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Rev. biol. mar. oceanogr. 51(1): 81-88



Factors accounting for variations in the parasitism by metacercariae (Digenea, Microphallidae) in the amphipod Apohyale hirtipalma (Gammaridea) in the Southeastern Pacific coast

Claudia Hurtado-Ormeño1,2 and This email address is being protected from spambots. You need JavaScript enabled to view it.1,3

1Departamento de Ecología, Facultad de Ciencias, Universidad Católica de la Santísima Concepción, Casilla 297, Concepción, Chile
2Programa de Magister en Ecología marina, Facultad de Ciencias, Universidad Católica de la Santísima Concepción, Concepción, Chile
3Centro de Investigación en Biodiversidad y Ambientes Sustentables (CIBAS). Universidad Católica de la Santísima Concepción, Concepción, Chile

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The southwestern Gulf of California has high-value commercial fisheries; however, there are few studies of the taxonomic diversity of fish in this area. Surveys of taxonomic diversity of the fish assemblage at 8 localities near the shore of Bahía de La Paz were undertaken from March 2002 to April 2003. Seasonal changes in diversity of rocky reef fish were analyzed, including taxonomic distance among fish species, using the alpha, alpha average, beta, and gamma diversity indices, the taxonomic distinctness index (TD D*), and the average taxonomic distinctness index (AvTD D+). Submarine visual censuses were carried out along 48 transects measuring 100 × 5 m (500 m2) at 5 m average depth from 09:00-16:00 h. Two seasons were studied: winter with an average temperature of 22.57°C, and summer with an average temperature of 27.09°C. 24,633 fishes, belonging to 92 species and 67 genera were recorded. According to the alpha average, beta, and gamma diversity indices, August had the highest diversity (19.5, 40.5, and 60 species, respectively), and December had the lowest diversity (20.6, 27.4, and 48 species, respectively). Spatial analysis of TD and AvTD were not significantly different, and analysis by season of these indices was not significant different. Greater anthropogenic impact would cause differences in TD and AvTD found at El Guano compared with other locations.
It was assessed the parasitic relationship between by 2 morphospecies of microphallid metacercariae and their second intermediate host, the amphipod Apohyale hirtipalma with the body length and sex of the hosts, and the abundance of shore birds (definitive hosts). Amphipod mortality induced by the parasites was assessed through the relationship between the variance/mean parasite abundance ratio with host body length for each metacercariae morphospecies. Four sites at the Biobío Region (36°S), Chile, were selected because of contrasting abundance of potential definitive hosts (Aves: Laridae), from where 240 amphipods were collected from intertidal pools (60 in each sampling locality). Total prevalence was 57.5% and metacercariae found, belonged to 2 unidentified morphospecies of microphallid subfamilies (Microphallinae, 28.3% and Maritrematinae, 36.7%). The prevalence and abundance of metacercariae increased with the amphipod body, although their variations were associated to the abundance of shorebirds. The prevalence of Microphallinae did not have differences among sexes in their relationship with the host body length, while among Maritrematinae, male amphipods showed higher prevalence than females of similar body length. It was also determined that Maritrematinae would cause more mortality than Microphallinae. Local variations of the abundance of other hosts involved in the microphallid life cycles as well as of prevailing local environmental conditions and amphipod behavior may be keys for a better understanding of the abundance and prevalence variations of these parasites.

Key words:  Shorebird abundance, host body length, host sex, parasite identity, mortality, Chile