Photosynthesis and calcification in four deep-water Halimeda species (Chlorophyceae, Caulerpales)

Measurements of organic and inorganic carbon production were made for deep-water (76 m) specimens of Halimeda discoidea Descaisne, H. cryptica L. H. Colinvaux and Graham, H. copiosa Goreau and Graham and H. lacrimosa Howe. Photosynthetic and calcification rates (CaCO3 production) were estimated on shore at stimulated in situ light intensities (20 μE m−2 s−1) and temperatures (27°C). Photosynthetic rates, as measured by both oxygen evolution and carbon-14 incorporation, agreed well and showed efficient light utilization, ranging from 0.04 to 0.24 mg organic C g dry wt−1 h−1. Calcification rates, measured by 14C incorporation, ranged from 0.06 to 0.16 mg inorganic C g dry wt−1 h−1 and were positively correlated (R2=77) with photosynthesis, implying a physiological mediation of the depositional process.