Orientation in complex chemical landscapes: Spatial arrangement of chemical sources influences crayfish food-finding efficiency in artificial streams

Fluid dynamics has been shown to alter ecologically important behaviors of aquatic organisms orienting to distant chemical sources. Because the fluid dynamics and chemical plumes change across hydraulic environments, it is un clear which of these factors influence orientation behavior more. This stud y examined how alterations in chemical signal structure, through changes in source spatial arrangement, affect chemically mediated search behavior. Mi croelectrochemical measurements of tracer molecules revealed that source ar rangement significantly alters the downstream fine-scale structure of chemi cal plumes. Flume hydrodynamic characterizations (as measured with laser Do ppler velocimetry) also differed among source arrangements; however, differ ences were minor and existed only at select upstream regions of the flume. Crayfish (Orconectes virilis) found the source faster and spent less time i n refuges when sources were separated, compared with sources together. Simi lar numbers of crayfish found the source regardless of source arrangement. Crayfish searched more efficiently with increased spatial complexity at the source. These results supported the hypothesis that spatial and temporal d ynamics of chemicals within plumes contain important information that organ isms use during olfactory-mediated orientation in streams.