Part of the reason is that corals live in tropical waters where there are very few nutrients in the water. Corals therefore capture zooplankton to get nutrients required for growth, like nitrogen, phosphorus, amino acids, or vitamins and minerals. If the coral lives deep in the water where there is little light, then it also requires food to supplement the limited energy it can get from the sun. As I began to study more about corals, I learned that nutrients from the zooplankton were made available to the symbiotic zooxanthella e. Also like any animal, the coral releases waste products that are good fertilizer for the zooxanthellae, just like we take manure and spread it on our plants on land.
Many atoms can have several different forms, called isotopes, that have different weights.
By following the fate of the 15 N label, you can figure out what happens to normal nitrogen in the system you're working with. Since I'm working on nitrogen from host feeding, I need to get the 15 N label into food to feed to anemones and corals. When the brine shrimp are fed to the anemones, it puts the label into the symbiosis, beginning with the animal host. By sampling at different times, I can look to see whether the zooxanthellae are using the nitrogen from the animal host, and I can look for the label in different biochemical pools in both the animal host and the zooxanthellae. This picture shows the anemones in the finger bowl after they have been fed.