Sexual ratio, reproductive period and seasonal variation of the gonochoric shrimp Hippolyte obliquimanus (Caridea: Hippolytidae)

Abstract

Hippolyte obliquimanus is a small, gonochoric shrimp found in algal substrates along the western Atlantic coast of Brazil, particularly in association with seaweed of the genus Sargassum. We studied population features (sexual ratio, reproductive period and temporal distribution) of H. obliquimanus in southeastern Brazil, including its relationships with the seasonality of banks of this alga. Specimens were collected at two-monthly intervals from March 2005 to January 2006, in Ubatuba Bay. The sex of individuals was checked, and the carapace length measured. In total, 668 individuals were collected: 211 males (0.70–2.50 mm carapace length), 341 non-ovigerous females (0.55–2.90 mm), and 116 ovigerous females (1.55–3.20 mm). Hippolyte obliquimanus showed seasonal–continuous reproduction and variable continuous recruitment. The highest number of animals (75%) was collected in fall–winter. The percentages of ovigerous females/total females (fall–winter: 27%; spring–summer: 26%) and the sexual ratio (fall–winter: 31%; spring–summer: 32%) were practically equal in both periods. The sexual ratio showed a predominance of females in almost all size classes, and we detected a new sex ratio pattern for this species. The seasonal variation in the number of individuals can be related to its migration to deeper areas, due to the decrease in the abundance of Sargassum sp. in shallower waters in spring–summer.

Keywords:

• Crustacea
• population
• reproduction
• sexual ratio

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Acknowledgements

This study forms part of a Master's dissertation by MT and was supported by a Fellowship from CAPES. FLM is grateful to CNPq for research fellowship (Proc. 301359/07-5) and MT for an ongoing PhD fellowship (FAPESP, Proc. 06/61771-0). Special thanks are due to all members of the Laboratory of Bioecology and Crustacean Systematics of FFCLRP/USP for their help during field and laboratory work, to Dra. Janet Reid (Virginia Museum of Natural History) for great assistance with English revision and suggestions, and to Dr. Daniel Roccatagliata (Universidad de Buenos Aires) for help with bopyrid identification. The support of the Postgraduate Program in Comparative Biology of FFCLRP/USP and CEBIMar/USP during field work is gratefully acknowledged. We thank Laura López Greco and Fernando D'Incao for commenting on an earlier version of the manuscript during the Master's thesis defence. We would also like to thank the anonymous reviewers and editorial board for their suggestions and contributions toward the improvement of this paper. All experiments conducted in this study complied with current applicable state and federal laws of Brazil (DIFAP/IBAMA, 121/05).

Notes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark