Episodic human activities and seasonal impacts on the Tachypleus gigas (Muller, 1785) population at Tanjung Selangor in Peninsular Malaysia

Abstract

The scientific literature on population dynamics, breeding biology and nesting behaviour of the Asian horseshoe crabs is limited and still to emerge from several locations in South and Southeast Asia The present study (2009-2011), aimed at observing the spawning activity of Tachypleus gigas (Muller, 1785) in relation to local environmental conditions, was carried out from Tanjung Selangor (Sites 1-3) on the east coast of Peninsular Malaysia Southwest (SW) monsoon (May-September) was found to be more favourable (range, 456-1309 eggs) than Inter-monsoon (IM) (April and October) (169-317 eggs), whereas no eggs at the time of Northeast (NE) monsoon (November-March) Meanwhile, T gigas preferred Site-1 (located close to River Pahang mouth) for its nesting in the SW and shifted to Site-2 and/or Site-3 (located 150-200 m interior) in the IM periods This nest shifting behaviour of T gigas was primarily associated with the seasonal water current that becomes intensive during NE monsoon However, the human activities such as sand mining (2010), jetty (2010-2011) and road/bridge (2011-present) constructions in the vicinity have affected the normal physicochemical conditions of the sediment/water Importantly, the sediment being represented largely by medium sand with moderate sorting, symmetrical and very leptokurtic properties in 2009 was changed into coarse sand with poor sorting, fine/very fine skewed and extremely leptokurtic in 2010-11 In addition, the heavy metal contamination of Cadmium and Selenium in the sediment and Hydrogen Sulfide in the water increased considerably (2010-11)