Decreased movement related to parasite infection in a diel migratory coral reef fish

Risk of infection by parasites may be an important contributing cause or consequence of animal movement patterns. The diel movement patterns of French grunt, a common Caribbean coral reef fish, are well documented and known to connect reef and seagrass habitat. In the northeastern Caribbean, French grunts are known to be infected by Anilocra haemuli, one of the largest and most conspicuous ectoparasitic isopods. Studies on Anilocra infection have demonstrated that infection reduces host swimming performance and condition and may alter host behavior. We tested predictions of the hypothesis that A. haemuli infection influences the movement patterns of host French grunt, specifically whether short-distance daytime movements and/or reef-seagrass migration at dusk was associated with infection. We conducted focal observations on infected and uninfected fish during both daytime resting and dusk migration periods. We also conducted daytime and nocturnal surveys in reef habitat, documenting changes in the proportion of infected individuals. We found that infected fish move significantly less than uninfected conspecifics during the day and observed 100 % of uninfected focal fish and 37.5 % of infected focal fish departing the reef during dusk. In reef habitat, the proportion of fish infected with Anilocra was also significantly greater at night compared to daytime. We suggest that A. haemuli infection alters host movement patterns and that parasitism may therefore indirectly influence trophic connectivity between reef and seagrass ecosystems

Female Gnathia marleyi (Isopoda: Gnathiidae) feeding on more susceptible fish hosts produce larger but not more offspring

The reproductive success of female Gnathia marleyi (Crustacea: Isopoda) was examined among individuals from eight species belonging to five families of common Caribbean reef fishes of St. John, US Virgin Islands that differ in susceptibility to G. marleyi infestation. Fish were placed in cages during times of peak gnathiid activity. Gnathiids were recovered from host fishes and reared to adulthood in the laboratory. Ovigerous females were then placed in individual containers until offspring were released. Measures of reproductive success used were the number of hatched zuphea 1 larvae that emerged from the brood pouch, "brood size," and the average total length of newly emerged zuphea larvae, "average z-length." Among the five host fish families tested, females that fed on the two families most susceptible to gnathiid infestation (Haemulidae and Lutjanidae) produced longer larvae than those feeding on the three less susceptible host families. However, there was no significant difference in the number of viable offspring produced. To our knowledge, this is the first study to examine the relationship between the source of the blood meal and any measure of reproductive success in female gnathiid isopods. These findings open the door to future research on potential differences in host blood quality and defense mechanisms that may cause variations in susceptibility to gnathiid among different host fishes

Host-dependent differences in measures of condition associated with Anilocra spp. parasitism in two coral reef fishes

Parasites account for over half of the biodiversity on coral reefs, yet their ecological impacts are poorly understood. Cymothoid isopods of the genus Anilocra are large, conspicuous ectoparasites of coral reef fishes. French grunt (Haemulon flavolineatum) and brown chromis (Chromis multilineata) are commonly infected by Anilocra spp. in the Caribbean. These fishes play a significant role in trophic connectivity through their foraging and activity patterns, and Anilocra spp. infection has been reported to influence the trophic interactions of some fishes. Yet, how these changes manifest physiologically has not been quantified. Thus to determine the energetic effects of Anilocra spp. on French grunt and brown chromis, the relationships between Anilocra spp. infection and condition factor, percent moisture in the muscle tissue, total muscle tissue calories, and gut content volume were examined. The results of these analyses revealed that A. haemuli-infected French grunt had greater percent moisture in the muscle tissue but similar condition scores, calorie values, and gut content volumes compared to uninfected conspecifics. By comparison, Anilocra chromis-infected brown chromis had reduced condition factor, but similar percent moisture in the muscle tissue and total muscle tissue calories, as compared to uninfected conspecifics. This study provides evidence that infection by parasites of the same genus and within the same localities can have differential effects on fish host species, such that generalizations about the effects of parasitism across and within genera should be made cautiously

The relationship between lunar periodicity and activity of fish-parasitic gnathiid isopods in the Caribbean

Gnathiid isopod larvae are members of the marine demersal zooplankton community and are common ectoparasites of coral reef fishes, emerging from the substratum, mostly at night and crepuscular periods to feed on fish blood. Given that the activity of many marine organisms is often linked to changes in the phase of the moon, we examined the relationship between lunar phase and activity in gnathiid isopods on Caribbean reefs. We employed two sampling methods to quantify gnathiid activity: (1) Emergence traps set on reefs over a 24 h period; and (2) live fish placed in cages on reefs and retrieved during night and dawn peaks in gnathiid activity. These were compared during discrete phases as well as a continuous metric, the lunar "angle", and an estimate of ambient light availability (luminance). Lunar phase and angle varied in their statistical effect on gnathiid activity patterns by sampling method and/or year. Luminance had a significant but inconsistent effect on measures of gnathiid activity. Our results suggest that changes in the lunar cycle are not a strong predictor of gnathiid activity at our shallow reef study sites

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

Escape from parasites in their native range is one of many mechanisms that can contribute to the success of an invasive species. Gnathiid isopods are blood-feeding ectoparasites that infest a wide range of fish hosts, mostly in coral reef habitats. They are ecologically similar to terrestrial ticks, with the ability to transmit blood-borne parasites and cause damage or even death to heavily infected hosts. Therefore, being highly resistant or highly susceptible to gnathiids can have significant fitness consequences for reef-associated fishes. Indo-Pacific red lionfish (Pterois volitans) have invaded coastal habitats of the western tropical and subtropical Atlantic and Caribbean regions. We assessed the susceptibility of red lionfish to parasitic gnathiid isopods in both their native Pacific and introduced Atlantic ranges via experimental field studies during which lionfish and other, ecologically-similar reef fishes were caged and exposed to gnathiid infestation on shallow coral reefs. Lionfish in both ranges had very few gnathiids when compared with other species, suggesting that lionfish are not highly susceptible to infestation by generalist ectoparasitic gnathiids. While this pattern implies that release from gnathiid infestation is unlikely to contribute to the success of lionfish as invaders, it does suggest that in environments with high gnathiid densities, lionfish may have an advantage over species that are more susceptible to gnathiids. Also, because lionfish are not completely resistant to gnathiids, our results suggest that lionfish could possibly have transported blood parasites between their native Pacific and invaded Atlantic ranges