DISTRIBUTION, POPULATION STRUCTURE AND REPRODUCTIVE BIOLOGY OF NIPA-OBLIGATE CRAB Labuanium politum IN WESTERN PART OF SARAWAK

Akma Iddin, Masini (2020) DISTRIBUTION, POPULATION STRUCTURE AND REPRODUCTIVE BIOLOGY OF NIPA-OBLIGATE CRAB Labuanium politum IN WESTERN PART OF SARAWAK. Masters thesis, Universiti Malaysia Sarawak (UNIMAS).

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Abstract

Labuanium politum is a nipa-obligate arboreal crab and may be facing threats from human exploitation and habitat disturbance for socio-economic development in Sarawak. In addition, the ecology of this crab in their natural habitat are still unknown and it is crucial to balance the needs between resource utilisation and conservation. Therefore, this study was performed to i) document the distribution and population structure of L. politum at four nipa forest (NF) conditions based on human activity, ii) correlate selected environmental factors of NFs with L. politum population structure, iii) determine sexual maturity size (SM50) of L. politum and iv) examine any form of parasitic infestation on L. politum. For the first objective, samplings were performed at selected NFs in three districts of Sarawak during daytime (15/04/2017–20/10/2018). The sites were then categorised into four conditions: i) managed NF, ii) managed NF with L. politum exploitation, iii) deforested NF and iv) undisturbed NF. It was observed that L. politum is not endemic since this crab were found from all NFs surveyed and majorities belong to 20–24 mm (28.39%) and 25–29 mm (31.17%) size classes while the minorities were recorded in 5–9 mm (1.23%), 10–14 mm (4.32%) and 35–39 mm (0.31%) size classes. Results showed that NF management via tree pruning seem to benefit L. politum populations which provide more green leaves and boost its food availability. In unmanaged nipa, the abundance of nipa palm tree was not affecting the L. politum population. For the second objective, the environmental parameters (total organic matter, sediment moisture, mud and air temperature and light penetration) at two different localities (Tambak and Tambirat) were measured simultaneously with crab collections for six month period (Jun-Aug 2017; Nov 2017-Jan 2018). Between localities, Tambak was significantly higher in mud temperature and light penetration, while Tambirat was significantly higher in sediment moisture. The carapace width (CW) ranged from 8.32–33.64 mm (males) and 10.80–32.74 mm (females). The density and CW of L. politum were equal throughout sampling periods at each site and between both localities. Overall, Tambak samples dominated bigger CW size classes than Tambirat and males were dominating bigger CW size classes than the females but no sexual dimorphism was observed in the carapace shape. A significant negative correlation was observed between TOM and L. politum CW at Tambak, while other parameters were not correlated for both localities. However, this finding may not reflect the real case since the environmental parameters were not measured on daily basis. Based on the SM50, Tambirat population achieved SM50 in smaller size (male = 17.54 mm, female = 20.27 mm) than Tambak population (male = 23.28 mm, female = 21.99 mm) which could be due to higher human exploitation pressure at Tambirat. Correspondance Analysis showed crabs with DE stage were closely associated in July and August (50%) for Tambak and June (<40%) for Tambirat, thus the ideal harvesting time suggested should be in July onwards. Furthermore, the ideal harvesting size limit set at 75% total maturation was approximately >23.00 mm (Tambirat) and >26.00 mm (Tambak). This study had newly discovered branchial bopyrid isopod Leidya distorta infesting L. politum in Southeast Asia region. Only female isopods of various stages were found harbouring the L. politum. Higher prevalence occurred at Tambirat (4.46%) than Tambak (2.41%) but this infestation did not show fully castration effect towards its host.

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