An experimental field test of susceptibility to ectoparasitic gnathiid isopods among Caribbean reef fishes

Abstract

Susceptibility to infestation by a gnathiid isopod (Gnathia marleyi: Crustacea: Isopoda) was examined among 16 species from 9 families and 3 orders of common Caribbean reef fishes off St. John, United States Virgin Islands. Fish were placed in cages during times of peak gnathiid activity. Individuals from most (n=14) species were compared against a single species (French Grunt, Haemulon flavolineatum) that served as a standard and effectively controlled for the effects of habitat and variation in gnathiid abundance on exposure to and the likelihood and intensity of host infestation by gnathiids. All species were susceptible to infestation by gnathiids, with individual hosts harbouring up to 368 gnathiids. However, there was significant variation in levels of infestation among the 14 comparison species. Controlling for body size, nocturnal species from the families Haemulidae and Lutjanidae had the highest gnathiid infestation. Our finding that haemulids and lutjanids are particularly susceptible has important implications for the role of gnathiids in Caribbean reef food webs, given the role members of these families play in trophic connectivity between reefs and associated habitats. To our knowledge this is the first manipulative field study to examine variation among potential hosts in susceptibility to an ectoparasite in any terrestrial or aquatic system and is the greatest number of teleost hosts documented for any gnathiid species.

Enhanced understanding of ectoparasite–host trophic linkages on coral reefs through stable isotope analysis

“…Thus, all three fish species demonstrate high site fidelity to resting sites (Nagelkerken et al., 2008) and French grunt in particular may play a significant role in the transfer of parasites among habitats. All three species are infected by the gnathiid isopod Gnathia marleyi (Farquharson et al., 2012) at our study sites, although their susceptibility varies (Coile and Sikkel, 2013). In addition, French grunt are infected by the cymothoid isopod, Anilocra haemuli , and squirrelfish by A. holocentric (Bunkley-Williams and Williams, 1981; Bunkley-Williams, 1984; Welicky and Sikkel, 2014).…”

Fish mucus versus parasitic gnathiid isopods as sources of energy and sunscreens for a cleaner fish

“…Although the taxonomic diversity in this study was low (two herbivorous parrotfishes vs. one wrasse and one snapper, both carnivorous), it appears that carnivorous species ''produce'' gnathiids of higher nutritional value. This combined with their lower mucus quality (and potentially their effectiveness as a barrier against gnathiids) has implications for host susceptibility to gnathiids and may explain differences in susceptibility among fishes (Coile and Sikkel 2013), as well as differences in fitness measures of gnathiids that had fed off of different hosts (Nagel and Grutter 2007;Coile et al 2014).…”

Low Susceptibility of Invasive Red Lionfish (Pterois volitans) to a Generalist Ectoparasite in Both Its Introduced and Native Ranges

“…As in the Coile and Sikkel study [62], fish host surface area and average density of gnathiids on 5 French grunt standards were used as covariates.…”