Population structure of the Gulf pipefish in and around Mobile Bay and the northern Gulf of Mexico.

The genetic structure of inshore aquatic populations can be influenced by a number of factors, including coastal configurations, flow rates, and local adaptation. Properties such as salinity and temperature can differ significantly along the coasts and into the bays and rivers that contribute to these systems. Within these environments, low migratory euryhaline species provide a unique system to examine how these factors influence population structure, even when these populations are continuously distributed. In this study, we utilized microsatellite data to assess the population structure of 7 Gulf pipefish populations located in and around Mobile Bay and the northern Gulf of Mexico. Global F (ST) values (F (ST) = 0.025) suggest moderate levels of genetic structure among the populations. Local genetic structure was present among all coastal pipefish populations. Significant levels of genetic structure were also observed between coastal and estuarine populations (P < 0.05), with bay populations being distinct from their coastal counterparts. Cluster analysis suggests 2 parental populations, with one consisting mainly of estuarine individuals and the other comprising mainly coastal individuals. However, although these populations were genetically distinct, the genetic data also suggested moderate levels of migration between coastal and estuarine areas. We suggest that the differentiation between these populations is likely due to the colonization of individuals from coastal populations followed by limited dispersal out of the bay. It is also possible that different selective pressures between coastal and estuarine habitats may be contributing to the genetic differences between these populations.