Recruitment to adult habitats in terrestrial hermit crabs on the coast of Ishigakijima Island, Ryukyu Archipelago, Japan

Abstract

Terrestrial hermit crabs in the family Coenobitidae (genera Coenobita and Birgus) are distributed in tropical and subtropical regions. They occupy various habitats ranging from shore to inland forests, and the two shore‐dwelling species, Coenobita rugosus and C. violascens, possess different distributional characteristics on Ishigakijima Island, Ryukyu Archipelago, Japan. Coenobita rugosus is distributed throughout the coast of the island and is abundant in beach areas, whereas C. violascens has mainly been found in river mouth areas. However, very little is known about the habitats used by the early life stages of coenobitid crabs because identifying the species of recently landed early juveniles is difficult. We tested whether the species compositions of early juveniles of coenobitids differed between beach and river mouth sites on Ishigakijima Island. We collected and identified the early stage coenobitids using PCR–RFLP techniques. A total of 576 early juveniles of five Coenobita species were collected, of which 0.7% were C. brevimanus, 7.3% were C. cavipes, 0.2% were C. purpureus, 70.1% were C. rugosus, and 21.7% were C. violascens. The early juveniles of Birgus latro were not found. The early juveniles of C. rugosus occurred at both beach and river mouth sites, and they were abundant at beach sites. The early juveniles of C. violascens were only found at river mouth sites. These findings indicate that C. rugosus and C. violascens complete their life cycles on land near the localities where they land. The early juveniles of the inland‐dwelling species, C. cavipes, were also mainly collected from river mouth sites, which suggested that juveniles of C. cavipes selected landing sites near river mouth areas and then migrated into the inland forests, passing through riverside areas. Our results highlighted the importance of river mouth areas for recruitment to adult habitats by some coenobitid species.

Effect of salinity on survival and emigration behaviour during the sea-to-land transition of three terrestrial hermit crab species (Decapoda: Anomura: Coenobitidae) under laboratory conditions

“…Megalopae and early juveniles of C. purpureus might have evolved the strong hypo-osmoregulatory ability to adapt to the high-temperature niche. On the other hand, C. brevimanus is a primarily coastal forest dweller; however, the main habitats of early juveniles of this species remain largely unknown because few early juveniles have been collected in the wild (Hamasaki et al, 2018). Our results suggest that the early juveniles of C. brevimanus may adapt to a niche similar to that of C. purpureus.…”

“…Early juveniles of C. purpureus inhabit sandy beach conditions (Hamasaki et al, 2018;Sanda et al, 2018aSanda et al, , 2018bInutsuka et al, 2020) with high ground temperatures (Hamasaki et al, 2018) that may induce overheating and desiccation, thereby leading to hypersaline environments. Megalopae and early juveniles of C. purpureus might have evolved the strong hypo-osmoregulatory ability to adapt to the high-temperature niche.…”

“…When animals are exposed to the unfavourable salinity conditions, delayed development, reduced survival, feeding and growth rates, and altered behaviour occur due to enhanced metabolic energy demands for osmoregulation and maintenance (Anger, 2003). Salinity fluctuates temporally and spatially in natural environments where coenobitids may recruit (Tottori et al, 2004;Kawachi & Ishikawa, 2008;Kawachi et al, 2009;Hamasaki et al, 2018). However, the influence of salinity on survival and emigration behaviour during the sea-to-land transition of coenobitid species remains largely unknown.…”

Seaward migration and larval release of the land hermit crab <i>Coenobita</i> <i>brevimanus</i> Dana, 1852 (Anomura: Coenobitidae) on Iriomote Island, Japan

“…Therefore, the larval dispersal duration of C. brevimanus is probably 4 to 5 weeks during which more juveniles are expected to be recruited to the coasts in September and October, which is about 1 month after the larval releases. Hamasaki et al, (2018b) investigated the species composition of early juveniles of coenobitids in beaches and river mouth sites on Ishigaki Island from late August and to the middle of September. Of a total of 576 early juveniles of five Coenobita species collected, C. brevimanus accounted for only 0.7%.…”

Occurrence and distribution of early juvenile land hermit crabs at a small beach on the Boso Peninsula, Japan

“…Therefore, the coastal habitats that earlylife-stage crabs use are essential for completing their life cycle. Hamasaki et al (2018) conducted surveys on the distributional characteristics of early juvenile land hermit crabs with 1-1.5 mm shield lengths (SL) at several sandy beach and river mouth localities along the coast of Ishigakijima Island in the Ryukyu Archipelago, Japan. The early juveniles of C. rugosus were abundant and mainly collected at beach sites, and those of other species were either collected at beach sites (C. purpureus) or river mouth sites (C. violascens) or both the beach and river mouth sites (C. brevimanus and C. cavipes).…”