HYPERSPECTRAL CHARACTERIZATION OF PHYSIOLOGICAL RESPONSES IN Palmaria palmata TO OPTIMIZE LAND-BASED ENVIRONMENTAL PARAMETERS

Background:

Seaweed farming is one of the fastest-growing sectors of European aquaculture. Despite the current market dominance of brown seaweed, native red seaweeds like dulse (Palmaria palmata) offer superior nutritional and phytochemical profiles, driving increased commercial interest. However, cultivation practices for these species remain in their infancy, with no established consensus on the environmental conditions required to optimize growth. Furthermore, while the antioxidant and phytochemical content of red seaweeds is a primary asset, quantifying these compounds currently requires labor-intensive laboratory procedures. In this study, we evaluated the effects of light spectra, simulated at depths of 0.5, 5, 10, and 20 meters, on the growth and physiological health of P. palmata within land-based systems. Using hyperspectral imaging, we characterized biochemical shifts in tissue composition across these light environments. By pairing spectral data with empirical phytochemical concentrations measured via mass spectrometry, we developed statistical models to assess the accuracy of rapid imaging as a high-throughput proxy for chemical quantification.

Results:

Preliminary results indicate that dulse populations from the Swedish west coast exhibit significantly higher growth rates under light conditions simulated at ~5m depth. Light spectra also influenced chemical composition; macroalgae grown at the shallowest simulated depth (0.5m) displayed spectral profiles distinct from those cultivated under deeper-water light conditions (Figure 1). Furthermore, we observed significant intra-thallus spectral variation along the length of the fronds. These gradients transitioned from the older, thicker base tissue to the newly developed tips, likely reflecting the maturation of photosystems as tissue ages. The extent of this transition zone (tip vs base) varied between treatments, likely reflecting not only the differential growth rates we observed, but also the quality of available light. This physiological shift is critical for cultivation strategy: while younger tissue drives biomass accumulation, older tissue may sequester higher concentrations of high-value carotenoids. Consequently, optimizing culture conditions solely for longitudinal growth may inadvertently produce less robust algae with diminished concentrations of the compounds that drive their market value.

Figure 1

Figure 1: TOP: Spectral profile of dulse grown at 0.5m and 20m simulated light conditions (green and red, respectively). BOTTOM: PCA of all individuals, based on average spectral profile.

Acknowledgment

This work was funded by the European Union and the Sustainable Blue Economy Partnership under project PalmariaPlus. This work received additional supported by a Young Researcher Mobility Grant from the Research Council FORMAS (grant number 2022/02838).