Recruitment, growth, and vertical distribution of the endangered mud snail Cerithidea rhizophorarum A. Adams, 1855: implications for its conservation

Abstract

Some fundamental natural-history traits of the endangered mud snail Cerithidea rhizophorarum were investigated for three years in an open, bare, sandy tidal flat located on the east of Shikoku Island in southwestern Japan. Our study demonstrated a highly aggregated distribution of younger snails and complicated differences in vertical migration patterns between younger and older snails that might have prevented comprehensive understanding of the precise demography of C. rhizophorarum in previous studies. From late summer, juveniles of the first-year cohorts appeared patchily at 12–16 cm lower tidal heights than snails of the oldest cohorts and reached 5.0–7.5 mm in mean shell length by the first mid-autumn. In the second year, juveniles gradually moved upward and appeared at higher tidal heights. The second-year cohorts reached 15.6–19.1 mm in mean shell length by the end of the second autumn and converged into the oldest cohorts during the third year or later. Our results suggest that C. rhizophorarum matures sexually and starts reproduction from the fourth summer at the earliest. On the other hand, older snails showed a similar seasonal migration pattern every year—downward movement in summer and upward movement in autumn—probably associated with their reproductive activity and/or a seasonal change in the maximum tidal height. For conservation of C. rhizophorarum, it is very important to preserve both the higher area as a main habitat for older snails and the lower tidal flat as the nursery ground.

Keywords:

• age dependent differences
• Caenogastropoda
• Cerithioidea
• Japan
• life-history traits
• Potamididae
• temporal variations
• tidal flat

Acknowledgements

This work was partly supported by the Fisheries Agency of Japan, a grant from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) (Grant-in-Aid for Young Scientists (B), no. 20710183 to N.O.) and a grant from the Japan Society for the Promotion of Science (JSPS) (Grant-in-Aid for Young Scientists (Start-up), no. 21860087 to T.K.). The authors would like to thank two anonymous reviewers and Winston Ponder for their valuable comments.

Additional information

Notes on contributors

Takashi Kawai

Current address: Transdisciplinary Research Organization for Subtropics and Island Studies, University of the Ryukyus, 1 Senbaru, Nishihara, Nakagami, Okinawa 903-0213, Japan.

Atsushi Hashimoto

Current address: Faculty of Life and Environmental Sciences, Department of Environmental Sciences, Prefectural University of Hiroshima, 562 Nanatsuka, Shobara, Hiroshima 727-0023, Japan.