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Journal of Threatened Taxa Building evidence for conservaton globally www.threatenedtaxa.org ISSN 0974-7907 (Online) | ISSN 0974-7893 (Print) Article Postembryonic development of the Tri-spine Horseshoe Crab Tachypleus tridentatus (Merostomata: Xiphosura) in a nursery habitat in the Philippines Dorkas Kaiser & Sabine Schoppe 26 December 2018 | Vol. 10 | No. 15 | Pages: 12916–12932 10.11609/jot.4125.10.15.12916-12932 For Focus, Scope, Aims, Policies and Guidelines visit htps://threatenedtaxa.org/index.php/JoTT/about/editorialPolicies#custom-0 For Artcle Submission Guidelines visit htps://threatenedtaxa.org/index.php/JoTT/about/submissions#onlineSubmissions For Policies against Scientfc Misconduct visit htps://threatenedtaxa.org/index.php/JoTT/about/editorialPolicies#custom-2 For reprints contact <[email protected]> Publisher & Host Partners Member Threatened Taxa Postembryonic development of TachypleusJournal tridentatus of Threatened Taxa | www.threatenedtaxa.org | 26 December 2018 | 10(15): K12916–12932aiser & Schoppe Article Postembryonic development of the Tri-spine Horseshoe Crab Tachypleus tridentatus (Merostomata: Xiphosura) ISSN 0974-7907 (Online) in a nursery habitat in the Philippines ISSN 0974-7893 (Print) Dorkas Kaiser 1 & Sabine Schoppe 2 OPEN ACCESS 1 Insttute of Biosciences, University of Rostock, Rostock 18051, Germany 2 Western Philippines University, Puerto Princesa City, Aborlan, Palawan 5302, Philippines 1,2, Katala Foundaton Inc., Puerto Princesa City, Santa Monica, 5300 Palawan, Philippines 1 [email protected] (corresponding author), 2 [email protected] Abstract Populatons of the Tri-spine Horseshoe Crab Tachypleus tridentatus have dramatcally decreased over their distributon range and conservaton eforts are now crucial. The implementaton of appropriate management strategies and stock assessment rely on accurate growth-rate estmates. The postembryonic development of the species in the tropics, however, is not elucidated. To provide the informaton needed to assess the demographics of juvenile populatons and to judge the status of T. tridentatus in the Philippines, we conducted a mark-recapture experiment in a nursery habitat on Palawan Island. The results obtained during the 10-month period provide the frst consecutve data on the stepwise growth of the species in the Philippines and the frst near comprehensive dataset collected within a single populaton of juveniles in the tropics. By analyzing size-frequency (prosomal width) distributons of 853 individuals and by using 94 juveniles that molted during the study, 13 molt stages were diferentated. Based on the intermolt periods of six instars, we estmated the growth curve of T. tridentatus following two models (non-linear and power functon). The data support the assumpton that growth contnues year-round in the tropics and also indicate that the average age of mature male and female T. tridentatus in the Philippines ranges from three to four years. The agreement with a feld study in Japan suggests that 14 postembryonic stages may be characteristc for the development of natural populatons throughout the range of the species. Though more data are needed to validate these results, the study provides a sound baseline for future studies in the tropics. Keywords: Tri-spine Horseshoe Crab, juveniles, development stages, intertdal zone, morphometry, allometry, size-age relatonship, growth curve. Abbreviatons: AA - Distance between the anal angles; BL - Body length (PL+OL+TL); BM beach - Bernardo Marcelo Beach (study site); CL - Carapace length (PL+OL); DS - Development stage; Eyes - Distance between the compound eyes; IMP - Intermolt period; OL - Opisthosomal length; OW1–3 - Opisthosomal width 1–3 ; PES - Postembryonic stage; PL - Prosomal length; PW - Prosomal width; SPSS - Statstcal Package for the Social Sciences; TL - Telson length; Statstcs: CI - 95% confdence interval; df - Degrees of freedom ; M - Mean value; Min / Max - Minimum and maximum values; n - Sample number ; p - Signifcance level; r - Pearson’s correlaton coefcient; SD - Standard deviaton; SE - Standard error of the mean; T - Statstcs of the one-sample t test; U - Statstcs of the Mann-Whitney U test; W - Statstcs of the Shapiro- Wilk Test ; Z - Statstcs of the Kolmogorov-Smirnov test. DOI: htps://doi.org/10.11609/jot.4125.10.15.12916-12932 Editor: Ruth H. Carmichael, University of South Alabama, Dauphin Island, USA. Date of publicaton: 26 December 2018 (online & print) Manuscript details: Ms # 4125 | Received 14 March 2018 | Final received 03 August 2018 | Finally accepted 02 December 2018 Citaton: Kaiser, D. & S. Schoppe (2018). Postembryonic development of the Tri-spine Horseshoe Crab Tachypleus tridentatus (Merostomata: Xiphosura) in a nursery habitat in the Philippines. Journal of Threatened Taxa 10(15): 12916–12932; htps://doi.org/10.11609/jot.4125.10.15.12916-12932 Copyright: © Kaiser & Schoppe 2018. Creatve Commons Atributon 4.0 Internatonal License. JoTT allows unrestricted use of this artcle in any medium, reproduc- ton and distributon by providing adequate credit to the authors and the source of publicaton. Funding: Mainly self-funded. The ‘Studienstfung des Deutschen Volkes’ provided a scholarship for the frst author in 2001. Competng interests: The authors declare no competng interests. For Author Details and Author Contributon see end of this artcle. Acknowledgements: We are especially grateful for the cooperaton of the Western Philippine University in Puerto Princesa City on Palawan, Philippines. We extend our special thanks to Prof. Günter Arlt from the University of Rostock, Germany. We further thank Sharah Barredo for her contributon to the collecton of juveniles in 2017. The authors are much obliged to the two anonymous reviewers for their constructve comments that considerably improved the manuscript. 12916 Postembryonic development of Tachypleus tridentatus Kaiser & Schoppe INTRODUCTION unambiguously determined for any horseshoe crab species (Carmichael et al. 2003; Chen et al. 2010). The Tri-spine Horseshoe Crab Tachypleus tridentatus Specifcatons for T. tridentatus vary strongly in the (Leach, 1819) (Xiphosura: Chelicerata) is the largest of literature, although there is a consensus that the females four extant species of ancient marine arthropods, the molt once more than the males to reach maturity. origin of which can be traced back to 445 million years Based on laboratory studies, Sekiguchi et al. (1988) (Shuster et al. 2003; Rudkin et al. 2008). The informaton calculated that the females spent 14 years to molt 16 about horseshoe crabs in the Philippines is especially tmes before ataining maturity, while Chen et al. (2010) scarce. Waterman (1958) recorded T. tridentatus and estmated that the females mature in stage 15 afer Carcinoscorpius rotundicauda (Latreille, 1802) for four years when reared in warm water. Goto & Hatori western and southern Philippines, respectvely; based (1929) identfed 14 postembryonic stages by measuring on a picture, both species were listed as occurring in the individuals in their natural habitats in Japan. Kawahara Province of Palawan (Sekiguchi 1988). The frst survey (1984), on the other hand, suggested that the females in conducted from northern to central Palawan confrmed Japan molt 15 tmes in 10 years to reach maturity, while the presence of T. tridentatus in the area (Schoppe Asano (1942, cited in Lee & Morton 2005) estmated 2002). that they molt 18 tmes in 16 years. To our knowledge, Recent harvest pressures and habitat loss prompted the postembryonic development of T. tridentatus the need for management actons to protect horseshoe in their tropical environment is not yet determined, crabs (Berkson et al. 2009). Although stll listed in the but laboratory studies indicate that the growth of Data Defcient category by the IUCN (2017), observatons juveniles could contnue throughout the year when the in Taiwan, Japan, Hong Kong, Singapore, Malaysia, temperature is greater than 28°C (Lee & Morton 2005; Borneo, and Thailand indicate that populatons of T. Chen et al. 2010). Most studies concerning the life tridentatus have dramatcally decreased (Itow 1993; history of T. tridentatus are from Japan, China, or Hong Hsieh & Chen 2009, 2015; Chen et al. 2015; Kwan et al. Kong — countries where ecdysis and spawning appear 2016; Lee & Morton 2016; Wada et al. 2016; Manca et to stop during colder seasons (for instance, Sekiguchi et al. 2017). Unlike other regions in Asia, in the Philippines, al. 1988; Chiu & Morton 2004; Zhou & Morton 2004; Lee there is no commercial exploitaton of T. tridentatus for & Morton 2005; Hu et al. 2009, 2015; Kwan 2015; Kwan the producton of amebocyte lysate or food, but habitat et al. 2015) — while fewer studies were conducted in the loss due to land reclamaton, sea sand mining, and tropics (Robert et al. 2014; Mohamad et al. 2016; Manca coastal development are destroying its natural breeding et al. 2017; Mashar et al. 2017). beaches and nursery habitats. As a result, T. tridentatus In this study, we characterized the postembryonic