Is ectoparasite burden related to host density? Evidence from nearshore fish larvae off the coast of central Chile

Variations in parasite populations may be temporal and/or spatial and can occur in relation to environmental factors. However, such changes may also occur due to differences in host population density, which is one of the main factors that affect the abundance of directly transmitted parasites. Fish larvae and their ectoparasites were collected via ichthyoplankton samplings during a 3-year survey near the coast of central Chile. To estimate the variations in ectoparasite abundance that occurred with fluctuations in host density, the prevalence and intensity of ectoparasites (copepods and isopods) were calculated and compared with the density (i.e., the larval fish abundance standardized to 1,000 m⁻³) of six species of nearshore fish larvae that belonged to the families Gobiesocidae, Labrisomidae and Tripterygiidae. Copepods (Penellidae and Caligidae) and isopods (Cryptoniscidae) were found to be parasitizing the fish larvae. Pennellid copepods were the most prevalent ectoparasite, and the clingfish Gobiesox marmoratus (Gobiesocidae) was the most parasitized fish species (12.81 %). The individual burdens of pennellid, caligid and isopod ectoparasites failed to exhibit any correlation with the larval densities of four fish species (i.e., Auchenionchus crinitus, Auchenionchus microcirrhis, Sicyases sanguineus and Helcogrammoides chilensis). Nonetheless, the prevalence and intensity of the pennellid copepods exhibited a significant and positive correlation with the density of a gobisesocid species. In contrast, the prevalence of pennellid copepods (5.10 %) exhibited a significant but negative correlation with the density of tripterygid fish. Ectoparasite abundance is a result of a species-specific relationship with their hosts, but the evidence found suggests no correlation between ectoparasite burden and host density in larval fishes from coastal environments.