Tai Ho Wan: breeding and nursery ground of horseshoe crabs

A new sesarmine crab for Hong Kong

A new leucosiid crab for Hong Kong

New moth species for Hong Kong, part 4; 1999 records (mostly)


Tai Ho Wan: breeding and nursery ground of horseshoe crabs
by Terence Ching-wai Fong

The horseshoe crab Tachypleus tridentatus requires a sandy or pebbled beach near the high tide line as a breeding site (Sekiguchi, 1988). By contrast, Carcinoscorpius rotundicauda lays eggs in muddy sand or in the mud on a flat slope of the bank of a freshwater stream (Rama Rao & Syrya Rao, 1972; Sekiguchi et al., 1977; Sekiguchi, 1988; Chatterji & Parulekar, 1992). The larvae of T. tridentatus do not leave their nest after hatching and usually pass the winter in the nests. They live near their natal beach in the following spring or summer (Sekiguchi, 1988). Juveniles of T. tridentatus measuring 1.4 - 7.0 cm in prosoma width bury themselves in the sandy bottom during high tide (Kawahara, 1982). They creep out and feed on the shore during low tide. The ecological features of the juveniles of C. rotundicauda are still poorly understood. In Hong Kong, T. tridentatus and C. rotundicauda are usually co-existent and share the same habitats, particularly along the shores of Deep Bay (Huang et al., 1998). Seagrass beds are important nursery grounds for both species of horseshoe crabs.

Juvenile horseshoe crabs are commonly found in seagrass beds, Halophila beccarii, Tai Ho Wan, Lantau. Ten juvenile horseshoe crabs were found within 10 minutes on a visit earlier this year. Eight Carcinoscorpius rotundicauda and two Tachypleus tridentatus were identified. The prosoma width of the juveniles ranged from 4 to 5 cm. According to the study of Kawahara (1984), T. tridentatus with this range is 7th to 8th instar (about three years old). The H. beccarii bed in Tai Ho Wan is, therefore, indicated as a nursery ground for C. rotundicauda and T. tridentatus. A mating pair of C. rotundicauda (prosoma width of male and female 18 cm and 22 cm respectively) was also found in one of the freshwater streams draining into Tai Ho Wan. This provides further evidence that Tai Ho Wan is a breeding ground for this species.

Chatterji, A. and Parulekar, A.H. (1992). Fecundity of the Indian horseshoe crab, Carcinoscorpius rotundicauda (Latreille). Tropical Ecology 33, 97-102.

Huang, Q., Chiu, H. and Morton, B. (1998). Nursery beaches for Horseshoe crabs in Hong Kong. Porcupine! December 1998, Number 18, pp. 9-10.

Kawahara, D. (1982). Investigations on ecology of horseshoe crab larvae. Aquabiology 4(5), 380-382. (In Japanese).

Kawahara, D. (1984). Growth and diurnal rhythm of Horseshoe crab. Nature and Animals 14, 22-26. (In Japanese).

Rama Rao, K.V. and Surya Rao, K.V. (1972). Studies on Indian king crab (Arachnid, Xiphosura). Proceedings of Indian National Science Academy 38(B3-4), 206-211.

Sekiguchi, K. (1988). Biology of Horseshoe Crabs. Science House. Tokyo.

Sekiguchi, K., Nishiwaki, S., Makioka, T., Srithunya, S., Machjajib, S., Nakamura, K. and Yamasaki, T. (1977). A study on the egg-laying habits of the horseshoe crabs, Tachypleus tridentatus and Carcinoscorpius rotundicauda, In Chonburi area of Thailand. Proceedings of the Japanese Society of Systematic Zoology no. 13, 39-45.

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A new sesarmine crab for Hong Kong
by Vincent C. S. Lai

A new sesarmine crab for Hong Kong, Episesarma versicolor (Tweedie, 1940), was discovered in Sai Kung last year.

In June 1998, I captured two male specimens of this crab inside a mangrove in Sai Kung. On the basis of external characters they appeared likely to be specimens of the genus Episesarma. They were later identified as Episesarma versicolor. During another field outing in August 1998, I collected another four specimens in nearby mangroves, again all males. The largest individual had a carapace width of 45 mm. Specimens were also sent to Prof. Dai A. Y. of Academica Sinica in Beijing for examination, and as material for a Hong Kong brachyuran fauna study.

Distinguishing features of Episesarma versicolor

The carapace has an earthen ground colour with deep purple patches. The carapace surface is granular and furnished with tufts of setae. The chelae are stout and have beautiful coloration. The manus are purple and the two fingers are white in colour. There are two anterolateral teeth including the outerorbital one on each side of the carapace. Both of them are acute. The most characteristic feature is the two tympana on the ventral side.

The discovery of this crab was unexpected. In early June last year, after days of heavy rainfall, the weather was still wet. I had just searched through a small stream and got down to a small mangrove. I found the usual species in that mangrove. When I was about to leave, I tried as a last effort to turn over a big boulder and strained through the shallow pool beneath the boulder with a shovel. I lifted up a big crab covered by mud in the shovel. At first sight, I thought I had found a mud crab because of its size. But its non-oval carapace and the absence of swimming legs told me it was something else. Its size also resembled that of a mitten crab, but the carapace was more squarish than that of Eriocheir. I washed off the mud with seawater. I found it was a sesarmine crab but of unusually large size. On initial inspection, I found the carapace and chelae had a bright colour pattern different from other sesarmine crabs. On closer examination, the tympana on the ventral side indicated that it was something new.

Sesarmine crabs are the most common crabs in mangrove and muddy habitats throughout the world. Crabs of this subfamily can be recognised by a specialised breathing structure which helps them to adapt to terrestrial life. All sesarmines have a net-like arrangement of setae on the pterygostomian region (the side of the carapace next to the mouth parts). Water stored among these setae can recirculate in the gill chamber, keeping the gills moist so they can breath atmospheric oxygen.

Sesarmine crabs have received more attention than other brachyuran groups in Hong Kong. Their roles in the mangrove ecosystem have been studied in detail (Poovachiranon, S. 1986; Lee 1989; Kwok 1995). Soh (1978) reported 15 species of sesarmine crabs, including the famous endemic Perisesarma maipoensis, which was previously known as Chiromantes maipoensis (this genus name has been incorrectly spelt as "Chiromanthes" for many years), and two other species new to science, Holometopus serenei and Pseudosesarma patshuni. The latter two species were once considered to be rare but it seems that they have a wider distribution than previously thought, being found in a few sites in Sai Kung. In an ongoing Hong Kong sesarmine study, a few more species have been confirmed and the number of species has been brought to over 20 (Dai, A.Y. pers. comm.). Episesarma versicolor not only is a new genus and species for Hong Kong brachyuran fauna, but is also the biggest sesarmine crab in Hong Kong.

This species is rare in Hong Kong. Despite its large size, the crab has not been reported before in Hong Kong. Only six individuals have been found so far, in two closely neighbouring mangroves in Sai Kung. Searches have been made in mangroves of other areas in Sai Kung but no other site of occurrence has been found. Their abundance is not known yet, but is not expected to be high. Their distribution and ecology in Hong Kong is unknown and needs further investigation.

Kwok, P. W. 1995. The ecology of two sesarmine crabs, Perisesarma bidens (De Haan) and Parasesarma plicata (Latreille) at the Mai Po Marshes Nature Reserve, Hong Kong. Ph.D. thesis. University of Hong Kong.

Lee, S. Y. 1989. The importance of sesarminae crabs Chiromanthes spp. and inundation frequency on turnover in a Hong Kong tidal shrimp pond. Journal of Experimental Marine Biology and Ecology. 131:23-43.

Poovachiranon, S. 1986. The food of Chiromanthes bidens (De Haan, 1835) and C. maipoensis (Soh, 1978) (Decapoda: Sesarminae) m Hong Kong mangroves. In The marine flora and fauna of Hong Kong and southern China (ed. B. Morton and C.K. Tseng), 727-35. Proceedings of the Second International Marine Biological Workshop: The Marine Flora and Fauna of Hong Kong and Southern China, Hong Kong, 2-24 April 1986. Hong Kong: Hong Kong University Press.

Soh, C. L. 1978. On a collection of sesarmine crabs (Decapoda: Brachyura: Grapsidae) from Hong Kong. Memoirs of the Hong Kong Natural History Society. 13. 9-22.

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A new leucosiid crab for Hong Kong
by Vincent C. S. Lai

Ebalia malefactrix Kemp 1915 was identified from specimens collected in the intertidal zone in Ha Pak Nai last summer (June 1998). In another search in December last year, however, they could not be found at the same location. Their abundance was probably affected by the seasons.

This is a new record for Hong Kong. It is a tiny leucosiid crab, with a carapace width usually smaller than 10 mm. This crab can be recognised by its uneven carapace with several ridges, crests and many granules, and a characteristic whorl near the distal portion of the male first pleopod.

Hill (1982) reviewed the family Leucosiidae in Hong Kong but did not include this species. This species inhabits muddy intertidal zones, and has been found in India and Hainan Island (Dai & Yang 1991), but has not been recorded in Hong Kong before.

Dai, A.Y. & Yang, S.L 1991. Crabs of the China Seas. China Ocean Press, Beijing.

Hill, D.S. 1982. The Leucosiidae (Crustacea: Decapoda) of Hong Kong. In Proceedings of the First International Marine Biological Workshop: The Marine Flora and Fauna of Hong Kong and Southern China, Hong Kong. 1980. (Eds. B. Morton & C. K. Tseng). Hong Kong University Press, Hong Kong, pp.195-205.

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New moth species for Hong Kong, part 4; 1999 records (mostly)
By Roger Kendrick

Moth recording continues more or less unabated. The number of "macro" moths recorded as new is finally slowing down, although there is a very long way to go with the 'micro" moths - something like 200 species remain tentatively identified only to genus, some only to family. The following list covers species recorded as new to Hong Kong during 1999 and also a couple of species from 1997 and 1998 whose identity has finally been solved.

All the identifications are by comparison with material at the BMNH (by way of publications), or by comparison with material from specialist publications, sourced from Japanese or European institutions.

Unless stated otherwise, the list contains first records of species recorded from Hong Kong using mercury-vapour light traps at Kadoorie Agricultural Research Centre, Shek Kong, N.T. Other sites are abbreviated as follows: Tai Tam Country Park, Hong Kong Island (TTCP); Kadoorie Farm & Botanic Garden (KFBG).

Plutella sera (Meyrick). 26 Apr. 1997; Shan Liu Road, Plover Cove.

Phycodes minor Moore, I881. July/August 1999; reared specimens found in larval webs by Mark Sterling; Red Hill & TTCP.; H.K.Island.

Alucita flavofascia (Inoue, 1958). 7 Apr. 1999, TTCP.

Pyralidae: Pyralinae
Loryma recusata Walker. 18 Jun. 1999.

Pyralidae: Phycitinae
Indomalaya flabellifera (Hampson, 1896). 26 June 1999; Butterfly Garden, KFBG.
Medanaria adiacritis (Turner, 1904). 24 Mar. 1999.

Pyralidae: Phycitinae; Peoriini
Patna eboricostella (Ragonot). 12 May 1999.

Pyralidae: Evergestinae
Crocidolomia pavonoma (Fabricius, 1794). 18 Aug. 1999; Kwun Yum Shan, KFBG.

Pyralidae: Pyraustinae
Antigastra catalaunalis (Duponchel, 1833). 26 Sep. 1998.

Geometridae, Larentiinae
Mnesiloba dentifascia (Hampson, 1891). 3 Oct. 1998.
Pasiphila sp. ? palpata (Walker, 1862). 4 Mar. 1999; Kwun Yum Shan, KFBG.

Geometridae: Ennominae
Coremecis maculata (Warren, 1899). 28 May 1999; TTCP.
Alcis sp. ? imbecilis (Moore, 1888). 4 Mar. 1999; Kwun Yum Shan, KFBG.
Hypomecis sp. ? luniferaa or cineracea (Hampson, 1891). 4 Mar. 1999; Butterfly Garden, KFBG.

Strepsigonia diluta (Warren, 1897). 19 Apr. 1999.

Noctuidae: Ipimorphinae
Callopistria placodoides (Guenée, 1852). 18 Aug. 1999; Butterfly Garden, KFBG.
Polia fasciata (Leech, 1889). 12 May 1999; Kwun Yum Shan, KFBG.

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