Zooxanthellae!
June 23rd, 2007
A recent article in PLoS Biology about coral reef bleaching caused my thoughts to turn to tiny creatures that live inside corals, the zooxanthellae (zoo-ZAN-thell-ee)! These are the little beasties that give corals their fantastic array of colours, along with being one of the most fun biology terms to scream (“ZOOXANTHELLAE!”).
Zooxanthellae are not actually beasties sensu stricto; they are algae, which are unicellular plants. So what the hell are algae doing living inside coral? Like lichens, coral have formed a symbiotic relationship with algae. By forming this association, the coral (an animal) receives photosynthetic products (sugars) and the zooxanthellic algae (a plant) receives shelter and the carbon dioxide it needs to survive. Also like lichens, the coral/zooxanthellae symbiotic relationship is “obligate”. That is, neither the coral nor the zooxanthellae could survive on their own if they were separated.
Weird under-sea animals aside, obligate symbiosis is by no means an exotic phenomenon in the natural world. For example, the mitochondria and the cells of your body are in an obligate symbiotic relationship. That’s right, mitochondria are in reality totally separate organisms from humans. They even have their own DNA. Like the zooxanthellae of plants, the mitochondria produce a resource (adenosine triphosphate) in exchange for a safe and happy environment in which to live their tiny lives in peace.
July 17th, 2008 at 4:01 pm
Great article about a topic that confuses many people!Although I’ve read about it a ton, and understand how it works, it still boggles my mind.
November 10th, 2009 at 7:32 pm
Awesome article. It really helped me with research about coral reefs…
The only problem now is that everybody around me might be a bit annoyed by me shouting ‘ZOOXANTHELLAE!’ at irregular intervals whenever it is least relevant to the conversation…
I didn’t know that they were algae… That is so cool
May 12th, 2010 at 11:21 am
I’m working on a site for students about coral reef preservation and need a pic file of a single zooxanthellae. Is the one on your site subject to copyright? I’d be glad to give credit if I could get permission to use it.
October 10th, 2010 at 12:16 pm
While your article is an intersting approach to understand the coral-zoox relantionship, it is indeed very misleading. First of all the scleractinian corals, cannot indeed survive without the zoox, but this is not true the other way around. Zooxanthellae can be free-living, that’s why we can cultivate and grow thousands of them in the lab for our coral experiments.
On the other hand, the conclusion tha you are making about the mitochondrial DNA vs the nuclear DNA is even more misleading. The fact that both have separate DNA doesn’t mean that they are different organisms, and clearly not that they are in “symbiosis”.
October 10th, 2010 at 2:56 pm
Audrey –
The article really wasn’t meant to be an exhaustive analysis of zooxanthellae, and hence glossed over some details. It was written for a general audience, based on the paper that I linked to. So, I think it’s definitely superficial, but hardly misleading.
Also, it is a well established fact that mitochondria were indeed separate organisms at one point in history (see Margulis, the *endosymbiotic* theory). The fact that they are now tightly reliant on each other (indeed many mitochondria genes are now in the nucleus) is secondary to the fact that they are phylogenetically distinct organisms.