Experimental Analysis of the Grazing Interaction Between a Mayfly and Stream Algae

Area of Science:

• Ecology
• Aquatic Biology
• Stream Ecology

Background:

• Periphyton, the community of organisms attached to submerged surfaces, forms the base of many aquatic food webs.
• Grazing invertebrates play a crucial role in structuring periphyton communities and influencing nutrient cycling.
• The mayfly Ameletus validus is a common grazer in northern California streams, but its impact on periphyton is not fully understood.

Purpose of the Study:

• To investigate the interaction between the grazing mayfly Ameletus validus and periphyton in a northern California stream.
• To determine how manipulating mayfly density affects periphyton biomass, structure, and algal community composition.
• To assess the impact of grazing on mayfly growth and infer population dynamics.

Main Methods:

• In situ flow-through plexiglass channels with natural cobble substrate were used to manipulate A. validus densities (0, 0.5, 1, and 4 times average).
• Periphyton standing crop (ash-free dry mass) and chlorophyll a content were measured after 23 days.
• Algal relative abundances were analyzed using principal component analysis to assess community structure changes.

Main Results:

• A. validus significantly reduced periphyton standing crop (AFDM) with increasing grazer density.
• Grazing increased chlorophyll a per unit biomass and decreased the relative contribution of the loose periphyton layer.
• Diatom community structure shifted, with a decrease in loose-layer species and an increase in adnate species, potentially mediated by sediment reduction.

Conclusions:

• Ameletus validus grazing strongly influences periphyton biomass and community structure in this stream ecosystem.
• The observed density-dependent growth of A. validus suggests that this mayfly population is food-limited in Barnwell Creek.
• Understanding these interactions is vital for managing stream ecosystems and predicting the effects of altered grazer populations.