Vol. 62, 2023

(update: 2023.5.26)

Seaward Migration and Larval Release Coincide with Lunar and Light-dark Cycles in Supratidal Land Crabs Cardisoma carnifex and Epigrapsus notatus

¹,

²,

³,

¹,

, and Yuan-Mou Chang

^1,*

¹Department of Ecology and Environmental Resources, National University of Tainan, 33 Su-Lin Street, Section 2, Tainan 700, Taiwan. *Correspondence: E-mail: changyuanmou@gmail.com (YM Chang).
E-mail: jsd995@gmail.com (CC Chang); wenbehwang@mail.nutn.edu.tw (Hwang)
²Department of Biology, Long Island University – Post, Brookville, NY, USA. E-mail: kent.hatch@liu.edu (Hatch)
³Taiwan Association for Marine Environmental Education, No. 5, Lane 111, Section 2, Zhiyuan 1st Road, Beitou District, Taipei City 11289, Taiwan. Biodiversity Division, National Institute for Environmental Studies, Tsukuba, Japan, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan. E-mail: johnson20535@hotmail.com (Hsu)
⁴Unaffiliated, 53, Chenggong 11th St., Jhubei City, Hsinchu County 302, Taiwan. *Correspondence: E-mail: labuanium@gmail.com (Liu)
E-mail: changyuanmou@gmail.com (YM Chang)

(Received 11 October 2022 / Accepted 10 February 2023 / Published 26 May 2023)
Communicated by Yoko Nozawa

Herein we investigated the synchronous breeding migration and larval release of ovigerous females in two dominant supratidal land crabs Cardisoma carnifex and Epigrapsus notatus in the mixed semidiurnal tidal regime in Taijiang National Park (Tainan, Taiwan). We mainly focused on the monthly and daily rhythms during the breeding season of migration and larval release for these two crabs. We also sought to understand what the main environmental cues were for these monthly and diel rhythms. Both lunar and tidal amplitude cycles are potential proximate causes for the monthly lunar/semilunar reproductive rhythm in crabs. Likewise, either the 24-hour (diel) light cycle or tidal cycle can act as the proximate cause for diel reproduction rhythm, and we investigated which one was the main factor that entrains the diel rhythm for these two species. We found that the season of migration and larval release in C. carnifex occured mainly between June and September during the rainy season while those of E. notatus occurred mainly between September and October, near the end of the rainy season. Regarding the rhythm of migration and larval release in monthly time scale, C. carnifex exhibited a semilunar rhythm following the syzygies and E. notatus exhibited a lunar rhythm following the full moon. However, these rhythms did not occur with the maximum amplitude nocturnal and diurnal high tides. This implies that the lunar cycle is a more important environmental cue than the tidal amplitude in the entrainment of the synchronous monthly breeding rhythm for these two species. This pattern is different from other intertidal crabs, most of which use the tidal amplitude cycle as the main environmental cue for larval release. In addition to Chiromantes haematocheir (a supratidal crab), our study provided two more species that live in the supratidal zone time their reproduction with respect to the lunar light cycle and independent of the tide amplitude cycles. For the diel rhythm, both species migrated to the shore and released larvae in the first half of the night during the flood tide. This suggests that the diel light cycle is a dominant cue for the determination of larval release timing for these two species. Larval release does not track the high slack tides, since larvae are only released during the first half of the night and these high slack tides occur only after midnight (0000–0600H) during the days of larval release for these two crab species.

Key words: Breeding migration, Larval release, Mixed semidiurnal tides, Supratidal land crabs, Semilunar rhythm.

Citation: Chang CC, Hatch KA, Hsu CH, Hwang W, Liu HC, Chang YM. 2023. Seaward migration and larval release coincide with lunar and light-dark cycles in supratidal land crabs Cardisoma carnifex and Epigrapsus notatus. Zool Stud 62:22. doi:10.6620/ZS.2023.62-22.