Date of Award

August 2013

Degree Type


Degree Name

Master of Science


Biological Sciences

First Advisor

John A. Berges

Committee Members

Erica B. Young, Harvey Bootsma


Carbon Acquisition, Dissolved Inorganic Carbon, Intertidal, pH Drift, Rhodophyta, Subtidal


The ability of macroalgae to photosynthetically raise the pH and deplete the inorganic carbon pool from the surrounding medium has been in the past correlated with habitat and growth conditions. The objectives of this study were 1) to test for differences among a variety of red algal species in their ability to deplete the dissolved inorganic carbon pool (DIC) from the surrounding medium, and to utilize the HCO3- fraction of the DIC, 2) to determine whether these differences were associated with red algal habitat defined as intertidal height and subtidal depth, and/or with taxonomic affinities of the species studied (taxonomic order or family), and 3) to investigate possible within-species differences in DIC acquisition abilities in Mastocarpus papillatus, a species with a wider vertical distribution within the intertidal. No attempts were made to identify the specifics of the mechanisms used by macroalgae for dissolved inorganic carbon uptake.

Measurements of pH drift were used to measure the ability of 38 red algal seaweeds to utilize bicarbonate and to deplete the DIC from seawater medium. Subtidal algae were typically restricted to the use of DIC in the form of dissolved CO2, reducing the initial DIC by only 9%. Intertidal species used both dissolved CO2 and bicarbonate, and reduced initial DIC by as much as 70%. DIC reductions and pH compensation points for the intertidal species tested were strongly correlated with their vertical zonation on the rocky shoreline. The efficiency in DIC depletion from the medium generally increased with tidal height, but species from the upper edge of the intertidal reversed the trend and demonstrated significantly lower DIC depletion abilities. This general pattern associated with tidal height was observed, not only among intertidal red algal species in general, but also among four species of the genus Porphyra (P. torta V. Krishnamurthy, P. papenfussii Krishnamurthy, P. perforata J. Agardh, P. fucicola Krishnamurthy) and among four populations of the broadly distributed species Mastocarpus papillatus (C. Agardh). The Mastocarpus observations suggest either that individuals of this species may be able to express alternate strategies for carbon acquisition, or that intertidal height may select for survivorship of genotypes with different carbon acquisition strategies. The four species of Porphyra were consistently less efficient in depleting the DIC from the medium than other macroalgal species from the same tidal height, providing the only evidence for a possible taxonomic effect on carbon acquisition. The physiological differences in DIC depletion from the medium were otherwise not related to phylogeny, tested as membership in red algal families and orders.

This work suggests that the carbon acquisition strategy found in red macroalgal species may be a physiological attribute that bears important ecological and evolutionary implications.