The lined seahorse was thought to be a vagrant visitor to the eastern seaboard of North America. Hippocampus erectus is a common animal in 3 areas of the western Atlantic. It was thought to die off when temperatures dipped off Virginia, but it has always persisted there and in the Caribbean and Carolina zoogeographic provinces

This seahorse species is a common inhabitant of beaches and estuaries, like several tropical fish species, during the summer. They are all regarded as strays off the north of the Gulf Stream or planktonic drifters, perhaps on Sargassum rafts that could shelter them. JT Boehm and 3 colleagues from the City College of New York and the South Carolina Department of Natural Resources used population genomics to work out just how resident the fish are, north of Cape Hatteras, which is basically a barrier to warmer currents.

This northern sub-population off Virginia comes out as persistently breeding in an isolated gene pool for many generations. The 3 zoogeographical regions each have distinct populations that mix very little. Larger populations in the south show more variability (heterozygosity) probably because of their numbers. The northern animals have been isolated for so long in a smaller population that they appear quite inbred.

The lined sea horse now seems to migrate into deeper water during winter, explaining its apparent disappearance. Hippocampus does not swim well, but has been found in NOAA offshore trawls. It has to be assumed that it reduces energy demand andhibernates on the intercontinental shelf even as far south as Florida. Conservation will certainly be helped by such research, as we can now discover elements of animal populations’ ancestry that have so far been impossible to work out. These genomic methods can extract many pieces of information about multiple ancestors, even from small samples. Many animals will benefit from these techniques, while some seahorse conservationists must now concentrate on a unique and small northern population of Hippocampus erectus

After the last effects of the Ice Age, it can be assumed these seahorse invaded the most northerly Atlantic coasts where seagrass habitat for them is available. Pipefish live in the same areas here, too, and the winter behaviour is similar. To link up with our own story, there is a New Zealand discovery of new species described here, while dwarf seahorse species were also threated by the Gulf oil spill, but seem to be hanging on.