Each coral colony is assessed for the presence and intensity of bleaching. Bleaching has been found to inhibit the ability of corals to recover from small-scale tissue damage and may increase partial or total mortality of a colony (Meesters et al. 1993). Severe and prolonged bleaching may result in diminished reef growth and the transformation of reef-building communities to alternate, non-reef building states (Glynn, 1996). There is a need to regionally quantify mass bleaching events and determine if they lead to extensive coral mortality.
The coral bleaching phenomenon has been well described in the literature (e.g., Glynn 1996). Several reef corals and other organisms with symbiotic zooxanthellae respond to various disturbances or stressors by bleaching (expelling zooxanthellae and/or losing photosynthetic pigments from the algae). Coral bleaching is often transient in nature with corals regaining their pigmentation after several weeks or a few months. However, while bleaching does not always cause corals to die, it can inhibit their ability to recover from small tissue damage and may increase the likelihood of damage from other natural and anthropogenic stressors such as storms, nutrients, sedimentation, freshwater dilution, and epizootics that may directly or indirectly have adverse and potentially synergistic effects. (e.g., Meesters et al. 1993). With severe or prolonged bleaching, corals may also experience reduced skeletal growth (Leder et al. 1991), decline in reproductive fitness or failure (Glynn 1990, Szmant and Gassman 1990, Guzman and Cortes 1992), and inability to resist competition from algae or other invertebrates. In extreme cases, bleaching can overtime lead to a reduction in species diversity, cover, and eventually, loss of reef framework. Distinct patterns of bleaching usually result from interspecific differences, spatial differences on various scales, and temporal differences (Glynn 1996). Differences in interspecific responses to bleaching is common, with individual taxa showing different degrees of discoloration and recovery times (e.g., Glynn 1984, Brown and Suharsono 1990, Coffroth et al. 1990, Glynn 1990, Williams and Bunkley-Williams 1988, 1990, Lang et al. 1992).
For AGRRA, we address only “mass” coral reef bleaching, which refers mainly to bleaching resulting from elevated sea surface temperatures and solar irradiance (the two primary factors believed to be involved with mass bleaching events) (Ogden and Wicklund 1988, Glynn 1993) and that affects a substantial percentage (>25%) of coral colonies; not bleaching due to algal overgrowth etc. Bleached tissue may appear white (translucent) or pale, but you can still see the polyp tissue above the skeleton. Bleaching usually is not uniform over individual colonies and may be mottled in appearance. Bleached tissues should not be included with the “recently dead” estimates.
Bleaching is characterized
according to the approximate severity of tissue discoloration using the
= Pale (discoloration of coral tissue)
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