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Click below to go to the Cruise Logs - (photo credit: Lophelia Coral - Open-File Report 2008-1148 & OCS Study MMS 2008-015)

Deep-sea Cruises 2010 - Cruise 1

Cruise Log: 9/28/2010    

Genetic connectivity between Gulf and Atlantic Lophelia populations

Cheryl Morrison

Figure 1. Map of DISCOVRE study sites in the Gulf of Mexico with arrows representing the direction of major currents (after Morey et al. 2003). - click to enlarge
One of the themes that tie many of our research objectives together is 'connectivity', or the extent to which spatially separated populations are linked through the exchange of juveniles or adults (link to connectivity blogs from 10/3/08 and/or 9/17/09). Since it is difficult to directly observe movements of Lophelia larvae as they travel with currents between reef areas (link to Lophelia larvae blog 9/23/09), we use other methods such as genetic markers to assess how closely related these reef areas are.

Oceanographic setting of our study sites
We originally thought that Gulf and Atlantic Lophelia populations would be highly connected since the Gulf of Mexico Loop Current meets the Florida Current in The Straits of Florida and then the Gulf Stream, potentially providing a means of transport for Lophelia larvae between the Gulf and the Atlantic regions. Data from genetic markers suggest that northern Gulf Lophelia populations are well connected to each other. However, Atlantic populations appear isolated from the Gulf. Closer examination of Gulf currents suggests that reefs in the northern Gulf, such as the Viosca Knoll reefs we just visited, lie to the north of the general flow of the Loop Current and are not transported southward toward the Straits of Florida. Instead reefs like those at Viosca Knoll may be influenced more by Loop Current eddies that may transport larvae westward (Figure 1). Conversely, populations sampled from off the coast of southern Florida (Miami and Cape Canaveral) have a mixture of Gulf and Atlantic genetic signatures.

Figure 2. A deep coral reef on the West Florida slope. Along with Lophelia, the orange colonial coral Madrepora oculata is fairly common, along with the orange cup coral Thecopsammia socialis, lace corals (Stylaster), and glass sponges. - click to enlarge
The West Florida Slope Lophelia reefs
Our next stop is the West Florida Slope (link to blog 9/18/09). The Lophelia reefs in this area are of great interest to our connectivity studies because several currents meet in this location making circulation patterns extremely complex. The West Florida Slope is influenced by the Loop Current; therefore, the potential for these reefs to receive larvae from the Caribbean Sea and provide larvae to the western Atlantic Ocean is high. We hypothesize that the Lophelia reefs on the West Florida Slope may have a mixed genetic background, with individuals recruiting to this region from the Gulf and Atlantic as we have seen in the Atlantic populations. On our first dive, several scientists have made the observation that the deep reefs on the West Florida Slope appear more similar to those off the east coast of Florida rather than those of the northern Gulf. For example, there are coral species common here that we don't see at Viosca Knoll, such as the colonial coral Madrepora oculata and the solitary coral Thecopsammia socialis (Figure 2). Glass sponges are more common, as well as stylaster (lace) hydrocorals. We have a lot left to learn about the biodiversity at this interesting area. Sampling Lophelia populations from the West Florida Slope will help us to better understand the complex interactions between Lophelia reefs in neighboring ocean regions.

Morey SL, Schroeder WW, O'Brien JJ, Zavala-Hidalgo J (2003) The annual cycle of riverine influence in the eastern Gulf of Mexico basin. Geophys Res Lett 30(16):1867

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