Nests placements and spawning in the endangered horseshoe crab Tachypleus tridentatus (Leach, 1819) (Merostomata: Xiphosurida: Limulidae) in Sabah, Malaysia

Abstract

Horseshoe crab populations are declining worldwide, and Tachypleus tridentatus (Leach, 1819) has recently been classified as Endangered in the IUCN Redlist. Among the keys for species survival is successful reproduction. Although there are reports on the reproduction, particularly details on the spawning behaviour, of the American species, Limulus polyphemus (Linnaeus, 1758), information on Southeast Asia species is very scant. This field study reports the nesting activities of T. tridentatus at Jambongan Island, Sabah, Malaysia. Observation were carried out on 16 spawning pairs that were spotted during full and new moon from April-July 2016 in Sabah. Nest placements, number of nests, number of eggs, time spent at each nest, and nest widths, depth, and distance from the highest tide line were recorded for each pair. Tachypleus tridentatus generally laid an average of 967 ± 54.1 eggs/nest (171–2,282) in as many as nine nests on the intertidal zone between 125 and 940 cm from the highest tide. The first nest was dug once the tide began rising, followed by the consecutive nests towards the highest tide line with nest depths ranging between 13 and 22 cm. The complete spawning session (first nest to the last) ended in less than two hours. Time spent in spawning correlates positively with the number of nests and the total number of eggs laid by each spawning female. The spawning area, which is made up mainly by fine and medium-size sediment grains, also experience stable temperature, salinity, and dissolved oxygen conducive for egg-laying and larval development for successful reproduction. The details of spawning are important for planning successful future conservation initiatives for the species, especially in tropical regions.

Spawning habitat suitability maps for the conservation of the tri‐spine horseshoe crab Tachypleus tridentatus in Tsuyazaki Cove, Fukuoka, Japan

“…This study suggests that beach elevation is an adequate parameter for predicting the suitable spawning zone for T. tridentatus (Table 3). The estimated suitable spawning zone was highly compatible with other T. tridentatus habitats with a wide range of grain compositions – fine to medium sand in the present study, medium to coarse sand in Fukuoka (Wakamiya, 1989), gravelly sand in Imari (Botton et al, 1996) and fine to medium sand in Malaysia (Mohamad et al, 2019) – indicating that the beach elevation model can be applied to other T. tridentatus spawning grounds.…”

“…In Japan, almost all nests in the significant T. tridentatus spawning habitats in Kyushu were found within the same tidal range: 86% (378 of 439 nests) in Imazu, Kafuri, Tsuyazaki and Sone habitats of Fukuoka (Wakamiya, 1989), 97% (400 of 414 nests) in Imari, Saga (Sekiguchi, 1999). Although comparative studies are limited in other Asian countries due to the lack of T. tridentatus spawning data (Wang et al, 2020), 75% of the nests (51 in 68 nests) were detected within the same tidal range in Malaysia (Mohamad et al, 2019). Thus, it can be concluded that although the sample size in this study was small ( n = 43) due to the rapid decline of the horseshoe crabs in the area (Itaya et al, 2019; Itaya, Wada & Shuuno, 2022), the estimated suitable zone reflects the actual spawning preference of the species.…”

“…Many studies have investigated the environmental conditions necessary for the successful spawning of T. tridentatus . For example, beach elevation, slope, grain composition, sediment moisture, exposure time and dissolved oxygen have all been suggested to be environmental factors that determine nesting location (e.g., Seino et al, 1998; Ohtsubo et al, 2005; Wada, Itaya & Shuuno, 2010; Hsieh & Chen, 2015; Mohamad et al, 2019; Itaya et al, 2022). It is also known from observations in captivity and in the field that appropriate salinity and temperature conditions are required for egg development and larval hatching (Sugita, Murakami & Sekiguchi, 1985; Sekiguchi, 1999; Maeda et al, 2000; Chen, Yen & Lin, 2004).…”

High genetic diversity and mixing of coastal horseshoe crabs (Tachypleus gigas) across major habitats in Sundaland, Indonesia

“…However, some others explained that this crab has a wide dispersal abilities based on long-term studies. Individual distances up to 30 km have been observed in Malaysian crabs ( Mohamad et al, 2019 ), while the movement abilities of tri-spined horseshoe crab did not exceed 150 km ( Yang et al, 2007 ). Similarly, the American horseshoe crab in the Great Bay Estuary (USA) has a maximum mean annual linear distance ranging between 4.5 km and 9.2 km ( Schaller, Chabot & Watson, 2010 ).…”

Effect of Intertidal Elevation at Tsuyazaki Cove, Fukuoka, Japan on Survival Rate of Horseshoe Crab Tachypleus tridentatus Eggs

“…97% of T. tridentatus spawning was found between the EHTL and the MHWN in Imari, Japan, but most were concentrated near the mid intertidal zone (Sekiguchi, 1999). In Malaysia as well, more than 50% of T. tridentatus spawning was concentrated in the mid intertidal zone (Mohamad et al, 2019). The Atlantic horseshoe crab (Limulus polyphemus) laid their eggs between the high intertidal and the mid intertidal zones.…”