Biomass production of the red macroalga Gracilariopsis tenuifrons (Gracilariales) using a low-cost commercial fertilizer and its additional benefits for carbon sequestration

Abstract

Gracilariaceae species are economically good options for aquaculture in Brazil. High-quality seedlings produced by vegetative reproduction is necessary to decrease pressure on natural beds and can be achieved in controlled environments. Commercial fertilizers are a low-cost option to increase quality and growth. Furthermore, CO₂ sequestration can be an added value to cultivation. This study aimed to analyze the biomass production and CO₂ sequestration of Gracilariopsis tenuifrons (C.J.Bird & E.C.Oliveira) Fredericq & Hommersand under two concentrations of a low-cost commercial fertilizer. Growth, pigment content, proportion of dry biomass, C, H, and N contents, and CO₂ sequestration were estimated. Gracilariopsis tenuifrons were kept for 28 days under two concentrations of the commercial orchid fertilizer Forth 30-10-10 (NPK), one with 250 µM of N (called 50%) and the other with 500 µM of N (called 100%). No significant differences were found in growth and growth rate between 50% and 100%, with maximal 4.4-times biomass at the end of the experiment. Significant increases were found in the concentrations of phycobiliproteins and N, which were 33% and 20% higher in the samples with Forth 100%, respectively. The C content was higher in the Forth 50% samples, with a CO₂ fixation of 14.8% per unit of fresh mass. Gracilariopsis tenuifrons showed a CO₂ sequestration rate equivalent to that of other macroalgae species, demonstrating its potential in culture. In addition, greater biomass production and CO₂ capture could be stimulated by combining the addition of nutrients with higher luminosity to increase the rate of photosynthesis and growth.