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.