How do grazers affect periphyton heterogeneity in streams?

Area of Science:

• Ecology
• Aquatic Ecology
• Stream Ecology

Background:

• Stream invertebrates significantly influence periphyton communities.
• Grazer behavior, including foraging activity and mobility, can alter algal biomass and spatial distribution.
• Predator cues can modify invertebrate grazing behavior, impacting ecosystem processes.

Purpose of the Study:

• To experimentally investigate the effects of grazing by stream invertebrates on algal biomass and spatial heterogeneity.
• To determine how grazer mobility and predator presence influence periphyton dynamics.
• To explore the mechanisms by which grazers like Baetis bicaudatus affect algal resources under different conditions.

Main Methods:

• Used flow-through microcosms with natural substrates (rocks) to simulate stream conditions.
• Conducted experiments with fixed densities of three grazer species (caddisfly, Epeorus, Baetis) and manipulated predator cues.
• Employed a three-factorial design to test effects of resource distribution, grazer density, and predator odor on algal resources.

Main Results:

• Grazing reduced mean algal biomass (chlorophyll a) but did not differ among grazer types.
• Algal heterogeneity increased with grazer mobility, with the most mobile grazer (Baetis without fish cues) showing the highest heterogeneity.
• Baetis exhibited resource tracking, selecting high-food rocks when resources were heterogeneously distributed, maintaining initial resource heterogeneity.

Conclusions:

• Mobile stream grazers can significantly alter algal spatial heterogeneity.
• Grazer foraging behavior, influenced by predator cues, plays a crucial role in structuring periphyton communities.
• Mobile grazers like Baetis bicaudatus have the potential to maintain observed periphyton distributions in natural streams.