Photosynthesis and Productivity of Benthic Macroalgae on the North Carolina Continental Shelf

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Abstract
The primary productivity of offshore benthic macroalgae was investigated using short-term 14C-incubations. Specimens were collected by SCUBA and incubated in situ and additional samples were returned to the laboratory for a complete analysis of the species photosynthetic response to various light intensities. Apparent Pmax values for Codium carolinianum and Lobophora variegata were 0.22 and 0.85 mg C (g dry weight)-1 h-1; apparent Ik values were 83 and 60 .mu.E [einsteins] m-2s-1. To estimate the daily contribution of organic matter made by these species to the system, the light responses of the 2 species were combined with knowledge of the available photosynthetic radiation and estimates of respiration to calculate net daily production. C. carolinianum produced from 0.85-1.55 mg C (g dry weight)-1 d-1 [per day] in turbid and clear coastal waters, respectively, while L. variegata produced 4.09 and 6.45 mg C (g dry weight)-1 d-1 in similar situations. The net daily C fixation of benthic macroalgae on the North Carolina continental shelf is strongly dependent on light availability and factors affecting light attenuation in the water column.