Resistance and Resilience of Lotic Algal Communities: Importance of Disturbance Timing and Current

Abstract

We examined effects of disturbance timing on resistance and resilience of epilithic algal communities growing in fast— (29 cm/s) and slow— (12 cm/s) current outdoor experimental stream channels in Kentucky, USA that were either left undisturbed (control) over 33 d following a simulated spate, or were subjected to an additional spate after either 9, 18, 27, 33 d. On day 33, all channels were subjected to a final spate to assess effects of short—term disturbance history on resistance, independently of seasonal influences. Succession proceeded from a sparsely populated community dominated by a small, monoraphid diatom (Achnanthes minutissima) immediately after the initial spate, to dominance by dense floating mats of filamentous green algae (Zygnematales: Mougeotia and Spirogyra) and Synedra spp. by day 21—24. Resistance was generally lower in slow—current communities, both in terms of cell—density reduction and displacement of taxonomic structure, than in fast—current communities. Resistance in slow—current communities varied temporally, with communities least resistant on day 18, when community composition and physiognomy was changing rapidly, and on day 33, when green algal mats began to senesce. On day 33, slow—current communities that had not been recently disturbed (control, D9) exhibited greatest spate—induced loss of algal biomass. Additionally, slow—current communities with high pre—disturbance phaeophytin content (an indicator of algal senescence) also changed most in diatom assemblage structure across the final spate. No such relationship was noted in fast current, suggesting that autogenic factors influenced communities in slow current more than those in fast. Resilience was higher in slow—current communities than in fast current, with disturbed communities reaching biomass and taxonomic structure similar to controls after 3—9 d. High resilience in slow current resulted from enhanced reproduction in some populations following spate—induced biomass reduction and presumed release from nutrient and light limitation, and low shear stress relative to fast—current channels where biomass accrual was limited by current. Interactions between disturbance timing, successional state, and habitat affect the susceptibility of epilithic algal communities to disturbance and likely influence temporal and spatial heterogeneity in stream ecosystems.

Spatial and seasonal variations in benthic algal assemblages in streams in monsoonal Hong Kong

“…Elsewhere, grazers can limit algal standing stocks in conditions that are otherwise favourable to production, and thus regulate biomass at levels lower than limits imposed by physical factors (Rosemond 1994;Hillebrand, 2005), or even alter the susceptibility of algal assemblages to spate-induced disturbance (Pringle & Hamazaki, 1997). In general, algae with erect or upright growth forms are vulnerable to scour, abrasion or sloughing (Peterson & Stevenson, 1992;Biggs & Thomsen, 1995) whereas prostrate taxa that adhere tightly to the substratum are relatively resistant (Luttenton & Rada, 1986;Bergey & Resh, 2006;Francoeur & Biggs, 2006). We did not observe a seasonal shift from assemblages dominated by upright taxa in the dry season to adherent taxa during the wet season, and variations in assemblage composition were due to minor changes in the relative abundance of species common throughout the study.…”

“…Biggs & Thomsen, 1995;Burkholder, 1996;Hill, 1996;Stevenson, 1996;Roberts et al, 2004;Hillebrand, 2005). Physical disturbance during spates, leading to washout, abrasion and scouring of the substratum, can cause dramatic declines in benthic algal biomass (Power & Stewart, 1987;Grimm & Fisher, 1989;Stevenson, 1990;Bergey & Resh, 2006), and assemblage composition in spate-prone streams may be dominated by prostrate species (mainly diatoms) that are less vulnerable to abrasion and turbulent flow (Luttenton & Rada, 1986;Peterson & Stevenson, 1992;Bergey & Resh, 2006;Francoeur & Biggs, 2006).…”

Responses of epibenthic algal assemblages to water abstraction in Hong Kong streams

“…The strength of grazing pressure upon epibenthic algae can vary according to flow conditions (Poff & Ward, 1995;Chester & Norris, 2006), potentially influencing the intensity of topdown control of assemblage composition and biomass (Opsahl et al, 2003). Because of the complex interactions among abiotic factors, such as discharge and nutrients, and biotic factors (Peterson & Stevenson, 1992;Ledger et al, 2008), the effects of flow on epibenthic algal assemblages vary substantially according to stream conditions (Jowett & Duncan, 1990;Downes et al, 2003;Wu et al, 2010).…”

The disturbance-driven changes of periphytic algal communities in a Danubian floodplain lake

“…At the same time, the denuded substrates were suitable for new colonizers, as evidenced by the high algal diversity. Given that microalgal growth is influenced by algal densities on the substrata, it is likely that the reductions in cell density increased the supply of nutrients and light to both persistent cells and new immigrants, thereby stimulating reproduction in a subset of populations (Peterson and Stevenson, 1992). The significant increase of the vertically positioned Nitzschia amphibia and the stalk-forming diatoms (G. parvulum and N. cryptocephala) contributed to a progressive development into a complex three-dimensional community.…”

“…substrate movement, rapid changes in hydraulic forces, heat, light) being mere episodes, can remove organisms at rates faster than the rates of accrual or recruitment (Stanley et al, 2010). Numerous investigations have been conducted in order to elucidate periphyton responses to disturbances, focusing on the resistance and resilience of lotic algal communities (Peterson and Stevenson, 1992). A particularly prominent one was a habitat matrix conceptual model for stream periphyton defined by Biggs et al (1998).…”