bleached coral showing loss of photosynthetic zooxanthellae

Coral Bleaching Study: Number of Zooxanthellae Affects Bleaching

Coral Bleaching Study: Number of Zooxanthellae Affects Bleaching

bleached coral showing loss of photosynthetic zooxanthellae

A new study from scientists at the University of Miami demonstrates that coral bleaching events are related to the number of symbiotic algae, called zooxanthellae, that are present in the coral at the time of a stress event (like an increase in water temperature).

Prior to this insight, it was thought that corals with more zooxanthellae would be less prone to bleaching—simply because the symbiotic algae were available in greater numbers. The new study, however, suggests that the opposite may be true.

The Miami research team studied a species of Pocillopora collected from the Pacific Coast of Panama, where the team manipulated temperatures as part of the experimental design. What the researchers concluded was that the corals regulated the number of zooxanthellae that were present based on the environmental conditions present—and those corals with more zooxanthellae bleached more severely than those with less.

“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 Rosenstiel School. Read original  story here

Of course this is just one of many studies designed to help us better understand the causes of coral bleaching events, but the data provide me with hope that we are starting to unravel the mystery.

What insights should we apply to the saltwater aquarium hobby?

The study makes me wonder…what are the environmental factors that would cause one coral to have a higher density of zooxanthellae than another?

Are there things that we do as hobbyists that promote the growth of Zooxanthellae to unhealthy (or unnatural) proportions?  Certain light wavelengths, a given level of PAR? Nutrient density in our water? Nitrate level? Phosphate level? Supplements?

It would be interesting to start peeling back the layers. I also wonder how many of us have tracked the temperature of our aquarium throughout the day—to even know how much, if at all, the temperature of our aquarium drifts through a day/night cycle or from summer to winter, etc. and if we aren’t a cold-front or heat-wave away from catastrophe with our own tanks.

What do you think about this? Please comment and let me know—especially if you have experienced a bleaching event in your aquarium—and even if not, just drop a comment and let me know what you think—thanks in advance!

If this is your first time reading the blog, check out some of the most recent saltwater aquarium blog posts. Be sure to sign up for the Saltwater Aquarium Blog newsletter so you don’t miss a thing.

The image above was from mattk1979 on Flickr.


Check out more Coral posts:

Coral overview page

How to frag your first coral

Fragging coral embryos






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