Size at maturation, sex differences, and pair density during the mating season of the Indo-Pacific beach star Archaster typicus (Echinodermata: Asteroidea) in the Philippines

Abstract

Mating of the relatively common sea star, Archaster typicus, provides an excellent opportunity to study maturation processes and behavioral differences between males and females, since monomorphism does not allow separation under normal conditions. The present study determined biological and behavioral features of males and females during the mating season in the Davao Gulf (Philippines). Thousands of pairs were observed in September and October 2008 with a mean density of 3 pairs m⁻². Around full moon, mean density reached 7 pairs m⁻², whereas during new moon very few pairs were found. Specimens reached maturity at a radius (R) of 29 mm, while mating specimens had a mean R of 35 mm. Two-thirds of the population were adults and about 35% participated in mating during each observation. Mean R of mating adults was constant throughout the mating season, but within pairs, males were significantly larger in September than in October. The locomotion rate increased with R from 40 to 60 cm min⁻¹ and there was no significant difference between males and females. The role of the lunar cycle as a trigger for reproduction and the significance of large males mating before small males are discussed.

Keywords:

• locomotion
• lunar cycle
• pseudo-copulation
• reproduction
• sea star

Acknowledgments

We acknowledge I. Ebol, C. Ganadores, E. Glimada, S. Nitza, D. Padrogane, C. Petiluna, F. Salac, J. Salinas, and R. Tejada for supporting the field study and three anonymous reviewers for providing valuable comments to an earlier version of this article. This study was partially financed through cooperation between Davao del Norte State College and the German Development Service – DED. The performed experiments complied with the current laws of the Republic of the Philippines.