Effects of Two-Species Infestation by Rhizocephalan Barnacles on the Population of the Kelp Crab Pugettia aff. ferox (Decapoda: Brachyura: Epialtidae) in the Northwestern Sea of Japan

Effects of two-species infestation by sympatric rhizocephalans, Parasacculina pilosella and Sacculina pugettiae, on the population of the brachyuran crab Pugettia aff. ferox Ohtsuchi & Kawamura, 2019 (Decapoda: Epialtidae) were studied in the northern part of the species range (Ussuri Bay, Peter the Great Bay, Sea of Japan) in 2020-2021. The sex structure in the Pugettia population was female-biased and represented by males (39.2%), females (56.7%), and modified females (4.1%). Their size-frequency distributions did not differ. The prevalence of the infestation by rhizocephalans reached 18.5%. Parasacculina pilosella was more abundant than S. pugettiae. Less than 1% of crabs were infested by both rhizocephalans simultaneously. Both parasites preferred female hosts. The modifications of the sex characters in the infested females were more pronounced than in the infested males. The abdomens in the externa-bearing males were slightly expanded, the chelae slightly decreased, and the gonopods slightly shortened. The pleopods in some of the externa-bearing females were completely atrophied. Pugettia aff. ferox produced only one clutch a year in the study area. Ovigerous females occurred from June to late August. The reproductive cycle of the host and those of both parasites were synchronous. None of the infested Pugettia females was ovigerous.