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 mu M)]; nitrogen enrichment (15 muM DIN as ammonium); phosphorus enrichme nt (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 w k experiment indicated that DIN enrichment increased the cellular chlo rophyll a and excess nitrogen fraction of the algae, but did not affec t C cell-1. DIP enrichment decreased both C and P cell-1, but the decr ease 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 an d could not be explained as a primary effect of external nutrient enri chment. The observed response of cellular P might be a consequence of in situ CO2 limitation. DIN enrichment could increase the CO2 (aq) dem and by increasing the net production per unit area. DIP enrichment cou ld slow down calcification, thus decreasing the availability of CO2 (a q) in the coral tissue.