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New Molecular Tools to Examine Paleo-phylogeographic Responses to Climate Change: Ancient Coral Migrations in the North Atlantic
Waller and Shank

The biodiversity of seamounts and, in particular, the fragility of deep-sea coral populations has received heightened media and scientific attention in recent years. The ability of corals to harbor a broad array of associated fauna (many endemic), including commercially important fish species, makes them of immediate interest to conservationists, managers and scientists. Yet our understanding of the historical processes that have shaped the biodiversity and biogeography of corals (and their habitats) is still in its infancy (see Census of Marine Life for Seamounts CenSeam report).

Hard corals (Scleractinians) have been present throughout the world's oceans for millions of years, and so have experienced many climatic changes and extinction events. They build skeletons that incorporate chemical traces indicative of conditions in the surrounding seawater, permitting fossilized individuals from Northwest Atlantic seamounts to now be used to define major changes in intermediate and deep ocean circulation that coincide with large swings in atmospheric climate since the Last Glacial Maximum1. These fossil corals are found in great abundance at depths below the thermocline, yet the phylogeographic relationships between, and the effect climate change has had upon these populations, is at present unexplored.

We are investigating ancient deep-water coral migration patterns from locations spanning 1,500m depth range, on three NW Atlantic Seamounts through the development of new techniques to extract ancient DNA from fossilized coral. In 2003, an Alvin cruise collected fossil Desmophyllum cristagalli and Lophelia pertusa in abundance from two New England Seamounts, and Muir Seamount north of Bermuda. Paleoclimatic history (14C, U-series data to infer water mass movement) from these corals is being amassed by our collaborators at the California Institute of Technology.

By developing and refining methods to extract DNA from these specific fossilized corals, we are elucidating historical patterns of migration and gene flow, coincident with oceanic circulation patterns and events. Patterns of gene flow among ancient coral populations inhabiting seamounts at different depth ranges (variably influenced by the Gulf Stream over time) will provide insights into this climaticallyinteresting region.

We are examining the evolutionary consequences of climate change first hand, and reconstruct ancient deep-water migrations and colonization events. We intend to use this technique to predict the impact of future climate projections and models on seamount biodiversity. Future uses of this tool for understanding the formation of biodiversity and biogeographic patterns will provide new opportunities to examine ancient migration patterns over a broad spectrum of fauna with suitable skeletal material, such as clams, mussels and gastropods, abundant in the fossil record.