Crevices as refugia for stream diatoms: Effect of crevice size on abraded substrates

Abstract

This study explored the mechanisms by which crevices act as refugia for small algae during abrasive disturbances. Four substrates with different crevice features were subjected to three levels of abrasion in a stream-based experiment. Substrates were sand-grain caddisfly cases and three glass rod substrates that mimicked caddisfly cases in size and shape, as well as forming a gradient of larger crevices (i.e., smooth with no crevices, sanded with shallow pits, and scratched with deeper grooves). Substrates were subjected to no, low, or high abrasion levels during 18 d of incubation by pulling substrates through a sand-gravel mixture in floating enclosures that housed the experiment. Diatom density, relative biovolume, location in crevices, detritus accumulation, and filamentous algal density were compared among substrate types and abrasion levels. Across all abrasion levels, diatom and filamentous algal densities were higher on caddisfly cases than on all three glass rod substrates. Although abrasion greatly reduced overall diatom density, diatoms within crevices were largely protected. Crevice size influenced diatom size and composition. The small crevices of sanded rods contained primarily small diatoms of a single species (Achnanthidium minutissimum), whereas the larger crevices of scratched rods and caddisfly cases contained a greater range of diatom size and, consequently, greater species diversity. Detritus accumulated in all crevices, and accumulation increased with level of abrasion. Diatom biovolume decreased and location in crevices increased with the level of abrasion on the less textured smooth and sanded glass rods. Abrasion level had little effect on algal assemblages on caddisfly cases. This study demonstrates that crevices can be important refugia from abrasive disturbances, and that the size of crevices relative to organismal size can influence the protective value of crevices.

Settlement preferences of leeches (Clitellata: Hirudinida) for different artificial substrates

“…Bergey (1999) showed that small crevices on rough surfaces are used by the diatoms as refuge against water waves and grazer pressure, resulting in more intensive development of periphyton on less smooth surfaces. Hart (1978), Clifford et al (1989) and Bergey (1999) noted that small aquatic organisms and detrital particles accumulate in depressions on rough surfaces which result in greater diversity and abundance of macroinvertebrates. Thus, an increase in food resources can be a key factor in more numerous occurrences of both predator and parasite leeches.…”

Effects of crevice size on the establishment of macroalgae in subtropical streams

“…Probably, the deposition of algae within the crevices is due to the accumulation of debris in them and the possible establishment of refuges (Bergey, 1999;Nowell and Jumars, 1984;Davis and Barmuta, 1989;Snelgrove et al, 1993). In the present study we tested surfaces with crevice sizes greater than previous studies (with periphytic community) considering that macroalgae would require larger crevices to get refuge, as reported for larger diatoms (Bergey, 1999). Actually, we found macroalgae within the crevices, but the shapes and dimensions used seemed to be insufficient and then limiting the growth of these organisms.…”

“…Nevertheless, investigating crevices size as refugia for diatoms, Bergey (1999) found that larger crevices had a better protection for larger algae. As macroalgae have a greater size and no experimental investigation focusing on influence of crevice size on development of this algal community was yet conducted, we carried out the present study to investigate the colonization and the establishment of macroalgal community on surfaces with milimetric crevices, a scale slightly higher than previous investigations.…”

Influence of substratum surface roughness on periphytic algal community structure in a shallow tropical reservoir

“…In lotic ecosystem, the higher proportion of algae firmly adhered to surface roughness can suggest the community resistance to scouring (Murdock and Dodds, 2007). The physical properties can have effects on resistance and resilience of the algal community in the face of environmental perturbations (Bergey, 1999, …”

“…The topography of the microhabitat is defined by irregularities on the substrate surface (depressions, crevices and protrusions), which may influence biomass accumulation (Johnson, 1994), cell adhesion (Sekar et al, 2004) and algae susceptibility to grazing and scouring (Bergey, 1999, Bergey andWeaver, 2004). The surface irregularities can also minimize water flow action around the substrate, modifying the diffusion boundary layers (De Nicola andMcIntire, 1990, Dodds andBiggs, 2002).…”