Measurement of Microscale Patchiness in a Turbulent Aquatic Odor Plume Using a Semiconductor-Based Microprobe

The distribution of chemical signals within aquatic environments is highly patchy and heterogeneous due to dispersion by turbulent eddies. We aimed to quantify the smallest spatial scales associated with chemical patches, and therefore measured the structure of chemical signals under turbulent flow simultaneously at two chemical sensors spaced from 200 to 800 {mu}m apart. Measurements were done under controlled stimulus and flow conditions with a novel semiconductor-based, multisite, microelectrochemical electrode (5-2000 {mu}m2 surface area sensors) and a high-speed computer-based recording system. The chemical signals received at the sensor were intermittent, with wide fluctuations in concentration. Patchiness in signal structure was found at spatial scales as small as 200 {mu}m. Significant differences in signal height were found between recordings made at probes spaced 200, 400, 600, and 800 {mu}m apart. These data demonstrate that sub-millimeter patches occur in aquatic turbulent odor plumes. Such differences in chemical signal structure over small spatial scales might be important for marine animals that employ olfactory orientation. We propose alternative ways by which organisms might deal with these fine scale differences in odor concentration. Animals much larger than microscale patches may have evolved elongated olfactory organs that integrate signals, thereby smoothing variations in sensory input. Animals about the same size as micropatches may be able to capitalize on microscale variation by extracting directional information from turbulent odor plumes.