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 (Müller, 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). These changes, not only reduced T. gigas spawning activity/egg counts between 2009 and 2010 (from an average of 912 ± 690 to 360 ± 288) (±SD), but also correlated with its total absence during 2011 (PRIMER v.6). Since Tanjung Selangor beach (adjoining the Terus and Pahang Tua estuary) is one of the very few known spawning grounds for the Malaysian horseshoe crab (T. gigas), it is imperative to conserve and manage this area and it should be sanctioned as a ‘Marine Protected Area’. |
