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

Abstract

The interaction between the grazing mayfly Ameletus validus and periphyton in a small, northern California stream was examined by manipulating the density of the mayfly in flow-through plexiglass channels. Containing natural cobble substrate and located in situ, the channels established an initial gradient of A. validus at 0, 0.5, 1, and 4 times the average density of the mayfly in Barnwell Creek. After 23 d, A. validus significantly depressed periphyton standing crop: ash-free dry mass (AFDM) at the 0, 0.5, 1, and 4 N grazer densities was 5.067 ± 1.389 (se), 1.829 ± 0.173, 1.741 ± 0.325, and 1.009 ± 0.199 g/m (ANOVA: P < .01). The mayfly also influenced two structural attributes of the periphyton, increasing the amount of chlorophyll a per unit biomass and decreasing the relative contribution of the loose, upper layer to total periphyton biomass. Principal component analysis of algal relative abundances contrasted the effect of grazing on two groups of diatoms. A group of species found primarily in the loose layer of periphyton (Nitzschia spp., Surirella spiralis, Cymatopleura elliptica, and Navicula cryptocephala) was disproportionately reduced in abundance, while an adnate group (Gomphonema clevei, Achnanthes minutissima, Synedra ulna, Rhoicosphenia curvata, and an undescribed species of Epithemia) increased its relative abundance with increasing grazing pressure. The decline in relative abundance of the loose layer diatoms did not appear to result from selective consumption by A. validus, but may have been mediated by a reduction of inorganic sediment in the periphyton by A. validus. Inorganic sediment was highly correlated with the relative abundances of the loose layer group of diatoms, a group of species that are adapted for locomotion on sediment substrates. A. validus growth in the experimental channels was strongly density dependent. Growth in length over 23 d for the 0.5, 1, and 4 N treatments was 2.24 ± 0.17, 1.80 ± 0.23, and 1.15 ± 0.25 mm (ANOVA: P < .01). The significantly greater growth of A. validus at subnormal densities in the experimental channels suggested that the A. validus population in Barnwell Creek was food-limited.

Competition between toxic Microcystis aeruginosa and nontoxic Microcystis wesenbergii with Anabaena PCC7120

“…The nontoxic strain Microcystis wesenbergii FACHB-929 (Mw929) was isolated from Lake Dianchi in China and was also obtained from the FACHB-Collection. Mean cell dimensions of the three strains were measured using an ocular micrometer at ×400 magnification (Hill and Knight 1987). Cell densities of cultures were converted to biovolume (μm 3 L −1 ) for each strain using the formula for the geometric shape roughly appropriate for the taxon (Hillebrand et al 1999).…”

Longitudinal patterns of periphyton biomass in Qinghai–Tibetan Plateau streams: An indicator of pasture degradation?

“…attached algae, bacteria and fungi) to a greater extent, play a key role in stream ecosystems (Schiller et al, 2007). Periphyta are commonly the dominant source of primary production in streams , providing high-quality food for a diverse group of vertebrate and invertebrate grazers (Power and Matthews, 1983;Hill and Knight, 1987). Although periphyta make up only a minor component of the total ecosystem carbon budget, they are vitally important for maintaining secondary production in streams (Mayer and Likens, 1987;Hall et al, 2001;McCutchan and Lewis, 2002).…”

Concurrent grazing effects of two stream insects on periphyton1

“…Only recently have field experiments been reported in which insect grazers have been excluded from stream periphyton (Lamberti and Resh 1983;McAuliffc 1984;Murphy 1984;Hart 1985a;Hill and Knight 1987).…”

“…Ameletus does not have scraping-type mandibles, but harvests diatoms and other fine particles in the periphyton with collector-gatherer mouthparts (Merritt and Cummins 1984). In a singlegrazer experiment, Ameletus substantially reduced periphyton standing crop and altered algal assemblage structure (Hill and Knight 1987). To measure the simultaneous grazing effects of Neophylax and Am&e&s, we manipulated the densities of these grazers and observed the effects on periphyton 15 standing crop and algal assemblage structure.…”