Chemosensory signals in stream habitats: implications for ecological interactions Mary C. Wolf 1 Center for Marine Science, University of North Carolina Wilmington, Wilmington, North Carolina 28403 USA Arthur L. Martin, III 2 Department of Biology, Saginaw Valley State University, Saginaw, Michigan 48710 USA Jodie L. Simon 3 , Jennifer L. Bergner 4 , AND Paul A. Moore 5 Laboratory for Sensory Ecology, J. P. Scott Center for Neuroscience, Mind and Behavior, Department of Biological Sciences, Bowling Green State University, Bowling Green, Ohio 43403 USA and University of Michigan Biological Station, 9133 East State Street, Pellston, Michigan 49769 USA Abstract. The combination of varying aquatic habitats and flow regimes creates a complex stimulus environment from which sensory information can be extracted. Previous studies with crayfish in artificial stream settings have shown that altering the temporal and spatial structure of an odor plume modifies orientation behavior. Exposure to more temporally complex odor signals enables crayfish to locate food more efficiently. To link these studies to a more natural setting, we examined how odor signals are dispersed in 3 physically different habitats within the Maple River in Pellston, Michigan, USA, by simultaneously measuring flow patterns and odor plume characteristics. These microhabitats consisted of sections of the stream with gravel, transition (gravel and sand), or sand substrate. Flow measurements were taken using an Acoustic Doppler Velocimeter while simultaneous in situ odor plume measurements were made with an Epsilon electrochemical system. Flow had more turbulent energy in gravel and transition habitats than in sand habitat. Mean velocity was significantly higher in gravel (67.8 6 2.00 cm/s) than in transition (30.5 6 0.46 cm/s) and sand (30.6 6 0.27 cm/s) habitats. In addition, eddy diffusivity rates were higher in gravel (173.3 cm 2 /s 3 ) than in sand (9.74 cm 2 /s 3 ) and transition (129.7 cm 2 /s 3 ) habitats. Differences in turbulent flow profoundly affected the fine-scale distribution of the chemical signal. The concentration of dopamine tracer in odor pulses was significantly lower in sand (range: 8.1–6.9 mmol/L) and transition (range: 26.2–8.9 mmol/L) habitats than in gravel (range: 46.5–5.39 mmol/L) habitat. Background (natural) concentrations of dopamine are undetectable with our current technology. Furthermore, spectral density of odor pulses showed larger fluctuations in chemical concentration at all frequencies (0.1–10 Hz) in gravel habitat than in sand or transition habitats. Our results illustrate the dynamic nature of turbulence structure within natural stream systems and its influence on the distribution of chemical odor signals. Our results provide evidence that natural stream settings influence both the distribution and concentration of chemical odors available for ecological and behavioral interactions. The combination of turbulence and odor plume variation creates habitat-specific information that influences orientation behavior of organisms within a river. Key words: river substrate, turbulence, odor plume dynamics, chemical signals, fluid dynamics, benthic organisms, orientation behavior. Ecological interactions in aquatic environments are mediated by information gathered through sensory systems. Inter- and intraspecific interactions rely on available sensory information, which in turn, can affect survivorship and reproduction of organisms in aquatic ecosystems. Organisms have a variety of 1 E-mail addresses: wolfm@uncw.edu 2 almarti2@svsu.edu 3 jsimon@bgsu.edu 4 jbergne@bgsu.edu 5 To whom correspondence should be addressed. pmoore@bgnet.bgsu.edu J. N. Am. Benthol. Soc., 2009, 28(3):560–571 ’ 2009 by The North American Benthological Society DOI: 10.1899/08-108.1 Published online 26 May 2009 560