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Journal of Marine Biology
Volume 2011, Article ID 730715, 9 pages
Review Article

Clade D Symbiodinium in Scleractinian Corals: A “Nugget” of Hope, a Selfish Opportunist, an Ominous Sign, or All of the Above?

Hawaii Institute of Marine Biology, School of Ocean and Earth Science and Technology, University of Hawaii at Mānoa, HI 96734, USA

Received 2 July 2010; Accepted 30 September 2010

Academic Editor: Kim Selkoe

Copyright © 2011 Michael Stat and Ruth D. Gates. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Clade D Symbiodinium are thermally tolerant coral endosymbionts that confer resistance to elevated sea surface temperature and bleaching to the host. The union between corals and clade D is thus important to management and coral conservation. Here, we review the diversity and biogeography of clade D Symbiodinium, factors linked to increasing abundances of clade D, and the benefits and drawbacks of associating with clade D for corals. We identify clade D Symbiodinium as uncommon pandemically distributed generalists found in higher abundances on reefs exposed to challenging sea surface temperatures and local stressors or with a history of bleaching. This distribution suggests that clade D Symbiodinium are mostly opportunistic endosymbionts, whereby they outcompete and replace optimal symbionts in health-compromised corals. We conclude by identifying research gaps that limit our understanding of the adaptive role clade D Symbiodinium play in corals and discuss the utility of monitoring clade D Symbiodinium as indicators of habitat degradation in coral reef ecosystems.