Using a similar protocol, he has found that Madracis is not capable of net uptake of nitrate whereas all other corals tested can utilize this nutrient. Even after an entire month exposed to high concentrations, this one coral still didn't show any interest whereas other corals removed from the reef were immediately capable of rapid uptake. Brian further characterized the effects of light, flow and preconditioning on several corals and is now writing his master's thesis. Phosphorus metabolism of corals has received little attention compared to carbon or even nitrogen. Another graduate student from University of Maryland, Ruth Kelty, has recently completed her Ph.D. using 33 P, a radioactive tracer, to trace the movement of phosphorus into the host and symbiont tissues.
Corals also acquire nutrients from feeding on a wide variety of zooplankton.
Within 2 hours of the host feeding on a shrimp, the zooxanthellae have all they will receive which implies that the host's digestion process releases nitrogen into the coelenteron that is rapidly assimilated by the zooxanthellae. This was a surprise as the received wisdom was that the host would initially retain all of the nitrogen and then slowly release it to the symbiont from catabolic processes rather than directly during digestion. Greg plans to use both the labelled brine shrimp and 13 CO 2 which will enter the zooxanthellae as they photosynthesize and then measure the 15 N and 13 C on amino acids to try to understand how the carbon and nitrogen cycles of these symbioses function. Following up on the questions raised by Greg's work on assimilation of food by the anemone, two students are working on Masters's projects measuring the assimilation efficiency of sponges and corals. The assimilation efficiency is the percentage of food nitrogen retained by the animal compared to what it ate.