Article
Shading as a mitigation tool for coral bleaching in three common Indo-Pacific species
Journal of Experimental Marine Biology and Ecology
(2017)
Abstract
Shading substantially reduced the degree of bleaching in Acropora muricata, Pocillopora damicornis and Porites
cylindrica in American Samoa. Experiments were conducted outdoors at two sites on Ofu and Tutuila Islands. An
aquarium experiment was set up near some reef-flat pools in the National Park of American Samoa on Ofu Island,
using different levels of shading (none, 50% and 75%) early in conditions of cumulative thermal stress corresponding
to NOAA's Coral Reef Watch-Bleaching Alert System. We analyzed the effects of cumulative thermal
stress regarding coral growth, as well as color changes (evaluated using a standardize reference card) as a proxy
for decreases in symbiont density and chlorophyll a content (i.e. bleaching). Thermally stressed corals grew less
than controls, but corals without shading experienced a more substantial decrease in growth compared to those
under 50% or 75% shade. The analysis of coral color showed that both levels of shading were protective against
bleaching in conditions of cumulative thermal stress for all species, but were particularly beneficial for the most
sensitive ones: A. muricata and P. cylindrica. Heavier shading (75%) offered better protection than lighter shading
(50%) in this experiment, possibly because of the intense light levels corals were subjected to. Although there
were limits to the extent shading could mitigate the effects of cumulative heating, it was very effective to at least
Degree Heating Week (DHW) 4 and continued to offer some protection until the end of the study (DHW 8). In
Tutuila, a shaded/not-shaded platform experiment was carried out in a reef pool in which corals have shown
repeated annual summer bleaching for several years. This experiment was designed to investigate if shading
could attenuate bleaching in the field and also if there were negative consequences to shading removal. The only
factor controlled was light intensity, and our main conclusion was that overall corals on the platform became
darker than field colonies in response to shading, but adjusted back to the same color level as field colonies after
shade removal. However, the latter results are preliminary and need to be confirmed by future studies under
more controlled conditions. As bleaching becomes more frequent and regular due to global warming, we should
consider proactively using shading to help mitigate the effects of thermal stress and prolong the survival of at
least some coral communities, until solutions to address global climate change become effective.
Keywords
- coral bleaching
Disciplines
Publication Date
2017
Citation Information
Vânia R. Coelho, D. Fenner, C. Caruso, Brett R. Bayles, et al.. "Shading as a mitigation tool for coral bleaching in three common Indo-Pacific species" Journal of Experimental Marine Biology and Ecology Vol. 497 (2017) p. 152 - 163 ISSN: 0022-0981 Available at: http://works.bepress.com/vania-coelho/86/