Stream periphyton response to grazing and changes in phosphorus concentration

Abstract

Grazing by the large caddisfly larva, Dicosmoecus gilvipes (Trichoptera; Limnephilidae), drastically reduced periphyton biomass in laboratory channels at a current velocity of 20 cm s-' . Reduction in biomass as chl a and AFDW ranged from 88 to 93% and 82 to 85%, respectively. On average, grazing rate increased with in-channel SRP (soluble reactive phosphorus) content from 6 to 10 pg 1-l. Grazing rates averaged 25.9-29.3 pg chl a mm2 d-i and 10.8-12.2 pg chl a mg-' d-' based o n area and grazer biomass, respectively, with most variability among treatments being due to the grazing effect. Grazing tended to shift the algal community increasingly to filamentous blue-green algae regardless of enrichment. After three weeks, Phormidium comprised over 61% of the community in grazed treatments but only 35% in ungrazed treatments. The stalked diatom Gomphonema comprised only 4% of the grazed community, but 11% in the three ungrazed channels with similar values for Scenedesmus. A model that includes grazing was calibrated to the data and produced a reasonable expectation of periphyton biomass over a range in SRP concentrations. While the model with constant grazer abundance predicts a gradually increasing grazed biomass as SRP increases, grazer production in natural streams may actually increase to accommodate the increased food production.

Food Limitation Affects Algivory and Grazer Performance for New Zealand Stream Macroinvertebrates

“…However, the relative frequency of erect, physiognomic forms of diatoms was significantly lower in our mayfly-and caddisfly-containing treatments compared to ungrazed controls. Moreover, all three grazer types significantly reduced the abundance of filamentous green algae, corroborating the results of similar studies (Jacoby, 1987;Lamberti et al, 1987a;Walton et al, 1995;Anderson et al, 1999;Opsahl et al, 2003). Though rare, the filamentous green algae Mougeotia sp.…”

Factors regulating epilithic biofilm carbon cycling and release with nutrient enrichment in headwater streams

“…Grazing activity has been found to be an important mechanism controlling the release of allochthonous DOC in streams (Meyer & O'hop, 1983) and the same may be the case for autochthonous C sources. Although increased activity of green algae may enhance grazing activities by increasing palatability of the biofilm and/or providing larger algal food sources (Walton et al, 1995), these biofilms are more likely regulated by bottom up controls due to disturbance regimes in these streams (Lohman et al, 1991;Fritz & Dodds, 2002). Further, green algae may exhibit high rates of exudation relative to other algae and cyanobacteria particularly with high light availability in streams with unforested riparian zones.…”

“…Low statistical power caused by the small sample size and our inability to test other factors, such as light availability, substrate, and grazing activities, and their possible combined effects with nutrient availability likely prevented the detection of any strong explanatory factors for the specific phototrophic group activities measured. For example, elevated nutrients have been noted to stimulate algal growth (Stevenson et al, 2006) and interact with other factors, such as light, causing changes in grazing rates, and algal community composition (Steinman et al, 1991;Walton et al, 1995;Liess et al, 2009). …”

Modelling Primary Producer Interaction and Composition: an Example of a UK Lowland River

“…Finally, there is some evidence that the biomass/chlorophyll-a ratio of algae changes with increasing grazing [74], because the algal community shifts to more filamentous species with thicker walls upon severe grazing, regardless of enrichment. To simplify the model, this ratio was assumed to be constant in this model (Ratio C:Chl-a ).…”