[Coral-List] Chronic nutrient enrichment increases prevalence and severity of coral disease and bleaching

[Rebecca Vega Thurber]

Hello Coral List,
   I would like to direct you all to our newest study published in the
journal *Global Change Biology*. This study concerns the effects of
inorganic nutrients on coral disease and bleaching. In summary, we found
that chronic nutrient (inorganic N + P) enrichment increased the prevalence
and severity of coral disease and bleaching. However, we also showed that
within 10 months after nutrient enrichment was removed the coral community
recovered. For more information, below are the abstract, a link to the
work, and to our current press release on the topic. -Becky

http://www.eurekalert.org/pub_releases/2013-11/osu-lss111413.php

http://onlinelibrary.wiley.com/doi/10.1111/gcb.12450/abstract

Abstract

Nutrient loading is one of the strongest drivers of marine habitat
degradation. Yet, the link between nutrients and disease epizootics in
marine organisms is often tenuous and supported only by correlative data.
Here, we present experimental evidence that chronic nutrient exposure leads
to increases in both disease prevalence and severity and coral bleaching in
scleractinian corals, the major habitat-forming organisms in tropical
reefs. Over 3 years, from June 2009 to June 2012, we continuously exposed
areas of a coral reef to elevated levels of nitrogen and phosphorus. At the
termination of the enrichment, we surveyed over 1200 scleractinian corals
for signs of disease or bleaching. *Siderastrea siderea* corals within
enrichment plots had a twofold increase in both the prevalence and severity
of disease compared with corals in unenriched control plots. In addition,
elevated nutrient loading increased coral bleaching; *Agaricia* spp. of
corals exposed to nutrients suffered a 3.5-fold increase in bleaching
frequency relative to control corals, providing empirical support for a
hypothesized link between nutrient loading and bleaching-induced coral
declines. However, 1 year later, after nutrient enrichment had been
terminated for 10 months, there were no differences in coral disease or
coral bleaching prevalence between the previously enriched and control
treatments. Given that our experimental enrichments were well within the
ranges of ambient nutrient concentrations found on many degraded reefs
worldwide, these data provide strong empirical support to the idea that
coastal nutrient loading is one of the major factors contributing to the
increasing levels of both coral disease and coral bleaching. Yet, these
data also suggest that simple improvements to water quality may be an
effective way to mitigate some coral disease epizootics and the
corresponding loss of coral cover in the future.

-- 
Dr. Rebecca Vega Thurber
Assistant Professor of Microbiology
Oregon State University
454 Nash Hall
Corvallis OR  97331-3804, U.S.A
541-737-1851 (office) 541-737-0496 (FAX)
rvegathurber at gmail.com;Rebecca.Vega-Thurber at oregonstate.edu<Rebecca.Vega.Thurber at oregonstate.edu>