Meeting Abstract

P1.59  Monday, Jan. 4  Kilometer-Scale Spatial Variation in Prevalence of the Rhizocephalan Lernaeodiscus porcellanae on the Porcelain Crab Petrolisthes cabrilloi SLOAN, L.M.*; ANDERSON, S.V.; PERNET, B.; California State Univ., Long Beach; California State Univ., Long Beach; California State Univ., Long Beach lms89@humboldt.edu

Because parasitic castrators have strong effects on both average individual host fitness and host population-level processes, understanding the causes of variation in their prevalence is an important goal in ecological parasitology. We studied spatial variation in the prevalence of the rhizocephalan barnacle Lernaeodiscus porcellanae, which castrates its host porcelain crab, Petrolisthes cabrilloi, at four southern California intertidal sites located within a few km of each other. The prevalence of rhizocephalan externae varied significantly among sites, with the southernmost site, White Point, consistently showing higher prevalence than the others. Externa prevalence was a good proxy of true (interna) prevalence. We examined several hypotheses that might explain observed spatial variation in prevalence. Host susceptibility to infection (indicated by the proxy of damage to host limbs), did not differ among sites. Among site differences in sex ratio contributed slightly to observed variation in prevalence; however, host size appeared to be the most important factor, explaining 80.4% of the variation. At all sites the probability of infection increased with increasing host size, and White Point crabs were on average much larger than crabs at other sites. Larger P. cabrilloi likely have had greater opportunity to be infected by rhizocephalans, either because they are older, or because they have undergone more molts (during which they are vulnerable to infection). A deeper understanding of small-scale spatial variation in prevalence in L. porcellanae will require information on the causes of among-site variation in host population size structure.