Estimation of the specific surface area in marine macroalgae using Langmuir isotherms as an alternative technique for studies of epibenthic assemblages

Background: Benthic macroalgae offer a suitable habitat for the development of different epibenthic species. Knowing the macroalgal surface area allows the study of epibenthic assemblages, as well as the evaluation of interactions between host and epibiont. Goals: The aim of this research was to estimate the specific surface area of benthic macroalgae collected at two coastal sites in Veracruz, southwestern Gulf of Mexico. Methods: From August 2016 to July 2017, 12 monthly collections were made. The formation of the Methylene Blue monolayer on the macroalgal surface was verified using the Langmuir isotherms. The biomass of brown algae was chemically treated to cause the formation of the monolayer. Results: For all examined algal species (11 Rhodophyta, 6 Chlorophyta and 4 Phaeophyceae from four morpho-functional groups) the adsorption equilibrium point was reached with a high correspondence between the experimental and calculated data (R2>0.96). The formation of the monolayer allowed estimation of the macroalgal specific surface area, which varied significantly among species, from 24 to 387 m2 g-1. The corticated algae exhibited the greatest specific surface area (143-222 m2 g-1), and the articulated calcareous forms had the least area (63-104 m2 g-1). However, no correlation between the specific surface area and the morpho-functional groups was found (P<0.05). In most algae, significant differences in specific surface area were observed in thalli of the same species (P<0.05). Conclusions: The results could be related to infraspecific variability in morphological characteristics of the thallus that occur during ontogenesis under environmental conditions. The Methylene Blue adsorption technique is suitable for determination of the surface area and allows the comparison of macroalgae of different morpho-functional groups, thus minimizing the uncertainty associated with species-specific characteristics.