EFFECTS OF NITROGEN AND PHOSPHORUS ENRICHMENT ON IN-VIVO SYMBIOTIC ZOOXANTHELLAE OF POCILLOPORA-DAMICORNIS

The reef coral Pocillopora damicornis (Linnaeus) was grown for 8 wk in four nutrient treatments: control, consisting of ambient, unfiltered Kaneohe Bay seawater [dissolved inorganic nitrogen (DIN, approximately 1.0 muM) and dissolved inorganic phosphate (DIP, approximately 0.3 muM)]; nitrogen enrichment (15 muM DIN as ammonium); phosphorus enrichment (1.2 muM DIP as inorganic phosphate); and 15 muM DIN + 1.2 muM DIP. Analyses of zooxanthellae for C, N, P and chlorophyll a after the 8 wk experiment indicated that DIN enrichment increased the cellular chlorophyll a and excess nitrogen fraction of the algae, but did not affect C cell-1. DIP enrichment decreased both C and P cell-1, but the decrease was proportionally less for C cell-1. The response of cellular P to both DIN and DIP enrichment appeared to be in the same direction and could not be explained as a primary effect of external nutrient enrichment. The observed response of cellular P might be a consequence of in situ CO2 limitation. DIN enrichment could increase the CO2 (aq) demand by increasing the net production per unit area. DIP enrichment could slow down calcification, thus decreasing the availability of CO2 (aq) in the coral tissue.