The effect of external nutrient resources on the optical properties and photosynthetic efficiency of <i>Stylophora pistillata</i>

Abstract

Abstract Enrichment of the hermatypic Red Sea coral Stylophora pistillata with dissolved inorganic nitrogen, inorganic nitrogen + phosphorus, and feed­ing on Artemia, all led to increases in areal pigmentation in comparison with control colonies. These increases, unlike photoadaptive ones, resulted from growth in cell numbers ranging from × 2.75 in the Artemia-fed to × 4.85 in the N + P-enriched corals. The treated corals absorbed 51-85% of incident light, whereas the controls absorbed only 33%. Areal photosynthesis increased with treatment, although to a lesser degree than absorptivity. This difference resulted in reduced photosynthetic effici­encies in the treated colonies. Photosynthetic rates, calculated on a percell basis, were inversely correlated with algal densities, indicating poss­ible competition among the algae for CO2.