Effect of intertidal elevation at Tsuyazaki Cove, Fukuoka, Japan on survival rate of horseshoe crab eggs

Itaya, Shinji, Shuuno, Mari, Onikura, Norio, Yano, Shinichiro

Physical factors affecting the survival of Tachypleus tridentatus eggs were investigated by translocating their eggs between the high intertidal zone and the low intertidal zone of a known spawning site. The mean egg survival rates per day were highest in the mid intertidal zone (45.1 ± 25.4%) and lowest in the low intertidal zone (13.3 ± 27.6%). Differences in the elevation, air exposure time, and water content of the spawning ground were significant factors determining the egg survival rates. Excessive or insufficient air exposure time resulted in inadequate water content at higher and lower intertidal zones reducing egg survival. On the other hand, moderate saturation and dehydration were repeated with each tidal movement in the mid intertidal zone. This dynamic is considered one of the crucial factors for the survival of eggs and is considered optimal for spawning. Therefore, the protection of the mid intertidal zone is imperative for maximizing the egg survival rate in Tsuyazaki Cove where almost all suitable nesting sites have disappeared due to coastal development. By protecting these optimal sites for spawning and recovering other optimal sites on suitable beaches a positive contribution could be made to future management and conservation. The study also suggests the possibility of translocating eggs from marginal to optimal spawning sites as a recovery strategy for this globally endangered species.

Effect of intertidal elevation at Tsuyazaki Cove, Fukuoka, Japan on survival rate of horseshoe crab eggs

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