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We investigated the seasonal and interannual changes in diversity, abundance, and prevalence of chaetognaths and their parasites collected monthly during 1996-1998 in the Mexi- can Central Pacific. We tested the hypothesis of a positive relationship between abundance and species richness of chaetognaths and their parasites, and investigated the influence of the 1997-1998 El Nin~o event on this host-parasite interaction. Of the 9 chaetognath species collected in the present study, only 7 were found to be parasitized. Of 78 154 chaetognath specimens col- lected, 790 were parasitized (1% prevalence) with at least 1 type of epibiont (cysts, perhaps pro- tists) and 6 types of endoparasites: protists (apicomplexans, dinoflagellates, and ciliates), dige- neans, cestodes, acanthocephalans, nematodes, and other unidentified endoparasites. Cysts, digeneans, and cestodes were the most abundant parasites. Mean intensity ranged from 1-4 endoparasites and from 1-21 epibionts host-1. Zonosagitta bedoti and Flaccisagitta enflata were the most abundant chaetognath species and had the highest parasite diversity. Mesosagitta min- ima and Parasagitta euneritica had the highest parasite prevalence (>2%). A 2-way cluster analy- sis defined sampling month groups as before, during, and after the 1997-1998 El Nin~o. The high- est abundances of chaetognaths and parasites were associated with a high thermal stratification index, salinity, and mixed layer depth. We conclude that there is a positive, non-linear correlation between the abundance of chaetognaths and their parasites. Although El Nin~o decreased the abundance and diversity of chaetognaths throughout the time series, the abundance and diversity of their parasites were not significantly different among hydro-climatic periods, suggesting that host abundance must decrease orders of magnitude to influence host availability for parasites

Palabras clave: Protists; Platyhelminthes; Acanthocephalans; Nematodes; Larval stages; Infracommunity; Component community

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