The elemental composition (C, N, and P) of zooxanthellae and
host tissue from the coral Pocillopora damicornis (Linnaeus) was determined
after maintenance in flowing seawater with 20-uM and 50-M ammonium
enrichments for periods of 2 to 8 weeks. Compared with ambient seawater
controls, total zooxanthellar nitrogen (ug N cm-2 colony surface) increased
four-fold during exposure to 20-uM ammonium. This resulted from increases in
N content of zooxanthellae and in zooxanthellae population densities. C: N
ratios of zooxanthellae decreased from 19.7 (±4.0) to 10.3 (±3.0), and N: P
ratios increased from 21.4 (± 3.1) to 30.4 (± 2.2) after 8 weeks in 20 uM ammonium.
Zooxanthellae from the 8-week 50-uM ammonium corals had values of
8.9 (±0.6) for C: Nand 40.4 (±2.3) for N: P. Coral animal C, N, and P
content were not affected by ammonium-enriched seawater. The C :N ratio of
coral animal tissue was 5.2 (±O.O), and the N: P ratio was 20.1 (±0.2) after 8
weeks in 20-uM ammonium seawater. There were no changes in host C: N,
N: P, or C: P with ammonium enrichment. Thus, most of the N from the
elevated seawater ammonium is retained by the zooxanthellae of P. damicornis,
rather than by the animal tissue. Accordingly, sustained high concentrations of
ammonium are likely to result in increased N storage by zooxanthellae and to
affect the relative size of zooxanthellar to animal N pools
