The Genomic Ghosts of Geukensia granosissima

Observations that biodiversity - particularly in coastal marine species - is redistributing itself as the environment changes has been a key indicator of the climate change era. Historical surveys help us identify such patterns in taxa that might not be typically monitored for distribution or abundance. As recently as 1992, the southern ribbed mussel Geukensia granosissima was considered to be relatively abundant in northeastern Florida. Climate velocity predictions might suggest that these mussels would now have cryptically invaded the marshes of Georgia, which has historically only harbored the congener G. demissa , with possible ecosystem consequences. I re-surveyed Geukensia from both coasts of Florida and sites in Georgia for mitochondrial and nuclear genomic diversity. As of this report, G. granosissima is all but gone from the Atlantic coast of Florida, though some signature of its history remains in these data. The reason for this rapid fluctuation in distribution is not known, but is important for clarification of regional biogeographic patterns.