Macroinvertebrate community patterns in relation to leaf‐associated periphyton under contrasting light and nutrient conditions in headwater streams

Abstract

Temperate headwater streams traditionally have been considered heterotrophic and brown food web dominated with little primary production. Recent work, however, suggests algae on leaves in these streams may play a greater role than previously thought through interactions with microbial decomposers like fungi. Algae also may be important for macroinvertebrates colonizing leaves in streams. Algae are a more nutritious food resource for shredders than fungi and bacteria and provide a food resource for non‐shredder macroinvertebrates. In a field experiment, we manipulated light in three low‐nutrient and three high‐nutrient streams using leaf bags filled with red maple leaves in winter and spring. After four weeks we measured algal and fungal biomass, leaf stoichiometry, and macroinvertebrate abundance and biomass associated with the leaf bags. We also identified the macroinvertebrate community and examined differences in functional feeding guilds and taxa under ambient‐ and shaded‐light treatments and low‐ and high‐nutrient concentrations in relation to measured leaf characteristics. Algal biomass on leaves was greatest in high‐nutrient streams and ambient‐light treatments in both seasons. Fungal biomass on leaves was greatest in high‐nutrient streams and showed a moderate marginally significant positive correlation with algae during the winter. Leaf C:N was negatively correlated to algae in winter and fungi in both seasons, while leaf N:P and C:P were negatively correlated to fungi in winter and algae in spring. Interactions between fungi and algae on leaves and the nutritional importance of each for macroinvertebrates likely change across seasons, potentially impacting macroinvertebrate community composition. Macroinvertebrate diversity did not differ, but biomass was significantly greater in shaded‐light treatments during spring. Abundance was highest in the high‐nutrient ambient‐light conditions in both seasons, corresponding to greatest algal biomass. Functional feeding guild biomass and abundance were related to different leaf characteristics by season and guild. Higher algal biomass was an important factor for colonization of certain macroinvertebrates (e.g., Ephemerella (Ephemeroptera: Ephemerellidae) and Stenonema (Ephemeroptera: Heptageniidae)), while others were more abundant under shaded treatments with lower algal biomass (e.g., Tipula (Diptera: Tipulidae)), indicating taxa‐specific responses. Leaf‐associated algae may be an important factor mediating macroinvertebrate communities associated with leaves in temperate headwater streams. Our results demonstrate that green and brown food webs intersect within leaf packs, and they cannot be easily disentangled. We therefore should consider both autochthonous and allochthonous resources within headwater streams when examining their communities or developing water management strategies.

Land use differentially alters microbial interactions and detritivore feeding during leaf decomposition in headwater streams

“…Because microbes also are key to channelling detrital energy and nutrients to upper trophic levels in streams (Marks, 2019), a second implication of autotroph-heterotroph microbial interactions is for the feeding ecology of detritivorous invertebrates (Eckert et al, 2020).…”

“…For example, most fungi and bacteria are low in essential polyunsaturated fatty acids, making them a poorquality food source compared to algae which are high in fatty acids (Guo et al, 2016). Because algae are likely to be more nutritious than heterotrophic microbes, algae growing on detritus may increase macroinvertebrate growth and feeding rates (Eckert et al, 2020).…”

“…Heavily nutrient-enriched streams, however, exhibit lower rates of leaf litter breakdown and exhibit a shift in macroinvertebrate community composition, losing species sensitive to nutrient pollution and gaining tolerant species (Eckert et al, 2020;Woodward et al, 2012). Our knowledge of nutrient pollution effects on detritivores is lacking controlled feeding responses across land-use and nutrient-pollution gradients to assess taxa-specific impacts.…”

“…Because microbes also are key to channelling detrital energy and nutrients to upper trophic levels in streams (Marks, 2019), a second implication of autotroph–heterotroph microbial interactions is for the feeding ecology of detritivorous invertebrates (Eckert et al, 2020). Detritivores rely on microbial communities, which increase the energy of decomposing leaves, an otherwise nutrient‐poor food supply (Suberkropp, 1992).…”

Multifunctional Periphytic Biofilms: Polyethylene Degradation and Cd2+ and Pb2+ Bioremediation under High Methane Scenario

“…These biofilms are classified into the following five main groups based on substrate use: epiphyton (plants), epilithon (rocks), epipelon (sediments), epixylon (wood), and epipsammon (sand). These biofilms are the constituents of phototrophic benthic microbial biofilms that play important roles as primary producers, and ultimately serve as a source of food for aquatic life [ 4 , 5 , 6 ]. They also play a crucial role in determining the degree of contamination due to their sensitivity to surrounding environmental variations and concentrations of different kinds of organic and inorganic pollutants in the aquatic ecosystem [ 7 , 8 , 9 , 10 ].…”