Effects of consumer identity and disturbance on stream mesocosm structure and function

Abstract

Consumers can alter the structure and function of aquatic ecosystems, but the interactions that regulate ecosystem functioning are context dependent. In many streams, environmental disturbance and consumer identity may interact to influence benthic ecosystem structure and function. We predicted that effects of two common consumers (central stonerollers (Campostoma anomalum), and Meek's crayfish (Orconectes meeki meeki)) in Ozark Mountain streams (Arkansas, USA) would be altered by disturbance. In stream mesocosms we crossed disturbance (simulated spate) and consumer identity (crayfish, central stonerollers, or no consumers). Stream ecosystem function was quantified as leafpack decomposition and net primary productivity (NPP). Ecosystem structure was measured as algal chlorophyll-a, ash-free dry mass (AFDM), and chironomid density. Disturbance and interactions between disturbance and consumer identity did not significantly affect any response variable. Chlorophyll-a, AFDM, and chironomid density were influenced by consumer identity, and effects differed between stonerollers and crayfish and with time. Crayfish and stonerollers reduced day 15 chironomid density compared with no consumer treatments. Stonerollers reduced day 30 chironomid density and day 15 periphyton abundance compared with crayfish and no consumer treatments. Crayfish increased leafpack breakdown rates above stoneroller and no consumer treatments, but NPP did not differ among consumer treatments. In this experiment, consumers had stronger effects on benthic structure and function than the disturbance treatment. Future studies should investigate a wider range of disturbance frequency and intensity.