An experimental field test of host-finding mechanisms in a Caribbean gnathiid isopod
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Field experiments were conducted from dusk to dawn off St. John (18° 18′ 59.32″ N, 64° 43′ 24.5″ W) and Guana Island (18° 28″ 28.31″ N, 64° 34′ 30.83″ W), Virgin Islands from June through August 2008-2010 to assess the sensory cues used by the nocturnal/crepuscular fish-parasitic gnathiid isopod, Gnathia marleyi, to locate fish hosts. Experimental traps providing both visual and olfactory cues from live French grunts (Haemulon flavioliniatum) attracted significantly more gnathiids than traps providing only visual cues or control traps (empty or with a rock), which were not significantly different from each other. In another experiment, traps providing both cues and only olfactory cues attracted significantly more gnathiids than empty control traps, but were not significantly different from each other. Our findings suggest that during nocturnal and crepuscular periods, visual cues provided by resting or slow-moving fish are not alone sufficient to attract gnathiids, while olfactory cues alone are. The traps designed for this study offer a new method of sampling free-living gnathiid isopods.
KeywordsReef Fish Great Barrier Reef Fish Host Central Chamber Emergence Trap
We thank the staff at the Virgin Islands Environmental Resource Station (VIERS), the Center for Marine and Environmental Studies (CMES), and Guana Island for logistic support and use of their facilities. We thank J. Artim, R. Ziemba, J. Methenia, D. Nemeth, A. McCammon, A. Demopolous, E. Brown, C. Risley, and volunteers from the 2008 and 2009 Virgin Islands Earthwatch teams for assisting with the design of traps and the collection and processing of parasite samples. We are extremely grateful to G. Crase of Centre College for assistance with construction of traps and to N. Smit for confirming the species identity of the gnathiids. J. Artim, A. Coile, R. Welicky, J. Stanley, and J. Sellers provided helpful comments on the manuscript. This work was generously funded by Earthwatch Institute, the Durfee Foundation, the Falconwood Corporation, and Microsoft Corporation. This is publication number 63 from the University of the Virgin Islands Center for Marine and Environmental Studies.
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