Population dynamics, reproduction and growth of the Indo-Pacific horned sea star, Protoreaster nodosus (Echinodermata; Asteroidea)
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The horned sea star (Protoreaster nodosus) is relatively common in the Indo-Pacific region, but there is little information about its biology. This study of the population biology of P. nodosus was carried out in Davao Gulf, The Philippines (7°5′N, 125°45′E) between September 2006 and May 2008. Protoreaster nodosus was found in sand and seagrass dominated habitats at a mean density of 29 specimens per 100 m2 and a mean biomass of 7.4 kg per 100 m2, whereas a significantly lower density and biomass was found in coral and rock dominated habitats. Adult specimens (mean radius R = 10.0 cm) were found at depths of 0–37 m, whereas juveniles (R < 8 cm) were only found in shallow sandy habitats with abundant seagrass (water depth ≤2 m). Increased gonad weights were found from March to May (spawning period), which coincided with an increasing water temperature and a decreasing salinity. Density and biomass did not change significantly during reproduction, but sea stars avoided intertidal habitats. All specimens with R > 8 cm had well developed gonads and their sex ratio was 1:1. Protoreaster nodosus grew relatively slowly in an enclosure as described by the exponential function G = 7.433 e−0.257 × R . Maturing specimens (R = 6–8 cm) were estimated to have an age of 2–3 years. Specimens with a radius of 10 cm (population mean) were calculated to have an age of 5–6 years, while the maximum age (R = 14 cm) was estimated as 17 years. Potential effects of ornamental collection on the sea star populations are discussed.
We greatly acknowledge E. Santos and K. Schröder for supporting the initiation of the project. We thank I. Ebol, C. Ganadores, E. Glimada, J. Lagarteja, B. Müller, S. Nitza, S. A. Nitza, D. Padrogane, C. Petiluna, M. Saceda, F. Salac, J. Salinas, I. Santamaria and R. Tejada for supporting the fieldwork. Furthermore, we would like to thank R. Scheibling, B. Wilkinson, and two anonymous reviewers for their comments on an earlier version of this manuscript. We for fine-tuning the English language. We are grateful to the communities from Samal Island and Talikud Island for sharing their knowledge of the local marine resources. The performed experiments complied with the current laws of the Republic of the Philippines.
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