Howells, E.J., van Oppen, M.J.H., and Willis, B.L. (2009) High genetic differentiation and cross-shelf patterns of genetic diversity among Great Barrier Reef populations of Symbiodinium. Coral Reefs, 28 (1). pp. 215-225.

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Abstract

The resilience of Symbiodinium harboured by corals is dependent on the genetic diversity and extent of connectivity among reef populations. This study presents genetic analyses of Great Barrier Reef (GBR) populations of clade C Symbiodinium hosted by the alcyonacean coral, Sinularia Xexibilis. Allelic variation at four newly developed microsatellite loci demonstrated that Symbiodinium populations are genetically diVerentiated at all spatial scales from 16 to 1,360 km (pairwise ST = 0.01–0.47, mean = 0.22); the only exception being two neighbouring populations in the Cairns region separated by 17 km. This indicates that gene Xow is restricted for Symbiodinium C hosted by S. Xexibilis on the GBR. Patterns of population structure reXect longshore circulation patterns and limited cross-shelf mixing, suggesting that passive transport by currents is the primary mechanism of dispersal in Symbiodinium types that are acquired horizontally. There was no correlation between the genetic structure of Symbiodinium populations and their host S. Xexibilis, most likely because diVerent factors aVect the dispersal and recruitment of each partner in the symbiosis. The genetic diversity of these Symbiodinium reef populations is on average 1.5 times lower on inshore reefs than on oVshore reefs. Lower inshore diversity may reXect the impact of recent bleaching events on Sinularia assemblages, which have been more widespread and severe on inshore reefs, but may also have been shaped by historical sea level Xuctuations or recent migration patterns.

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