Invertebrate algal grazer densities were manipulated in a temperate river to discover the impact of differences in riffle-scale architectural complexity on the strength of the trophic interaction between grazers and epilithic algae. Animal densities were manipulated by manual removal in architecturally complex boulder-cobble riffles and simpler bedrock riffles, with the complexity of smaller-scale architecture held constant. Responses in algal density were recorded before and after a month of manipulations, together with grazer colonization rate and body sizes. The experiment was carried out in winter and again in summer. The interaction between grazers and algae differed between habitats and seasons. In winter, when algae were growing, the more complex riffle-scale architecture in the boulder- cobble riffles created a refuge from grazing for algae. This was probably the result of the movement abilities of the grazers interacting with habitat architecture, and potentially also due to the control of predatory fish densities by habitat architecture resulting in greater predation pressure on grazers in boulder cobble riffles. Therefore the impact of highly complex riffle-scale architecture was to weaken the strength of the trophic interaction between algae and their grazers by reducing grazer densities, while potentially strengthening the trophic interaction between grazers and their fish predators.

Item Type:	Refereed Article
Research Division:	Biological Sciences
Research Group:	Ecology
Research Field:	Freshwater ecology
Objective Division:	Expanding Knowledge
Objective Group:	Expanding knowledge
Objective Field:	Expanding knowledge in the environmental sciences
UTAS Author:	Robson, BJ (Ms Belinda Jane Robson)
ID Code:	8733
Year Published:	1996
Web of Science® Times Cited:	16
Deposited By:	Zoology
Deposited On:	1996-08-01
Last Modified:	2011-08-19
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