Carbon Dioxide and Earth's Future Pursuing the ... - Magazooms

www.co2science.org
P a g e | 94
a significant variability in bleaching susceptibility for many species (Edmunds, 1994; Marshall
and Baird, 2000), suggesting some potential for a shift in thermal tolerance based on selective
mortality (Glynn et al., 2001; Jimenez et al., 2001) and local population growth alone.” Above
and beyond that, they said their results suggest “a capacity for acclimatization or adaptation.”
In concluding their paper, Maynard et al. wrote “there is emerging evidence of high genetic
structure within coral species (Ayre and Hughes, 2004),” which suggests, in their words, that
“the capacity for adaptation could be greater than is currently recognized.” Indeed, as stated
by Skelly et al. (2007), “on the basis of the present knowledge of genetic variation in
performance traits and species’ capacity for evolutionary response, it can be concluded that
evolutionary change will often occur concomitantly with changes in climate as well as other
environmental changes.” Consequently, it can be appreciated that if global warming were to
start up again (it has been in abeyance for about the last decade), it need not spell the end for
earth’s highly adaptable corals.
But how is it done? How do corals adjust to rising temperatures?
One adaptive mechanism that corals have developed to survive the thermal stress of high water
temperature is to replace the zooxanthellae expelled by the coral host during a stress-induced
bleaching episode by one or more varieties of zooxanthellae that are more heat tolerant.
Another mechanism is to produce heat shock proteins that help repair heat-damaged
constituents of their bodies (Black et al., 1995; Hayes and King, 1995; Fang et al., 1997). Sharp
et al. (1997), for example, demonstrated that sub-tidal specimens of Goniopora djiboutiensis
typically have much lower constitutive levels of a 70-kD heat shock protein than do their
intertidal con-specifics; and they have shown that corals transplanted from sub-tidal to
intertidal locations (where temperature extremes are greater and more common) typically
increase their expression of this heat shock protein.
Similar results have been reported by Roberts et al. (1997) in field work with Mytilus
californianus. In addition, Gates and Edmunds (1999) observed an increase in the 70-kD heat
shock protein after six hours of exposure of Montastraea franksi to a 2-3°C increase in
temperature, which was followed by another heat shock protein increase at the 48-hour point
of exposure to elevated water temperature. And in their case, they wrote that the first of these
protein increases “provides strong evidence that changes in protein turnover during the initial
exposure to elevated temperature provides this coral with the biological flexibility to
acclimatize to the elevation in sea water temperature,” and that the second increase “indicates
another shift in protein turnover perhaps associated with an attempt to acclimatize to the more
chronic level of temperature stress.”
So how resilient are earth’s corals to rising water temperatures? No one knows for sure; but
they’ve been around a very long time, during which earth's climatic conditions have changed
dramatically, from cold to warm and back again, over multiple glacial and interglacial cycles.
And in this regard, we see no reason why history cannot be expected to successfully repeat
itself, even as the current interglacial experiences its “last hurrah.”
[ search engine powered by magazooms.com ]