The Role of Artificial Structures in Facilitating Range Expansion of the Introduced Barnacle Megabalanus Coccopoma in the Southeastern U.S.A.

The barnacle Megabalanus coccopoma is a recent invader of the southeastern U.S.A. from the tropical eastern Pacific. In Georgia, M. coccopoma populations along the immediate coastline often suffer extensive mortality during the winter, but population rebuilding is common after these events suggesting that there may be nearby larval sources. I investigated the hypothesis that artificial structures (i.e., buoys, towers), occurring far enough offshore of Georgia for water temperatures to be moderated by the Gulf Stream, provide refuges for breeding adults of M. coccopoma and can serve as the larval source. I investigated this hypothesis by first developing thirteen microsatellite primer pairs specific to M. coccopoma. I also developed the polymerase chain reaction (PCR) and sequencing protocols for use with the primers. These 13 primer pairs were tested on 42 individuals from two populations of M. coccopoma. The results indicated high allelic diversity in all of the loci making these primers useful in evaluating population genetics questions related to M. coccopoma. To further evaluate the role of artificial structures in the range expansion of M. coccopoma, I collected demographic information on existing populations, monitored temperature and salinity both on and offshore, and assessed genetic diversity and structure at 8 research sites ranging from the shoreline to ~50km offshore in the southeast. Demographic information and abiotic parameter monitoring indicated that offshore artificial structures are suitable habitats for M. coccopoma adults and these structures also house M. coccopoma populations that are composed of stable, mature individuals that can serve as an abundant source of larvae. The genetic assessment revealed high allelic diversity and significant deviations from Hardy-Weinberg Equilibrium (HWE) in all subpopulations. The analysis of genetic structure indicated that the M. coccopoma population in the Georgia Bight is panmictic and suggested that a Wahlund Effect is acting to increase allelic diversity and causing HWE deviations. The combined results support my hypothesis that offshore structures in the Georgia Bight can act as refuges for breeding adults, however there are likely additional larval sources from beyond the region examined that are facilitating the range expansion of M. coccopoma in the southeastern U.S.A