Uptake of P³² and Primary Productivity in Marine Benthic Algae1

Abstract

The rate of uptake of tracer P 32 from normal sea water and the primary productivity of seven species of large intertidal benthic algae were measured simultaneously in light and dark bottles suspended in a running seawater aquarium under constant light and temperature. Per cent uptake of P 32 per hour per gram biomass was similar in the light and dark for a given species, but markedly different between species. In the extremes of the series the relative rate of uptake was 25 times greater in Cladophora than in Fucus. Both the uptake rate and gross productivity were proportional to the surface‐per‐volume ratio in the series of species. These data suggested that when environmental concentration of phosphorus is low, as is usual in the sea, it is absorbed at a rate related to the inherent surface area features of the alga, high surface‐to‐volume ratio increasing the rate of uptake as well as increasing the ability of a given biomass of plant to fix energy under favorable light conditions. Therefore, under these conditions uptake is related to potential productivity and not to the current metabolic level.