New distribution records of the rough chela crab, perisesarma maipoense (soh, 1978), in the mangrove ecosystem of north central Viet Nam

JOURNAL OF SCIENCE OF HNUE Chemical and Biological Sci., 2013, Vol. 58, No. 9, pp. 163-168 This paper is available online at NEW DISTRIBUTION RECORDS OF THE ROUGH CHELA CRAB, Perisesarma maipoense (SOH, 1978), IN THE MANGROVE ECOSYSTEM OF NORTH CENTRAL VIETNAM Hoang Ngoc Khac Hanoi University of Natural Resources and Environment Abstract. Perisesarma maipoense (Soh, 1978) was previously considered endemic in Hong Kong and Macau but it was recorded in Northern Vietnam in 1995 and then again in 2010. A zoobenthos survey was done in a coastal mangrove area in North Central Vietnam in 2013 at which time P. maipoense was found in Dien Chau District, Nghe An Province. This paper presents the morphology, ecology and distribution characteristics of the rough chela crab (Perisesarma maipoense). Regarding morphological characteristics, Perisesarma maipoense looks like Perisesarma bidens, which is common in Vietnam, however there are differences between the two species in shape and color. While others species of the genus Perisesarma generally live in mangrove estuaries, Perisesarma maipoense live only on at the edge of the mangrove forest at high tide level. Perisesarma maipoense has been found both in the costal mangrove ecosystem in Northern and North Central Vietnam. Keywords: Brachyura, Perisesarma maipoense, Sesarmid, distribution, mangrove, crab, Vietnam. 1. Introduction The rough chela crab, Perisesarma maipoense (Soh, 1978), is one of 23 species of crustaceans of the genus Perisesarma De Man, 1895 [5]. This is not a well known species which was discovered and described in 1978 by Soh based on three specimens collected in Hong Kong, named Chiromanthes maipoensis Soh, 1978. This species has long been considered endemic to Hong Kong and Macau because studies in other parts of the world as well as in the Indo-Pacific region had not recorded the presence of this species. In 2010, this species was found in the estuary of the Red River in the area of Ramsa-Xuan Thuy and many specimens collected over a five year period from 2005 Received October 13, 2013. Accepted November 15, 2013. Contact Hoang Ngoc Khac, e-mail address: khachn@hnue.edu.vn 163 Hoang Ngoc Khac to 2010 [6]. When a survey to determine benthic biodiversity was conducted in North Central Vietnam mangrove ecosystems in 2013, specimens of Perisesarma maipoense were found. This paper presents notes on the regional distribution, and biological and ecological characteristics of Perisesarma maipoense in coastal areas of North Central Vietnam. 2. Content 2.1. Materials and methods Eleven specimens (6 male, 5 female) were collected in the high tide areas of mangrove forests near coastal dykes of Dien Bich, Dien Chau District, Nghe An Province in April 2013. The geographical coordinate is 19◦00 ’56 "N, 105036’38" E. Specimens were fixed in an 8% formalin solution and preserved in a 4% formalin solution. Identification was based on a description by Soh, 1978 [7] of the carapace, chelipeds, ambulatory legs, maxillipeds and gonopods. 2.2. Results and discussion Perisesarma maipoense (Soh, 1978) (Figure 1). Chiromanthes maipoensis Soh, 1978: 11, Pls. 1a, d, 2c, 5a, b. Sesarma (Perisesarma) maipoensis – Easton & Leung, 1993: 96; Lee & Leung, 1999: 65 Pl. 6. Perisesarma maipoense – Ng et al., 2008: 222. Description The carapace is subquadrangular, the distance between the two outerorbital angles is the widest and 1.21 - 1.25 times broader than long. The shape of a bigger adult male is nearly square with the ratio 1.21. With a smaller female, the width of the carapace is distinctly broader than the length (1.25 - 1.35 times), averaging 1.3 times. The carapace is lightly convex, regions well defined with mesogastric and cardiac regions clearly demarcated; the lateral carapace surface is lined with strong oblique striae; the carapace surface has sparsely scattered tufts of setae anteriorly, less setae posteriorly. The anterolateral margin is sharp and at an exorbital angle and a single prominent epibranchial tooth. The posterolateral margin is lined by 6 rows of short setae. The forehead is 0.50 - 0.55 times the carapace width with frontal margin deflected downwards. Post frontal lobes are prominent, median lobes are broader than lateral and separated by narrow, deep grooves. Antennae are small and close to the inner margin of the orbital. Chelipeds are subequal, large and robust in shape. Those of males are bigger and more robust than those of females. Merus with a inner margin have tuberculates and a large subdistal spine at the end; inner surface has a longitudinal row of setae. The carpus has a row of granules on the inner margin and the inner surface has longitudinal row of granules. The distal dorsal surface has a manus with 2 short oblique pectinated crests. The outer pectinated crest is longer than the inner crests. The outer surface of the manus 164 New distribution records of the rough chela crab, Perisesarma maipoense (Soh, 1978)... is coarsely granulated, larger on the median area, with a distinct lower longitudinal row of granules. The inner surface of the manus has several tubercles on the lower half and a large transverse row of tubercles is near the articulation with the dactylus. An immovable finger is slightly flattened laterally, the outer surface almost smooth or with very low tubercles. The dorsal surface is an movable figure with 5 - 8 flattened, indistinct tubercles, each tubercle with fine transverse lines. The inner edge of the dorsal border, behind the main row of striated tubercles has 12 - 14 relatively smaller conical granules which gradually become smaller distally. Figure 1. Perisesarma maipoense. A. Dorsal surface of the male; B. outer surface of the cheliped; C. inner surface of the cheliped; D. dorsal surface of the cheliped; E. front view Figure 2. Perisesarma maipoense gonopod and distal surface, enlarged (A), outer surface of the palm (B) 165 Hoang Ngoc Khac Remarks: In general, characteristics of specimens collected in Dien Chau are similar to the description of Soh (1978). Compared with species common in Vietnam such as Perisesarma bidens (De Haan, 1835) and Perisesarma eumolpe (De Man, 1895), the Perisesarma maipoense (Soh, 1978) is closer to the Perisesarma bidens in shape and color of carapace and gonopod. The differences in chelipeds: In Perisesarma maipoense it is light blue and the dorsal margin of manus (nearby pectinated crest) and carpus are red-purple. Chelipeds of Perisesarma bidens are dark red on the fingers, manus is pale yellow. Therefore, many people confuse these two species and oftentimes the P. maiposnse is recorded as Perisesarma bidens. Color: In adult males, the carapace is grayish blue or rocky gray, with many small black spots which are scattered on the setae tufts. Generally, the body and the legs are grayish blue or rocky gray. The dactylus are yellowish brown. The outer surface of the chelipeds is creamy in color, slightly blue at the base of manus. In small and female individuals, the carapace is grayish blue or rocky gray mixed with brown. The ventral surface base of the merus, the dorsal edge of the merus, and the carpus and manus of the cheliped are red. In larger males, the dark red parts of the cheliped become more maroon and duller. Figure 3. Habitat of the rough chela crab, Perisesarma maipoense, grassy area near the base of the sea dyke (A), a burrow (B), grass area beside the mangrove forest (C-D) Ecology: Perisesarma maipoense lives in high tidal areas of the mangrove forest (Figure 3) and burrows in the muddy substratum at the high tide level close to mangrove trees or near marshes. Lee & Leung [4] believe that in Mai Po, this species is found only on the dam’s drainage canals and levees edge, close to the tidal mangrove areas, and is absent on the landward side of the border fence road. In Giao Thuy District, Nam Dinh Province, this species burrows at the edge of the high tidal aquaculture ponds and the base of drier bunds into which salt water flows when there is a high tidal current. We even saw them burrowing in the garden of the Mangrove Ecosystem Research Station at Giao Thuy District (P.K.L. Ng. et al., 2010). 166 New distribution records of the rough chela crab, Perisesarma maipoense (Soh, 1978)... In Dien Chau (Nghe An Province), Perisesarma maipoense is found in muddy substratum with grass near the salt fields and the edge of canals inside the sea dyke in or grassy areas outside the sea dyke close to mangrove forest. Thus, it is seen that this species lives beside and not in the mangroves environment, and only at high tide levels with low salinity, from 8 - 20%, and not in areas of high salinity. Figure 4. Map of Ocean currents of the Indo-Pacific region (left) [8] and Map of Perisesarma maipoense distribution (right) Distribution: In the world: Perisesarma maipoense is thought to be endemic to Hong Kong andMacau endemic (Lee [3]; Lee & Leung, Anonymous [1, 2]). Lee & Leung also noted that “P. maipoensis has a very restricted geographical distribution even within Hong Kong. Recent studies of sesarmids in Hong Kong and southern China did not record this species. Anonymous [1] suggested that this species had not been found in Hong Kong in the last 10 years (prior to 2009). In Vietnam: According to our investigation, this species is found in coastal areas, around 3 - 5 km of Red River estuaries, specifically in Giao Thuy District, Nam Dinh Province and Tien Hai District, Thai Binh Province (P.K.L. Ng. et al., 2010). Research done in 2013 discovered additional specimens expanding their geographical range to North Central Vietnam (Lach Van estuary, Dien Chau District, Nghe An Province). Thus, Perisesarma maipoense is not endemic to Hong Kong and Macau. Moreover, the number of specimens of this species found in Hong Kong have been very few while many are found in Vietnam, and Vietnam is close to biodiversity centers of the Indo-West Pacific regions. Therefore, this species could have come from Vietnam, the larvae emigrating 167 Hoang Ngoc Khac via the warm marine currents (Figure 4) spreading north to Hong Kong and Macao, but present there in minimal numbers because climatic conditions are not optimal for this species such that it does not prosper as it does in Vietnam. 3. Conclusion The rough chela crab, Perisesarma maipoense (Soh, 1978), was previously considered endemic to Hong Kong and Macau. Recent studies have discovered populations of this species living in coastal North and North Central Vietnam. The morphological characteristics of this species are close to that of Perisesarma bidenswhich is commonly found in Vietnamese mangrove areas. Perisesarma maipoense lives only in areas at high tide level beside mangrove forests. These findings suggest that this species may be present in Hong Kong as a result of larval dispersal from Vietnam via the warm water current in the Indo-Pacific region. REFERENCES [1] Anonymous, 2008. RAMSAR Site. Hong Kong Wetland Park, Factsheet 14. p. 4. [2] Anonymous, 2009. Priority Research Areas and Suggested Topics for Deep Bay. World Wide Fund for Nature Hong Kong, p. 14. [3] Lee, S. Y., 1995. Endemic sesarmine crabs rediscovered. Porcupine, 12: 3. [4] Lee, S. Y. & V. Leung, 1999. The brachyuran fauna of the Mai Po Marshes Nature Reserve and Deep Bay, Hong Kong. In: S. Y. Lee (editor), "The Mangrove Ecosystem of Deep Bay and the Mai Po Marshes, Hong Kong". Proceedings of the International Workshop on the mangrove ecosystem of Deep Bay and the Mai Po Marshes, Hong Kong, 3-20 September 1993, Hong Kong University Press, pp. 57-82. [5] Ng, P. K. L., D. Guinot & P. Davie, 2008. Systema Brachyurorum, Part I. An annotated checklist of extant brachyuran crabs of the world. Raffles Bulletin of Zoology, Supplement 17: 1-286. [6] Ng, P.K.L., Hoang Ngoc Khac, D.L.Rahayu, 2010. On the taxonomy and ecology of Perisesarma maipoense (Soh, 1978) (Crustacea: Decapo: Brachyura: Sesarmidae) from Vietnam. The Raffles Bulletin of Zoology Vol. 58 (2): pp. 239-243. [7] 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: pp. 9-22. [8] Ocean Currents and Sea Ice from Atlas of World Maps, United States Army Service Forces, Army Specialized Training Division. Army Service Forces Manual M-101 (1943). Doi: (access on 1.9.2013) 168