Coral Bleaching: Genotypic and Photosynthetic Diversity in Symbiotic Algae
It is well publicized that coral reefs world-wide
are undergoing severe declines, a consequence of increasingly frequent
episodes of ocean warming during the past few decades. As they are primarily
photosynthetic systems, our laboratory has become focused on understanding the diversity of symbiotic algae in corals and
their related cnidarian species in reefs around the globe.
Most conspicuously, loss of coral pigmentation reflecting the death or retarded growth of colonies, is due to reduced densities or nearly complete elimination of symbiotic algae (dinoflagellates; Symbiodinium sp.) associated with their hosts. Toward a greater comprehension of the phenomena that are increasingly decimating the ocean's "rain forests", we are pursuing when and why corals and their symbionts respond differentially to global climate changes. Our collaborative projects with the laboratory of Bill Fitt of the UGA Institute of Ecology, therefore are directed to finding the causes for coral bleaching in studies of the responses of dinoflagellates to increased temperature (exacerbated by global warming) and light stress (exacerbated by ozone layer depletion and clear, shallow water environments).
From PCR-based denaturing gradient gel electrophoresis (DGGE) and DNA
sequencing analyses, we now have a rather
comprehensive grasp that their is
considerable symbiont genotypic variation that largely corresponds with
host-specificities, and often heat-stress susceptibility vs. resistance, in the
Caribbean, the western Atlantic coast, Hawaii and much of the Pacific.
We also have documented that certain symbiotic dinoflagellate species confer
greater sensitivity to stress conditions while other symbiont genotypes
correlate with high light and elevated temperature tolerance. This conjecture is
substantiated is reflected in our long-term monitoring various reef sites, mostly in the Caribbean, using non-invasive measurements of photosynthetic rates
but also seasonal sampling of tissue pigmentation, photosynthetic capacity and
tissue accretion. Importantly, employing molecular genotyping techniques to define the
prevalent dinoflagellate species in hosts,
there are occasional shifts in predominant symbiont subtypes, but this varies among coral hosts. These endeavors have led to a
greater appreciation of roles of symbiont genotypic diversity and acquisition as a function of geographical location and, more recently, the extent to which symbiont populations vary as function of depth, illumination, seasonal change and episodes of temperature flux.
In parallel with the coral reef studies, we have an extensive collection of dinoflagellates in the laboratory that have been cultured from various coral and other cnidarian sources; these are essential for detailed studies of gene expression and photosynthetic responses to controlled environmental changes. Through laboratory studies, we can reconstruct stress conditions to further dissect causative factors involved in bleaching. So far, we now know loss of dinoflagellate viability at elevated temperature closely correlates with rapid declines of photosynthetic activity. The deterioration stems from inefficient repair mechanisms, including impaired synthesis of photosynthetic components due to insufficient mRNA levels or impaired protein synthesis.
Finally, we are extremely excited to have developed new photosynthesis measurement methods that
have revealed novel photosynthetic protection mechanisms that are prominent in among certain, stress-resistant, species of
Symbiodinium.
Laboratory Personnel and Their Major Projects:
Publications from Our Current NSF Funding Period
LaJeunesse, T.C. (2002) Diversity and community structure of symbiotic dinoflagellates from Caribbean coral reefs. Mar. Biol. 141: 387-400.
Warner, M.E., Chilcoat, G.C., McFarland, F.K. and Fitt, W.K. (2002) Seasonal fluctuations in the photosynthetic capacity of photosystem II in symbiotic dinoflagellates in the Caribbean reef-building coral Montastraea. Mar. Biol. 141: 31-38.
LaJeunesse, T.C., Loh, W.K.W., van Woesik, R., Hoegh-Guldberg, O., Schmidt, G.W. and Fitt, W.K. (2003) Low symbiont diversity in southern Great Barrier Reef corals, relative to those of the Caribbean. Limnol. Oceanogr. 48: 2046-2054.
Wellington, G.M. and Fitt, W.K. (2003) Influence of UV radiation on the survival of larvae from broadcast-spawning reef corals. Mar. Biol. 143: 1185-1192.
Iglesias-Prieto, R., Beltran, V.H., LaJeunesse, T.C., Reyes-Bonilla, H. and Thome, P.E. (2004) Different algal symbionts explain the vertical distribution of dominant reef corals in the eastern Pacific. Proc. R. Soc. Lond. B Biol. Sci. 271: 1757-1763.
LaJeunesse, T.C., Thornhill, D.J., Cox, E.F., Stanton, F.G., Fitt, W.K. and Schmidt, G.W. (2004) High diversity and host specificity observed among symbiotic dinoflagellates in reef coral communities from Hawaii. Coral Reefs 23: 596 - 603.
LaJeunesse, T.C., Bhagooli, R., Hidaka, M., deVantier, L., Done, T., Schmidt, G.W., Fitt, W.K. and Hoegh-Guldberg, O. (2004) Differences in relative dominance beween closely related Symbiodinium spp. in coral reef host communities across environmental, latitudinal, and biogeographic gradients. Mar. Ecol.-Prog. Ser. 284: 147-161.
Pochon, X., LaJeunesse, T.C. and Pawlowski, J. (2004) Biogeographic partitioning and host specialization among foraminiferan dinoflagellate symbionts (Symbiodinium; Dinophyta). Mar. Biol. 146: 17-27.
Lajeunesse, T.C. (2005) "Species" radiations of symbiotic dinoflagellates in the Atlantic and Indo-Pacific since the Miocene-Pliocene transition. Mol Biol Evol 22: 570-581.
LaJeunesse, T.C., Lee, S., Bush, S. and Bruno, J.F. (2005) Persistence of non-Caribbean algal symbionts in Indo-Pacific mushroom corals released to Jamaica 35 years ago. Coral Reefs 24: 157-159.
LaJeunesse, T.C., Lambert, G., Andersen, R.A., Coffroth, M.A. and Galbraith, D.W. (2005) Symbiodinium (Pyrrhophyta) genome sizes (DNA content) are smallest among dinoflagellates. J. Phycol. 41: 880-886.
Thornhill, D.J., LaJeunesse, T.C., Kemp, D.W., Fitt, W.K. and Schmidt, G.W. (2006) Multi-year, seasonal genotypic surveys of coral-algal symbioses reveal prevalent stability or post-bleaching reversion. Mar. Biol. 148: 711-722.
Todd, B. D., Thornhill, D. J. and Fitt, W. K. (2006) Patterns of inorganic phosphate uptake in Cassiopea xamachana: A bioindicator species. Marine Pollution Bull. 52: 515-21.
Dove, S., Ortiz, J. C., Enriquez, S., Fine, M., Fisher, P., Iglesias-Prieto, R., Thornhill, D. & Hoegh-Guldberg, O. (2006) Response of holosymbiont pigments from the scleractinian coral Montipora monasteriata to short-term heat stress. Limnol Oceanogr 51: 1149-58.
Kemp, D.W., Cook, C.B., LaJeunesse, T.C. and Brooks, R.W. (2006) A comparison of the thermal beaching responses of the zoanthid Palythoa caribaeorum from three geographically different regions in south Florida. J. Exp. Mar. Biol. Ecol. 335: 266-276.
Rotjan, R.D., Dimond, J.L., Thornhill, D.J., Leichter, J.L., Helmuth, B., Kemp, D.W. and Lewis, S.M. (2006) Chronic parrotfish grazing impedes coral recovery after bleaching. Coral Reefs 25: 361-368.
Thornhill, D.J., Daniel, M.W., LaJeunesse, T.C., Bruns, B.U., Schmidt, G.W. and Fitt, W.K. (2006) Natural infections of aposymbiotic Cassiopea xamachana scyphistomae from environmental pools of Symbiodinium. J. Exp. Mar. Biol. Ecol. in press.
Thornhill, D.J. LaJeunesse, T.C., Kemp, D.W., Fitt, W.K. and Schmidt, G.W. (2006) Highly stable symbioses among Western Atlantic brooding corals. Coral Reefs. In press
Lajeunesse, T.C., Reyes-Bonilla, H., Wills, M., Schmidt, G.W. and Fitt, W.K. (2006) A case study in the analysis of rDNA by PCR-DGGE: Coral-algal symbioses from the Sea of Cortéz. Mol Ecol submitted.
Long, T.A., Schmidt, G.W. and Covert, S.A. Manipulation of PGR5 expression confers altered stress tolerance. Plant Physiol. in revision.
Other Related Publications
Warner, M.E., W.K. Fitt, and G.W. Schmidt. 1999. Damage to photosystem II in symbiotic dinoflagellates: A determinant of coral bleaching. Proc. Natl. Acad. Sci. USA. 96:8007-12.
Schmid, V., P. Beutelmann, G.W. Schmidt, and H. Paulsen. 1998. Ligand requirement for LHCI reconstitution. In Photosynthesis: Mechanisms and Effects. Vol. I. G. Garab, editor. Kluwer Acad. Publ., Nordecht, Netherlands. 425-429.
Melkozernov, A.N., V.H.R. Schmid, G.W. Schmidt, and R.E. Blankenship. 1998. Energy redistribution in heterodimeric light-harvesting complex LHCI-730 of photosystem I. J. Phys. Chem. B. 102:8183-8189.
Bruns, B.U., J.L. Blanchard, and G.W. Schmidt. 1998. On the modulations of thylakoid structure and function upon adaptation to prolonged nitrogen-deficiency. In Photosynthesis: Mechanisms and Effects. Vol. IV. G. Garab, editor. Kluwer Acad. Publ., Nordecht, Netherlands. 3081-3086.
Summer, E.J., V.H. Schmid, B.U. Bruns, and G.W. Schmidt. 1997. Requirement for the H phosphoprotein in photosystem II of Chlamydomonas reinhardtii. Plant Physiol. 113:1359-1368.
Schmid, V.H.R., K.V. Cammarata, B.U. Bruns, and G.W. Schmidt. 1997. In vitro reconstitution of the photosystem I light-harvesting complex LHCI-730: Heterodimerization is required for antenna pigment organization. Proc. Natl. Acad. Sci. U. S. A. 94:7667-7672.
Warner, M.E., W.K. Fitt, and G.W. Schmidt. 1996. The effects of elevated temperature on the photosynthetic efficiency of zooxanthellae in hospice from four different species of reef corals: a novel approach. Plant Cell Environ. 19:291-299.
Blanchard, J.L., and G.W. Schmidt. 1996. Mitochondrial DNA migration events in yeast and humans: Integration by a common end-joining mechanism and alternative perspectives on nucleotide substitution patterns. Mol. Biol. Evol. 13:537-548.
Plumley, F.G., and G.W. Schmidt. 1995. Chlorophyll a/b complexes: Interdependent pigment synthesis and protein assembly. Plant Cell. 7:689-704.
Blanchard, J.L., and G.W. Schmidt. 1995. Pervasive migration of organellar DNA to the nucleus in plants. J. Mol. Evol. 41:397-406.
