Zoological Studies 46(3): 347-354 (2007) Some Reproductive Aspects of Gecarcoidea lalandii (Brachyura: Gecarcinidae) in Taiwan Hung-Chang Liu1 and Ming-Shiou Jeng2,* 1Department of Ecology, Providence University, Shalu, Taichung County, 433 Taiwan. E-mail:[email protected] 2Research Center for Biodiversity, Academia Sinica, Nankang, Taipei 115, Taiwan (Accepted May 10, 2006) Hung-Chang Liu and Ming-Shiou Jeng (2007) Some reproductive aspects of Gecarcoidea lalandii (Brachyura: Gecarcinidae) in Taiwan. Zoological Studies 46(3): 347-354. The reproductive biology of the land crab Gecarcoidea lalandii was documented on the Hengchun Peninsula, southern Taiwan. Ovigerous females have an average carapace width of 57 ± 7 (range, 42-78) mm (n = 287). The breeding season is variable, depending on the beginning of the rainy season, and in 2003, it lasted from June to Oct., a relatively longer breeding season than determined for its congener, G. natalis. Ovigerous females usually release their larvae during 7-10 d in the last quarter of the lunar cycle. Larval release shows a closer relationship with the timing of sunrise than with the high tide. This species exhibits an unusual larval release behavior while clinging to verti- cal rock faces in which the ovigerous females drop egg masses into the water without actually entering the water. This unusual larval release from above the water and the choice of surge channels as release sites are thought to be adaptations to life on land which may reduce the risks of mortality to ovigerous females. http://zoolstud.sinica.edu.tw/Journals/46.3/347.pdf Key words: Gecarcoidea, Gecarcinidae, Larval release, Reproduction. Land crabs have successfully colonized both land crabs may even occupy the top of the energy tropical islands and continental maritime forests, pyramid (Burggren and McMahon 1988). and may have large populations exhibiting high The robust, heavy-shelled gecarcinid crabs, densities (Green 1997, Sherman 2002). such as Cardisoma, Gecarcinus, and Gecarcoidea, Alexander (1979) suggested multiple roles for land are often the subjects when the term“land crab” crabs in the ecosystems of small islands, including is used without elaboration (Hartnoll 1988). These the transfer of energy from land to sea and vice crabs are medium- to large-sized individuals, with versa, preventing or reducing colonization by exot- large Gecarcoidea natalis (Pocock) reaching 120 ic plant species, hastening leaf litter breakdown, mm in carapace width (Green 1997). The reducing the number of carrion-breeding flies, aer- Gecarcinidae currently consists of 20 species and ating the soil, speeding erosion, aiding soil forma- has been recognized to include 4 (Hartnoll 1988) tion, and providing drinking and breeding places or 6 genera (Ng and Guinot 2001). Although all for other animals. The abundant land crabs on species of the Gecarcinidae show distinct terrestri- Christmas I. (Green et al. 1997) and in Costa Rica al adaptations, their eggs have to hatch in the sea, (Sherman 2002) have been proven to strongly where the larvae undergo typical planktonic devel- affect seedling diversity in rain forests through opment (Hartnoll 1988). The mass migration of their selective seedling consumption. These land reproductive individuals to the surf for larval crabs are also important in hastening leaf litter release has been reported for many gecarcinid , breakdown through digestion (O Dowd and Lake species, such as Cardisoma guanhumi (Latreille) 1989, Sherman 2003). On many small islands, (Henning 1975), Cardisoma hirtipes Dana (Shokita *To whom correspondence and reprint requests should be addressed. Tel: 886-2-27899514 or 27899577. Fax: 886-2-27858059. E-mail:[email protected] 347 348 Zoological Studies 46(3): 347-354 (2007) 1971), Gecarcinus lateralis (Freminville) (Bliss et species of land crabs have been recorded within al. 1978, Wolcott and Wolcott 1982), and the forest, including 2 recently reported arboreal Gecarcoidea natalis (Hicks 1985, Adamczewska species. Nine of them have sufficiently large pop- and Morris 2001). Such breeding migrations to the ulations which are suitable for reproductive biologi- sea are highly synchronized with lunar and sea- cal research such as that carried out by the sonal cycles (Johnson 1965, Shokita 1971, Hicks authors since 1995. 1985). Reproductive synchrony is a common phe- To study the timing and behavior of larval nomenon among coastal land crabs and is release, a 100 x 30 m rectangular portion of the believed to be under the control of environmental supralittoral and littoral zones outside the coastal cycles that occur with predictable regularity. The forest was marked and regularly monitored. This most important factors that influence marine ani- area has a gently sloping profile of rugged, fossil mals are the light-dark cycle, tidal cycle, tidal coral reefs with many crevices and rock pools. amplitude cycle, and lunar cycle (Morgan and The site is interspersed with 8 roughly parallel Christy 1995). Most crabs living close to the high surge channels, two of which touch the edge of the tidal zone prefer to release larvae during the forest, while the others reach about halfway up into largest-amplitude nocturnal high-tide period the supralittoral zone. These surge channels are (Morgan 1995). Planktivorous fish are believed to marked by precipitous cliffs of up to 3 m high. be the most important selective agents influencing A thorough, month-long continuous observa- the reproductive synchrony of these crabs (Morgan tion, carried out from Sept. 1 to Oct. 4, 2002, and Christy 1994 1997). established that larval release in G. lalandii occurs Gecarcoidea consists only of 2 species and is during the last quarter of the lunar cycle. Larval confined to the Indo-Pacific region. The distribu- release of G. lalandii during the last quarter of the tion of G. natalis is limited to Christmas I. and lunar cycle in May 2003 was monitored, but no Cocos I. in the Indian Ocean (Hicks et al. 1990). ovigerous females of G. lalandii were observed Gecarcoidea lalandii H. Milne Edwards has a wider because of a delay in the rainy season. Observa- distribution in the Indo-West Pacific islands starting tions were conducted during the 2 wk following from the Andaman Is. eastward (Hartnoll 1988). each full moon from June to Dec. 2003. Previous studies on G. natalis are numerous The timing of larval release and the behavior including physiological research (Adamczewska of ovigerous females were observed and recorded. and Morris 1994, Adamczewskad and Morris After ovigerous females had released their larvae, 1998), and breeding migration and behavioral the females were caught, measured, marked on , studies (Hicks 1985, O Dowd and Lake 1989, the carapace, and released. The following infor- Green 1997, Adamczewska and Morris 2001). In mation was taken and recorded for each crab contrast, very few ecological studies on G. lalandii encountered: sex, carapace width (CW), carapace have been conducted, although it has a wider dis- length, maximum height of the propodite of each tribution, and abundant populations have been cheliped, abdominal width (between the 4th and described on Jarak I. (Audy et al. 1950), Pulau 5th abdominal segments), and body weight. Not Aor, and Pulau Ular in Malaysia (Johnson 1965). all crabs were suitable for measurement because The aim of this study was to describe the repro- of the loss of various appendages. Size at maturi- ductive biology of G. lalandii, including population ty for females was determined both from the mor- data, breeding season, and larval release timing phology of the abdomen and from the smallest and behavior, with particular focus on the unusual size of ovigerous females. After being measured, larval release behavior carried out from above the the crabs were marked on the carapace with differ- water surface that is unique to Gecarcoidea. We ent colored marking pens in different months, and also propose an explanation for the timing and released back into their original habitats. behavior of larval release of G. lalandii. Fecundity data were taken from 23 migrating ovigerous females, who were captured at the surf zone before midnight and brought back to the lab- MATERIALS AND METHODS oratory. The weight of each ovigerous female was determined. After larval release in the laboratory, The study was conducted at Hsiangchiaowan, the weight of the females was measured again. (21 55'30''N, 120 49'31''E), Hengchun Peninsula, The number of eggs in 0.05 g eggs of the egg Pingtung° County,° southern Taiwan. There is a mass was counted for 5 ovigerous females, and coastal forest about 2 km long in this area. Twenty the total number of released larvae from each Liu and Jeng -- Reproduction of Gecarcoidea lalandii 349 female was calculated. were sensitive to light and would take temporary In order to understand the relationship refuge in crevices if illuminated. Even when the between the reproduction of G. lalandii and the larvae were ready for hatching, the ovigerous local climate, seasonal precipitation data were females would still hide in crevices when subjected obtained from a weather station at Kenting (locat- to continued light disturbance. Bad weather and ed at 21 56'52''N, 120 47'39''E), about 4 km from heavy rain did not affect the migration of ovigerous the study° area, while °seasonal temperature data females. were obtained from a weather station at Hengchun After females had reached the surf zone, they (located at 22 00'20''N, 120 44'17''E), about 13 waited 1-2 m from the water until the larvae were km from the study° area. Tidal° data were obtained ready for hatching. The waiting time lasted from a from a meteorological station at Houpihu (located few minutes to a few hours. Some females even at 21 56'50''N, 120 44'14''E), about 9 km away. remained at the surf zone until the following night ° ° to release their larvae.