Preliminary study for the mass cultivation of Porphyra dioica J. Brodie et L.M. Irvine

The use of macroalgae for human nutrition is constantly increasing, especially in Europe (FAO 2018). The causes are numerous and could be related essentially to the high nutritional values of algae. Among these, the species of the genera Porphyra and Pyropia, known commercially as "nori" (Japan) or "laver" (Northern Europe), have the highest commercial value ($ 523 per wet metric tonnes, FAO 2018). Since the interest in nori has grown considerably in the western world, the need to identify a highly productive species among European ones, which is able to support an industrial cultivation, has attracted the attention of researcher on Porphyra dioica, present in all of Northern Europe with a lower distribution limit at low latitudes and considered a species suitable for aquaculture (Pereira et al. 2004). This species, like the others of the same genus, is characterized by a life cycle in which laminar gametophytes alternate with microscopic filamentous sporophytes (conchocelis phase) (Brodie, Irvine 1997). The aim of the present research was to study the influence of different environmental parameters on thalli growth to improve the knowledge on mass cultivation methods for P. dioica in Europe. This work is part of the project “Evaluación de recursos ficológicos de interés industrial en costas gallegas”, which aims to improve large-scale production of algae of industrial interest. For this study thalli of P. dioica were collected along the north-western coasts of Galicia, Spain. The blades were transferred to the laboratory at a low temperature, cleaned from epiphytes and cultured at 14°C. The main target was to test the effects on biomass yield of photoperiod (12L: 12D, 16L: 8D and 8L: 16D) and irradiance (250 μE m-2 s-1, 140 μE m-2 s-1 and 70 μE m-2 s-1), and to test the "free-living" growth conditions on the conchocelis phase, traditionally cultivated on a calcareous substrate. To support the obtained data, the health status of the gametophytes was evaluated by the Fv/Fm index (variable fluorescence/maximum fluorescence of chlorophyll). Among tested culture conditions, the highest growth of thalli was obtained at the photoperiod 16:8 and the light intensity of 140 μE m-2 s-1. The further increase of light intensity (250 μE m-2 s-1) caused a reduction in the growth due to a high light stress, as shown by the Fv/Fm index. The cultivation of the conchocelis phase in free-living conditions gave excellent results.