Clayton Vondriska* - Rosenstiel School of Marine, Atmospheric, & Earth Science, University of Miami; College of Science & Mathematics, University of the Virgin Islands

J. Rudi Strickler - Department of Biological Sciences, University of Wisconsin - Milwaukee; Marine Science Institute, University of Texas

Paul C. Sikkel - Rosenstiel School of Marine, Atmospheric, & Earth Science, University of Miami; Unit of Environmental Sciences, North-West University

​

Abstract

All aquatic organisms may rely on chemical signals in at least some aspect of their life cycle. Chemical signals can be used in association with numerous fitness-consequential functions, including food-, mate-, and habitat-finding and predator avoidance. Research on how small (millimeter scale) aquatic organisms interact with their chemical environment has been largely hampered by the lack of sufficient technology for accurately recording and interpreting their behavior at relevant temporal and spatial scales. Here, we demonstrate the effectiveness of a novel aquatic olfactometer by observing the host-finding behavior of a parasitic gnathiid isopod. This olfactometer allows us to observe organisms in a structured chemical landscape. This landscape consists of a choice arena with four equally divided sections, each fed with water while not mixing with its neighboring sections. Organisms within the choice arena can be recorded using a NIR-camera, giving us video data on speed and behavior within the landscape. It also allows us to observe whether an organism has habituated to the chemicals while roaming within the choice arena. Gnathiid isopods (gnathiids) are among the most common free-living external parasites of coral reef fishes. These isopods must navigate complex and inhospitable environments to locate several different hosts throughout their life cycles. We exposed the gnathiid Gnathia marleyi to the chemical cues of the French grunt (Haemulon flavolineatum), a common host. G. marleyi spent significantly more time in the zone of the chemical landscape containing host cues. Swimming parameters, such as speed and frequency of “zone” transitions indicate G. marleyi’s ability to detect and respond to host cues in the absence of any other stimuli. We associate the observed activities as parts of a typical searching behavior. Our results indicate that this ecologically important parasite relies heavily on chemical signals when locating its hosts. They also demonstrate the utility of the olfactometer for similar studies on small aquatic invertebrates.