Abstract
BackgroundPyropia is an economically advantageous genus of red macroalgae, which has been cultivated in the coastal areas of East Asia for over 300 years. Realizing estimation of macroalgae biomass in a high-throughput way would great benefit their cultivation management and research on breeding and phenomics. However, the conventional method is labour-intensive, time-consuming, manually destructive, and prone to human error. Nowadays, high-throughput phenotyping using unmanned aerial vehicle (UAV)-based spectral imaging is widely used for terrestrial crops, grassland, and forest, but no such application in marine aquaculture has been reported.ResultsIn this study, multispectral images of cultivated Pyropia yezoensis were taken using a UAV system in the north of Haizhou Bay in the midwestern coast of Yellow Sea. The exposure period of P. yezoensis was utilized to prevent the significant shielding effect of seawater on the reflectance spectrum. The vegetation indices of normalized difference vegetation index (NDVI), ratio vegetation index (RVI), difference vegetation index (DVI) and normalized difference of red edge (NDRE) were derived and indicated no significant difference between the time that P. yezoensis was completely exposed to the air and 1 h later. The regression models of the vegetation indices and P. yezoensis biomass per unit area were established and validated. The quadratic model of DVI (Biomass = − 5.550DVI2 + 105.410DVI + 7.530) showed more accuracy than the other index or indices combination, with the highest coefficient of determination (R2), root mean square error (RMSE), and relative estimated accuracy (Ac) values of 0.925, 8.06, and 74.93%, respectively. The regression model was further validated by consistently predicting the biomass with a high R2 value of 0.918, RMSE of 8.80, and Ac of 82.25%.ConclusionsThis study suggests that the biomass of Pyropia can be effectively estimated using UAV-based spectral imaging with high accuracy and consistency. It also implied that multispectral aerial imaging is potential to assist digital management and phenomics research on cultivated macroalgae in a high-throughput way.
Highlights
Pyropia is an economically advantageous genus of red macroalgae, which has been cultivated in the coastal areas of East Asia for over 300 years
Comparison of multispectral reflectance The multispectral reflectance of P. yezoensis submerged in seawater was very similar to that of seawater, but quite different to that of P. yezoensis exposed to the air, which implied that seawater had a significant effect on seaweed (Fig. 2a)
Laboratory experiments showed that the values of difference vegetation index (DVI), ratio vegetation index (RVI), normalized difference of red edge (NDRE), and normalized difference vegetation index (NDVI) varied differently along with decreased relative water content (RWC) (Fig. 4)
Summary
Pyropia is an economically advantageous genus of red macroalgae, which has been cultivated in the coastal areas of East Asia for over 300 years. Che et al Plant Methods (2021) 17:12 been cultivated and consumed in East and Southeast Asia for over 300 years [3, 14, 30]. Fisheries and Aquaculture Information and Statistics Branch 2019). In comparison to other cultivated macroalgae, Pyropia has the highest commercial value per unit mass at $905 per tonne. It has high nutritional value, in high protein content at ~ 25–30% of the blade dry weight and a delicious flavour [3, 12]
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