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Diseases of Aquatic Organisms

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DAO 21:91-101 (1995)  -  doi:10.3354/dao021091

Influence of trematodes on the demography of Littorina saxatilis (Gastropoda: Prosobranchia: Littorinidae) in the White Sea

Sokolova IM

ABSTRACT: Five populations of the rough winkle Littorina saxatilis (Olivi) with different levels of trematode infection were investigated in the White Sea, NW Russia: 2 control populations N1 and N2 (ca 5% infection), 1 moderately infected population M (ca 10 to 15% infection) and 2 heavily infected populations H1 and H2 (50 to 80% infection). Trematode prevalence was the lowest in snails collected from macrophytes, intermediate on gravel and highest on stone surfaces at all collection sites. The distribution of infection in different age groups of snails was random in the control populations, but prevalence increased with age in moderately and heavily infected populations. Demographic structure was variable. The following parameters were typical for all populations regardless of infection level: (1) total sex ratios were close to 1:1 or biased slightly towards females; (2) the relative abundance of males decreased with the age of snails; (3) no sex-specific differences in infection prevalence were found in any population; and (4) females became mature at 3 to 4 yr. However, the following demographic parameters showed significant differences that were correlated with trematode infection: (1) fewer juveniles were found in populations H1 and H2, probably a result of reduced recruitment due to severe infection; and (2) fecundity of uninfected females increased with the increase in trematode infection at the collection sites and was the lowest in populations N1 and N2, intermediate in population M and the highest in population H1. These results suggest an adaptation that ensures periwinkle survival under conditions of heavy infection pressure.

KEY WORDS: Littorina saxatilis . Trematoda . Demography

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