## 2 Materials and Methods
### Experimental Setup  
The growth trial took place over 10 weeks, during which plants were allowed to develop with minimal disturbance on a deep-water culture hydroponics configuration using extruded polystyrene floating-rafts without intermediary harvests during this period. An overview of experimental units under different lighting systems at week 1 and week 9 are displayed in Figure 1.  
The hydroponic units were made of opaque polypropylene boxes (300 \(\times\) 200 \(\times\) 170 mm) with an overflow outlet to keep water volume at the 5 L mark. The base for the hydroponic solution was artificial seawater prepared by dissolving commercial Red Sea salt (Red Sea, Cheddar, UK) in freshwater purified by reverse osmosis (V2 Pure 360 RO System, TMC, Hertfordshire, UK) until achieving a salinity of 20 ppt. The experimental hydroponic media was a modified version of [PERSON]'s solution described previously, where N and P concentrations were modified to resemble realistic values of dissolved inorganic N and P as measured in fish-farming effluents (2016). The detailed nutrient composition of the experimental hydroponic solution is presented in Table S1 (Supplementary Materials). The experimental design consisted of a two-way factorial design with two levels, resulting in 4 treatments. The levels of artificial lighting were 'fluorescent lights' and 'LEDs' and the levels of plant density were '110 plants m\({}^{-2}\)' and '220 plants m\({}^{-2}\)'. Treatment labels were as follows: F110 = fluorescent lights + 110 plants m\({}^{-2}\); F220 = fluorescent lights + 220 plants m\({}^{-2}\); L110 = LEDs + 110 plants m\({}^{-2}\); and L220 = LEDs + 220 plants m\({}^{-2}\). Each treatment was assigned to five replicate hydroponic units, resulting in a total of 20 units, each having a surface area of 0.0455 m\({}^{2}\). Therefore, the F110 and L110 units were assigned 5 plants each, and the F220 and L220 units were each assigned 10 plants, for a total of 150 plants distributed across all hydroponic units. To do so, 150 fully rooted cuttings of similar weight were selected, identified by a number from 1 to 150 and randomly assigned to the hydroponic units following a randomized sequence of integers (from 1 to 150) generated by a tool provided at [[https://www.random.org](https://www.random.org)]([https://www.random.org](https://www.random.org)) (accessed on 18 June 2018). Each plant was individually photographed and weighed at the beginning of the experiment. The average initial biomass was 6.8 \(\pm\) 1.8 g plant\({}^{-1}\). Afterward, the cuttings were fixed to the floating rafts using natural cotton, to hold each plant in place at the base of the aerial portion. The hydroponic medium was continuously aerated to maintain aerobic conditions, and the hydroponic units were refilled as needed with freshwater purified by reverse osmosis to compensate for evapotranspiration. The fluorescent light was provided by tubular fluorescent lamps (Philips 54W/830 Min Bipin T5 HO ALTO UNP), while the LED light was provided by solid-state LED lighting tiles (AquaBeam 1500 Ultima NP Ocean Blue Light). Their photometric and colorimetric information is presented in Table 1. Each fluorescent lighting system was composed of two fluorescent lamps and each LED system was composed of three LED tiles. The spectral profiles of artificial lighting sources are presented in Figure S1 as Supplementary Materials. The photoperiod was set at 14 h light: 10 h dark and the photosynthetically active radiation (PAR) was adjusted at the beginning of every week so that all artificial lighting sources delivered identical PAR to the plants. PAR, the fraction of electromagnetic radiation that can be used by plants during photosynthesis, is found within the spectral range of 400-700 nm. It is normally expressed as photosynthetic photon flux density (PPFD, umol photons m\({}^{-2}\) s\({}^{-1}\)).