Does ambient substrate composition influence consumer diversity effects on algal removal? |
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Authors: | Todd Wellnitz Matt Troia Megan Ring |
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Institution: | (1) Biology Department, University of Wisconsin—Eau Claire, Eau Claire, WI 54702-4004, USA;(2) Biology Department, University of Texas at Tyler, Tyler, TX 75799-6699, USA |
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Abstract: | Benthic substrates constitute an important habitat template for aquatic communities and may affect the contributions of benthic
organisms to ecological processes. To test the effects of ambient substrate composition on the process of algae accrual and
removal, we conducted an experiment to examine how substrate type influenced consumer richness effects. We hypothesized that
algal removal from focal substrates (ceramic tiles) would be influenced by the surrounding ambient substrate through its effect
on nutrient cycling and subsequent algal growth. We manipulated consumer richness in mesocosms at one or three species while
holding consumer biomass constant. Aquatic consumers were an amphipod, a snail, and a water boatman, and ambient substrates
were either sand or gravel. After 21 days, ambient substrate influenced epilithic algal accrual on tiles, affected physio-chemical
parameters within mesocosms, and modified consumer behavior. Chlorophyll a was approximately 2× greater on control tiles surrounded by sand, and FPOM and turbidity were greater on sand than gravel
when consumers were present. Substrate modified consumer behavior such that consumers congregated around focal substrates
in sand, but dispersed around them in gravel. Consumers also had substrate-specific influences on epilithic chlorophyll, causing
a decrease in sand and an increase in gravel. Algal assemblages on focal tiles were dominated by diatoms, and their composition
responded to consumer richness and identity, but not substrate. Our data suggest that direct effects (e.g., consumptive removal
of epilithon from focal tiles) were more pronounced in sand, whereas indirect effects (e.g., bioturbation and enhanced mixing)
promoted algal accrual in gravel. These results show that algae production on exposed surfaces may change as underlying substrate
composition changes, and that substrate type can alter consumer diversity effects on algal removal. |
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