Trapezia Septata Dana, 1852 (Brachyura, Trapeziidae): a New Record for Singapore with Notes on Its Relationship with the Host Coral, Pocillopora Verrucosa
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TRAPEZIA SEPTATA DANA, 1852 (BRACHYURA, TRAPEZIIDAE): A NEW RECORD FOR SINGAPORE WITH NOTES ON ITS RELATIONSHIP WITH THE HOST CORAL, POCILLOPORA VERRUCOSA BY AI-CHIN LEE1,3) and TSAI M. SIN1,2) 1) Tropical Marine Science Institute, National University of Singapore, 18 Kent Ridge Road, Singapore 119227, Republic of Singapore 2) Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543, Republic of Singapore Lim et al. (1994: 92) recorded the ectosymbiotic trapeziid crab, “Trapezia areolata Dana, 1852” from an unidentified species of the scleractinian hard coral, Pocillopora (Pocilloporidae) in Singapore. That species, however, has a southeastern Pacific distribution, the type locality being French Polynesia (Castro et al., 2004: 41), and it has often been confused with T. septata Dana, 1852, until Galil & Lewinsohn (1985) clarified their taxonomy and showed them to be separate species. Trapezia septata has a wider distribution, ranging from the east of Sri Lanka, the Andaman Sea, the western and central Pacific Ocean, and the Philippines, to the Marshall Islands and Samoa (Castro et al., 2004: 42). Castro et al. (2004: 48, 53) have subsequently selected neotypes for both species, and stabilized their taxonomy. Re-examination of the available Singapore material in the Raffles Museum of Biodiversity Research (RMBR), National University of Singapore, showed that all the material in RMBR previously identified as “T. areolata” should be referred to T. septata instead. Trapezia septata Dana, 1852, is thus a new record for Singapore, and only the second species of trapeziid known from there, the other being T. cymodoce (Herbst, 1801). Trapezia septata Dana, 1852 Trapezia septata Dana, 1852: 260, pl. 15 fig. 9. Trapezia areolata auct. non Trapezia areolata Dana, 1852: 259. 3) Corresponding author; e-mail: [email protected] © Koninklijke Brill NV, Leiden, 2009 Crustaceana 82 (12): 1603-1608 Also available online: www.brill.nl/cr DOI:10.1163/156854009X463838 1604 NOTES AND NEWS Material examined. — One female (ZRC 1984.5692), on Pocillopora, Siloso Beach, Sentosa Island, Singapore, coll. P. K. L. Ng, 29 Apr. 1982; 2 females (ZRC 1985.1550-1551), Siloso Beach, Sentosa Island, Singapore, coll. P. K. L. Ng, 1981; 6 males, 6 females (ZRC 1965.11.22.67-76), Pedra Blanca Island, Horsburgh Lighthouse, Singapore, coll. M. W. F. Tweedie, Jul. 1934; 1 male, 3 females (ZRC 1970.7.13.61-65), Pedra Blanca Island, Horsburgh Lighthouse, Singapore, coll. M. W. F. Tweedie, 1934; 2 males, 1 female (ZRC 1965.11.22.46-48), Raffles Lighthouse, Singapore, coll. A. Monteiro, 12 Mar. 1947. Remarks. — Trapezia septata has been observed alive on the high-current reefs that fringe two islands, Pulau Satumu and the Sisters Islands, to the south of Singapore, on the branching pocilloporid corals Pocillopora damicornis (Linnaeus, 1758) and P. verrucosa (Ellis & Solander, 1786). Interestingly, the older Singapore material had all been collected from areas with strong currents. Raffles Lighthouse and Horsburgh Lighthouse are isolated islands at the edge of Singapore’s territorial waters, the reefs there being characterized by strong currents. The two samples from Sentosa were from the southeastern corner of the island where currents are also strong at high tide. A total of 89 colonies of Pocillopora damicornis and 24 colonies of P. ver- rucosa, ranging in size from 5 to 40 cm diameter, and a total of 16 T. septata were recorded between 2007 and 2008. Of the 16 specimens of T. septata ob- served, 12 were recorded from P. verrucosa. In Singapore, individual colonies of P. verrucosa were noted to harbour a relatively low diversity of crustacean ec- tosymbionts. Most P. verrucosa colonies were inhabited by only one species of such ectosymbiont, and never more than two co-occurring species of crustacean ectosymbionts were observed (fig. 1). Pocillopora verrucosa was predominantly occupied by T. septata (50%), less commonly by T. cymodoce (25%), and rarely (13%) by the coral-dwelling alpheid shrimps, Alpheus lottini Guérin-Méneville, 1829 (Alpheidae) (fig. 2). Other known crustacean ectosymbionts of pocilloporid corals (including pontoniine shrimps and the xanthid crab, Cymo) were absent (fig. 1). In comparison, the ectosymbiont diversity of similar-sized P. damicornis was much higher, with up to five different crustacean ectosymbiont taxa observed. These included T. cymodoce, Cymo spp., and Kemponia amymone (De Man, 1902) (Palaemonidae), which occurred in at least 25% of the P. damicornis examined (fig. 2). Chi-square tests were used to test the null hypothesis that ectosymbiont utilization of host species was purely a function of availability/abundance. The fre- quency with which each species of ectosymbiont was observed on either P. dam- icornis or P. verrucosa was compared against the frequency distribution of each species of coral; for significance testing, species were subsequently categorized as using hosts either more, or less than available, if proportions were greater or less than, respectively, the 95% confidence interval around the proportional abun- dance of the host coral (see Sin, 1999, for details). Results indicate that T. septata were observed on P. verrucosa significantly more often than expected (table I)..