of highly reactive hydroxyl radicals in the absence of
a robust defense in the form of antioxidant enzymes or
non-enzymatic scavengers of active oxygen. Symbiotic
cnidarians and their zooxanthellae do produce hydroxyl
radicals upon illumination (Dykens et al. 1992), and the
increased activities of antioxidant enzymes in the algal
symbionts of tropical cnidarians appears to be insu¦cient
to scavenge the increase in the cellular ßux of superoxide
radicals and hydrogen peroxide produced during exposure
to UV radiation or elevated temperatures (Lesser and
Shick 1989; Lesser et al. 1990; Lesser 1996). The objective
of this study was to examine the role of oxidative stress
during high temperature-induced bleaching in corals. Previous
studies have shown that the use of exogenous antioxidants
can help elucidate the role of oxidative stress in
the photoinhibition of cultured zooxanthellae exposed to
elevated temperatures by ameliorating the detrimental
e¤ects of toxic oxygen (Lesser 1996). Here, I present data
that strongly supports a mechanistic role for temperatureinduced
oxidative stress in the bleaching phenomenon
using the Caribbean coral, Agaricia tenuifolia.