Distribution and recruitment of Anilocra chromis Williams & Williams, 1981 (Isopoda, Cymothoidae) on brown chromis, Chromis multilineata (Guichenot, 1853) (Perciformis, Pomacentridae), following experimental removals

Anilocra chromis Williams & Williams, 1981 (Isopoda, Cymothoidae) from the brown chromis, Chromis multilineata (Guichenot, 1853) (Perciformis, Pomacentridae) in the northeastern Caribbean were previously named and described. A. chromis occurred allopatrically on blue chromis, Chromis cyanea Poey, 1860, in other localities in the Caribbean. Brown chromis hosts were found to be predisposed to the presence of A. chromis, and that adult and juvenile brown chromis could be infected with juvenile A. chromis. The isopod in this study always occurred as an adult under one eye of an adult brown chromis host. Mancae juveniles were thought to have limited dispersal abilities, but this has not been experimentally tested. After natural release, each juvenile swims up to near the surface apparently to avoid planktivores near the reef, and at night, returns to the reef to infect small fishes as transfer hosts or mixes under female A. chromis to breed. Despite these previous studies, how far the juveniles can disperse is not known. Understanding the dispersal of Anilocra spp. and other isopod mancae juveniles is a critical, and largely unknown, part of their life history. A series of field experiments were conducted over 3 years to solve this question out of the NOAA Hydrolab Habitat in the St. Croix Salt River Canyon. We censused and removed, respectively, 96 and 98% of C. multilineata infected with A. chromis in 2 years. After 18 and 12 months, respectively, we re-censused the infected fish. Hosts numbers recovered completely in both experiments. A. chromis numbers recovered completely in 18 months, but only recovered 39% of their number in 12 months. A. chromis sectors established on the ends of the study area on a linear and uniform reef recovered to levels of control sections (approx. 18-19% hosts). However, A. chromis prevalence on the inner segments was only 35% of the control segments. Therefore, juveniles only traveled a short distance before infecting a host. Although description of the “complete” life cycles of several parasitic isopods have been published, the natural release, behavior before attaching to the final host, and now natural dispersal have only been documented in A. chromis. This is important for understanding distributions, isolations, and speciation of fish-parasitic isopods or even methods of control.