Population genetics and mating systems of European seahorses Hippocampus guttalatus and Hippocampus hippocampus

Molecular genetic studies of European seahorses revealed the presence of two native species (European long snouted seahorse Hippocampus guttulatus and European short snouted seahorse Hippocampus hippocampus) the primary focus of the present study. Ecological studies across the entire geographic range of the species confirmed low density and patchy population distribution.

Habitat and holdfast preferences were different for the two seahorse species, with substantial variation between population locations. Morphological characteristics of the seahorses varied considerably across their range, but significant differences were observed within just one population of each species. No environmental parameters were consistent across all populations, and no specific indicators for seahorse presence were discovered. The tissue collection technique, fin clipping, was confirmed to not significantly affect seahorse mortality or growth; this technique was used for all tissue biopsies during this study. Genetic analysis using mitochondrial DNA sequences and data from five microsatellite markers revealed significant population structuring across both species’ geographic range.

Contemporary environmental factors for this structuring were both physical barriers to gene flow and geographic distance between populations. Most physical barriers identified have also affected other marine species; however a proposed barrier at Cape Finisterre, observed for both seahorse species, has previously only been documented in a few other species. Historic events appear to have influenced the contemporary structure of the two seahorse species differently, with H. hippocampus showing less population structuring. Population expansion and founder effects were seen in most geographic regions.

Previously acknowledged refugia sites of the last glacial maximum were also seen in seahorses, but these were different in each species. Microsatellite markers revealed monogamy within broods and breeding cycles for the social polygamous H. guttulatus. Finally the findings of this study were used to suggest specific management and conservation practises for seahorse species across Europe.

Woodall, L. (2009). Population genetics and mating systems of European seahorses Hippocampus guttalatus and Hippocampus hippocampus. Doctoral dissertation, Royal Holloway, University of London, UK.