Induction of 70-kD heat shock protein in scleractinian corals by elevated temperature: significance for coral bleaching.

In this study, the induction of the 70-kD family of heat shock proteins (hsp70) has been examined in stony coral tissues. In these experiments, the only difference from control conditions has been exposure to a temperature approximating that at which field bleaching in the Caribbean is known to occur, approximately 30 degrees C or 1 degree-2 degrees C above long-term average seasonal maximum temperatures. A constitutive hsp70 has been identified both in the zooxanthellate (hermatypic) coral, Montastrea annularis, and in two corals lacking symbiotic algae, Tubastrea cocchinea and Astrangia danae (Cnidaria, Anthozoa, Scleractinia). Western blots of experimental tissues fractionated by polyacrylamide gel electrophoresis indicate that the initial induction of hsp70 occurs rapidly, within one hour of transfer to water of elevated temperature. Thereafter, the level of hsp70 decreases within 12-24 hours to approximately the constitutive level. In field-bleached specimens of M. annularis, hsp70 is not detected. Since this coral tissue, once bleached to whiteness, contains no 70-kD heat shock protein, we conclude that the process of coral bleaching might include, among other metabolic alterations, a failed heat shock response. In addition to being compromised in other normal functions, the bleached coral would lose the capacity to protect itself against environmental stress. The eventual loss of algae by bleached coral is likely to be consequent to several metabolic changes in the coral tissue. However, the uncoupling of that symbiotic relation is not concomitant with the initial stress response of heat shock protein synthesis.