A cheap and sensitive method for imaging Gracilaria (Rhodophyta, Gracilariales) growth

Abstract

Growth rate is an informative measurement for the culture of any organism, as it provides cues about fitness and allows selection of strains. For seaweeds, the gain of mass has been the most used methodology at the laboratory, but it can be laborious and increase the contamination. In this work, we present an easy, accessible, and sensitive method that uses imaging to measure the growth rate at a laboratory scale of three Gracilaria species (Rhodophyta, Gracilariales): G. caudata J. Agardh, G. domingensis (Kutzing) Sonder ex Dickie, and G. tenuistipitata C.F.Chang & B.M.Xia. A CMOS camera with a flex clamp and a macro lens was attached to a common retort stand in order to measure the algae thalli from the bottom of a Petri dish. Then, the images were batch processed for area and length measurement and correlated to mass. A high correlation between mass and area was verified for all three species, but not for length (G. domingensis, R2 = 0.68). G. tenuistipitata had the highest growth rate in area (17.9% day−1) and G. domingensis the lowest (3.1% day−1). Correlation differences between area and mass can be due to species-specific morphology. Area measurement can efficiently replace weighing. The present method is highly adaptable to many experimental setups, uses a cheap camera and free software, is not labor intensive and does not require much computer knowledge.