Shifting effects of rock roughness across a benthic food web

Abstract

Habitat heterogeneity affects the spatial pattern of stream organisms, but it is unclear how broadly heterogeneity affects the distribution of organisms within a food web. Specifically, rougher rocks have greater algal biomass than smoother rocks, and we hypothesized bottom-up food web control of food web structure, in which rougher rocks would also have higher grazer and predator abundance. We surveyed algal biomass and macroinvertebrates on rocks of differing roughness. We also conducted a field experiment to separately examine rock roughness and algal biomass effects by manipulating algal biomass by raking or scrubbing rocks within created rock clusters. Neither the survey nor the experiment strongly supported a bottom-up scenario. Algal biomass increased with rock roughness. Grazing mayfly abundance was distributed evenly among geologic rock types, except for a higher abundance of baetids on rocks with large cavities, where predatory stoneflies were also abundant. In the rock cluster experiment, the moderate raking disturbance produced higher grazer abundance and reduced algal biomass relative to unmanipulated controls. We concluded that fine-scale roughness directly promoted algal biomass, whereas larger-grain roughness (crevices) affected the distribution of the food web components by forming clumped distributions of grazing baetid mayflies and predatory stoneflies.

Comparison of a wood sampler for macroinvertebrate bioassessment of non-wadeable streams in the southeastern coastal plain

“…Moreover, this study provided an assessment of passive sampling devices in large (i.e., non-wadeable) rivers of the southeastern Coastal Plain, where fine sediments and variable discharge often limit the use of common active sampling techniques. In previous studies, dissimilarities in the taxonomic composition of macroinvertebrates colonizing artificial substrates have been attributed to differences in the roughness and particle size of the samplers (O'Conner 1991;Schmude et al 1998;Downes et al 2000;Bergey and Cooper 2015). Furthermore, Brua et al (2011) hypothesized that semi-quantitative sampling methods collected more widespread animals (e.g., Chironomidae) rather than rare, narrowly distributed taxa because of a lack of standardization of area sampled.…”

“…While studying a lowland stream in northern Victoria, O'Connor (1991) determined that the number of individuals collected was attributed to roughness or particle size of substrates. Surface complexity (i.e., particle size or roughness) has been observed as affecting abundance and diversity (De Pauw et al 1994;Downes et al 2000;Adamiak-Brud et al 2015;Bergey and Cooper 2015) due to the physically complex habitat which provides different niche exploitation to occur. Leaf samplers could have a less complex or rough surface than Hester-Dendy or wood samplers and may be a physically less complex habitat that would allow for less niche diversification to occur (Downes et al 1998).…”

“…From these studies, habitat selection by benthic macroinvertebrates has been determined as an important mechanism for assessing macroinvertebrate community composition, richness, distribution, and density (Magoulick 1998). Substrate type, particle size, texture, and mesh size are important in influencing macroinvertebrate distribution and structure (Battle et al 2007;Bergey and Cooper 2015). These and similar studies have suggested the importance of habitat selection based on substrate characteristics using artificial substrates to determine habitat preferences (Czerniawska-Kusza 2004;Hoffmann 2005).…”

A River of Bones: Wildebeest Skeletons Leave a Legacy of Mass Mortality in the Mara River, Kenya

“…In the river, biofilms growing on bones had five times more chl a and two times more OM than biofilms growing on rocks (Figure 8), suggesting bones may support greater quantity and/or quality of biofilms. Increased biofilm growth on bones could be due to leaching of nutrients from the bones and/or greater surface roughness of bones as compared to rocks, which could provide increased surface area for growth (Bergey and Cooper, 2015). There did not appear to be a difference in algal composition on bones versus rocks (Figure 9).…”