Reproductive Characteristics of the Hermit Crab Pagurus middendorffii Brandt, 1851 (Decapoda: Paguridae) from Peter the Great Bay, Sea of Japan

Some aspects of the reproductive biology of the widespread boreal hermit crab Pagurus middendorffii Brandt, 1851 were studied. Samples were collected monthly from November 2022 to November 2023 at a depth of 1–3 m in Zhitkov Bay (Russky Island, Peter the Great Bay, Sea of Japan). About 38% of the specimens were infected with parasitic crustaceans. Among healthy hermit crabs, the size of the calcified part of the carapace (SL) ranged from 1.9 to 6.6 mm (average 4.53 ± 0.95) for males, from 1.9 to 5.5 mm (average 3.67 ± 0.68) for females, and from 1.9 to 5.3 mm (average 3.56 ± 0.62 mm) for ovigerous females. The male to female ratio during the study period varied from 0.6 to 4.0 with an average of 2.2. Spawning commenced in late October and ceased in late November; the incubation period lasted 6.5 months and the embryonic diapause was absent. Repeated spawning was not observed. A comparative analysis of the reproductive characteristics of hermit crabs from different regions showed that changes in the temperature regime influence the timing of spawning and the duration of the incubation period, which significantly increases due to slow embryonic development at low temperatures in some species and due to embryonic diapause in others.