Spawning and Nesting Behaviour of Tachypleus gigas along the East Coast of Peninsular Malaysia

Abstract

Present study was aimed to address the spawning and nesting behaviour of Malaysian horseshoe crab (Tachypleus gigas) in observed nesting grounds of East coast of Peninsular Malaysia during monsoonal period. Field sampling was carried out in every full and new moon days between September and December 2009 in Balok (Lat3°56.194' N, Long103°22.608' E) and Pekan (Lat3°36.181' N, Long103°23.946' E) nesting grounds. A total of 26 nests were found throughout the sampling period (Balok = 4 nests [~15%]; Pekan = 22 nests [~85%]) with higher percentage nesting was noted in November (N = 11 nests [~50%]) in Pekan. No nests were found in Balok station in all sampling months except during September (4 nests). It was also noted that the horseshoe crab preferred nesting during full moon time compared to new moon period. Mean depth × width of the T.gigas nests were 19.96±5.6×10.72±2.1cm. Number of eggs and larval counting in each nest were also recorded together with hydrographic and sedimentological parameters of the nesting grounds. This study clearly showed negative influence of monsoonal cycle on the nest preference and spawning behaviour of T.gigas. Long term monitoring studies would enable us to understand the number of shore reaching horseshoe crabs which is an essential source for the wild population.

Trailing the Spawning Horseshoe Crab Tachypleus Gigas (Müller, 1785) at Designated Natal Beaches on the East Coast of Peninsular Malaysia

“…While acoustic transmitters were sensitive to wind and time consuming to locate crabs [26,27], manual tracking of spawning horseshoe crabs by observing the release of bubbles before and after spring tide is effective, feasible and low cost. Presently, the emergence of T. gigas to Balok was lower than previous records [15,18,20]. Past surveys at Tanjung Selangor, the only T. gigas spawning site with long term investigations in Malaysia showed that beach conditions during SW monsoon was most favourable to the horseshoe crab for spawning [21].…”

“…The arrival of three spawning amplexus at Cherating and another six at Balok is evident to small T. gigas populations in Malaysia [15,18,21] that consist of assemblages [31,32]. While dissimilar operational sex ratio (OSR) were observed in small population groups such as 1.07:1 at Maine [33] and up to 9:1 in larger groups [34], the absence of satellite male and solitary female produced OSR 1:1 at Balok and Cherating.…”

“…A male crab attach to the rear end of one female crab using their pedipalps is distinguished as a mating pair or amplexus [10][11][12]. A female crab is usually capable of laying 200-300 eggs [13] in varying depths (5-20 cm) below the sand [14,15]. However, the crab's spawning output is largely influenced by season and local environmental, such as edaphic and hydrology conditions [16,17].…”

“…Following the usual method to obtain horseshoe crabs in Malaysia via net catching [18,19], the assessment of spawning crabs by hand collection is only limited to the studies of [15,20,21]. Although covering different sites, estimation of spawning crabs were based on arrivals and random finding of nests during low-tide periods.…”

Macrobenthic diversity in Horseshoe Crab nesting ground – Balok station, Pahang, Malaysia

“…Balok (Lat3°56.194' N, Long103°22.608' E) in the Pahang state of East coast of Malaysia were observed to be the nesting ground of Horseshoe crabs Akbar John et al, 2011Zaleha et al, 2012). Adult horseshoe crabs migrate from the off shore continental shelf to spawn on intertidal sandy (T.gigas) and mud sandy beaches and mangrove area (C. rotundicauda) at every full and new moon at these sampling locations (Fig.…”