Abstract
In the Western Mediterranean, the gilthead sea bream Sparus aurata Linnaeus, 1758 is parasitized by two gill monogeneans, Furnestinia echeneis (Wagener, 1857) Euzet and Audouin, 1959 (Monopisthocotylea : Diplectanidae), and Sparicotyle chrysophrii (van Beneden and Hesse, 1863) Mamaev, 1984 (Polyopisthocotylea : Microcotylidae). The spatial structure of these parasitic populations were studied on the French coast in the Gulf of Lions in 1984 and 1985. The relations between the two species forming this guild have been demographically analyses. Their distribution profiles are very similar and display some stability with time, although some increasing trends are perceptible in the spring. These two monogeneans are globally frequent, but always present in only moderate intensities in infrapopulations. Recruitment of F. echeneis is independent of that of S. chrysophrii. This mode of contamination limits massive and simultaneous infestations of a single host, and interspecific competition risks are consequently considerably reduced. Our results suggest these parasites can affect the size of a natural gilthead population to only a limited degree.