CORAL HEALTH ASSESSMENT PROGRAM STUDIES

Microspatial Scale Genetic Differentiation on a Coral Reef

The primary goal of this research was to understand how coral colonies within a reef are genetically related to each other. To this end we attempted to completely census Porites lobata colonies of a single reef at French Frigate Shoals. Initial surveys identified two reefs as potential candidates for the census. The basic characteristics of an acceptable reef were less than 100% coral cover, a relatively shallow depth (to allow enough bottom time to survey efficiently), and a small enough area to not exceed the number of colonies allowed in the collection permits. Reef 29, a 0.025 hectare patch reef in the northwest of the atoll (166° 15.7825W, 23° 49.9316N) fairly well fit these criteria.

Figure 1. Map of GPS / hydrophone array positioned around Reef 29, a patch reef in French Frigate Shoals. (Click on the image to open a larger version.)

To place both the reef and the colonies on the reef in a global position context, an underwater GPS system was used. This system included four buoys each mounted with an above water GPS unit and a below water hydrophone (Figure 1). Divers carried two acoustic transmitters (32 KHz and 39 KHz) that the buoyed hydrophones used to triangulate the underwater position. These signals were then relayed via radio from each of the buoys to a receiver connected to a computer on a nearby boat where the data were processed and converted into position (Figure 2). Measuring tapes were set in a grid on the reef and the acoustic transmitters were placed at the beginning and end of one of the tapes. The grid headings were 310° for the Y transect and 220° for the X transect. The exact location of every colony within the transect grid was determined based on the distance from the measuring tape. These locations will be converted into a global position in relation to the underwater acoustic transmitters.

Figure 2. Spatial distribution of 264 coral colonies sampled at Reef 29. (Click on the image to open a larger version.)

Preliminary results indicate that the combination of airbrushing and extracting with the PowerSoil DNA Isolation Kit (MoBio Laboratories Inc., Carlsbad, CA) result in the highest yield of PCR-amplifiable bacterial DNA and the highest quality TRFLP bacterial community profiles for both Porites compressa and Porites lobata. We were unable to obtain high quality TRFLP bacterial community profiles for Montipora capitata using the methods employed in this study. Further analyses are being carried out to determine the best method for extracting bacterial DNA from this coral species.

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