Nordemar, I., Nystrom, M. and Dizon, R. 2003. Effects of elevated seawater temperature and nitrate enrichment on the branching coral Porites cylindrica in the absence of particulate food. Marine Biology 142: 669-677.
There are numerous ways in which man adversely impacts coral reefs [see our Editorials of 1 Jan 1999 and 19 Sep 2001]; and we have long suggested it is the intensification of this host of widespread but localized anthropogenic-induced stresses that has predisposed the world's corals to more readily succumb to the stress of rising temperatures as time has progressed [see our Editorials of 23 Jan 2002, 6 Mar 2002 and 26 Mar 2003]. The study of Nordemar et al. is one of the very first to seriously investigate this hypothesis.
What was done
In the words of the authors, "the physiological response of the reef-building coral Porites cylindrica was investigated, when exposed to enrichment of dissolved inorganic nitrate (+15 µM for 14 days) and elevated seawater temperature (+2°C for 48 h), in the absence of particulate food." "As far as we know," say the authors, "this is the first reported study to experimentally investigate the combined effects of elevated temperature and nutrient enrichment," the latter of which factors is typically detrimental to the health of corals.
What was learned
The authors report that "P. cylindrica was able to tolerate the temperature exposure without losing symbiotic microalgae or chlorophyll pigments, although the photosynthetic capacity was affected." However, they add that "the combination of elevated temperature and nitrate enrichment produced an even more pronounced reduction of the production rate."
What it means
"Based on the results from this study," in the words of the authors, "it seems that corals on nutrient-exposed reefs may be more susceptible to periods of elevated temperature, compared to corals in more pristine areas," which is essentially what we suggest in our Editorials of 23 Jan 2002, 6 Mar 2002 and 26 Mar 2003, i.e., that the insidious worldwide increase in a host of localized anthropogenic assaults upon reef environments over the course of the Industrial Revolution has gradually weakened corals to the point where they now succumb to increases in temperature that in the past would not have affected them.
Reviewed 1 October 2003