Academic journal article The American Midland Naturalist

Differential Response of Algae on Small Streambed Substrates to Floods

Academic journal article The American Midland Naturalist

Differential Response of Algae on Small Streambed Substrates to Floods

Article excerpt

ABSTRACT.-

The effect of floods and base flow on temporal variation in algal biomass on small smooth streambed stones and creviced sand-cases of the caddisfly (Insecta: Trichoptera) Gumaga nigricula was examined in Big Sulphur Creek in coastal Northern California. Replicates of stones and cases were sampled 34 times over a 14 mo period that included nine floods. Stones had ~2× the algal biomass of cases, based on chlorophyll a concentration. The lower algal biomass on caddisfly cases is consistent with this species' burrowing behavior, which reduces algal biomass by abrasion and light limitation. Algal biomass on stones was reduced by floods and generally increased in the absence of floods. In contrast, neither floods nor extended base flow affected the pattern of algal biomass on caddisfly cases, and biomass on caddisfly cases often exceeded that on stones following floods. Streambed substrates with different textures may provide different degrees of disturbance-protection for benthic microalgae, and rougher substrates in streams may have more relict algae following floods than smoother substrates.

INTRODUCTION

The beds of most streams contain several different types of inorganic substrates that vary in size, shape and parent rock. Even in streams with apparently homogeneous parent rock types, there can be variation in crystal size, the distribution of intrusions and the amount of weathering.

Small-sized (<2 mm in diameter) inorganic particles of sand and silt are a major compositional component of the substrate in the majority of benthic habitats. They are also an essential component of the cases made by many species of caddisfly (Trichoptera) larvae. Most caddisfly cases, if examined at fine scales, are far from smooth (e.g., see case illustrations in Wiggins, 1996). Their surface roughness is an example of the type of small-scale spatial heterogeneity of benthic substrates that has been implicated in the colonization, establishment and protection of algae from some disturbances (e.g., Dudley and D'Antonio, 1991; Bergey and Resh, 1994).

Surface roughness on stream beds consists of low areas or crevices and raised exposed areas (Johnson, 1994). Many algae settle in crevices (Dudley and D'Antonio, 1991; Downes et al., 1998) and their survival may be enhanced by surface roughness because of the protection offered within crevices (Dudley and D'Antonio, 1991). Consequently, more algae are often found on rough than smooth substrates (Hardin and Lindbergh, 1977; Clifford et al., 1992).

Crevices and other refuges can protect organisms when the sizes of the organism (s) and the refuge, and the scale of the disturbance are appropriate (Bergey, 1999; Bergey and Weaver, 2004). That is, to be protected, organisms must be able to fit within the space of the refuge and also be sheltered from the effects of disturbance. Crevices have been implicated in protection from disturbances such as grazers and predators (Lubchenco, 1983; Dudley and D'Antonio, 1991), abrasion (Bergey and Resh, 1994; Bergey, 1999), water flow (Holomuzki and Biggs, 1999) and desiccation (Gosselin and Chia, 1995).

In streams, floods are a major disturbance. Floods reduce algal biomass on streambed substrates (Power and Stewart, 1987; Grimm and Fisher, 1989), influence algal richness (Biggs and Smith, 2002) and patchiness (Matthaei et al., 2003) and affect the temporal pattern of algal biomass in many streams (directly: Biggs and Close, 1989; indirectly through altering grazer density: Power, 1992; Marks et al, 2000).

The protection of benthic algae in crevices can affect the recovery trajectories of algal assemblages following scouring floods. Algae remaining in crevices following floods include both microalgae, such as diatoms that may fit entirely within crevices, and holdfasts of attached filamentous algae, such as Cladophora glomerata (L.) Kützing. (Dudley and D'Antonio, 1991; Bergey, 1999). Algae remaining in crevices after disturbance are relict algae that can contribute to the rapid recovery of algal assemblages by direct growth, and by supplementing algal drift and subsequent settlement. …

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