis neo-mexicana), sand, pebbles and cobbles. An ANOVA test demonstrated that insect densities varied significantly with substrate type (P < 0.05), and that total insect density in moss clumps differed significantly from densities in mineral substrates. Insect densities were 4-18 times greater in moss clumps than in mineral substrates under and adjacent to moss; sands under moss supported the lowest densities. During most tests, densities in pebble and cobble substrates adjacent to moss clumps were not significantly different from those found in similar substrates in the moss-free channel. The 20% moss-covered channel had 1.6 to 7.2 greater insect density and 1.4 to 6.1 greater biomass than did the moss-free channel for the tests conducted. Generally, midges (Chironomidae) made up over 50% of the insect community; annelids were the principal non-insect invertebrates.In spite of greater insect density and biomass in a moss-covered than in the moss-free channel, we did not demonstrate universally increased drift of the immature stages from the moss-covered channel, at least during daylight hours. As a consequence, we infer that salmonid fishes, feeding primarily on drifting insects during the daytime, may not derive increased caloric benefit from moss habitats until the insects emerge as adults.

Stream mosses as chemically-defended refugia for freshwater macroinvertebrates

“…Host-plant selection by small invertebrates in freshwater systems has traditionally been assigned to differences among macrophytes in the provision of habitable living spaces, entrainment of particulate organic matter, surfaces for epiphytic algal growth, and shelter from turbulent flow (Lodge 1985, Brusven et al 1990, Suren 1991, Linhart et al 2002. Our data do not allow us to control for these potentially covarying factors, but some of the variation in plant traits and herbivore use in our study are inconsistent with these viable alternative hypotheses.…”

“…Selective feeding by large, generalist herbivores, including waterfowl (Sondergaard et al 1996, Van Donk and Otte 1996, Weisner et al 1997, Santamaria 2002, crayfish (Lodge and Lorman 1987, Lodge 1991, Lodge et al 1994, Dorn and Wojdak 2004, mammals (Qvarnemark and Sheldon 2004), and fish (Van Donk and Otte 1996), can alter the abundance and species composition of freshwater plant communities and drive plant assemblages towards dominance by chemically defended plants (Parker et al 2006). Although macroinvertebrates are often abundant on submersed aquatic plants (Brusven et al 1990, Bowden 1999, Hutchens et al 2004, and suffer intense predation from omnivorous crayfish (Lodge et al 1994), fish (Sheldon 1987, Johansson 1991, Flecker and Townsend 1994, and waterfowl (Marklund et al 2002), the feeding and host-plant preferences of small, plant-associated grazers relative to the feeding preferences of larger consumers in the same freshwater system have rarely been considered.…”

Meiofaunal communities associated with bryophytes and gravels in shaded and unshaded alpine streams in New Zealand

“…This was implicated by Suren (1991) who observed distinct seasonal cohorts in larval chironomid density, attributable to oviposition by emergent adults following peaks in pupal densities. This would be responsible for the often reported numerical dominance of large (> 250 |im) chironomids within bryophytes (e.g., Percival & Whitehead 1929;Hynes 1961;Stern & Stem 1969;Cowie & Winterbourn 1979;Brusven et al 1990) and would reflect a high abundance of smaller (unsampled) animals in these studies.…”

“…Overseas investigations of bryofauna have also concentrated on macroinvertebrates (e.g., Percival & Whitehead 1929, 1930Hynes 1961;Thorup & Lindegaard 1977;Maurer & Brusven 1983;Brusven et al 1990), but an overlooked aspect in these communities, however, is the occurrence of the meiofauna (O'Doherty 1985;Meyer et al 1988;Rundle & Hildrew 1990). Although lotic meiofaunal communities have occasionally been examined (e.g., Williams & Hynes 1974;Jones 1986;Shiozawa 1986;Williams 1989;Rundle & Hildrew 1990), only Cox (1988) has investigated the occurrence of meiofauna within aquatic bryophytes.…”

Environment shapes invertebrate assemblage structure differences between volcanic spring-fed and runoff rivers in northern California

“…Bryophytes and macrophytes can increase invertebrate density by increasing structural habitat complexity relative to complexity in typical stream bedforms, such as gravels (Brusven et al 1990, Strayer and Malcom 2007, Shupryt and Stelzer 2009). Bryophytes and macrophytes were a dominant habitat feature in our spring-fed rivers, where they accounted for up to 95% of the entire sampling reach depending on season.…”