Effect of Ammonium Enrichment on Animal and Algal Biomass of the Coral Pocillopora damicornis

Abstract

Algal and animal biomass parameters of colonies of the Pacific
\ncoral Pocillopora damicornis (Linnaeus) were measured as a function of time of
\nexposure to elevated concentrations of seawater ammonium (20 and 50 uM
\n[(NH4)2S04]) ranging from 2 to 8 weeks. Areal concentrations of zooxanthellae,
\nchlorophyll, and protein increased with 20 uM ammonium addition. During
\nthe 8-week period of exposure to 20 uM ammonium, the population density
\nof zooxanthellae increased from 3.5 to 7.5 x 105 cells cm-2, chlorophyll a
\ncontent of zooxanthellae increased from 5.7 to 8.6 pg, and animal protein
\nconcentration doubled (from 0.74 to 1.38 mg cm-2). These data indicate that
\nboth the coral animal and the zooxanthellae respond to the addition of exogenous
\ndissolved inorganic nitrogen provided as 20 uM ammonium. Growth of
\nthe symbiotic association in response to the addition of 20 uM ammonium adds
\nfurther evidence to support the argument that growth of tropical symbioses is
\nlimited by the availability of nitrogen. However, the coral response is likely to
\ndepend on the concentration of ammonium provided, because the biomass
\nparameters of corals held at 50 uM ammonium did not change significantly
\nwith time of exposure to the added nutrient.