Journal of Fish Biology (2011) 78, 1738–1756 doi:10.1111/j.1095-8649.2011.02974.x, available online at wileyonlinelibrary.com Historical and contemporary population genetic connectivity of the European short-snouted seahorse Hippocampus hippocampus and implications for management L. C. Woodall*†, H. J. Koldewey‡ and P. W. Shaw* *School of Biological Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, U.K. and ‡Project Seahorse, Zoological Society of London, Regent’s Park, London NW1 4RY, U.K. This first genetic study of Hippocampus hippocampus covers the species’ entire geographic range and employs two mtDNA markers (control region and cytochrome b) to establish patterns of population structuring. A total of 255 specimens from 21 locations were used to obtain 89 con- catenated haplotypes. The common haplotype was present in all but one population, however, most haplotypes were unique. The haplotype network had a star-like construction, suggesting expansion from a bottleneck event. F ST and AMOVA revealed population subdivision into three geo- graphic regions (English Channel + Bay of Biscay, Mediterranean Sea + Atlantic Ocean Iberian coast + Macaronesian Islands, and West Africa) with barriers to gene flow indentified at Cape Finisterre and the Cape Verde frontal zone. Neutrality tests and nested clade analysis suggest a complex demographic history, with both historic events and contemporary processes shaping pat- terns of genetic differentiation. The genetic population subdivision detected in this study indicates that H. hippocampus should be managed as three separate units. This is especially pertinent as H. hippocampus populations within the West African region are the only ones known to be specif- ically targeted for exploitation. © 2011 The Authors Journal of Fish Biology © 2011 The Fisheries Society of the British Isles Key words: conservation; cytb; mtDNA; Syngnathidae. INTRODUCTION Molecular techniques have an important application in studies of fishes to understand concepts such as phylogeography, gene flow and population structure and to identify drivers of population connectivity in the marine ecosystem. Marine fishes generally have large populations, high fecundity, a dispersive larval phase and adult migra- tion, all of which are predicted to contribute to a highly connected metapopulation structure (Grant & Bowen, 1998; Waples, 1998). Features of a particular species’ biology or environment such as larval behaviour and retention by hydrographic fronts, and fragmented habitats, however, may all contribute to population structuring †Author to whom correspondence should be addressed at present address: School of Biological & Envi- ronmental Sciences, University of Stirling, Stirling, Scotland FK9 4LA, U.K. Tel.: +44 (0) 1786 467757; email: lucywoodall@compuserve.com 1738 © 2011 The Authors Journal of Fish Biology © 2011 The Fisheries Society of the British Isles