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The relationship between bleaching and mortality of common corals
McClanahan, T.R. (2004). The relationship between bleaching and mortality of common corals. Mar. Biol. (Berl.) 144(6): 1239-1245.
In: Marine Biology. Springer: Heidelberg; Berlin. ISSN 0025-3162, more
Peer reviewed article  

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  • McClanahan, T.R.

    Reef corals are likely to have many subtle but four gross responses to anomalous warm water. These are (1) not bleach and live (mortality <10%), (2) not bleach and die (mortality >20%), (3) bleach and live, and (4) bleach and die. The frequency of these four possible gross responses was determined for 18 common coral taxa over an exceptionally warm 1998 El Niño where intense bleaching was observed, and mortality determined from line transects averaged 41.2±34.7 (±SD). Field studies included (1) recording the loss of color (bleaching) and observing recently dead individuals among 6,803 colonies during five sampling periods and (2) estimating mortality based on 180 m of line-intercept transects completed 4 months before and near the end of the bleaching episode. There was no clear relationship between the loss of color and either direct observation or transect-based estimates of mortality for the 18 taxa. The morphology of the taxa did not influence color loss but branching and encrusting taxa had higher mortality than massive and submassive taxa. Loss of color and mortality are the most common responses to warm water as only Pavona did not lose color or die and only two taxa, Cyphastrea and Millepora, did not significantly lose color but died. Of the 15 taxa that lost color, five taxa, Astreopora, Favia, Favites, Goniopora, and Leptoria, did not die. These taxa are those most likely to have reduced potential mortality by the loss of pigments and associated algal symbionts. Death of the branching taxa was detected reasonably by direct field observation but some taxa were underestimated when compared with mortality estimates based on line transects. Death of encrusting and massive taxa including Echinopora, Galaxea, Hydnophora, Montipora, Platygyra, and massive Porites was poorly detected from direct observations but they proved to have modest to high mortality (20–80%) based on line transects. There was no single response of these common corals to warm water but these data, collected during an extreme warm-water anomaly, indicate that the loss of color is most frequently a sign of morbidity, particularly for branching and encrusting taxa.

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