Evidence for Sequential Hermaphroditism in Sabellastarte spectabilis (Polychaeta: Sabellidae) in Hawai‘i

Understanding the reproductive characteristics of Sabellastarte spectabilis (Grube, 1878), an economically important polychaete worm collected for the aquarium trade, is essential to the development of artificial propagation and conservation of coral reefs. The purpose of this study was to determine whether S. spectabilis is hermaphroditic. Using histological techniques, 180 individuals were examined for gametes. Gametes were present only in abdominal segments. Primary oocytes were 7–8 mm in diameter in histologically prepared sections. Sperm appeared as round black dots about 2 mm in diameter on histologically prepared slides. Most individuals sampled had only one type of gamete in the coelom, but both eggs and sperm were seen in the coelom of 15% of individuals, demonstrating the occurrence of hermaphroditism in Hawaiian populations of S. spectabilis. The sex ratio of males to females was skewed significantly toward males in both the small (6–8 mm diameter) and medium (9–10 mm diameter) sized worms. Among the largest worms (11–13 mm diameter), the sex ratio did not diverge significantly from 1 : 1. There was a significantly higher proportion of hermaphrodites (30%) in the large size class. Worms of unknown gender, although present in all size classes examined, were most frequent (33%) in the medium size class. These patterns are consistent with sequential (protandrous) hermaphroditism. The sabellid polychaete Sabellastarte spectabilis (Grube, 1878) is common in bays and harbors in the main Hawaiian Islands and particularly in Kāne‘ohe Bay, on the windward coast of O‘ahu. Kāne‘ohe Bay is partially cut off from the ocean by a barrier reef, which protects it from large waves and provides an ideal habitat for these softtubed filter feeders. Sabellastarte spectabilis is very abundant in the bay, which is the principal collection site for this commercially important ornamental species (Walsh et al. 2003). These worms settle in cracks and crevices of living and dead reef corals, making collection difficult and damaging to the reef community. Reproduction is currently being studied in this species (Bybee et al. in press) with the goal of facilitating artificial propagation to reduce pressure on coral reefs due to destructive collecting practices. Pacific Science (2006), vol. 60, no. 4:541–547 : 2006 by University of Hawai‘i Press All rights reserved 1 The PADI Foundation, the Edmondson Fund (University of Hawai‘i), and The Center for Tropical and Subtropical Aquaculture provided financial support for this project. This paper is funded in part by grants/ cooperative agreements from the U.S. Department of Agriculture, CSREES Agreement No. 2002-3850012039; National Oceanic and Atmospheric Administration, Project No. A/AS-1, which is sponsored by the University of Hawai‘i Sea Grant College Program, SOEST, under Institutional Grant No. NA16RG2254 from the NOAA Office of Sea Grant, U.S. Department of Commerce, and the State of Hawai‘i Department of Agriculture, Aquaculture Development Program, Contracts No. 49855 and 52663. The views expressed herein are those of the authors and do not necessarily reflect the views of NOAA, USDA, the State of Hawai‘i, or any of their subagencies. UNIHI-SEAGRANT-JC-04-09. Facilities were generously made available for this research at the Hawai‘i Institute of Marine Biology (contribution no. 1216). Manuscript accepted 9 December 2005. 2 Department of Zoology, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i. 3 College Sea Grant Program, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i. 4 Corresponding author (fax: 808-956-9812; e-mail: