Atoll morphometry controls lagoon nutrient regime

Abstract

Nutrient control of phytoplankton was studied in 12 atoll lagoons of contrasting morphology in the Tuamotu Archipelago in the South Pacific. In large lagoons and in small lagoons well open to the ocean, N limitation was indicated by dissolved inorganic N (DIN, NO3/- + NO2/- + NH4/+) < 0.5 μM, by DIN/P-PO4 ratios < 3 atom atom-1, and by increased phytoplankton and bacterioplankton productivity after N enrichment. This trend shifts to P limitation for shallow, enclosed lagoons. N or P limitations are empirically predictable and explainable according to atoll-scale morphometric factors.