A new study by scientists at the University of Miami (UM) Rosenstiel School of Marine & Atmospheric Science shows that corals may be more severely impacted by climate warming if they are found in environments such as coastal reefs polluted by wastewater and runoff.
Having too many algal symbionts makes corals bleach more severely in response to warming October 14, 2012 A new study by scientists at the University of Miami (UM) RosenstielSchool of Marine & Atmospheric Science shows that corals may be more severely impacted by climate warming when they contain too many symbiotic algae. The single-celled algae living inside corals are usually the key to coral success, providing the energy needed to build massive reef frameworks. However, when temperatures become too warm, these algae are expelled from corals during episodes of coral ‘bleaching’ that can lead to widespread death of corals. Until now, it was thought that corals with more algal symbionts would be more tolerant of bleaching because they had ‘more symbionts to lose.’ The new study shows that the opposite is true.
We discovered that the more symbiotic algae a coral has, the more severely it bleaches, showing that too much of a good thing can actually be bad,” said Ross Cunning, Ph.D. student and lead author of the study. “We also learned that the number of algae in corals varies over time, which helps us better understand coral bleaching risk.”
His research was conducted using cauliflower coral (Pocillopora damicornis) collected from the Pacific coast of Panama. The corals were monitored for six months at the UM’s Experimental Hatchery, where they slowly warmed up and ultimately bleached. The number of symbiotic algae in the corals was studied by analyzing DNA samples with new highly sensitive genetic techniques that determine the ratio of algal cells to coral cells. This improved technique made the discovery possible by showing that corals with more algae bleached more severely than those with fewer algae.
“Corals regulate their symbionts to match the environment in which they are found, and this study shows there is a real cost to having too many,” said co-author Andrew Baker, associate professor at UM’s RosenstielSchool. “There are real-world implications of this. Corals will be more vulnerable to bleaching if they are found in environments which increase the number of symbionts, such as coastal reefs polluted by wastewater [nutrients] and runoff. If we can improve water quality, we might be able to buy some time to help these reefs avoid the worst effects of climate change.
“Other environmental changes, including ocean acidification as a result of increasing carbon dioxide emissions, might also influence bleaching vulnerability in ways we haven’t thought of before,” Baker added.
More information: “Excess algal symbionts increase the susceptibility of reef corals to bleaching”, Nature Climate Change, 2012.Journal.
In July 2008 the Florida legislature passed a bill to end sewage disposal from ocean outfall pipes. The legislation requires ocean outfalls meet Advanced Wastewater Treatment standards, effectively reducing the nutrient pollution discharged 95%, by 2018 and shutdown all ocean outfalls by 2025.
On April 1, 2009 the Delray Beach sewage outfall went off-line, the first of six south Florida outfalls to close.
In 2011, three years after the passage of the law the Florida legislature, led by Senator Miguel Diaz de la Portilla of Miami introduced a bill (SB 796) designed to delay the implementation of the 2008 legislation and allow the continued dumping of 396 million gallons a day of sewage into Florida waters until 2030.
Conservation and SCUBA organizations supported by 1,000’s of emails help defeat SB 796.
In 2012, Senator Miguel Diaz de la Portilla of Miami introduced bill SB 794 designed to delay the implementation of the interim AWT deadline until 2020.
At the 11th hour South Florida dive operators find the outfall bill is close to passage and mount opposition to prevent the bill from being brought before the Senate for a vote. The 2012 attempt to derail the outfall legislation fails. See: Reef Rescue Action Alert.
2013: Expect more of the same from the Florida legislature.