It is easy to liken coral reefs to tropical rainforests; much like these remarkable terrestrial biological hotspots, coral reef habitats are widely held in awe on account of their astounding abundance and diversity. That notwithstanding, coral reefs can just as easily be thought of as marine deserts. While we may think of the warm, crystal clear waters of the coral reef as exceedingly hospitable, they are in fact located in some of the most nutrient-poor areas to be found in the oceans.
Nutrients are indeed so scarce in coral reef ecosystems that they are a key factor in the competitive interaction between corals. The bulk of these nutrients cannot be scavenged by the coral itself; rather, they are assimilated and processed by symbiotic algae that dwell within the coral’s tissue. Consequently, corals must act as the very best host they can be. Corals engage in an unending race to outgrow each other in their drive to fully expose themselves to photosynthesis-fueling sunlight. If any environmental condition throws a wrench in the process of photosynthesis, the algae—and ultimately its host—face the threat death by starvation.
While certain phenomena such as bleaching might make this particular symbiotic relationship appear to be rather noncommittal, new evidence provided by researchers at the Aquarium Tropicale Porte Dorée in Paris and the Laboratory for Biological Geochemistry suggests that the two partners do stick it out (at least for a while) during periods of extended starvation. Remarkably, when nutrients are dangerously limited, corals can draw from reserves leached by the algae. By converting nitrogenous compounds to uric acid crystals, the algae apparently build these reserves during times of better nutrient availability.
Scientists made the discovery by tracking nitrogen isotope tags after exposing coral subjects to excess nitrate. Electron microscopy and mass spectrometry was used to determine where the nitrogen was processed and stored. Crystallographic analysis was used to conclude that the minute crystals were formed from uric acid.
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