Habitat structure, resources and diversity: the separate effects of surface roughness and macroalgae on stream invertebrates

Abstract

Habitat structure has pervasive effects on community composition and diversity, with physically complex habitats often containing more species than physically simple ones. What factors or mechanism drive this pattern is little understood, but a complicating problem is that different sources of habitat structure can be confounded in both surveys and experiments. In this study, we carried out an experiment in which two sources of habitat structure, attached macroalgae and substrate surface texture, were separately manipulated to discern their joint and separate effects upon the diversity and composition of colonizing macroinvertebrates in a stony, upland stream. Because stream algae vary markedly in abundance in both space and time, we also sampled the epilithon of stream stones at two spatial scales on eight dates over 2 years to gain some preliminary data on how stream algae vary between individual substrata over time. Experimental substrata had either a smooth (siltstones, sandstones, crystal-poor felsic volcanics, plain paving bricks) or rough (granodiorites, crystal-rich felsic volcanics, sand-blasted paving bricks) surface. We allowed these substrata to be colonized naturally by macroalgae, mostly the filamentous red alga Audouinella hermannii. Half of each of the rough and smooth substrata were selected at random and the macroalgae gently sheared off. All substrata were defaunated with a household insecticide with little field persistence, set out randomly through the study riffle, and invertebrates allowed to colonize them for 14 days. Some substrata were sampled immediately to check the efficacy of faunal and algal removals, which proved to be successful. Experimental results showed that both surface texture and macroalgae increase species richness independently of each other. Surface texture had no effect on densities, while macroalgae increased colonization densities, but rarefaction showed that both sources of habitat structure increased species richness above values expected simply on the basis of the numbers of colonists. However, reference stones with high macroalgal cover had the same species richness as those with low cover, suggesting that the effects of macroalgae on species richness are transient relative to those associated with surface texture. Epilithon samples taken at different times suggest that the magnitude of spatial variation in plant growth alters with time. If plants generally recolonize rough surfaces more quickly than smooth, then the effects of habitat structure on macroinvertebrates ought to be strongest after major disturbances during growing seasons of plants.

Effects of grade control structures on the macroinvertebrate assemblage of an agriculturally impacted stream

“…Our results are consistent with previous studies finding overall positive effects of coarse substrate on macroinvertebrate assemblages (Beisel et al, 1998;Downes et al, 2000;Negishi and Richardson, 2003). Figure 5.…”

“…GCS rip-rap sampled in this study supported substantially greater abundance and diversity of benthic macroinvertebrates than sites dominated by fine substrate. In both lentic and lotic ecosystems, rocks, woody debris and a variety of other structurally complex substrates usually support higher macroinvertebrate abundance and diversity than finer substrates (Schmude et al, 1998;Downes et al, 2000;Voelz and McArthur, 2000). Relative to fine, soft substrates, both natural and artificial coarse substrates provide greater surface area for colonization and foraging and reduce likelihood of localized extinctions due to chance (Downes et al, 2000).…”

“…In both lentic and lotic ecosystems, rocks, woody debris and a variety of other structurally complex substrates usually support higher macroinvertebrate abundance and diversity than finer substrates (Schmude et al, 1998;Downes et al, 2000;Voelz and McArthur, 2000). Relative to fine, soft substrates, both natural and artificial coarse substrates provide greater surface area for colonization and foraging and reduce likelihood of localized extinctions due to chance (Downes et al, 2000). In streams, heterogeneous habitat created by coarse substrates also support taxa with diverse requirements, and provide refuges from predation and shear forces caused by floods (Hart and Finelli, 1999;Voelz and McArthur, 2000).…”

“…Environmental features, including flow velocity, depth, canopy cover, water chemistry and food supply, have been shown to affect the composition and distribution of macroinvertebrate communities (Merritt and Cummins, 1996). In particular, substrate is a primary determinant of community structure, with taxa richness and total macroinvertebrate abundance often increasing with increased habitat heterogeneity (Beisel et al, 1998;Downes et al, 2000;Negishi and Richardson, 2003). Previous studies demonstrated that macroinvertebrates readily colonize rip-rap and boulders placed in lakes and streams, and achieve relatively high levels of abundance and diversity because of increased habitat surface area and complexity offered by these substrates (Schmude et al, 1998;Negishi and Richardson, 2003).…”

Impacts of a Small Dam on Riverine Zooplankton

“…Physical habitat was considered as a primary factor influencing the structure, composition and diversity of stream faunal communities (LAMMERT and ALLAN, 1999;DOWNES et al, 2000). Many stream organisms ranging from algae and aquatic plants to invertebrates and fish have close associations with the physical habitat, which is mainly determined by flow in streams (BUNN and ARTHINGTON, 2002).…”