By Guest Blogger Niels Rijneveld
In my previous blog I explained the way corals feed using their tentacles. Now that’s not the whole story. Corals actually receive only 10% of their energy from this. There is a far more important way of “feeding” for corals, and I’m sure the vegetarians amongst us will be happy to hear it.
Herbal life
Most corals can’t survive without their herbal counterpart – the competition on the reef is simply too fierce to live without. Those plant cells are in fact single-celled algae, or zooxanthellae (just call them zoox). They are doing a similar job to what plants and trees do: converting sunlight and CO2 into sugars and oxygen, better known as a process called photosynthesis.
Zoox are barely visible with the naked eye, unless they are joined together under the skin of the coral animal, the polyp. They are the ones that give colour to the coral and come in 4 different families , or clades: A, B, C, and D. Clearly the marine biologist who discovered this missed out on his moment of fame, he wasn’t the most imaginative soul – even I might have done a better job on naming those algae! Anyway, those 4 clades of zoox live in a different, but narrow temperature range. That means that if the temperature drops or rises just a bit, the zoox are not able to photosynthesize anymore and become useless. The polyp then might decide to expel the useless algae and turns white. Well, what you actually see is a transparent polyp (same like a jellyfish, remember) in a white skeleton.
Algae
The algae are actually the most important contributor to a coral’s growth. In shallow and tropical regions, corals are constantly exposed to sunlight which enhances photosynthesis. It results in more than 90% of the required energy for a coral. This is also the reason why the most thriving coral reefs can be found in shallow tropical waters.
In my next installment I will explain the clever way algae and polyp work together to create a fascinating symbiosis which drives the incredible diversity on the reef.
